OUTLINES OF PLANT LIFE 



WITH SPECIAL REFERENCE TO FORM 
AND FUNCTION 



CHARLES REID BARNES 

Professor of Plant Physiology in the University of Chicago 



NEW YORK 

HENRY HOLT AND COMPANY 
1900 



TWO COPIES RECEIVED, 

Library of Congtat* 
Office Qf the 

MAR I 1900 

Keglstsr of Copyrights 



55819 



Copyright, igoo, 

BY 

HENRY HOLT & CO. 



SfcUONU COPY, 



ROBERT DRUMMOND, PRINTER, NEW YORK. 



• 



OUTLINES OF PLANT LIFE. 



PART I: THE PLANT BODY. 

CHAPTER I. 

INTRODUCTION. 

1. Living matter. — By the combination of powers called 
life, each living thing controls, for a longer or shorter time, 
a certain amount of material, which constitutes its body. 
This material is arranged into definite form ; some remains 
only for a short time as part of the body and is then discarded; 
other material remains part of the body as long as life exists. 

That which is changing most rapidly is the living substance, 
called protoplasm. If there are parts of the body not living, 
they have been formed by the protoplasm and are generally 
controlled by it. 

2. Members. — When the body is large, it is easy to see 
that it is made up of more or less distinct parts. These are its 
members. As a rule, the smaller it is, the fewer and less dis- 
tinct are the members. There are many thousands of plants 
in which the body does not have any members, but can be 
distinguished only into the units of which it is built, called 
cells. Still others consist of a single cell. 

In the largest plants the more important members may be 
divisible into smaller subordinate ones. When these are in- 



2 OUTLINES OF PLANT LIFE. 

spected they too are seen to be made up of a great many 
minute parts, each consisting of a bit of living protoplasm 
and some other things which it has made. These parts are 
called cells. (See ^[ 4.) 

Thus, a corn plant has two principal members, a root, below ground, 
and a shoot above ground. The root consists of many subordinate mem- 
bers, the roots and the rootlets; the shoot consists of stem and leaves ; 
the leaves of sheath and blade, etc. But a duckweed shoot has no dis- 
tinction of stem and leaf, and only a single root. The pond scums have 
no members, but consist of a row of cells; while in many diatoms the 
body is a single cell. 

3. Reproduction. — Every plant must provide for its own 
existence. To do this, it must possess means for securing, or 
for making, and using food. During this feeding period its 
most striking characteristic is growth. It must also provide 
before it dies for the production of new plants of the same 
kind. When the plant is very simple, both duties must be 
done by the same cell, but in more complex plants special 
cells, and in many cases special members, are provided for 
reproduction. The two processes are sometimes carried on 
at the same time, but more commonly reproduction occurs at 
some particular or limited period. 

It is convenient to consider first the form of the plant body 
and those members which are not concerned in reproduction. 
Parts I and II therefore, treat of the work and parts of the 
plant which promote its own life and growth, i.e. the vegeta- 
tive body. Part III discusses the form and action of the re- 
productive parts, so far as these can be studied without a 
microscope. 

4. The cell. — A plant-cell is a minute portion of living 
matter, called protoplasm, generally surrounded by a mem- 
brane, called the cell-wall (fig. 1). 

The protoplasm is the essential part of the cell. It con- 
structs the cell-wall. Rarely, if ever, is it uniform through- 



INTAOD UCTION. 




out, but shows distinct parts, each having special work to do. 
In the most complete and active cells the greater part of the 
protoplasm consists of a finely granu- 
lar or nearly transparent, colorless 
portion, in which the other parts 
seem embedded. 

Protoplasm is not a single sub- 
stance, but a mixture of several dif- 
ferent substances, so intimately 
mixed and so easily destroyed that 
it is not possible to analyze it. More- 
over, the nature and amount of the 
components are probably variable. 
In all but the youngest cells there are 
one or more bubbles of water in the 
protoplasm. 

5. Nucleus. — The nucleus is one 
of the most important parts of the 
cell. It is generally spherical or ovoid, but in long cells it 
may become elongated (fig. 2, z). The nucleus may divide 
into two, and this is commonly followed by the formation 
of a partition-wall separating the cell into two parts, each con- 
taining one of the daughter-nuclei. 

6. Plastids. — In most cells there are also other parts, 
called plastids. In young cells these are small, rounded, 
colorless bodies. As the cell grows older they increase in 
size and number. When mature and in cells which lie near 
the surface of green plants, they are commonly roundish or 
biscuit-shaped, of spongy texture, and colored yelllowish- 
green by a substance known as chlorophyll . These are con- 
sequently known as chloroplasts or chlorophyll-bodies (fig. 
2). In other cells, particularly those for the storage of food, 
they may develop into smaller, denser, flattened or roundish, 
uncolored bodies, whose work is usually to gather starch into 



Fig. i.— A cell (the meajaspore) 
from a lily ovule, filled with 
granular protoplasm, in which 
is embedded a large spherical 
nucleus, containing a nucle- 
olus, and accompanied by two 
centrospheres, a. The line 
around the protoplasm repre- 
sents the cell-wall, with those 
of the adjacent cells connected. 
Magnified 500 diam. — After 
Guignard. 



4 OUTLINES OF PLANT LIFE. 

grains (fig. 3). In other cells, particularly in highly colored 
parts, the plastids may become of most diverse form and 

size, and take on a red or yellow 

color (fig. 4). 

7. Wall. — The cell-wall is 





Fig. 2. Fir.. 3. 

Fig. 2. — A cell from the interior of the leaf of the oat, showing its wall, and some 
inclusions of the protoplasm. 2, the nucleus ; c , chloroplasts ; o, an oil-drop. Mag- 
nified about 1000 diam. — After Zimmermann. 

Fig. 3. — Part of the cell contents of an inner cell of white potato, z, nucleus ; s, starch 
grains, each having been formed by a leucoplast, /, which is still attached to one side 
of the grain ; £, crystalloid. Magnified about 1000 diam.— After Zimmermann. 

formed by the protoplasm. In green plants when first 
formed it consists chiefly of cellulose, with which, as it grows 
older, various other substances may be mixed. Some of these 





b c 

Fig. 4. — A, chromoplasts from flower leaves of an orchid ; B, from the root of carrot ; 
C, from the fruit of mountain-ash. Embedded in the protoplasmic body of the 
chromoplast are sometimes proteid crystalloids, />, pigment-crystals, f, or starch- 
grains, s. Magnified about 1000 diam — After Schimper. 

are present even in the young wall, and may increase with 
age ; others are characteristic of special changes which the 
wall may undergo. 



IN TROD UCriON. |> 

8. Growth of the cell-wall. — As the cells become older 
the wall may increase in thickness. It must also increase in 
area as the cells grow in size. The growth in area is usually 
accomplished by putting new particles between the older 
ones. Growth in thickness is rarely uniform. Pits or pores 
are formed in the wall when it thickens except at these spots. 
When the thin parts are large and only certain spots or lines 
grow thicker, the wall shows projecting spikes, bands, or 
threads. 



CHAPTER II. 



SINGLE-CELLED PLANTS AND COLONIES. 



In the lakes and pools, in ditches and slow streams, on 
the surface of damp rocks and wood, may be found many 
sorts of microscopic plants, whose entire body is merely a 
single cell. 

9. Fission-algae. — The simplest forms of the single-celled 
green water plants are the fission -algae. In the central part 
of the cell is the nucleus, and the whole of the protoplasm is 
colored by the yellowish-green dye, chlorophyll. Along 
with it, there is a blue coloring matter, so that in mass these 
algae look bluish-green or even black- 
ish. For this reason they are called 
blue-green algae to distinguish them 
from those in which only the yellow- 
green color is present. 

10. Gelatinous colonies. — The cell- 
wall may be thin, but commonly it is 
composed of several layers, of which 
the outer are changed into mucilage. 
This swells into a transparent jelly when 
wet, either becoming alike throughout 
or showing distinct layers. When a 
number of such forms grow in company (fig. 5), this jelly-like 
material blends into a single mass in which the associated 
plants seem to be embedded. 

6 




Fig 



- A blue-green alga 
{GIa?oca/>s<i). Single indi- 
viduals, A, and colonies 
(B-E) of various ages. 
Magnified 300 diam. — After 
Sachs. 



SINGLE-CELLED PLANTS AND COLONIES. 



11. Gelatinous filament-colonies. — In other cases, instead 
of being held together only by the weak jelly-like portion of 
the cell-wall, the plants, still practically independent the one 
of the other, remain connected by the firmer portions of the 
wall into rows, forming irregularly coiled or serpentine fila- 
ments, which are embedded in a profuse jelly (fig. 6). The 





Fig. 6. — Nostoc. A, a gelatinous colony, irregularly lobed. Natural size. />, a por- 
tion of a serpentine filament with five heterocysts (one at each end by which it was 
separated from the rest of the cells composing the filament, and three intermediate 
ones) and the jelly belonging to it. Magnified about 400 diam. — After Thuret and 
Janczewski. 

real independence of the cells, even though they remain con- 
nected, is shown by the fact that such a chain may be broken 
up into any number of pieces and each piece will retain all 
its powers. Here and there in the chain there occur cells 
unlike the rest, whose purpose seems to be to break the chain 
into pieces, which work their way out of the jelly and grow 
into independent colonies. The association of considerable 
numbers of these plants in colonies gives rise to masses of jelly 
which vary from the size of a pin -head to 2-5 centimeters in 
diameter. They may be found adhering to water-weeds as 
clear- or dirty-green masses, or sometimes floating free 
(A, fig. 6). 

EXERCISE I. 

Nostoc or Kivularia. — I. Observe the size and form of the colonies 
and the consistence of the jelly enclosing them. (|n.) 



8 



OUTLINES OF PLANT LIFE. 



2. Crush a bit of a Nostoc colony or a whole one of Rivularia between 
two glass slips, remove the upper slip, cover with water and observe the 
coiled (Nostoc) or radiating straight filaments (Rivularia) embedded in 
the jelly. (Fig. 6.) 

12. Filaments of loose organization. — Of very near kin 

to these plants are the oscillarias, which have received this 
name from the pendulum-like swinging 
of their tips (fig. 7). In them the cell- 
walls remain connected more extensively 
and more firmly, so that each cell is 
disk-shaped, and the filament is much 
less easily separated into its parts. 
Moreover less of the wall has become 
jelly-like, so that often this part is not 
apparent and is difficult to see even when 
the plants are looked at with the micro- 
scope. Even though invisible, it may 

Fig. 7. r-Oscillaria. a, the r ° ' J 

tip; b, a portion of the be detected by the slippery feel of the 

middle of a filament. Mag- 
nified 540 diam. — After plants when rubbed gently between the 

Strasburger. 

fingers. 




EXERCISE II. 

Oscillaria. 1. Observe the color of a bit of Oscillaria. (^[ 9.) 

2. With needles tease out the specimen in a drop of water on a glass 
slip; observe the delicate thread-like form. (Fig. 7.) 

3. Transfer a bit of living Oscillaria to a small glass dish or white in- 
dividual butter plate with a little water; protect it from drying up with 
a cover; 24 hours later observe the position of the filaments. (^[ 12.) 

4. Demonstration. Dip a considerable mass of Oscillaria in hot water 
for a moment and put in a white butter plate with as small a quantity of 
water as will cover it. As the water evaporates observe the color depos- 
ited on the dish at the edge of the water. (^[ 9.) 

13. Feeding habits. — The feeding habits of the oscillarias 
are worth notice. These plants are found in permanent pud- 
dles and ditches where organic matter is decaying. The sig- 



SINGLE-CELLED PLANTS AND COLONIES. 9 

nificance of this is that some of the ancestors of the green 
oscillarias probably had offspring which, instead of living 
upon food prepared by means of the green coloring matter 
(^[ 185 ff.), learned to use the organic matter in the water, 
at first perhaps no more than the present oscillarias do ; but 
gradually they came to live exclusively upon it. As a conse- 
quence, they lost their green color and became incapable of 
existing where organic food cannot be had. 

Bacteria. 

14. Fission-fungi. — Along with the loss of color and change 
of habit went a diminution in size. They have now become 
so different that they are known as fission-fungi, and popu- 
larly as bacteria, bacilli, microbes, germs, etc. These plants, 
probably the descendants of common ancestors with the fis- 
sion-algae, are the smallest known living things (figs. 8, 9). 
The diameter of many sorts does not exceed .0005 of a milli- 
meter. That would allow 1 75 to lie side by side upon the edge 
of the paper on which this book is printed. Though so minute 
these plants have the same sort of protoplasm and cell -wall as 
larger ones. They increase in number rapidly by each cell 
dividing into two, which separate readily into independent 
plants. 

15. Gelatin. — In the fission-fungi, as in the fission-algae, 
considerable masses of jelly-like material are produced, in 
which the plants may lie embedded. The films, sometimes 
smooth, sometimes wrinkled, which appear on an infusion of 
organic matter, such as tea or broth, are formed by masses 
of bacteria which rise to the surface and become embedded in 
the gelatinous material they produce (3, fig. 8). 

Demonstration. — Steep a cupful of chopped hay in hot water for fifteen 
minutes, and set the infusion, loosely covered, in a warm place. After a 
day or two, show the film of bacteria which covers the surface of the 
liquid. 



10 



OUTLINES OF PLANT LIFE. 



16. Cilia. — Most species are furnished with organs of 
movement consisting of fine threads of protoplasm protruded 






Fig. 8. — Various bacteria, a, Micrococcus, the " blood-portent " ; b, zooglcea form 
of the same; c, Bacterium aceti, the ferment of vinegar; d, Sarcina, a harmless 
parasite of the human intestine, a, b, magnified 300 diam.; c, 2000 diam.; d, 800 
diam.— After Kerner. 





r 



Fig. 9.— Bacteria stained to show cilia. A, cilia tufted at one end; B, cilia irregularly 
distributed over body ; C, cilium single at one or both ends. B, the bacillus of typhoid 
fever; C, the bacillus of Asiatic cholera. Magnified 775 diam. — After Migula. 

through the wall. These, by their sudden contraction on one 
side, lash about like whips, and propel the cell by jerky, 
darting motions through the fluid in which it swims, These 



SINGLE-CELLED PLANTS AND COLONIES. II 

lashes, called cilia, may be single at the ends of the cell (C, 
fig. 9), or many at ends or sides (A, fig. 9), or the whole cell 
may be covered with them like hairs (B, fig. 9). They may 
be withdrawn or drop off when the plant comes to rest, as 
when they form the scums previously mentioned. 

These plants are most interesting on account of their rela- 
tion to health and disease, decay, fermentation, etc., which 
cannot be discussed here.* 

17. Yellow-green algae. — Among the single-celled green 
plants, one of the most common groups is that represented 
by fig. 10, which shows one of a large series, in which the 
body consists of a single cell with its wall, protoplasm, 
nucleus, and a few relatively large chloroplasts. In this 
greater specialization of the protoplasm, these plants show 
the only advance upon the blue-green algae. The wall in 
such as this Pleurococcus is almost uniform and quite thin. 
The cells of some kinds are frequently associated in colonies, 
embedded in jelly or not. 

EXERCISE III. 

Pleurococcus. — I. Examine with a lens pieces of bark bearing Pleuro- 
coccus and similar algse. Note the irregular distribution of the green 
granular heaps of plants. Is there any similarity to the distribution of 
higher plants over uncultivated areas ? 

2. After soaking a piece of bark for a few minutes, scrape off with 
the nail or a dull knife blade some of the green material, spread it as 
well as possible in a drop of water on a slip of glass, cover it with a 
piece of thin glass, avoiding air-bubbles, and examine with a lens. 
Observe the minuteness of some of the specks, which are mostly single 
plants The larger ones are clusters of plants. 

3. Dejnonstration. Show a slide under microscope and have pupils 



* For further information on these plants, see Frankland : Our Secret 
Friends and Foes ; Prudden : Story of the Bacteria, Dust and its Dan- 
gers. Drinking-water and Ice Supplies ; Russell: Dairy Bacteriology; 
Frankel (tr. by Linsley): Bacteriology (medical). 



12 



OUl^LINES OF PLANT LIFE, 



observe the form and color of single plants, many consisting of two or 
more cells still joined together, resulting from cell division. (^"17, fig. 10.) 






Fig. 10. — Pleurococcus viridis. A , a single individual ; B, a colony shortly after 
division ; C, the same after separation. Magnified 540 diam. — After Strasburger. 




FlG. 11. — Various diatoms, a, Synedra ; b, Pleurosigma ; c, d, Grammatofihora, 
side and top views ; e, colony of Govifihonema, with branched stalks attached to an 
alga ; f, g, single cells of same, more magnified, top and side views; /z, colony of 
Diatoma, the cells connected into a zigzag band ; /, k, colony and individuals (top and 
side views) of Fragillaria ; I, w, n, Coccovema. In m the pair is surrounded by 
jelly preliminary to the escape of the protoplasm and the formation of two new cells 
(auxospores) which has been completed in n.— After Kerner. 

18. Shelled plants. — Other one-celled plants constitute a 
group known as diatoms, found in both fresh and salt waters, 
either attached or free-swimming (figs. 11, 12). The dia- 



S1XGLE-CELLED PLANTS AND COLONIES. 



3 



toms are very various in form, and present two different 
aspects. When seen from the side they are generally elon- 
gated-rectangular. When looked at from above they are 
short-cylindric, disk-shaped, boat-shaped, or variously curved 
or angular. They are peculiar in having the cell-wall so 
filled with silica that scarcely any other material is left. In- 
deed the plants may be heated to a red heat and boiled in 
acid without destroying the form and markings of the cell- 
wall, so completely has it become silicified. To permit 
growth this rigid cell- wall is constructed in two pieces which 
fit together like the two parts of a pill-box (fig. 12). Each 




Fig. t2.— A single diatom (Navicula amphirhynchus). A, top view; B, side view, 
showing overlapping of the valves. The parts shaded by lines are the chloroplasts ; 
the dotted part the protoplasm, with nucleus about the center of cell. Magnified 
750 diam. — After Pfitzer. 



of these pieces, or valves, is sculptured into regular patterns 
in lines and dots, which are often so excessively minute or 
close together as to be barely visible with the highest powers 
of the microscope (b, fig. 11). Seen in mass, as they may 
often be on the sides of a glass aquarium, living diatoms ap- 
pear yellowish-brown. The chloroplasts, which are some- 
times single and always few, have a brownish color in addi- 
tion to the green chlorophyll. 

It is not uncommon for the diatoms to form colonies by 
the adhesion of several or many individuals by means of 
gelatinous cell-walls. These colonies are ribbon-like, or zig- 



14 



OUTLINES OF PLANT LIFE. 



zag chains, or even branched filaments {h, i, fig. n). 
Other sorts may be attached singly or in clusters by a gelati- 
nous stalk (e, fig. n). In all cases the jelly, like the rest 
of the cell-wall, is a product of the protoplasm. The slow- 
gliding movements of some free diatoms are due to the pro- 
trusion of strands of protoplasm through slits in the valves. 




Fig. 13. — Various desmids. a, Micrasterias ; b, Cosmarium ; c, Xanthidium ; 
d, Ciosterium ; e, Staurastrum ; f, Aptogonum. Magnified about 200 diam. 
— After Kerner. 

19. The desmids. — These form another group of one- 
celled green algae. They have neither the brownish color 
nor siliceous wall characteristic of diatoms, but are bright 
green cells of remarkably diverse and often beautiful forms. 
As a rule the cell is flattened and is divided almost into two 
by a deep constriction near the middle (a, b, c, e, fig. 13). 
Often the body of the cell is covered with warts or spine-like 



SINGLE-CELLED PLANTS AND COLONIES. 1$ 

projections (&, c, fig. 13), or is prolonged into horn-like or 
hair-like lobes. These plants also frequently cohere into 
colonies {/, fig. 13). In that case tooth-like projections of 
the cell-wall may interlock. 

20. Summary. — The simplest plants consist of a single 
cell, which is often protected by a copious mucilage. By 
this means also the plants are often associated in colonies of 
various forms. Among the green plants some possess in 
addition a blue coloring matter ; others a brown. Many 
can move about from place to place. The bacteria are de- 
generate relatives of the blue-green algae which have lost their 
green color, and thus their power to make their own food. 



CHAPTER III. 



FILAMENTOUS ALG^E. 



Obviously some of the plants mentioned in the last chap- 
ter, such as the oscillarias, are colonies of cells well on the 

way to complete union into co- 
herent filaments whose elements 
are attached to each other by con- 
siderable areas of the cell-wall. 




In order clearly to understand this 
condition, we must consider the mode 
of origin of the individual cells composing 
the row. 

21. Fission. — Under conditions mostly 
unknown to us, in the course of its growth 
a cell may divide by a process known 
as fission. The material of the nucleus 
passes through a complex series of 
changes and separates into two parts. 
In a plane between these daughter-nuclei particles are deposited to form 
a cell-wall (A, fig. 14). In this way a single one-celled plant of Plenro- 



Fig. 14. — A, one of the final stages 
in cell-division. The daughter- 
nuclei are still connected by fila- 
ments, and across the equatorial 
plane particles of new cell-wall 
material are formed Z>, the com- 
pletion of cell - division ; the 
daughter-nuclei have rounded off 
and the new wall is like the 
lateral walls. Magnified 880 diam. 
— After Strasburger. 




Fig. 15 — Diagrams of cell-division 
spherical cells, a, b, by the wall 1 



A, division of a spherical cell into two hemi- 

B, the same after further division in planes 2, 
2, 3, parallel to 1. a has divided by wall 2 into a' and another cell which has again 
divided by wall 3 into a", a", b has divided into b' , b\ the inner of which has 
elongated preparatory to a division into b" , b" , as by wall 3. C, fig. A, after a second 
division, by wall 2, at right angles to 1. 

16 



FILAMENTOUS ALGyE. 



coccus [A, fig. io) may divide 
into tAvo, so that it consists of 
two hemispherical cells, each 
capable of independent growth 
(fig. 23, A). 

In the filamentous algoe the 
cells formed by such divisions 
remain connected throughout 
their whole extent, and as the 
successive divisions are parallel 
a cell row results (£, fig. 15). 
When the divisions are in two 
planes the cells form a flat sheet 
(c, fig. 15); and when in three 
planes, a mass. 

22. Filamentous algae. 

— There is a large number 
of plants in which the vege- 
tative body throughout life 
has the form of a filament. 
The green plants of this 
sort live almost entirely in 
water or in wet places, and 
may be conveniently desig- 
nated as filamentous algce. 

23. Pond scums. — 
Among these none are 
more beautiful or interest- 
ing than the pond scums, 
represented in our waters 
by several genera (Spiro* 
gyra, Zygnema, Mougeotia 
and some others *) . They 

* To the same group also 
belong the single-celled desmids 
already described. 




Fig. 16. Fig. 18. 

Fig. 16. — A cell from filament of Spirogyra. 
ch, chloroplast (there are three in this cell) ; 
/, pyrenoids ; k, nucleus. Magnified 200 diam. 
— After Strasburger. 

Fig 17. — Two cells from filament of Zygnema, 
showing the gelatinous sheath greatly swollen, 
and stellate chloroplasts, in which is a pyrenoid, 
with the nucleus in a strand of protoplasm 
between them. Magnified 245 diam.— After 
Klebs. 

Fig. 18.— A cell from filament of Mougeotia. 
The darker body nearly filling cell is the chloro- 
plast (face view) in which are pyrenoids, /, and 
tannin vesicles, g. If seen from a direction at 
right angles it would appear as a narrow stripe 
in the center of the cell, z, the nucleus. Mag- 
nified about 200 diam. — After Zimmermann. 



1 8 OUTLINES OF PLANT LIFE. 

may be readily recognized, during their vegetative period, 
by their unbranched filaments, bright green color, and slippery 
" feel " between the fingers.* 

Under the microscope, they are at once distinguished from other filamen- 
tous algae by the shape of their chloroplasts. In Spirogyra these form one 
or more flattish, spirally wound ribbons, notched on the edges, and em- 
bedded in the protoplasm near the cell-wall (ch, fig. 16). In Zygnema 
there are generally two irregularly star-shaped chloroplasts (fig. 17) ; while 
in Mougeotia a single flat, plate-like chloroplast, nearly as wide as the cell, 
traverses its center (fig. 18). See also fig. 19. 

Embedded in the chloroplasts of these and other algae are usually seen 
one or more angular, colorless bodies, often surrounded by a jacket of 
starch. These are stores of reserve food, known as pyrenoids (J>, figs. 
16, 18). 

In these plants there is little or no difference between the 
parts of the filaments. If broken into two, each part may 
continue growing with no damage to any part except the cells 
which were ruptured in severing the plant. 



EXERCISE IV. 

Spirogyra. — If fresh material is available examine a few filaments in a 
white dish for color. If preserved material is used, stain red by immers- 
ing for a few minutes in eosin (cheap red ink will answer). 

Examine with a lens. Observe 

1. Length ; whether broken or whole ; whether with or without 
branches. 

2. The delicate partitions, like white lines, crossing the green (or red) 
filaments, dividing the protoplasm of one cell from another. Can the 
form of the chloroplasts be seen ? (Cf. fig. 16.) This can be readily seen 
only in the larger species. (][ 23.) 

3. Demonstration. Mount a few fresh filaments in water. Show under 
moderate power the form of the chloroplasts ; the reserve food nodules ; 
the nucleus. (Fig. 16.) 



* This slipperiness is due to the gelatinous outer part of the cell-wall 
(fig. 26), which is only visible after special treatment or on examining 
the filaments in a thin mechanical solution of Chinese ink. 



FILA MEN TO US. A L GAZ. 



19 



24. Base and apex. — But other filamentous algae show a 
distinction between base and apex. In Ulothrix (fig. 19) 
the basal cell is elongated and pointed, and 
is colorless, because it is not furnished with 
chloroplasts like the others. By this pointed 
cell the plant is loosely attached, at least when 
young, to the substratum, while the green por- 
tion waves freely in the water. Thus arises a 
distinction into two parts, viz., the rhizoid and 
the thallus. 

In Cladophora, Vaucheria, and their allies, 
the plants are generally attached by a well- 
developed rhizoid region, which is often 
branched (w, fig. 20), as is also the thallus. 
In contrast with the preceding, therefore, 
localization of growth, producing branching, 
may be observed. 

25. Branching. — A branch begins by the 
growth in area of a limited portion of the cell- 
wall. Since growing cells are usually stretched 
by the water they absorb, the pressure upon 
the enlarged region causes the wall to bulge out- 
ward there. The convexity gradually increases 
as the region grows, until the swelling becomes 
an outgrowth whose further lengthening consti- 
tutes a branch similar to the main filament. 
Growth in length may be limited to the tip of 
a filament, or to a narrow zone including one or more cells, 
or it may occur indifferently in any cell, or in all cells. 



Fig. 19. — Ulo- 
thrix zonata. 
A young fila- 
ment with rhi- 
zoid cell, r, at 
base. Magnified 
482 diam. — Af- 
ter Dodel-Port. 



EXERCISE V. 



Cladophora. — If fresh material is at hand observe in a white dish 
preserved specimens are used stain for a few minutes in eosin. 
1. How is the plant attached ? 



20 



OUTLINES OF PLANT LIFE. 



2. Observe form and particularly the abundant branching. Can a 
single main axis be traced ? How many branches arise at one point ? 




Fig. 20. — A young plant of Vaucheria, developing from the spore. A, mature spore ; 
B, the same after germination has begun ; C, plant further developed from spore, sp, 
with growing apex, s, and rhizoid, iu, by which it attaches itself to the mud. The 
chloroplasts are numerous and close together next the wall on all sides. Magnified 28 
diam.— After Sachs. 

26. Partition walls unnecessary. — Many algae, while ex- 
ternally like others, which are divided into true cells, have not 
the units of structure separated by cell-walls. In Vaucheria, 
for example, the whole of the vegetative body forms a single 
chamber, in which lies the undivided protoplasm, corre- 
sponding to many cells, as shown by the numerous nuclei 
which are distributed through it. The external walls of the 
cells are formed, but the partition walls are not formed. 

27. External segmentation. — A plant body of this con- 
struction may attain considerable size and complexity, as in 
Caulerpa (fig. 21),* even to mimicking, upon a small scale, 
the form of leafy plants. In such cases the external walls 
become considerably thickened, and across the chamber, from 
one side to the other, run irregular bars of similar material 
which act as braces to prevent the collapse of the outer walls 
(fig. 22). 

In Caulerpa, particularly, a high degree of development as 
to external form is reached (fig. 21). There is a stem-like 



* Note carefully the scale of the figures. 



FILAMENTOUS ALGM. 



21 



axis, v-s, creeping in the mud, which bears green leaf-like 
branches, b, on one side and clusters of colorless root-like 




Fig. 21. — Part of a plant of Caulerf>a. See text, IF 27. Two-thirds natural size. — 

After Sachs. 




branches, w, on the other. Not only are a base (posterior 

end) and an apex (anterior end) distinguishable, but the 

plant shows a difference between an 

upper (dorsal) and under (ventral) side, 

the leaf-like thallus lobes arising from 

the dorsal side, while rhizoids spring 

from the ventral side. 

28. The thallus.— To the loose ag- 
gregation of single cells into colonies of 

Fig. 22.- Transverse section 

definite form, as well as to the body of axis of Cauier/>a, show- 
ing cross-bars to stiffen wall. 

formed by their more intimate union in Magnified about 25 diam.— 

nil After Murray. 

the cell rows and masses just described, 

the name thallus is applied. The term is most frequently 
applied to those more complicated forms which constitute 
the vegetative bodies of the higher algae, which are now 
to be described. 

29. Summary. — Instead of being loosely associated in e©l- 



22 OUTLINES OF PLANT LIFE. 

onies, plant cells may remain firmly united in rows or sheets. 
Such an aggregation of cells is then called a plant. The 
form of the plant depends upon the mode of division of the 
cells. The body may be thread-like, and alike at both ends. 
Or it may be distinguishable into a base and apex, or even 
into a root-like part, the rhizoid, and a shoot-like part, the 
thallus. Either may branch. Branching is due to more 
rapid local growth of certain regions. In some plants the 
protoplasm is not, or only incompletely, divided by cell- 
walls. 



CHAPTER IV. 



THE THALLUS OF THE HIGHER ALG^E. 



30. The larger algae. — From the thread-form algae, 
whose body is a single row of cells, it is but a step to those 
forms whose body consists of a single sheet of cells. One 
common form has a leaf-like body, which grows attached to 
stones or other algae. The broader forms are sometimes 
20-25 cm. wide. 

The body of the sea-lettuce is somewhat similar in structure, 
but consists of two layers of cells, 
and, as fig. 23 shows, is very clearly 
distinguishable into an organ of 
attachment, the rhizoid, and the leaf- 
like part for which the name thallus 
may be kept. 

So, from the thread-like bodies we 
pass through sheet-like to massive 
bodies of a broadly extended form. 
Likewise there may be found all in- 
termediate forms between the thread- 
like algae and those whose bodies 
are slender, but are more than one 
row of cells thick. 




Fig. 23.— A small plant of Ulva 
lactuca, the sea-lettuce, show- 
ing thallus, and rhizoid for 
attaching it to rocks. Natural 
size.— From 



In other marine algge a still higher specialization of members is reached. 
One of the red seaweeds may be used to show the gradual advance in 
complexity. 

23 



24 



OUTLINES OF PLANT LIFE. 



Polysiphonia. 

31. External form. — The body of Polysiphonia, a slender 
alga (fig. 24) which grows in abundance upon rocky sea- 
coasts, is much branched. The main axis is 
made up in its larger parts of five or more rows 
of cells, the central row being surrounded by a 
jacket of at least four others (fig. 25) ; but at 
the tips even of the main axis there is only 
a single row of cells, as in the simplest algae 
(fig. 26). The body of Polysiphonia, there- 






Fig 24. Fig. 25. Fig 26. 

Fig. 24.— An entire plant of Polysiphonia, showing mode of branching. Natural size. 
— After Kiitzing. 

Fig. 25. — Transverse section of one of the branches of rolysif-honia, showing a 
minute central cell with four large and four small cells surrounding it. Magnified 
about 50 diam. — From a drawing by Mr. Grant Smith. 

Fig. 26. — Apex of a branch of Polysiphonia which has nearly ceased growing. Mag- 
nified about 100 diam. — From a drawing by Miss Rowan. 



fore, is one of the simplest forms composed of cells massed 
together. 

32. Growth. — Growth in length can take place only at the 
ends of the main axis and its branches, because there each 
apical cell (fig. 26) produces, by division near its base, the 
new cells whose later division and enlargement make the 
mature axes. 

33. Color. — In this plant, as in very many of the marine 
algae, there is present, in addition to the green of the chloro- 
plasts, a special red coloring matter. To the naked eye, this 



THE THALLUS OF THE HIGHER ALG/E. 2$ 

color overpowers the green and gives the plant a pink tinge. 
In other red algre it is often present in greater quantity and 
variety of hue, so that brilliant reds and purples, with shadings 
of brown and green, mark the more striking species. 

EXERCISE VI. 

Polysiphonia. — Place a plant in a glass dish over a black or white back- 
ground. Observe 

i. The form of the body and the mode of branching. (Fig. 24.) 

2. The mode of attachment at the base, if specimens are entire. 

3. Demonstration. Mount the tip of one of the branches and show the 
high, dome-shaped, apical cell, with segments cut off successively from its 
base, to be later themselves divided longitudinally. (^[ 32, fig. 26.) 

4. Cut a transverse section of a medium-sized axis and observe the four 
large peripheral cells, surrounding a central cell ; the latter to be seen only 
under compound microscope. (][ 31, fig. 25.) 

Between the very simple body of Polysiphonia and the much 
larger and more complex body of the common bladder- wrack, 
or Fucus vesiculosus, there are all gradations, which cannot 
be described here. 



Fucus. 

34. External form. — The body of Fucus (fig. 27) is large 
as compared with the plants previously described. It is often 
75-100 cm. long by 1-2 cm. broad, of greenish- brown color 
and somewhat leathery texture. Near the base the thallus is 
contracted into a stalk whose extremity is broadened into a 
sucker-like disk (often irregularly branched) which attaches 
the plant firmly to the wave-washed rocks, on which it grows. 
Above, the thallus is flattened, with a thicker rib in the mid- 
dle (fig. 28), and branches abundantly by forking. These 
branches, though often twisted, really lie in the same plane 
as the flattening (fig. 27). Here and there the thallus has 



26 OUTLINES OF PLANT LIFE. 

pairs of oval bladdery swellings, which, by the gases they con- 
tain, give greater buoyancy to the plants in the water. 




Fig. 27. — Upper part of a plant of Fucus vesicu.osus. r, midrib of thallus ; /, 
bladders ; s, swollen tips covered by numerous elevations, in each of which is a pit 
which contains many sex-organs. Two thirds natural size.— After Luerssen. 

35. Growing point. — The very tip of each growing branch 
is notched and at the bottom of the notch is a group of cells 
which by division produce all the parts of the thallus. This 



THE THALLUS OF THE HIGHER ALG^E. 2J 

youngest region, found also at the tips of the growing axes of 
the higher plants, is the growing point. It has no limit below, 
but as the parts further and further from the apex are exam- 
ined, they are seen to become more and more unlike with age 
until the mature form is reached. 

36. Mature thallus. — If the mature part of the thallus be 
cut at right angles and a thin slice be cut off one end, placed 
on a glass slip and examined with a lens, it shows two distinct 
regions ; a central one, quite translucent, the pith, bounded 
by an outer brownish opaque region, the cortex. The 
central part is very full of mucilage, produced by a change 
in the substance of the cell-walls of the pith region. In the 
bladders this mucilaginous pith does not increase to fill the 
central space, but this is occupied by a great chamber filled 
with air and other gases. In the midrib the structure is 
plainly denser than elsewhere, except in the stalk below, 
which is like an enlarged midrib without the side wings. 

37. Division of labor. — Complete examination of other 
parts, the attachment disk, the hair pits (fig. 28) with which 




'-;:..-- - ■---' - :.v -.'■>■:_■■ ' ■■ ,-■ ■_.'■■.-'.■... : ' a ■,■.:■:.:■ .-:;„, 



Fig. 28. — A transverse section of the thallus of Fucus, showing midrib, r\ cortex, c\ 
pith, m ; and a hair pit, p. Magnified 10 diam.— From a drawing by Mr. C. E. Alien. 

many species are covered, etc., would reveal still other ways 
in which unlikeness arises with age from the uniformity of the 
growing point. With the change of form there is always di- 
vision of labor, which we can interpret only in a very imper- 
fect fashion from our own standpoint. The compact cortex 
is nutritive and probably in part protective ; the bladders serve 
to increase the buoyancy of the plants when the tide is in ; 
while the abundant mucilage, found in the interior, probably 
serves to retain the moisture when the plants are exposed by 



28 OUTLINES OF PLANT LIFE. 

the ebbing tide ; the hair pits are useless, so far as known ; 
and the strong, elastic disk and stalk above hold the plants in 
place as they sway constantly back and forth in every wave 
of the rising or falling tide. 

38. Color. — The coloring matter in Fucusand other brown 
seaweeds is of two kinds, a green (chlorophyll), and a brown. 
These colors are found chiefly in the cortex, which is, there- 
fore, the food-making tissue (see 1" 190), while the internal 
tissues may be used for storage of reserve food. 

EXERCISE VII. 

Bladder Wrack. (Facits vesiculosus). — Place a plant in a glass dish or 
a pan of water. Observe 

1. The general form of the body or thallus ; its mode of branching. 

a 34.) 

2. The thicker central region forming a midrib, with thinner wings. 
(Eigs. 27, 28.) 

3. Downwards, the thickening of rib and death of wings to form stalk 
near base. 

4. The lobed attachment disk at base of stalk. 

5. The swollen regions of the wings here and there. Cut into one of 
these and observe that it is a bladder. 

6. The notched tips of some branches ; the enlarged and more or less 
distorted tips of most, forming the receptacles. 

7. Scattered on the thallus minute elevations, from which protrude 
through an opening at the top a tuft of fine hairs. These are the mouths of 
the hair pits. (Fig. 28.) 

8. Crowded on the receptacles, larger warts with a hole at top and sim- 
ilar protruding hairs. These are the mouths of larger pits, conceptacles , 
which contain the sex-organs. 

Cut two thin transverse sections of the thallus, one through the bladder 
and the other through the general thallus. The latter should include a 
hair pit. Examine them with a lens and observe 

9. In the latter, the denser outer tissues ; the cortical region ; the looser 
inner ones, of elongated threads and much mucilage, the medullary region; 
the thicker denser midrib; the form of the hair pit. 

10. Note the difference between the structure of the bladder and the 
unswollen wing. Which region is altered to form the bladder ? 



THE THALLUS OF THE HIGHER ALGM. 29 

39. Summary. — Comparing the thread-form with the thin 
broad algae, we find the body of the latter often nearly as 
simple ; but, when the body is thicker, it is often seen to con- 
sist of unlike regions. The outer parts are arranged so as to 
enable the plant to make food for itself by getting the proper 
material from the water and absorbing the light that falls 
upon the surface. The inner parts, being too much shaded 
by the outer to serve for food making, are used for other pur- 
poses. Special organs for floating the plant are formed in 
some of the brown seaweeds. 

Other algae, of slender form, are more complex by having 
the older cells of an at first single row divided by partitions 
parallel to the length into five or more cells. 

With greater complexity* of the body, growth in length 
usually becomes localized at the tips where all the cells are 
rapidly dividing. 



CHAPTER V. 

THE FUNGUS BODY. 

Fungi are plants without the green coloring matter chloro- 
phyll (see U" 6), whose body is generally made up of long 
filaments, either loosely or densely interwoven and united. 

40. Origin. — As the bacteria (see ^j 14), the smallest and 
simplest plants, were probably derived from the lowest algae 
by slowly adapting themselves to get ready-made food, so, at 
various times in the past and therefore at various points in 
the ascending scale of algal life, certain algae have adapted 
themselves to the use of food which they could secure from 
other beings. Then, having no use for the chlorophyll and 
chloroplasts, they have gradually lost them. The adoption 
of the habit has proved highly successful, both among the 
simple bacteria and the more highly organized true fungi. 
The ancestors of the present species were — how long ago no 
one can say — probably at first chiefly, if not exclusively, 
aquatic. Some, at the present time, have the same habit, 
growing in infusions of organic matter. Others attach them- 
selves to dead or even living animals or plants in the water. 
The bodies of dead or living organisms furnish places of growth 
for a great number of species which have adapted themselves 
to other than aquatic life. Many live in the soil because it 
contains in its upper layers more or less organic matter from 
the offal of plants and animals, or from their dead bodies. 

41. Hyphae. — The filaments of which the fungus body is 
composed are called hyphae. Each is the result of growth 

30 



THE FUNGUS BODY. 



31 



from a single cell, and is comparable to the thread-like body 
of the filamentous algae. 

There is, naturally, a great variety in the hyphae of differ- 
ent species of fungi. Some are relatively large ; others very 
small ; some of even diameter and caliber, others irregular 
and with unequally thickened walls ; some very thin- walled, 
others very thick-walled. Between these extremes is to be 
found a complete gradation. 

They grow in length at the apex only. In many kinds 
partitions are formed at more or less regular intervals, as the 
growth in length proceeds, while in others no partition-walls 
are formed. Even when transverse partitions form, they do 
not separate the filaments into cells, but each chamber, or 
sometimes the whole filament, represents several or many 
cells. (Compare % 26.) 

42. Branching. — As the hyphae elongate, branching may 
occur. If a branch is to be formed, a limited area of the 
cell-wall begins to grow more rapidly than the rest. This 
allows a slight bulging of the growing region ; the swelling 
increases and soon takes the form of 
a branch, like the main axis. It may 
remain short or continue to grow 
indefinitely in length. Commonly a 
cross-wall is formed at the base of the 
branch. If such a branch arises first 
as a minute pimple, so that it remains 
connected with the parent axis by a 
small neck, and has only limited 
growth in length, it is called a bud 
and the process is known as budding 
(fig. 29). Such branches are usually 
easily broken off, thus readily produc- 
ing independent plants. (See further 
under Reproduction, ^[ 261.) In some species of fungi, 




Fig. 29. — Beer-yeast {Saccharo- 
myces cerevisice). a, a full- 
grown plant with a branch 
(bud) partially developed, b, 
c. colonies formed by budding, 
the individuals still attached. 
Magnified 750 diam.— After 
Reess. 



32 



OUTLINES OF PLANT LIFE. 



profuse branching is the rule ; in others, the branches are 
few. 

43. Mycelium. — When branching is profuse, or when a 
considerable number of individuals grow near together, the 
filaments often become interwoven and entangled in so com- 
plex a web that it is impossible to follow a single hypha for 




Fig. 30. — A single plant of Mucor Mucedo, showing the mycelium as it developed from 
a single spore. It bears a single erect reproductive branch rising above the fluid. 
Magnified 25 diam. — After Brefeld. 

any distance. Such a mat of hyphae is called a mycelium, a 
term which is also used to designate the vegetative hyphae 
collectively, whether forming a felted mass or not (figs. 30, 
31). The mycelium may be formed wholly upon the surface 
of the object upon which the fungus lives ; or part of it may 



THE FUNGUS BODY. 



33 



lie on the surface, and part may penetrate that object ; or all 
of it may be hidden within the substratum.* In some of the 
common molds (Mucorini), the cobwebby threads lying upon 
the surface of the substratum constitute the exposed part of 
the mycelium, while other hyphae penetrate deeper ; in 
others (Penicillium, etc.), the superficial hyphae become so 




Fig. 31. — A section of part of the aerial body of Polyporus. sp, hyphae running at an 
angle to the section, cut across ; K } crystals of oxalate of lime. Magnified about 500 
diam.— After Vogl. 



interwoven that they may be lifted off the substratum (as 
from jellies, jams, syrups, etc.) as a coherent layer. But in 
most cases, especially when the fungus grows on a solid 
medium, the hyphae become adherent to it and permeate it 
so that they cannot be separated from it, even by the most 
careful dissection. 



* This non-committal term may be used to designate the material upon 
which the vegetative part of the fungus grows, whether it be a living 
body, a dead organism, or organic matter in solid or liquid form. 



34 OUTLINES OF PLANT LIFE. 



EXERCISE VIII. 

Black mold {Rhizopus nigricans). — Before any white or black dots ap- 
pear on the mold examine the vegetative hyp ha. (^[ 41.) These are of 
two kinds, (a) those running over the surface of the bread ; (b) those 
penetrating it. 

1. Examine a. Lift up a few threads with a needle and mount them 
in water. Study with a lens. Are they white or colorless ? Why 
then is the body composed of them (the mycelium, ^ 43) white ? 

2. Examine b. With needles tease out hyphse from a bit of bread in 
water ; free them as far as possible from the dehris and mount. Com- 
pare with a. 

After mold has begun to show black dots (spore cases, ^[271) examine 

3. Determine how the branches are placed which bear the spore cases. 

(Fig- 30- ) 

4. Compare the white (young) and black (mature) spore cases. Can 
you find the very smallest ones ? 

5. Snip off a few ripe spore cases with scissors, handling them cau- 
tiously to avoid breaking or tangling them ; mount in alcohol * and ex- 
amine. Crush (if not already broken) and observe numerous dust-like 
particles, the spores, which escape. (Fig. 146.) 

44. Parasites. — Especially is this true of those fungi 
which grow in the interior of living organisms. The higher 
plants are liable to be fastened upon by parasitic fungi, and 
compelled to act as hosts to their unbidden and unwelcome 
guests. Such a host plant may be entered when a mere 
seedling, in which case the fungus grows with its growth, or it 
may not be attacked until older or even mature. The host 
may be permeated in all its parts by the fungus filaments ; or 
certain members only, such as the leaves, flower parts or 
twigs, may be affected. The effect of the fungus upon the 
host is often scarcely visible to the unaided eye ; sometimes 
a local disturbance is manifested by swelling, unnatural color 
or growth ; sometimes the affected members become distorted 



* Because water will not wet them. Replace alcohol as it evaporates ; 
it does so rapidly. 



THE FUNGUS BODY. 35 

and useless or are even killed j sometimes the disease is gen- 
eral and is followed, slowly or quickly, by general death of 
the host. (See further ■ ^j 184, 369.) 

45. Infection. — These internal parasites obtain entrance to 
their hosts in various ways. Sometimes the young hypha, 
growing from a special reproductive body (spore),* so min- 
ute that it may easily float in the air and fall upon a leaf, 
creeps along the surface till it finds one of the microscopic 
openings in the skin of the leaf, into which it grows (sfi, fig. 
32). These external openings are connected with irregular 




Fig. 32. — Young hyphse of Exobasidittm developing from spores, s/>, entering the 
air-pores of the leaf of the cranberry. Others, from s/>' , sp" ', penetrate the skin 
directly. Magnified about 600 diam. — After Woronin. 

spaces between most of the cells of the softer parts (fig. 106), 
which are also the parts in which the food-supply is most 
abundant. In these, therefore, the fungus develops, break- 
ing out to the surface again to form or set free its reproduc- 
tive bodies. 

Or, the young hyphae may excrete at their tips a substance 



See ^f 263 and the following. 



36 



OUTLINES OF PLANT LIFE. 



which so softens or dissolves the cell -walls of the host that 
they penetrate these cells readily, not only at the surface 
(sp', sp" ', fig. 32), but in the interior.* They then branch 
freely, often growing in the spaces 
between the cells, often passing through 
the cells themselves (fig. 33). 

Plants are often attacked when mere 
seedlings. From either a bit of my- 
celium or a spore that has survived 
the winter or the dry season, a hypha 
grows, which, almost as soon as the 
seedling emerges from the seed, pene- 
trates it. The fungus, in these cases, 
may develop quickly and kill the young 
plant (as in the ''damping off" disease 
in greenhouses), or it may develop slowly 
and not reach its maturity until the host 
is also mature. 

46. Haustoria. — Those fungi which 

grow upon the surface of living plants 

(and those which grow in the internal 

;• air-spaces) often have special branches 

for fastening themselves to the host or 

Hyphae of Tm- absorbing food from it. In the surface 

111,'tes Pirn perforating at c . 

the walls of a wood-ceil of lungi these are usually very snort, disk- 

Scotch pine and destroying iiji t, v • i a 

the primary wail of the ceil, like or Jobed branches which do not 

<i, e, holes made by hvphae. . , . t 

Magnified about 800 "diarn. penetrate the cells 01 the host. In 

-After R. Hartig. . 

other cases they are branches of minute 
diameter, which enter the cells, and either enlarge into a 
knob (fig. 34) or branch profusely (fig. 35). 




* The penetration of cell-walls is probably assisted by such pressure 
as the growing hypha can exert. 






THE FUNGUS BODY. 




FlG. 34. — Epidermis and a few cortical cells of cowberry with mycelium of Calyptospora 
occupying the intercellular spaces and pressing knob-like ends against the cells from 
which a slender branch penetrates the wall and enlarges in the interior into sac-like 
haustoria, b, b. a, c, reproductive branches. Magnified 420 diam. — After R. Hartig 



EXERCISE IX. 
Mildew {Microsphara), a surface parasite. — Examine dried leaf bear- 



1. The whitish interlacing hyphse on surface of leaf, forming the 
mycelium. (*[| 43.) 

2. The distribution of the fungus : does it cover the whole leaf or only 
occur in patches ? Compare the earlier and later gathered leaves as to 
this. 

3. Demonstration. Scrape a bit of the mycelium from the surface of 
the leaf after moistening it for a few minutes with a 5$ solution of 
potassic hydrate. Mount and show (a) the colorless branching hyphse ; 
{b) the erect branches bearing the spores ; (c) the spores. 

4. Examine, as before, one of the older leaves. Observe the yellow- 
ish dots scattered over the mycelium, the immature fruits. Associated 
with these the black mature fruits, which contain sporangia with 
spores. (^| 271.) 

White fust {Cyst opus portu/acce), an internal parasite. 
I. Demonstration. Boil a leaf of purslane for a minute or two in $% 
potassic hydrate. Tease apart the tissues of leaf with needles on a slide, 



38 



OUTLINES OF PLANT LIFE. 



mount and show the mycelium of the fungus consisting of tangled hyphse 
ramifying among the cells of leaf. (UH 44, 45-) 

Examine a dried leaf. Observe 

2 The white blisters [spore beds) here and there on the surface ; the 
thin membrane (the epidermis of the leaf) by which they are covered ; 
in older blisters the cracking and final disappearance of this skin. 

(% 269, fig. 141.) 

3. The white powdery scores which jar out or can be dislodged with 

needle. 

47. Fusion.— When the hyphse of a fungus grow very close 

together, they frequently cohere and become so changed in 

appearance as to lose all trace of resemblance to filaments. 

Not only fusion but thickening and division occur, and a 

section of the resulting structure has much the appearance of 





Fig. 35- 



Fig. 36. 



bSinfthereta The other contents of host-cells not shown. Magmfied about 400 

Sflaments recognizable. The dark spheres are imprisoned alga,. Magnified 650 diam. 
— After Bornet. 

a section of the tissues of a higher plant (fig. 36)- These 
changes are particularly apt to occur at and near the surface 



THE FUNGUS BODY. 39 

of the more massive parts, where they are necessary to impart 
firmness, rigidity, or durability. 

The interweaving and fusion of the hyphae sometimes pro- 
dace cord-like or strap-like structures of considerable size. 
The mycelia of the higher fungi frequently form them, and 
they may be found in the leaf-mold of forests or in rotten 
stumps or between boards in wet places. 

48. Lichens. — The body of lichens is a mycelium woven 
about the simpler algae, rarely about other small green plants, 
which are thus imprisoned. The fungus hyphae usually pre- 
dominate and in great measure determine the form of the body 
and its texture. Sometimes the algae are present in such 
numbers that the hyphae seem merely distributed among them. 
In form the body maybe broad and thin (fig. 215), or slender 
and shrub-like ; in some cases it is so thin and adherent, or so 
interwoven with the substratum, that it seems to form a mere 
crust over it. In texture it may be tough and leathery, with 
the hyphae near the surface fused into a false tissue [a, b, fig. 
36). When gelatinous algae, such as Nostoc (see ^| n) are 
imprisoned, the body may be gelatinous while wet. In all 
cases the algae supply the fungus with food, and are in turn 
supplied with water absorbed by the spongy mycelium. (See 
further ft 164, 185, 367.) 

EXERCISE X. 

Lichen {Physcia stellaris). — Soften a plant by soaking it in water for 
a few minutes. Observe 

1. The mycelium, forming a connected leaf-like lobed thallus. Com- 
pare as many other forms as are available. (^[ 48, fig. 215.) 

2. Compare the color when dry and wet. In the latter condition, the 
mycelium is more translucent and the imprisoned green algse show 
through more plainly. (Figs. 36, 216.) 

3. The tufts of hyphae extending from lower surface to bark, the hold- 
fasts or rhizines. 

4. Occupying the central region on the upper surface, the round 
colored disks, the clusters of spore cases. 



40 OUTLINES OF PLANT LIFE. 

Cut a vertical section through a part of the thallus. Observe 
5. The layers of the thallus ; above and below, dense layers, the 
upper and lower cortical layers ; between them, the medullary layer, 
with green algce distributed unequally through it. (Fig. 36.) 

49. Summary. — The fungi, though descended from the 
algae, have adapted their body to new conditions of life so 
completely that it shows little resemblance to that of the algae. 
All have colorless (non-green) bodies, composed of slender 
hyphae, frequently much branched and interwoven, and either 
applied to the surface or penetrating the substratum. Some 
kinds live on dead organic matter (saprophytes); some are 
external and some internal parasites. The latter enter the 
host through pores, or by perforating the skin, often causing 
deformity or disease or death. When strength or protection 
or durability is necessary, the hyphae may become insepara- 
bly fused into a false tissue. Lichens are special kinds of 
fungi, associated for life with simple algae from which they 
derive their food. 



CHAPTER VI. 

LIVERWORTS AND MOSSES. 

50. Alternation of generations. — In the liverworts and 
mosses, as in all the plants higher in the scale, there occur 
two well-marked phases in the course of their lives. One of 
these phases is marked by the formation of sexual repro- 
ductive cells, or gametes, the egg and sperm (see ^[ 304), 
whence it is called the sexual phase, or the gametophyle. The 
other is characterized by the formation of non -sexual repro- 
ductive cells, the spores (see ^[ 263), whence it is called the 
non-sexual phase, or sporophyte. These two phases alternate 
with each other ; i.e., the eggs produced by the gametophyte 
do not form a new gametophyte but a sporophyte ; and the 
spores of the sporophyte do not form a new sporophyte but a 
gametophyte. Representing the gametophyte by G and the 
sporophyte by S the sequence is G^-^S^-^G-m-^S-m-^G^-^S, 
and so on, generation after generation. Often the gameto- 
phyte forms other gametophytes repeatedly, but usually the 
succession is interrupted, sooner or later, by the formation of 
fertile eggs and from these a sporophyte. In such cases the 
sequence may be represented thus: GGGGm-^Sw^>GGG^-^S 
»^>GG, etc. The sporophyte of these plants never propagates 
its own form. To this regular sequence of the two phases 
the phrase alternation of generations has been applied.* 

* Rather obscure suggestions of the alternation of generations are to 
be found among the algge and fungi, but they are not definite enough to 
warrant discussion in this book. Let the student notice, however, that 
this feature does not appear suddenly in plant life, though introduced 
abruptly into the account of it. 

41 



42 OUTLINES OF PLANT LITE. 

In each phase, a body of form and structure suited to its 
special work is produced. In the higher liverworts and 
mosses both phases have nutritive work to do, but in many 
this is confined to the gametophyte, and in all the gameto- 
phyte carries on the greater part of it. To this phase, there- 
fore, attention is first given. 

Liverworts. 

51. The thallus. — The form and structure of the vegeta- 
tive body of the simplest liverworts is scarcely different from 
that of some of the green algae. The body is a thallus with 
rhizoids (fig. 37). The rhizoids are usually filaments arising 





Fig. 37.—/}, plants of Riccia sorocarpa, on the ground. Gametophyte phase. Nat- 
ural size. B, a vertical section of one of the thick lobes of the thallus, showing nearly 
uniform structure. The thallus has nearly covered over two young sporophytes 
which appear as though in the interior. Rhizoids arise from the ventral side and 
flanks. Magnified about 25 diam. -After Bischoff. 



from the under side and flanks of the thallus. They serve to 
fasten the thallus to the substratum, and perhaps assist it in 
absorbing water. The thallus is usually thin and flat, though 
sometimes much crisped. Most liverworts lie broadside to 
the substratum. Very rarely is the thallus erect and attached 
by a narrow stalk. 

52. The dorsiventral thallus. — In the simplest forms the 
thallus is uniform in structure from upper to under side. In 
others there is a decided difference between the two sides. 
The upper part is green, while the under is not. In one 
family there are large air-chambers in the upper part of the 



LIVERWORTS AND MOSSES. 



43 



thallus, from the floor of which arise green filaments (fig. 38). 
On the under side, also, are frequently found scale-like out- 
growths as in fig. 38, i. 

A part which shows constant differences between an upper 
(dorsal) and an under (ventral) side is said to be dorsiveniral. 




Fig. 38 Fig. 39. 

Fig. 38. — Portion of a vertical section of the thallus of Lumilaria cruciata. a, dor- 
sal, b, ventral epidermis ; c, an air-pore ; e, air-chamber, from whose floor rise green 
filaments, d\ f, partition between adjoining air chambers ; e, colorless cells contain- 
ing starch, some showing net-like thickenings of the walls, others with oil-bodies, h ; 
i, a ventral scale ; /, a rhizoid. Magnified no diam. — After Nestler. 

Fig. 39. — Lunularia cruciata, showing horizontal thallus and rhizoids with two erect 
branches (one young, one mature), for carrying sex-organs. Natural size. -After 
Bischoft. 



These differences are usually called forth by the action of 
light (see f 325). 

53. Branching. — The branching of the thallus is always 
by forking, in a single plane or direction, as in Fucus, but 
the branches do not always develop equally. Sometimes 
special branches, instead of remaining horizontal, grow up- 
right and develop into peculiar forms adapted to producing 
the sexual reproductive organs (fig. 39). 



44 OUTLINES OF PLANT LIFE. 



EXERCISE XL 

A thallose liverwort {Marchantia polymorpha). — Examine an entire 
plant in water. Observe 

i. The flattened horizontal body [thallus) with central line, the mid- 
rib, and thinner wings on each side. 

2. The notched apex (the wings outgrow the midrib somewhat). 

3. The mode of branching (forking). Examine the tips and find one 
just branched. Do not confuse with notch of apex ; when a tip branches 
there will soon appear two notches. Docs the branch appear on the 
side of the older thallus, or are the branches equal at first ? Are they 
equal when older? (^[ 53.) 

4. The green lens-shaped bodies [brood-buds) growing at certain spots 
along the midrib, surrounded by an outgrowth which forms a cupdike 
rim about the cluster. Remove a brood-bnd and observe its form, 
especially in full grown ones the two opposite notches, the growing 
points. (1 297, fig. 177.) 

5. The air-chambers {areola) of the upper part of the thallus, showing 
through the skin, best seen in older parts and with a lens. What is 
their form? Are they all alike ? («[ 52.) 

6. The openings into the air-chambers, in the skin over each one, 
like a little pinhole. 

7. Compare the under surface with the upper. Observe the numerous 
hairs. Discover the difference in place of origin and direction of 
growth of these. (^[ 51.) 

8. Carefully pull off with forceps as many of these hairs as possible 
and notice the dark-colored overlapping outgrowths along the midrib, 
curving outward as they are followed forward, attached along their 
edges. These are the so-called " leaves." 

Cut a transverse section of the thallus through a brood-bud cup. 
Observe 

9. The origin of the brood-buds (only the younger still remaining) over 
the midrib. 

10. The difference between tissue of upper and under parts of thallus. 
(If fresh plants are available observe especially the difference in color.) 

11. Demonstration. Cut a very thin transverse section of the thallus. 
Select a part passing through stoma and show 

(1) The air-chamber ; its roof, the skin, with chimney-like stoma in 
center ; its sides a vertical plate of cells ; its floor, with branched fila- 
ments of chlorophyll-bearing cells. (Fig. 38.) 



LIVERWORTS AND MOSSES. 



45 



(2) The large-celled colorless tissue forming the lower half of section ; 
the sections oi " leaves " arising near midrib and concave towards center. 

54. The shoot. — In the greater number of liverworts the 
mature vegetative body is a shoot, which is differentiated 
into stem and leaves (figs. 40, 41). Even in such a body 
the dorsiventral character is well 
marked. The stem is slender 
and bears three (rarely more 
or fewer) rows of leaves, of which 
the two dorsal rows are the larger, 





Fig. 40. Fig. 41. 

Fig. 40.— Gametophyte of Bazzania Nov ce- Ho Hand 'ice. Besides the ordinary branches 

there are slender ones (fiagella) with sparse minute leaves. Natural size. — After 

Lindenberg and Gottsche. 
Fig 41. — A , dorsal view ; /?, ventral view of a piece of fig. 40, magnified about 12 

diam., showing the stem, bearing two dorsal rows of large leaves and one ventral 

row of small ones.— After Lindenberg and Gottsche. 

while the under leaves are much smaller, even to being incon- 
spicuous or wanting. These leaves consist of a single sheet 
of uniform cells richly supplied with chloroplasts, as are also 
the outer cells of the stem. Their form is very varied and 
often of great beauty. They are usually crowded so closely 
as to overlap each other more or less, and hide the stem 
completely (fig. 41). 



46 OUTLINES 01 PLANT LIFE. 



EXERCISE XII. 

A leafy liverwort {Porella platyphylla). 

i. In what position do the plants grow with reference to the sub- 
stratum ? 

Disentangle carefully a single plant.* Observe 

2. The growing apex ; the dying base ; the distinctly dorsiventral 
habit. Enumerate the differences between the upper and under sides. 

(II 54-) 

3. The mode of branching : a central axis, with lateral branches, 
themselves with lateral branches ; i.e., monopodial and bipinnate. (^ 58.) 

4. The yellowish or brownish stem, covered with leaves unequally 
distributed. 

5. The two rows of large leaves on the upper flanks of the stem. 
How do they overlap ? Turn the shoot over and note a third row of 
small underleaves in the center below ; also right and left the lobes of 
the upper leaves. Determine the form of the under and upper leaves. 
Make an enlarged paper pattern of the latter showing how their ventral 
lobes are arranged. (Figs. 40, 41.) 

6. Demonstration. Mount a leaf and point out the uniformity of cells 
and their abundant chloroplasts. 

Mosses. 

In the mosses the complexity of the mature vegetative body 
is somewhat greater. It is always developed as a shoot dif- 
ferentiated into stem and leaves. 

55. Rhizoids. — The shoot is anchored, as in the liver- 
worts, by numerous usually much branched rhizoids (A, fig. 
42 ; w, fig. 43). Similar filaments may be produced, often 
in great numbers, along the stem and especially inthe axils 
of the leaves, or they may even arise from the leaves them- 
selves, when the plants grow in dense patches or in a very 
moist place. 

56. The stem is usually cylindrical and covered by the 
crowded leaves. In structure it generally shows an advance 
upon that of the liverworts, which is nearly uniform, in hav- 

* If dry, first soften by placing plants in hot water for a few minutes. 



LIVERWORTS AND MOSSES. 



47 



ing the whole of the outer region occupied by a distinct mass 
of mechanical tissue for stiffening the stem, and, near the 
center, a strand known as " conducting tissue," which may 
act as a line of transfer for water or food. 




Fig. 42. — A, gametophyte of Polytrichum commune, with rhizoids below. B, gameto- 
phyte of tlylocomitini splendens, bearing three sporophytes near top. Natural size 
—After Kerner. 



57. The leaves are also more highly developed than in 
liverworts. They are always sessile and are arranged in two 
(rarely), three, or more vertical ranks along the stem, and 
consist usually of a single sheet of green cells, the blade (figs. 
43, 44), and a central rib running from base to apex (fre- 
quently wanting), which is composed of elongated conduct- 
ing and strengthening cells (figs. 43, 44). In some the 



43 



OUTLINES OF PLANT LIFE. 



amount of green tissue is increased by the formation of verti- 
cal plates similar to the blade (fig. 44). 

58. Branching. — The stem branches, often very profusely. 
Sometimes the growth of the lateral branches, as of the 
original main axis, is checked by the formation of sex organs. 
In that case a new branch is likely to arise some distance 





Fig. 43. Fig. 44. 

Fig. 43. — A, leaf of a moss {Funaria Americana), showing central rib. Magnified 

about 40 diam.; B, upper portion of the same leaf, highly magnified, showing single 

layer of cells forming the blade and the narrower cells of the thick rib —After 

Sullivant. 
Fig. 44. — Tip of leaf of a moss (Oligotrichum aligerum), showing the thickened 

rib, and the plate-like ridges on. blade and rib greatly increasing the surface of 

nutritive tissue. Magnified about 75 diam. — After Sullivant. 

below the apex, so that the stem is merely a succession of 
lateral branches (fig. 45). This mode of branching is called 
sympodial. In other cases the main axis continues its growth 
unchecked, and more or fewer branches also develop. These 
lie plainly upon the sides of a central axis. This mode of 
branching is called monopodia/. Often the growth of the 
lateral axes is definitely limited and their development regu- 
lar, forming a pinnate branch-system. If the secondary axes 






LIVERWORTS AND MOSSES. 



49 



themselves branch, there is formed a bipinnate or even tri- 
pinnate system, as in figure 42, B. 

59. Protonema. — In its early stages the vegetative body 
of the leafy liverworts and the mosses is either a flat thallus, 
similar to the mature form of the 
thallose liverworts, or a branching 
filamentous body, called the pro- 
tonema, almost identical with the 
form of the branched filamentous 
algae. Upon this protonema the 
leafy shoot arises as a lateral bud, 
which soon outstrips it in growth 
and develops leaves. The pro- 
tonema may live for some months, 
but generally perishes after having 
produced a few leafy plants. 

60. Sporophyte. — The non- 
sexual phase in the liverworts and 
mosses has almost no vegetative 
functions. It consists at maturity 
of a yellowish or brown spherical or 
cylindrical case (fig. 46), which is 
sessile or raised upon a short or 
long stalk and contains (a few or) 
hundreds or thousands of repro- 
ductive cells called spores. The 
pointed or swollen base of this 
stalk is called the " foot," and is embedded in the gameto- 
phyte (/", fig. 47) to absorb food from it. 

61. Nutrition. — The surface of the young sporophyte, 
when large and well developed, as it is in the higher liver- 
worts and mosses, is green. To a limited extent, therefore, 
it is able to make food ; but not sufficient for its needs, for 
these are great on account of its rapid growth and the amount 




Fig. 45.— Axis of a moss {Ortho- 
trie hum) showing sympodial 
branching. S 1 , 6" 2 , S 3 , A 4 , suc- 
cessive clusters of sex-organs, 
produced at apex, which check 
the growth or axis. Beneath 
each a lateral growing point 
develops, producing successively 
the branches b 1 , b 2 , b s . Magni- 
fied 10 diam. — After Bruch & 
Schimper. 



5o 



OUTLINES OF PLANT LIFE. 





4/w-, 



Fig. 46 — A, two capsules of Bryum ; from the right-hand one the lid has fallen, show- 
ing the teeth. Magnified 5 diam. />', four gametophyte shoots of Splachnuni am- 
put lace u in, bearing four sporophytes. Natural size. C, a capsule of one of the 
same sporophytes, showing enlarged apophysis, a, below the spore case, s. Mag- 
nified 10 diam. D, capsule of Splachnuni luteum, with umbrella-like apophysis, a, 
below spore case, j. Magnified 2 diam. 

required to supply each spore. 
The foot, being in close contact 
with the tissue of the gameto- 
phyte, acts as an absorbing organ, 
receiving food solutions from it. 
The sporophyte thus lives, in 
part at least, as a parasite upon 
the gametophyte. 

In some mosses there is a tendency 
to increase the nutritive work of the 
sporophyte by developing at the top 
of the stalk, below the spore case, a 
mass of green tissue. In Bryum {A, 
fig. 46) this gives the capsule a pear- 
shape, while in Splachnuni (£, C, D, 
fig. 46) it is so far developed as to ex- 
ceed the spore case. In some species 
it is expanded into a miniature um- 
brella which, one can imagine, might 
readily become divided into leaves. 

The intimate attachment of 
sporophyte to gametophyte con- 
tinues throughout the life of the 
former. Sometimes the gameto- 




Fig. 47. — Young sporophyte of Phas- 
cuni cuspidatum. c, columella : f, 
foot, embedded in gametophyte stem ; 
s, seta (cells not shown) : sps, spore 
case ; sp, spore-mother-cells. Mag- 
nified 80 diam . —After Kienitz-Gerloff . 



LIVERWORTS AND MOSSES. 5 I 

phyte perishes at the close of the growing season, but more 
commonly it is perennial, growing and branching at the 
anterior end as the older posterior parts die away. 

62. Summary. — Liverworts and mosses show a distinct 
alternation of generations. The vegetative body of the sim- 
pler liverworts is a flat thallus, like that of the larger algae, 
but the higher forms have the central part developed as a 
roundish stem, and the wings so branched as to form separate 
leaves. The latter form is general in all the mosses, which 
further have the stem and often the leaves stiffened by the 
differentiation of mechanical tissues. The non-sexual genera- 
tion in all is relatively small and depends for its food upon 
the sexual generation. 

EXERCISE XIII. 

A moss {Milium cuspidatum). — Examine plants with capsules attached. 
Observe the two connected plants : 

1. The leafy stemmed plant or gametophyte. (^[50.) 

2. The slender plant attached to its tip, the sporophyte, consisting of 
a wire-like stalk, the seta, enlarged above to form the hanging capsule. 
(16o, fig. 46.) 

3. Boil for a few minutes in 5 per cent, potassic hydrate, rinse in 
water and gently pull sporophyte until it separates from the gametophyte. 
Observe the smooth pointed end which was sunk in gametophyte. If 
properly separated no sign of tearing can be seen. (Fig. 47.) 

Examine gametophyte in water. Observe 

4. The differentiation of the body into stem and leaves. 

5. The brown hairs (rhizoids) about the stem, which attach plant to 
ground. Do they branch ? (Tf 55- ) 

6. The strength of the stem ; test it by breaking it with a lengthwise 
pull. Cut a thin transverse section and observe dark colored mechanical 
tissues in outer region. (<[[ 56.) 

7. The form and structure of the foliage leaves : note midrib of me- 
chanical cells (test strength) ; latnina of one layer of cells large enough 
to be visible under lens ; border of mechanical cells, some projecting 
pretty regularly as teeth. (^[ 57, fig. 43.) 

8. Smaller, scale-like leaves on part of the stem. 



52 OUTLINES OF PLANT LIFE. 

Examine sporophyte with mature capsule. Observe 

9. The slender seta. 

10. The thin yellow inverted capsule, from whose end a piece has 
fallen leaving it open. (^[ 274, fig. 46.) 

11. About the edge of the capsule a fringe of pointed projections, 
teeth) curved inward, constituting the peristome. Break off these outer 
teeth and notice the pale fringed membrane within, forming the inner 
peristome or endostome. (Figs. 46, 148.) 

12. Among these, or to be pressed out of capsule, many fine spores. 
Examine young sporophytes of this or other mosses. Observe 

13. The cylindrical form of the embryo sporophyte. 

14. The hood covering its apex and carried up by it until the develop- 
ing capsule forces it off. 

15. The lid which falls off to open capsule. 



CHAPTER VII. 



FERNWORTS AND SEED-PLANTS. 



Fernworts. 

Among the still more complex plants, the ferns and their 
allies, the same ''alternation of generations " can be seen. 
The two "generations," or phases, have, however, changed 
much in relative size. Whereas in the liverworts and mosses 
the gametophyte is much the larger and more conspicuous, 
as well as the longer-lived, among fernworts the sexual phase 
is so much smaller that it is seldom seen ; and in some 
species it is almost microscopic. On the other hand, the 
sporophyte is the phase which is usually 
seen and the only part popularly known. 

63. The gametophyte. — The vege- 
tative body of this phase of the fern- 
worts iu its best developed forms is a 
small, flattened, green body of oblong, 
orbicular, or cordate outline, commonly 
less than half a centimeter in diameter, 
rarely as much as 2 cm. (fig. 48). It 
is strikingly like a thallose liverwort in 
general form, being distinctly dorsiventral 
and having rhizoids on its under side, 
which fasten it in place. Only the central 
part of the gametophyte consists of more 
than one layer of cells. On the under 
side of this central " cushion," as it is called, are borne the 
sex organs. 

53 




Fig. 48 —Ventral side of 
the gametophyte of a 
fern, Asftleniuvi. The 
notched end is the an- 
terior. Rhizoids near 
posterior end. The small 
circles show position of 
male organs ; the chim- 
ney-like projections near 
anterior end the female 
organs. Magnified 10 
diam. — After Kerner. 



54 



OUTLINES OF PLANT LIFE. 



64. Reduction of gametophyte. — In a few of the fern- 
worts the gametophyte is filamentous, or tuberous, and more 
or less completely subterranean and colorless ; such derive 
their food from decaying plant-offal. 

In higher plants of this group the gametophyte becomes 
still further reduced in size and structurally simplified, until 
in some species it is hardly more than a few cells surrounding 




Fig. 49. — Sporophyte of a fern, Polvf>odium vulgare, showing horizontal underground 
stem, bearing secondary roots and leaves. Natural size. — From Bessey. 



the sex organs. These reduced forms grow by the use of food 
stored in the spore from which they originate. Thegameto- 



FERN WORTS AND SEED-PLANTS. 55 

phyte of such species has lost wholly its vegetative character, 
and is restricted in function to the production of the sex 
organs. 

65. The sporophyte. — In contrast with the smallness and 
simplicity of the gametophyte is the relatively large size and 
complexity of the sporophyte (fig. 49). It is always differ- 
entiated into stem and leaves, and, with rare exceptions, 
roots also. It is also noteworthy that, as compared with 
mossworts, the chief work of nutrition has been shifted from 
the gametophyte to the sporophyte ; and this even when the 
gametophyte has its largest size and greatest duration, while 
nutritive work is wholly abandoned in the smaller forms. 
The sporophyte has also become the long-lived stage, the 
gametophyte being usually transitory (only exceptionally 
living more than one season), while the sporophyte lives 
through one season in the few annuals, and commonly for 
several or even many years. 

66. Members. — The mature sporophyte is differentiated 
into root, stem, and leaves. The important adaptations of 
the structure and forms of these members are so similar to those 
of the seed plants that they will be discussed in connection 
with them. 

EXERCISE XIV. 

Maidenhair fern [Adiantum pedatuni). 
I. The Gametophyte. 

1. Observe its shape and size ; the notch at the growing point (anterior 
end); the dying (posterior) end; the thicker central region, with thin 
wings. (T[ 63, fig. 48.) 

2. On the under side, a cluster of rhizoids near the posterior end. 

3. Compare this plant with the thalius of Marchantia. 

If gametophytes with young sporophytes attached are available, ob- 
serve 

5. That the young sporophyte is fastened to the under side of the gam- 
etophyte. 



56 OUTLINES OF PLANT LIFE. 

II. The Sporophyte. 

Taking the underground parts in a dish of water, observe 

I. The slender wire-like roots. How are they branched ? (^[83 ff.) 
Where are they attached to the stem ? Trace an unbroken one to the tip. 
The following points can only be seen on roots carefully gathered and 
cleaned. What difference of color near tip ? Can you find many fine 
tangled root hairs ? Where present ? Where absent ? (^[ 73.) 

Cut a transverse section of an old root, mount and observe 

3. The outer brown mechanical tissues (also used for storage). (^[ 78.) 

4. The central whitish tissue, chiefly the stele, in which the visible 
openings are the larger vessels. (^[ 75.) 

5. In what position does the stem naturally stand ? Observe its occa- 
sional branching (^[ 89); the surface covered with chaffy scales; the grow- 
ing apex and dying base. 

6. Its nodes and internodes ; the nodes are indicated by the attachment 
of a single leaf at each ; the internodes are the intervals between the nodes. 
How are the leaves placed? (*[ 104.) 

Cut a transverse section of the stem and observe 

7. The outer brown mechanical tissues (also used for storage). (^[ 
108.) 

8. The circular, oval, or C-shaped white tissues, most of which belong 
to the stele. Trace the course of the stele through at least two internodes 
by cutting a series of rather thick (1 mm.) sections, observing the mode 
in which the stele branches to pass out into a leaf. Cut also a longitudinal 
section through the base of a leaf stalk and trace course of stele. (^[' 
109.) 

Taking a perfect leaf, dried under pressure, observe 

9. The stalk or petiole, with its branches. Note the mode of branch- 
ing; the petiole divides into two equal divergent branches; each of these 
forks, one branch carrying leaflets while the other again forks, and so on. 

HHf 126, 128.) 

10. The hardness of the mechanical tissues at surface of polished petiole. 

II. The leaflets. Note (a) shape as to outline and margin, comparing 
basal, median, and terminal leaflets of any branch; (b) the veins, con- 
taining branches of the stele; (c) the green tissues between the veins (^[ 
127.) 

12. Demonstration. Strip off a bit of epidermis, mount and show (a) 
the irregular form of epidermal cells; (b) the intercellular openings with 
guard cells (stomata). (^T 137.) 

13. At the edges of the leaflets on the under side crescentic brown spots, 
clusters of spore cases. (^[ 275, figs. 149, 150.) 






FERNWORTS AND SEED-PLANTS. $7 

14. Boil a leaflet for a minute in water. With a needle turn back a 
flap which covers the spore cases; observe that it is a specialized portion 
of the edge of leaflet. 

15. On the under side of the flap a mass of yellowish spheroidal bodies, 
the spore cases. Scrape away most of them and notice the relation of 
their points of attachment to the veins. 

Mount some of the spore cases and observe 

16. Their shape ; the stalk by which they were attached. (Fig. 236.) 

17. The darker ridge, annulus, which serves to burst them when ma- 
ture. (Fig. 236.) 

18. Study the manner of bursting. Tear a bit of indusium from a dried 
specimen previously soaked in water, removing most of the sporangia. 
Allow it to dry while watching it with a lens, illuminating from above. 

19. Demonstration. Mount sporangia and spores and show their 
structure, especially the annulus. 



Seed-plants. 

67. Development. — Among the highest plants, those 
which produce seeds, the differentiation of the body is essen- 
tially the same as in fernworts. The alternation of sexual 
and non-sexual phases is still traceable, though greatly 
obscured by the extreme reduction of the gametophyte. 

This tendency to the reduction of the sexual phase, which was re- 
marked in passing from the mossworts to the fernworts, continues, until 
in the highest seed-plants the gametophyte is wholly microscopic. 
Even by the aid of the microscope, it is possible to identify only the sex- 
ual organs which it produces, and one or more cells which are, perhaps, 
the rudiments of its vegetative body. 

The sporophyte, consequently, is the only phase of the 
seed-plant visible to the unaided eye. 

The body of the sporophyte exhibits the same members, 
viz., stem, root, and leaf, having the same general form, and 
subject to the same modifications, as in the fernworts. An 
account of the vegetative members of the fernworts and seed- 
plants occupies the following three chapters. 



58 OUTLINES OF PLANT LIFE. 



EXERCISE XV. 

Marsh Marigold {Caltha pahistris). 

i. Examine the roots. Observe (a) their surface, wrinkled from short- 
ening; (b) their structure. 

2. Cut a transverse section as in fern; observe that mechanical tissues 
are wanting. 

3. Bisect longitudinally the base of a plant. Observe, as shown by 
the origin of leaves, the variable length of internodes; at base the inter- 
nodes are very short so that leaves are crowded ; in the middle the inter- 
nodes are long and leaves distant; above, the internodes become shorter 
until, in the flower, they are not developed and the leaves are very much 
crowded. (^[ 104.) 

Study one of the well developed foliage leaves (^[ 123). Observe 

4. The broad rounded blade with slight branches (teeth) at the margin. 

5. The long slender stalk, petiole, gradually passing into 

6. The sheathing base, in upper leaves branched to form two stipules. 

(IF 125O 

7. Examine and compare the various forms of leaves : (a) the lowest, 
having sheathing bases without petiole or blade, passing gradually into 
(b) the best developed foliage leaves; (c) these near the flowers losing pet- 
iole and diminishing blade, becoming bracts; (d) the yellow perianth 
leaves; (<?) next within these the yellowish stamens; {/) the flattened pod- 
like green carpels each forming a simple pistil. (f*[ 133, 134.) 

(Further study of flcwer, p. 210.) 

68. Summary. — In fern worts and seed-plants the sexual 
generation is small, often microscopic, while the non-sexual 
generation is conspicuous and often long-lived. The nutri- 
tive work of the gametophyte is either temporary, ceasing 
when the sporophyte develops green leaves, or is entirely 
wanting. The sporophyte forms stems, leaves, and roots and 
does most of the nutritive work. These members are very 
various in form and are described in the following chapters. 



CHAPTER VIII. 

THE ROOT. 

69. True roots. — It has been pointed out that, among the 
lower plants, there are very many which possess structures 
similar in form and function to the root, and by some called 
by this name. Although these parts serve to hold the plant 
in place, and perhaps to absorb material from the substratum, 
they are not to be looked upon as equivalent to the roots of 
the higher plants either in origin or structure. In the algae, 
fungi, liverworts, and mosses, the gametophyte is the promi- 
nent phase. In no case does the gametophyte produce true 
roots. It is not until the sporophyte becomes an independent 
plant that true roots are found in the vegetable kingdom. It 
is, therefore, only among fern worts and seed-plants that these 
organs are to be found. When the sporophyte is developed 
as an independent plant, it becomes necessary for it to pro- 
duce some organ capable of holding it in place, or of absorb- 
ing materials from the outside, or of doing both. The organ 
developed to meet this need is the root. 

70. Primary and secondary roots. — In accordance with 
their origin, roots are either piimary or secondary. Primary 
roots are the first formed roots, i.e., those which are de- 
veloped directly by the young embryo. In both fernworts 
and seed-plants the primary root is rarely wanting, but often 
short-lived, dying after the plant has established itself and 
has formed secondary roots to take its place. In many cases, 

59 



60 OUTLINES OF PLANT LIFE. 

however, the primary root persists throughout the life of the 
plant. 

Secondary roots are later formed. They are roots which 
arise upon stem or leaf, or even upon the primary root itself. 
In the last case they are distinguished from branches of the 
primary root, which arise in regular succession toward the 
apex, by originating out of this regular order. Secondary 
roots are also called adventitious roots. They may take their 
origin at any point upon any of the members. Their point 
of origin will depend largely upon external conditions. A 
wound may cause them to appear. They are especially likely 
to be formed upon those parts which are in contact with the 
substratum, or from those parts which are kept moist. Upon 
stems they are most apt to appear near the nodes. (See 
^[ 104.) If the plant as a whole is surrounded by very moist 
air, roots may appear at any point of the surface. Secondary 
roots arising thus upon a part of the plant exposed to the 
air, and growing for all or part of their existence in the air, 
are also called aerial roots. Familiar examples are to be 
seen about the lower part of the stem of Indian corn, the 
English ivy, the poison-oak, the trunks of palms and tree- 
ferns. Secondary roots often arise in regular succession 
toward the growing apex of the stem, particularly in plants 
which have creeping or subterranean stems. 

71. Growing point. — Primary and secondary roots do not 
differ materially in their structure. Near the tip they consist 
of a mass of actively dividing cells, the growing point of the 
root (compare ^j 87). The real tip of the root is covered by 
a mass of cells called the root-cap (ep, fig. 50), which is at- 
tached only to the growing point. Since the cells of the 
free surface of the root-cap are older and firmer than the 
inner ones and the growing point, and lie in front of them, 
they serve to protect these more delicate parts as the growth 
constantly pushes the apex forward through the soil. 



THE ROOT. 



6\ 



The youngest parts of the root are very much alike, but as 
they become older they grow unlike. The just mature por- 
tion of roots shows three characteristic regions, namely, (i) 
an outer layer or layers, the epidermis ; (2) an inner region, 
the stele ; (3) between these, the 
cortex. 

72. 1 . The epidermis usually 
becomes many-layered. At the 
apex it constitutes the root-cap 
(ep, fig. 50). On the other 
parts of the root it sometimes 
sloughs off entirely, exposing 
the cells of the cortex itself, as 
in the monocotyledons (lilies, 
grasses, sedges, etc.) ; or, more 
commonly, only the outer layer 
sloughs off, leaving the inner- 
most as the covering of the 
cortex. It is too delicate to be 
distinguished by the unaided 
eye, except at the tip and 
further back where it produces 
root-hairs. 

73. (a) Root-hairs. — Those 
cells which form the surface of 
the root, whether they be the 
original epidermis or cortical 
ones which have been exposed 
by its loss, usually develop a large number of hairs, known as 
root-hairs (figs. 51, 52). 




Fig. 50.— Median longitudinal section 
through the extremity of a root of 
Marsilia. The larger triangular cell 
near center of figure is the apical cell. 
The segments from the inner faces 
may be readily traced backward ; 
thus the dotted line ec points to the 
fourth, c to the sixth segment from 
the posterior right-hand face of apical 
cell, ep, root-cap (epidermis") ; ec, 
cortex ; c, stele ; en, endodermis 
(part of cortex* ; />e, pericycle (part 
of stele) Magnified about ioo diam. 
— After Van Tieghem. 



These root-hairs are branches of the superficial cells (fig. 52), and may 
be looked upon as simple extensions of them, as the finger of a glove is 
the extension of its palm. Only one root-hair arises from a superficial 
cell. They are usually unbranched and without transverse partitions. 



62 



OUTLINES OF PLANT LIFE. 



Only in rare cases are they wanting. They live for a 
shorter or longer time, but are always, as compared with the 
duration of the root, quite, transient. The older part of the 
root, therefore, is without root-hairs because of their death. 




^=% 



Fig. 51. — Transverse section of a young root grown in soil, showing root-hairs with 
adherent soii-particles, the cortex, and the stele. Magnified about 20 diam. — After 
P'rank. 



The youngest part of the root is likewise free from them, 
because they have not yet been produced. As the root 
grows in length, new root-hairs are continually being pro- 



THE ROOT. 



63 



duced and the older ones are dying at an equal rate, so that 
a zone of hairs is found only upon the younger parts of the 
roots. 

74. (b) The root-cap. — If the finger be supposed to rep- 
resent the root, a short finger-stall, if it were attached to the 
tip of the finger, might be fairly taken to 
represent the position of the root-cap. 
Only in rare cases is the root-cap entirely 
wanting. Serving to protect the tenderer 
portion of the root behind, the root-cap is 
itself constantly exposed to injury. The 
outer and older parts of the root-cap are, 
therefore, either worn away through me- 
chanical contact ; or, dying, they degener- 
ate and break down into a slightly muci- 
laginous material which facilitates the 
passage of the root through the substratum. 
This degeneration or the mechanical wear 
is constantly repaired within at the grow- 
ing point. The thickness of the root- 
cap, therefore, is maintained throughout 
its existence without considerable change. 

75. 2. The stele. — Occupying the cen- 
ter of the root, and surrounded on all sides 
by the cortex, is an aggregate of tissues 
called the central cylinder, ox stele (figs. 51, 
53). The most noticeable part of this are 
the groups of elongated cells or cell- 
fusions,* called vascular bundles, or vas- 
cular strands. These strands are of two 
kinds, wood strands, specially for the con- 




Fig. 52. — A nearly ma- 
ture root-hair, showing 
structure and relation 
to superficial cell of 
root ; grown in water 
and therefore not dis- 
torted as in fig. 51. 
n, nucleus embedded 
in protoplasm; vacuole 
single and very large. 
Highly magnified. 
—After Frank. 



* These are continuous chambers formed by the breaking down of the 
partition-walls between the abutting ends of cells. They are usually de- 
void of living contents. 



6 4 



OUTLINES OF PLANT LIFE. 



ducting of water, and bast strands for carrying foods. (See 
^[^y 172-174, 197.) They are so placed that they alternate 
with each other about the outer part of the stele (figs. 51, 
53). The strands may be in contact with one another in 




Fig. 53.— Transverse section of the stele and a portion of the surrounding cortex of the 
root of calamus s, s, innermost layer of cortex, adjoining outermost layer of stele ; 
/, wood strands; fih, bast strands. In the center of the stele and between the 
bundles is conjunctive tissue. Highly magnified.— After Sachs 

the center, or the center of the stele may be occupied by 
a pith (fig. 53). 

The number of vascular strands constituting the stele is 
various, being as few as four or as many as forty. The 
ordinary number, however, is from eight to twenty. (See 

fig- 530 

76. 3. The cortex generally consists of large thin-walled 
cells which have become partially separated from one another, 
leaving larger or smaller intercellular spaces (fig. 53). 



THE ROOT. 65 

77. Duration. — Even when the primary root persists 
throughout the entire life of the plant secondary roots often 
appear. When the primary root perishes, its functions must 
be performed wholly by secondary roots, which are developed 
in succession upon those parts where they are useful. The 
secondary roots themselves may be either permanent or 
transient. In creeping plants particularly, whether growing 
on land or in water, the functions of the root are likely to be 
handed on to successively younger roots, the old ones perish- 
ing and dropping off. If the roots endure for a considerable 
time, they may retain their primitive structure and form, or 
they may undergo secondary changes which unfit them for 
absorbing organs, and adapt them to subserve various special 
functions. 

78. Secondary changes. — Shortly after any portion of 
the root has ceased to increase in length, and, therefore, 
within the first season, it ordinarily undergoes minor second- 
ary changes which may or may not be followed by more 
profound alterations. These changes affect its primary 
structure in various ways and to various degrees according to 
the parts concerned. 

In some cases the older roots differ from the younger in 
scarcely more than the loss of the external layer of cells, from 
which the root-hairs arose. The sloughing off of this layer 
carries with it the hairs themselves and exposes the next inner 
layer of cells, which had before become slightly altered so as 
to be rather impervious to water. Upon their exposure, this 
alteration proceeds further, so that they become almost or 
quite incapable of absorbing the soil-water to which they may 
be exposed. It follows from this that it is only the younger 
part of the root, that is, the portion which has not undergone 
secondary changes, which is capable of absorbing water. In 
many roots this is the only change which occurs. In a 
greater number the root is also strengthened. 



66 



OUTLINES OF PLANT LIFE. 



In a large number of roots, the secondary changes result 
in increasing the diameter, sometimes very greatly, by the 
formation of concentric layers of new tissue in two or more 
regions, called the cambium regions. 

The outer growing layer, or cork cambium, usually formed in the 
cortex, produces tissues which are of such a nature as to protect the 
parts within. They constitute the periderm, and are ordinarily cork-like, 
he., thin-walled and impervious to water. Those cells which lie outside 




Fig. 54 — A. diagram of primary structure B, C, diagrams showing the results of 
secondary thickening from the stelar cambium in the two extreme forms c, cortex ; 
en, its innermost layer; /, outermost layer of stele; />/i', primary bast ; f>h", sec- 
ondary bast ; x', primary wood ; x"x", secondary w ood ; cl>, stelar cambium ; r, sec- 
ondary pith-rays ; m, pith.— After Van Tieghem 

a layer of cork are therefore cut off from a supply of food and soon 
perish. 

The inner growing layer, or stelar cambium, is developed within the 
stele and follows a tortuous course, lying outside the wood strands and 
inside the bast strands (fig. 54). As a result of tangential divisions in 
this region, tissues similar to those already existing in the stele are pro- 
duced. 

The relative amount of the new tissues goes far to deter- 
mine the character of the mature root. 

79. (a) Woody roots. — If mechanical tissues predomi- 
nate, the root will become strong and rigid, as in the case of 
trees and shrubs. When the root is long-lived, the forma- 
tion of new tissues is usually resumed with each season, and 
the central part, especially, shows in cross-section concentric 
rings indicating the yearly additions. As the root thickens 



7 "HE ROOT. 67 

the outside parts become fissured lengthwise. Thus, in an 
old and large root of the woody type, all the parts outside the 
central wood constitute a bark, which becomes furrowed 
lengthwise, like the bark of the stems of many trees. Such 
secondary thickening finally produces in the roots a structure 
which is almost identical with that of stems which have under- 
gone secondary thickening. (Compare ^f m.) 

80. (b) Fleshy roots. — But if thin-walled cells are the 
chief products, the root often becomes very thick and fleshy, 
as in the carrot, turnip, radish, sweet potato, beet, dahlia, 
artichoke, etc. Such roots serve the plant as storehouses of 
reserve food, and are consequently useful to animals as food. 
This thickening for storage purposes may affect either the 
primary or secondary roots, or both. 

81. (c) Float roots. — Plants which grow in water or in 
very wet swamps sometimes modify their roots to serve as 
floats. In these cases, the voluminous cortex consists of large 
cells, with huge intercellular spaces which are filled with air. 
The root thus serves to buoy up the parts of the plant to 
which it is attached, and assist in its respiration. (See *j 
202.) 

82. (d) Tendrils, thorns, etc. — In a very few plants, 
aerial roots are modified into tendrils, being slender, sensitive 
to contact, clasping the objects which they touch, if of suit- 
able size, and thus assisting the plant to climb; in some in- 
stances they are altered into thorns, being short, rigid, and 
sharp-pointed ; in others, being exposed to the light, they 
develop chloroplasts, which enables them to act as organs for 
the manufacture of food. 

83. Branching. — Both primary and secondary roots may 
branch. The mode of branching is commonly monopodial, 
i.e., the central axis grows most vigorously, and bears lateral 
branches upon its sides. The normal branches arise from 
lateral growing points, which originate in regular succession 



68 



OUTLINES OF PLANT LIFE. 



behind the apical growing point. But 
sometimes branches appear out of this 
regular order. Such are called ad- 
ventitious roots. (See ^[70.) 

Branches generally originate oppo- 
site the wood strands, or with definite 
relation to them. (See figs. 55, 56.) 
The number of vertical ranks of bran- 
ches can, therefore, be predicted with 
some certainty from the structure of 
the root, but the longitudinal intervals 
at which the branches will be formed 
cannot, because they are unequal (fig. 

55)- 

When secondary roots arise from 
the shoot, they have a fixed relation 
to the leaves, or they are formed upon 
the buds produced in the axils of the 
leaves, or they may arise at indefinite 
points along the internodes. In the 
first case, roots may be produced 
either opposite a leaf, or in pairs, right 
and left of the base of the leaf. 

84. Origin. — The origin of root- 
branches and of secondary roots is 
rarely external ; that is, the root is 
not commonly produced by growth at 
the surface of a member. In the great 
majority of cases the origin of the 
roots is internal ; that is, the forma- 
tion of the root is begun by the growth 
Fig 5 s.-Seediing pea. showing in the interior of the member pro- 
SK^JS^Si ducing it. In most cases growth 
sYz^-Ahe'rlvank 3 ' Natural begins very near to the surface of the 




THE ROOT. 



6 9 



stele. Soon a growing point is formed (fig. 56). The rootlet 
is thus in its early stage completely hidden, being buried 
beneath the cortex, through which it gradually makes its way, 
partly by disorganizing the tissues by pressure, and, probably, 




Fig. 56. Fig. 57 

Fig. 56. — Transverse section of a root of a fern {Pier is cretica), passing through a 
rootlet which has not yet emerged Only the stele and three rows of cortex shown. 
a, apical cell of rootlet, forming anteriorly the root-cap, e/>, and posteriorly the body 
of the root, ec, e, c, ftd; b, wood strands ; /, bast strand with its fellow opposite ; pe, 
outer layer of stele ; en, inner layer of cortex ; p, cells partly disorganized and 
digested ; d, cells of cortex, which will be disorganized as rootlet advances. Highly 
magnified — After Van Tieghem. 
Fig. 57. — The same as fig. 56, but older ; not quite so much magnified. The rootlet 
is just emerging from the parent root, pd, c, stele of the rootlet ; ec, its cortex; d, 
disorganized cells of cortex ec' , of parent root ; b' , secondary wood ; other letters as 
in fig. 56. — After Van Tieghem. 



partly by actually digesting and absorbing the material of 
these cells. When the rootlet reaches the surface it emerges, 
therefore, from a distinct rift in the cortex (fig. 57). 

85. Buds. — New shoots may be formed by the roots, either 
as a result of injuries, or normally. In a partially developed 
form, these constitute buds (see ^j 91). Whether formed as 



/O OUTLINES OF PLANT LIFE. 

a result of injuries or normally, they are known as adventitious 

buds. 

They arise in the same places and develop in the same way as lateral 
roots ; that is, they are internal in origin, and, as they continue to grow, 
burst through the cortex. The shoots so produced grow in the normal 
manner. Very rarely the growing point of the root, casting off the root- 
cap, becomes itself the growing point of the shoot. This alteration is 
usually the result of artificial reversal of the position of the root, being 
brought about in some potted plants by being turned upside down. 



EXERCISE XVI. 

Roots. — Germinate seeds of wheat, corn, white (or any) bean, pea, and 
white mustard in clean damp pine sawdust or chopped peat moss. 

Observe the form and distribution of the root-hairs on younger parts 
of the root. Let wheat grow for several weeks and observe on what part 
of the roots the root-hairs are dying away. (^[ 73.) 

Observe arrangement and origin of branches in the roots of pea seed- 
lings. (1T1F 83, 84, fig. 55.) 

Grow wheat in soil, planting it about one inch deep. After two to 
four weeks examine roots, washing away sand carefully. Distinguish 
primary and secondary roots. (^J^[ 70, 77.) 

Observe roots of sweet potato, beet, or dahlia, thickened for storage. 

(IT 80.) 

Examine a smoothly cut end of a root (as thick as one's finger) of any 
tree (maple, oak, elm, etc.). Observe the bark ; the wood with concen- 
tric layers (annual rings). ( r 79.) Compare with the stem of same tree. 
Contrast with structure of a root of lily or marsh marigold. 

Examine the root of a lily, or marsh marigold, by cutting cross-sec- 
tions and by dissection. Observe (a) the central stele, {b) the cortex. 

86. Summary. — True roots are found only in fernworts 
and seed plants. Primary roots are usually transient ; second- 
ary roots may be transient or permanent. Both grow at the 
tip only, which is protected by the root cap. The young parts 
form numerous root-hairs, which are sloughed off after a short 
time (a few days or weeks) with the outer surface. The cen- 
tral stele is chiefly for conduction of water and foods in young 



THE ROOT. 71 

roots. In older roots these functions may be maintained 
with the addition of mechanical tissues for strength and cork 
tissues outside for protection. Other roots as they grow older 
may be transformed into storage places, floats, tendrils, thorns, 
etc. The branching of roots is usually monopodial. Branches 
arise in longitudinal rows, originating internally near the 
surface of the stele. Roots may produce adventitious buds 
instead of root branches. 



CHAPTER IX. 

TH E SHOOT. 

87. Primary shoot. — The first shoot which develops is 
called the primary shoot. Rarely no primary shoot develops. 
Sometimes the primary shoot early ceases to grow, and its 
place is taken by secondary shoots arising from the root. 

The tip of the shoot is the region in which the formation 
of new cells is taking place. This region of young cells has 
no definite limit below, but passes insensibly into the older, 
which it produces. The tip of the shoot may be either a 
sharp cone or a low dome. Between these forms a complete 
series of gradations exists. Close below the apex the shoot 
begins to show a differentiation into a central axis and lateral 
outgrowths. The first of these to appear are swellings which 
form the leaves. Later, above the leaf rudiments, the rudi- 
ments of the lateral shoots may appear. The older leaves upon 
the sides of the axis outgrow the younger ones and the de- 
veloping axis, and arch over them in such a way as to form 
a more or less compact structure, which is a terminal bud. A 
bud is, then, an undeveloped shoot, whose older leaves pro- 
tect the younger, and particularly the youngest region, the 
apex (fig. 58). From the terminal bud arise all the mem- 
bers of the primary shoot. 

88. Differences from root. — From what has been said of the origin of 
the shoot, it will be observed that it is distinguished from the root by not 
forming in front of the apex a protecting cap. In further contrast with 
the root, the shoot possesses an uninterrupted epidermis over its entire 

72 



THE SHOOT. 



n 



surface, consisting always at first of a single layer of cells. This epider- 
mis persist^ as a surface covering either throughout the life of the shoot. 
or for a long period, being replaced only upon the older surfaces of the 
stem by subsequently formed protective layers. (See ^\ III.) 




Fig. 58.— Diagram of a section through a bud. V, the apex ; 1, 2, 3, 4, successively older 
leaf rudiments ; a, b, c, successively older branch rudiments ; d, e, vascular bundles. 
— After Hansen. 

89. Branching. — Branches of the shoot arise from lateral 
buds, which are in all respects like the terminal buds just de- 
scribed. If, for any reason, the terminal bud of the stem is 
destroyed, or its growth arrested, a branch, developing from 
a lateral bud near by, may assume the position and habit of 
the main axis. In many plants the death or arrest of the 
terminal bud recurs at regular intervals. In such plants, 
therefore, the main axis is really a succession of lateral 
branches, i.e., the branching is sympodial (cf. fig. 59 and 
^[58). In some plants, e.g., lilac, two lateral buds standing 
at the same level may develop, if the terminal one fails. In 
this case the shoot divides into two equal branches. Ordi- 
narily, however, the terminal bud develops without interrup- 
tion. In case it is more vigorous than any of the lateral 



74 



OUTLINES OF PLANT LIFE. 



buds, the plant will have a central axis, from the sides of 
which distinctly smaller branches arise. If, however, the 
lateral buds are almost or quite as strong as the central one, 
the plant seems to be broken up into branches, and, after it 
has attained its mature form, no one can 
be pointed out as the main axis.* Such 
branching is monopodia! (see ^j 58). 
These two types of monopodial branch- 
ing and the sympodial type are all illus- 
trated in the forms attained by common 
forest trees. (See frontispiece.) 

90. Inflorescence. — Especially profuse 
branching commonly occurs in the parts 
of the seed plants where flowers are pro- 
duced. Such clusters of branches bearing 
flowers constitute an inflorescence. Each 
sort has received a special name which 
indicates the type of branching, and also 
the relative length of the branches, f 

91. Lateral buds. — Lateral buds are 
ordinarily formed in definite relation to 
the leaves. They stand usually in the 
upper angle formed by the leaf with the 
stem. This angle is the axil of the leaf, 
and such buds are said to be axillary 
(fig. 60). Ordinarily a single bud arises 
in the axil of each leaf. Its origin is 
always later than that of the leaf-rudi- 
ment (fig. 58). 

There are many cases in which the lateral buds are not 




Fig. 59.— Shoot of Euro- 
pean linden, t, the last 
internode formed by the 
bud of present season. 
This dies and drops off 
and the shoot will be 
formed next year by the 
last auxiliary bud, a, 
which appears to be ter- 
minal after loss of t. 
Half natural size —Af- 
ter Frank. 



* The obscurity is greatly increased by the death of more branches than 
survive, owing to various causes resulting in poor nutrition or disease. 

f For these names and further discussion see Gray: "Structural Bot- 
any," p. 144; Goebel: " Outlines of Classification, p. 407. 






THE SHOOT. 



75 



found precisely in the axils of the leaves, but slightly to one 
side, or at a greater or less distance above the axil (figs. 61, 




Fig. 60. 

Fig. 60.— I, terminal shoot of an elm. b, leaf- 
scars ; k, axillary buds. Natural size. II, 
one of the buds cut lengthwise through 
center, magnified 3 diam. a, young axis; 

b, leaf-scar ; bl, young leaves ; d, bud- 
scales. — After Behrens. 

Fig. 61. — A, twig of red maple with ac- 
cessory buds in addition to axillary bud. 
B, twig of butternut, with leaf-scar, a, small 
axillary bud, b, and larger accessory buds, 

c, d, above axil. Natural size. — After 
Gray. 

Fig 62. — A bit of stem of a honeysuckle 
(Lonicera xylosteum} bearing large axillary 
and smaller superposed accessory buds above 
the axils of the scars, ww, from which 
leaves have fallen. Natural size. — After 
Frank. 




Fig. 62. 



62). Buds are frequently formed without any relation what, 
ever to the leaf-axil, and even on the leaf itself (fig. 179). 
Sometimes these extra-axillary buds are produced without the 



j6 OUTLINES OF PLANT LIFE. 

action of any extraordinary cause, but more commonly injury 
of one sort or another acts as a stimulus to the production of 
such buds. Buds which do not originate in regular succes- 
sion on the parent shoot (i.e., the younger nearer the apex) 
are called adventitious buds. 

Adventitious buds may arise upon stems, leaves, or roots. 
They are most commonly and abundantly produced upon 
stems and roots. 

92. Dormant buds. — Many buds continue to grow without 
interruption from the time of their formation, but more cease 
to develop after they have reached a certain stage. Such 
buds may remain dormant for a considerable period, and 
may even be overgrown and completely enclosed by the 
wood upon old shoots. The bud in this case grows slowly 
and maintains itself near the surface of the wood. It is quite 
possible that these dormant buds should for some reason 
begin to develop later, when they are liable to be confounded 
w r ith adventitious buds. 

In case they have been buried by the growth of tissues over them, the 
shoots which they produce will seem to come from the interior of the 
organ upon which they are borne. This apparent internal origin must 
not be confounded with the real internal origin of roots. 

Since in most cases lateral buds have a definite relation to 
the leaves, the shoots which arise from them will have a 
similar relation. But, as many buds are produced which 
never develop into branches, this relation is often obscure 
and difficult to see. 

93. Special forms. — The primary shoot may grow under- 
ground, in which case its stem usually takes a horizontal 
direction and becomes much thickened for storage of reserve 
food fl[ 196), while its leaves are so reduced as to be scarcely 
recognizable. Such a shoot is a rhizome. When the primary 
stem is short, erect, and crowded with thickened leaf bases it 
forms a bulb, as in the hyacinth and onion. When the 



THE SHOOT. 77 

primary stem is short and thick, and has thin scale leaves 
upon it, it forms a conn, as in cyclamen and Indian turnip. 

Branches of the specialized primary shoot may be like it, 
as when some branches of the rhizome or conn are them- 
selves rhizomes or conns. Others, however, will be adapted 
to other purposes, as when aerial branches arise from rhizomes 
to carry foliage and flowers, or when slender leafless shoots 
called runners develop from the main axis of the strawberry 
(fig. 183). Offsets and stolons (figs. 182, 207) are similar 
branches likewise adapted to propagation. (See ^f 301.) 

Branches of the secondary shoots may also be different 
from their parent axis. In different plants the shoots assume 
the most varied forms. 

Such specialized branches may be confined to a definite 
region of the plant, or may be distributed over it. The 
more important of these kinds of branches may now be 
enumerated. 

94. (a) Dwarf branches. — It is not uncommon to find 
branches specialized merely by their slight development in 
length and their capacity for being separated readily from 
the parent shoot. Such short branches are particularly com- 
mon among the cone-bearing trees. In these plants the 
short branches carry the clusters of needle leaves (figs. 63, 
64, 198). After the death of the leaves the branches them- 
selves drop off. Somewhat similar short branches are to be 
recognized among many deciduous trees, and, in the apple, 
the so-called fruit spurs are not dissimilar (fig. 65). 

95. (5) Flowers. — The most common of the specialized 
branches among the seed plants are those which constitute 
the flower. In these the axis usually remains short, the 
leaves are crowded, and often some of them are highly 
colored (fig. 66). Commonly these flower branches are 
short-lived and drop off with the fruit or earlier. 

96. (c) Leaf-like branches. — A few plants have developed 



78 



OUTLINES OF PLANT LIFE. 






Fig. 63. Fig. 65. 

Fig. 63. -A shoot of Scotch pine showing two regions of dwarf branches each with a 
pair of needle leaves, and three regions of flower branches; the flowers have fallen 
from lower two, showing scale leaves covering the stem. Natural size. — After Will- 
komm. 

Fig. 64.— The base of leaves and dwarf branch of Scotch pine cut through the center 
lengthwise. Besides the two needle leaves the dwarf branch carries a number of 
scale leaves, d. Between the bases of the needle leaves is seen the conical apex of the 
dwarf branch, showing their lateral origin. Magnified about 4 diam. — After Luerssen. 

Fig. 65.— Twig of apple, bearing fruit spurs. A, points at which fruit was detached 
the preceding year; //", leaf scars. Natural size.- After Hardy. 



THE SHOOT. 



79 



shoots which replace leaves in function and resemble them 
in form. These branches may be either broad and flattened, 
as in the "smilax" of the greenhouses, or they may be slen- 
der and needle-like, as in the common garden asparagus 
(fig. 67). In any case, since they replace leaves in function, 





Fig. 66. Fig. 67. 

Fig. 66.— Flower of Sedum acre, s, sepal; /, petal; st, stamen; c, carpel. Magni- 
fied 3 diam.- -After Baillon. 

Fig. 67. — Piece of a twig of asparagus; in the axil of the scale leaf, b, arise a flower 
shoot, and three leafless needle-like branchlets. Magnified about 2 diam. — After 
Frank. 

they are abundantly supplied with green coloring matter for 
manufacturing food. 

97. (d) Bulblets. — Other branches remain undeveloped 
as buds, but their leaves become thick and fleshy. These 
bulblets are easily detached and serve for propagation. (See 
T 299.) They are to be found in many plants. In the 
tiger-lily they occupy the axils of the leaves (fig. 180), and 
are modified lateral buds, while in the garden onion they 
usually replace the flowers. 

98. (e) Tubers. — Some underground shoots have their 
ends suddenly and greatly enlarged, adapting them to the 
storage of food. They are then called tubers. In the white 
potato the tuber consists of several terminal internodes of 
an elsewhere slender underground stem, the "eyes" being 
lateral buds in the axils of minute scale leaves. In a few 
plants tubers may even be formed above ground, as in certain 
polygonums whose flowers are often replaced by little tubers 
which are readily detached (fig. 68). 



8o 



OUTLINES OF PLANT LIFE. 



99. (/) Tendrils. — Some shoots take the form of slender, 
leafless, sensitive tendrils, which assist the plant in climbing 

by coiling about suitable objects 
(fig. 69). 

100. (g) Thorns. — Many 
plants produce defensive shoots, 
which are leafless, rigid, short, 
and sharp, called thorns, which 





Fig. 68. Fig. 69. 

Fig. 68. — ,4, upper part of a plant of Polygonum viviparum, showing flower cluster, 
the flowers in lower half being replaced by tubers. Two-thirds natural size. B, a 
fallen tuber. Magnified about 3 diam. C, a plantlet growing from tuber. Natural 
size. — After Kerner. 

Fig. 69. — A portion of the stem of white bryony, B, from which a tendril, u.r, arises 
near the leaf stalk, b, and the bud, k. tt, rigid portion of tendril ; the portion between 
u and the portion x, clasping the support, A , has become coiled into a spiral which 
reverses the direction of the coils at iv and w' . Nearly natural size.— After Sachs. 



may be either simple or branched (fig. 70). The honey- 
locust furnishes an excellent example of branched, or com- 
pound, thorns. 



THE SHOOT. 



81 



Leaves themselves may be developed as tendrils or as thorns, so that 
it must not be assumed from appearance alone that such members are 
forms of the shoot. Observation of the origin and relation of the mem- 
bers will reveal their true nature. If shoots, they will usually be sub- 
tended by a leaf ; if leaves, they will often have a bud or a shoot in their 
axils. Thorns or tendrils which do not arise at the nodes are reckoned 
as shoots. 

101. Duration. — Shoots are either annual, biennial, or 
perennial. If the entire shoot dies this generally involves 
the death of the whole plant, though new adventitious shoots 




Fig. 70.— Shoots of Vella spinosa, showing thorns. Natural size. — After Kerner. 

may arise from the roots, as in sweet potatoes. In many 
plants, in which the shoot seems to die at the close of the 
growing season, an underground portion really survives, and 
sends up the new shoots. Such plants, if they live for two 
years, are called biennials ; or, if they live for several or 
many years, are called perennials. 

The shoot may be composed mainly of soft tissues, and 
persist underground, where it is protected against unfavorable 
conditions, such as drought and cold, and especially against 



82 OUTLINES OF PLANT LIFE. 

sudden changes ; or it may be composed mainly of mechan- 
ical tissues, and be fully exposed, as are the shoots of trees. 
In these cases the leaves generally perish and drop off an- 
nually, but in the "evergreen" plants they live more than 
one growing season. 

EXERCISE XVII. 

Shoots. — Examine the shoots of the linden, elm, maple, oak, and lilac 
and observe the mode of branching, and the arrangement of the buds. 

(IT 89). 

Study the construction of winter buds of lilac, horsechestnut, or hick- 
ory. (This can be done most easily by examining them just as buds are 
unfolding in spring, or by keeping shoots in a warm room for a few days, 
when the buds will begin to open.) Observe the form and arrangement 
of the scales and the way in which foliage leaves are folded. How are 
these buds protected against water ? Against sudden changes of temper- 
ature? HI 87, 133.) 

Examine the rhizomes of couch grass, mint, Solomon's seal or blood- 
root; the bulb of the onion or hyacinth; the tuber of the white potato, 
as forms of underground storage shoots (^[ 93, 98). Do these shoots 
have buds on them ? 

Examine the tendrils of the passion flower (or the wild cucumber vine); 
the thorns of the haws or the honey locust, as special leafless forms of the 
shoot. 

102. Summary. — The shoot grows at the tip, new lateral 
members being formed in regular succession below it. These 
young members and the tender tip itself, protected by some 
older leaves, compose the terminal bud. Similar growing 
points arise on the sides of the main shoot and exist for a 
time as lateral buds. Some buds die, and some live but re- 
main undeveloped. Others develop into branches similar to 
or different from the main axis. Special forms of the shoot 
are produced to serve special purposes, such as storage, 
reproduction, protection, climbing, etc. The branches, 
some or all, and even the main shoot, die after a time. An- 
nual shoots die after one growing season, biennial shoots 
after two, and perennial shoots after several or many. 



CHAPTER X. 

THE STEM. 

103. Definition. — The shoot is almost always segmented 
into members of two kinds, the stem and leaves. The stem 
is the central axis of any shoot, and the leaves are lateral 
outgrowths, or branches, of it. These two members cannot 
be accurately defined, but are in most cases readily recog- 
nized. Leaves commonly differ from the stem in their 
flattened form, limited growth, and position, subtending the 
lateral shoots. (See further p. 96.) 

104. Nodes and internodes. — Upon examining the surface 
of the stem, it is almost always readily distinguishable into 
distinct regions, the nodes and internodes. The nodes are 
the narrow zones, often somewhat swollen (whence the 
name), at which one or more leaves arise. The internodes 
are the zones between the nodes. Upon watching the de- 
velopment of the stem from the terminal bud, it will be 
seen that new nodes and internodes are constantly emerging 
from its base, and that the leaves formed at the nodes are 
successively expanding. This emergence of the internodes 
is due to their growth. The amount of growth, however, 
varies greatly in different plants, and even in different parts 
of the same plant. In many cases the internodes are con- 
siderably and uniformly elongated; the leaves are then dis- 
tributed along the stem at considerable and regular intervals. 
In other cases the internodes remain very short, and the 
leaves are, therefore, crowded. They may be so crowded as 

83 




84 OUTLINES OF PLANT LIFE. 

to envelop the stem completely and hide it from view. This 
is well seen in the scale-like leaves of such plants as the pines 

(fig. 63), cedars, and arbor vitae 
(fig. 71). Or, certain of the 
internodes may elongate, while 
others remain undeveloped. 
For example, in the shepherd' s- 
purse, the first internodes re- 
main short, so that the lower 
leaves are crowded into a tuft 
or rosette; the following inter- 
nodes are elongated, the corre- 
sponding leaves being scattered 

Fig. 71. — A shoot of arbor vitae or white + 1 ' + 1 • V,'1 

cedar, showing scale leaves covering at regular intervals; Wnlle, 
stem. Natural size.-After Kerner. stiU higher> the internodes are 

again shortened and the leaves brought into close clusters in 
the flowers. 

105. A section of the stem commonly presents an irregularly circular 
outline (fig. 72). Occasionally the surface of the stem is fluted or chan- 
neled, and, if these grooves or channels be few, and the corresponding 
angles prominent, the section of the stem is polygonal, with three, four, 
five, six, or more sides (fig. 131). 

106. Habit. — As to habit, stems are commonly erect 
when enough mechanical tissue is developed to render them 
sufficiently rigid to carry not only their own weight, but that 
of the leaves and other members attached to them. Other 
stems lie flat upon the ground, to which they may or may 
not attach themselves by the development of secondary roots. 
Between these prostrate, or creeping, stems and the erect form 
every conceivable position exists. The direction of growth 
is determined largely by the relation of the plant to gravity 
and light as stimuli. (See ^f^f 243, 245.) Other stems rise 
into the air, not by their own rigidity, but by the develop- 
ment of special members for climbing purposes, such as 



THE STEM. 



35 



recurved spines, tendrils, sensitive Leaf stalks, or even by 
recurved normal branches. (See \\ 99, 131.) Others wrap 
themselves about objects of suitable size, and are called 
twining steins. (See \ 249.) 

107. Primary structure. — If a thin section be cut from 
an internode which has just reached its full length, three 
definite regions maybe distinguished, viz. : (1) the epidermis; 
(2) the cortex; (3) the stele (figs. 72, 73). 

1. The epidermis is a single layer of cells forming the 
extreme edge of the section, being, therefore, the layer which 





Fig. 72. Fig. 73- 

Fig. 72. — Diagram of a transverse section of stem of Iberis amara, showing outline, 
and paired vascular strands. The black is the wood strand ; the gray is the bast 
strand. The outer line represents the epidermis ; a circle including the bundles would 
mark the limits of the stele, with its central pifh ; the cortex lies between the epidermis 
and stele. — After Nageli. 
Fig. 73.— Diagram of a transverse section of a palm stem. The epidermis is represented 
by the outer line ; the narrow cortex lies between this and the inner circle ; the stele, 
with numerous bundles scattered through the pith, is within the cortex. — After 
Frank. 



covers the surface of the stem. Here and there are minute 
openings which permit communication between the outside 
air and spaces between the cells of the cortex. These open- 
ings are usually bordered by two specialized cells, and are 
called stomata. (See *|f 137.) Naturally they are wanting 
m submerged stems of water plants and in most subterranean 
stems. The epidermis is often furnished with hairs, scales, 
and like outgrowths (figs. 74, 75, 200-203). 



86 



OUTLINES OF PLANT LIFE. 



2. The cortex consists of several layers of cells, usually 
thin-walled and not in close contact, and hence abundantly 
provided with intercellular spaces. These cells usually con- 
tain many chloroplasts, to which the green color common to 
young stems is due. 

3. The stele forms the central region. Its most striking 
parts are several or many clusters of smaller cells, the cut ends 
of the vascular strands. Occupying the space between the 
vascular strands is the pith (figs. 72, 73). 

108. The cortex. — In certain plants the cortex undergoes 
an enormous development, forming in some tubers the 
greater part of the massive stem; 
in others it is so reduced that it 
consists only of two or three layers 
of cells. With the epidermis it 
very commonly enters into the for- 
mation of outgrowths, such as 





Fig. 74. Fig. 75. 

Fig. 74.— Forms of hairs from Plectranthus. a, simple pointed hair ; b, stalked 

glandular hair ; c, sessile glandular hair with secretion covering the two glandular 

cells. Highly magnified. — After De Rary. 
Fig. 75. — T-shaped hair of the wall-flower (Cheiranthus). e, epidermis. Highly 

magnified.— After De Bary. 



warts, prickles, wings, etc. Very frequently the intercellular 
spaces of the cortex are greatly enlarged, forming air passages 
of considerable size (fig. 76). In other cases the cortical 
cells, instead of remaining thin-walled, may become greatly 
thickened in certain regions, or even throughout the cortex. 
These mechanical cells are likely to be aggregated in clusters 
or strands, and serve an important purpose in strengthening 
the stem. 



THE STEM. 87 

109. Stele. — The outermost part of the stele often pro- 
duces mechanical cells with thick walls and small cavities. 
They are either aggregated in strands opposite to the vascular 
strands of the stele, or they constitute a complete zone 




Fig. 76. — Transverse section of the stem of Elatine, showing intercellular canals, C. 
Magnified about 15 diam.— After Reinke. 

around it. Many of the most valuable textile fibers, such as 
those of flax, hemp, and ramie, are obtained from this region 
of the stem (fig. 77). 

In any section of the stem the number of vascular strands 
in the central cylinder varies greatly, not only in different 
plants, but even in different parts of the same plant. The 
strands are commonly arranged in pairs, a bast strand and a 
wood strand being placed side by side, the former occupying 
the side next the surface of the stem, and the latter the side 
next the center (figs. 72, 78). The number and position of 
these bundles is, however, subject to change. In some 
cases one of the strands surrounds the other. Commonly 
it is the bast which surrounds the wood, as m the fernworts. 
Sometimes independent bast strands are found with which 
are associated no wood strands. In the bast certain cells 



88 OUTLINES OF PLANT LIFE. 

may develop into fibers, which are quite like the fibers 




Fig. 77,-Portion of a transverse section of the stem of flax, m, pith ; h, secondary 
wood forming a cylinder ; ph, bast ; 6, strands of mechanical tissue (fibers) among 
the thin-vvalled cells, the two sorts making up the cortex ; ,/, the epidermis. Magni- 
fied about 25 diam.— After Frank. & 




Fig. 78.— Transverse section of a bundle pair from the stem of a begonia. Th. 
part is the wood strand; the small irregular cells above are the bfst strand ; between 
hem is a zone of growing cells the stelar cambium, which extends also right and 
left of the bundle pair. The radius of the section passes through CP C next the 
center. Magnified 150 diam.-After Haberlandt. S ' ' he 

occurring in the outer part of the stele. 
are valuable in the textile industries. 



Some of these, also, 



THE STEM. 



8 9 



The paired vascular strands within the stele occupy various positions, 
and for purpose of location may be spoken of as though single. If trans- 
verse sections of the stem are observed, they may be seen either in a sin- 
gle row, roughly parallel with the surface of the stem (fig. 72), or in 
several concentric rows (fig. 79), or they may be irregularly disposed 
throughout it (fig. 73). No one method of arrangement is confined to any 
of the larger groups of plants, although the first is characteristic of most 



sr» 




Fig. 79. —Transverse section of the aerial stem of an onion (Allium Schoenopraswui). 
e, epidermis ; ch, chlorophyll-bearing tissue of cortex; r, colorless tissue of cortex; 
g, g' , vascular bundles (wood bundles black, bast bundles dotted); sr, mechanical 
tissues connected into a cylinder; m, pith; h, pith canal formed by destruction of 
cells. Magnified 30 diam.— After Sachs. 

dicotyledons, while both the second and third methods are common 
among the monocotyledons. But so many exceptions are found to these 
last statements that it is best not to indicate the arrangement of the bun- 
dles by the terms dicotyledonous or rnonocotyledonous, as has been com- 
monly done; nor is it possible to maintain the terms exogenous and en- 
dogenous, which have long since become obsolete because misleading. 



110. Pith. — The pith is frequently found enormously 
developed in those parts of the stem used for storing reserve 
food, such as the tubers of the white potato and the yam. In 
other plants, particularly those growing in water, it suffers 



9 o 



OUTLINES OF PLANT LIFE. 



extreme reduction or is often completely wanting, in which 
case the bundles of the stele are in close contact, and the 
cortex usually shows a corresponding increase. In other 
plants the cells constituting the pith are greatly thickened, 
so as to form a mechanical tissue. 

The thickened areas are usually either opposite the vascular strands, 
forming a strand closely adherent to their inner faces, or they may extend 

to their flanks, thus forming an arc 
embracing each. Sometimes the thick- 
ened region becomes extended between 
the vascular strands and joins other 
mechanical tissues of the stele, or even 
those of the cortex, so as to enclose 
completely the individual strands (fig. 
80). 

In other plants the pith dies 
early and shrivels up. Very large 
canals may thus be formed 
through it, or it may even disap- 
pear entirely (fig. 79). Such 

Fig. 80.— Transverse section of a bundle . , . _ , . . 

pair of Indian corn. ?■, bast bun- early disappearance ot the pith 

die; .r, g, g, s, r, wood bundle; />, , ,, , .. , 

pith; /, an intercellular space formed prOQUCeS the hollOW Stem cha- 
by the tearing of some of the wood .... 

tissues. The bundle pair is surrounded raCteriStlC Ot the graSSeS, the 
by a sheath of thick-walled mechanical , , 

tissues. Magnified 235 diam.— After sedges, and various members of 

Sachs. 

the sunflower family. 
111. Secondary structure. — Some stems retain through- 
out their entire existence the primary structure which has 
just been described, undergoing only slight changes which 
do not materially alter the structure. This permanence of 
primary structure is frequent in the stems of monocotyledon- 
ous plants. But the stems of the great majority of dicoty- 
ledonous plants, as well as the conifers, quickly lose their 
primary structure, adding tissues of considerable amount, so 
as to bring about a more or less striking rearrangement of 
the first formed tissues (fig. 81). This is due chiefly to the 




THE STEM. 



91 



formation of one or two layers of actively dividing cells, 
roughly parallel to the surface. When there are two such 
layers they are concentric. 
They are formed from existing 
cells which retain or resume 
their power of active growth 
and division. The develop- 
ment of the tissues from the 
external growing layer, called 
the cork ca?nbium, results in the 
formation of secondary cortex, 
called periderm, while the 
tissues arising from the in- 
ternal growing layer, or stelar 
cambium, form the secondary 
wood and secondary bast (fig. 

so. 

112. Cork. — The outer tis- 
sues of the periderm rarely 
remain living. The close-set 
flat cells early lose their con- 
tents, and the walls become 
waterproof, forming cork (fig. 
82). Other cells may be al- 
tered into mechanical tissues by 
the thickening of their walls 
and the death of the proto- 
plasm. Zones Of Cork Often Fig. 81.— Part of a transverse section of 

alternate in the periderm with 
zones of mechanical tissues. 
Since almost no water can 
pass through a cork zone, it is 
evident that all parts lying out- 
side of one are cut off from a supply of nourishment, and must 




a young stem of cinchona in process of 
secondary thickening, tz, hairs ; <?, epi- 
dermis ; k, cork-cambium ; mr, cortex ; 
s, gum-resin tubes in cortex ; sb, primary 
bast strand ; c, stelar cambium ; g, h, 
secondary wood ; mk, pith rays ; m, 
pith The tissue between sb and c is 
secondary bast. Highly magnified. — 
After Tschirch. 




92 OUTLINES OF PLANT LIFE. 

therefore perish sooner or later. How much of the stem will 
thus be killed depends upon the position of the layer of cells 
which produces the cork. 

Annual shoots have usually but a small amount of periderm 
formed, or sometimes none at all. 
In perennials, periderm is formed not 
only during the first year's growth, 
but the activity of the cork cambium 
is resumed at the beginning of suc- 
ceeding seasons, so that annual addi- 
tions are made to it. 

113. Bark. — The dead tissues 

which accumulate from year to year 

upon the outside of perennial stems 

F s C ;cLr P of /oung tr stem er of constitute a large part of what is 

peSn. ho t 1 ?p f rd r eTn5s ; n t known as the bark. The inner part 

S[h ; o/e A rowof seTondT; of the bark belongs to the stele. (See 

S&.5S£SLL^iBSi 1"7.) In the bark of most trees 

one or more cork-forming layers 

originate in addition to the first, giving rise thus to sheets 

of cork either concentric with the first, or intersecting it 

(fig- 83). 

In the first case the dead outer parts may peel off in con- 
centric sheets, as in the birch. In the second the dead parts 
break away in the form of scales or flakes, as in the hickory, 
sycamore, or apple. In many trees the dead outer portions 
are only gradually worn away by the action of the weather, 
becoming seamed or deeply furrowed lengthwise. 

114. Secondary wood and bast. — The position of the in- 
ternal growing layer, the stelar cambium, is not subject to the 
same variations as the external one. 

In the many dicotyledons whose stems increase in 
diameter, the strands of wood and bast are in a single circle 
parallel to the surface, the bast bundles in each pair being on 






THE STEM. 93 

the outside. The stelar cambium arises between the wood 
and the bast strands of each pair, and extends across the 
pith rays which intervene, thus forming a complete zone 
nearly concentric with the surface of the stem (figs. 78, 81, 




Fig. 83. — Part of a transverse section of the bark of cinchona, c, layers of cork formed 
by a transient cork cambium, s, thin-walled tissues, with occasional stone cells. The 
sheets of cork cells are lines of weakness along which the flakes of bark split off. 
Magnified 665 diam.— After Warnecke. 



84, A). On the inside of the cambium there arises, opposite 
the primary wood, secondary wood. Outside the cambium, 
opposite the primary bast, there arises secondary bast. Each 
strand is thus increased in its radial thickness (fig. 81). 

115. Pith rays. — The cambium in the pith between the 
bundles either produces pith tissue (B, fig. 84), or it forms 
secondary wood and bast corresponding to that produced 
between the adjacent bundles. In the latter case, therefore, 
a complete zone or ring of secondary wood and bast is 



94 



OUTLINES OF PLANT LIFE. 



formed, so that the pith occupies the center. Upon the ring 
of secondary wood thus produced the primary wood strand 
projects into the pith, and upon the ring of secondary bast 
the primary bast strand projects into the cortex (C, fig. 84). 
Intermediate between these two methods, it is common to 
have new strands produced by the cambium formed in the 
pith rays, these strands remaining separated by narrower pith 
rays {D, fig. 84). 




Fig. 84. — Diagrams of transverse sections of stems illustrating modes of secondary 
thickening. In all c, cortex; en, its inner boundary; /, limit of stele ; />/i', primary 
bast; ///", secondary bast; cb, stelar cambium; x' ', primary wood; .v" , secondary 
wood; r', primary pith rays; r", secondary pith rays.— After VanTieghem. 



The secondary strands thus formed can, of course, have 
no direct connection with those which enter the leaves. In 
this they differ from the primary strands, branches from 
which enter each leaf. (See ^f 136.) 

116. Annual rings. — If the stem is perennial, year after 
year the stelar cambium resumes its growth, adding layer 
after layer to the secondary wood and bast. Thus most trees 
have their shaft-like trunks formed. The cambium forms a 
line of weakness, and the parts outside separate readily from 
the wood. They constitute the bark. 

117. The bark. — As has been already shown (^f 113) the 
outer part of the bark consists of the dead, dry, shriveled 
parts of the periderm lying outside the cork cambium. The 
inner portions of the bark are composed of the tissues which 



THE STEM. 95 

lie between the cork cambium and stelar cambium. This 
inner part contains a greater amount of water than the outer, 
and always some living tissues. It may consist of a part of 
the cortex and both primary and secondary bast. As the 
tree grows older the bark may come to consist almost wholly 
of secondary bast. It attains considerable thickness only 
when the loss from weathering is slow. 
EXERCISE XVIII. 

Stems. — Cut cross-sections of the stem of (i) a seedling beam and (2) 
a young stem of asparagus and compare. Observe in (1) the three 
regions, epidermis, cortex, and stele (^[ 107). In the stele observe (a) 
the cut ends of the vascular strands and their arrangement. (Each pair 
looks like a single strand except in very thin sections.) (b) The central 
pith. In (2) observe the epidermis, very narrow cortex, and the stele 
occupying the greater part of the section. In the latter observe the cut 
ends of the strands, distributed throughout the pith. 

Cut a cross-section of the three-year-old shoot of any shrub or tree. 
Observe (a) the central pith, {b) the wood strands increased in number 
and thickness until they form a cylinder of wood, in which three annual 
layers can be observed (how marked?); (c) the stelar cambium, a line of 
weakness (young cells) outside the wood; (d) the bark, composed of the 
bast strands on the inside, the cortex (in part) next, and the periderm 
(brown) on the outside. Compare with the bean stem, How much is 
the stele? fl[f Hi-«7.) 

118. Summary. — The stem shows nodes, i.e., the zones of 
attachment of leaves, and internodes. The length of the 
latter determines the distribution of the leaves. Stems may 
be erect, prostrate, or climbing. They show three regions, 
epidermis, cortex, and stele; each with great variety of struc- 
ture in different plants. The stele consists of vascular strands 
of two kinds, arranged in pairs, and embedded in pith. As 
stems grow older they frequently increase in diameter by the 
formation of concentric growing zones in the cortex and 
stele. The outer one produces the periderm, the inner one 
wood and bast. In trees and shrubs the wood and bast 
receive annual additions. They separate readily at the stelar 
cambium, the outer cylinder being the bark. 



CHAPTER XI. 

THE LEAVES. 

The leaves are very important nutritive organs in most 
green plants. They are adapted to catch the sunlight; 
therefore their form, structure, and position are largely con- 
trolled by this relation to light. (See ^f^f 190, 191.) 

119. Primary and secondary leaves. — Leaves are dis- 
tinguishable as primary find secondary. The primary leaves 
are those first developed, usually in the youngest stage, the 
embryo. In fernworts the primary leaf can be traced back in 
its development even to the egg. In seed plants they are 
usually formed before the young plant (embryo) enters its 
resting state as the seed becomes ripe. 

The primary leaves of seed plants are called cotyledons 
(figs. 85, 86). They are usually transient, and not rarely so 
distorted by acting as storage places for reserve food that they 
do not serve as foliage leaves at all. In extreme cases of this 
kind they remain in the seed coats when the embryo resumes 
its growth, as in pea and oak. 

Secondary leaves are generally numerous and much more 
conspicuous. It is these which are usually meant by 
" leaves," unless primary leaves are specially named. 

120. Development. — If the apex of the shoot be ex- 
amined, its progressive differentiation into stem and leaves 
can be observed. Upon the sides of the growing point 
swellings of various size appear, the smallest being nearest 

96 



THE LEAVES. 



97 



the apex (fig. 58, *»***). These swellings are the rudiments 
of the leaves, into which they become transformed by further 
development. Similar swellings appear later just above the 
leaf rudiments, which are at first not distinguishable from 
them, except by position (fig. 58, a, b, c). These become 
the branches. Both leaf and branch have their origin usually 
in the outer layers of the shoot, and can only be distinguished 




Fig. 



Fig. 85. 



Fig. 85. — A seedling of wheat, with grain still attached, cut through 
lengthwise, showing the single primary leaf with its back applied 
to the store of reserve food in the grain (the shaded part). The 
first two secondary leaves are also developing, and the primary 
root has extended. Magnified 4 diam.— After Kerner. 

Fig. 86. — Seedlings, showing primary leaves. A, a fir ; B, the 
dog-rose ; C, a morning-glory. Natural size. — After Kerner. 



by the later course of development. The growth of the 
branch is commonly indefinite, while that of the leaf is gen- 
erally limited ; the branch usually develops leaves and often 
buds as lateral outgrowths, while the leaf rarely forms buds 
normally; the axis of the branch is generally radial, like the 
parent axis, while the leaf is generally flattened and dorsiven- 
tral. In most cases, also, the leaf subtends the branch. 
Both leaf and branch mark those points of the stem known 
as the nodes. 



98 OUTLINES OF PLANT LITE. 

121. Arrangement. — Leaves appear in regular succession 
upon the stem, the youngest being nearest the apex. Their 
distribution along the sides of the stem, though extremely 
various, may be reduced to two main types. Either (i) the 
leaves are formed singly at the nodes, or (2) more than one 
leaf occurs at each node. When the leaves are single, suc- 
cessive leaves may stand upon exactly opposite sides of the 
stem, so that the third leaf, counting from below upwards, 
stands over the first ; or the fourth leaf may stand over the 
first ; or the sixth over the first, and so on. A transverse sec- 
tion of an opening bud shows the mode of arrangement, and 
a study of such sections makes it evident that each leaf 
appears in the widest space between the two preceding 
leaves, i.e., where it encounters the least resistance. That 
this is the determining factor is shown by the fact that the 
order of arrangement may be artificially altered by pressure 
or distortion of the bud. When two or more leaves occur 
at each node, the members of successive circles ordinarily 
alternate with each other. This alternation is due to the 
same cause. 

122. Form. — Leaves show a great variety of form and 
structure. Even upon the same plant leaves of various forms 
occur. The primary leaves are usually different from the 
secondary leaves, both in form and size. The most abun- 
dant form of secondary leaves is foliage leaves. These may 
be very simple, as the "needles" of the pines, or differen- 
tiated more completely, as in the deciduous trees. The 
mature form of the complex foliage leaf is frequently not 
attained until several nodes above the point at which the 
primary leaves arise; and, if only one or two leaves are pro- 
duced each season, as in many ferns, the mature form may 
not appear for several years. 

123. Foliage leaves. — A well-developed foliage leaf has 
three parts, the base, the stalk, the blade (fig. 87). The 



THE LEAVES. 



99 



leaf base is always present, but either the leaf stalk or the 
leaf blade or both may be absent. The leaf blade is ordi- 
narily winged ; indeed it is for this reason that it received the 
name "blade." Either the stalk or 
the base or both may also be winged. 

124. i. The leaf base. — The leaf 
base is generally enlarged so as to 
form a sort of cushion by which it is 
attached to the stem. When a broad 
base is attached over a considerable arc 
of the circumference of the stem, so 
that it encircles it more or less, the 





Fig. 87. Fig. 88. 

Fig. 87. — Leaf of Ranunculus Ficaria. b, leaf base; /, petiole, or leaf stalk; /, 

lamina or leaf blade. Natural size. — After Prantl. 
Fig. 88.— A leaf of a grass, with part of stem to which it is attached, s, sheath (leaf 

base) attached all around node k of the stem h, h ; f, blade ; /, the ligule, an outgrowth 

from the surface. Natural size.— After Frank. 

& base is said to be sheathing (fig. 87). In grasses, for ex- 
. ample, the leaf base is attached over the entire circumfer- 
ence of the stem, and enwraps it completely for a considerable 
distance above the node (fig. 88). 

125. Stipules. — The leaf base frequently branches. These 
branches, commonly two in number, are called stipules 
(fig. 89). They vary from slender, awl-shaped bodies to 



100 



OUTLINES OF PLANT LLFE. 



flattened and leaf-like ones. The stipules may remain 
attached to the base throughout the life of the leaf, or may 
fall away early. Usually the two are separate, but they may 
be united with the leaf base itself, forming wings for it, as 
in roses (fig. 90), or they may be united with one another so 
as to form a sort of sheath encircling the stem (fig. 91). 
When the leaf base is winged, the wings extend downward 




Fig. 89. — A growing shoot of a thorn (Cratcegns punctata), n, leaves developed as 
bud scales which protected the parts above when in the bud ; S, stipules. Natural 
size.— After Reinke. 



as lobes more or less encircling the stem. In many cases 
the leaf is said to be clasping (fig. 92). These lobes may 
even unite on the other side of the stem, so that the stem 
seems to penetrate the base of the blade (fig. 93). When 
two leaves occur at the same node, corresponding lobes 
of the leaf bases may unite, so that the stem seems to pass 
through the center of a leaf which extends equally on each 
side of it (fig. 94). 



THE LEAVES. 101 

126. 2. The leaf stalk. — The leaf stalk is also known as 
the petiole. Its form is more or less cylindrical, usually 
with a groove or channel upon the upper side. Sometimes 



Fig. 90. — A young flowering shoot ot dog-rose, showing \ arious forms of leaves and 
transition from one to the other. n x -n h , scale leaves; <W 3 , foliage leaves; /z 1 -/? 3 , 
bracts; the flower leaves not clearly shown. The scale leaf, m 1 , shows a leaf base, 
winged by stipules 6, with only a trace of stalk and blade a. Trace these parts into 
foliage leaves, where the blade becomes compound, and subsequent reduction through 
the series of bracts. Natural size.— After Luerssen. 

the petiole is flattened in a vertical plane, as in aspen poplars. 
When this flattening is extensive, so that the petiole becomes 
thin and leaf-like and the blade is wanting, it functions as a 
foliage leaf (fig. 95). Not infrequently, the petiole is 



102 



OUTLINES OF PLANT LIFE. 



*». Jfc 



winged, as in the orange. It may be entirely wanting, in 
which case the blade arises directly from 
the base, as in most grasses (fig. 88). 

127. 3. The leaf blade.— To this part 
of the leaf the word ' ' leaf ' ' itself is fre- 
quently applied. In gen- 
eral, the leaf blade is so 
broadly winged as to be 
thin and flat; but all 
gradations exist between 
such forms and those that 
are much folded or crum- 
* pled, thick and fleshy, or 




Fig. 



Fig. 92. 
Fig. 91. — Stipules of Polygonum forming 

sheath, a, above the sheathing leaf base s, 

the cut-off leaf /; cc, the stem ; ca, an axillary ^..^t, ~,-'K,-»^i-iVol 

shoot. Natural size. -After Frank. even C} linariCai. 

Fig. 92. — Leaf of I klasfii with clasping base. 

Natural size. — After Prantl. 



If a thin blade be held 





Fig. 93. Fig. 94. 

Fig. 93. — Shoot of Uvular ia, showing perfoliate leaves below. About half natural 
size. — After Gray. 

94.— A shoot of wild honeysuckle, showing upper leaves connate-perfoliate. 
-After Gray. 



Fig. 
About half natural size. 



THE LEAVES. IO3 

between the eve and the light, two parts become evident: 
(1) a green tissue, more or less opaque; and (2) translu- 
cent " nerves" or " veins." * The larger of these, usually 
called the " ribs," * frequently form ridges upon the under 
surface. 




Fig. 95. -A shoot of Acacia, showing at a a twice-branched (compound) leaf with 
roundish petiole ; at b. a similar leaf with flattened blade-like petiole ; at c, phyllodia, 
i.e., blade-like petioles without true blades. About half natural size (?)— After Frank. 

128. Branching. — The outline of the blade is extremely 
various. It is dependent upon the character and extent of 
its branching, which may be either slight or extensive. 
Slight branching gives rise to teeth of various forms (fig. 96). 
More profound branching is evident in divided or parted 
leaves (fig. 97). In some blades the branching is so exten- 
sive and complete that the green tissue no longer fills the 

* These words must not be thought to indicate any resemblance in 
function to the same parts in animals, but only similarity of position or 
appearance. 



104 



OUTLINES OF PLANT LIFE. 



intervals between the larger ribs, but the blade is made up 
of a series of independent portions united to a common stalk. 
Each ultimate branch of the blade is known as a leaflet. 
Blades in which the green 
tissue is continuous, even 
though deeply divided, are 




B 

Fu;. 96. Fig. q' ; . 

Fig. 96.— Diagrams of slight leaf branching. A , leaf with crenate edge ; B, leaf with 

dentate edge ; C, leaf with serrate edge. - After Bessey. 
Fig. 97 —Leaf of A morfhophallus, showing sympodial branching. The successive 
lateral axes are numbered in order. The extent of branching makes the blade divided. 
Reduced. -After Sachs. 

called simple leaves. (See figs. 87, 89, 92, 96, 97.) Those 
which are branched into distinct leaflets are called compound 
leaves. (See figs. 90, 95.) 

129. Venation. — The ribs and veins, being composed in 
part of the vascular strands which enter the leaf, and in part 
of stiffening mechanical tissues, branch profusely and in such 
a way that no part of the green tissue is far from a vein. In 
figures 98 and 99, though none of the finest branches are 
shown, some idea of the complete distribution of the veins 
may be obtained. 

The branching of the ribs and veins agrees in the main with the differ- 
ent modes described for the shoot, ^[ 89, which see. A formal account of 
venation may be found in Gray's Structural Botany, pp. 90-94. 

130. Special forms. — Foliage leaves may be modified to 
serve special purposes without wholly losing their function 



THE LEA FES. IO$ 

as foliage. For example, the petiole may be made sensitive 
to contact, and adapted to wrap about slender objects, like 
a tendril, as in clematis and nasturtium (fig. ioo). Such 
plants are called leal-climbers. 

Some plants develop their leaves into the form of sacs or 




Fig. 98. Fig. 99. 

Fig 98. — Parallel venation of leaf of Polygonattim latifolizim. Natural size. — After 
Ettingshausen. 

Fig. 99. — Pinnately netted venation of leaf of a willow. Natural size. — After Ettings- 
hausen. 

pitchers. These ordinarily represent the blade of the leaf, 
and are more or less urn- or trumpet-shaped. They may be 
either without petiole, as in Sarracenia (fig. 101); or 
petioled, as in Utricularia (figs. 221, 222); or the petiole 



o6 



OUTLINES OF PLANT LIFE. 




may be winged to serve for foliage, as in Nepenthes (fig. 

220). A few plants have their leaves modified so as to serve 

as traps, which, by their 
sudden movements, capture 
small animals (figs. 224, 
225, 226). 

But generally the foliage 
function is subordinated to 
the other work, and the leaf 
takes on peculiar forms, the 
more important of which are 
as follows: 

131. (1) Tendrils.— The 
leaf blade alone, or some of 

Fig. too.— Portion of a plant of the dwarf its branches, Or the petiole 
garden-nasturtium (Tropceolum minus) 

The long petiole a, a. a of the leaf i is and blade, may develop as 

a cylindrical body, without 
wings and sensitive, known 
as a tendril. In the pea, the stipules become very large, 
and take the function of the reduced blade (fig. 102). In 
other plants the base may be broadly winged for the same 
purpose. 

132. (2) Thorns. — The leaves may develop into slender 
conical and sharp-pointed thorns or spines, either branched 
or unbranched (fig. 228). Sometimes the stipules alone 
become thorns, as in locust and acacia (fig. 103). Neither 
tendrils nor thorns can be distinguished structurally from 
similar forms of the shoot. 

133. (3) Scales. — In buds, on underground stems and on 
various parts of the aerial stem, are found small, scale-like 
leaves of various shapes (figs. 63, 64, 67, 71, 89, 90, 198). 
These scales may represent the sheathing base only; they 
may be the base with the stipules (fig. 90) ; or they may 
represent the leaf base and the blade. The petiole in all 



The long petiole a, a. a of the leaf / is 
sensitive to contact and has coiled about 
the support and its own stem, st. z, axil- 
lary branch. Natural size.— After Sachs 



THE LEAVES. 



IO/ 



cases is wanting. In addition to the adaptation of their 
form, scales, especially those that protect buds, are firm and 
resistant to cold and other unfavorable external conditions. 
Not infrequently they are supplied with hairs or surface 
glands, whose function is to produce and excrete resins and 




Fig. ioi. — Pitcher-plant {Sarracenia />ur/>urei > ). Leaf above A cut off to show 
trumpet form One-third natural size —After Gray. 

similar materials which make the parts so covered waterproof. 
The inner scales of buds (fig. 60) are often covered with an 
abundant coating of woolly hairs, wmich serve to prevent 
rapid change of temperature in the interior of the bud. 

134. (4) Flower leaves and bracts. — On certain parts of 
the stem, leaves are commonly profoundly modified to carry 
the spore cases (c, st, fig. 66). (See p. 196.) Close below 
these are others which may be highly colored and adapted 



io8 



OUTLINES OF PLANT LIFE. 



in form to protect the inner ones, and to facilitate the visits 
of insects (s, p, fig. 66). A shoot whose leaves are thus 
clustered and specialized constitutes a "flower." The 
leaves adjacent to the flower leaves are also more or less 
modified in form and reduced in size. 
They are called bracts (h I,2 -3> fig. 90). 

135. (5) Storage leaves. — Other 
leaves are utilized for purposes of stor- 
age. For this purpose the ribs are re- 
duced in number and size, while the 
softer tissues of the leaf are often 





Fig. T02. Fig. 103 

Fig. 102. — Portion of shoot of pea, with a pinnately compound leaf whose upper 

leaflets are modified into tendrils and the stipules greatly developed to serve as foliage 

About half natural size.— After Frank. 
Fig. ro3. — Piece of the stem of locust {Robin ia Pseudacacia), showing stipules in the 

form of thorns. Natural size. — After Kerner. 



enormously developed, and serve as the receptacles of 
the reserve food. The primary leaves of the seed plants 
(cotyledons) are often much distorted by the deposit in them 
of reserve food for the embryo. When such leaves possess 
sheathing bases the structure resulting from the union of a 
number of such leaves upon a short axis is called a bulb. 



THE LEAVES. 



109 



(See also \ 93.) The leaves of buds are sometimes thick- 
ened by the deposit of food material, and when such buds 
loosen from the plant they may produce a new plant, as in 
the tiger-lily (see \ 299). Both base and blade may be used 
for storage, as in the century-plant; or the entire leaf may 
serve the same purpose, as in the cultivated cabbage. 

136. Structure. — Three regions in each part may be distinguished, as 
in the root and stem : (1) the epidermis ; (2) the cortex ; both continu- 
ous with that of the stem ; (3) the steles, continuous with those of the 
stem when the latter contains several steles, or branches of it when the 
stem contains a single stele. 

The structure of the petiole agrees in all essentials with that of the 
stem (see ^j 107, ff. ). The following is a brief summary of the structure 
of the blade of a foliage leaf. 




Fig. 104* — Surface view of epidermis from under side of leaf of bracken fern (Pteris), 
showing wavy cells, except over veins, v, where they are elongated, st, stomata. 
The dot in each cell represents the nucleus. Highly magnified. — After Sedgwick 
and Wilson. 

137. Epidermis. — In broad leaves, the epidermis of the blade is made 
up of tabular cells, often with wavy lateral walls (fig. 104), and, except 
in shade plants, usually without green color. It usually consists of one 
layer, but in some plants becomes several-layered, either to serve as ad- 



no 



OUTLINES OF PLANT LIFE. 



ditional protection against evaporation or for use as a water-storing 
tissue. (See % 34 2 -) Numerous narrow slits, each bounded by a pair 
of specialized cells called guard cells, are formed in the epidermis. The 
whole apparatus is called a stoma (figs. 104, 105). The guard cells are 
crescent-shaped, and are sensitive to various external conditions, espe- 
cially light, so as to control the size of the slit-like passage between 
them by becoming straighter or more curved (fig. 105). This passage 





Fig. 105. — A, perspective view of a stoma from the under epidermis of the beet leaf, 
showing the sloping sides of the slit, the crescentic guard cells with chloroplasts. 
£, sections through stomata of beet at right angles to their length. The upper figure 
shows the stoma open : the lower closed. The black line represents the primary wall, 
to which additional material, especially in the guard cells, has been added. These 
thickenings serve by their elasticity to close the stoma. Opening is due to turgor of 
the guard cells. The chloroplasts and granular protoplasm are shown. Highly mag- 
nified.— After Frank. 



The stomata are 
here enclosed, 
30,000, some- 
to 70,000 in 



sq. cm. 



is formed by the partial splitting apart of the guard cells and com- 
municates with extensive spaces between the green cells in the in- 
terior. 

numerous. In different plants, in the space 
the numbers usually vary from 4000 to 
times, however, reaching as many as 60,000 
the olive and rape. They are not equally 
distributed on the two sides of the leaf, being usually more numerous on 
the under side, where there are more internal spaces. They may be 
wanting on the upper side, as in lilac, begonias, and oleander. There 
are no stomata on submerged leaves nor on the under side of floating 
leaves. In some plants they are found in clusters, in others uniformly 
distributed. 

138. Cortex. — The cortex of leaves is called the mesophyll. It con- 
sists of thin-walled, active cells, for the most part richly supplied with 
chloroplasts. In very thick leaves the internal cells are colorless. In 
some leaves the cells of the mesophyll are nearly uniform, but in most 



THE LEA VES. 



Ill 



those near the upper surface are more elongated and close set, form- 
ing one or two rows, with their ends outward, while cells near the 
lower surface are irregular in form, with large intercellular spaces 
(fig. 106). 

The cortex (gs, fig. 106) often develops along the larger steles into 
one or two strands or a sheath of mechanical tissues. These tissues, to- 




Fig. 106. — Diagrammatic vertical section of a leaf, e, e, epidermis, with cuticle c, c, 
and stomata, sA, s/>. Between upper and lower epidermis lies the mesophyll, with 
cells abundantly supplied with chloroplasts. The upper row of elongated cells is the 
palisade parenchyma; the rest form the spongy parenchyma, both with many inter- 
cellular spaces a, i, f, communicating with outside air through stomata. In the meso- 
phyll lies a small vein, here cut across, composed of a ventral wood bundle £, a 
dorsal bast bundle s, surrounded by the endodermis gs, and the pericycle (between 
g and gs). — After Sachs. 

gether with a stele, constitute the rib or vein, often so massive as to pro- 
ject beyond the other parts in thin leaves. 

139. Steles. — The steles are numerous and ramify through the blade. 
Their structure is essentially as described for the stem (^[ 107). Each 
of the smaller consists of little more than a single pair of vascular strands. 
The wood strands alone form the last branches (fig. 107), the bast disap- 
pearing earlier. The larger ribs may be accompanied by one or two 
strands or a complete sheath of mechanical tissues, and the vascular 



112 



OUTLINES OF PLANT LITE. 



strands may be increased by the development of secondary wood and 
bast. (See ^114-) 

The growth of the leaves is ordinarily limited, rarely extending over 
a single season. In a few ferns and coniferous plants the leaves live for 
two to eight years, and some continue to grow for a longer time than 
one season. 





Fig. 107. Fig. 108. 

Fig. 107. — A few meshes of the finest veins of a leaf of A nthyllis. m, main vein : b, b, 
branches ; a, a, a, a closed mesh ; c, ends of the finest veins within the mesh. The 
drawing shows only the wood bundles ; the bast bundles accompanying them and 
the mesophyll cells filling the meshes are not shown. Moderately magnified.— After 
Sachs. 

Fig. 108. — Ending of a vein in the mesophyll of a leaf, v, v, v, the spirally thickened 
cells of the wood; c, c, mesophyll cells with chloroplasts ; a, a, cells specialized to 
transfer water from wood to mesophyll. Magnified 230 diaro. — After Frank. 



140, Wintering. — In those plants which live from year 
to year, producing new leaves each spring, the unfolding ot 
these from the winter buds is due chiefly to the enlargement 
of the rudimentary leaves already formed. New leaves are 
ordinarily produced before the close of the growing season 
preceding that in which they are expanded, and are protected 
in the winter buds. The partly developed leaves in the bud 



THE LEAVES. 1 1 3 

may be flat, but broad leaves are commonly folded or rolled 
in various ways. 

141. Production of the other members. — Leaves give 
rise under certain conditions to roots or to shoots. The 
number of plants, however, in which this occurs is compara- 
tively limited. Roots arise from leaves in precisely the same 
way as lateral roots arise from stems (^f 84), that is, they are 
internal in their origin, and begin to develop always near the 
surface of a stele. 

When a leaf produces a shoot, it is from the epidermis or 
from the green tissue underlying it, never from a stele. 
Shoots thus arise from the part of the leaf correspond- 
ing to that from which branches arise upon the parent 
shoot. 

142. Leaf fall. — Leaves, like roots and stems, undergo 
certain secondary changes, but these are neither so common 
nor so extensive as in the other two members. One of the 
secondary changes of most importance is the preparation for 
the fall of the leaf. This is made by the formation of a 
transverse plate of cells, some of which may become trans- 
formed into cork, making a line of weakness; or, without 
such alteration, the cells may round themselves off by 
loosening along a definite line, so that the leaf is held only 
by the steles. The access of water to this crevice, and its 
freezing, serve to rupture the remaining tissues, and thus 
allow the leaf to fall by its own weight, or to be torn off by 
the wind. 

The scar left by the fall of the leaf is protected either by 
the cork already produced, or by mere drying of the exposed 
tissues. The leaflets of compound leaves fall in like manner. 
Sometimes provision for the leaf fall is begun as early as 
June, as in the Kentucky coffee-tree. In other plants pro- 
vision for leaf fall is begun late in the season, and in some, 
such as the oaks, it is very imperfect, so that the leaves are 



114 OUTLINES OF PLANT LIFE. 

finally wrenched off by winter storms, or pushed off in the 
spring by the developing buds beneath them. 

EXERCISE XIX. 

Leaves. — Examine the forms, branching, and venation of such leaves 
as can be secured. Unfolding buds show modes in which leaves are 
folded or rolled. Special directions for study seem unnecessary. A 
demonstration of the structure of a lily or lilac leaf (^[ 136-139) is 
desirable. (For flower leaves see p. 210.) 

143. Summary. — The form, structure, and position of 
foliage leaves are chiefly dependent upon the amount and 
direction of light. The first leaf or leaves of the embryo are 
usually transient; even secondary leaves rarely live more 
than a single season. They arise in regular succession on 
the stem and at such points as are least crowded. The parts 
of a leaf are blade, base, and stalk; any one or two may be 
wanting. The base is often sheathing or branched to form 
stipules. The stalk may be winged to act as a blade. The 
blade is in one piece or more or less branched into lobes or 
into leaflets. The veins, containing vascular strands, supply 
all parts with water, and when strong prevent tearing. The 
leaf rudiment, instead of developing into a foliage leaf, may 
form a pitcher, a tendril, a thorn, a scale, a flower leaf, a 
storage place, etc. The internal spaces of the leaf connect 
with the air through stomata, which are guarded by a pair of 
valve-like cells. These by changing form can regulate the 
evaporation of water from the leaf, and also permit ready 
entrance of air. Leaves often live over winter in a rudimen- 
tary condition in the bud. They fall usually because of the 
formation of a separation layer of cells across the leaf base. 



PART II. PHYSIOLOGY. 

CHAPTER XII. 

INTRODUCTION. 

144. Division of labor. — The study of the external form 
and internal structure of plants may be carried on as well 
upon dead as upon living material. Even the observation 
of the course of development requires only the examination 
of the plant as it exists at a particular moment. But the 
plant may also be studied as a working organism. For this 
purpose living material is indispensable. The work that 
plants do, by which they are distinguished from non-living 
bodies, is extremely varied, and the more complex the plant 
the more varied it is. In the preceding part the aim has 
been to show that there exists great variety of form, and that 
from the smaller to the larger plants there is gradually in- 
creasing complexity by differentiation into tissues and 
members. 

Nutrition, respiration, growth, movement, and reproduc- 
tion are all executed by the single cell of the simplest plant. 
But with specialization in structure there occurs division of 
labor. Each kind of physiological work is known as a 
function, and each part of the organism which does a par- 
ticular work is called an organ. 

145. Physiology and ecology. — Physiology proper treats 
of the plant at work, discussing the different functions and 
the way in which these are affected by external forces, such 
as light, heat, etc. In its broadest sense it also treats of the 

115 



Il6 OUTLINES OE PLANT LIFE. 

relation of the plant as a whole to external forces and to 
other living beings, both plants and animals. But it is con- 
venient to separate the latter from physiology proper as 
ecology* (See Part IV.) 

The study of physiology proper requires methods of controlling these 
external forces, carefully planned and repeated experiments, and cau- 
tious inferences. 

The study of ecology requires observation, in the field, of the physical 
surroundings of plants, of their relation to their neighbors, and of their 
adaptations to prevent injury by unfavorable physical conditions and the 
attacks of other beings, and to take advantage of the favorable forces and 
beneficent agents. 

146. Chemical and physical forces. — The functions of a 
plant may be divided for the sake of convenience into nutri- 
tion, respiration, growth, movement, and reproduction. 
These are largely special modes of chemical and physical 
action. Nutrition and respiration, for example, consist 
chiefly of a series of chemical changes; while movement is 
mainly a result of physical alterations in certain organs. 
But the action of chemical and physical forces does not 
suffice at present to explain all the activities of the living 
plant. Moreover, the peculiar manifestation of these forces 
which we call life occurs only in connection with the sub- 
stance which we call protoplasm. 

147. The powers of protoplasm. — Although only a por- 
tion of any plant is composed of living matter, it is to that 
living matter only that we are to look for the seat of its 
powers. 

The fundamental powers of protoplasm are four; it is 
metabolic, irritable, contractile, and reproductive. 

148. Metabolism. — Protoplasm is metabolic, that is, it is 
capable of initiating chemical changes in itself and in sub- 

* Spelled in lexicons, cecology, but best usage drops the o; sometimes 
improperly called biology or plant biology. 



PHYSIOLOGY. 117 

stances which come directly under its influence. These 
changes are of two kinds. They may be constructive, i.e., 
they may build up complex substances out of simpler ones, 
and so fit them for use in repairing the waste caused by the 
activity of the protoplasm; or they maybe destructive, i.e., 
they may break down complex substances into simpler, so 
setting free the energy necessary for the work of the proto- 
plasm. The substances broken down may be repaired in 
whole or in part, i.e., may take part in constructive met- 
abolism. Those in which no repair occurs often undergo 
further destructive changes by which they become converted 
into materials useless to the plant, and to be gotten rid of. 
Metabolism, therefore, includes all the chemical changes 
by which food is either manufactured or utilized, and by 
which waste materials are produced and eliminated. 

149. Irritability. — Protoplasm is irritable, that is, it 
exists in such a state that it is sensitive to external influences, 
which thereby affect the various functions of the whole 
plant. By reason of its irritability, it may even transmit the 
effects of an external stimulus from one part to a distant 
part. Moreover, it is capable of initiating similar changes 
without the action of any observable external influences, and 
is, therefore, not only irritable but automatic. 

150. Contractility. — Protoplasm is contractile, that is, it 
has the power of altering its form, of shortening in one direc- 
tion and elongating in another, by virtue of inherent forces 
whose action is not understood. 

151. Reproduction. — Protoplasm is reproductive, that is, 
it is capable of so directing the chemical and physical forces 
inherent in it that a new organism similar to that of which it 
forms part may be produced. 

152. Adaptation. — The interrelation of these powers, 
their harmonious co-working and their variation to suit the 
varying conditions of the surrounding media (air, water, 



lib OUTLINES OF PLANT LIFE. 

soil, etc.), result in the proper performance of all the func- 
tions of the plant. By means of these powers it is brought 
into relation to the world about it, being adapted to other 
organisms in whose company it lives, and enabled to with- 
stand the adverse conditions by which it is frequently 
threatened. Every organism, indeed, must adjust itself first 
to the external physical conditions, and, second, to other 
organisms. (See Part IV.) 

153. Physical conditions set limits upon the discharge of 
its functions. Varying amounts of light, of heat, of moist- 
ure, determine more or less rigidly how rapidly, or to what 
extent, each function may be discharged. Every function of 
the plant is adapted, therefore, to an upper limit, the maxi- 
mum, and to a lower limit, the minimum, above or below 
which the performance of the function in question is im- 
possible. Between these limits there lies some point at 
which it proceeds most rapidly and effectively. This point 
is known as the optimum. 

154. Summary. — Increasing size and complexity permits 
an advantageous division of labor among different organs. 
Physiology treats of the work of the plant as a whole; 
ecology of its adaptations to external conditions and to other 
organisms. All plant work depends on the living proto- 
plasm. Its power of initiating and carrying on chemical 
changes in itself and other substances provides for nutrition ; 
its power of receiving impressions from the world about 
enables it to regulate all its work and adapt itself to its sur- 
roundings; its power of contractility enables it to move; and 
its power of making and separating special parts of its own 
substance secures a succession of like plants. All work is 
limited by the physical conditions which surround the plant, 
and may bring any or all of them to a standstill, because the 
plant can only adjust itself to them within narrow limits. 



CHAPTER XIII. 



THE MAINTENANCE OF BODILY FORM. 



Every plant is capable of attaining and maintaining a 
specific form, which is not permanently altered by the direct 
action of external forces, and is dependent upon the nature 
of the plant itself. 

155. Naked cells. — If the plant consists of a single mass 
of naked protoplasm, it may assume a spherical or ovoid 
shape (fig. 109). In attaining this form the physical forces 




Fig. iog. — Zoospores (naked pro.oplasm) of various kinds, swimming in water by means 
of one or more cilia. A, Botrydium ; B, Draparnaldia ; C, Coleochcete ; D, 
CEdogoninm. Highly magnified.— After Kerner. 

play a part, but the form is determined chiefly by unknown 
internal forces peculiar to living protoplasm. This is par- 
ticularly well shown when such organisms extend delicate 
protoplasmic threads, the cilia (fig. 109), and maintain these 

119 



120 



OUTLINES OF PLANT LIFE. 



in active motion, or when they extend a large portion of 
the body for creeping (fig. no). The extension of such 
organs, whether slender or thick, is directly opposed by 
strong physical forces acting at the surface which tend to 
contract the body into a sphere, as they do a drop of liquid. 




Fig. no.— Plasmodia, creeping bits of naked protoplasm, showing varied shapes as 
parts are protruded or withdrawn. Highly magnified. — After Kerner. 

156. Turgor. — If the organism be one surrounded by a 
cell-wall, or if it be made up of a number of cells united, 
the cell-wall itself plays a considerable part in maintaining 
the form. This is due to the condition of the cell known as 
turgor. When fully mature the cell -wall of each active cell 
is lined by a more or less thick layer of living protoplasm. 
In the interior of the protoplasm there exist one or more 
water chambers, the vacuoles (■[ 4, and fig. 117). If such a 
cell as this be measured in its normal condition, and then 
surrounded for a few moments by a 10 per cent, solution of 
common salt, re-examination will show that the vacuoles 
have been diminished and the protoplasm shrunken away 
from the wall; remeasurement will show that the cell has 
diminished both in length and diameter. In its normal con- 
dition, therefore, the wall was stretched by the pressure of 
the contents within. If a cell which has been thus shrunken 
by immersion in a solution of salt be again placed in water, it 
may regain, in the course of a few hours, its original condi- 
tion, that is, it may again become turgid. This would be 
brought about by the entrance of water into the vacuoles to 



THE MAINTENANCE OE BODILY FORM. 121 

replace that withdrawn when the cell was placed in the solu- 
tion of salt. 

If a thin piece of rubber tubing be connected with a pump 
and filled with water until it is stretched, it increases its 
diameter and length slightly, and gains, at the same time, a 
condition of rigidity greater than in its unstretched condition. 
In a similar way turgid cells are more rigid than those which 
are flaccid. The union of turgid cells produces a member 
more rigid than one in which the cells are not turgid. An 
illustration of this is to be seen in the condition of a wilted, 
as compared with a fresh, leaf. The turgor of thin-walled 
cells may play an important part in maintaining the form 
and position of the parts of a plant. 

EXERCISE XX. 

Demonstration. To show the existence of turgor in the individual cell. 

Mount a bit of Spirogyra under microscope ; observe position of 
chlorophyll bands. Irrigate with 5 per cent, solution of salt and note 
effect. 

(If Spirogyra is not at hand use hairs on stamens of Tradescantia ; or 
the epidermis, filled with purple cell sap, from the under side of the 
leaves of the variegated Tradescantia (" wandering Jew"); or the hairs 
of geranium leaves. ) 

To show effect of turgor of cells on rigidity of young parts containing no 
mechanical tissues. 

Remove carefully a young plant with vigorous primary root grown in 
sawdust or moss. Lay in water for a few minutes. Note rigidity. 
Transfer to 5 per cent, salt- solution for a few minutes. Has rigidity in- 
creased or diminished ? Remove to water again for 15 min. What is 
the result ? 

157. Tissue tensions. — But turgor can affect only those 
cells whose walls are thin and extensible. Those whose 
walls have become thick and rigid are not stretched by this 
force. In the larger plants, however, where both thick- 
walled and thin-walled tissues exist, it is possible that a mass 



122 



OUTLINES OF PLANT LIFE. 



of thin-walled cells may, by the united tension of its com- 
ponent cells, stretch those tissues which are not themselves 
turgid. Such strains in the younger regions, particularly, 
play an important role in maintaining the form of these 
parts. But the tensions in the older parts are generally due 
to the unequal growth of different tissues. (See \ 218.) 

158. Mechanical rigidity. — The rigidity of the cell-wall 
itself must be relied upon by all the larger plants. Certain 
tissues are specialized by having their cell-walls greatly 
thickened, and such tissue regions constitute a sort of frame- 
work or skeleton, which is filled out by the more delicate 
parts. These mechanical tissues are so distributed within 
the body as to afford frequently the maximum resistance to 
bending and breaking strains. 

In the accompanying diagrams the position of the mechanical tissues is 
indicated in transverse sections of a number of different stems (fig. 111). 
It will be seen that they illustrate well-known mechanical principles in 




C D E 

Fig. hi. — Diagrams showing the arrangement of mechanical tissues and vascular strands 
in the cross-section of various stems. The mechanical tissue is gray ; the vascular 
strands black, with white dots. A, linden (young); B, a mint; C, a sedge; D, a 
bamboo ; E, a grass. — After Kerner. 

their distribution. The hollow column (E) and the I-beam (A, B, C), 
two of the most rigid mechanical constructions, are frequently imitated 
in plants. 



THE MAINTENANCE OF BODILY FORM. 1 23 

In stems of trees rigidity is secured not by the distribution 
of the mechanical tissues, but by their massiveness. In 
them the chief mechanical tissues belong to the wood, which 
forms a solid column occupying the center of the body. 
Aquatic plants, which are supported by the medium in which 
they live, are usually without mechanical tissues. 

159. Summary. — Bodily form is maintained by naked 
protoplasm chiefly by unknown forces inherent in the living 
substance. In larger plants it is maintained partly by turgor, 
which develops opposing strains in masses of cells, and partly 
by the mechanical stiffness of the cell-walls formed by the 
protoplasm. These rigid parts are either massed or definitely 
placed in the plant body, so as to carry its weight and meet 
the strains due to winds, water-currents, etc. 



CHAPTER XIV. 

NUTRITION. 

160. Repair and growth. — Since the body of every plant 
is constantly wasting away by reason of its own activity, it 
is necessary that it should be as constantly repaired. It 
must also, for a considerable time or throughout its whole 
life, be furnished with material which can be used in the 
making of new parts. Without an adequate supply of food, 
Iherefore, neither repair nor growth is possible. To under- 
stand what materials are necessary for repairing waste and 
forming new parts of the living plant, the constituents of a 
plant may be determined by chemical analysis. 

161. Chemical composition. — The greater portion of the 
weight of every plant is found to be water. Of the firmer 
parts it forms as much as 50 per cent , while of the softer 
parts it may form 75 or even 90 per cent. The most watery 
portions of some plant bodies, such as the juicy portions of 
fruits and the whole body of the algae, may contain only 2 to 
5 percent, of solid matter. 

If the solid matter left after driving off the water at a temperature of 
no° C. is burned, there remains a white material which crumbles under 
pressure, the ash. The dry matter consists chiefly of three elements, 
carbon, hydrogen, and nitrogen. The most abundant element in 
addition to these is nitrogen. When the dry substance is burned 
these four elements are driven off in gaseous form. An analysis of the 
ash reveals the presence of sulfur and phosphorus in considerable amounts, 
and also smaller quantities of the following elements: calcium, magne- 

124 



NUTRITION. 125 

shim, potassium, iron, sodium, chlorine, and silicon. Of these seven, the 
first lour are found in the ash of all plants, and the remaining three are 
\vr\ common. In addition to the elements enumerated, about 25 others 
are known to occur in the ash of plants, but only in minute quantities. 



A. The water in the plant. 

162. Necessity. — Since water forms such a large percent- 
age of the weight of fresh plants, it is manifest that it must 
be supplied in relatively large quantities, if the plant is to 
continue in an active condition. A portion of this water 
may be used up in the chemical changes occurring in the 
body, but it is not possible to discriminate between this and 
the water which is necessary to furnish the proper physical 
conditions of life. Water is the great solvent in which 
materials of various kinds enter the plant body, and by which 
a still greater variety within it are transported from place to 
place. Before discussing the food of plants, therefore, the 
relation of water to the plant may be examined. 

163. Air, water, and land plants. — Some plants are not 
in contact with water except at irregular intervals. These are 
called air plants, and include some algse, liverworts, mosses, 
fernworts, and seed plants. All these, however, are able to 
live only in an atmosphere containing large quantities of 
water vapor, or in those regions where they are frequently 
sprayed with water. Water plants float upon the water, or 
are submerged in it. As distinguished from both air and 
water plants, are those which have the root system (and some- 
times a portion of the stem buried in the soil) continually or 
intermittently in contact with liquid water, while the shoot 
system is occasionally sprayed by rain. Such may be called 
land plants. 

164. Solutions in water. — In no case, however, is the 
water in which plants are immersed, or with which they are 
sprayed, pure water. It always holds in solution substances 



126 OUTLINES OF PLANT LIFE. 

derived from the atmosphere or from the soil with which it 
has come in contact. These substances, whether organic or 
inorganic, enter the plant, together with the water, through 
those organs which are adapted to absorption. 

165. Absorption of water. — In air plants of the simpler 
sorts, any parts exposed to the moist air or rain can absorb 
water. In liverworts and mosses the thallus or the leaves are 
active absorbents. In the higher plants, such as the aerial 
orchids, the external cortex of the roots is especially adapted 
to absorb liquid water, or to condense the water vapor of the 
atmosphere.* In water plants the surfaces which are normally 
in contact with the water are absorbing surfaces. Such 
plants may be either wholly without a root system, or it may 
be only sufficiently developed to anchor them in the mud. 
In land plants the root system is especially adapted to the 
absorption of water. Only minute quantities of water are 
absorbed by the leaves and other aerial parts. The root sys- 
tem of the land plants is developed in contact with the soil. 

EXERCISE XXI 

To show that water is not absorbed by leaves in quantity adequate to 
supply evaporation. 

Cut off a vigorous shoot of a plant with abundant foliage; close end of 
stem with grafting -wax; expose to sunlight until well wilted; then im- 
merse it in water. Does the plant recover its turgidity slowly or rapidly ? 

166. Soil. — The soil consists primarily of finely divided 
particles of rock, whose nature and size determine the quali- 
ties by which soils are ordinarily distinguished into gravelly, 
sandy, loamy, clayey, etc. Mixed with these rock particles 
is more or less material derived from the offal of plants or 
animals. When decaying plant offal predominates, the soil 
is known as vegetable mold or humus, which naturally forms 



* If such condensation really occurs (as is generally alleged), it does 
not suffice to keep the plants supplied with the required amount of water. 



NUTRITION. 



127 



the upper layer of the soil of forests. To garden or field soils, 
not naturally rich in organic matter, this is frequently sup- 
plied artificially by adding manures and artificial fertilizers. 

167. Soil water. — No matter how fine the soil may be, 
the rock particles are not in close contact, but, on ac- 
count of their angular outline, leave spaces of greater or 
less size to be occupied by other materials. If a soil be 
examined immediately after a heavy rain-fall, these spaces 




Fig. 112.— Diagram of a portion of soil penetrated by root hairs, h, h' ', arising from 
root, e. At z, s, s' the hair has grown into contact with some of the soil particles, T, 
which are surrounded by water films 1 shaded by concentric lines), /3, a, t. The white 
spaces are air-bubbles, 6, 8', y, y'. When water enters the hair at a, the thichness of 
the film a, /3, t will be diminished, and some water will flow towards this point, re- 
ducing all the other water films in the vicinity. More air enters from above When 
rain falls, the reverse process occurs ; the films thicken, and the air may be entirely 
driven out, to return as the surplus water drains away.— After Sachs. 

will be found completely occupied by rain-water. If the soil 
be so situated as to be naturally drained, considerable quanti- 
ties of this water will disappear gradually, and the larger spaces 
between the soil particles will be occupied partly by films of 
water adherent to the soil grains, and partly by bubbles of 
air (fig. 112). 

168. Salts dissolved. — The water which thus filters through 
the soil dissolves and retains certain of its constituents. As 
the rain passes through the atmosphere it also dissolves cer- 



128 OUTLINES OF PLANT LIFE. 

tain substances found therein, notably minute quantities 
of compounds containing nitrogen, which are useful to the 
plants for food making. 

169. Root absorption. — The structure of the root system 
has been explained (^[ 72-76). The root hairs come into 
close contact with the soil particles, pushing them aside 
somewhat, and being in turn more or less deformed by their 
resistance {z, s, fig. 112). So close does the contact of the 
root hairs and soil grains become that many particles of the 
soil are embedded in the walls of the root hairs (fig. 51). 
The root hairs are not only in contact with the soil particles, 
but also with the films of water, which occupy the spaces be- 
tween them (a, fig. 112). They are thus in a position for 
absorbing water from the adjacent films. 

EXERCISE XXII. 

To shoiv the location of root hairs and especially their adhesion to soil 
particles. 

Germinate wheat in sand and when seedlings have several strong roots 
dig up carefully; shake sharply in water; note where soil clings most 
tenaciously. Brush away most of this with camelhair brush and examine 
a bit of this part of root under a low power of microscope. Observe dis- 
tortion of root hairs, and particles of sand partly embedded in them. 

170. Limit of absorption. — Not only is the water imme- 
diately in contact with the root a source of supply, but even 
that in the deep and more distant parts of the soil. For 
when, by the entrance of some water into the root hair, the 
thickness of that layer has been decreased, the disturbance of 
equilibrium causes a flow from neighboring layers ; and this 
goes on until the films of water upon the soil grains become 
so thin that the water particles are held too tenaciously to be 
pulled away by the root. There remains in such exhausted 
soil, which seems dry as dust to the touch, 2 to 12 per cent, of 
water unavailable for the plant. 



NUTRITION. 129 

171. Solvent action. — The root hairs also exert a slightly 
solvent action upon the soil particles themselves by reason of 
the carbonic acid and the acid salts which they excrete. By 
this means various minerals, which could not be dissolved by 
the water alone, may be brought into solution. 

EXERCISE XXIII. 

To show excretion of acid salts by roots. 

Fill a wide-mouthed bottle holding 250 cc. with tap water; add 2-3 
drops of ammonia and several drops of phenolphthalein. * If the water 
does not now remain pink add a drop or two more of ammonia. Select 
a vigorous seedling bean grown in sawdust; rinse roots well to remove 
impurities. 

Cut in two a cork which fits the bottle; in the halves cut two cor- 
responding notches of such size that with a little cotton for packing the 
plant will be firmly held. Place the plant with enough cotton to secure 
it in the cut cork and set in bottle with roots immersed. 

As the plant grows from day to day watch for the disappearance of 
color in the solution, which will indicate when the alkaline fluid has be- 
come acid. Arrange a control experiment in exactly the same way, but 
without plant. Surround each bottle with opaque shade of heavy paper, 
to avoid effect of light on the roots and fluid. 

To show the corrosion of carbonate of lime by the carbonic acid 
excreted by the roots. 

Cover a polished marble slab to a depth of 5 cm. with clean sand, in 
which plant corn or beans. After the plants are 10-15 cm. high, remove 
sand carefully and rinse off the marble. Examine the surface by reflected 
light. A. little graphite rubbed into lines etched by roots will make them 
more readily visible. 

172. Movement of water within the plant. — Once the 
water has gained entrance to the plant, it must move to those 
parts where it is to be used — i.e., to all the organs of the 
plant, but especially to the leaves, since from these there is 



* An indicator for acids, colorless when a fluid in which it is dissolved 
is acid, rose pink or darker when alkaline. For use the crystallized 
phenolphthalein is dissolved in alcohol. 



130 



OUTLINES OF PLANT LIFE. 



the largest loss of water by evaporation (^[ 177). From the 
root hairs the water passes inward through the cortex, and 
reaches the stele. The forces which determine this move- 
ment and its direction are not fully understood. They are 
comprehended under the general phrase root pressure. 

173. Root pressure. — The action of root pressure may be 
demonstrated by severing a suitable stem close to the ground 
and observing that water flows out, 
after a short time, from the cut end- 
Careful examination of the cut surface 
shows that the water is forced out chiefly 
from the woody parts of the stele, and 
this continues for a considerable time. 
The force with which water is extruded 
may be measured by attaching to the 
stump, by means of a rubber tube, a 
pressure gage (fig. 113). In this way 
it may be ascertained that in woody 
plants, such as the birch, the pressure 
sometimes becomes great enough to 
sustain a column of mercury about two 
meters high (2.5 atmospheres). 

EXERCISE XXIV. 

Fig. 113. — Apparatus for Demonstration. To sliow root pressure as a 
measuring root pressure. r . ; ,, . , . , 

For explanation see Ex- factor in the movement of water in plants. 




ercise XXIV. p. 
After Sachs. 



— Cut off the stem of an actively growing plant 
(plants of castor bean and tomato 25-30 cm. 
high are especially recommended) a short distance above the soil and 
fasten tightly to the stump, by means of rubber tubing, a piece of glass 
tubing a meter long, and about the diameter of the stump. Wrap joint 
with tire or electric tape to prevent stretching of rubber and leakage. 
Add enough water to rise 10 cm. above the rubber connection. Keep 
roots well watered and mark the height of the water in tube from time 
to time until it reaches the top or begins to fall. Does the water rise 
from the first ? 



NUTRITION. 131 

A more satisfactory record may be reached by attaching to the stump 
a T-tube as shown in tig. 113. To the horizontal arm attach a mercury 
pressure gage. (A pressure gage may be readily constructed by bending 
a glass tube, about 5 mm. diameter (3 mm. bore) and 80 cm. long, upon 
itself 30 cm. from one end, so that it forms a |J with unequal legs 3-4 cm. 
apart. Bend 5 cm. of the end of the short leg at right angles, in the 
plane of the (J- Tie the legs to a piece of cork between the legs near top, 
so that the tube will not be easily broken by the leverage of the legs on 
the bottom bend. ) Fill the space between stump and mercury with water. 
In the third arm insert a short tube drawn out to a slender point to per- 
mit the escape of air and extra water. Seal this with a flame after filling. 
There must be at least 15 cm. of mercury in U -portion, of manometer. 
At beginning mark, with a bit of gummed paper, height of mereury in 
each leg; measure difference at intervals thereafter until mercury begins 
to fall. 

174. Route to the leaves. — After entering and traversing 
the wood strands of the roots, the water is thence trans- 
ferred along the stem in the same tissues, which are con- 
tinuous with those of the root. Since the wood strands form 
an unbroken line to the most remote parts of the leaves, 
passing out in the ribs and forming the finer veins, the water 
may be distributed to every part of the plant body. 

Within the wood it travels chiefly in the cavities of the large ducts or 
vessels, when these are present, though the walls, also, are saturated 
with it, and permit a slower movement. These ducts, although of great 
relative length (some up to I m. ), are not continuous tubes like the veins 
of an animal, nor are they always filled with water. The water is often 
broken into short columns by numerous gas-bubbles, and in ascending to 
any considerable height must traverse many cell-walls. 

EXERCISE XXV. 

To show roughly the path of evaporation stream in woody plants. 

A. From a leafy shoot of a woody plant remove a ring of bark 5 mm. 
wide. With grafting wax protect the exposed surface against drying. 
Observe whether the leaves wilt or not, and if they wilt, the time re- 
quired. 

B. With a knife or fine saw cut a little over half through the stem of a 
plant of the same sort used in A; 1 cm. above this cut make a similar one 



132 OUTLINES OF PLANT LIFE. 

on the opposite side. The two must be so placed and at such a depth 
that all the tissues are severed. Support the branch or stiffen it against 
breaking by bandaging it with strips of wood. Make same observations 
as in A. Examine the pith. Is it alive ? Does it contain water ? In 
what tissues, therefore, do you infer water travels to leaves ? 

To show restoration and maintenance of an interrupted evaporation 
stream. 

Fit a well wilted shoot into the short arm of an unequal |J-tube filled 
with water to the level of the short end. Allow it to stand for half an 
hour. Does the shoot recover ? If not, pour mercury into the longer 
arm until it stands 10 cm. above its level in the short arm. Does the 
shoot now recover turgor ? Why ? Allow it to stand for some days. 
Does the level of the mercury change ? 

175. Motive power. — The force by which water is raised 
in the larger plants remains yet to be ascertained. The water 
does not flow along the ducts in a continuous current, as the 
blood in the veins, propelled by a force behind, for root 
pressure is not adequate to push it to the height attained. 
On the contrary, during the times of most active evaporation 
from the leaves, i.e., when the greatest supply is needed, 
root pressure becomes almost or quite negative. Capillarity 
is also inadequate. The diameter of the largest ducts is too 
small and the resistance to the flow consequently too great to 
permit the movement, by this means, of a sufficient amount of 
water to supply the evaporation. The most recent researches 
point to the evaporation of water from the leaves as a very 
important or even the chief factor in lifting the water. That 
the movement is not the work of living cells is shown by ex 
periments in which stems of plants have been subjected to 
poisonous agents, or heated for many hours to a degree suf- 
ficient to kill all the living cells, yet without materially affect 
ing the suppl) o water to the leaves. 

EXERCISE XXVI. 

To show tht lifting power oj evaporation. 

Cut off under water a shoot from a thrifty plant ; fasten it air-tight in 
the end of a piece of glass tubing 3G cm. long, ol appropriate diameter, 



NUTRITION. 133 

by means of a piece of rubber tubing slipped over the end of the stem, 
taking care not to expose the cut cud to air. Fill glass tube with water 
before fitting in plant ; erect the whole with lower end of tube dipping 
in a cup of mercury. Set in light and note height of mercury in I-48 
hours. 

176. The loss of water. — Water is constantly evaporating 
from the whole surface of the plant exposed to the air. Since 
this loss is more or less modified by the vital activity of the 
plant, it has received the special name, transpiration. 

EXERCISE XXVII. 

To show the loss of water by evaporation. 

Clean and dry the surface of a pot in which a thrifty single-stemmed 
plant is growing ; close the hole in the bottom with a cork ; with a 
brush paint the whole surface thickly and evenly with melted paraffin. 
Cut out a piece of stiff paper which will fit around stem and just cover 
the soil in pot. Using this as a pattern cut a cover for the soil from a 
sheet of lead ; slit the cover from the central hole to circumference ; ad- 
just it around plant and cement all cracks with grafting wax.* Weigh. 
Weigh again at intervals of 24 hours, -for 4 days. 

177. Transpiration. — In the higher plants transpiration 
from the surface is reduced by the waterproofing of the epi- 
dermis, so that most of it takes place from the surfaces of 
internal cells into the intercellular spaces, wherever these 
exist. Since the intercellular spaces are connected with each 
other and also, through the stomata, with the outside air, 
water vapor is constantly passing off by diffusion (see fig. 
106). The leaves, affording the largest exposure, are espe- 
cially organs of transpiration. After they have become fully 
expanded no considerable amount of water is lost directly 
from their surfaces. 



* Or the pot may be set in a tin or glass vessel which it fits ; this may 
be covered by sheet rubber tied to the edge and about the stem ; or the 
lead cover may be cemented on as above. 



34 OUTLINES OF PLANT LIFE. 



EXERCISE XXVIII. 

To show the variation in the rate of evaporation due to the difference 
in structure of the organ. (See also ^[ 339.) 

Compare as shown by shrinkage or by loss of weight, (a) Through 
cork tissue and without it. Take two potatoes ; peel one ; expose side 
by side ; compare day by day. (0) Through skin. Compare in same 
way two apples, (c) Through stomata. Take three equal leaves of 
oleander ; of one close the stomata (which are on underside only) with a 
thin coat of grafting wax, or cocoa-butter melted and brushed on (taking 
care not to kill cells by having wax too hot) ; coat the upper surface of 
second in same way ; leave third uncovered. Compare day by day. 

178. Amount and regulation. — The amount of transpira- 
tion, therefore, varies with the structure of the leaf rather 
than with its area. The temperature, percentage of moisture 
in the air and movements of the air affect profoundly the 
rapidity of transpiration. Hence arises the need of regula- 
tion by the plant, to prevent excessive loss. The guard cells 
of the stomata are irritable, so that external conditions affect 
their turgor. If both are turgid, they become curved away 
from each other so as to increase the size of the opening be- 
tween them. If they are flaccid, the thick ridges along the 
inner face of each cell straighten them, and so close the 
orifice more or less completely (fig. 105). The presence or 
absence of hairs upon the leaves, the existence of stomata 
upon one or both surfaces, the sinking of the guard cells 
below the general leaf surface, the distribution of the stomata, 
the thickening of the leaves, their inrolling (fig. 197), or 
revolution, have a decided effect upon the rate of transpira- 
tion, and may be adapted to regulate it. (See ^[ 335 ff.) 

EXERCISE XXIX. 

To show that many leaves are not zvetted by water. 
Immerse various sorts of leaves in water. Does the water wet the 
surface ? What is the cause of the silvery reflection of light from the 



NUTRITION. 135 

surfaces of some? What relation does this repulsion of water have to 
blocking of stomata by rain ? 

Demonstration. — To show the conditions affecting evaporation. 

Construct a potometer as follows : Bend the central stem of a J-tube 
until it is parallel with the cross piece. Fit into the lower opening of 
the straight leg a capillary tube 30-40 cm. long, with 3 cm. of each end 
bent at right angles to the main part and in opposite directions. Into 
the bent leg fit a shoot of a thrifty plant cut off under water, at the 
same time filling the T-tube with water. (To accomplish this, bend the 
shoot to be cut off so that the place of the cut is submerged in a deep 
pan of water. Fit it in tube without exposing cut surface at all to air.) 
Dip the lower end of the capillary tube in water and allow apparatus 
to stand until capillary tube fills with water. Remove the water for a 
moment and allow a bubble I cm. long to enter ; time it as it moves be- 
tween a series of equidistant marks on capillary tube. Try the rate 
under various conditions of light, temperature, and moisture acting on 
shoot. 

To show loss of liquid water when absorption is great and evaporation 
slow. 

Grow seedlings of wheat or oats until 5-10 cm. high ; then cover with 
a glass bell for an hour or two. Where do drops of water appear ? 
Why ? 

B. Foods in general. 

179. Foods. — In addition to an adequate supply of water, 
plants require food. To be a food, the material must consist of 
certain elements put together in such proportions and in such 
a way that it can be used, either at once or by the expendi- 
ture of comparatively little work upon it, to repair or renew 
the living protoplasm. All foods are compounds of carbon 
with two to four other elements. The best foods are very 
complex in their construction. Only the smallest and sim- 
plest plants can live upon the simpler carbon compounds. For 
most plants the proper foods are precisely of the same nature 
as for animals, and though each sort of plant has certain 
kinds of food which it can use best, it may be fed with many 
different kinds 



13^ OUTLINES OF PLANT LIFE. 

Plant foods, like animal foods, belong mainly to three groups, carbo- 
hydrates, fats, and proteids. Examples of the first are the sugars, of 
which grape sugar, fruit sugar, and cane sugar are the commonest ; 
starch, which can be broken up into grape sugar ; and cellulose, the 
material of cell-walls. Examples of the fats are olive oil, palm oil, cot- 
ton oil, etc. Proteids are generally recognizable by their property of 
coagulating upon application of heat, acids, etc. Examples are the 
albumen of "white of egg," the fibrin of blood, casein of milk, etc. 
Examples from plants are abundant, but less generally known. Proteids. 
always, and either carbohydrates or fats, or both, must be available in 
order that a plant may be properly nourished. 

Green plants obtain their food chiefly by manufacturing it 
out of simple materials taken into the plant body from the 
soil and air. They are the only living things, so far as 
known, which have the power of building up foods out of 
such simple materials as carbonic acid gas and water. They 
are, therefore, the ultimate source of the food supply of the 
world. 

C. Nutrition of colorless plants. 

180. Colorless plants. — By this really inaccurate phrase 
are meant plants which do not possess chlorophyll, though 
some of them are highly colored by other pigments. 

The colorless plants among the thallophytes constitute two 
large groups, known as bacteria and fungi. Among the seed 
plants, also, are found some de-void of chlorophyll. 

Many plants possessing chlorophyll show to the eye other 
tints than green, when other pigments are present in such 
quantity as to mask the green. This is notably the case with 
the so-called " foliage plants," in vvhich reds, yellows, 
purples, and browns are common. (See also ^[^[ 9, 33, 3%.) 

Colorless plants necessarily live either upon the material 
once produced by a living being, oftentimes upon its dead 
and decomposing body, or in company with living organisms. 
Those which live upon dead bodies, whether these have lost 



NUTRITION. 137 

their natural form completely or not, are known as saprophytes. 
Those organisms which live in association one with another 
are called symbionts and their relation is known as symbiosis. 
(See Chap. XXIV.) If one plant preys upon and injures 
another living plant or animal, it is called & parasite and the 
being which supports it is called its host. (See ^[ 44.) 

181. Saprophytes. — Saprophytic bacteria live immersed 
in solutions of food, or surrounded by films of fluid on the 
surface or in the interior of the solid material upon which they 
flourish. Saprophytic fungi either form their mycelium upon 
the surface of the substratum, which contains their food, or, more 
commonly, they penetrate it more or less extensively by a pro- 
fusely branched system of hyphse. A few saprophytic seed 
plants form at the base of the stem an enlarged, tuber-like mass 
from whose surface great numbers of profusely branched roots 
arise. These penetrate the decaying food material in all direc- 
tions, and act as absorbing organs. A few have abundantly 
branched underground stems and have no permanent roots. 

182. Digestion. — Saprophytes whose surfaces are sur- 
rounded by food solutions have only to absorb them. Some, 
however, have power to convert into material soluble in 
water the solid insoluble food with which they are in contact. 
This is brought about in most cases by substances excreted by 
the living protoplasm. Such chemical changes, by means of 
which insoluble solid materials are transformed into soluble 
ones and are dissolved, are identical in nature with those 
which occur in the digestive tract of the higher animals, and, 
therefore, may be properly termed digestion. 

183. Assimilation. — After the food is absorbed, it under- 
goes various changes, collectively known as assimilation, by 
which it is enabled to become part of the living material of 
the plant body.* 

* This is not to be confused with the manufacture of food by green 
plants, to which the term assimilation is inaptly applied by most writers. 



I38 OUTLINES OF PLANT LIFE. 

184. Parasites obtain their food either by growing upon 
the surface of the host and thrusting into its interior absorb- 
ing organs ; or by growing wholly in the interior of the host, 
breaking out to its surface only to form reproductive bodies. 

Parasites may work little apparent harm, or they may bring 
about local disease and death of the host. Their mode of 
obtaining food is not essentially different from that of sapro- 
phytes. They either digest solid foods, or absorb liquid 
foods, prepared by the host for its own use. Among the 
green plants there are some partial parasites, such as the 
mistletoe, which seem to obtain from their host chiefly the 
water and salts which they have absorbed. These materials 
they themselves elaborate into food. (See further ^| 370.) 

D. Nutrition of green plants. 

185. Raw materials. — In order that the green plants may 
be able to manufacture their food, they require certain raw 
materials, which are obtained from the water and air. The 
water is always a weak watery solution of various mineral salts. 
From the air (or the water in the case of submerged plants) 
they absorb a gas, carbon dioxid. 

186. Salts absorbed. — Along with the water which is 
taken into the plant go various amounts of dissolved material, 
a considerable portion of which consists of mineral salts. 
When plants grow in humus, or in water or soils containing 
organic matter, a variable amount of carbon compounds suited 
for food may be dissolved by the water and be taken up by the 
plant. To this extent the plant will live as a saprophyte, 
and no doubt many field and garden plants have been bred to 
require this sort of life. 

Among the mineral salts the most important are the salts of potassium, 
magnesium, calcium, and iron, which are present in all soils, in greater 
or less quantity, and are dissolved in surface waters. In the same way 



NUTRITION. 139 

main- additional compounds, of no use in forming food, are taken in. 
These are all found in the ask, when a plant is completely burned, 
though not necessarily in the same form in which they were absorbed. 

187. Selective action. — The compounds which exist in 
the water in various, though small amounts are not taken into 
the plant in the same proportions as they exist in the water. 
Substances which are utilized by the plant and which, there- 
fore, disappear as such within it by having their chemical 
composition altered or by being stored up in a different form 
and so removed from solution, will enter the plant contin- 
uously, as long as the supply outside exists. Substances ab- 
sorbed and not utilized accumulate in the water inside the 
plant, and these solutions soon attain the same degree of con- 
centration as those outside. Then they are no longer ab- 
sorbed. It is for this reason that two plants growing upon 
the same soil may contain very unequal quantities of any im- 
portant material. Plants thus exert a sort of selective action, 
but this selection is dependent upon purely physical laws, and 
is only indirectly under the control of the plant. 

188. Carbon dioxid. — Carbon dioxid is a gas, which is 
always present in the air, in which, however, it exists in small 
quantities, rarely exceeding one part in twenty-five hundred. 
An abundant supply of it is constantly being returned to the 
air by the breathing of animals and plants, by burning of fuel 
and by slow decomposition of dead bodies of plants and 
animals. The constant currents in the atmosphere make its 
distribution practically uniform. On account of its ready 
solubility, this gas also exists in abundance in soil waters and 
in the larger bodies of water constituting streams, lakes, or 
pools. The water which passes through the soil therefore 
has a larger percentage of this gas than the air, sometimes 
containing as much as one per cent. 

189. Absorption. — Water plants readily absorb the dis- 
solved gas by such surfaces as are exposed to the water. 



HO OUTLINES OF PLANT LIFE. 

Floating plants have opportunity to obtain it both from the 
water and from the atmosphere. Land plants, although their 
roots are surrounded by a comparatively concentrated solution 
of carbon dioxid, do not take up appreciable quantities by 
these organs. On the contrary, the absorption of this gas 
seems to depend entirely upon those cells which contain 
chlorophyll. The stomata, which allow the internal spaces 
free communication with the outside air, are important organs 
for facilitating the absorption of this gas. Its continued ab- 
sorption depends upon its continuous removal from the cell 
sap in the manufacture of food. 

EXERCISE XXX. 

To show the permeability of stomata for air and their communication 
with the system of intercellular spaces. 

Fasten a leaf with a long petiole air-tight in a rubber cork, through 
which also passes a short glass tube. Fit the cork into a bottle holding 
sufficient water to cover end of petiole. Attach a filter-pump or air- 
pump to glass tube. Observe whether air bubbles leave the end of the 
leaf stalk. 

Reverse the leaf, so that the blade is immersed, and make same ob- 
servation. Where do bubbles appear ? Is there any difference between 
upper and lower sides ? 

190. Photosynthesis. — The process by which carbohydrate 
foods (sugar, starch, etc.) are produced is called photosyn- 
thesis.* The steps in the process are not thoroughly known ; 
indeed they can only be guessed at, and the theories need 
not even be stated here. The final product is not neces- 
sarily the same in all plants, but in many it is cane 
sugar. Starch appears later in the form of minute granules 
in the interior of the chloroplasts. It is probably formed 
as a means of removing some sugar from the cell-sap 



* This term seems to be more generally approved than photosyntax, 
which was first proposed as a name for this process. 



NUTRITION. 141 

and storing the accumulated food for a time. In all green 
plants oxygen is a by-product. The amount given off about 
equals in volume the carbon dioxid used in making the 
foods. 

The conditions under which photosynthesis occurs are 
three : (a) the presence of chlorophyll, (£) the action of 
light, and (c) the presence of potassium salts. 

EXERCISE XXXI. 

Demonstration. — 71? show that oxygen is a by-product of photosynthesis. 

Collect the gas mixture evolved from a vessel full of aquatic plants by 
inverting over them a funnel to whose tip is connected a test-tube filled 
with water to be displaced by the rising gases. Keep the plants in sun- 
light. When the tube is filled, test the contents for oxygen by inserting 
a glowing splinter. 

191. (a) Chlorophyll. — Chlorophyll, as has been shown 
in Part I, sometimes colors the whole protoplasm of the cell, 
but is more commonly found only in certain special structures, 
the chloroplasts. The real work of forming the food de- 
pends, therefore, upon the protoplasm of the chloroplast. 
The purpose of the chlorophyll is to absorb certain portions 
of the light which falls upon it. 

192. ib) Light. — The light absorbed by the chlorophyll 
furnishes the energy necessary to do the work of taking apart 
the carbonic acid and rearranging the material into a more 
complex substance. This energy cannot be supplied by the 
plant itself. An external source of energy is therefore neces- 
sary. What this source is is unimportant, provided the 
energy be sufficient. The light of an electric arc serves the 
purpose as well as sunlight, if its intensity be equal. 

EXERCISE XXXII. 

71? show that manufacture of starch occurs only in cells directly illu- 
minated. 



I4 2 OUTLINES OF PLANT LIFE. 

Darken portions of some leaves of a plant previously found to show 
starch in its leaves * (sunflower, bean, tomato, or nasturtium) by attach- 
ing two plates of cork on opposite sides by means of two pins driven 
through both and the leaf. On the afternoon of the following day, ii 
sunny, cut off the leaves and test for starch as before. What has become 
of starch in cells under the cork ? 

193. (c) Potassium salts. — These take no part in the 
composition of the food produced, and their exact role is not 
understood. It is well established, however, that their pres- 
ence is essential to the formation of the carbohydrate food. 

194. Proteids. — The foods thus formed are sooner or later 
built up into still more complex foods, the proteids. The 
process by which this is accomplished is even more obscure 
than the preceding, neither the steps in the process nor its 
conditions being known. The formation of proteids occurs 
abundantly in green leaves while they are illuminated, and 
therefore making sugar, etc. But even in green plants pro- 
teids are made in other parts than leaves, and in darkness. 
They are also formed by colorless plants. Proteids are used 
directly in the repair of the protoplasm, and for making new 
protoplasm. 

E. Storage and transfer of food. 

195. Storage and transfer. — Both in the colorless and 
green plants it is necessary that the foods should be trans- 
ferred from the point where they are made or absorbed to the 
place where they are to be used. The larger the plant, the 



* To ascertain this, test as follows : Boil a few leaves of various plants 
for a few minutes. Place in alcohol at about 6o° C. until all chlorophyll 
is dissolved. (Do not heat over open flame, but set bottle, loosely corked, 
in a vessel of hot water.) Bring the leaves into a tincture of iodine, 
diluted to a bright brown, for half an hour. The leaves or parts con- 
taining starch will become bluish, dark blue, or black, according to 
amount of starch present. 



NUTRITION. 



143 



more important (because the longer) does this transfer be- 
come. In many plants, also, it is desirable that a supply of 
reserve food be stored for use when a supply is no longer 
available from the outside or by manufacture. 

196. Storage form. — In the higher plants, storage places are secured 
by the enlargement of roots, stems, and leaves, to form reservoirs. 
Similar specialization of parts in the lower plants occurs. The most 
common form of reserve food, especially in thickened stems, roots, etc., 
is starch. This is deposited in the form of rounded or oval grains, 
which often show layers due to different composition and density (e.g., 
in the potato tuber, A, fig. 114), and are sometimes adherent into com- 
pound grains, e.g., the oat (B, fig. 114). Ins eeds also, much reserve 




Fig. 114.— Reserve starch. A, two cells of a potato, showing enclosed starch grains. 
The other contents not shown. B, compound starch grains from a grain of oats. 
Three of the component granules of a large grain are shown separately. C, starch 
grains from a bean. All highly magnified. — After Kerner. 

food may take the form of starch, and fats are common. Fats occur in 
liquid form, as droplets of various size (e.g., cotton seed), and are only 
rarely solid. In some seeds the cell walls are enormously thickened, so 
that the seed is of bony hardness (e.g., the date). Reserve proteids are 
stored in the form of aleurone grains. These are small granules, often 
packed in between the larger starch grains, as in the cotyledons of the 
bean. 



197. Digestion and transfer. — When solid foods, insol- 
uble in water, are to be moved from one part of the plant to 



144 OUTLINES OF PLANT LIFE. 

another it must be done by altering them into soluble sub- 
stances, that is, by digestion. (See ^f 182.) 

This is accomplished by means of enzymes of different kinds, adapted 
to effect the alteration of various foods. The most abundant enzyme is 
diastase, which has the power of altering starch into a sugar. Enzymes 
fitted to transform proteids are also found in considerable amounts. 

When the foods have been brought into a soluble condi- 
tion, they dissolve in the water present. If one cell rhen 
contains more of that particular substance, say sugar, than its 
neighbor, the sugar particles will pass into the neighboring 
cells until the amount is equal. If this sugar is being used 
up in growth or repair, or is altered into another substance 
at any point, a constant stream of particles of sugar moves 
toward the point at which it is disappearing. Thus from 
the food sources it is transferred to the reservoirs and stored 
in suitable form. Thence, when needed, it is redissolved 
after digestion and carried to the active parts which utilize it. 
This movement may be hastened if elongated cells are pro- 
vided along the more important lines of travel. This is 
done in the bast strands. The movement is made still easier 
also in these by the perforation of the ends of some of the 
elongated cells, so that there is less resistance to movement. 
Foods, therefore, travel chiefly in the bast bundles and in 
either direction as may be necessary. 

EXERCISE XXXIII. 

To show in what tissues food most readily travels. 

Girdle as in Exercise XXV A a shoot of willow. Cut it off 5 cm. 
below ring. Place shoot in water. After some weeks note where new 
roots are formed. Why ? 

To show the digestion of starch by diastase. 

Powder a handful of malt in a mortar or obtain ground malt. To 25 
grams of the powder add 100 cc. of water ; stir well together ; allow 
mixture to stand (with occasional stirring) one to two hours ; filter ; pre 
serve the filtrate. Take 1 gm. of starch and rub it up in a dish with 



NUTRITION. 145 

5 cc. water ; pour this into 95 cc. of boiling water, stirring as it enters. 
With 25 cc. of this paste mix thoroughly 5 cc. of the filtrate (which con- 
tains diastase extracted from the malt). Test a small portion of the 
mixture at once for starch by adding a few drops of tincture of iodine, 
and similar portions at intervals of half an hour until starch reaction 
ceases. Taste the remaining paste. Into what has the starch been 
converted ? 

F. Respiration. 

198. Destructive changes. — Coincident with the processes 
which result in the formation of complex foods and from 
them still more complex living protoplasm are those which 
result in its destruction. In the green plants the construc- 
tive changes predominate (because of extensive food making), 
with the result that the plant accumulates additional organic 
matter ; while in colorless plants destructive processes pre- 
dominate, with the result that the plant increases in bulk, but 
only at the expense of organic materials previously existent. 
In all plants, however, both the constructive and destructive 
changes go on at the same time and without conflict. 

199. Respiration. — A series of destructive changes is in- 
cluded under the term respiration. It is a familiar fact that 
the higher animals cannot live without a constant supply of 
oxygen and a corresponding excretion of carbon dioxid. 
This is not so generally known to be true of plants. It is, 
nevertheless, true that no plant can live without a constant 
supply of oxygen and a corresponding excretion of carbon 
dioxid. The processes by which (a) oxygen is obtained, (b) 
united with the living protoplasm, (c) this substance decom- 
posed, and {d) carbon dioxid excreted constitute respiration. 

EXERCISE XXXIV. 

To show evolution of C0 2 by respiration of seedlings. 
Fill a wide-mouthed glass jar or bottle of 1 liter capacity one-third full 
of peas and beans which have been swollen for a day in water, then 



146 OUTLINES OF PLANT LIFE. 

rinsed thoroughly in 5 per cent, formalin and again rinsed in water. 
Cork or cover tightly. After 24-48 hours remove cover and thrust in a 
burning match or candle attached to a wire. If C0 2 has been produced 
it will extinguish flame. Test also by lowering into jar a vessel of 
baryta-water. If precipitate or film forms it shows presence of C0 2 . 

Demonstration. — To show evolution of C0 2 by respiration of leaves 
and fozoers. 

Provide a piece of plate glass and a bell jar with ground rim, of suit- 
able size to cover a blooming plant growing in a pot. Alongside the pot 
place a shallow dish of baryta-water ; cover both with the bell, daubing 
its edge with vaseline to make contact with glass plate air-tight. Place 
in darkness. Note film of barium carbonate on surface of water after a 
day. Conduct a control experiment, identical but for the absence of 
plant. Is more or less barium carbonate formed ? Why darken ? 

200. Respiratory ratio. — The ratio between the amount 
of oxygen consumed and carbon dioxid produced varies 
somewhat with the age and condition of the plant, as well 
as with the circumstances under which respiration occurs. 
Ordinarily the volume of carbon dioxid produced is approx- 
imately equal to the volume of oxygen consumed, and the 

^ U C0 2 

ratio may be expressed thus : -— - = 1. 

201. Respiration and photosynthesis. — In the green plants 
respiration is masked in daylight by photosynthesis. When- 
ever the green parts are sufficiently illuminated, the carbon 
dioxid produced by their respiration is consumed in the 
formation of food. But when these parts are not adequately 
illuminated, the process of photosynthesis is interrupted, and 
respiration can be more easily studied. The parts of plants 
which are free from chlorophyll, such as young flowers, buds, 
embryos, and the like, and all the non- green plants, allow 
the respiratory changes to be demonstrated readily. 

202. Aeration. — The oxygen consumed comes from the 
atmosphere, or from that dissolved in water. Certain plants 
are adapted to aerial respiration, while others are adapted to 
aquatic respiration, but in either case the gas used is the 



NUTRITION. 147 

same. In the smaller and simpler plants the protoplasm 
absorbs oxygen directly through the cell wall. In multi- 
cellular plants, however, especially when they become large 
and complex, only the cells at the surface could do this. 
The internal cells are too far from the source of supply to 
allow an adequate amount of oxygen to reach them by travel 
through other cells. In large plants, therefore, internal 
spaces are provided, and through these oxygen moves readily. 
In the land plants the internal spaces open into the air 
through the epidermis, in which, with the guard cells, they 
constitute the stomata (*|J 137)- In the absence of stomata, 
however, the oxygen may pass through any part of the sur- 
face of the plant. In submerged water plants, very large 
intercellular spaces are formed (fig. 76), permitting the ex- 
istence of an internal atmosphere of considerable amount, 
within whose limits gaseous exchanges may occur. Oxygen 
may reach these intercellular spaces from the water through 
the superficial cells. 

203. Intramolecular respiration. — While free oxygen is ordinarily 
utilized for respiration, all plants seem to be capable of obtaining their 
supply for a short time from the living matter of the plant itself. In 
most plants it can exist for a few hours at most without producing disease 
and, sooner or later, the death of the plant. It is precisely parallel to 
the similar method of respiration possible among cold-blooded animals. 
A few plants of the simpler sort, such as the bacteria, rely wholly upon 
combined oxygen for their respiratory supply. Such plants have adapted 
themselves to grow in the absence of free oxygen, which, instead of 
facilitating their life processes, really checks them. 

204. Excretion. — The carbon dioxid produced by respira- 
tion, when not used for food making, is gotten rid of by 
the reverse of the methods described for the absorption of 
oxygen. 

205. Release of energy. — The purpose of respiration is to 
set free energy required for growth and movement. While 



14$ OUTLINES OF PLANT LIFE. 

certain plants are capable of utilizing radiant energy of the 
sun for food making, all must set free within their own 
bodies the energy requisite for putting in place particles of 
new material to form new parts, and for the execution of 
movements, whether internal, such as the streaming or rota- 
tion of the protoplasm, or mass movements, such as those of 
leaves and other members, or movements of locomotion, such 
as those of swarm spores and sperm cells. (See ^f 236 ff.) 
The required energy is set free by the destruction of the sub- 
stance formed when oxygen united with the protoplasm. 

EXERCISE XXXV. 

To show the necessity of respiration for growth. 

Germinate a number of beans in sawdust. Select eight with straight 
roots about 2 cm. long. Clean and dry the surface slightly by brushing 
with frayed edges of strips of filter paper, taking care not to expose roots 
so long that they are injured by dry air. With a very fine sablehair brush 
and thick Chinese (or waterproof black drawing) ink, mark each root by 
distinct lines into ten spaces I mm. apart, commencing with tip. This 
can be done most conveniently by pinning the seedling to a strip of soft 
wood and laying alongside the root a ruler whose graduated edge has 
been blunted by a plane until it is about 2 mm. thick. 

Pin half the seedlings to a strip of soft wood set into a jar partly filled 
with wet sawdust, so that the roots will be vertical in damp air. Put 
the other half into a similar jar and cover them with water recently 
boiled and cooled. After 24 hours, remeasure and compare total growth. 
(See also Exercise XXXVI.) 

206. Loss of weight. — As a consequence there ensues a 
loss of weight. If a plant, such as a seedling abundantly 
supplied with reserve food, be compelled to develop in dark- 
ness, and so allowed to make no additional food, it may be 
easily demonstrated that a large part, often as much as one 
half, of its weight will be lost (as gases) in respiration. This 
loss of weight comes primarily from the decomposition of 
portions of the living protoplasm. These, however, are soon 



NUTRITION. 149 

replaced by the formation of new protoplasm from the foods. 
Ultimately, therefore, respiration results in a diminution of 
the reserve food. 

207. A vital function. — Respiration is a function of the 
protoplasm, and does not occur simply because substances 
are present in the plant which are destroyed when oxygen is 
brought into contact with them, as fuel is in a furnace. On 
the contrary, the oxygen seems to enter into loose combina- 
tion with protoplasm, forming an extremely unstable com- 
pound. This, under unknown conditions, and often some 
time after its formation, breaks down into simpler substances, 
so setting free energy. Some of these materials are again 
used in building protoplasm, while others break down still 
further, ultimately into water and carbon dioxid. The sup- 
ply of oxygen is so necessary that if a plant cannot obtain 
oxygen from the air or water, it will secure it by the destruc- 
tion of part of its own substance for a time, thus burning the 
candle of life at both ends. 

208. Heat. — While this decomposition of the protoplasm 
in ordinary respiration is not a true combustion, it neverthe- 
less results, as combustion does, in the evolution of heat. 
The amount of heat produced is usually not great enough, 
and its loss too rapid, to make it readily perceptible. Any- 
thing which prevents the loss of heat will make its measure- 
ment possible. The germination of large quantities of seeds 
or the blossoming of a number of flowers in a confined space 
may raise the temperature as much as 15 or 20 above that of 
the air. 

The heating of hay, grain, and similar substances, which have been 
stored when moist, is due partly to the respiratory activity of bacteria 
and fungi, which grow rapidly under these conditions. Fermentation, 
which also occurs under the same conditions, adds largely to the evolu- 
tion of heat. 



150 OUTLINES OF PLANT LIFE. 

EXERCISE XXXVI. 

To show the evolution of heat during respiration. 

Take three-fifths the amount of dry wheat required to fill two 3 -inch 
flower pots ; swell in water over night ; rinse one half in 5 per cent 
formalin ; kill the other by boiling in water for five minutes. Stop bottom 
hole in pot with a cork ; fill one with dead, the other with living seeds, 
and bring the two to same temperature by running water through the 
dead and hot one. Insert a thermometer in the center of each mass of 
seeds ; place both under one box or bell jar. Observe changes of tem- 
perature for two days.* 

209. Contrast between respiration and photosynthesis. 

— Since the processes of respiration and photosynthesis in 
green plants are so frequently confused, a contrast is here 
drawn between them. 

Respiration. Photosynthesis. 

Occurs in all living cells. Occurs only in green cells. 
Indifferent to or retarded by Requires light. 

light. 

Consumes organic matter. Produces organic matter. 

Produces carbon dioxid. Consumes carbon dioxid. 

Consumes oxygen. Produces oxygen. 

Sets free energy. Stores energy. 

210. Other destructive changes. — Besides those constitut- 
ing respiration, a considerable number of other destructive 
changes occur, which are not so closely connected with the 
vital functions of the plant. They result in the production 
of substances which are of no further use in nutrition and 
only of incidental value for any purpose. Such substances 
may be stored in some out of the way place ; or put into such 
parts as are transient, so that, by the loss of these parts, the 



* Compare thermometers previously to see that they register alike ; if 
not ascertain the correction. Greater differences in temperature of seeds 
will be observed if pots are surrounded with cotton batting. 



NUTRITION. 



151 



useless materials are gotten rid of; or they may be excreted 
directly. They may be called waste materials. 

211. Waste materials. — Among the most important are the carbon 
acids, such as oxalic, malic, etc., the tannins, the resins, the gums, the 
volatile oils, and the alkaloids. These substances are either by-products 
of photosynthesis, or they arise in the course of the assimilation of foods. 
Oxalic acid is usually gotten rid of by being combined with calcium to 
form calcium oxalate, which crystallizes either in the form of squarish 
crystals or as long needles (fig. 115). The resins, usually dissolved in an 
oil, are generally excreted into special intercellular spaces. Volatile oils, 
to which most odors of plants are due, are secreted by glandular hairs 
(«?, fig. 74) ; or are formed in the epidermis itself, as in flowers ; or are 





Fig. 115. Fig it6. 

Fig. 115. — Crystals found in plants. I, calcium carbonate; II-IV, calcium oxalate; 

II, octahedron with blunt ends ; III, compound crystals from the nectary of a mallow ; 

IV, a, 6, needle crystals (raphides) from leaf of fuchsia. All highly magnified.— 

After Behrens. 
Fig. x 16. — Section through oil-receptacles in rind of orange. The upper figure shows 

the structure at the beginning of the disorganization ot the oil-producing cells ; the 

lower, the final condition, with two drops of oil occupying the cavity Moderately 

magnified. — After Tschirch. 



produced in chambers near the surface, the cells which produce the oil 
being disorganized to form the cavity in which the drops lie (fig. 116). 
Many of the alkaloids, such as quinin, morphin, strychnin, nicotin, etc., 



152 OUTLINES OF PLANT LIFE. 

are important medicines. They occur in the seeds, bark, or leaves, and 
are gotten rid of when these are dropped. 

212. Summary. — The elements required for the nutrition 
of plants may be determined by analysis. The chief com- 
pounds are found to be water and carbon compounds. Water 
and the mineral salts dissolved in it are absorbed by land 
plants from the soil by means of root-hairs. Since the water 
tends to become equally distributed through the soil the 
roots draw their supply of solutions not only from parts with 
which they are in contact, but also from more distant regions. 
They are also able to dissolve certain solids. The water ab- 
sorbed moves into the stele, often under pressure, and is 
carried, by unknown forces, to the leaves, through the wood 
strands. It is constantly evaporating from the leaves, which 
regulate the amount in various ways. 

Foods are required to repair waste and provide for growth. 
Colorless plants must absorb these from solution ; if the foods 
are not already soluble they must be made so by digestion. 
The foods they use are carbon compounds which have been 
made by some other living being. Green plants can use 
ready-made food, or, if suitably illuminated, they can make 
foods out of carbon dioxid and water, with small quantities 
of mineral salts. The carbon dioxid is absorbed from air by 
the leaves. Light furnishes the energy for building up the 
simple substances into carbohydrates. Proteid foods are 
also made by working into the carbohydrates additional 
necessary elements. Foods may be used at once or stored, 
usually in solid forms, for a longer or shorter time. When 
needed they are digested and transferred. 

Respiration of plants is exactly like respiration of animals. 
Its purpose is to release energy stored in the living proto- 
plasm to enable it to work, i.e. to grow, move, etc. Respi- 
ration consists in the absorption of oxygen, the decomposi- 
tion of protoplasm, and the excretion of carbon dioxid and 



NUTRITION. 153 

water. A considerable amount of food is used to repair the 
necessary destruction in respiration. A plant which is not 
taking in food from without, or making food, is decreasing 
constantly in (dry) weight through respiration. Respiration 
and other destructive chemical changes incident to work re- 
sult in the formation of a great variety of products called 
waste products because they take no further part in the pro- 
cesses of repair or growth. 



CHAPTER XV. 

GROWTH. 

213. Definition. — The growth of plants is continued for a 
much longer time than that of animals. In most cases it is 
continued in some part throughout the existence of the plant. 
There are also changes in the form of certain parts, particularly 
of the lower plants, which must be distinguished from true 
growth. Growth is a permanent change of form accompanied 
usually by an increase in size. 

214. Formation of new parts. — Each new cell originates 
by the division of some previously existing cell. The two 
cells so formed grow until they attain the size of the parent 
cell, when one or both may continue to grow until they at- 
tain a permanent form ; then growth ceases. Those cells 
which do not develop into permanent tissue, but retain their 
power of division, constitute a mass of tissue at the tip of each 
branch or root, from which all new parts regularly arise. 
(If 71, 87). It will be seen, therefore, that every cell of a 
plant has been at some time in an undeveloped or embryonal 
condition. 

215. Phases of cell growth. — The more striking charac- 
teristics of this embryonal condition are the nearly uniform 
and small size of the cells, and the absence or small size of 
the water spaces (A, fig. 117). As the cells which are des- 
tined to become the permanent tissues grow older they pass 
gradually from the embryonal stage into a second phase of 

i54 



GROWTH. 



155 



development, the stage of enlargement. This stage is marked 
by the rapid increase of the cells in size and a much less 
marked increase in amount of protoplasm present. The in- 
crease in size, therefore, is mainly due to a great increase in 
the volume of water, which accumulates in one or more large 
spaces (C, fig. 117). If the organ in question has an elon- 




Fig 117 —Cells from young and mature fruit of snowberry (Symphoricarpus), seen in 
section A, three young cells, very small, walls thin, nuclei relatively large, vacuoles 
very minute; B, two, somewhat older, larger, walls thicker, nuclei smaller, vacuoles 
severai. A and B magnified 300 diam. C. a single cell, mature, magnified 100 diam.. 
one third as much as A and B ; vacuole single, very large. 1 he volume of C is more 
than 1500 times one of the cells in A. h, cell-wall \ p, protoplasm ; k, nucleus; 
kk, nucleolus ; s, vacuole.— After Prantl. 

gated form, such as the stem or the root, growth of the cells 
takes place chiefly in the direction of its long axis. During 
this phase the cells may attain a hundred or even a thousand 
times their former volume. 



EXERCISE XXXVII. 

To measure the rate of growth in length. 

Construct an auxanometer as follows : Take a board 30 cm. square, a 
common spool, a wheat or oat straw 35 cm. long, and a piece of glass 
tubing 5 cm. long, which will just allow spool to revolve easily on it. 
Close one end of the glass tube by holding it in the flame of a Bunsen 
burner; when hot spread it enough to stop spool from passing over end, 
by pressing it endwise against a piece of iron. With a fine saw cut a 
section 5 mm. thick from middle of spool, thus making a wheel. File a 
groove in edge of this wheel, deep enough to carry a thread. Slip wheel 
on glass tube and fasten it in board near lower left corner so deep that 



56 



OUTLINES OF PLANT LIFE. 



the spool-wheel will revolve smoothly but have no unnecessary play. 
On the board, with hole for glass tube as a center, mark an arc of 90 de- 
grees. The radius of the arc should be a multiple of the radius of wheel. 
Divide arc into half centimeters. Attach wheat straw to wheel as a 
pointer. 

To the tip of a growing seedling bean fasten a thread by a slip noose 
Pass thread over wheel once and to its free end attach a light weight, 
just enough to turn wheel and pointer when plant is lifted. Set pointer 
at o and at intervals read the multiplied growth. By taking observation- 
at regular intervals determine the rate of growth of stem for a week. 
What regular variation can you discover ? 

216. Grand period of growth.— The entire duration of 
growth of an organ is known as its grand period of growth. 
The growth is not uniform, but is at first very slow, increasing 
gradually, and then more rapidly, to a maximum, from which 
it falls rapidly, and then more gradually, until it ceases en- 
tirely. The accompanying curve (fig. 118) represents the 









2V 


t s 


"t \ 


4 V 


t s 


r A 


7 V 


t S^ 


4 S^ _Z 


t ^v 


J ^ 




7 N 

U - 4 8 12 16 20 



Fig. 118. — Curve representing the rate of growth ot an internode of crown imperial for 
each day during the grand period— in this case 20 days. The height ot each vertical 
line where it intersects the curve represents the total growth for the corresponding 24 
hours. The numbers indicate days. The maximum growth occurred on the 6th day 
—After Sachs. 



course of growth in length of a short section of a stem. 
Growth, however, is not uniform from day to day or from hour 
to hour. If the line should be drawn so as to show these 
variations it would be irregularly zig-zag, but would follow 
the same general course as the smooth curve. (See ^j 222.) 



GROWTH. 



157 



217. Growing region. — The part of any one of the 
larger plants which is growing in length is limited. The 
elongating region of a root rarely 
exceeds a centimeter, and is often 
not more than one-half a centi- 
meter in length. In stems, how- 
ever, the elongating part may 
measure twenty or even fifty cen- 
timeters, and in rare cases much 
more. Figure 119 shows a root, 
A, upon whose surface marks were 
made 1 mm. apart. Twenty-four 
hours later the root presents the 
appearance of B. Only the tis- 
sues in the first five spaces were 
capable of elongation. The 
others had passed into the third 
phase. The second and third 
millimeters grew most in length. 
The growing regions of stems may 
be determined in the same way. 

EXERCISE XXXVIII. 

To determine the zone of maximum Fig. tiq.— A, a young root of the pea 
growth inroots and stems. 

A. Arrange four seedlings as in 
5[ 205, with roots vertical, in moist air. 

Which spaces grow most? 

B. Mark several upper internodes 
of a bean plant in a similar way, but 
at 5 mm. intervals. After 48 hours observe how many have elongated 
and which have grown most. 

218. Tension due to growth. — The different regions in 
any organ usually do not grow at an equal pace, and con- 
sequently certain parts are under strain, while others are 
compressed. The curled and crinkled leaves or the curved 




ink into 13 spaces of 1 millimeter 
each. B, the same root, 24 hours 
later, showing elongation only in 
terminal 5 millimeters. The rate of 
growth is greatest in the ?.d and 3d 
millimeters, and slow in the 1st, 4th, 
and 5th. Magnified 2 diam.— After 
Frank. 



158 OUTLINES OF PLANT LIFE. 

capsules of mosses illustrate this inequality. It may be pres- 
ent, however, without manifesting itself in the external form. 
If the rapidly growing flower-stalk of the dandelion or the leaf- 
stalk of rhubarb be carefully split lengthwise the parts will 
curve or even curl outward. Separating the pith and the 
cortex of a young elder shoot from the wood and carefully 
measuring them shows that the pith elongates and the cortex 
actually shortens. The experiment, therefore, shows that the 
pith really grew more rapidly than wood, but were com- 
pressed in the uncut stem, while the cortex was slightly 
stretched. The strains thus set up are spoken of as longitudi- 
nal tensions. Similar tensions due to unequal transverse 
growth may be shown to exist. If a thin transverse slice 
from the fleshy leaf-stalk of the rhubarb be divided into 
equal parts by a longitudinal cut it will be found in a few 
moments that the halves can no longer be made to touch 
throughout the line of the cut, because it has become convex. 
Both sorts of tensions will be exaggerated if the parts be 
placed for a few moments in water. 

EXERCISE XXXIX. 

To show the existence of longitudinal tensions of tissues due to unequal 
growth or turgor. 

A. Cut a young internode of elder 10 cm. long, making ends as square 
as possible. Measure accurately. Remove wood all around and meas- 
ure pith. Place pith in an atmosphere saturated with moisture and re- 
measure after 1 hour. Compare measurements. (If elder is not at hand 
use young shoots of grape, wild or cultivated.) 

B. Split a scape of dandelion lengthwise with a sharp knife into four 
strips. Note immediate effect upon their form. Lay the strips in water 
for a few minutes. Observe form. Transfer them to 5 per cent salt so- 
lution. What effect? What causes these changes of curvature ? (The 
young stems (hypocotyls) of castor bean may be substituted for dandelion 
scapes, but are not so responsive.) 

To show the existence of transverse tensions of tissues due to unequal 
growth. 

A. From a piece of willow or poplar stem separate a ring of bark 1 cm. 



GROWTH. 159 

wide, slitting it on one side only, taking care not to stretch it. Keep 
it in a moist atmosphere for a few minutes, and then replace it. Does 
it meet about the wood ? 

B. Cut a slice about 2 mm. thick from the end of a stalk of rhubarb. 
Bisect this and keep the halves for a few minutes in a moist atmosphere, 
then place severed edges together. Do they touch throughout? 

219. Conditions of growth. — That plants may grow cer- 
tain conditions are prerequisite. (1) There must be an 
adequate supply of constructive materials. These may be de- 
rived either from food recently manufactured or from that 
stored in reservoirs, or, in the case of the colorless plants, 
from that absorbed from without. (2) There must be a 
supply of oxygen for respiration. This is needed, as previously 
explained, to set free the energy necessary for growth. (3) 
There must be a supply of water adequate to supply the mate- 
rial for filling the cells during the phase of enlargement. 
(4) A suitable temperature is required. The range of tem- 
perature within which growth may take place is extensive, 
and varies with the individual plant. In general, the upper 
limit may be stated as about 40 C. , and the lower about o° C. 
The minimum of plants of tropical regions is approximately 
io° C, while the maximum for plants of the arctic or alpine 
regions is much below 40 C. Between the maximum and 
minimum temperatures there is an optimum temperature for 
each plant, at which growth takes place most rapidly. For 
most plants the optimum lies between 25 ° and 32 C. 

220. External conditions exercise a very important influ- 
ence upon the rate or character of growth by reason of the 
irritability of the protoplasm. (See further ^| 317.) Many 
of these conditions act upon members of the plant so as either 
to bring about permanently unequal growth in a certain part, 
or to cause one part to grow more or less rapidly for a time 
than another. Such variations in growth produce curvatures 
in the parts concerned and move members connected with 
them. They are discussed in the chapter on Movements. 



l6o OUTLINES OF PLANT LIFE. 

Those conditions which act more generally and uniformly upon 
a large number of plants serve to determine the form and 
mode of development of members. 

221. Light. — The effect of light on growth is different in 
different plants and even in different members of the same 
plant. In general light retards growth in length. Stems 
grown in darkness usually become excessively elongated. 
Those which under normal illumination have very short in- 
ternodes, in diminished light may have them well developed, 
as occurs, for example, in dandelions growing in deep shade. 

In general, light accelerates the growth of leaves in area. 
Leaves of shoots grown in darkness remain small. 

Light affects not only the external form but the internal 
structure. The difference in structure between the upper and 
lower surface of the thallus of Marchantia (^] 52, fig. 38) and 
of the leaves of higher plants (fig. 106) is due to the greater 
illumination of the upper surface. In diminished light cell 
walls may not thicken normally, and mechanical tissues are 
weakened. "Lodging" of oats and such grasses is mainly 
due to this cause (fig. 120.) 

222. Light and temperature. — The combined variation 
of light and temperature between day and night establishes a 
daily period in the growth of all plants. The withdrawal of 
light at night permits an increase in the rate of growth in 
length, which reaches its maximum in some plants shortly 
after midnight, in others not until the early morning. During 
the day its retarding effect diminishes the rate of growth, 
which reaches a minimum some time in the afternoon. The 
minor fluctuations in temperature, as well as the generally 
higher temperature during the day and lower during the night, 
introduce variations in the rate of growth, which obscure, but 
do not counteract, the retarding influence of light. (See fig. 
121). This daily period is so impressed upon the constitu- 
tion of the plant that it maintains it for a considerable time 



GROWTH. 



161 




Cnoti 





Fig. i 20.— Part of the transverse sections of the stem of rye. A, from a plant grown 
fully exposed to light: B, from a "laid" plant imperfectly exposed to light. 



epidermis ; b, c, mechanical tissues ; d, thin-walled tissues. 
Koch. 



Highly magnified.— After 



T 



2,0 mm 
1,5 
1,0 
0,5 



9 11 
N 



11 1 
M 



3 5 7 9 



Fig. 121. — Curve showing the daily period in the growth of a stem of rye. The vertical 
lines represent 2-hour periods from 5 p.m. of one day to 5 a.m. of the second day, 
the shaded parts indicating the actual hours of darkness. The horizontal lines repre- 
sent tenths of a millimeter. The curve is drawn by taking the record from an aux- 
anometer and laying off on the vertical line for each interval the growth shown. The 
points are then ioined. It will be observed that the maximum rate of growth occurs 
shortly after the period of darkness (5 a.m.) and the minimum rate after the period of 
most intense illumination (5 p.m.). During the experiment the thermometer varied 
from 18 to 22 C— After Frank. 




162 OUTLINES OF PLANT LIFE. 

even when kept in complete darkness. Stems of sunflower 

after two weeks in complete darkness still showed distinctly 

the daily period. 

223. Moisture and oxygen. — The amount of moisture 

and oxygen present in the medium surrounding a plant pro- 
foundly affects its form. Amphibious 
plants, that is, those which are capable 
of growing either on land or in water, 
often show this in a striking way. 
When grown submerged, the leaves 
are usually finely divided, while the 
same leaves, if allowed to develop in 
the air, have broad blades scarcely 
more than lobed (fig. 122). 

fig. 122 -a shoot of water 224. Mechanical pressures or 

crowfoot (Ranunculus 

aguatiiis) The lower leaves strains also exert an influence upon 

have developed under water r 

and are branched into many trie rate and mode of STOWth. Coni- 
narrow divisions ; the two 

upper leaves have developed pression of tissues retards their growth : 

in air and at maturity float r ° ' 

on the surface of the water, strains accelerate it. Thus, stems en- 

About half natural size.— 

After Frank. closed in plaster casts or ligatured grow 

more slowly in thickness. Tensile strains, such as those exerted 
by wind or weight, promote the development of mechanical 
tissues. Petioles, which would break under a strain of 700 gm,, 
after enduring a pull of 500 gm. for five days, broke only at 
1600 gm. After five days more under a strain of 1200 gm. 
they could not be broken with less than a weight of 6500 gm. 
225. Variations in rate. — There are not only variations 
in growth in the course of each day throughout the growing 
period, but also minor variations independent, so far as 
known, of external conditions, which are therefore called 
spontaneous variations. Irregular variations occur from hour 
to hour in the course of the day. Regular spontaneous vari- 
ations, also, occur in various organs, particularly in the ten- 
drils of climbing plants, and in the leaves of flowers and buds. 
These regular variations, which affect different sides of flat- 



GROWTH. 163 

tened organs and different sectors of cylindrical ones, bring 
about a bending of the entire organ from one side to another. 
These curvatures produce nutation, and will be further de- 
scribed under movements. (See ^| 241.) 

226. Duration. — Even when the external conditions of 
growth are kept as uniform as possible, growth does not con- 
tinue for an indefinite time. Having passed through the 
phases above named, it ceases, no matter how favorable the 
external conditions. Yet some organs, even after growth has 
ceased, may resume it, under certain circumstances. Thus, 
the leaf cells which have long since ceased to divide may re- 
sume the power of division in the neighborhood of a wound, 
and by division and the growth of new cells may form a scar 
covering the wound. The formation of fruits of the seed 
plants is also a case of resumption of growth after an appro- 
priate stimulus. (See ^[ 306.) 

227. Summary. — Growth is permanent change of form 
and increase in size. Every part passes successively through 
three stages of growth, the first marked chiefly by the forma- 
tion of new cells, the second by the enlargement of cells al- 
ready formed, and the third by the acquisition of mature 
characters by these cells. The second stage is the stage of 
visible and measurable growth. Only a very short part of 
the root and a limited region of the stem is growing in length. 
During the stage of enlargement the growth is not uniform. 
The rate varies on account of internal (unknown) and exter- 
nal (known) causes. Among the latter are light and heat. 
Light generally retards growth in length, but promotes the 
growth in area of leaves and other broad parts. It may also 
produce changes in structure as well as form. Rising tem- 
perature (up to a limit) hastens growth ; falling temperature 
retards it. Combined effects of light and heat produce a 
daily fluctuation in growth. Pressure, amount of water, and 
oxygen also affect growth. Growth may be resumed by 
mature parts. 



CHAPTER XVI. 

THE MOVEMENTS OF PLANTS. 

228. Irritability. — Among the inherent properties of 
protoplasm are irritability and automatism. We know prac- 
tically nothing of the nature of either of these properties, 
though upon them depend all the activities of plants. They 
seem to be merely two phases of the same property. Auto- 
matism is the name given to the ability of protoplasm to in- 
itiate internal changes without the action of any external 
force. Irritability expresses the power of the protoplasm to 
respond or react to the influence of an external change. 

229. Stimuli. — The external change which brings about 
the reaction is known as a stimulus, and its application is 
called stimulation. External forces which may act as stimuli 
are light, heat, gravity, moisture, electricity, chemical sub- 
stances, etc. Most of these act constantly in some measure 
upon plants. In order that they may act as stimuli, there- 
fore, a change in their intensity or direction must occur. If 
the change be great or sudden, the reaction is likely to be 
more marked. Sometimes, however, a slow change will still 
produce a distinct reaction. For example, the gradual with- 
drawal of light may cause movements of leaves. (See ^[ 255.) 

230. Conditions limiting irritability. — Protoplasm is ir- 
ritable only under certain conditions, which coincide in the 
mnin with those that promote the general well-being or life 
of the organism. But the limits of temperature, moisture, 

164 



THE MOVEMENTS OF PLANTS. 1 65 

and the supply of oxygen, which permit irritability, are much 
narrower than those which permit life. Thus, irritability 
may be lost when the conditions are unfavorable, though life 
may persist under such conditions for a longtime. Irritabil- 
ity may also be lost through fatigue, as when, after repeated 
reaction, no response occurs even to a greatly increased 
stimulus. Upon the return of suitable conditions, or after 
sufficient rest, irritability may be regained. 

231. Reaction. — The response of the protoplasm to a 
stimulus is out of all proportion to the physical or chemical 
action of the stimulus itself. The action of the stimulus upon 
the irritable protoplasm may be roughly compared to the 
action of the trigger upon a primed and loaded gun. It 
sets free forces vastly in excess of those which it exerts. 

232. Reaction time. — The observable reaction does not 
follow instantly upon stimulation. The interval, which is 
known as the reaction time or the latent period, is ordinarily 
much longer in plants than in the higher animals. In ex- 
treme cases no reaction may be manifest until several hours 
after stimulation. In other cases, however, as in the well- 
known sensitive plant, the movements of the leaves follow 
almost instantly upon stimulation. 

233. Form of reaction. — The character of the reaction is 
not dependent upon the nature of the stimulus, but upon the 
nature of the organ itself. It is not in the least understood 
what the inherent peculiarities are which determine the form 
of the reaction. In different organs exactly opposite effects 
may be produced by the same stimulus, and the same organ 
at different ages may respond differently to the same stimulus. 
Thus the young internodes of the Virginia creeper (A??ipe- 
lopsis) are sharply recurved, but become erect when older. 
The stalk bearing the flower of the peanut is erect, but as it 
becomes older it becomes strongly reflexed, and thrusts the 
fruit under ground. 



1 66 OUTLINES OF PLANT LIFE. 

234. Localization of irritability. — In multicellular plants 
irritability to certain stimuli is usually localized in certain 
organs, and often in special parts of these organs. In many 
tendrils, for example, the free end is curved and only the 
concave side is irritable to contact. In the Venus fly-trap, 
although the whole leaf moves at the contact, only the three 
hairs upon the upper face of each lobe are sensitive to a 
touch. (See figs. 224, 137.) 

235. Transmission of impulse. — In these cases, as in many 
others, the effect of the stimulus must be transmitted in some 
way from the point of application to the cells which produce 
movement. At present it is not known how this is accom- 
plished. 

The movements of plants may be conveniently considered 
as (1) movements of protoplasm itself; or, (2) mass move- 
ments of multicellular members of the higher plants. 

I. Movements of protoplasm. 

236. Naked cells. — Plants which consist of a single cell 
may be either naked or furnished with a cell wall. If naked, 
they may exhibit either amoeboid ox ciliary movements. Amoe- 
boid movements are slow creeping movements brought about 
by the protrusion of a portion of the protoplasm toward 
which the remainder gradually flows (fig. no). Ciliary 
movements are due to the extension of one or more very 
slender threads, called cilia, whose rapid bending in different 
directions propels the organism (fig. 109). According to 
the nature of the movements, the course will be zigzag or 
steady, accompanied by the rotation of the cell on its axis. 
When the cell comes to rest the cilia are either withdrawn or 
drop off. 

237. Cells with a wall. — Movements of locomotion in 
plants possessed of a cell wall are either ciliary or creeping. 



THE MOVEMENTS OF PLANTS. 



167 



A 



The latter are usually due to the protrusion of portions of the 
protoplasm through slits in the wall, as in some diatoms 
(fig. 11). The filaments of the water slimes bend from side 
to side, and so creep over wet surfaces very slowly (fig. 7). 
Bacteria (fig. 9) and some diatoms move by means of cilia. 

The direction of all these movements maybe so controlled 
by stimuli that the organisms move toward or 
away from the source of stimulus. Thus, ciliated 
spores of algae (fig. 109) swimming in a dish of 
water, will gather next the lighter side. 

238. Streaming and rotation. — In multicel- 
lular organs it is common to find the protoplasm 
within each active cell moving about from point 
to point within the cell. The protoplasm is 
filled with numerous large vacuoles, so that it 
forms a next layer the wall, with threads or 
ribbons extending across it (fig. 123). When 
currents start along the wall and through the 
strands, the motion is designated as the stream- 
ing of the protoplasm. These currents along 
any particular portion of the protoplasm may 
run side by side and in opposite directions. 

When the protoplasm surrounds a single 
large vacuole (fig. 117, C), the whole mass cenlrom a hai?of 

.-, . . . . . - . , C h e 1 1 do niii m. 

may rotate, usually in the direction of its long The arrows show 

r,,, . . .... the direction of 

axis. I he portion immediately in contact 
with the wall is motionless, and there must 
necessarily be a strip between the half moving 
up and the half moving down the cell, which 
is also quiet. Such movements are called 
rotation of the protoplasm. It is not known 
whether either streaming or rotation has any immediate re- 
lation to the well-being of the cell. 

In addition to the mass movements of the protoplasm, the 



movement of the 
protoplasm in the 
peripheral layer 
and in the bands 
which separate the 
vacuoles, n. the 
nucleus, with nu- 
cleolus. Highly 
magnified. — After 
Dippel. 



1 68 OUTLINES OF PLANT LIFE. 

smaller protoplasmic bodies within the cell, such as the 
nucleus and the chloroplasts, are capable of moving about. 

II. Movements of multicellular members. 

239. Forces. — The movements of multicellular parts may 
be brought about either by special organs known as motor 
organs, or by the unequal growth of the immature parts. 
Motor organs are generally responsible for the movements of 
mature parts, while movements of the younger regions are 
generally due to growth. The force exerted by the motor 
organs is dependent upon the altered turgor of the cells of 
which the organ is composed. If the cells upon one side of 
it lose their turgidity, those upon the other, being unresisted, 
will extend and bend the organ toward the side upon which 
the turgor was diminished. It will be convenient, therefore, 
to distinguish movements due to growth and movements due 
to variation in turgor. 

240. (A) Movements of growth. — These depend upon 
some inequality in the rate of growth of the organ concerned. 
They are of two sorts, (i) Those in which variation in 
growth is produced by causes not yet known (apparently in- 
ternal) are called spontaneous movements. (2) Those in 
which the variation in growth results from stimulation by 
external agents are called paratonic movements. 

241. 1. Spontaneous movements. — Among spontaneous 
movements are those in which the variation in growth occurs 
upon different sides of a cylindrical organ, or the two faces 
of a broad one. The opening of all flower and leaf buds 
illustrates this movement, which is called nutation. During 
the development of the interior parts, the outer leaves (often 
scale-like) which protect them grow more rapidly upon their 
outer (dorsal) surfaces. They are thus pressed together into 
a compact bud. When the internal parts are suitably de- 



THE MOVEMENTS OF PLANTS. 1 69 

v eloped a change occurs in the rate of growth of the outer 
leaves; their inner (ventral) faces now grow more rapidly 
and the bud expands. Similar spontaneous variation in the 
growth of different sides of tendrils produces a nodding or 
waving motion, or even a rotation of the tip, by means of 
which they are often enabled to reach a support. In most 
tendrils the region whose growth is hastened travels irregu- 
larly around the axis, so that their tips rotate in a roughly 
circular or elliptical orbit from the time the tendril is two- 
thirds grown until growth ceases. The further changes in 
the tendril, by which it wraps the tip about the support and 
coils the remainder into a double spiral, are paratonic move- 
ments induced by contact. The rotating movements by which 
twining plants climb are also paratonic and not spontaneous. 
242. 2. Paratonic movements are also of the highest im- 
portance for the well-being of the plants concerned. By 
means of them the different organs are developed in such 
situations that they can properly perform their work. The 
stimuli which influence the rate of growth are chiefly light, 
gravity, heat, mechanical contact, and moisture. The pecul- 
iar states in which a plant or an organ exists when it can 
respond to the different stimuli have received different names, 
and those names indicate the nature of the stimulus. A 
plant or an organ i"S heliotropic when it places itself in a cer- 
tain position with reference to the direction of the rays of 
light falling upon it ; geotropic, when it reacts thus to the 
force of gravity; thermotropic, when it reacts thus to the 
presence of a warm body ; hydrotropic, when it reacts thus to 
the presence of a moist surface, etc. In each case the plants 
are said to react positively when the movement is toward the 
source of the stimulus ; negatively, when the movement is 
away from the stimulus ; transversely, when it is transverse to 
the direction of the stimulus. These reactions are to a cer- 
tain extent related to one another, and it will be convenient, 



170 



OUTLINES OF PLANT LIFE. 



therefore, to consider the effect of each stimulus upon the 
two common forms of plant organs — namely, the radial (such 
as stems and roots) and the flattened (such as leaves). 

243. (a) Heliotropism. — Heliotropism is the state of a 
plant or organ when it is irritable to the direction of light 
rays. Light thus plays an important part in determining the 
position of organs. As a rule radial organs are either posi- 
tively heliotropic, as the stems and leaf-stalks, or negatively 
heliotropic, as the roots. In ordinary light leaves are all 
transversely heliotropic, assuming a position at right angles 
to the direction in which the light comes. This is the most 
favorable position possible for the manufacture of food by 
the green parts (fig. 124). Intense light, however, may 




n n 



Fig. 124.- Diagrams representing the transverse heliotropism of leaves of the garden 
nasturtium ( Trofatoluvi). Potted plants were subjected successively to light strik- 
ing them in the direction shown by arrows. The petioles curved so as to place the 
blades at right angles to the incident light.— After Vochting. 



bring about a different reaction, so that the leaves set them- 
selves edgewise to the light. A fixed light position is usually 
reached by leaves by the time they become mature, and this 
is generally at right angles to the source of greatest light. 
Branches of trees show the leaves so arranged as to size and 
position that they shade each other as little as possible, form- 
ing the so-called leaf mosaics (figs. 125, 126). The leaves of 
window plants also exhibit these movements very strikingly, 



THE MOVEMENTS OF TLA NTS. 



because usually illuminated from one side, 
darkness have their leaves irregularly placed. 



171 

Plants kept in 




Fig. 125. — Leaf mosaic formed by a horizontal shoot of Norway maple. The lengthen- 
ing of the petioles of individual leaves to avoid shading of tfhe blade is marked. 
About one-third natural size.— After Kerner. 




Fig. 126. — A rosette of leaves of a bellflower (Campanula fiusilld), showing length- 
ening of petioles of lower leaves so as to carry blades from under upper leaves. — 
After Kerner. 

EXERCISE XL. 

To show the effect of direction of light as a stimulus on leaves. 
Set a potted plant (geranium, sunflower, nasturtium, or mallow) in the 
dark for 24 hours; then place it before a window, shading it so that 



172 OUTLINES OF PLANT LIFE. 

light reaches it chiefly from one direction. Mark certain leaves and 
record the position of the plane of the blade ; 24 hours later observe the 
position and compare with first. 

To show effect of direction of light as a stimulus upon stems and roots. 

Grow seedlings of white mustard thus: Tie loosely over the mouth of a 
jelly-glass a double piece of fine bobbinet ; fill vessel with tap water to 
the net, on which place seeds; set in dark, replacing water as it evapo- 
rates, until seedlings are 3 cm. high, with roots as long or longer. Then 
place in a box, blackened inside, into which light is admitted through a 
hole 4-5 cm. in diameter, at right angles to stems and roots. Observe 
curvatures 24 hours later. 

244. (b) Combined movements due to variations in the 
intensity of light or heat or both are especially exhibited by 
flowers, whose opening and closing are frequently determined 
thereby. With some plants the predominant stimulus is 
heat ; with others, light. Closed flowers of the tulip or 
crocus may be made to open in 2 to 4 minutes by raising the 
temperature 15 to 20 . The flowers of the white water-lily 
and of the dandelion open in sunlight and close in shade. 
By marking upon their leaves a series of equidistant parallel 
lines with Chinese ink, and measuring later the distances to 
which they have been spread, all such movements can be 
clearly shown to be due to accelerated growth of the outer or 
inner surfaces, respectively. The protection of the flower 
parts or their proper working is secured by these movements, 
which must not be confounded with those due to the direction 
of light or heat rays. 

245. (c) Geotropism. — Geotropism is the state of a plant 
or an organ when it is irritable to the force of gravity. 
Since gravity is exerted always in the same direction, it is 
plain that reactions to this force cannot be studied, as in the 
case of light, by altering the absolute direction in which 
gravity acts, but only by so changing the position of the 
plant that the force acts in a relatively different direction. 
The reaction to this stimulus and the fixed gravity position 
must not be confused with the simple effect produced by the 



THE MOVEMENTS OF PLANTS. 



173 



weight of the parts concerned. Such effects are to be seen 
in the downward bending of some plants with slender 
branches, or the curvature of the flower or fruit stalks by the 
weight of the parts. True geotropic curvatures are brought 
about by acceleration of the growth of the irritable cells, and 
the curvatures produced may even be contrary to the direc- 
tion of the force. If seedlings be grown in boxes upon the 
rim of a wheel rotating slowly in a vertical plane, so that 
they are successively subjected to the action of gravity in 
relatively different directions, it will be seen that while their 




Fig. 127.— Seedling mustard plants grown on a cube of peat, 7, attached to the slowly 
rotating axle, A, A, of a clinostat. The direction of growth of roots and stems is 
controlled only by the nearness of moist surfaces, the action of gravity and light being 
eliminated. Note the variable direction of roots and stems. At m and r// 2 aerial 
hyphae of a mold have taken direction as far from the repellant moist surfaces as pos- 
sible. One half natural size. — After Sachs. 

members grow in nearly straight lines, the direction assumed 
by the stems and roots is quite as frequently abnormal as 
normal, because the effect of gravity which normally deter- 
mines the direction of growth of these axes is neutralized, 
since it now acts upon them from a new direction at each 
successive moment (fig. 127). If the wheel upon which 
such seedlings are grown be rotated at a high speed, the cen- 



174 



OUTLINES OF PLANT LIFE. 



trifugal force will become a constant one, and, acting in 
place of the neutralized force of gravitation, will determine 
the direction which the stems and roots will assume. Since 
the primary stems of most plants are negatively geotropic, 
when grown under such conditions they will turn toward the 
center of the wheel, while the positively geotropic roots grow 
toward the rim. Similarly, if the wheel be rotated rapidly 
in a horizontal plane the parts will be controlled by a com- 
bination of the force of gravity and the centrifugal force (the 
latter predominating if the speed is great) ; the stem will 
grow inward and upward, while the roots will grow down- 
ward and outward (fig. 128). 




Fig. 128.— Part of centrifuge, a, the axle, rotated at a high speed by water or electric 
motor, to which is attached the circular metal piate, r, r, carrying a disk of cork, k. 
To the latter are attached two seedling beans, A , B, by means of pins ; st, the primary 
stem ; h, the primary root. Ovc the seedlings the cover, #, is placed to keep them 
moist. After a few hours the lateral roots have turned into the direction of the cen- 
trifugal force, which was sufficiently powerful to overcome that of gravity except near 
axis of rotation, x. One halt natural size. -After Sachs. 

EXERCISE XLI. 

To show the effect of gravity as a stimulus on roots. 

Arrange the marked root of a seedling bean as in ^[ 205, except that 
the root is horizontal, and a pin just above the extremity marks its posi- 
tion. After 24 hours observe curvature and which spaces have become 
curved. Compare with those which have grown most. 

To show the effect of gravity as a stimulus on growing regions of upright 
leaves. 



THE MOVEMENTS OF PLANTS. 175 

Support an onion, roots down, in a vessel of water so that it is half im- 
mersed, until the leaves are about io cm. long. Then turn it so that 
leaves are horizontal and observe where curvature occurs. 

246. Transverse geotropism. — Not all stems, however, 
are negatively geotropic, nor all roots positively geotropic. 
The central axis of both root and stem in the majority of 
plants is so, but lateral branches of both place themselves at 
an angle to the action of gravity, sometimes at a right angle, 
at other times at a highly obtuse or acute angle. That is, 
they are more or less transversely geotropic. Whatever the 
normal position of any organ, it will be regained by the 
growing parts as rapidly as possible when the plant is forcibly 
displaced. This can only be brought about by the curva- 
tures produced by unequal growth of the younger parts. 

If a potted plant be laid upon its side for a short time and 
then erected before any response to the stimulus occurs its 
growing parts still curve to one side, although not so far as if 
they had been allowed to remain in the horizontal position. 

247. Grasses. — In only a few cases do the maturer parts 
of plants regain their power of growth under the stimulus of 




Fig. i2g. — Part of a wheat-stalk, showing strong geotropic curvature. The shoot was 
placed horizontal, and the growth of the basal part of the internode with the leaf-sheath 
connected with it was stimulated on the under side, the upper remaining short. No 
curvature occurs in the older part of the internode. About two thirds natural size. 
—After Pfeffer. 

gravity. The basal portion of the internodes of grasses, 
how r ever, remain for a long time capable of growth ; hence, 
when grasses are blown down or trampled their stems erect 
themselves by the geotropism of this basal growing zone 
and of the leaf-sheath (fig. 129). 



176 



OUTLINES OF PLANT LIFE. 



EXERCISE XLII. 

To show the effect of gravity on the growing regions of the stems of 
grasses. 

Cover the bottom of a deep dish about 25 cm. long with a layer of wet 
sand, and bank this against one end to the top. Into this bank stick 
horizontally several grass stems having at least one node ; cover with a 
glass plate. After 24-48 hours observe curvature. Cut a longitudinal 
section of the node and observe what part the leaf-sheath takes in this 
curvature. 

248. . oot-cage. — Experiments upon the response of root- 
lets to the stimulus of gravity when their position is altered 

may be carried on by means 
of a root-cage. It consists 
essentially of two parallel 
panes of glass fastened to- 
gether, between which, in 
finely sifted soil, the rootlets 
are grown. By inclining this 
root-cage at various angles it 
may be shown that not only 
the primary root, but its 
branches, strive to regain 
their normal angle with the 
direction of gravity. This is 
illustrated in figure 130, in 
which the dark portion of the 
rootlets represents the grow- 
ing parts while the cage was 

inverted. They then took about the same angle with the 

horizon as when in normal position. 

249. Twining plants. — The movements of twining plants 
are due to a peculiar reaction to gravity. As the upper inter- 
nodes of a seedling elongate they soon become too weak to 
support themselves and bend over, becoming nearly horizon- 
tal. When this occurs the growth of the right or left flank of 




Fig. 130. — Part of the root system of a broad 
bean, grown in a root-cage, first in the 
normal, then in the inverted, and again 
in the normal position. The arrows show 
the direction in which gravity acted in 
the different positions. The black por- 
tion of the roots were the parts growing 
during inversion. Two thirds natural 
size.— After Sachs. 



THE MOVEMENTS OF PLANTS. 



177 



the stem near the bend is accelerated (whence the stem is said 
to be laterally geotropic). The horizontal part is thus swung 
around, twisting the stem and bringing a new flank under the 
influence of the stimulus. If in its continued rotation the stem 
comes in contact with a nearly erect support the free part con- 
tinues to rotate, growing longer at the same time, and encircles 
the support. The part below the 
point of contact now becomes nega- 
tively geotropic, and its growth on 
all sides is equally accelerated. The 
coils are thereby straightened until 
the stem clasps the support very 
closely, from which it is often pre- 
vented from slipping by angles or 
outgrowths of various kinds, which 
roughen the surface (fig. 131). 

While gravity thus plays a large 
part in determining the position 
of both aerial and subterranean FlG _ 
organs, it must be remembered 




131. — A, a bit of the stem of 
the hop, showing the six angles, 
each carrying a row of emergences, 

that it works conjointly with many ^^"^pS.^MaS 
other stimuli. The position of the ^| ^/■^SSSSto 

members is, therefore, a resultant Kerner - 
of the reactions to the various external forces which stimu- 
late them. 

250. (d) Hydrotropism. — Hydrotropism is the state of a 
plant or an organ when it is irritable to moisture. Hydro- 
tropic organs may bend toward or away from a moist surface. 
Roots are particularly sensitive to the presence of moisture. 
If a cylinder of wire gauze be filled with damp sawdust and a 
number of seeds planted near its surface they germinate and 
the roots start to grow in the normal direction — i.e., directly 
downward. If now the cylinder be suspended at an angle, 
as shown in figure 132, the roots which pass into the air, 



178 OUTLINES OF PLANT LIFE. 

stimulated by the moisture, curve toward the damp sawdust. 
Upon entering it the stimulus ceases, and they start again to 
grow downward, being positively geotropic. Again the 
stimulus of the moist surface overcomes that of gravity, and 
they turn back to it, often threading themselves in and out 
of the wire gauze. Since only one-sided action of a stimulus 




Fig. 132 — Apparatus for demonstrating hydrotropism, a, a, a zinc disk, with hooks 
to which is attached a cylinder or trough of wire netting filled with damp sawdust. In 
this are planted peas, g, whose roots, h,i, k, m, first descend into the air but soon turn 
toward the damp sawdust again, m has threaded itself in and out of the netting. — 
After Sachs. 

determines direction of movement, if the air be saturated they 
continue to react to the stimulus of gravity alone. 

251. (e) Movements due to contact. — Contact, either 
gentle or forcible, and friction act as stimuli to modify the 
growth of many plant parts. Only rarely is the main axis of 
a plant sensitive to mechanical stimuli, except, perhaps, to 
long continued contact (or pressure) in the case of some 
twining plants. But in many plants tendrils and leaf-stalks 
are irritable to contact, even to a degree far surpassing that 
of our nerves of touch. 

If the tip of a tendril (T 225), while still capable of growth, 



THE MOVEMENTS OF PLANTS. 1 79 

come in contact with a solid body, it will quickly become 
concave on the side touched, and thus will wrap about the 
object, if it be of suitable size. This curvature is due first to 
the shortening of the cells upon the concave side and later to 
unequal growth on the convex and concave sides. Finally 
this effect extends to all parts of the tendril, which begins to 
curve. As both ends are fast, it is a mechanical necessity 
that the curves become spiral coils, both right- and left- 
handed, accompanied by a twisting of the tendril on its axis 
(fig. 69). After the coils are formed the tissues of the 
tendril become thick-walled and rigid, so that the plant is 
attached to the support by a spiral spring. 

Other tendrils do not nutate, but are negatively helio- 
tropic, and by contact their tips are stimulated to develop 
disks which apply themselves closely to the support and send 
into its irregularities short outgrowths from the surface cells. 
Such plants are adapted to support themselves by walls, tree- 
trunks, etc. The Japanese ivy and one form of the Virginia 
creeper are notable examples. 

The coiling of the leaf-stalks is not unlike the first curva- 
tures described for tendrils (fig. 100). 

EXERCISE XLIII. 

To show effect of contact as a stimulus to tendrils. 

Stroke with a pencil the concave side of the tip of a tendril of passion 
vine, squash, wild cucumber, or balsam-apple, on a warm day or in a 
hothouse, and observe curvature which follows in a few minutes. 

252. (B) Movements of turgor. — The movements already 
described are confined to members which are growing, either 
throughout, or in some part. As turgor can affect only tissues 
whose cell-walls are elastic (^f 156), the movements pro- 
duced directly by variation in turgor can occur only in such 
mature members as are provided with special motor organs. 
In almost all cases these are leaves. Stimuli which regulate 



1 80 



OUTLINES OF PLANT LITE. 



growth (If 242) may also affect motor organs, producing like 
curvatures. But elongation of any part of a motor organ by 
increased turgor is reversible, 
not permanent (cf. T 213) ; it 
is therefore not growth. 

253. Motor organs. — The 
motor organ in leaves is usually 
the leaf base (% 124) or a modi- 
fled portion of the stalk, some- 
times greater but generally less 
in diameter than the rest. Its 





Fig 133. -Transverse sections through petiole of scarlet runner. A, through the rigid 
portion ; B, through the motor organ. G, g, vascular strands ; c, cortex ; /«, pith ; 
r, deep channel along ventral side of petiole. Magnified about 10 diam. — After Sachs. 

Fig. 134. -Portion of a scarlet runner, which, originally growing erect, has been inverted 
for several hours, resulting in geotropic curvatures of the primary motor organs P, P 1 , 
P' 2 . The lowest pair of leaves show secondary motor organs at the juncture of petiole 
and blade. Similar ones are present in the upper compound leaves, but are not clearly 
shown in the figure. The arrows show the position of the petioles when the plant was 
first inverted. About two thirds natural size.— After Sachs. 



cortex consists of large cells, and the stele occupies a rela- 
tively small part of the transverse section. In other parts of 
the petiole the stele is much larger, or there may be several 



THE MOVEMENTS OF PLANTS. l8l 

steles distributed about the center. (See ^f 136.) In figure 
133, A and B show the contrast. If the leaf be a compound 
one, there are usually secondary motor organs at the base of 
the leaflets, as in the leaf of the bean (fig. 134). Variation 
in the turgor of the cells of the cortex upon one side or the 
other produces a sharp curvature of the motor organ, which 
alters the position of the leaf or leaflet (fig. 134). The con- 
cave surface of the motor organ becomes deeply wrinkled 
transversely, while the convex surface is smooth. 

254. Spontaneous movements. — Only a few plants exhibit 
spontaneous movements by means of motor organs. The 
lateral leaflets of the telegraph plant (s, 
fig. 135), under normal conditions of 
rather high temperature (about 32 ° C), 
show jerky movements of such direction 
that their tips describe an irregular el- 
lipse, which is completed in 1 to 3 
minutes. The leaflets of the clovers and 
oxal is show much slower movements 
described in the next paragraph. 

More commonly the turgor movements Fl( f-. 135-— Leaf of nesmo- 

J ° amm gyraiis. 1 w o 

are induced. The most common stimuli thirds natural size.-After 

Sachs. 

are light and contact, although many 
others suffice to induce them. 

255. Light movements. — Movements produced by the 
variations of light have long been known as "sleep move- 
ments." They are best observed upon the leaves of the 
bean family, though many other plants exhibit them. Figure 
136 shows the positions assumed by various leaves toward 
nightfall. It will be seen that in compound leaves the leaf- 
lets sometimes rise, so as to apply their outer faces to each 
other ; others sink, so that the under surfaces are in contact; 
others become folded in various ways. This position is main- 
tained throughout the night. Upon the increase of light in 




182 



OUTLINES OF PLANT LLFE. 



the morning, the day position is assumed. The cutting off 
of light artificially from any of these plants causes them 




Fig. 136. -Photeolic movements, a, leaf of a mimosa in day position ; a', the same in 
night position. />, leaf of Corotiilia varia in day position ; b' , the same in night po- 
sition, c, leaf of A»iorpka fruticosa in day position ; c', the same in night position. 
d, leaf of Tetragonolobus in day position ; d' , same in night position.— After Kerner. 

within a short time to assume the nocturnal position. Their 
purpose is not certainly known. 

EXERCISE XLIV. 

To show effect of intensity of light as a stimulus on certain leaves. 

Observe the position of the leaflets of white, red, or sweet clover, bean, 
locust, or oxalis at 3 p.m., 6 p.m., at dusk (or after nightfall by using a 
lantern) and at 8 A.M. In the morning darken with a box a plant show- 
ing these movements. After an hour or two, observe the position of leaf- 
lets. 

256. Contact movements. — Some organs are sensitive to 
contact, as the leaves of Venus' fly-trap, and other related 



THE MOVEMENTS OF PLANTS. 



183 



plants. The motor organ in the Venus' fly-trap (figs. 224, 
137) is the cushion of tissue running along the back of the 
leaf between the two lobes. By the sudden variation in 
turgor of some of these cells the two halves of the leaf are 
thrown quickly together when one of the six bristles upon its 




Fig. 138. Fig. 139. 

Fig. 137. — Part of a transverse section of a leaf of Venus' fly-trap, w, the cushion of 
tissue constituting the motor organ ; b, one of the sensitive bristles which, upon being 
touched, cause the leaf to close : t, one of the interlocking teeth. The minute pro- 
jections over inner (ventral) surface are glands which secrete the digestive fluid and 
later absorb the food. Magnified about 5 diam.— After Kurz. 

Fig. 138.— A leaf of the sensitive plant fully expanded. Natural size.— After Duchartre. 

Fig. 139. — A leaf of the sensitive plant after stimulation The motor organ at the base 
of each leaflet has thrown it forward and upward ; the motor organs at the base of 
the four divisions have moved them together. The motor organ at the base of the 
main petiole has moved the whole leaf sharply downward. Natural size. -After 
Duchartre. 



upper surface is touched. The sensitive plant drops one of 
its leaflets or the whole leaf quickly when stimulated by con- 
tact, heat, or electricity. The position of the leaves when 
normally expanded is shown in figure 138, and their position 
after stimulation by figure 139. The stamens (^j 287) of 
some flowers and the stigmas (^[ 283) of others are sensitive 



1 84 OUTLINES OF PLANT LIFE. 

to a touch, shortening, elongating, or bending in such a way 
as to promote pollination ( ^f 295). 

The motor organs of the leaves of a number of the bean and 
oxalis families also react to more violent mechanical stimuli. 
Their movements are similar to those described in ^f 255. 

257. Summary. — By irritability, that is, the sensitiveness 
of protoplasm to external agents, plants are able to regulate all 
their activity and adjust themselves to the world about them. 
Under unfavorable conditions this sensitiveness is temporarily 
lost. If permanently lost, it is death. It is more marked in 
some parts than others and its effects in these parts are capable 
of being transmitted to distant parts. 

The reactions of plants to stimuli are most easily observed 
when they result in movements. Movements of the proto- 
plasm itself seem to be automatic, but can be directed by ex- 
ternal stimuli. Movements of multicellular plants are due 
either to unequal growth or to unequal turgor. Light, 
heat, gravity, moisture, or contact may so influence the rate 
of growth, or the amount of turgor as to cause curvature of 
growing parts or of a special motor organ. The parts affected 
may thus be turned toward or away from the source of the 
stimulus, or may be placed transverse to it. Movements in 
response to gravity, light, and heat are most important. 
These work conjointly to determine the position of organs. 



PART III: REPRODUCTION. 

CHAPTER XVII. 

VEGETATIVE REPRODUCTION. 

258. Introduction. — Having considered in Parts I and II 
the structures and functions by which the nutrition of the 
individual is secured, Part III is devoted to the consideration 
of the structure and functions of some of the simpler repro- 
ductive organs and the functions by which a succession of 
similar individuals is insured. (For fuller discussion see 
Plant Life.) 

One of the fundamental powers of protoplasm is its ability 
to produce new organisms as offspring from the older ones. 
In the simpler plants the two great functions, nutrition and 
reproduction, are often carried on by the same cell. This 
must always be so in the unicellular plants. In the higher 
plants, however, these two functions become completely 
separated, organs being specialized for each, so that the 
functions may be more certainly and efficiently performed. 

Any part capable of growing into a new individual may be 
called a reproductive body, and the part on which or in which 
it is produced is a reproductive organ. If the reproductive 
bodies consist of one or two cells only, they are usually 
called spores. If they are cell-masses, they are generally 
called brood buds or gemmce to distinguish them from ordi- 

185 



1 86 OUTLINES OF PLANT LIFE. 

nary buds. In both cases it is necessary that the cells to be 
separated from the parent should be capable of growth — that 
is, in the condition known as the embryonic phase (^f 215). 
The reproductive organs produced by some plants are ex- 
ceedingly complex and varied, while others form reproduc- 
tive bodies in very direct ways. The reproductive bodies 
themselves are generally very simple. In addition to com- 
plex reproductive organs, there are sometimes accessory parts 
by which the plant adapts its reproductive functions to the 
conditions under which it lives. Among these accessory 
structures are many, as among the flowers of seed plants, by 
which the aid of other plants or animals is secured. 

259. Vegetative and sexual reproduction. — In all the 
diversity of organs and processes two chief methods may be 
distinguished, called vegetative reproduction and sexual repro- 
duction. 

Vegetative reproduction consists in the formation of repro- 
ductive bodies by processes of growth only. The modes in 
which they arise are varied in detail, but consist essentially 
in the production by the parent of a body, unicellular or 
multicellular, which at maturity develops, under suitable 
conditions, into a new plant. It is scarcely to be doubted 
that the earliest methods of reproduction were vegetative, and 
that sexuality has been acquired by a gradual adaptation of 
cells previously devoted wholly to ordinary processes of 
growth. 

Sexual reproduction consists in the formation of reproduc- 
tive bodies by the union of two specialized cells, neither of 
which alone is capable of developing into a new plant. 

I. Fission and budding. 

260. Fission. — In single-celled plants cell division and 
reproduction are practically identical, since shortly after 
division occurs the two cells so produced separate and lead 



VEGETATIVE REPRODUCTION. 1 87 

an independent existence (C, fig. 10). Such a method of 
reproduction evidently interferes Little with the processes of 
nutrition, which probably are scarcely even suspended during 
the process of reproduction. 

261. Budding. — A slight variation of the method of fission 
just described is to be found in those single-celled plants, 
such as the yeasts, whose growth is so localized as to form 
upon one side a small enlargement which ultimately attains 
the size of the parent, with which it is connected by a very 
narrow neck (fig. 29). Across this neck the partition wall 
is formed in the usual way. This becomes mucilaginous, 
rendering the adhesion of the daughter cell at this point so 
weak that it is easily separated from the parent. This 
method of reproduction is known as budding. 

262. Fragmentation. — In those plants which consist of 
a row of cells more or less closely united, the breaking up of 
the filaments into separate pieces, either through external 
force or the death of one of the cells, may produce a number 
of smaller colonies or of new individuals, each of which may 
grow to full size. In some of the more loosely organized 
filament-colonies, such as Nostoc (see *\ 11, and fig. 6), 
there are specialized cells whose function seems to be to 
loosen pieces of definite length, which creep out of the jelly, 
grow, and thus produce new colonies. 

The greater size reached by most multicellular plants soon 
renders impossible the continuance of this method of repro- 
duction, except among those whose cells are all alike. 
Should such separation into nearly equal parts occur among 
more highly specialized plants, it is evident that one portion 
might easily be left without nutritive organs adapted to its 
needs. The higher plants, therefore, specialize certain 
regions or members, where, by division or budding or similar 
processes, reproductive bodies may be formed. 



188 



OUTLINES OF PLANT LIFE. 



II. Spores. 
263. Sexual and non-sexual spores. — A spore is a single- 
s' celled body capable of producing 
« a new plant. Spores may be 
formed either by a process of 
growth or by the union of two 
cells. The former are called non- 
sexual spores; the latter, sexual 
spores. Only non-sexual spores 
are discussed in this chapter. 

264. Motile spores. — Spores 
may be either naked and motile 
or furnished with a cell-membrane 
and non-motile. The former are 
commonly produced by plants 
which pass all or part of their lives 
in water, such as the algae and 
aquatic fungi. They are usually 
pear-shaped and furnished with one 
or more cilia, by means of which 
they swim about (figs. 109, 140). 
When locomotion was supposed 
to be a distinctive power of ani- 
mal bodies they were called zoo- 
spores, a name still retained. They 
are also called swarm-spores. 

Zoospores are formed either in 
a general body-cell, not visibly 




Fig. 140. — Development and escape 
of zoospores of an aquatic fungus 
{Saprotegnia lactea). The ends 
of two hyphae are shown, the ter- 
minal cells being spore cases. In 



a, the protoplasm is gathering to different 
form spores. From b many of 



from 
in a 



spores 
the zoospores have escaped polio or 
through the perforation in the ^ tlia > ^ 

wall near the upper end of the f m anc J structure, the SDOre Case 
I. From c all have escaped ' r 



the other body- 
cell specialized in 



cell. 



but one which is just slipping Th entire contents of the spore 

through the opening (here in pro- x ^ ^ * 

Keraer Magnified30odiam ' _After case ma >' form a single zoospore, 
or it mav divide into several or many. 



The zoospores are 



V EG ETA TIVE REP ROD UCT10N. 



189 



set free by the rupture or by the solution of a portion of the 
enclosing wall (lig. 140). They may begin to move before 
the rupture of the wall, in accomplishing which their activity 
may materially assist. They then work their way out and 
swim freely in the water. After a time of movement they 
usually lose their cilia, either withdrawing them into the 
protoplasm or dropping them off, come to rest, and begin to 
grow into a new plant. 

265. Non-motile spores are formed by all classes of land 
plants without exception. They are often produced in great 
profusion, especially by the fungi, the mosses, the ferns, and 
the seed plants. 

266. Form and food. — Their form is exceedingly various. 
Many are spherical or ovoid, while some are cylindrical or 

co - 




Fig. 141.— Part of a vertical section of a leaf of a willow, attacked by a fungus (Melamp- 
sora salicina). eo. epidermis of upper side lifted by the young teleuto-spores, t, de- 
veloping from the spore-bed above the ends of the palisade cells of the host (par) ; 
eu, epidermis of the under side, broken through by the spore-bed from which spring 
uredo-spores, st, and paraphyses, p. eo will also finally be ruptured to- set free t. 
Magnified 260 diam. — After Prantl. 

even needle-shaped (figs. 141, 143, 166). Irregular forms, 
also, are not uncommon. The same plant may produce at 



190 OUTLINES OF PLANT LIFE. 

different stages or in different parts spores which are unlike 
in form and nature (compare / and st, fig. 141). In almost 
all cases there is a supply of reserve food within the spore, 
which varies in amount with the conditions under which they 
are formed. It is ordinarily greater in resting spores than in 
those intended for immediate growth. 

267. Growth. — Spores germinate by absorbing water, 
thus bursting the more rigid outer layer or layers of the cell- 
wall. The inner layer then grows in area to accommodate 
the increasing protoplasm, which so controls the mode of 
growth as to produce a plant of definite form. In many 
cases the plant produced is essentially like that which gave 
rise to the spore. In others it is different, but sooner or 
later in the life cycle the same form recurs. 

268. Origin. — Non-motile spores are either free, being 
produced at the ends of branches specialized for that pur- 
pose, or enclosed in a spore case. Often the same plant 
forms spores by both methods at different stages in its 
development. 

269. Free spores. — The formation of free spores is con- 
fined to the lower plants, and is especially characteristic of 
the non-aquatic fungi. The branches producing spores may 
occur singly, or, more commonly, they are grouped at 
certain points, forming a spore-bed (fig. 141). If the fungus 
develops its mycelium in the interior of a host, the formation 
of a spore-bed is often necessary to rupture the host, so that 
the spores may be brought to the surface and set free. Thus 
the spore-beds of parasitic fungi commonly blister the surface 
of the host by lifting up its outer tissues (eo, fig. 141). 

Spores may be produced either singly at the ends of the 
branches, or in chains (fig. 142). 

A modification of the production of spores singly occurs 
when the branch destined to produce them gives rise to two 
to eight very slender branches, each of which enlarges at the 



V EG ETA TIVE RE PROD UCTION. 



I 9 I 



tip into a single spore, so that the main branch appears to 
carry two to eight spores upon slender stalks (fig. 143). 





Fig. 



Fig. 



142. biG. 143- 

Fig. 142.— An outline showing the formation of a spore-chain of the biue-green mold 
{Penicillium glaucuni). b, branch of spore-bearing hypha, budding beneath two 
older spores. Across the narrow neck a partition wall is formed, the spores round off, 
and from this wall a device, c, for loosening the spores is developed. The terminal 
spore is oldest. Highly magnified.— After Frank. 

Fig. 143.— Longitudinal section through the edge of a gill of a mushroom {Coprinus) 
after spore-formation is completed. /, interwoven hyphae of the gill, branching to 
form the spore bed, composed of sterile branches, /, swollen branches, c, and spore- 
bearing branches, b. The latter give rise to four slender branches, whose tips enlarge 
to form each a single spore. / and c do not produce spores. Magnified 300 diam. — 
After Brefeld. 

270. Fructifications. — In the higher fungi whose my- 
celium is developed within a dead substratum many hyphae 
are aggregated to constitute a reproductive structure or fruc- 
tification, which is the only conspicuous part of theiungus. 
(For an account of the vegetative parts, see \*{ 43, 47). 

The body of the fructification is made up of hyphae, more 
or less interlaced and adherent, and is of a form adapted 
not only to break through the substratum, but also to 
furnish an extensive surface for the spore-beds (fig. 143). 

The fructification may be irregularly lobed, sessile and 
gelatinous, or much branched and cylindrical or flattened; 
the shapes being adapted in various ways to form an exten- 
sive surface on which spores may be formed (figs. 144, 145). 



192 



OUTLINES OF PLANT LIFE. 



271. Simple spore cases. — Spores are also formed loose 
in the interior of cells. Each spore-containing cell is 




Fig. 144. 

Fig. 144.— A fructification of Clavaria 
aurea. The spore beds cover the upper 
part of the branches. Natural size.— v . n _._, 

After Kerner. r 1G - I45 

Fig. 145. — A fructification of a mushroom, Amanita f>halloides. p, the cap or pileus; 
7; the veil, originally connected with edge of cap, covering the gills which radiate 
from the stipe, st, to the edge of cap ; vo, the volva. The surface of the gills is 
covered with the spore beds. Most mushrooms showing a distinct volva are poison- 
ous. Natural size.— After Kerner. 



called a simple spore case (fig. 146). In the lower plants, 
the spore case may be merely one of the general body-cells, 
or it may be specialized in form as well as in function. It 
may be spherical, sac-like, or linear. The number of spores 
formed within a simple spore case may be two or more, up 
to several hundred. Simple spore cases may be formed 
singly or they may be grouped. 

272. Compound spore cases. — In the higher plants, in- 



VEGE TA TI VE REPR ODUC TION. 



193 



eluding the mossworts, fernworts, and seed plants, the spore 
case is always formed of two or more spore-producing cells, 
surrounded by a covering of cells (one or more layers) which 
do not produce spores. These spore cases may be developed 





Fig. 146. Pig. 147. 

Fig. 146. — Longitudinal section of the simple spore case of a mold (Mucor). The aerial 
hypha, h, has partitioned off a cell, s, within which spores are produced. The walls 
of this spore case are studded with needle crystals of calcium oxalate. The partition 
protrudes far into the spore case. Magnified 260 diam. — After Kerner. 

Fig. i 47. — Longitudinal section of the stem, s, of a moss gametophyte, bearing leaves, 
b. Embedded in the stem is the sporophyte, consisting of a stalk, si, and a compound 
spore case, of which iu is the wall, formed of a sheet of cells, enclosing the spores, 
s/> (contents not shown). Magnified 100 diam. — After Hofmeister. 



either from superficial or from internal cells. As a conse- 
quence, the mature sporangia will be either free or more or 
Less enclosed within the tissues of the organ by which they 
are borne. 

273. The sporophyte. — Among the mossworts, fernworts, 
and seed plants reproduction by spores has become so fixed 
and important that one stage in the plant is devoted espe- 
cially to producing them. This phase is different from that 
producing sex cells, the difference becoming greater the more 
complex the plant. The stage set apart for spore production 
is called the sporophyte. In the mossworts the sporophyte 
has very little green tissue, and therefore carries on little 
nutritive work, but depends for its supply of food chiefly 



I 9 4 



OUTLINES OE PLANT LIFE, 



spin 



upon the sexual stage, with which it is connected throughout 

its entire existence' (^f 60). In 
the fernworts and seed plants, 
however, the sporophyte pos- 
sesses extensive nutritive tissues, 
the leaves, stems, and roots be- 
longing entirely to this stage. 
Sporangia in these plants may 
be formed either upon the stem 
or the leaves — never upon the 
roots. 

274. Liverworts and mosses. 
— In most liverworts and mosses 
the spore case is developed within 
the enlarged upper part of the 
sporophyte, to which the name 
capsule is given (figs. 46, 148, 
and \ 59). By the time the 
spores are mature the capsule 
has become filled with the loose 
spores. It bursts at the top or 
opens by the falling off of the 
lid-like upper end, and thus 

Fig. 148.— Longitudinal section of the A x 

youngcapsuleofatruemoss(£rj/«w). allows the SDOreS to escape. 

j, spore case. At this stage the mother r 

cells of the spores, spm, have become 275. FemS. 111 the ferns the 

free (only a few are shown, still en- 
closing the spores, which are later re- sporophyte phase is the plant 
leased i ; sw, the wall of the spore r r J * 

case, lined by the remains of another with TOOtS and leaves. The 
layer of cells now disorganized : c, the 

columella, of partly collapsed ceils ; spore cases are either produced 

fs, intercellular space ; cw, wall of r 

the capsule; an, the annulus, a ring upon the Under Surface of the 

of cells which pries off the lid, at r 

whose edge they develop; ot, the foliage leaves or upon specialized 

outer, 7>i, the inner peristome, formed * 

by the thickening of parts of the wails leaves. Thev are usuallv numer- 

of certain rows of cells ; nt, nutritive J 

tissue, with chioropiasts and intercei- ous stalked, free, and often as- 

lular spaces. Magnified 25 diam. — 

Original. sociated in clusters. The clus- 

ters are often arranged in elongated groups or lines (fig. 149)- 




VEGE TA Tl VE RETROD UCTION. 



195 



Each cluster may be protected by a special outgrowth from 



the cells in its neighborhood (figs. 149, 150) 
case consists of a stalk expanding above 
into a body composed of a single outer layer, 
enclosing at maturity the loose spores (fig. 
236). 

276. Spore leaves. — In many of the ferns 
the leaves which produce spore cases are 
not different from the foliage leaves. In 
others, certain leaves are so specialized for 
bearing the spore cases that they abandon 
their nutritive work in part or entirely. To 
such specialized leaves the name spore 
leaves is applied. 



Each spore 




Fig. r4g.— A leaflet of 
a fern {Aspiditim') 
seen from the back. 
Eight clusters of 
spore cases are 
shown, each cov- 
ered by its own in- 
dusium, i. Mag- 
nified 2 diam. — 
After Sachs. 



276a. Differentiation of sp res — Among higher 
fern worts the spores are of two sizes: large ones, 
known as megaspores, and much smaller ones known 

as microspores (fig. 151). Each kind, when it germinates, produces a 
sexual plant. The megaspores give rise to plants bearing female organs 
only, the microspores to those bearing male organs only. A similar 
separation of sexes in the gametophytes frequently occurs when the spores 




Fig. 150.— Vertical section through the leaflet shown in fig. 149, passing through the 
center of a spore-case cluster, e, ventral epidermis; e', dorsal epidermis; between 
them the mesophyll, showing 3 veins cut across ; over the central one is a cushion of 
tissue from whose surface arise the stalked spore cases s, s. i, 2, the indusium. Mag- 
nified about 30 diam.— After Sachs. 

are equal in size, as in Marchantia and horsetails, but it always occurs 
when they are unequal. A corresponding difference in size is often found 



196 



OUTLINES OF PLANT LIFE. 



between the spore cases containing small spores and those containing large 

spores (fig. 151). 

In the seed plants this difference in the spores is always found. The 

microspores are called J>o//engrains 
and the megaspores after germination 
are called embryo-sacs .* The spore 
cases also are always different in form 
and structure, and the leaves upon 
which they are usually borne are also 
of two distinct forms. In no case do 
spore leaves perform nutritive work; 
they are always specialized. Those 
leaves which bear pollen grains are 
called stamens, and the leaves which 




Fig. 151.— Section through three spore produce the megaspores are called 
case clusters of an aquatic fernwort 
(Salvinia nataiis). Each is cov- 
ered by a double indusium. i, 2, 
two clusters consisting of small spore 
cases, each containing 64 micro- 
spores; a, a cluster consisting of 
large spore cases, each containing 
one megaspore. Magnified 10 diam. 
— After Sachs. 



carpels* (figs. 156, 157). In spite of 
these special names, it must be care- 
fully borne in mind that the spore cases 
and spore leaves of the seed plants are 
not different from those of the fern worts 
or mossworts in anyessentialparticular. 

277. The spore leaves of the seed plants are usually 
clustered by the failure of the internodes of the axis to 
lengthen as much as between the foliage leaves. Very often, 
also, the leaves adjacent are modified in form and color to 
adapt them to securing the dispersal of the pollen by various 
agents, especially insects. Such a shoot bearing stamens, 
carpels, and accessory leaves is called a flower. As a similar 
aggregation of the spore leaves occurs in horsetails and many 
club-mosses it is evident that the flower is not distinctive of 
the seed plants, though it attains the highest specialization 
among them.f 



* These special names were given because the seed plants were first 
studied, and it was long before the real nature of the parts and their re- 
lation to similar ones in the lower plants were known. The terms are 
still in use, and are likely to continue to be used for convenience. 

f It is for this reason that the term seed plants is preferred to flowering 
plants. 



V EG ETA TIVE REP ROD UCTIOA 7 . 



I 9 7 




Fig. 152. — A flower of linden, halved ; show- 
ing a pestle-like pistil. Magnified about 
3 diam. — After Kerner. 



The parts and functions of the flower of seed plants are 
now to be discussed. 

The Flower. 

278. A flower usually consists of a shortened axis, the 
torus, bearing several floral leaves (figs. 66, 152). The 
spore leaves are known as 
essential organs, the accessory 
leaves as the perianth and 
bracts. 

The essential organs are of 
two sorts, stamens and carpels. 
In any flower they may be all 
stamens or all carpels, or may 
include both sorts. The 
perianth may be composed of 
one or two kinds of leaves, 
often bright-colored. If there are two sorts, those next the 
spore leaves are generally highly colored, and constitute the 
corolla. Each leaf of the corolla, when distinct, is a petal. 
The leaves below the corolla are often green. They con- 
stitute the calyx, and each, when distinct, is a sepal. 

279. Carpels. — The leaves bearing the ovules are called 
carpels. They may be flattened; or so curved that in the 
course of their development the edges unite and a cavity is 
more or less perfectly enclosed; or neighboring carpels may 
grow together in such a way as to form a case. Such hollow 
structures, whether composed of one or more carpels, are 
often somewhat pestle-shaped, whence they early received 
the name pistil (fig. 152). A flower whose only essential 
organs are pistils is called pistillate. 

280. Ovules. — Among seed plants the spore cases which 
the carpels bear are universally known as ovules, a name 
given to them under the supposition that they were the eggs 
which, upon fertilization, produce new plants. Though they 



I9& 



OUTLINES OF PLANT LIFE. 



are not in any respect comparable to the real eggs (since they 
are produced by the non-sexual or sporophyte phase), the 
name is retained for convenience. The ovules arise usually 
upon the ventral (inner) face or the edges of the carpels. 
In the open carpel they are exposed, but in the closed carpels 
they are completely shut in, except for a narrow opening 
which sometimes remains, by which the interior cavity com- 
municates with the outside air. 

281. Gymnosperms and angiosperms. — When the changes 
through which the ovule passes are complete, it becomes the 
seed. When the ovules are produced 
upon the free surface of an open carpel, 
the seeds are, therefore, exposed. On 
the contrary, when the ovules are borne 
within a closed pistil (formed by one or 
more carpels) the seeds are developed 
within this case, by which they are pro- 
tected until mature, or longer. 

These two methods of seed produc- 
tion form the basis for the separation 
of the seed-bearing plants into two 
great groups, one known as gymno- 
sperms, or plants with naked seeds, the 




young cone- 



Fig. 153 
scale of Scotch pine show- 
ing the two ovules ; the 
latter halved parallel to 
the scale, showing the 
body of ovule and the pro- 

!hfS e ^ en ^ 0n Tt! other as the angiosperms, or plants 

scale is attached at b. 
Magnified about 8 diam. — 
After Kerner. 



with encased seeds. Open carpels (fig. 
153) are found exclusively among the 
gymnosperms, to which belong the cone-bearing, mostly 
evergreen, trees, while the closed pistils are chiefly found 
among angiosperms, to which belong the majority of garden 
and field plants and the deciduous forest trees. 

282. The closed pistils of angiosperms are usually distin- 
guishable into (1) an enlarged basal part, the ovulary* 

* This part was early called the ovary (a name which is still in general 
use), meaning the organ which produces eggs, under the impression that 



VEGE TA T1VE RETROD UCTION. 



I 99 



containing the ovules, surmounted by (2) a slender part of 
variable length, the style, which is terminated by (3) a rough, 
sticky, or branched part, the stigma. (See figs. 152, 156.) 

283. Stigma and style. — The stigma may take the form 
of a knob, a ridge, a straight or wavy line, or be lobed or 
branched. However compact, it is usually roughened by 
the prolongation of its surface cells into rounded, pointed, or 
hair-like extensions (fig. 154), which frequently secrete a 
sticky fluid. Its purpose is to secure 
the adhesion of the pollen spores 
brought to it by various agents, among 
the most important of which are the 
wind and insects. 

The style may be thick or slender, 
long or short, branched or unbranched, 
hollow or solid. It is frequently 
wanting. 

284. Simple and compound pistils. 
— When several carpels are present in 
one flower they may form as many 
separate simple pistils as there are 
carpels. If numerous, the axis will 
be enlarged or elongated to accom- 
modate them. (See \ 296, and fig. 
173.) Instead of forming separate 
pistils, the carpels may be united to form a single compound 
pistil. 

The union of the carpels may be only at the base; or it 




Fig. 154.— One of the hairs 
from the stigma of corn 
cockle {Lychnis git h ago) 
to which a pollen grain ad- 
heres. The pollen tube has 
penetrated the hair and is 
making its way down the 
style. Magnified 175 diam. 
— After Strasburger. 



the ovules (= little eggs) were like the eggs of birds, an idea which was 
further carried out in the name albumen given to the food stored in the 
seed. (See \ 305.) To avoid confusion with the true ovary in which 
the real egg is produced, I use the name ovulary — i.e., the organ which 
produces ovules. The word ovule, though as bad in etymology as 
ovary, is convenient, and does not lead to any confusion. 



200 



OUTLINES OF PLANT LIFE. 



may involve the entire ovulary, leaving the styles free; or 
the union may be complete, with the exception of the 
stigmas; or it may involve even them (figs. 155, 156). 






Fig. 



Fig. 



[55. .TIG. 156. *IG. 157. 

Fig. 155. — Pistil of white hellebore {Veratrum album) showing three carpels separate 
above only. Magnified about 6 chain.— After Berg and Schmidt. 

Fig. 156.— Calyx and pistil of the manna ash (Fraxinus or mis) showing calyx leaves 
united at base and carpels united throughout, the slightly 2-lobed stigma only giving 
external evidence of their number. Magnified several diam. —After Berg and Schmidt. 

Fig 157. — Pistil of white potato halved transversely, showing two carpels united at 
center where their edges form a large placenta on whose surface the ovules arise. 
Magnified several diam.— After Kerner. 

285. The ovulary.— The cavity of the ovulary is either 

undivided or partitioned into as many chambers as there are 

component carpels (fig. 157); or the normal number of 

-rs r— ^-"~i~" T^ A chambers in the ovulary may be in- 

^S ^SIIJ^ S^y creased by outgrowths from the carpels 

themselves (fig. 158). 

286. Ovules. — An ovule consists of a 
central body, the spore case, in which the 
megaspores are formed. In a few ovules 
as many as 20 to 40 megaspores begin to 
develop ; in most only one to four. Even 
when several megaspores begin to form it 
is rare for more than one to reach per- 
fection; the remainder disappear almost completely. The 
megaspore never escapes from the spore case ; for this reason 
the megaspore looks more like a cavity in the ovule than like 



Fig. 15S. — A transverse 
section of the capsule of 
shepherd's purse. The 
pistil consists of two 
carpels, at whose united 
edges two placentas are 
formed carrying the 
ovules (now seeds). The 
partition from one pla- 
centa to the other is an 
outgrowth (false parti- 
tion) and not part of the 
carpel. Magnified about 
6 diam.— After Bessey. 



J 'EGE TA TIVE REP ROD UCTION. 



20 1 



a spore. Because an embryo appears later inside this ap- 
parent cavity, the megaspore of seed plants has long been 
called the embryo-sac. 

The spore ease is surrounded by one or two integuments. 
These arise as outgrowths from the parts adjacent. If the 
spore case is to have two coats, 
the inner appears first as a low 
ring around its base gradually 
growing up around it; the outer 
shortly appears in the same way 
(fig. 159). These integuments, 
as well as the spore case, often 
grow unsymmetrically, so that at 
the maturity of the megaspore the 
ovule is often variously curved 
(figs. 159, 160). The megaspore 
itself may be distorted by this means so as to lose still more 
its likeness to a spore. 

Ovules are borne either upon the axis itself or upon 




Fig. 159. — Two very young ovules 
of the California poppy (Esch- 
scholtzia\, seen from the outside. 
B, somewhat older than A. nc, 
the rudiment of the spore case ; 
jc, rudiment of the inner integu- 
ment ; pr, rudiment of the outer 
integument ; fn, the stalk. Mag- 
nified 140 diam. — After Duchartre. 




Fig. 160.— Diagrams of median longitudinal sections of three sorts of ovules to show 
curvatures due to unsymmetric growth. A, a straight, B, an inverted, C, a bent ovule. 
In all : f, the stalk ; k, the spore case; it, the inner integument; ai, the outer in- 
tegument ; m, the micropyle ; c, the base of the spore case where the integuments 
arise (called the chalaza) ; r, ihe ridge (rhaphe) formed by the union of stalk and outer 
integument; e>n, the megaspore. As C develops further em may become sharply 
bent on itself. — After Prantl. 

the carpels. It is usual for the ovules to arise upon a car- 
pel, either singly or in clusters, from a cushion or ridge, 



202 OUTLINES OF PLANT LIFE. 

called the placenta. The placenta in angiosperms is com- 
monly located at the united edges of the carpel or car- 
pels. If the carpels are united into a compound pistil, the 
placentas will be either isolated, as ridges upon the inner 
face of the wall of the ovulary (fig. 158), or aggregated at its 
center (fig. 157). Occasionally the ovules arise upon the 
entire inner face of the carpels, as in the gentians. 

287. Stamens. — A stamen is a leaf of the seed plants 
which bears the pollen sacs. The flowers whose essential 
organs are all stamens are said to be staminate. Rarely a 
single stamen constitutes a flower. Except for the crowd- 
ing, the stamens are arranged like all the other leaves of the 
plant, arising on the axis alternately, or in one or more 
circles. The stamens exhibit great diversity of form and size. 
Each usually consists of two parts, a stalk, called the 
fila?nent, bearing an enlarged portion, called the anther {si, 
fig. 66). 

The anther is usually larger than the filament and com- 
monly two-lobed, having the sporangia located in the thicker 
parts. 

288. Spore cases. — The anther bears from 1-12 pollen 
sacs (spore cases) upon its surface, or wholly or partly sunk 
in its tissues. In most anthers the pollen sacs are either two or 
four (fig. 161). When there are four they are often paired, and 
each pair may become confluent by the absorption of the 
partition between them (fig. 162). This occurs about the 
same time that the outer wall bursts in order to set free the 
spores. Such anthers, at the time of opening, are apparently 
two-chambered. 

289. Dehiscence. — The opening of the chambers occurs 
in one of three ways: by pores, by slits, or by valves. (1) 
A small area of the outer wall is absorbed or breaks away so 
that the pollen spores sift out through the pore so formed 
(fig. 163); or (2) a crack begins at one point and extends 



VEGETA TIVE REP ROD UCTION. 



203 



lengthwise of the anther (fig. 164); or (3) the break occurs 
along a line considerably curved, and the flap (valve) thus 




Fig. 161.— Transverse section of the anther of thorn-apple {Datura Stramonium), 
c, connective, with a small stele embedded in parenchyma ; a,/>, a,/>, the four spore 
cases, arranged in pairs showing pollen grains. When the spore cases break, the 
walls rupture at the groove between a and/. Magnified about 25 diam.— After Frank. 

loosened curls up or lifts so as to allow the escape of the 
spores (fig. 165). All three methods are dependent upon 
some special structure of the wall of 
the spore case at the lines of rupture 
(figs. 161, 162). 

290. Union. — The stamens are 
not infrequently united with one an- 
other or with some of the neighbor- 
ing leaves of the flower. They may 
be united to one another by their fila- 
ments only, or by their anthers only, 
or throughout their whole length. 
Union with the pistil or pistils is 
rather uncommon, but union with 
the corolla or calyx is very frequent. 
The stamens also branch just as 
ordinary leaves do. 

291. Pollen grains. — The spores produced in the spore 
cases of the stamens are of various forms, being round, 




Fig. 162. — Transverse section of 
bursted anther of a lily (Bzito- 
mus tunbellatus). Sporangia 
have ruptured at z, so that the 
two pairs have each formed a 
single cavity. The connective 
is relatively small ; in the cen- 
ter a single stele. Magnified 
about 20 diam. — After Sachs. 



204 



OUTLINES OF PLANT LIFE. 



ovoid, or even angular, with the surface smooth, grooved, or 
roughened with few or many bosses, points, or ridges, as in 
other spores (A-D, fig. 166). They are either dry and 
powdery when the sporangia burst, or are moist and sticky, 




Fig. 163. Fig. 164. Fig. 165. 

Fig. 163. — Anther and pollen of a Rhododendron. A, the anther, opening by pores at 
the end and allowing the pollen to escape. Magnified 8 diam. B, pollen grains ad- 
herent in fours (tetrads) as formed in the mother cells; the tetrads are held together 
by a sticky material which draws out into cobwebby threads as they are separated. 
Magnified 50 diam.— After Kerner. 

Fig. 164. — Anther of the sweet violet {Viola odorata), showing the pollen sacs opening 
by slits. Magnified about 5 diam.— After Kerner. 

Fig. 165. — A flower of cinnamon, halved. The calyx and stamens are raised on a cup 
developed around the pistil. The anthers open by uplifted valves, one for each spo- 
rangium, which here are arranged in two stories instead of in pairs side by side. Mag- 
nified about 7 diam. — After Luerssen. 



adhering to each other in larger or smaller clusters (fig. 163). 
Sometimes, as in orchids and milkweeds, they are all held 
together in one mass and are attached to a part of the anther 
which carries the mass like a stalk or handle (fig. 167). Dry 
spores are usually adapted to distribution by wind; while the 
coherent spores are adapted to carriage by small animals, 
especially insects. (See further \ 295.) 



VEGE TA 77 1 'E REP ROD UCTION 



205 



292. Perianth. — The perianth is not present in any 
gymnosperms (If 281), except in a rudimentary form in a 
few species of the highest order. In angiosperms the 







b E b 

Fig. 166. — Pollen grains. A , white water lily (Nymphcea alba). B, a thistle (Cirsium 
neitiorale). C, a mallow {Hibiscus ternatus). D, dandelion {Taraxacum offi- 
cinale). Magnified 200 diam. — After Kerner. E, pine, showing bladdery enlarge- 
ments, b, b, of the outer layer of the cell-wall. Magnified 400 diam. — After Stras- 
burger. 

perianth, which is rarely wanting, is primarily for the protec- 
tion of the stamens and pistils. As in all cases where leaves 
are produced rapidly and close together on a short axis, they 
grow during their early stages more 
rapidly upon the outer face than the 
inner. They are, therefore, concave in- 
ward and closely pressed together, form- 
ing a bud. At a certain stage the growth 
upon the two faces becomes equal, and 
later is more rapid upon the inner face 
than the outer. At this time the flower 
unfolds, the perianth spreading more or 
less and exposing the stamens and pistils 
within. These variations in growth are 
often repeated, the stimulus being light 
or heat or both, when it is necessary to protect the spores 
against unfavorable weather. Such flowers open and close 
several times before their leaves wither. (See also \ 244.) 




Fig. 167. — Pollen mass 
from an orchid. The 
pollengrainsare arranged 
in packets, />, which are 
aggregated at the end of 
a stalk, cd, terminating in 
an enlarged sticky disk, 
g, by means of which the 
pollen mass adheres to 
insects. Magnified about 
10 diam.— After Engler. 



206 OUTLINES OF PLANT LIFE. 

293. Calyx and corolla. — The leaves of the perianth are 
usually arranged upon the torus in two or more circles or in 
a low spiral. They may be all alike or differentiated into 
two series, an outer and an inner. In the latter case those 
of the outer row or rows constitute the calyx, and the inner 
set the corolla. 

The calyx leaves, or sepals, are generally green and show a 
great variety of form. When separate, the sepals are usually 
sessile and broad, with more or less pointed apex. The 
sepals are often apparently united, the originally separate 
portions appearing as teeth or lobes at the rim of a cup or 
tube, or some similar structure. Occasionally the sepals are 
not persistent, but fall as the bud opens or shortly thereafter. 
More commonly, however, the calyx, especially when un- 
divided, remains throughout the entire development of the 
flower, and often of the fruit. 

The inner set of perianth leaves, the petals, constitutes the 
corolla. The corolla presents a greater variety of form and 
color than does the calyx. 

The corolla is ordinarily not persistent, usually falling or 
withering shortly after the microspores have been lodged 
upon the stigma. 

294. Irregularity. — The parts of both corolla and calyx 
are often of equal size and like shape, and may be divided 
into several like halves by radial planes (figs. 168, 169). 
But often the symmetry of the calyx, and still more fre- 
quently that of the corolla, is so altered by unequal growth 
of the parts that the flower can be divided into like halves by 
only one, or at most two, planes; or it may even be entirely 
unsymmetrical. This unlikeness in the size and shape of the 
accessory leaves not infrequently extends to the stamens and 
pistils (figs. 170, 171). 

The irregular form and color of the perianth (when other 
than green), including the variegation of the ground color 



/ 'EGE TA TIVE REP ROD UCTION. 



207 



by lines and spots, seem to be dependent upon the relation 
of the flower to insects. (See further \ 390.) 





Fig. 168. Fig. 169. 

Fig. 168. — A flower of the flax, halved ; showing radial symmetry. See fig. 169. Mag- 
nified 2 diam. — After Bessey. 

Fig. 169. — Diagram showing the arrangement of the parts of a flower of flax. Outer 
circle, 5 sepals ; second, 5 petals ; third, 5 stamens ; fourth, 5 carpels, each divided by 
a false partition into 2 chambers. Five different radial planes will, therefore, divide 
this flower into halves. — After Bessey. 

295. Pollination. — To bring about the formation of a 
new plant within the ovule the pollen spores must lodge near 





Fig. 170. Fig. 171. 

Fig. 170. — An unopened flower of the sweet pea, halved ; showing bilateral symmetry 

(irregularity). Slightly enlarged. — After Bessey. 
Fig. 171.— Diagram showing the arrangement of the parts of the flower of sweet pea. 

Outer circle, calyx (5-lobed) ; second, 5 petals, the two lower united ; third, 10 stamens, 

9 united by filaments, 1 separate ; center, one carpel. Only one plane will divide this 

flower into halves.— After Bessey. 



the ovule and develop. To insure this a portion of the pistil 
forms a receptive surface, the stigma, to which the pollen 
spores readily adhere. It is advantageous, also, to have the 



2o8 



OUTLINES OF PLANT LIFE. 



pollen spores of one flower lodged upon the stigma in 
another flower of the same sort rather than upon the stigma 



d c 





Fig. 



Fig. 



'7 2 - f ig. 173. 

Fig. 172.— The torus of a flower of stonecrop {Sedum ternatuni), with the leaves re- 
moved to show scars ; two leaves of each kind shown, a, sepal; b, petal ; c, stamen ; 
d, carpel. Magnified several diam.— After Gray. 

Fig. 173. — Flower of mousetail (Myosurus minimus), halved; showing s, spurred 
sepal ; st, stamen ; si', a staminode or sterile stamen, having the position and form of 
a petal ; t, elongated torus covered with carpels, some of which are cut through, 
showing enclosed ovule. Magnified several diam.— After Engler. 




Fig. 174.— Flower of the strawberry, halved ; showing elongated and thickened torus, 
covered with carpels. Magnified about 3 diam. — After Bessey. 



of the same flower. The process of transfer and lodgment 
of pollen on a stigma is called pollination. If the pollen 
from one flower is carried to the pistil of another, it is called 



VEGETATIVE REPRODUCTION. 2CX) 

cross-pollination.* To secure pollination, and especially 
cross-pollination, the agency of wind or water or insects is 
employed. To the peculiarities of these various agents, 
flowers adapt themselves in character of pollen, color, nectar, 
odor, form of parts, time of deveolpment of stamens and 
stigma, etc. For an account of these see \\ 383-394- 

296. The torus. — In the vicinity of the flower leaves the 
internodes of the stem are rarely developed, so that the nodes 
from which the flower leaves arise are close together. More- 





Fig. 175. Fig. 176. 

Fig. 175. — Flower of sweetb^er rose, halved ; showing urn-shaped torus. Compare fig. 

go. Natural size.— After Bessey. 
Fig. 176. — The inflorescence of a fig, halved lengthwise ; showing common torus on 

whose interior surface many flowers are formed. Two fig wasps are near the opening 

of the flower chamber, one outside, while the other has just crawled in among the 

flowers. Natural size. — After Kerner. 

over, the axis is usually enlarged, so as to give greater space 
for the numerous leaves. This enlarged portion is called the 
receptacle or torus. When the leaves are removed or fall 
naturally the torus shows ordinarily a rounded or conical 
surface, with close-set scars left by their bases (fig. 172). 



* Since fertilization of the egg is the ultimate object of pollination and 
generally its final result, the terms close- or self-fertilization and cross- 
fertilization were formerly used. The word pollination is preferable. 



210 OUTLINES OF PLANT LIFE. 

When a great number of spore leaves are to be borne, the 
torus is elongated, as in the mousetail (fig. 173); or greatly 
enlarged, as in the strawberry (fig. 174); or transformed into 
a cup, as in the rose (fig. 175). 

When flowers in large numbers are very closely associated, 
as in the sunflower and its allies, the receptacles are joined 
to form a large common receptacle. The receptacle in such 
plants may be a cone, a dome, or a more or less flattened 
disk. In the fig the common receptacle is pear-shaped, with 
the edges almost meeting above and the flowers distributed 
over the inner face of the fleshy sac (fig. 176). 



EXERCISE XLV. 

1. Bisect a flower of marsh marigold lengthwise. Observe the three 
sorts of leaves, perianth, stamens, and carpels ; their relation to each 
other and their insertion separately on the enlarged stem, the torus. 
Separate some from an old flower and note the scars left by their fall. 

(1 278.) 

2. Are perianth leaves similar, or of two sorts? (% 293.) 

Dissect off a stamen. Observe the two parts : (a) the slender stalk, 
filament, and (0) the enlarged part, anther. Note in the anther the two 
lobes, each with a shallow groove marking the position of the two pairs 
of spore cases. Tear open the spore case with a needle and observe the 
innumerable pollen grains which they contain. Examine a naturally 
bursted anther and determine how they open. (^[ 287-289.) 

Dissect off and examine a pistil. (^[ 282.) Observe 

3. At the apex the roughened area, the stigma (^[ 283), sessile upon 

4. The enlarged part, the ovulary. Observe its flattened form and 
the grooves along one edge. Split it along this line, flatten it out care- 
fully and note the ovules attached to the edges. (^[ 286.) 

5. Cut several transverse sections of the pistil and observe the thick- 
ened edges of the carpel, forming the placenta, to which ovules are at- 
tached. Compare sections. Are all ovules attached to same edge ? 

6. Study and compare the flowers of the sweet pea {Lathyrus odora- 
tus), apple, fuchsia, and garden lily. 



VEGE TA Tl VE RE PROD UCTION. 



211 



III. Brood buds, etc. 

297. Simple forms. — In their simplest form brood buds 
consist of a single cell, though more commonly they are two- 
to several-celled. Like spores, they are supplied with re- 
serve food. The shape of brood buds is various. When not 
furnished with distinct organs, they are club-shaped, lentic- 
ular, or spherical. In some thalloid liverworts {Marchantia 
and Lunularia) they are produced on the surface of the thal- 
lus, surrounded wholly or on one side by an outgrowth from 
the surface forming a cup or a crescentic ledge (figs. 39, 
177). In some mosses brood 
buds arise from the apex of the 
stem, either in cup-like clusters 
of leaves or exposed (A, A', fig. 
178) ; in others they are smaller 





^MhJf 



tS^ 



A 
Fig. 177. Fig. 178. 

Fig. 177.— Thallus of Marchantia, seen from above, showing the cups containing brood 

buds. Natural size —After Kerner. 
Fig. 178. — Brood buds of mosses. A, upper part of the stem of Aulacomnium an- 
drogynum, with a cluster of brood buds at apex (magnified about 8 diam.), one of 
which is enlarged 120 diam. "in A'. B, tip of leaf of SyrrJiopodon scaber (magnified 
about 10 diam.) showing brood buds ; B' some more enlarged (about 40 diam.). — After 
Kerner. 

and simpler and are developed upon the leaves (£, B' , fig. 

178). In all the mossworts they belong to the gametophyte. 

298. Shoots. — In fernworts and seed plants the brood 

buds are especially abundant, and often reach considerable 



212 



OUTLINES OF PLAN '7' LIFE. 



size and complexity before being separated from the parent 
plant. They usually consist of a short axis with a growing 




Fig. 179. — Young plants developing from adventitious buds on leaves of a fern (As/>le- 
nium bulbiferum) % from which they readily separate to form new plants. A, natural 
size. B, magnified 2 diam. — After Kerner. 

point and at least rudimentary leaves. They generally arise 
upon the stem, more rarely from the leaves or the root (fig. 
179). Upon the stem they usually 
take the place of shoots of other forms, 
developing from axillary buds (figs. 
180, 182). If formed on leaf or root 
it is always from adventitious buds. 

Every possible gradation exists, from 
the simplest to those with well-devel- 
oped members, constituting a plant of 
some size. They may be artificially 
grouped as follows : 

299. (a) Buds. — In these the axis is 
short and the leaves scale-like. When 
Fig ,80— Fleshy buds in axils mos t highly developed the quantity 

of the leaves of a lily (Lili- ° J l i. J 

of reserve food is considerable and the 
parts of the bud are often distorted 
by enlargement to contain the food. The fleshy buds which 




um bulbi/eruni). Some- 
what reduced. — After Van 
Tieghem. 



V EG ETA TIVE REP ROD VCTION. 



213 



readily separate from the axils of the leaves of some garden 
lilies (fig. 180), and those which replace the flowers in some 
cultivated onions, are well known. (Compare also fig. 68.) 




Fig. 181. — Pond weed (Potamogeton crispiis). Detachment of special shoots, hiber- 
nacula, which are to hibernate under water. The plant A has one of these shoots at 
the tip ; B has just loosened one, h, which is sinking to the bottom. Two thirds natural 
size.— After Kerner. 

300. {b) Winter shoots. — Somewhat similar but more 
highly developed brood buds are formed at the approach of 
winter about the base of the stem in many perennials with 
herbaceous tops. These are separated by the death of the 
parent stem and produce new plants in the spring. Some 
aquatics show a similar habit, dropping short shoots to the 
bottom of the water in autumn, which are to grow in the 
spring (fig. 181). 

301. (c) Offsets, etc. — Some plants produce special 
branches, either underground or aerial, which develop at 
their extremities new plants, or special structures for their 



214 



OUTLINES OF PLANT LIFE. 



formation. The house-leek or live-for-ever (fig. 207) and 
stonecrop (fig. 182) reproduce themselves by offsets. These 
are short branches with a rosette of leaves at the tip which 
are readily detached and roll away, to take root at the first op- 
portunity and establish a new plant. 
The strawberry forms long leafless 
branches which take root at the tip 
and produce new plants, the slender 
runner subsequently perishing (fig. 0" 
183). The white potato forms at the 
end of slender underground branches 
elongated tubers upon which are 
numerous buds, any one of which, 
nourished by the reserve food in the 
tuber, may produce a new shoot. 
The slender stem by which the tuber 





Fig. 182 —A plant of stonecrop (Sedum dasyphyllum) Offsets are produced near 
the base on short branches O, O ; at the tip of longer branches, O' ; and in place of 
the flowers, O" . Natural size.— After Kerner. 



is connected with the main axis perishes at the end of the 
growing season (fig. 184). 

302. (d) Cuttings or scions. — Closely related to this 
mode of reproduction is that by the separation of fleshy 
members, upon which later are developed adventitious buds 
that give rise to new plants. The thick leaves of Bryophyl- 
lum are often blown off by storms, and produce new plants 
from buds formed at the teeth along the edge. Some species 
of Kleinia, natives of Cape Colony, have fleshy stems, jointed 



V EG ETA T1VE RETROD UCTION. 



215 



at intervals, so that they easily break there. When broken 
off by an accident, the piece rolls away, takes root from the 
under side, and sends up shoots from the upper. 

Advantage is taken of this power of several parts to form 
adventitious roots and shoots in the artificial propagation of 




Fig. 183. — Formation of runners in the strawberry, a, the mother plant ; b, young plant 
formed at tip of first runner ; c , plantlet at tip of second ; a third has put out from c. 
Slightly reduced. — After Seubert. 



domestic plants. Suitable portions of shoots or leaves for 
the development of new plants under proper conditions are 
called cuttings, scions, or " buds." They may generally be 
grown in water or soil ; or they may be securely fastened in 
a slit or wound in another plant. The latter process is 
known as grafting or budding, according to the form of the 
implanted part. Indeed brood buds in general may be 
looked upon as natural cuttings or scions. 

303. Summary. — Vegetative reproduction is usually ac- 
complished by the formation of small bodies which at matu- 
rity separate from the parent and grow into new plants. In 
the simplest plants the process consists of a separation of the 



2l6 



OUTLINES OF PLANT LIFE. 



parent into nearly equal parts, each of which then continues 
to grow. In most plants the bodies separated are small or 
minute, compared with the parent. They are either spores 




Fig. 184.— A seedling potato plant, c is the base of the stem, below which is the primary 
root, r. The primary leaves ct, are still present. The early leaves,,/, are not so. 
much branched as later ones will be. In the axils of the lower leaves arise the 
branches b, with scale leaves, e'c, and secondary roots, > '. The tips of these branches, 
when illuminated, bear foliage leaves,/'; but usually they thicken into tubers, tb, 
which have scale leaves, e'c' , in whose axils buds, br, are formed, the so-called " eyes " 
of the tuber. Natural size. — After Duchartre. 

or brood buds. Spores of water plants are often motile ; 
those of some water plants and most land plants are not, but 
must be distributed by winds, water, or animals. The 
spores are formed singly or in chains at the tips of special 



VEGE TA Tl VE REP ROD UCTION. 2 1 7 

branches ; or they are produced in spore cases, which break 
or are broken to set free the spores. The parts producing 
the spores are usually numerous and are closely associated. 

In the fernworts and seed plants the spore cases are usually 
formed on specialized leaves. When such leaves are clus- 
tered on a short stem, and especially when they are accom- 
panied by colored accessory leaves, they form a flower. The 
accessory leaves form the perianth (calyx and corolla) and 
the spore-bearing leaves are the essential organs (stamens 
and pistils). The stem from which they grow, the torus, is 
often enlarged when the leaves are numerous. 

Brood buds are usually larger and more complex than 
spores. In the lower plants they show no distinct members. 
In the fernworts and seed plants they often have rudiments 
of leaves and stems. Similar, but more developed parts, are 
separated by some plants to form new individuals. Propa- 
gation by cuttings, grafting, and budding is merely an imita- 
tion of natural methods. 



CHAPTER XVIII. 

SEXUAL REPRODUCTION. 

304. Cell union. — All methods of sexual reproduction 
consist in the formation of a single cell by the union of two 
specialized cells, known respectively as the male cell, or 
sperm, and the female cell, or egg, neither of them capable 
of growing further without such union. 

The organs and processes of sexual reproduction in plants are scarcely 
visible except with the microscope, and therefore will not be further dis- 
cussed here. (See the author's riant Life. ) 

The cell formed by sexual union is capable of developing 
into a new plant under suitable conditions. It may grow at 
once into a new plant, or it may remain dormant for a longer 
or shorter time. If it remains dormant it forms a resting spore. 
To protect itself, it thickens its wall, often very greatly.* It 
may then escape from the parent, but more commonly re- 
mains enclosed until set free by the death and decay of the 
parent. In the other case, the spore develops at once. 
Except in the brown seaweeds, whose eggs are ejected into 
the water before union of the sperms with them, the spore 
remains enclosed in the parent, within which it begins to 
form a young plant, the embryo. 

305. Seed. — In all but the seed plants the development of 
the embryo is uninterrupted until a mature plant is formed. 



* Thick-walled resting spores are also formed vegetatively. 

213 





SEXUAL REPRODUCTION. 2IO. 

In seed plants the embryo, which forms within an ovule (see 
T 280), and stimulates it to renewed growth, develops to a 
certain stage and then ceases to grow. With suitable protec- 
tion and food supply, it is then cast 
off as a seed, and, usually after a 
dormant period, continues its de- 
velopment until mature. The ripe 
seed consists of the following parts: 
(1) In the interior, occupying 
various positions and of exceeding- 
ly variable relative size, is the FlG . l8s . _ Seed of pansy; en tire"and 
embryo. (2) Immediately around K$ f^T^^SS^ 

:+. K^.„ « «-,•„„. „ ~ *. ■_■ (white and dotted 1. the seed-coats ; 

it lies a tissue containing reserve U, micropyie. Magnified about 10 
food, but this may be so shrunken diam - After Baillon - 
and emptied as to be recognizable only by microscopic 
examination. In that case the reserve food will have been 
absorbed by the embryo itself, which is then likely to be 
large and to occupy most or all of the space 
within the seed coats. (3) Upon the exterior 
one or two seed coats, more or less readily distin- 
guishable from each other (figs. 185, 186). 

Fl S l86 okeb S e e iS! Induced result of cell union. 

( Phytola cca 

decandra), 306. Fruit. — The growth of the embryo 

halved ; show- ° J 

ing curved em- excites not only the ovule to further develop- 

bryo next the y A 

two seed-coats me nt, but also the carpels which bear the ovules, 

and nearly sur- *■ 

rounding the an d no t infrequently even more remote parts. 

endosperm. x J x 

Magnified The carpels and their contents and adherent 

about 10 diam. x 

—After Baillon. p ar ts, when fully developed, constitute the fruit. 
The carpels are then known as the pericarp. The changes 
which the parts undergo are chiefly of two sorts — an increase 
in size and an alteration of texture. The increase in size re- 
quires no special explanation. The carpels may become 
dry at maturity, or may thicken and become soft and fleshy, 




220 



OUTLINES OF PLANT LIFE. 



or even juicy. In accordance with these differences,, two sorts 
of fruits are recognized, namely, dry fruits and fleshy fruits. 
Between these, however, there is no sharp Une of demarca- 
tion. 

307. Dry fruits. — If the pistil contain only one or two 
seeds, it very often does not open at maturity. Consequently, 
the seed-coats ordinarily remain thin, and the protective 
function is put upon the pericarp. In some cases the carpels 
become adherent at an early stage to the surface of the ovule, 



12 34 




187. — A small portion from the margin of a transverse section of grain of oats, 
1, 2, pericarp; 3, seed-coats; 4, remains of the sporangium; 5-7, endosperm; 5, 
gluten cells ; 6, cells containing large compound starch-grains (compare fig. 114) at 
7, richer in gluten, with less starch. Magnified about 325 diam.— After Harz. 

and at maturity the pericarp is so firmly attached that it can 
scarcely be distinguished from the seed-coats themselves. 
Such a change takes place in the fruit of most grasses, and the 
grain so formed is ordinarily mistaken for a seed (fig. 187). 
When dry fruits are one-seeded and indehiscent the pericarp 
usually bears whatever special contrivances are necessary for 
the distribution of the seeds. (See further ^f 395 ff. ) If, 
however, the pericarp contains many seeds, it generally breaks 
at maturity to allow the loosened seeds to escape. The ex- 
tent and position of the opening into the seed chamber or 



SEXUAL REPRODUCTION. 221 

chambers are exceedingly various. In some cases the open- 
ings are so small as to be mere slits or pores (fig. 188). In 
others a more or less circular line of breakage forms a little 
door or valve which opens and closes with changes of moisture 
(fig. 189). In other cases the pericarp splits lengthwise into 





Fig. 189. 
Fig. 188. — Ripe capsules of a wintergreen (Pyrola cklorantha'), showing dehiscence 

by pores. The opening is a short split at the middle of the base of each carpel. 

Natural size. — After Kerner. 
Fig. 189.— Ripe capsules of a bellflower {Campanula rapunculoides), showing small 

reflexed valves. Natural size.— After Kerner. 

two or more pieces (fig. 190), or, less often, cracks trans- 
versely so as to loosen a lid (fig. 191). 

308. Fleshy fruits. — The changes which produce fleshy 
fruits consist in a transformation of certain parts of the peri- 
carp into masses of thin-walled juicy cells. Other parts may 
remain unchanged, or may even become hardened. The 
inner part of the pericarp sometimes becomes of a stony hard- 
ness, while the outer portion becomes soft and juicy. Such 
changes produce a fruit like that of the peach or the cherry. 
The pericarp encloses a single seed with delicate brown seed- 
coats whose protective function has been completely usurped 
by the stone (fig. 192). In other cases, while the inner face 
becomes stony, the outer becomes fibrous, tough, and dry, as 



222 



OUTLINES OF PLANT LIFE. 



in the almond, walnut, and hickory nut. The outer part in 
the last even breaks regularly into four pieces. Such fruits 




P'iG. 190. — A, capsule of violet split open at maturity, the seeds still attached to the 
placentae. B, three pods of Lotus corniculatus ; a, just beginning to crack; t>, 
split throughout, with the pieces somewhat twisted ; c, empty of seeds, the two pieces 
fully dried and twisted. Natural size.— After Baillon. 



furnish a transition from the most perfect fleshy fruits to the 
dry fruits. In other cases the placentas become very much 
enlarged, and the whole of the pericarp 
becomes fleshy, as in the tomato. In 
others the outer part of the pericarp is hard 
and firm, while the inner becomes pulpy, 
as in the pumpkin and squash. 

309. Accessory fruits. — Parts adjacent 
to the carpels, either flower leaves or axis 
or both, stimulated to growth, frequently 

Fig. 191.— Ripe capsule 

ofpimpemeii04»rt£vi/- enter into the formation of fleshy fruits. 

lis arvensis), opening 

by a lid. Magnified These may be accompanied by either a 

several diam. — After 

Baillon. fleshy or a dry pericarp. In the winter- 

green berry the calyx grows thick and fleshy and surrounds a 
dry pericarp, which cracks at maturity (fig. 193). 




SEXUAL REPRODUCTION. 



223 




Fir. 



Fruit of the cherry, 
halved, e, epidermis of peri- 
carp ; m, fleshy layer of 
pericarp ; en, stony layer of 
pericarp ; s, seed ; cot, one 
of the pair of thickened seed- 
leaves of embryo. Natural 
size. — After Focke. 



In the strawberry (fig. 174) the torus becomes greatly enlarged 

and fleshy, while the minute, one-seeded, dry fruits are scat- 
tered over its surface, imitating small 

seeds. The fig has the same parts, 

with the torus concave, instead of 

convex (fig. 176). The apple consists 

of a fleshy torus carrying at its free 

end the withered calyx and enclosing 

the tough, thin pericarp (fig. 194). In 

the blackberry the receptacle becomes 

fleshy, and each pistil forms a minute 

fruit like a cherry, adherent to its 

neighbors and to the pulpy torus. 

The raspberry is like it, except that 

the adherent mass of fruits separates 

as a cap from a firm torus (fig. 195). 

310. Multiple fruits. — If the flowers are crowded, either 

dry or fleshy fruits resulting from them may be closely 

crowded at maturity. Under these conditions fleshy fruits 

frequently become adherent, and may thus constitute a 
multiple fruit quite similar in form to the fruit 
formed by the aggregated carpels of a single 
flower. Compare the multiple fruit of the 
mulberry (each section from a separate flower 
whose floral leaves and pistil both become 
pulpy; fig. 196) with such an aggregate fruit 
as the blackberry, in which each section is one 
pistil out of the many belonging to a single 
flower (fig. 195). The pineapple is similar to 
the mulberry in origin. 

Even more remote parts are stimulated to 
development by fertilization of the egg. The 
stem bearing the flower generally grows and 

becomes stronger, to carry the fruit, especially if large. The 




Fig. 193.— Fruit 
of wintergreen 
(Ga ultheria 
fir o c u >>ibe?is), 
halved, showing 
thin (dry) peri- 
carp, surround- 
ed by thickened 
fleshy calyx. 
Magnified 
about 2 diam.- 
After Gray. 



224 



OUTLINES OF PLANT LIFE. 



minute bractlets sometimes become highly developed beneath 
the fruit. The cup of the acorn and the husk of the hazle- 
nut originate in this way as the nuts form. The similar husk 
of the beechnut and chestnut encloses more than one fruit. 




Fig. 194.— Fruit of the apple. A, halved longitudinally; B, halved transversely. /, 

{>ericarp, enclosing seeds ; g t vascular bundles of the fleshy torus entering k, the calyx 
eaves. One half natural size.— After Focke. 





Fig. 195. Fig. 196. 

Fig. 195. — Vertical section of a flower of raspberry (Rubus uieeus), showing numerous 
pistils which form the caplike fruit over the enlarged torus ; stamens, corolla, and 
calyx all united at base. Magnified about 2 diam.— After Kerner. 

Fig. 196. — A, pistillate flower cluster of white mulberry; B, multiple fruit from same. 
Natural size.— After Baillon. 



311. Distributive arrangements. — The young of all plants 
must be so scattered as to prevent them from coming into 
sharp competition with the parents. In seed plants this dis- 
tribution occurs at the time of maturity of the seed, i.e., when 
the embryo has become dormant, and the food store and pro- 



SEXUAL REPRODUCTION. 22$ 

tective coverings have been completed. The devices by 
which seeds are scattered are dependent upon the number and 
character of the seeds and the nature of the pericarp. Plants 
adapt themselves so as to employ as distributing agents wind, 
water, and animals, or they develop special mechanisms for 
casting off the seed as a projectile. A consideration of these 
adaptations belongs to ecology. (See Chap. XXVI.) 

312. Renewed growth. — After a time, if the seeds become 
wet and are kept at a suitable temperature, with a supply of 
air, the embryo resumes its growth, i.e., the seed "germi- 
nates. ' ' This growth soon bursts the seed coats ; the food is 
digested and absorbed ; the young plant sends its roots into 
the soil and its leaves to the light, and by the time the food 
store is exhausted, is ready to make its own living. 

313. Summary. — Sexual reproduction consists in the 
union of a male cell and a female cell (neither able to grow 
further) to form a single new cell capable of growing into a 
new plant. The processes and organs are not described here. 
The direct result is the formation of a " resting spore " which 
remains dormant for a time ; or else the immediate develop- 
ment of an embryo plant. In the latter case the embryo, in 
all but seed plants, continues its growth, interrupted only by 
external conditions, until it becomes a full-grown plant. In 
the seed plant it becomes dormant while still small. Before 
its growth is interrupted, its development has induced the 
growth of the ovule, in which it lies, until the two form the 
ripe seed. Adjacent parts also grow and with the seed con- 
stitute the fruit. The changes in the growing parts produce 
dry, fleshy, accessory, or multiple fruits. The seeds are finally 
scattered by various ingenious devices. With a suitable sup- 
ply of heat, air, and water, the embryo resumes its growth 
and continues to grow until it forms a mature plant. 



PART IV : ECOLOGY. 

314. Definition. — Physiology, in its broadest sense, may 
be divided into physiology proper and ecology. Ecology is 
that portion of botanical science which treats of the relations 
of the plant to the forces and beings of the world about it, 
as distinguished from physiology proper, which treats of the 
relations of the plant as a whole to the chemical and physical 
forces within it. The forces without the plant necessarily 
limit and modify the action of the forces within it : conse- 
quently it is quite impossible to draw a sharp distinction be- 
tween those subjects which belong to ecology and those which 
belong to physiology proper. Parts II and IV, therefore, will 
be found to overlap in many places. Several of the subjects 
already treated under physiology belong in part to the present 
section. For example, the movements of plants are due not 
to internal causes alone, but to internal causes as modified by 
external conditions. In this part only a bare outline of the 
adaptations of plants in form and habit to their physical sur- 
roundings and to other living beings can be given. 

226 



I. NUTRITIVE ADAPTATIONS. 

§ I. ADAPTATIONS OF FORM AND STRUCTURE TO 
ENVIRONMENT. 

CHAPTER XIX. 

FORMS OF VEGETATION. 

315. Adaptation. — The various physical conditions which 
make up the " climate ' ' of any particular region of the earth's 
surface, together with the nature of the material upon or in 
which the plant grows, largely control the form and functions 
of the plants found in that region. Stated in other words, 
plants, in order to exist at all, are compelled to adapt them- 
selves to the places in which they grow. This compulsion is 
on pain of death. 

316. The struggle for existence. — The competition be- 
tween plants is intense. Only a very small portion of the 
seedlings which start in any particular area can come to ma- 
turity. Far the greater number will be killed by being robbed 
of light and of water by the overshadowing leaves and inter- 
lacing roots of their companions. Since such competition 
exists, it is evident that only those best suited to the condi- 
tions under which they grow will have any chance whatever 
to survive. 

Not only are individuals subject to this competition, but 
all individuals of a particular kind (a species) may be de- 
stroyed in any region through the competition of other 

227 



228 OUTLINES OF PLANT LIFE. 

species better suited to the conditions of that region. 
Through this competition between species one kind may be 
forced to migrate to some different region in order to main- 
tain itself. The capacity of a plant to adapt itself to differ- 
ent surroundings determines the possibility of its occupying 
a new region, for here it must come into competition with 
other sorts, and can only maintain itself if it is capable of so 
modifying its form and structure as to adapt them to the new 
conditions, and that, at least as well as the occupants it finds 
in possession. In the beginning it was probably by competi- 
tion between species that water plants were gradually forced 
to adapt themselves to an amphibious life, and then to a ter- 
restrial life, all the while advancing in complexity ; later some 
green plants adapted themselves to a parasitic or saprophytic 
life ; plants of moist regions gradually moved out and occu- 
pied even the deserts ; plants loving the shade adapted them- 
selves to the direct light of the sun ; and so on, until all 
parts of the earth's surface and even considerable depths of 
the ocean have been occupied. 

317. Environment. — In order to understand the variety of 
factors which are acting upon any particular plant, it will be 
instructive to consider the conditions which surround the or- 
dinary land plant. A portion of such a plant is embedded in 
the soil, and the remainder rises into the air. The subterra- 
nean part is profoundly influenced by the size and form of the 
soil particles, as well as by their chemical composition. It 
is exposed to contact with water varying in amount, some- 
times from day to day and always from time to time during 
the year, holding many substances in solution in varying 
amounts and kinds at different periods. It is subject, also, 
to variations of temperature from day to day and from season 
to season. 

The aerial part of such a plant is exposed to greater or less 
variations of temperature from hour to hour, from day to 



FOfiMS OF VEGETATION. 229 

night, from day to day, and from season to season. It is 
exposed to light varying in intensity from day to night, and 
from day to day, and to light differing in direction from hour 
to hour of each day. It is enveloped by fogs or mists, or is 
pelted by rain, hail, sleet, or snow, and sometimes completely 
buried in ice or snow. 

A plant has little or no power to alter any of the agents 
which act upon it, but it must be able to withstand the injuri- 
ous ones, or even to turn them to its advantage. It would 
be difficult to conceive a more complex set of factors to 
which adjustment must be effected ; and the more, since these 
conditions are combined with each other in an infinite 
variety of ways. Because the physical conditions vary in 
different parts of the earth's surface, the vegetation in each 
region differs from that in others. 

In any particular locality certain conditions of water, soil, 
air, temperature, light, and rainfall are likely to be associated. 
It is possible, in a somewhat arbitrary way, to recognize four 
general sets of conditions to which plants must adapt them- 
selves, in each of which the relation to water is the dominant 
factor. It should be understood clearly, however, that these 
sets of conditions pass into each other imperceptibly. Cor- 
responding to these four sets of external conditions, we may 
recognize certain characteristics in plant form and structure, 
which are likely to be associated, and it thus becomes possi- 
ble to distinguish four forms of vegetation corresponding to 
the four sets of external conditions. 

318. The first set of conditions consists of those charac- 
acterized by no extremes. Both the air and the soil are mod- 
erately moist; the rainfall is distributed through the year, or 
at least through the growing season ; there is no excess of salts 
in the water or in the soil ; the soil is usually enriched with 
organic matter, often in considerable amount. The plants 
which grow under these conditions are the ones most familiar 



23O OUTLINES OF PLANT LIFE. 

to people in the fertile regions of temperate climates. These 
may be reckoned as the average, or mean, plants, and are 
therefore called technically mesophytes. 

319. A second set of conditions is characterized by defi- 
cient water supply throughout the year, the amount of water 
present in the soil often being less than 10$. Such regions 
may be considered as regions of continuous drought. The 
plants adapted to these conditions are known as drought 
plants, or xerophytes. 

320. A third set of conditions, prevailing over compara- 
tively limited regions, is characterized by an excess of salts in 
the soil or water. These salts are chiefly common salt, gypsum, 
and magnesium chloride. Plants which can live under these 
conditions are known as salt plants, or halophytes. 

321. A fourth set of conditions is characterized by an 
excess of water. The plants grow wholly or partly sur- 
rounded by water, or their roots are embedded in a soil 
supersaturated with water, that is, containing at least 80$. 
Such plants are called water plants, or hydrophytes. 

It will be noticed that the first three groups, namely, meso- 
phytes, xerophytes, and halophytes, are essentially land plants 
in distinction from the fourth group, which are water plants. 

322. Summary. — In order to exist at all, plants must 
adapt themselves to the places in which they live. Compe- 
tition for light, water, and soil room is intense because of the 
number of individuals. Competition of better adapted kinds 
may exterminate or force migration. The factors to which 
plants must adjust themselves are many. Each factor is more 
or less variable and different factors may be combined in any 
ratio, producing almost infinite diversity. Plants differ, 
chiefly because of this diversity of conditions under which 
they grow, For convenience the water relation is used to 
group plants into four vegetation forms, mesophytes, xero- 
phytes, halophytes, and hydrophytes. 



CHAPTER XX. 

M E S O P H Y T E S . 

323. I. Mesophytes show certain general relations to ex- 
ternal conditions, many of which are also shared by other 
forms. Except to these minor variations in the environment, 
they show no special adaptations ; or, rather, they are looked 
upon as the normal plants, and the ways in which others 
differ from them are spoken of as special adaptations. In 
reality, however, the general methods by which they adapt 
themselves to their environment, which are now to be con- 
sidered, are quite as much special adaptations as those shown 
by plants living in extreme climates. These adaptations will 
be discussed in relation to each of the main factors of the 
environment. 

324. i. Air. — The composition of the air varies little from 
place to place. It is only in those regions in which it is 
rendered impure by artificial means, such as the vicinity of 
cities and factories, and in the few isolated regions in which 
it is vitiated by natural means, as in volcanic regions, that 
any special adjustments may be looked for. Artificial vitia- 
tion of the air kills off certain plants. A few plants have 
adapted themselves to air in the neighborhood of fumaroles, 
where they are subjected to vapors containing large amounts 
of sulfurous acid. Whatever special adaptations are found 
are internal, since only the very simplest plants find it pos- 
sible to live in such conditions. 

231 



232 OUTLINES OF PLANT LIFE. 

The movements of the air, however, influence profoundly 
the form of plants. This they do indirectly by the shifting 
of sands in sandy regions, and by their effect upon the pre- 
cipitation and upon the moisture of the atmosphere. Winds 
increase evaporation from the soil and from the surface of 
plants, and thus directly influence form. Trees growing in 
wind-swept regions are always low, bushy-branched, with 
the trunk and limbs inclined to leeward. The twigs on the 
windward side are often dead. Forests in wind-swept regions 
often thin out to windward, the trees becoming smaller and 
smaller, finally being replaced by bushes which become 
sparser until no woody vegetation is present. The leaves 
upon such plants are small and often peculiarly spotted. 
These effects upon the form have been ascribed to the me- 
chanical action of the air, to the presence of salts when in 
the neighborhood of the ocean or salt lakes, and to the re- 
duced temperature ; but probably none of these causes is to 
be looked upon as so efficient as the drying brought about by 
the prevalent wind. 

325. 2. Light. — Light affects plants directly through its 
influence upon their nutrition and upon the evaporation of 
water from their surfaces. In this way it affects ( i ) the rate 
of development. For example, the blossoming of flowers 
and the production of leaves occur earlier upon the sunward 
side of a tree or shrub than upon the other side. In the 
same cultivated crops of the north and south there will often 
be several days difference in the total number between sow- 
ing and maturing. Thus barley at northern Norway, in 68° 
N. lat., matures in 89 days, while at Schonen, in 56 N. lat., 
it matures in 100 days. Since the total hours of illumination 
must be about equal, the longer days of the north enable the 
plants to produce more food, and so to mature more rapidly. 
The forcing of vegetables under glass by the aid of electric 
light during the night depends upon the same principle. (2) 



ME SOPH YTES. 233 

The form of plant parts is directly influenced by light. Plants 
accustomed to the direct sunlight and those accustomed to 
shade show profound differences in habit. Light plants are 
stocky and compact ; their stems are inclined to be woody, 
the leaves are usually folded or crisped and often set at an 
acute angle with the direction of the light, and the surfaces 
are frequently hairy. In contrast, shade plants are slender 
and sprawling ; their stems often thin and weak ; the leaves 
flat and smooth and set transverse to the direction of the light- 
rays, while the surface is slightly, if at all hairy. (3) In inter- 
nal structure, also, there are decided differences, particularly 
in the leaves. These differences affect the skin, the number 
and distribution of the stomata, the form of the cells, and 
their contents. The sum of the differences distinguishes an 
upper (illuminated) from an under (shaded) side. 

326. 3. Temperature. — Temperature exercises an im- 
portant influence upon plants, both upon their aerial and sub- 
terranean parts. The temperature of the air is really much 
more important in controlling the adaptations, and conse- 
quently the geographic distribution, of plants than is light. 
The reason for this is to be found in the much more unequal 
distribution of temperature in various regions of the earth's 
surface. Moreover, temperature affects every vital function 
of the plant, for each of which a maximum, minimum, and 
optimum point may be determined. (See ^f 153, 219.) The 
variations in temperature to which plants are subjected require 
special adaptations. 

327. (a) Protection against changes of temperature. — 
These adaptations are to be found in the presence of special 
substances, such as oils or resins, which reduce the liability 
of the parts containing them to freeze ; in the reduction of 
the amount of water in the plant so that less damage results 
from freezing ; and, finally, in the presence of poor con- 
ductors of heat, such as scale-leaves and hairs in profusion, 



234 OUTLINES OF PLANT LIFE. 

a jacket of old withered leaves, etc., all of which insure slow 
thawing if the plant is frozen. The winter buds of trees in 
temperate climates illustrate all of these adaptations. 

328. (&) A dormant period is necessitated by low tem- 
perature during part of the year in temperate and arctic cli- 
mates. The period of vegetation in the higher latitudes is 
often very short. The same conditions prevail at high alti- 
tudes, with the same effects. In these regions, therefore, the 
plants are almost all perennials. In many cases the rudi- 
ments of flowers are formed in the year preceding that in 
which they are developed, in order that full opportunity may 
be given for the ripening of the seeds and fruits in the short 
growing season. Some plants adapt themselves to short 
periods of vegetation by the presence of evergreen leaves, 
which are ready at the first opportunity to resume their work 
of food manufacture. 

329. (c) The form of plants is modified by the tem- 
perature of the air and soil. Low temperatures are also 
likely to bring about the formation of dwarf plants. 

330. (d) The rate of development is strikingly influenced 
by variations in the temperature of the soil. The soil heat is 
chiefly derived from the sun. The amount of heat absorbed 
varies with the exposure of the soil, its color, porosity, 
amount of water, and the duration of illumination. The 
influence of the temperature of the soil is mainly indirect, 
acting through its effect on the water supply of the plant. 

331. 4. Moisture and precipitation. — The amount of 
moisture in the atmosphere largely determines the amount of 
evaporation from the surface of the plant. The relative 
amount of moisture in the atmosphere is exceedingly variable, 
and bears a direct relation to its temperature. Indeed, so 
closely related are the conditions of temperature, light, and 
moisture in the air, that the adaptations of shade plants, 
mentioned above, may be considered as the sum of the 



ME SOPH Y TES. 2$$ 

effects due to these three factors. It is difficult, if not im- 
possible at present, to say which are the effects of light and 
which of evaporation. 

Precipitation affects plants chiefly as it influences water 
supply. A few plants only of the higher forms are able to 
absorb moisture directly from the air, except as a last resort. 
(See ^J 165.) Many of the lower plants, such as the algae, 
lichens, and mosses, absorb rain instantly by their aerial 
parts. Some plants have adapted themselves to frequent and 
prolonged rainfall, bearing it often for months at a time ; 
other plants under such conditions lose their leaves very 
quickly. Rain-loving plants have their leaves furnished with 
elongated tips or with grooves and hairs to carry off the rain 
quickly. Their surfaces, also, are not readily wetted by 
water. Others protect themselves against the rain by adjust- 
ing the direction of their leaves to it so that a heavy, splash- 
ing rain strikes them at an acute angle. Others, by a move- 
ment of their leaves as soon as the sky is clouded, avoid 
injury from heavy rains. The branching of leaves in certain 
cases may be looked upon as a protection against heavy rain- 
fall. 

The snow cover through cold periods is for many plants 
essential as a protection against low temperatures during the 
dormant period. Others have adapted themselves to growing 
even in the midst of snow, putting forth their leaves and 
blossoms while still surrounded by melting snow. 

332. 5. Soil. — Both the chemical composition and the 
physical properties of the soil affect plants. The latter are, 
however, by far the most important. Here, again, the rea- 
son is to be found in the relation of the physical qualities of 
soil to the water supply. 

The water which permeates the soil takes up from it certain 
substances, and becomes thus a dilute solution of various 
salts. That the salts thus present in the soil water may affect 



236 OUTLINES OF PLANT LIFE. 

the form of the plant is strikingly shown in the occurrence 
of certain species of a genus only upon soils containing lime, 
while others of the same genus are found only in soils free 
from lime. When the local distribution of corresponding 
species of the same genus within the same region is deter- 
mined by the presence or absence of lime in the soil, com- 
parison of them indicates the general effect of lime salts upon 
the plant. Plants growing upon lime are usually stronger 
and more densely hairy, often hoary, while those on other 
soils are smooth or furnished with glandular hairs. The 
lime -loving plants have bluish-green leaves, as contrasted 
with the grass-green. Their leaves are also more numerous 
and more deeply branched, the flowers larger and their colors 
duller and paler. 

333. Summary. — Mesophytes have a moderate water sup- 
ply. Arbitrarily selected as the norm, their adaptations are 
nevertheless as numerous and important as those of other 
plants, but less striking only because they are familiar to the 
eye. Thus they adjust themselves in form and structure to 
the wind, the light, temperature, moisture and rainfall, and 
the soil. The light influences the rate of growth and de- 
velopment, and especially internal structure, often inducing 
a two-sided structure, as in leaves. Changes in temperature 
call out protective adaptation against sudden changes, and 
a dormant period (during winter), and also affect the form 
of plants, as do moisture of the air, rain and snow. The 
substances in the soil may also modify the form of a plant. 



CHAPTER XXL 

XEROPHYTES AND HALOPHYTES. 

334. II. Xerophytes. — The plants of dry regions blend 
by imperceptible gradations with the mesophytes. They 
reach their best development in desert and rocky regions. 
Some, especially of the lower forms, grow in such situations 
that they must adapt themselves to become so dry at certain 
periods that they may be powdered. Such, for example, are 
a few algse, many lichens, mosses, and a few fernworts. 
Adaptations in these cases must be looked for in the character 
of the cell contents. 

Other plants must adapt themselves to endure dry periods, 
such as those occurring from day to day, or between the wet 
and dry seasons, by retaining in their bodies sufficient water 
to sustain life. The following are some of the chief methods 
by which plants adapt themselves to periodic or continuous 
drought. 

A. Adaptations for reducing transpiration. 

335. i. Periodic reduction of surface exposed. — The 

dying away of an annual plant after forming its seed may be 
looked upon as an adaptation of this sort. Little evaporation 
occurs from the surface of the seed, which is thus adapted to 
withstand prolonged dryness. Perennial plants accomplish 
the same results when their annual shoots die off and leave 
only the rhizomes, tubers, and similar parts buried in the soil. 

237 



2 3 8 



OUTLINES OF PLANT LIFE, 



Perennial plants with perennial shoots may drop their leaves 
during the dry period and form them again upon the return 
of the growing season. The fall of leaves in our woody vege- 
tation is a similar adaptation to the cold season. The rolling 
or curling of leaves is a common mode of avoiding evapora- 
tion. It is common in grasses (fig. 197) and mosses. 

336. 2. The constant reduc- 
tion of exposed surface.— This 
may be secured among the leaves 
I by reducing them either in area 
or in number or both, or by 
much branching, with little 




*p 



Fig. 197. — Transverse sections of a grass leaf (Lasz'agrostis). A, open; B, rolled, 
when dry. The white plates are the ribs of mechanical tissue above and below a stele, 
one in each ridge ; the shaded areas are green tissue. The stomata are located low 
on the sides of the narrow grooves between the ridges, so that when the leaf is rolled, 
evaporation through them is hindered. Magnified 16 diam. — After Kerner. 



green tissue. Plants with bristle-shaped or needle-shaped 
leaves (figs. 63, 198), those with permanently rolled leaves 
(permanent form similar to temporary rolling shown in 
fig. 197), or those with scale-like leaves (fig. 71) show 
the various phases of such adaptations. Extreme reduction 
of surface is secured by suppression of leaves. In this case 
any further adaptation depends upon the stems, which must 
also provide for nutritive work. These may take the form 
of leaves (see ^| 96) ; or the branches may be thick, rigid, 
and fleshy (fig. 199) j or they may be thread-like or needle- 
shaped, as in the asparagus (fig. 67); or the stems them- 
selves may reduce their area by becoming fleshy and cylin- 
drical, prismatic, or spheroidal, as in the various forms of 
Cereus and melon cactuses. 

337. 3. Movements of parts to reduce the illumina- 



XEROPHYTES AND HALOPHYTES. 



239 



tion. — Certain leaves are adapted to a permanent profile 
position, that is, with the edges turned toward the sky, in- 
stead of the surfaces. (See ^| 243.) Others assume a profile 
position when the illumination 
becomes too intense. These 
positions, by placing the leaf 
surface oblique to the direction 
of the light rays, reduce the 
amount of evaporation very con- 
siderably. 

338. 4. Coverings, consisting 
of living or dead scale-leaves, 
stipules, leaf-bases or entire 
leaves, reduce transpiration by 
obstructing the free exchange of 
air, or by holding water and so 
keeping moist the surfaces they 
cover. 

339. 5. Structural modifica- 
tions. — These may occur either 
in the epidermis or some inter- 
nal tissues. (a) The epidermis 
may greatly reduce evaporation 
by the formation of hairs in such 
profusion as to form a cover for 
the surface (figs. 200-202). 
Hairs intended to protect from 
evaporation are usually dead and 
filled with air. Reflecting light 
from many points, they look white, and the surface seems hoary, 
or woolly, or silky. Hairs in the form of scales which overlap 
reduce the rate of evaporation by covering the stomata (fig. 
203). Further adaptations of the epidermis are to be found in 
the water- proofing of part or all of the outer wall of the epider- 




FiG. 198.— Shoot of larch, with ripe 
cone ; showing needle-shaped leaves 
on dwarf branches ; scale leaves on 
main axis. Natural size. — Afttr 
Kerner. 



240 



OUTLINES OF PLANT LIFE. 



mis (ep f fig. 205) ; the development of two or more layers of 
epidermal cells (fig. 208) ; or the excretion of wax or of 
varnish upon the surface of the epidermis. The latter often 




Fig. 201. 
Fig. T99.— Prickly pear (Ofnmtia vulgaris) with flattened jointed stem and no leaves. 

About one fourth natural size. — After Frank. 
Fig. 200. — Multicellular hairs of edelweiss. Magnified about 50 diam. — After Kerner. 
Fig. 201. — Silky unicellular hairs of Convolvulus Cneorum. Magnified about 50 diam. 

— After Kerner. 




Fig. 202.— T-shaped hairs of Artemisia mutellina. Magnified about 50 diam.— After 
Kerner. 



becomes very thick, giving to the leaves a shiny appearance. 
Wax is usually in the form of a bluish-white powder, which 
can be readily wiped off with the fingers, as from the surface 
of fruits, such as plums or grapes, the leaf of cabbage, or the 



XEROPHYTES AND HALOPHYTES. 



2 4 I 



stalk of sugar-cane (fig. 204). The interior layers of the 
wall of the epidermis are sometimes converted into mucilage, 
which retards the evaporation of water. 
The sinking of the stomata below the 
general level (fig. 205), their arrangement 
in pits (fig. 206) or in grooves (fig. 197), 
and their restriction to the under side of 
the leaf (fig. 206) may- 
be looked upon as 
further epidermal 
adaptations to reduce 
evaporation. In the 
leaves of some xero- 
phytes the guard cells 
of the stomata are 
only when 
young, becoming 
thick-walled and fixed when the leaf is mature. The stoma 
itself sometimes becomes closed, also. ( V) The internal 




Fig. 203. — Shieldlike scales of an oleaster (Elceagnns 
angustifolia), seen from above. Magnified about niOtile 
50 diam. — After Kerner. 




Fig 204. Fig 205. 

Fig. 204. — Portion of a transverse section through a node of sugar-cane, showing rods 
of wax secreted by the epidermis. Magnified 142 diam. After De Bary. 

Fig. 205. — Transverse section of a portion of the margin of a leaf of Aloe socotrina. 
r, thick cuticle; <u, cutinized layers of wall of epidermis, ef> ; p, green cells; cr, 
a crystal cell with needle crystals of oxalate of lime ; s/>, guard cells of stoma, 
sunk below surface ; a, intercellular space under stoma. Magnified about 175 diam. — 
After Tschirch. 



242 



OUTLINES OF PLANT LIFE. 



tissues of the leaves may be more compact. This reduces 
transpiration by restricting the area of the air passages. 








Fig. 206.— Portion of a vertical section of a leaf of oleander. ef>, epidermis of upper 
face ; e/>', same of lower face with stomata, .v, in deep pits with numerous hairs, t ; 
pal, palisade cells in two layers : s/>, spongy cells ; //, h', cells adapted to water stor- 
age. Chioroplasts shown only in left-hand side of the figure. Magnified about 175 
diam.— After Van Tieghem. 



B. Adaptations for taking up water. 

340. Absorption. — i. Some plants are adapted to imme- 
diate absorption of moisture in the air or of liquid water 
falling on their aerial parts. Such are, usually, the algae, 
lichens, and mosses which grow in exposed situations. 2. 
Certain of the higher plants are furnished with hairs adapted 
to the prompt absorption of rain or dew, e.g., Spanish moss. 



XEROPHYTES AND HALOPHYTES. 243 

3. Other plants adapt aerial roots to the absorption of 
moisture from the air, as well as falling water. (See ^[ 165.) 

4. Many are surrounded by the bases of dead leaves, which 
act as a sponge for absorbing water, and supply it gradually 
to the stem or younger leaves. Living leaves, sometimes 
singly, sometimes in clusters, form cuplike or tubular 
structures, acting as water receptacles, from which it can be 
absorbed as required. Such adaptations occur chiefly in 
epiphytes. (See •[ 357.) 5. Many xerophytes develop 
exceedingly long tap roots, which penetrate the soil deeply 
to a permanent water supply. 

C. Adaptations for storing water. 

341. 1. Special cell contents. — The simplest of these 
adaptations is the presence of mucilage. The presence of 
acids, tannins, and certain salts perhaps aids in the retention 
of water. 

342. 2. Water-storing tissues. — (a) Fleshy plants, or 
succulents, are those which thicken their parts by the devel- 
opment of cells, which contain a large quantity of water, and 
usually much mucilage. 
These mucilage-con- 
taining parts form a 
reservoir for the storing 
of water. In such 
plants the epidermis is 
very strongly water- 
proofed ; the stems are 
thick, cylindrical, pris- T 

J -"■ tig. 207. —A plant of houseleek (Semperznv7t)n 

matic Or Spheroidal ; tectorum), showing fleshy leaves arranged in a 

1 ' rosette, with offsets formed at the ends of special 

the leaves are Wanting branches. These become detached and form in- 

& ' dependent plants. About one half natural size. — 

or they are thick and After Gray. 

fleshy, cylindrical or broad (fig. 207), and arranged in 

rosettes. 




244 



OUTLINES OF PLANT LITE. 



(3) In non-succulents, the epidermis itself may be greatly 
developed as a water-storing tissue, or it may form great num- 
bers of bladdery hairs which 
are richly supplied with 
water, as in the well-known 
"ice-plant," on which the 
hairs glisten like ice. 

In the first case, the epi- 
dermis, instead of forming a 
single layer of cells, may 
develop into several layers, 
the lower ones large and 
thin-walled, as in begonias, 
figs, and peppers (fig. 208). 
The cells immediately under 
the epidermis sometimes 
become transformed into a 
water-storing tissue, as in 
the oleanders (fig. 206) ; or 
strips of tissue extending 
from the upper to the lower 
side of the leaf may act as 
reservoirs of water. 

343. 3. Tubers and bulbs. 
— These forms of the shoot, 

Fig. 208. — Strip from a vertical section of ... , • t^i v A 
leaf of Peperomia trichocarpa. J, from which are HCMy Supplied 
a fresh leaf; w. water-storing tissue, com- . . ■, ■, 

posed of the multiple epidermis of the upper With Water, may alSO De 
side ; a, chlorophyll-bearing cells; s, spongy , . , , , 
parenchyma with sparse chloroplasts and COUnted, in part at least, aS 
much water. B, the same after four days' , . r 
transpiration at 18-20 C. The tissue to is ail adaptation IOr Water- 
much collapsed, the walls being plaited ; 
j also shrunken, but a as before. Magnified Storage, 
about 50 diam. — After Haberlandt. _ . . __ T TT <■ ■% . 

344. III. Halopnytes. — 

The salt-loving plants, though they may grow where water 
is abundant, are strikingly similar in most of their characters 
to the xerophytes. This similarity is to be explained prob- 




XEROPHYTES AND HALOPHYTES. 2\% 

ably by the difficulty of securing a suitable water supply. 
They grow near the ocean, upon the shores of salt lakes, by 
salt springs, and in the interior of the great continents in old 
lake basins in which the salts have accumulated by the rains. 
A few of the halophytes are trees and shrubs, with leathery 
leaves, but almost all are succulents. In habit they are gener- 
ally low, often creeping, with thick, fleshy, and more or less 
translucent leaves and stems, containing comparatively little 
chlorophyll and abundantly supplied with water, and the 
surface generally smooth. 

345. Summary. — Drought plants adapt themselves to a 
scanty supply of water by (a) reducing the transpiration, [b) 
providing means of securing water, or (c) by storing water. 
Reduction of transpiration may be secured by periodic or 
permanent reduction of evaporating surface, by avoiding di- 
rect light, by water-proof or wax-covered skin, by mucilage in 
the cells ; or by obstructing the stomata with coverings of 
scales or hairs. Adaptations for securing water are special 
absorbing organs on aerial parts, cuplike parts for holding 
water, and long roots to reach deep soil w r ater. Adaptations 
for water-storage are water-holding substances in the cells, 
cell specialized as water reservoirs, and thickened shoots such 
as tubers and bulbs. 

Salt plants are mostly succulents, and show adaptations 
similar to the drought plants. 



CHAPTER XXII. 

HYDROPHYTES, 

346. IV. Hydrophytes may be divided into three groups : 
i. Slime plants, which grow in the mud or slime at the bot- 
tom of bodies of water. Here belong many algae, especially 
diatoms, many species of low fungi, and -bacteria in great 
numbers. 2. Submersed plants, either free or attached. 
Many algae, including both the diatoms and the filamentous 
algae, are found floating in the water at various heights, 
sometimes near the surface, sometimes more deeply submersed. 
Since their substance is heavier than water, their capacity to 
sustain themselves depends upon the production of gases in 
the interior of the cells, or upon the presence of gases en- 
tangled among their filaments. A few of the higher plants 
are also found submerged and free, such as the bladder-worts. 
The number of free-floating plants of the larger kinds is 
small compared with those attached. The higher algae, 
moss-worts, fern-worts, and seed plants are usually fastened 
in the mud or to sticks and stones. The thallus of the algae 
is usually profoundly branched and the shoots of the mosses 
are richly supplied with leaves. All of the submerged fern- 
worts and seed plants are characterized by a very delicate 
epidermis, the absence of stomata, and the extensive surface 
due to the very profuse branching of the stems or leaves, or 
to the great number of these, or to both. In all cases the 
extensive green surface may be looked upon as an adaptation 
to securing carbon dioxid and the manufacture of sufficient 
food by means of the weak light in a situation where there is 

246 



HYDROPHYTES. 247 

no danger from lack of water. 3. Floating or partly sub- 
mersed plants, either free or attached. Many of the filamen- 
tous algae and diatoms float free at the surface. The chief 
characteristics of the higher floating plants which root in the 
mud are these : their floating leaves are simple, little branched 
or not at all, roundish or elliptical in form, leathery, and the 
surface not easily wetted; stomata are present only on the 
upper surface, and the leaf stalks are adapted in length to 
the depth of the water in which they grow ; the woody 
tissues are either entirely absent or poorly developed, be- 
cause there is no occasion for the transportation of water, 
nor need of rigidity, since the medium in which they grow 
supports most of the w r eight. 

347. Light. — Green water plants are limited in their 
distribution by the depth to which light can penetrate water. 
This does not exceed, even in pure waters, four or five hun- 
dred meters. No seed plants have been found at a greater 
depth than thirty meters, and few algae at a greater depth 
than forty meters. Plants which are brought up by dredging 
from lower depths than this are usually those which have been 
detached and sunk. 

348. The temperature of the water is very much less sub- 
ject to variation than that of the air, never falling, except at 
the surface, below 0.5 C. 

349. The movements of the water are of much importance 
to plants in bringing air and food materials to them. These 
movements are wave movements, or surf, and currents. 
Plants growing within the limits of wave action are often 
damaged or torn away by the waves. The Sargasso Sea is 
marked by an accumulation of such plants, mainly of brown 
algae, which have been swept to the quieter parts of the North 
Atlantic by currents after having been detached by the waves. 
Such plants may often live for a long time and may even 
continue their development. 



248 OUTLINES OF PLANT LLFE. 

Plants adapt themselves to currents, such as those in fresh- 
water streams, by their slender form, which is characteristic 
of plants in flowing waters, as seen in filamentous algae and 
the much-divided leaves of higher plants. Currents of water 
act as a stimulus upon certain plants, producing a direct re- 
action in the mode of growth. 

350. The composition of the water affects chiefly the dis- 
tribution of plants, in a manner similar to the presence of 
salts in the soil. In the ocean waters the percentage of salts 
is extremely variable in different regions ; in some places it 
is as low as 0.5 per cent., while in others it reaches 4 per 
cent. In fresh waters the differences in kind and amount of 
dissolved salts are chiefly due to differences in the soils which 
the streams drain. 

351. Summary. — Water plants may grow in the mud or 
slime at the bottom ; submersed, and either free or attached; 
or floating and either free or attached. The light, temperature, 
movements of the water and the composition of the water are 
the principal factors to which water plants must adapt them- 
selves. 



§ II. ADAPTATIONS TO OTHER PLANTS. 

352. Plant associations. — Each set of external conditions 
brings about the association of certain plants with one another, 
because they have adapted themselves to those conditions. 
The four groups just considered may be looked upon as plant 
societies of the most general kind. Within each of these 
four it is possible to distinguish a number of smaller societies 
determined by a more limited range of conditions. 

Besides these plant associations, however, there are those 
which are determined by the relation of the plants to one 
another, as affording mechanical support, or assistance in the 
work of nutrition. The plant associations of this kind only 
are now to be considered. 



CHAPTER XXIII. 

ADAPTATIONS TO OTHER PLANTS AS SUPPORTS. 

Certain plants serve others as carriers, acting purely as 
mechanical supports. To these supports plants have adapted 
themselves in various ways. In many instances dead objects 
of similar form may serve the same purpose. The supported 
plants are, therefore, partly independent of the others, though 
in most instances in nature they rely upon living supports. 

353. i. Climbing plants. — Climbing plants are those that 
develop lateral organs, sensitive to contact, which become 
recurved or coil about a support of suitable shape and size, or 
form adhesive disks by means of which they cling to rough 

249 



25O OUTLINES OF PLANT LIFE. 

surfaces. These lateral organs take the place of leaves or of 
lateral shoots, and are known as tendrils (figs. 69, 102). 
(For their form see ^[ 99, 131; for their action, 1" 225, 251). 

354. 2. Clambering plants are those which form lateral 
organs not sensitive to contact, and by means of them sup- 
port themselves on adjacent plants. Recurved leaves, shoots, 
and prickles (fig. 99) may serve these purposes. 

355. 3. Twining plants are those which have adapted their 
shoots to winding about a support of suitable size. (See % 
249.) 

356. 4. Root climbers have adapted their aerial roots to 
attaching the plant to rough surfaces. (See ^[ 82.) Such 
structures are found only in fernworts and seed plants. 

357. 5. Epiphytes. — This name is rather loosely applied 
to those plants which are attached only to other plants, though 
they derive no food from them. All kinds of plants have 
representatives in this group. Algae, diatoms, and other 
small water plants attach themselves to other algae and the 
higher water plants. Lichens, liverworts, mosses, ferns, 
orchids, bromelias, etc., are abundant upon trees. Epiphytes 
are attached by hairdike rhizoids, or by hold-fasts, which 
apply themselves to the roughnesses or even penetrate the 
outer dead parts of the supporting plant, but do not absorb 
from the living tissues either water or food materials. The 
water supply is provided for (1) by adaptations for absorbing 
rain or dew, mists, or even dampness, instantly, either by the 
surface, as in algse, mosses, and lichens, or by means of hairs, 
as in the Spanish moss and other seed plants ; (2) by adap- 
tations to catch the water in living or dead leaves and hold 
it, either by capillarity or as a vessel, long after precipitation 
has ceased. Many of the simpler epiphytes are adapted to 
become dry without injury, while the larger ones are inhabit- 
ants of moist tropical regions, where the danger of drying is 
avoided and it is possible to obtain an adequate water supply. 



PLANTS AS MECHANICAL SUPPORTS. 25 1 

Their food materials are derived entirely from the air and the 
water which falls upon them, while the mineral salts are ob- 
tained from the dust which has been carried by the air and 
accumulated upon the surface of the supporting plant, or 
among the mass of dead and decaying leaves and other de- 
bris about the base of the epiphyte. Organic matter from 
the decay of the older parts may also be reabsorbed. 

An adaptation to this mode of life is marked in the repro- 
ductive bodies. Of all epiphytes the seeds or spores are either 
light and carried by the wind ; or the seeds are sticky and 
carried by birds and other animals ; or they are eaten by 
birds and voided upon the trees where they are adapted to 
germinate. 

358. Purpose. — In most cases, the use of other plants as 
supports has been adopted to secure for the smaller and 
weaker plants proper exposure to light for making food. 
For example, so dense are the tropical forests that only by 
climbing to the tree-tops or perching on the branches can the 
lowlier plants secure an adequate amount of light. Even in 
the temperate zone the advantage in climbing for light is 
obvious. 

359. Summary. — Plants rooted in the soil adapt them- 
selves to use others as mechanical supports by the develop- 
ment of tendrils or aerial roots for climbing ; recurved leaves, 
shoots, or prickles for clambering ; and long, swinging sensi- 
tive shoots for twining. Others use their neighbors as the sole 
support, being perched upon them but deriving no food from 
them. (Those which do absorb food are parasites. See 
^[ 184). In most cases the purpose of such adaptations is to 
secure light. 



CHAPTER XXIV. 

SYMBIOSIS. 

360. Living contact. — Not only are different species as- 
sociated through the influence of similar surroundings which 
they find congenial, but certain plants adapt themselves to 
such an intimate relation with others that they live in imme- 
diate contact with them. This intimate association is known 
as symbiosis. When the parties to symbiosis stand to each 
other in the relation of partners, each furnishing certain 
materials or conditions advantageous to the other, the asso- 
ciation is called mutualistic symbiosis or mutualism. When the 
relation of the parties is that of master and slave, one indi- 
vidual deriving advantage from the labor of the other and in 
return furnishing it suitable conditions for existence, the 
association is a form of mutualism known as helotism. Finally, 
when the relation of the parties is that of an unwilling host 
and an unwelcome guest, one individual being fastened upon 
by the other from whose presence it is unable to free itself, 
the symbiosis is called parasitism. (See ^[^j 44, 45, 46, 
184.) 

A. Mutualism. 

361. 1. Between plants of the same species. — Mutualism 
may occur between individuals of the same species. Illus- 
trations of this are to be seen in the massing of the lower 
algae into colonies, in some of which certain individuals may 
be differentiated from others for the purpose of carrying on 

252 



SYMBIOSIS. 253 

a function of advantage to the colony. (See •^j 10, 11, 
17.) In a somewhat similar way certain bacteria are found 
always massed into colonies of characteristic outline, of 
which one form is shown in fig. 209. In the higher fungi, 




a 



A B 

Fig 209. — A, worm like colonies of Chontlrowyces serpens, composed of numerous 
rod-shaped individuals, />', a, which multiply by fission, />, and secrete a mass of jelly 
which holds them together. A, magnified 45 diam. ; B, 750 diam. — After Thaxter. 

also, the mycelium may be looked upon as a thallus formed 
by the aggregation of many individuals ; for, while it is pos- 
sible to have mycelium produced from the development of a 
single spore, it is not common. The mycelium is generally 
the result of the union of hyphae (see ^| 43) arising from 
many spores. Even in such cases the mycelium may con- 
stitute a single body, and may give rise to a single fructifica- 
tion. 

362. 2. Between plants of different species. — Mutualism 
is more common between plants of different species. It 
takes the following forms : 

363. (a) Lodgers. — The higher plants often shelter vari- 
ous species of lower ones within their internal chambers, or 
in pockets formed by lobes or bladders of various sorts. 
This relation is especially common between water plants and 
algae. Species of Nostoc live in the air spaces of liverworts 
and duckweeds, in the roots of some land plants, and in the 
leaf-lobes of liverworts. Some species of the higher algae, 
also, are frequently associated with other species to which 
they attach themselves. That they are not merely epiphytes 
(see 1] 357) is shown by the fact that certain algae are found 
only upon certain other kinds, and do not grow indifferently 



254 



OUTLINES OF PLANT LIFE. 



upon any plant which would furnish them similar external 
conditions (fig. 210). 

364. (b) Mycorhiza. — Mutualism between the roots of the 
seed plants and certain fungi is common. Such a combina- 
tion of root and fungus is called a mycorhiza. The fungus 




Fig. 210. Fig. zix. Fig. 212. 

Fig. 210. — A portion of a filament of an alga {Ectocarftus) showing at a another alga 

(Entoderma Wittrockii) which has embedded itself in the cell-wall. Magnified 480 

diam.— After Wille. 
Fig. 211. — A tuft of rootlets of white poplar forming mycorhiza. Natural size. — 

After Kerner. 
Fig. 212. — Tip of a rootlet of beech (Eagus sylvatica) with fungus mantle, the loose 

hyphae acting as absorbing organs in place of root hairs. Magnified 100 diam. — After 

Frank. 

forms a jacket over the outside of the root (figs. 211, 212), 
taking the place and work of the root hairs by means of 
strands of hyphae extending from the surface of the fungus 
jacket (fig. 212) ; or it grows inside the cortex and epider- 
mis, forming knotted masses (fig. 213) ; or it is confined to 
certain definite portions of the roots, forming upon them 
swellings from the size of a hazelnut to the size of a man's 
head. The first form is especially common upon the roots 
of the oak, elm, walnut, apple, pear, maple, ash, and related 
trees. It has also been found upon the roots of a large num- 
ber of herbaceous plants. The second form belongs chiefly 



SYMBIOSIS. 



255 



to the heaths and orchids. The third form grows upon 
alders, bayberry, etc. 

365. (c) Root tubercles of Leguminosae. — A peculiar case 
of mutualism appears in the bean family between the roots 
and bacteria. The latter produce 
upon the roots small swellings from 
the size of a grain of wheat to that 
of a hazelnut (fig. 214). The 
presence of these bacteria, in a 
way yet unexplained, certainly en- 
ables the plant to use free nitrogen 
from the atmosphere, while other 
plants are required to obtain it 
from the soil in combination with 
other things. The enrichment of 
the soil by growing clover and 
similar crops upon it and plowing 
them under is explained by their 
ability thus to accumulate nitrogen 
from the air. 

366. 3. Between plants and 
animals. — Mutualism also occurs 
between plants and animals. 
Various species of plants attach 
themselves to animals by which 
they are carried about. The plant 
is thus aided in obtaining the ma- 
terials for food, and not infrequently the plant conceals the 
animal from another which seeks it as prey. In this way 
certain crabs are hidden by algae attached to them. 




Fig. 213. — Mycorhiza of orchids. 
A bit of longitudinal section of 
root of Neottia, near the tip. e, 
epidermis ; p. a series of cortical 
cells filled with fungus. Into the 
cell a (nearer the tip of root) the 
hyphae are just entering; in the 
cells above, i, recently entered, 
they have only formed a small 
knot about the nucleus. Magni- 
fied about 200 diam. — After 
Frank. 



B. Helotism. 

367. 1. Fungi and algae. — Helotism exists between fungi 
and algae, constituting the bodies known as lichens, in which 



256 



OUTLINES OF PLANT LIFE. 



the fungus is the master and the alga the slave. (See 1" 48, 
and figs. 215, 216.) The same fungus may be found en- 
slaving more than one species of alga? even within the same 

mycelium. The proto- 
nema of mosses (see ^[ 
59) or even the leaves of 
some small plants may 
be surrounded by a my- 
celium. The enslaved 
green plants are generally 
unicellular or filamentous 
algae. If the latter are 
the species whose colonies 
produce voluminous gela- 
tin, the texture of the 
lichen body is gelatinous ; 
otherwise it is tough and 
leathery. Some of the 
fungi which ordinarily 
associate themselves with 
algae to form lichens may 
exist free as saprophytes. 
The alga itself influences 
the form of the thallus more or less profoundly according 
to its relative amount. The same fungus associated with 
different algae produces lichens which are described as differ- 
ent species, or even as different genera. 

368. 2. Animals and algae. — Helotism exists between 
animals and algae. Various simple animals, such as radio- 
laria, stentors, hydras, sponges, echinoderms, and worms, 
enclose algae in their bodies and utilize the products of their 
food manufacture. The algae thus enslaved are all minute 
unicellular forms which multiply within the animal body by 
fission (*[ 260). 




Fig. 214. — A young clover plant, showing tuber- 
cles, t, on the roots. Natural size. — After 
Goff. 



S Y MB 10 SIS. 



257 



C. Parasitism. 



369. 1. Fungi. — A very large number of colorless plants 
have adapted themselves to live upon living plants or ani- 
mals which they 
force to act as their 
unwilling hosts. By 
the presence of the 
parasite the normal 
functions of the host 
or its normal growth 
or both are more or 
less seriously inter- 
fered with, so as to 
produce disease, 
slight or grave, local 
or general, accord- 
ing to the circum- 
stances. Many ani- 
mals are thus preyed 
upon by 
and fungi, 




Fig. 215. — A lichen {Parmelia conspersa) growing on 
a stone, showing the leaf-like thallus (mycelium), with 
many cup-like fructifications. Natural size. — After 
Frank. 



bacteria 
Most communicable diseases, such as typhoid 
fever, diphtheria, and tuberculosis, are 
known to be due to the transfer of the 
parasite from the diseased individual to the 
healthy one. In a similar way bacteria live 
as parasites upon green plants, causing 
disease and often death. The number of 
fig. 216 -Hyphae of bacterial diseases among plants is relatively 

a lichen, Cladotaa 

furcata (see fig. 36), small, for comparatively few bacteria have 

enveloping an alga, 

Protococcus. Mag- been able to adapt themselves to living in 

nined 950 diam. — x 

After Kemer. the acid cell sap of plants. The number of 

diseases of plants due to parasitic fungi, on the contrary, 




258 



OUTLINES OF PLANT LIFE. 



is very large. (For the mode by which parasitic fungi gain 
entrance to the bodies of their hosts, see ^[45.) 

G 




Fig. 217.— Roots of a yellow Gerardia, G, attached to the root of a blueberry bush, B. 
They enlarge at the points of contact and there send haustoria into the host root. 
Natural size.— After Gray. 

370. 2. Seed plants. — A few seed plants have adapted 
themselves to a parasitic life upon others. Some may be 




Fig. 28. — A, European dodder twining about a hop stem. All but the uppermost coils 
show the groups of wartlike swellings from which haustoria penetrate the host stem. 
Natural size. B, Germination of same. The various stages are arranged in order 
from right to left. In the last stage the seedling has found a suitable support and has 
absorbed all the reserve food in the thickened lower end, which has withered and died, 
freeing the plant from the ground. Magnified about 2 diam. — After Kerner. 



SYMBIOSIS. 



259 



reckoned as semi-parasitic, having still green leaves and true 
roots. In addition, however, special organs are developed 
for attaching the parasite to the roots of other plants, from 
which at least a water supply and probably food materials 
are absorbed (fig. 217). Other semi-parasites, such as the 
mistletoe, attach themselves to the host above ground, and 
have no true roots of their own. Some parasitic seed plants 
twine about their hosts, and send 
into them absorbing organs by means 
of which they derive all their food 
from the host. Such is the yellow 
parasitic vine known as dodder (fig. 
218, A). These plants germinate 
in the ground, and as seedlings 
possess true roots, but after attaching 
themselves to the host the lower part 
of the stem dies away so that the 
true roots are transient (fig. 218, B). 
Some parasites have the body so 
reduced that it merely forms a net- 
work or a hollow cylinder outside 
the wood of the host and under the 
bark. From this curious body the 
few flowers break through the bark 
and appear upon the surface of the 
root or stem of the host, quite as though they were a part of 
it (fig. 219). 

371. Summary. — Plants may live in such relations that 
one is directly dependent upon the other for its food supply, 
or they are mutually dependent for food or advantageous 
conditions. Animals may likewise be directly dependent on 
plants associated with them. Mutual dependence may exist 
between plants of the same species, but is commoner between 
plants of different kinds. One kind may lodge in cavities or 




Fig. 219. — A twig infested with 
a parasitic seed plant {Afiodan- 
thes) whose body is hidden 
under the bark of the host, 
through which a short branch 
bearing a few scale leaves and 
a single flower bursts. Natural 
size.— After Kerner. 



260 OUTLINES OF PLANT LIFE. 

internal chambers in the other. Fungus filaments associate 
themselves with roots, particularly of trees. Bacteria, in con- 
nection with roots of the bean family, enable them to acquire 
nitrogen from the air, as other plants cannot. Fungi and 
algae, in the relation of master and slave, form the lichens. 
Algae are similarly enslaved by a few animals. A great 
number of fungi and bacteria attack other plants and also 
animals, causing more or less extensive deformity and dis- 
ease. Only a few seed-plants live as parasites upon others. 



§ III. ADAPTATIONS TO ANIMALS. 

CHAPTER XXV. 

ANIMALS AS FOOD, FOES, OR FRIENDS. 

1. Carnivorous plants. 

372. Nitrogen supply. — The ordinary source from which 
green plants obtain nitrogen for the making of their food is 
the nitrogen compounds dissolved in the soil water. Plants 
which live where the soil water contains little or no nitroge- 
nous material are forced to resort to another source of supply. 
Some plants solve the problem by entrapping animals, deriv- 
ing from their bodies the desired nitrogen compounds. Such 
plants are called carnivorous plants, or, since the bulk of 
their catch consists of insects, insectivorous plants. The 
catching of animals is done 

373. i. By pitfalls and traps. — (a) The various pitcher 
plants furnish a fine example of well-devised pitfalls. The 
leaves of these plants have a deep, trumpetlike tube making 
up the body of the leaf; or they carry at the end of a long 
petiole a deep cup with a lid, as in the tropical pitcher plants 
(fig. 220; see also fig. ioi). The tube is one-third or half 
full of water, in which are always found numbers of dead or 
dying insects. The sides of the tube without are often made 
attractive by gaudy colors or by lines of sweet secretion, 
which draw both flying and crawling insects. Within, its 
surfaces are either excessively smooth, so as to afford no foot- 

261 



262 



OUTLINES OF PLANT LIFE. 



hold to an insect attempting to crawl out ; or covered by- 
stiff, downward-pointing hairs to oppose its passage ; or the 
side of the tube is filled with thin translucent spots through 
which the captives vainly strive to fly, while the real opening 

is concealed. By one or 
other of these means the 
prey is prevented from 
escaping, and sooner or 
later is drowned in the 
liquid. In this liquid di- 
gestive substances or bac- 
teria quickly dissolve the 
softer parts of the insect 
bodies, and the soluble 
portions are absorbed by 
the leaf. 

(5) The bladderwort, 
which abounds in quiet 
pools, furnishes an excel- 
lent illustration of traps 
(figs. 221, 222). Upon 
the leaves are numerous 
minute bladders, each with 
a small opening about 

Fig. 220.— .4 , trumpet-shaped sessile leaf of Sar- which divergent hairs Serve 
racenia variolaris, showing thin membran- 
ous windows in the meshes of the veins of the as guides to the entrance. 

hood which arches over the mouth of the 

trumpet. B, cup-shaped petioled leaf of Ne- The entrance is lightly 

penthes villosa, with elevated lid and margin 

ribbed. One-third natural size.— After Kerner. closed by a flap of mem- 
brane, which is readily lifted by minute water animals. 
After they have passed through the opening the membrane 
drops behind them, and is stiff enough to prevent their 
escape. Death ensues sooner or later, and absorbing hairs 
on the inner face of the trap take up the nutritive ma- 
terials. 




ANIMALS AS FOOD, FOES, OK FFJENDS. 



263 



374. 2. By adhesive surfaces. — Animals are also cap- 
tured by adhesive surfaces. These surfaces are covered by a 




Fig. 22t. — A bladderwort iUtricularia Grafiana), showing an aerial flower stalk 
carrying an open flower and a second one above from which the corolla has fallen. 
Some stems bear numerous, finely branched leaves, b, and others the large bladders, 
b'. See fig. 222. A shoot of a smaller species is shown at ft, with bladders and 
leaves on same stem. About two-thirds natural size.— After Kerner. 



sticky fluid secreted by numerous glandular hairs, and upon 
these many small insects may be found dead. In many 



264 



OUTLINES OF PLANT LIFE. 



cases the softer parts of the insect bodies are digested and 
absorbed. It should be noted, however, that adhesive sur- 




Fig. 222. B Fig. 223. A 

Fig. 222. — A bladder of Utricularia vulgaris, halved lengthwise, with an imprisoned 
crustacean, Cyclops, a to b, opening, with hairs, //, /, about it; b to c, cushion-like 
rim, b-c part cut through, d-e surface on which the flap, /", rests, opening inwards 
only ; g, wall of bladder set with absorbing hairs within and glandular hairs without ; 
k, the stalk (secondary petiole). Magnified 20 diam. — After Cohn. 
Fig. 223. — Two leaves of sun-dew (Drosera rotundi/olio). A, in expanded position 
showing the tentacles B, shortly after the capture of an insect. The tentacles on the 
right half are inflexed to bring the glandular tips in contact with the prey. Magnified 
2| diam.— After Kerner. 

faces are also merely protective against the visits of unwel- 
come guests, who steal nectar or pollen. (See ^f 394.) 

375. 3. By move- 
ments of traps and 
adhesive surfaces. — 
Somewhat more com- 
plex methods of cap- 
ture are exhibited by 
leaves which have 
special movements 
connected with traps 
or sticky surfaces. 

Fig. 224. — Cluster of leaves at the base of flower-stalk 
of Venus' fly-trap {Dioncea muscipula). One-half The SUndeW Of Olir 
natural size. — After Drude. , 

swamps has the edges 
and surface of the leaves covered with many outgrowths, 




■-35V 



ANIMALS AS FOOD, FOES, OR FRIENDS. 



265 



each of which is tipped by a large gland (fig. 223). The 
clear, glistening fluid, a large drop of which is secreted by- 
each gland, is sticky enough to 
entangle even insects of consider- 
able size, which alight upon the 
leaves. The viscid secretion 
envelops the struggling insect, 
and at the same time the branches 
Jf_ of the leaves bend slowly inward 
until more and more of the sticky 
glands are thrust upon it. The 
character of the secretion then 
changes. It becomes 
more watery and con- 
tains substances which 
soon digest the softer 
parts of the body. 





Fig. 225. P"ig 226. 

Fig. 225. — A, blooming plant of Aldrovandia vesiculosa. Natural size. — After 

Drude. B, a single circle of leaves seen from the center above, showing stalk and 

two semicircular lobes. Magnified \\ diam.— After Caspary. 
Fig. 226. — Transverse section through closed trap of Aldrovandia, showing on inner 

face long sensitive hairs and many absorption hairs. Only the central part is three 

layers of cells thick ; a broad margin is only one cell thick. Compare appearance in 

£, fig. 225. Magnified 20 diam.— After Caspary. 

These are absorbed, and play an important part in the nu- 
trition of the plant. 

Dioncea (fig. 224) and its water mate, Aldrovandia (fig. 
225), have leaves whose blades are somewhat like a spring 
trap. The blade is two-lobed, with a hinge along the middle 



266 OUTLINES OF PLANT LIFE. 

(figs. 137, 226). The hinge is in reality a cushion of tissue 
upon the back, which quickly throws the two halves of the 
leaf together when the sensitive hairs on the inner face of 
the trap are touched. The movement is sudden enough in 
Dioncea to catch the slow-flying insect, or, in Androvandia, 
the minute water animal. The prey is prevented from escap- 
ing by the interlocking, tooth-like lobes along the edges of 
the leaf. Digestion and absorption of the foods follow.* 

II. Herbivorous animals. 

376. Protection. — While a really insignificant number of 
minute animals are eaten by plants, a very large number of 
plants find it necessary to protect themselves in some way 
against destruction by browsing animals, insects, snails, and 
slugs. Since the animal world relies for its food supply 
ultimately upon the green plants, it is plain that no such 
protective measures are completely effective. The protec- 
tion, therefore, may be looked upon as a protection against 
extermination rather than against injury. As protective 
adaptations against browsing animals are usually reckoned : 

377. 1. Armor, in the form of hard, leathery, sharp- 
edged, woolly, bristly, or sticky parts, especially leaves 
(figs. 200, 201, 202, 227); or thorns (figs. 103, 228), prickles, 
or stinging hairs (fig. 229). 

378. 2. Distasteful or injurious substances, such as 
volatile oils, camphors, acids tannins, alkaloids, etc. The 



* Travesties upon these strange methods of nutrition appear periodic- 
ally in newspapers, and plants of remarkable size and forbidding aspect 
are represented as capturing birds, animals, and even men, that ven- 
ture into their neighborhood. It should be noted, therefore, that in all 
cases the plants which capture animal food entrap only the smaller ani- 
mals, scarcely any of them, except those caught by the pitcher plants, 
larger than the common house-fly. 



ANIMALS AS FOOD, FOES, OR FRIENDS. 



267 



milky juice of plants like milkweeds, which often contains 
acrid substances, may also be protective. 

379. 3. Mimicry. — Certain plants c 

which are not distasteful or disagreeable 
have adopted the same form of leaves 
and stem and the general habit of those 
which grazing animals have found dis- 
tasteful. This mimicry causes them 
to be avoided, as well as the really 
hurtful ones which they imitate. 

380. 4. Ants.— In the 
tropics particularly, cer- 
tain plants secure them- 
M' 




Fig. 227. Fig. 228. Fig. 229. 

Fig. 227. — Edge of a leaf of a sedge {Carex stricta), showing alternate epidermal cells 
pointed and underlaid by two layers of mechanical cells. Magnified 200 diam.- -After 
Kerner. 

Fig. 228. — Part of a shoot of barberry in spring showing leaves of preceding year as 
persistent three-pointed thorns, in whose axils the buds are developing into the sea- 
son's shoots. Natural size. — After Kerner. 

Fig. 229. — A stinging hair of the nettle {Urtica), in longitudinal section, x, emerg- 
ence in which the single-celled hair nbc is sunk below ab. The knoblike apex c is 
easily broken off because the cell wall just below it is thin and brittle. The oblique 
cutting edge left pierces the skin like a hypodermic needle and some of the acrid cell 
contents enters the wound, causing intense itching. Magnified 60 diam.— After 
Frank. 

selves from the attacks both of browsing animals and leaf- 
cutting insects by encouraging the presence of colonies 
of warlike ants upon them, and making provision for 



268 



OUTLINES OF PLANT LIFE. 



their defenders' wants. A very large number of species * 
protect themselves in this way. For the ants the plants 
provide (a) nec/ar, similar to that secreted in the flower 
(i.e., a watery solution of various 
sugars), but secreted by nectaries 
outside the flower ; (b) fodder, in 
the form of hairs (fig. 230), often 
of peculiar from, richly supplied 
with nutritive substances, grow- 
ing from special parts of the sur- 
face, which are regularly eaten 
by the ants and grow again, so 





Fig. 230. Fig. 231. 

Fig. 230. — Bit of a section through the cushion (c, fig. 231) at base of leaf of Cecrofiia, 
showing the velvety hairs with which it is covered, and among them the egg-like 
bodies, rich in proteids and fats, which the ants collect and carry into their nests in 
the interior of the stem. Magnified about 10 diam. — After Schimper. 

Fig. 231. — Apex of the hollow stem of a young Cecropia. a, the thin spot above a 
leaf, which at b has been gnawed through by the ants to make their nests in the cavity 
of the stem ; c, the cushion at base of leaf stalk where food bodies grow. See 
fig. 230. Two-thirds natural size. — After Schimper. 

that a constant supply is at hand ; (c) dwellings of various 
sorts. Certain plants have the stems hollow throughout, 
with special modification of the structure at certain spots, so 
that an entrance to these hollows may be readily made (fig. 



* More than three thousand are listed by Delpino. 



ANIMALS AS FOOD, FOES, OK FRIENDS. 269 



231). In others, portions of the internodes are much en- 
larged and hollow ; sometimes only the internodes in the 
region of the flower clusters are thus transformed. In other 
plants chambers are produced by the bladdery enlargement 
of the under part of the leaf near the midrib (fig. 232). In 
some acacias the stipules are developed 
as large hollow thorns, which the ants 
inhabit. 

381. 5. Crystals. — Plants protect 
themselves against soft -bodied animals, 
such as snails and slugs, by means of 
the sharp-pointed crystals which are 
present in the leaves of many species. 
According to Stahl, all tissues contain- 
ing these crystals are avoided by such 
animals, but will be readily eaten by 
them after the crystals are removed. 

382. Summary. — Carnivorous plants 
use small animals, especially insects, 
as food, capturing them by pitfalls, 
traps, or adhesive surfaces, and either 
digesting and absorbing the useful parts, 

or after the slower decay, absorbing certain substances. Many 
plants protect themselves against browsing animals by armor, 
by distasteful or injurious juices, by mimicking distasteful 
or hurtful plants, or by harboring fierce ants which attack 
anything that disturbs the plant they have made their home. 
For the ants some plants provide not only shelter but food. 




Fig. 232.— Under side of the 
base of the leaf blade of To- 
coca lanci/olia, showing 
bladder on each side of mid- 
rib, each with entrance at 
a, a. Natural size (?). — After 
Schumann. 



II. REPRODUCTIVE ADAPTATIONS. 

CHAPTER XXVI. 

PROTECTION AND DISTRIBUTION OF SPORES 
AND SEEDS. 

The present knowledge of reproductive adaptations among 
the fiowerless plants is very imperfect, though probably many 
exist. This chapter, therefore, must discuss chiefly the 
adaptations in the more complicated reproductive structures 
of seed-plants which have been most studied, with only inci- 
dental allusions to such arrangements in the lower plants. 

I. Protection against bad weather. 

383. By movements. — Pollen unfitted to resist low tem- 
peratures or wetting must be protected from rain, cold, and 
similar conditions. When nectar is secreted in the flower as 
an attraction to insects it is liable to be washed out by rain 
unless access of water to the interior of the flower is pre- 
vented. To avoid these dangers, many plants upon the 
approach of unfavorable weather bend their leaves so as to 
close the flower (fig. 233), or arch the stalk so as to turn the 
blossom into such a position that the rain or snow will not 
reach the sporangia or the nectaries. These movements of 
the leaves and stalk are combined in various ways to meet 
the needs of each particular form. All of them are growth 

270 



DISTRIBUTION OF SPORES AND SEEDS. 27 1 

movements, brought about by variations in light and tem- 
perature, which act as stimuli. (See % 244.) 

II. Adaptation to distribution of spores. 

The fact that spores are found in every group of plants 
from the lowest to the highest makes it probable that a great 





Ftg. 233. — A, flower of California poppy (Esckscholtzia), opened in sunshine; B, the 

same, closed in wet weather. Natural size. — After Kerner. 
Fig 234. — A, aerial hypha of Pilobolus crystal/inus, with spore case. The hypha is 

swollen beneath the spore case and very turgid. B, the same with spore case torn 

off at base and being shot away by the violent escape of the mucilaginous contents of 

the hypha. Magnified about 10 diam. — After Kerner. 

variety of ways will have been adopted by plants to secure 
their distribution. The more important ways may be grouped 
as follows : 

384. 1. By turgor and tension. — Among the fungi, spores 
are often forced out of the spore case by the pressure upon 



272 



OUTLINES OF PLANT LLFE. 



it of neighboring parts, increasing until the spore case rup- 
tures suddenly and the spores are shot out like projectiles. 
In some plants the whole spore case is thrown off in this 
fashion, often to the distance of a meter or more (fig. 234). 
The fungus which attacks and kills house flies in summer 
casts off the single spore from the end 
of the stalk carrying it by the bursting 
of the end of this stalk through ex- 
cessive turgor (fig. 235). With the 
spore goes the contents of the stalk, 
so that it is surrounded by a mass 
of mucilage, thus enabling it to adhere 
to any object which it strikes. 
Filaments carrying the 
spores often twist upon drying 
and thus jerk off the spores 
as they suddenly slip past 
some obstruction. When 
spores are produced in chains, 
there are devices to separate 
B A them at maturity so that the 

FIG.235-/J a fly killed by the fly fungus lightest breath may carry 

(hm/>iis<t M usees), stuck to wall by hyphae ^ J 

and surrounded by a halo of the spores, them away. The teeth around 

Iwo-thirds natural size. />, hyphae pro- J 

jecling into the air from the body of the the mOllth of the CaOSllle of 
fly, from whose tips spores are being shot x 
off Several are shown in various stages m0 SSeS Serve tO distribute the 
of development. 1 he turgor of the en- 
larged end of hypha finally ruptures the S p res at opportune intervals, 

attachment of the spore and it is shot off * 1 L ' 

surrounded by the mucilaginous contents instead of having them 
which cause it to adhere to any object ° 

struck. Magnified 200 diam C, a spore emptied Ollt all at OllCC (See 

enveloped in mucilage. Magnified 420 r v 

diam. -After Kerner. fig. 46, A.) Ill SOIlie Cases 

the teeth, by their form and hygroscopic curvatures, serve to 
sling out the spores to a short distance. In many ferns the 
spore cases are furnished with a spring-like structure (the 
annulus) along the greater part of the edge, which tends to 
straighten itself upon drying, thus rupturing the spore case. 




DISTRIBUTION OF SPORES AND SEEDS. 273 

After bending backward for some distance until the tear 
gapes wide, the spring suddenly straightens and hurls the 
spores to a considerable distance (fig. 236). 




Fig. 236. — Spore cases of the male fern {Aspidium Filix-mas) scattering the spores. 
A , closed ; B, burst by the drying of the annulus ; C, the annulus after becoming 
strongly recurved is just returning to a nearly straight form and the spores are thereby 
being hurled toward B. Magnified about 65 diam. — After Kerner. 

385. 2. By water. — In perfectly quiet water, distribution 
of spores depends solely upon their own motor organs. Only 
zoospores (see \\ 264) are so furnished. For these a film of 
water is sufficient, and they may swim some distance over 
what appear to be merely moist surfaces. Most of the algse 
and fungi living in water form zoospores. Their production 
is often controlled by external conditions, the formation of 
new individuals being thus provided for when the old are 
threatened with destruction. 

In flowing water and by currents, non-motile spores are 
readily distributed, and even relatively heavy spores may be 
carried long distances by water currents. The pollen of 
aquatic seed-plants is sometimes carried to the stigma by 
water currents, as in Vallisneria (fig. 237). 

386. 3. By air currents. — Spores may be readily carried 
by the air on account of their small size and their ability to 
withstand dryness. Most spores float in the air for some 
time as dust particles, and the slightest current is adequate 



274 



OUTLINES OF PLANT LIFE. 



to lift many and carry them along. Spores of most non- 
aquatic fungi, mosses, and fernworts are distributed by air 
currents. The pollen of some seed-plants, especially the 
common forest trees, is carried in this way. 




Fig. 237.— Pollination of eel-grass {Vallisneria spiralis). The large flower is a pis- 
tillate one, with stigmas fringed on under side. About it are floating staminate flow- 
ers in various stages of development, having broken from submersed stems which 
bore them. The ones on the right and left have the boat-shaped perianth lobes turned 
back, stamens mature, and pollen exposed ; one has floated so that the pollen is 
brought into contact with the stigma of the pistillate flower. Magnified 10 diam — 
After Kerner. 

387. 4. By animals, especially insects. — It is the seed- 
plants, particularly, which have adapted themselves to the 
distribution of spores by this means. The pollen must be 
carried to the ovules of gvmnosperms or to the stigmas of 
angiosperms and lodged there. It has been clearly shown 
not only that adaptations for securing this result have been 
developed, but also that there have arisen various ingenious 
adaptations to secure cross-pollination and to prevent close- 
pollination. (See % 295.) Some of these may be here 
enumerated. 



DISTRIBUTION OF SPORES AND SEEDS. 2?$ 

388. Adaptations for cross-pollination. — (a) The sepa- 
ration of the stamens and pistils, staminate flowers and pistil- 
late flowers being produced upon different parts of the same 
plant or even upon different plants of the same species ; (b) the 
early ripening of the stamens so that they discharge their 
spores before the stigma of the same flower is exposed or 
receptive, or vice versa ; (c) arrangements preventing the 
pollen from reaching the stigma of the same flower, which 
vary according to the different modes by which the transfer 
of the pollen is made ; (d) the failure to form good seed 
when close-pollination happens. 

389. Adaptations for close-pollination. — But close-pollin- 
ation, even though it results in weaker offspring, is better 
than entire failure to produce progeny. Therefore, some 
plants permit close-pollination in the event of failure to 
secure cross-pollination, while a few have adaptations which 
insure it. Our common violets produce in the late spring 
and early summer inconspicuous blossoms which do not open, 
containing stamens with few pollen grains. These flowers, 
however, produce seed abundantly, and always by close- 
pollination. Various other species have similar arrange- 
ments. 

390. Adaptations to insects. — The adaptations to secure 
cross-pollination through the visits of insects are so numerous 
and so varied, and the advantage in the number and weight 
of seeds produced is so marked, that for most seed-plants 
cross-pollination must be considered the far more desirable 
process. Flowers are adapted to insect visitors in the fol- 
lowing w T ays : 

391. (a) Food, etc. — They provide for their visitors edi- 
ble substances, such as nectar and pollen, * material for nest 
building, shelters, or breeding places. 

* The pollen is often produced in great excess of the plant's own 
needs. 



2?6 OUTLINES OF PLANT LITE. 

392. (b) Advertisements. — They advertise the presence 
of such attractions in two ways, which are sometimes com- 
bined, and insects accustomed to visit flowers quickly learn 
to know what the advertisements mean. (i) By color. 
Flowers are so colored as to attract notice ; and this is fur- 
ther secured by the large size of individual flowers or by 
massing many small flowers into close clusters, (ii) By odor. 
Odors are due to volatile oils, usually in the petals or sepals, 
often curiously localized. Dusk- and night-blooming plants 
often have heavy odors. 

393. (c) Form and position of parts. — Many plants by 
the form of their flower-leaves provide landing places for 
welcome visitors. Guides to the location of the nectar, in 
the form of grooves, folds, hairs, lines of color, etc., are 
often present. The form and position of the stamens and 
pistils are often such as to insure the desired transfer of pollen. 
These positions may be permanent or they may be secured by 
movements at opportune times. Among the movements are 
those due to turgor and those due to the presence of motor 
organs. In a very large number of cases, by the form of the 
flower-leaves and the essential organs the plant is adapted to 
visitation by particular insects, and if these are not present, 
or if their access is denied, constant failure to set seeds is the 
result. Thus one may distinguish plants adapted to bees, 
moths, butterflies, flies, birds, or even snails. 

394. (d) Exclusion of unwelcome visitors. — In addition 
to provision for welcome guests must be enumerated the 
methods of excluding unwelcome guests, which on account of 
their size and habits are unable to bring about the desired 
transfer of the pollen, while at the same time they rob the 
plant of nectar or pollen provided for more acceptable visitors, 
(i) Various obstructio?is within the flower may render access to 
the nectar impossible to the smaller and weaker insects, while 
allowing others to reach it. Such obstructions are formed 



DISTRIBUTION OF SPORES AND SEEDS. 2JJ 



by folds, hairs, and other outgrowths upon the flower-leaves 
or on the essential organs (fig. 238). (ii) Obstructions out- 




Fig. 238.— Flower of Cobeea scandens, halved; showing tu r ts of hairs on the base of 
the filaments, of which there are five ; these close the bottom of the corolla cup, where 
nectar is secreted, against intruders. Three-fifths natural size. — After Kerner. 

side the flower may exclude crawling insects. Such are sticky 

surfaces and hairs (fig. 239), moats about the stem formed by 

cup-shaped leaves holding 

water, or those formed by / . 

water in which swamp plants | 

grow. (iii) The time of 

blooming also prevents the 

visits of any insects except 

those flying at that particular 

season. 

III. Adaptations to the 
distribution of seeds. 

395. After the ripening 

Fig. 239.— Flower of a saxifrage (Saxifraga 
Of the Seed Various devices controversa), protected against invasion 

by the numerous sticky glandular hairs on 
and forces Operate tO Scatter the flower stalk, ovulary, and calyx. Mag- 
nified several diam. — After Kerner. 

them at as great a distance as 

possible from the parent, so that the young plants will not 
come into competition with the old ones or with each other. 
This object, which is secured in lower plants by the distri- 
bution of the spores, can only be attained in seed-plants by 




278 



OUTLINES OF PLANT LIFE. 



scattering the seeds, which contain the young plants in a 
dormant condition. 

The methods by which distribution is secured may be 
grouped as follows : 

396. 1 . Distribution by tension and turgor. — Some plants 
(e.g., witch hazel) as they ripen the seed vessel, alter its tis- 
sues in such a way that the contained seeds are compressed as 




Fig. 240.— Elastic valves for slinging seeds. A, fruit of wild geranium (G. fialustre) 
with persistent calyx. The five carpels surround an elongated torus, from which they 
break first at bottom ; curling upward suddenly they sling the seed out of the basal 
part which has cracked along the inner side. B, fruit of touch-me-not (f»i/>atie>/s 
noli-»ie tangere), one sound, the other bursted. The carpels have curled up elasti- 
cally from the base and slung out the seeds. Natural size. — After Kerner. 

it dries, and after it opens they are pinched out from the nar- 
rowing valves, as a wet apple or melon seed may be shot from 
between the thumb and finger. In others (e.g., touch-me- 
not and cranesbill) the parts of the seed pod shorten on one 
side until the strain breaks them loose, when they suddenly 
become elastically curled and sling the seeds contained to a 
considerable distance (fig. 240). Somewhat similar causes, 
i.e., curvatures due to unequal shrinkage or swelling of the 
parts, enable some fruits with long awns or bristles to creep 



DISTRIBUTION OF STORES AND SEEDS. 279 




over the ground or to bury themselves in it when alternately 
moistened and dried (fig. 241). The seed vessel of the 
squirting cucumber is so distended by the almost liquid pulp 
surrounding the seeds that it ejects the mass through the 
opening formed by its separation from the stem. 

397. 2. Distribution by water. — In some plants 
this is secured by the fact that the fruits open only 
when moistened. In such cases the seeds may be either 
washed out from the opening pods by rain, or may be 
loosened in many other ways. The seeds are thus set 
free at the time best suited to their prompt germination. 
Some plants, adapted to dis- 
tribution by water, are pro- 
vided with floats. These 
floats may consist either of 
the enlarged and bladdery 
seed pod (or some portion of 
it), or of the spongy, air- 
filled seed coat. The fruits 
or seeds are thus made more 
buoyant and float upon the 
surface instead of sinking as 
usual. Naturally, water-lov- 
ing plants are chiefly adapted 
to distribution in this manner. 

398. 3. Distribution by- 
winds. — Some plants which 
secure their distribution by 
winds are only lightly attached 
to the soil at maturity, so that they are readily uprooted and 
carried bodily, when dry, for considerable distances by the 
wind. The transfer is facilitated by the incurving of the 
branches upon drying, so that the uprooted plant is more or 
less spherical in outline, or by the fact that the plant is nor- 



Fig. 241. -Pieces into which the fruit of 
storksbill breaks. There are five of 
these each corresponding to a carpel and 
arranged on the sides of a prolonged 
torus as in A , fig. 240. A , when dry the 
beak is spirally coiled ; B. when moist. 
The base is hard and very sharp. Magni- 
fied about 2 diam. — After Noll. 



28o 



OUTLINES OF PLANT LIFE. 



mally spherical by the proportion of the branches. Such 
plants are known as " tumble weeds." Singly or aggregated 
in large bundles they are rolled over plains and prairies for 

long distances, shaking out 
their seeds as they go, or 
opening their fruits when 
moistened. 

Another adaptation for 
distribution by the wind 
is the small size of some 
seeds. Those of some 
orchids are so diminutive 
that it takes 500,000 to 
weigh 1 gram. Such 
minute seeds are readily 
blown long distances by 
the wind. Relative light- 
ness is also secured by the 
construction of some seeds, 
which are surrounded by a 
voluminous coat contain- 
ing many large air spaces 
(fig. 242). Outgrowths 
from parts of the seed coat 
or pericarp also secure 
the same end. In such 
cases the fall of the fruit or seed through the air is so retarded 
that it may be carried laterally some distance by the wind. 
No seeds, however small, float long in quiet air, since buoy- 
ancy is derived only from air-containing tissues. A flattened 
form of the fruit or seed is very common, and this form is 
often exaggerated by the formation of wings, i.e., of thin out- 
growths from the surface (fig. 243). The center of gravity 
in such cases is so placed that the plane of flattening will be 




Fig. 242. — Seeds of an orchid i Va7i<ia teres), 
with cells of seed coat bladdery and filled with 
air. These seeds are ejected from the capsule 
by the contortions of the hairs on its inner 
faces which curve and twist as the moisture in 
the air varies. Magnified 100 diam. — After 
Kerner. 



DISTRIBUTION OF SPORES AND SEEDS. 28 1 



nearly horizontal when the seed falls. These fruits or seeds 
sink from 2 to 30 times as slowly as the same bodies without 
the wing. Sometimes special floats are used for this purpose, 




A B 

Fig. 243.— Fruits with wings. A , fruits of ailanthus tree (A . glandulosus), each carpel 
with double wing. B, fruits of a maple tree, each carpel with a single wing. Natural 
size. — After Kerner. 

as in dandelion and thistle (fig. 244). Hairs of the most 
various origin are produced in such numbers and position as 
to form either parachutes or tangled woolly envelopes to the 
fruit or seeds (figs. 245, 246). 

399. 4. Distribution by animals. — To secure this there 
are two general methods observable, (a) The seed or fruit 
is either adapted for transport by adhering to the body of the 
animal ; or (#) the seeds are surrounded by edible parts, and 
at the same time so protected against the digestive juices that 
they may pass uninjured through the alimentary canal. A few 
plants are distributed by animals which collect and hide their 
fruits or seeds (e.g., the squirrels). The adhesion of fruits or 
seeds to animals, especially to those which are provided with 
fur, is generally secured either by surfaces made adhesive by 
the sticky secretion from glandular hairs, or by the develop- 
ment of outgrowths in the form of hooks or barbed prickles 



282 



OUTLINES OF PLANT LIFE. 



(figs. 247, 248, 249, 250). A few water animals and wading 
birds distribute seeds which happen to fall into the mud by 
the adhesion of this mud to their bodies. 

The fleshy fruits with edible parts are usually colored to 
attract the notice of the fruit-eating animals. Seeds which 



escape crushing by 
the teeth or grinding 
in the gizzard are 
apt to be in condition 
to germinate when 
voided. The seeds 
of the mistletoe are 
separated from the 



.... ■ V :'■ V : ; 




Fig. 245. 



Fig. 244. 



Fig. 244. — Heads of fruits of the dandelion ; single fruits falling, exposing common 

torus and involucre. Natural size.— After Kerner. 
Fig. 245.— Fruits of a willow, burst, and allowing the seeds, each with a tuft of silky 

hairs (coma), to escape. Natural size. — After Kerner. 



pulp of the berry by the birds which eat them, and, sticking 
to the bill, are wiped off on the branches of trees, where they 
germinate. 

The adaptation of plants to any one of these agents of dis- 
tribution is likely to be more or less effective with other 
agents. For example, the tufts of hairs which increase the 
buoyancy of the seed in air would be equally effective should 



DISTRIBUTION OF SPORES AND SEEDS. 283 




Fig. 246. — A fruit of Barbadoes cotton, open, exposing the voluminous hairs (commer- 
cial cotton) which clothe the seeds. Natural size.— After Kerner. 




A B 

Fig. 247. Fig. 248. 

Fig. 247.— Fruit of Agrimonia, halved; showing torus, carrying calyx and withered 
stamens above, covered with hooks, and enclosing the hard pericarp, with a single 
seed. A pistil which did not mature lies to the right. Compare torus in fig. 175. 
Magnified about 8 diam. — After Baillon. 

Fig. 248. — Fruit of tick trefoil (Desmodium Canadense). A , pods which separate into 
sections, each containing one seed. They are covered with stiff hooked hairs, some 
of which are shown enlarged at B. A, natural size. B, magnified about 20 diam. — 
After Kerner. 



284 



OUTLINES OF PLANT LLFE. 




the seed chance to alight upon water, or they may suffice to 
entangle the seed in the fur of animals. 

400. Adaptations for germination. — Adaptations for dis- 
tribution not infrequently also secure advantage in germina- 
tion. It is important for 
many seeds that they be 
anchored to the ground when 
they have once been trans- 
ported, so that they may not 
be subject to further disturb- 
ance. Such anchorage is 
sometimes secured by the 
transformation of the outer 
layer of cells into mucilage, 
so that the seed, upon be- 
coming wet, is stuck fast to 
the soil ; or by the tufts of 
hair which, once wetted, 

to the surface of the 

fruit enlarged, showing barbed awns, rep- T , u t J i ■ .1.1 

resenting the calyx lobes, by which it earth; or by barbed bristles 

adheres to animals. A , natural size ; B, , , . i • i 

magnified 2 h diam.— After Kerner. and hygroscopic awns Which, 

Fig. 250.— Fruit of cockle-bur iXanthium , . , -, j 

strum*rzum),hdved, showing two seeds, having become entangled 

the upper of which usually germinates a ^ 1 

year later than the lower. Natural size among the graSS, WOrk a 

pointed seed body deeper 
by every change of moisture (fig. 241). 

401. Summary. — Plants have developed many ways for 
protecting and distributing their spores and seeds. Pollen is 
often protected against rain by closure of the flower-leaves or 
bending of the stalk. Fungus spores may be shot off or 
slung off. Many ferns sling out their spores from the cases. 
Water and air currents carry spores. Insects are also efficient 
distributors, especially for the seed-plants, which provide food, 
shelter, nest-building materials, etc., to secure their aid. 
This they advertise by color and odor. By irregular form 



B A 

Fig. 249. Fig. 250. 

Fig. 249. — A, cluster of fruits of Spanish 
needles {Bidens bipinnata). B, a single Cllllg 



DISTRIBUTION OF SPORES AND SEEDS. 285 

they also provide suitable landing places, and exclude ineffi- 
cient visitors by obstructions both inside and outside the 
flower. 

Seeds are distributed by being pinched or slung out by the 
drying seed pod, or shot out with the juice of the seed vessel 
when it breaks loose. Currents of water may float fruits or 
seeds long distances ; winds also carry them, especially if light 
or winged. Animals transport fruits or seeds which adhere to 
their bodies in mud or by hooks. Seeds in edible fruits may 
also escape destruction and be dropped far from the place 
where they were eaten. 

Conclusion. — Study of plants in relation to their surround- 
ings, therefore, yields the conclusion that these organisms are 
wonderfully plastic, responding either temporarily or perma- 
nently to every change in conditions. It is greatly to be de- 
sired that the too common thought of plants as only things to 
be classified may be replaced by the conception of them as 
beings at work, to be studied alive. 



APPENDIX I. 

DIRECTIONS FOR COLLECTING AND 
PRESERVING MATERIAL. 

Those who cannot collect the plants they require can order them from the Cambridge 
Botanical Supply Co., 1286 Massachusetts av., Cambridge, Mass.; or the Ithaca 
Botanical Supply Co., Ithaca. N. Y. Orders should be placed in advance of the 
collecting season to insure obtaining the material. 

Pleurococcus. — For this and similar one-celled algae, collect pieces 
of shaded fence boards near the ground, or flakes of bark from 
the north side of trees in groves and parks, which show a bright 
yellow-green color. These may be preserved dry. 

Oscillaria. — Search in drippings about watering troughs, city 
gutters where water stands, or any open drain which contains 
organic matter decaying in stagnant water. A glass jar or 
aquarium in which water plants have decayed will usually con- 
tain this plant. It may be recognized by its bluish or blackish 
green color, and often occurs in coherent films or thicker masses. 
It may be obtained fresh at any time of year, either out doors or 
in the laboratory. 

Rivularia. — Collect in midsummer or later the larger water 
plants to whose leaves and stems adhere jelly-like lumps of a 
dirty green color, from the size of a pinhead to 1-2 cm. in 
diameter. The margins of lakes, pools, and slow streams furnish 
the best localities. 

Nostoc colonies form similar jelly masses, commonly larger and 
free floating or attached. Preserve both like the following. 

Spirogyra or Zygnema. — Search in spring or early summer in slow 
streams fed by springs. It will be recognized when in vegetative 
condition by rich green color and slippery " feel." Under the 
microscope the form of the chloroplasts will show the genus. 

287 



288 APPENDIX. 

When conjugating it often loses the deep green and becomes 
yellowish, and the filaments seem to be double. 

This condition can be recognized under the lens. Spirogyra 
may often be obtained all through the year in pools and springs. 
It should be preserved in the following solution: Camphor water 
50 cc. ; water 50 cc; glacial acetic acid 0.5 cc. ; copper nitrate 
2 gm. ; copper chloride 2 gm. 

Cladophora. — Species of this genus may be found attached to 
sticks and stones at the edge of lakes or pools, It often covers 
these completely with a thick mat of long, yellowish green, 
branched filaments. It may be found throughout the growing 
season. For winter use preserve in same solution as above. 

Polysiphonia. — All species are marine, and any common species 
will serve, They are found in reddish brown, feathery tufts 2- 
10 cm. high, on other larger sea-weeds, or on piles and stones, 
about low-water mark. They collapse completely when with- 
drawn from the water. 

The plants should be fixed in one per cent, chromic acid (or in a 
saturated solution of picric acid in sea-water) for 12-24 hours, 
washed in sea-water as described for C/iara, and hardened in 40, 
60 and 80 per cent, alcohol successively, remaining in each 6- 
24 hours. They may be preserved in the latter. They may also 
be preserved in formalin. 

Fucus. — All species are marine and any one will serve. The 
commonest is Fucus vesiculosus (fig. 42), which may be found on 
rocks between tide marks. It is of olive-brown color, with 
swollen tips to many of the branches, and bladders in pairs along 
the thallus. Plants may be obtained fresh at almost any season. 
Various species of brown sea-weed may be found fresh at the 
fish stores of all large cities, whither they are sent as packing. 

Mucor or Rhizopus. — Saturate a piece of bread with water and 
keep it under a bell jar, in a warm place, for a few days. 
Several species of molds will appear, the most common of which 
is the black mold, Rhizopus nigricans. This may be recognized 
by its white fluffy mycelium, on which arise tufts of erect hyphae 
developing at tips spherical sporangia, at first white, later black. 
These tufts occur at intervals along a stolon-like hypha. The 
same mold may be found on rotting vegetables and fruits, 
especially sweet potatoes and lemons, and may be raised more 
rapidly on bread by sowing spores. It will be followed by the 
green mold, Penicillium glaucum, and often later by other 



COLLECTING AND PRESERVING MATERIAL. 289 

species. Since the plants may be grown promptly, the material 
used should be living. 

Microsphaera or Uncinula or Erysiphe. — Any species of mildew 
will answer. Microsphcera grows everywhere on the leaves of 
the cultivated lilac. Erysiphe is abundant on the leaves of blue 
or white vervain {Verbena hastata and V. urticcefolid) and many 
Composite. Uncinula attacks leaves of many willows. About 
midsummer, when the fungus has a white powdery aspect, gather 
leaves and dry them under light pressure. Later, gather leaves 
of the same species showing yellow and black dots (the fruits) on 
the mycelium. Preserve in the same way. 

Cystopus portulacae. — This species is abundant throughout the 
summer on leaves and stems of purslane {Portulaca oleracea) 
which grows in every garden and cornfield. Another species 
grows in late spring on shepherd's-purse {Capsella bursa-pastoris) 
and another on the pigweeds {Amaranthus sp.). Any one will 
answer. The species on Capsella {Cystopus candidus) only oc- 
casionally forms resting spores in that host. They may be found 
in abundance in the flowers of radish which become much enlarged 
and distorted when this fungus is parasitic thereon. All species 
may be known by the white blisters formed by lifting the skin of 
the host. Preserve in formalin or alcohol leaves and stems of 
host bearing blisters. Some may also be dried. 

Lichens. — Any common foiiose species which forms apothecia 
abundantly will answer. A bright gray species with black apo- 
thecia {Physcia stellaris) is abundant on tree trunks, as is also a 
yellowish species with orange apothecia {Theloschistes polycarpa). 
These may be collected at any convenient time, and kept dry. 
Besides these, collect other foiiose forms; also species of Cladonia 
growing on the ground, with body much lobed and the apothecia 
coral-red knobs on upright gray stalks; also species of Usnea, 
clothing the branches of trees with gray-green shrub-like or hair- 
like tufts. 

Mushroom. — Any species with cap and gills will answer. They 
may be found in woods throughout the summer and especially 
in late summer or autumn during a rainy season following 
drought. Only the fructification need be collected. Select a 
small firm species with well defined stalk, cap and gills. Col- 
lect fructifications in all stages of development from young to 
mature. Preserve as soon as gathered in formalin or 70 per cent, 
alcohol. 



29O APPENDIX. 

Other Hymenomycetes. — Collect fleshy cap fungi with hanging 
points instead of gills (Hydnum, fig. 217), or intersecting plates 
forming tubes (Boletus). Preserve these as mushroom. Collect 
also the woody bracket fungi (Polyporus, fig. 218), which grow on 
rotten trees and fallen limbs, showing innumerable fine tubes 
underneath. Preserve dry. Also the much branched firm- 
fleshed Clavaria (fig. 215). Preserve as mushroom. All will be 
found in damp woods. 

Marchantia. — Common on wet ground and rocks, or even in 
drier places among grass in the shade of walls or fences. It 
may be recognized by flattish green body about 1 cm. wide and 
5-8 cm. long, attached by silky hairs. At some times it bears on 
the upper surface sessile cups containing green grains, and sends 
up erect slender sexual branches which spread out into flat heads 
6-8 mm. across, some scalloped at edge and some with finger-like 
rays. When cups or sexual branches are present no other liver- 
wort can be mistaken for it. A very similar one, except in these 
parts (Conocephalus conicus) may be distinguished by its larger 
size and larger stomata, looking like needle pricks over the sur- 
face, while those of Marchantia are just visible. It may be used 
for the vegetative parts. Collect in July. Free from dirt as 
much as possible, and preserve in formalin or 70$ alcohol. 

Porella. — Abundant everywhere on the bases of trees especially 
in low grounds or wet bottom lands. It may be recognized by 
its dirty-green pinnately branched shoots, 1-2 mm. wide, with 
crowded overlapping rounded leaves. The plants are always in- 
tricately interwoven. Flakes of the bark may be peeled off with 
a broad knife or chisel, taking care not to tear up the plants into 
too small patches. Collect in summer. Preserve dry, after dry- 
ing under light pressure. Some should be kept in formalin or 
alcohol for demonstration of finer structure of sex organs. 

Mnium. — Any species of the genus will do. The commonest 
species eastward is M. cuspidatum. It is abundant everywhere in 
patches on shady banks and in open woods about the bases of 
trees. It may be recognized by the yellow or orange oval cap- 
sule, thin and irregularly wrinkled when dry, horizontal or pen- 
dent on a stalk 2-3 cm. long. The leaves are broadly oval, with 
fine sharp teeth under lens, and a distinct midrib. When moist 
the leaves are rather pale green, and not crowded or overlapping. 
When dry the clump is a dull, dirty green, and the leaves are 
much curled and twisted, expanding quickly when wetted. The 



COLLECTING AND PRESERVING MATERIAL. 29 1 

male and female organs are in the same cluster, at the apex of 
the axis. Under the microscope the species may be recognized 
by the orange inner peristome with double rows of perforations 
in the membrane below the segments. Preserve as directed for 
Porella. Almost any similar moss will serve equally well, espe- 
cially the common species of Bryutn. 

Adiantum. — Gametophytes of any fern will answer. They are 
fiat green heart-shaped bodies 2-5 mm. in diameter, attached to 
soil by rhizoids. They may be collected on fern pots or grown 
in greenhouses, or may be obtained from supply company named. 
Especial care should be taken to have some young sporo- 
phytes still attached to gametophytes. The sporophytes of 
the maidenhair fern are easily recognized by the peculiarly 
branched leaf. The stem is wholly underground. Each leaf 
has a slender polished stalk which forks into two equal 
branches ; these fork, one branch of each pair growing straight 
and bearing leaflets while the other again forks in the same way ; 
and so on until 4-8 branches have been formed on each half. 
Collect underground stems and roots, loosening them gently and 
washing off dirt carefully to avoid destroying all root tips and 
hairs. Preserve these in alcohol or formalin. Gather leaves 
when the crescent-shaped fruit dots at edges of leaflets are yel- 
lowish brown (August). Preserve by drying, spreading out 
each leaf to show its mode of branching clearly. 

Caltha. — This plant is common in wet meadows and swamps 
northward. It is 15-30 cm. high, smooth, with rather coarse 
hollow ribbed stems, orbicular or kidney-shaped alternate leaves, 
with broad clasping base to the petiole, and numerous bright 
yellow flowers 20-25 rn m - in diameter, produced for two weeks 
or more in April or May. Gather entire plant; wash the roots. 
Preserve a few plants and an extra supply of flowers and fruits 
in alcohol or formalin. Dry most of the entire plants. 

Lathyrus. — The sweet pea is grown in almost every flower gar- 
den and is known everywhere. Flowers and leaves of as great 
variety as desired may be preserved at the proper season in 
summer in alcohol or formalin. Or, simple flowers may be se- 
cured at greenhouses. 

Stems. — The various sorts recommended may be collected at 
any convenient time and preserved in fluid. 

Seeds. — The most useful seeds for laboratory work are Indian corn, 
wheat, buckwheat, castor bean (Ricinus), white lupine, {Lupinus al» 



292 APPENDIX. 

bus), scarlet runner {Phaseolus), broad bean {Vicia fabd), hemp, 
white mustard. These should be obtained fresh each year, as they 
deteriorate more or less with age. Those which cannot be had 
everywhere (such, perhaps, as lupine, castor bean, scarlet 
runner, and broad bean) may be purchased of seedsmen in large 
cities. See advertisements in magazines. 

Potted plants. — Such as are grown in window gardens or all 
greenhouses will suffice. A commercial greenhouse, if accessi- 
ble, will raise tomato, castor-bean, bean, and sunflower plants as 
ordered, and will furnish active young plants at any season re- 
quired, in case pupils cannot grow them either at school or home. 

Malt. — Can be obtained ground or unground at any brewery, 
or may be made by sprouting barley until the seedlings appear 
and then drying at about ioo° C. 



APPENDIX II. 
APPARATUS AND REAGENTS. 

The chemicals required are so few that in most cases they 
may be most conveniently obtained through local dealers. It is 
desirable, however, to order apparatus from dealers who make a 
specialty of manufacturing or supplying optical, chemical, and 
physical apparatus. Schools are entitled to import such appara- 
tus free of duty, and by doing so through importing firms a large 
part of the cost may be saved. The list is given here for its 
convenience as a summary. The amounts necessary are not 
specified as they vary with the size of classes, and the teacher 
who is prepared to conduct the experiments can readily deter- 
mine how much is needed. 

CHEMICALS. 

Acetic acid. — Used for fixing protoplasm. 

Alcohol. — Large schools should buy in barrel lots free of reve- 
nue tax. For regulations apply to the revenue collector of the 
district in which the school is situated, or to the Secretary of the 
Treasury. 

Ammonium hydrate (ammonia). 

Barium hydrate. — For making baryta water; or this can be ob- 
tained fresh as needed from druggist. 

Chromic acid. — Used in fixing and decalcifying. 

Corn starch. — As prepared for table or laundry. 

Formalin. — This is a 40 per. cent solution of formaldehyde in 
water. Dilute solutions can be prepared as needed. Most 
plants require a 10 per cent solution, i.e., formalin 1 part, water 
9 parts. 

Grafting wax. — Made as follows : Melt together resin (by 

293 



294 APPENDIX. 

weight) 4 parts, beeswax 2 parts, tallow 1 part; mix well; pour 
into a pail of cold water; grease the hands and " pull " till nearly 
white. In using it should be handled with greased fingers to 
prevent its sticking to them. 

Iodine. — Either solid, from which the tincture can be prepared 
by dissolving a few flakes in alcohol, or the tincture may be pur- 
chased. 

Mercury. — For directions for keeping it clean and dry, see 
Botanical Gazette 22 : 471. Dec. 1896. 

Paraffin. — A common quality, melting at about 65 C. 

Phenolphtalein. — A few grams will last a long time. 

Potassic hydrate. — May be bought in sticks and the solution 
made, but it is more convenient to buy the liquor potasses of 
druggists. 

Sodium chloride. — Table salt is pure enough. 

Vaseline. 

APPARATUS FOR MORPHOLOGY. 

Dissecting microscopes. — Each pupil should be provided with one. 
A most effective low-priced dissecting microscope was designed 
by the author and is manufactured by several firms. In no case 
has the author any financial interest in the instruments. The 
stand T I, manufactured by the Bausch & Lomb Optical Co., 
Rochester, N. Y., with i-inch lens, and a similar one by Queen 
& Co., Philadelphia, have been approved by the designer. Many 
forms offered to schools by jobbers are not worth buying. 

Compound microscopes. — The school should be supplied with at 
least one good compound microscope for demonstrations, and as 
many more as can be profitably used. If the teacher is capable 
of using such instruments properly he will be able to select it 
wisely with such advice as he may obtain from personal acquaint- 
ances on whose judgment he can rely. S hools are advised to 
deal directly with manufacturers of established reputation. 

Scalpels. — Each pupil should be provided with a sharp knife 
with slender blade for dissection. It is desirable for the school 
to furnish scalpels of suitable form. The slender blades, 3-3.5 
cm. long on cutting edge, are recommended. 

Forceps.— Straight form, with smooth points, will be found use- 
ful, though not indispensable. 

Needles. — Each pupil should have a pair of needles (No ; 6, 



APPARATUS AND REAGENTS. 



295 



sharps) with the eye end set into a soft pine penholder or similar 
handle. They must be kept sharp on a fine od-s.one 

Drawing materials.-A medium penal (No. 3 or M) and * ve 7f 
hard one (No. 6 or 6 H) should be used and kept sharp. Slips of 
heaviest linen ledger paper (,*> lb.) out r 4 X 8 em. are reeom- 
mended. Only one drawing should be put on a sl.p. 

APPARATUS FOR PHYSIOLOGY. 

Sinee much of the apparatus needs to be put together by the 
,Tl Te reauisites are mainly tools and a good supply of tub- 
Tg both glarAndrubber, bottles, and be,, jars. The following 
will enable the foregoing experiments to be earned out. 

Lb -Hammer, fine saw, three or four eh.sels, assorted files, 
bra « and assorted bits, screw-driver, smooth ng plane.wh 
Supply of nails (especially finishing nails) and screws will be 

£ 7"^.-A little capillary tubing (0.5 mm. bore) will 
be needed. Most used sizes are 5 mm. (3 mm. bore) , mm 
"5 mm. bore.) Some larger sizes (13 and .9 mm.) will also be 

US 1 U L, ft**.-3 and 5 mm. bore mostly ; some of .0 and .5 

mm. bore. .. 

Bottles —Wide-mouthed, various sizes, up to I liter. 

rllT/^.-Jelly glasses answer well. Odd lids and glass dishes 
from homes and stores can be made useful. 

^.-Assorted sizes. Several rubber stoppers, sizes 8, 10, 12, 

vhole, are desirable. 

*// *r,.-Several sizes are necessary ; 15 X 20 and 20 X 3° cm. 
will be found useful ; also at least one 30 X 50 em. All should 
have ground rim and tubulure at top. 

Funnels.-GX.ss, assorted sizes. 6, 8, and » cm. diam. are 
most used ; there should also be two or three larger ones. 

Filter paper.-Buy cut filters 15 and 18 cm. in diameter 

r*eJJeters.-ShoM be graduated in degrees, -10 to + 100 
C, with milk-glass scale. 

Test tubes.— 1 X 15 cm. is a convenient size. 

7 -tubes.— Two sizes, 5 and 10 mm. bore. 

Bunsen burners.-U gas is not available, gasolene burners 
should be substituted. 



296 APPENDIX. 

Marble. — A plate 25 X 25 X 2.5 cm., polished on both sides. It 
can be re-polished after etching and used as often as desired. 

Filter pump. — Can be used if water service is available, or if a 
head of 5 m. can be secured by tank. Korting's is excellent. 

Rulers. — 30 cm. long, graduated in millimeters. 

Brushes.— Camelhair brush of large size, and sablehair, smallest, 
are useful. 

Pins. — Ordinary toilet pins. 

Tin tube.— 3 X 15 cm. See experiment 20. 

Absorbent cotton. — Also a roll of cotton batting. 

Sheet /W.— Light weight, used by plumbers. 

Plate glass.— Cul into pieces 20, 25, and 35 cm. square. 

Pine sawdust and clean sand.— For germinating seeds. 



APPENDIX III. 
REFERENCE BOOKS. 

The following books will be found useful to teacher or pupil or 
both, and are recommended as suitable reference books for the 
school library. The list is not intended to be exhaustive, nor 
does it include books for popular reading. 

FOR GENERAL REFERENCE. 

erner : Natural history of plants. New York : Henry Holt & 
Co. $15.00. (Translated by Oliver.) 

Strasburger, Noll, Schenck and Schimper : Text-book of 
botany. New York : The Macmillan Co. $4.50. (Trans- 
lated by Porter.) 

Rennett and Murray : Handbook of cryptogamic botany. New 
York : Longmans, Green & Co. $5.00. 

Vines : A student's text-book of botany. New York : The Mac- 
millan Co. $3.75. 

Sachs : Lectures on the physiology of plants. New York : The 
Macmillan Co. $7.00. (Translated by Ward.) 

Goebel : Outlines of classification and special morphology. New 
York: The Macmillan Co. $5.50. (Translated by Garnsey 

and Balfour.) 



Warming: Handbook of systematic botany. New York: The 

Macmillan Co. $3.75. (Translated by Potter.) 
Gray : Systematic botany. New York : The American Book Co. 
$2.00. 
^_J3essey : Botany, Advanced Course. New York : Henry Holt & 
Co. $2.20. 
Geddes : Chapters in modern botany. New York : Charles 
Scribner's Sons. $1.25. 

297 



290 APPENDIX. 

Campbell : Evolution of plants. New York : The Macmillan Co. 

$1.25. 
Coulter : Plant relations. New York : D. Appleton & Co. 

$1.10. 

: Plant structures. New York : D. Appleton & Co. $1.20. 

Warming: Lehrbuch der okologischen Pflanzengeographie. Ber- 
lin: Gebr. Borntrager. (A German translation by Knoblauch. 

An English translation is now in preparation.) 
Pfeffer : Pflanzenphysiologie. Ed. II., vol. 1. Leipzig: Wil- 

helm Engelmann. M. 20. (An English translation is now in 

preparation by Dr. A. J. Ewart.) 
Vines : Lectures on the physiology of plants. New York : The 

Macmillan Co. $5.00. 
Goodale : Physiological botany. New York : The American 

Book Co. $2.00. 



FOR LABORATORY DIRECTIONS. 

Bergen: Elements of botany. Boston: Ginn & Co. $1.10. 
Spalding : Introduction to botany. Boston : D. C. Heath & Co. 

80 cts. 
Macbride : Lessons in elementary botany. Boston : Allyn & 

Bacon. 60 cts. 
MacDougal : Experimental plant physiology. New York : Henry 

Holt & Co. $1.00. 
Arthur : Laboratory exercises in vegetable physiology. Lafay- 
ette, Ind.: Kimmel & Herbert. (Pamphlet.) 35 cts. 
Darwin and Acton : Practical physiology. New York : The 

Macmillan Co. $1.60. 
Arthur, Barnes and Coulter: Plant dissection. New York: 

Henry Holt & Co. $1.20. 
Ganong : The teaching botanist. New York : The Macmillan 

Co. $1.10. 



OUTLINE OF CLASSIFICATION. 301 



Subkingdom II. BRYOPHYTA. Bryophytes. Mossworts. 

Class I. HepaticaD. Liverworts. 
Order 1. Ricciales, 
Riccia. 
Order 2. Marchantiales. Liverworts. 

Marchantia. Lunularia. 
Order 3. Anthocerotales. Horned liverworts. 
Order 4. Jungermanniales . Leafy liverworts. Scale mosses 
Porella. 
Class II. Musci. Mosses. 

Order I. Sphagnales. Peat mosses. 

Sphagnum. 
Order 2. Andreceales. 
Order 3. Archidiales. 
Order 4. Bryales. True mosses. 

Bryum. Mnium. Hypnum. 



Subkingdom III. PTERIDOPHYTA. Pteridophytes. 
Fernworts. 

Class I. Filicineae. 

Order 1. Filicales. True ferns. 

Adiantum. Pteris. Aspidium. Asplenium. 
Order 2. Hydropteridales . Water ferns. 
Class II. Equisetineae. Horsetails. Scouring rushes. 

Equisetum. 
Class III. Lycopodinese. 

Order 1. Lycopodiales. Ground pines. 

Lycopodium. 

Order 2. Selaginellales. Club mosses. 

Selaginella. 



Subkingdom IV. SPERMATOPHYTA. Seed plants. 

Class I. Gymnospermae. Gymnosperms. 
Order I. Cycadales. Cycads. 
Cycas. 



302 APPENDIX. 

Order 2. Coniferales. 

Pines, spruces, larches, firs, etc. 
Order 3. Gnetales. 

Welwitschia. 
Class II. Angiospermae. Angiosperms. 

Sub-class I. Monocotyledones. Monocotyledons. 

Orders several. Lilies, irises, grasses, sedges, rushes 
palms. 
Sub-class II. Dicotyledones. Dicotyledons. 

Orders numerous. Most herbs with net-veined leaves 
deciduous shrubs and trees. 



I 



INDHX. 



All references are to pages. Italic figures indicate illustrations. 



Absorption, limit of 128; of gases 
139; of water 242 

Acacia, shoot of 103 

Accessory fruits 222 

Adaptation 1 17, 227 

Aeration 146 

Agrimonia, fruit of 283 

Ailanthus, fruit of 281 

Air, composition 231, plants 125 

Aldrovandia vesiculosa 265 

Algse 254, 255; filamentous 17; 
fission 6; larger 23; yellow- 
green 11 

Allium, stem 89 

Aloe socotrina 241 

Alternation of generations 41 

Amanita phalloides 192 

Amorphoph alius 10 4 

Anagallis, capsule of 222 

Angiosperms 198 

Anther 202, 203, 204 

Anthyllis 112 

Ants 267 

Apodanthes 259 

Apple 224, twi g of 78 

Arbor- vitas, shoot of 84 

Armor, 266 

Artemisia, hairs of 240 

Ash, calyx and pistil of 200 

Asparagus, twig of 79 

Aspidium 195 

Asplenium bulbiferum 212, spore 
cases 273, gametophyte of 53 

Assimilation 137 

Bacteria 9, 10 
Bacterium aceti 10 
Barberry 267 
Bark 92, 93, 94 



Bast, secondary 91, 92 

Bazzania Novae- Hollandiae 45 

Bean, roots of 176 

Beech, rootlet of 254 

Beet, stoma of 110 

Begonia 88 

Bellflower 171, capsules of 221 

Bidens, fruits of 284 

Bladderwort 263 

Bracts 107 

Branches, dwarf 77, leaf-like 77 

Branching 19, 31, 43; monopodial 
74; of leaves 103, 104 ; of mosses 
48 ; of roots 83 ; of shoot 73 

Bryony SO 

Bryum 194, capsules of 50 

Budding 31, 187 

Buds 73, 212; adventitious 70, 76; 
axillary 74; brood 211 ; dormant 
76; fleshy 212; lateral 74; on 
roots 69 

Bulb 76, 244 

Bulblets 79 

Butomus, anther of 203 

Calamus, root of 64 

California poppy, ovules of 201 

Calyptospora 37 

Calyx 206 

Campanula pusilla 171; rapuncu- 

loides 221 
Capsule 200,_ 221, 222 
Carbon dioxid 139 
Carex stricta 267 
Carnivorous plants 261 
Carpels 197 

Carrot, chromoplasts of 4 
Caulerpa 20, 21 
Cecropia 268 

303 



3Q4 



INDEX. 



All references are to pages. Italic figures indicate illustrations. 



Cells I, 2, 155, 167; division 16; 
growth 154; guard no; naked 
119, 164; union of 218; wall 2, 4 

Cellulose 4 

Centrifuge 174 

Cilia 10 

Cinchona, bark of 93; stem of 91 

Cinnamon flower 201/. 

Cirsium, pollen grains 205 

Cheiranthus, hairs of 86 

Chelidonium 167 

Cherry, fruit of 223; stem of 92 

Chlorophyll 3, 140 

Chloroplasts 3 

Chondromyces serpens 253 

Cladonia furcata 257 

Cladophora 19 

Clambering plants 250 

Clavaria aurea 192 

Climbing plants 249 

Clover 256 

Cobaea scandens 277 

Cockle bur, fruit of 284 

Colonies, of Chondromyces 253; 
gelatinous 6, 7 

Color 24 

Contractility 1 17 

Convolvulus, hairs of 240 

Coprinus 191 

Cork 91 ; cambium 66, 91 

Corm 77 

Corn, cockle 199; bundles of In- 
dian 90 

Corolla 206 

Cortex 27, 61, 64, 85, 86, no 

Cotton, fruit of 283 . 

Cowberry 37 

Crataegus, shoot of 100 

Crowfoot 162 

Crystals 151, 269 

Cuttings 214 

Dandelion, fruit 282; pollen grains 

205 
Datura stramonium, anther of 203 
Dehiscence 202; of seed pods 278 
Desmids 14 

Desmodium, fruit 283; gyrans 181 
Development, rate of 234 
Diatoms 12, 13 



Digestion 137, 143 
Dionaea muscipula 183, 264 
Distribution of seeds and spores 

270 
Dodder, European 258 
Dormant period 234 
Drosera rotundifolia 264 
Duration, of growth 163; of shoot 

81 

Ecology 115, 226 

Ectocarpus, filament of 254 

Edelweiss, hairs of 24O 

Eel grass 274 

Elaeagnus angustifolia 241 

Elatine, stem of 87 

Elm, buds 75 

Embryo 219, sac 201 

Empusa Muscse 272 

Energy, release of 147 

Entoderma Wittrockii 254 

Environment 228 

Epidermis 61, 85 

Epiphytes 250 

Eschscholtzia 271, ovules of 201 

Excretion 147 

Exobasidium, hyphoe of 35 

Fagus sylvatica 254 

Fern 109, 194, 212; leaflet 195 

Fern worts 53 

Fig, inflorescence of 209 

Filament 202 

Fission 16, 186; algae 6 

Flax, flower of 207; stem of ££ 

Flowers 77, 197; leaves 107; of 

flax 207; of mousetail 208; of 

mulberry 224; °f raspberry 22 4\ 

of sweet pea 207 
Fly fungus 272 
Foods 135, 275; of spores 189; 

storage of 142; transfer of 142 
Fragmentation 187 
Fraxinus, calyx and pistil of 200 
Fructifications 191 
Fruit 219, 220, 282, 283, 284; 

fleshy 221; of apple 224; of 

cherry 223; of wintergreen 223; 

winged 281 
Fucus 25, 26, 27 



INDEX. 



305 



All references are to pages. Italic figures indicate illustrations. 



Funaria Americana 4S 
Function 1 15 
Fungi 255, 257; fission 9 
Fusion 38 

Gametes 41 

Gametophyte 41; of Bazzania 45; 

of fernworts 53; of Polytrichum 

47; reduction of 54 
Gaultheria procumbens 223 
Gelatin 9 

Geotropism 172; transverse 175 
Geranium pods 278 
Gerardia, parasitic 258 
Glceocapsa 6 

Grasses 175 ; leaf of 99, 238 
Growth 24, 124, 154; conditions 

of 159; localization of 19; of 

cell-wall 5; of spores 190; period 

of 156 
Gymnosperms 198 

Hairs 86, 199, 24O; of nettle 267 

Halophytes 237, 244 

Haustoria 36; of Peronospora 38 

Heat 149 

Heliotropism 170 

Hellebore, pistil of 200 

Helotism 255 

Hibiscus, pollen grains of 205 

Honeysuckle, buds 75; leaf 102 

Hop, stem of 177 

Hosts 34 

Houseleek 243 

Hydrophytes 246 

Hydrotropism 177; apparatus for 

178 
Hyphse 30; of Exobasidium 35; 

of lichen 257; of Trametes 36 

Iberis, stem of 85 
Impatiens pods 278 
Impulse, transmission of 164 
Infection 35 
Inflorescence 74 
Internodes 83 
Irregularity 206 

Irritability 117, 164; localization 
of 164 



Land plants 125 

Larch, shoot of 239 

Lasiagrostis 238 

Leaves 96; arrangement 98; base 
99; blade 102; compound 104; 
fall of 113; foliage 98; form 98; 
margin 241 ; mosaics 170; of 
mosses 47; sections 109, 111, 
112, 183, 238; simple 104, 
spore 195; stalk 101; storage 
108 

Lichens 39, 257; mycelium of 38 

Light 141, 160, 232, 247 

Lilium bulbiferum 212 

Lily 212; anther off 03; cell of 3; 
pollen grains of water 205 

Linden, shoot of 74 

Liverworts 42, 194, thallose 44 

Locust, stem of 108 

Lodgers 253 

Lonicera buds 75 

Lotus corniculatus 222 

Lunularia cruciata 43 

Lychnis githago 199 

Mallow, pollen grains of 205 

Maple, bud of red 75; fruit of 281; 
Norway 171 

Marchantia 211 

Marsilia, root of 61 

Megaspore of lily 3 

Melampsora salicina 189 

Mesophytes 231 

Metabolism 116 

Micrococcus 10 

Mildew 37 

Mimicry 267 

Moisture 162, 234 

Mold, black 34 

Monopodial branching 48 

Mosses 46, 194; brood buds of 211; 
capsules 194; gametophyte 193 

Motor organs 180 

Mougeotia 17 

Mountain ash, chromoplast 4 

Mousetail 208 

Movements 164; air 232; com- 
bined 172; contact 178, 182; 
growth 168; light 181 ; multi- 
cellular members 168; paratonic 



306 



INDEX. 



All references are to pages. Italic figures indicate illustrations. 



168, 169; photeolic 182; proto- 
plasm 164; spontaneous 168, 
181; to reduce illumination 238; 
turgor 179; water 247 

Mucor 193, Mucedo 32 

Mulberry flower 224 

Multiple fruits 223 

Mustard 173 

Mutualism 252 

Mycelium 32 ; of lichen 38 

Mycorhiza 254; of orchids 255 

Myosurus minimus 208 

Nasturtium 106, 170 

Nepenthes villosa 262 

Nettle 267 

Nitrogen supply 261 

Nodes 83, 241 

Nostoc 7 

Nucleus 3 

Nutation 168 

Nutrition 49, 124; of green plants 

138 
Nymph aea, pollen grains of 205 

Oat, cell of 4; grain 220 

Offsets 77, 213 

Oil receptacle 151 

Oleaster, scales of 241 

Oligotrichum aligerum 48 

Onion stem 89 

Opuntia vulgaris 240 

Orchid, chromoplast of 4\ myco- 
rhiza of 255; pollen mass of 205 \ 
seeds of 280 

Organ 115 

Orthotrichum 49 

Oscillaria 8 

Ovulary 200 

Ovules 197, 198, 200, 201 

Oxygen 162 

Palm stem 85 
Pansy seed 219 
Parasites 34, 138 
Parasitism 257 
Parmelia conspersa 257 
Pea, root of 157; seedling 68; 
shoot of 108 



Pear, prickly 240 

Penicillium glaucum 191 

Peperomia trichocarpa 244 

Perianth 205 

Pericarp 219 

Periderm 66, 91 

Peronospora 38 

Petiole, scarlet runner 180 

Phascum cuspidatum 50 

Photosynthesis 140, 146; product 
of 141 

Physiology 115 

Phytolacca decandra 219 

Pilobolus crystallinus 271 

Pimpernell, capsule of 222 

Pine, Scotch 78 

Pistils 200; closed 198; simple and 
compound 199 

Pitcher plant 107 

Pith 27, 89; rays 93 

Placenta 202 

Plasmodia 120 

Plastids 3 

Plectranthus, hairs of 86 

Pleurococcus 11, 12 

Pokeberry seed 219 

Pollen 203, 204, 205 

Pollination 207, 275 ; of eel grass 
274 

Polygonatum, leaf of 105 

Polygonum, stipules of 102; vivi- 

parum SO 
Poly podium vulgare 54 
Polyporus 33 
Polysiphonia 24 
Polytrichum commune 47 
Pond weed 213 
Poplar, white 254 
Poppy, California 271 
Porella platyphylla 46 
Potamogeton crispus 213 
Potassium, salts 141 
Potato 216; cell of 4; pistil of 

white 200 
Precipitation 234 
Protection 233, 266; of spores and 

seeds 270 
Proteids 142 
Protococcus 257 
Protonema 49 



INDEX. 



307 



All references are to pages. Italic figures indicate illustrations. 



Protoplasm 1, 2, 119; movements 

of 164; powers of 116 
Pteris 69, 109 
Pyrola chlorantha 221 



Ranunculus aquatilis 162; leaf of 

99 
Reaction 165 
Repair 124 
Reproduction 3, 117, 185; sexual 

186, 218; vegetative 186 
Respiration 145 ; intramolecular 

M7 

Rhizoid 19, 21, 46, 76 

Rhododendron, anther and pollen 
of 204 

Riccia sorocarpa 4% 

Rigidity, mechanical 122 

Rings, annual 94 

Robinia, stem of 108 

Roots, 59, 62, 70; absorption 128; 
cage 176; cap 60, 63; climbers 
250; fleshy 67; float 67; hairs 
61, 63; hairs and soil 127; of 
fern 69', pressure 130; tubercles 
255; woody 66 

Rose, flower of 209; shoot of 101 

Rotation 167 

Rubus idseus 224 

Runners 77 

Rye, stem of 161 



Saccharomyces cerevisiae 31 

Salts, absorbed 138; dissolved 127 

Salvinia natans 196 

Saprolegnia lactea 188 

Saprophytes 137 

Sarcina 10 

Sarracenia purpurea 107; vario- 

laris 262 
Saxifrage 277 
Scales 106, 24I 
Scarlet runner 180 
Scions 214 
Scotch pine 198 
Sedge 267 
Sedum, acre 79; dasphyllum 214; 

ternatum 208 



Seed 218; coats 219; of orchid 

280; plants 57; pods, dehiscence 

of 278 
Seedlings 97 

Sempervivum tectorum 243 
Sensitive plant, leaf of 183 
Sepals 206 

Shepherd's purse 200 
Shoot 45, 72, 82, 211; of larch 

239; of linden 74; winter 

213 
Snowberry, fruit of 155 
Societies 249 
Soil 126, 235; water 127 
Spanish needle, fruits of 284 
Spirogyra 17, 18 
Splachnum ampullaceum 50; lu- 

teum 50 
Spores 41, 185, 188; cases 192, 

196, 273; chain 191; free 190; 

leaves 196; non-motile 189 
Sporophyte 41, 193; of fernworts 

55; of mosses 49; of Phascum 

50; of Polypodium 54 
Stamens 202 ; union of 203 
Starch, reserve 143 
Stele 61, 63, 85, 86, 87, in 
Stem 46, 83, 95; habit 84; sec- 
tions of 85, 87, 88, 89, 91, 92, 

94, 122, 161 
Stigma 199 
Stimulation 164 
Stipules 99 
Stolons 77 
Stoma no 
Stonecrop 208, 214 
Storksbill pods 279 
Strains 162 
Strawberry, flower 208; runner 

215 
Streaming 167 
Style 199 

Sugar cane, node of 241 
Sundew leaves 264 
Sweetbrier rose 209 
Sweet pea, flower of 207 
Sweet violet, anther of 204 
Symbiosis 252 
Symphoricarpus 155 
Sympodial, branching 48 



308 INDEX. 

All references are to pages. Italic figures indicate illustrations. 



Taraxacum, pollen grains 205 

Temperature 160, 233, 247 

Tendrils 67, 80, 106 

Tension, due to growth 157; of 
tissues 121 

Thallus 19, 21, 23, 27; of liver- 
worts 42, /j$, 4$; of Marchantia 
211 

Thistle, pollen grains of 205 

Thlaspi, leaf of 102 

Thorns 67, 80, 100, 106; apple, 
anther of 203; of Vella 81 

Tick trefoil, fruit of 283 

Tococa lancifolia 269 

Torus 209, 208 

Touch-me-not, pods of 278 

Trametes Pini, hyphse of 36 

Transfer of food 142 

Transpiration 133, reducing 237 

Tropaeolum 170 

Tubers 79, 244 

Turgor 1 20; movements 179 

Twining plants 176, 250 

Ulothrix 19 
Ulva lactuca 23 
Urtica 267 

Utricularia, Grafiana 263; vul- 
garis, bladder of 264 
Uvularia. leaf of 102 



Vallisneria spiralis 274 
Vanda teres 280 
Vascular bundles 63 
Vaucheria 19, 20 
Vella spinosa 81 
Venation 104, 105 
Venus' fly-trap 183, 26, 
Veratrum, pistil of 200 
Viola, anther of 204 
Violet, capsule 222 



Water, composition of 248 ; loss of 

I 33> 2 37; movements of 247; 

movement of in plant 129 ; plants 

125; solutions in 125 
Weight, loss of 148 
Wheat, seedling 97; stalk 175 
Willow, fruit 282; leaf of 105, 189 
Wintergreen, capsule 221; fruit 

223 
Wood, secondary 91, 92 



Xanthium fruits 284 
Xerophytes 237 



Zoospores 119, 188 
Zygnema 17 



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