MARINE BIOLOGICAL LABORATORY,

Received JU^-a/,,2.^, J.A./.Z....

I I iJ-^
Accession No. ..4? -.'.

Given by f
Place,

/

book OP pamph.let is to be removed ffom the Liab-
tuitbout tlae pepmission of tbe Trustees.

fig

LARCH AND BUR OAK, SHOWING TWO TYPES OF

MONOPODIAL BRANCHING.

Frontispiece.

PLANT LIFE

CONSIDERED WITH SPECIAL REFERENCE TO
FORM AND FUNCTION

BY

CHARLES REID BARNES

Professor of Plant Physiology in the University of Chicago

NEW YORK

HENRY HOLT & COMPANY

1898

Copyright, 1898,

BY
HENRY HOLT & CO.

ROBERT DRUMMOND. PRINTER. NEW YORK.

PREFACE.

IN recognition of the fact that the study of botany in the
past has been too much a study of books about plants, numer-
ous laboratory manuals have been published which make pos-
sible the study of plants themselves. Laboratory work has
now become well-nigh universal. With the strenuous insist-
ence that this method should be used in the secondary schools,
there has been a growing danger that such study would de-
generate into mere memory training, unless the relation of
the facts, often entirely isolated in the pupil's mind, were
clearly brought out. Since laboratory study soon came to
include the examination of the lower plants as well as seed
plants, and has now begun to include some experiments in
their physiology, the absence of an elementary account of
the form and functions of plants of all groups has made itself
felt. I am not aware that any book at present attempts to
meet this need.

To the proper teaching of botany in secondary schools
such a book is indispensable. However capable the teacher
may be to gather up the facts observed in the laboratory and
to relate them with others so as to produce a clear concep-
tion of plant life, he cannot wisely rely upon the lecture for
pupils of 13 to 1 8 years. They need the printed page,
which appeals to eye as well as ear, if the principles and facts
are to be firmly grasped.

• • •

in

IV PREFACE.

PLANT LIFE is an attempt to exhibit the variety and pro-
gressive complexity of the vegetative body; to discuss the
more important functions ; to explain the unity of plan in
both the structure and action of the reproductive organs ;
and finally to give an outline of the more striking ways in
which plants adapt themselves to the world about them. I
have made an effort to treat these subjects so that, however
much the student may have still to learn, he will have little
to unlearn ; for eradication of false notions is the despair of
the college teacher of science.

This is not a book to be memorized and recited. If so used it
is abused. It aims to be intelligible to pupils 13 to 18 years
of age who are engaged in genuine laboratory study — not at
irregular hours, without supervision, in a school desk, or at
home, but in a suitable laboratory, with regular time (an
hour and a half daily if possible), under the direction of a
live teacher who has studied far more botany than he is
trying to teach. I am aware that such conditions are yet
unrealized in many schools ; but they may be gradually
reached. That PLANT LIFE may prove useful in botanical
instruction even under the most unfavorable conditions, I
permit myself to hope rather than to expect.

This book may be used to supplement any laboratory guide
or the directions prepared by the teacher. For the sake of
teachers who may not wish to use two books, or who lack time
and facilities for preparing laboratory directions, I have out-
lined a course of study in Appendix I which can be carried
out with the equipment listed in Appendix III. A description
of the material needed and of suitable methods of preserving
it forms Appendix II. Each teacher will, of course, need to
modify the directions to suit the material available. I have
always found it easier to prepare directions to fit the material
than to create the material to fit the directions. The "dem-
onstrations " of Appendix I are intended as suggestions to the

PREFA CE. V

teacher of things which it is advisable to show to pupils under
the compound microscope, in case inadequate equipment,
lack of time, or difficulty of preparation forbid class study.

I have made the directions fullest in relation to cryptogams
and physiology because these fields are most unfamiliar to
teachers at present. Further directions for the study of seed
plants can readily be provided from the books listed in Ap-
pendix IV.

For laboratory study it is necessary to select certain illus-
trative types and observe their structure. In the text I have
not specifically discussed these plants, but have treated gen-
eral topics so as to correlate the facts gained by a study of
types with others which can be readily interpreted by means
of the experience in the laboratory. References from the
bare directions of Appendix I to the paragraphs and figures
of the text are abundant and are intended to aid the student
in the comprehension of the type under observation. It may
be objected that he is thus aided too much. But I believe
that in his first steps in laboratory training the student re-
quires a large amount of help, and that its results are more
often nullified by too little assistance than by too much.

In the text I have neither sought nor avoided the use of
technical terms. I have refrained from making the book a
mere illustrated glossary. Yet I see no advantage, even for
young students, in repeated circumlocution, for which a
single word might stand. Definitions of most of the tech-
nical terms used may be found by means of the index ;
others are defined in the standard dictionaries. The careful
teacher will insist upon a clear understanding of the meaning
of terms and the accurate use of language.

I have refrained from frequent citation of plants by name
as examples of facts stated, chiefly because beginners are
rarely familiar with any plants except the commonest domes-
ticated ones and a few forest or shade trees.

VI PREFA CE.

No apology is necessary for the exclusive use of the metric
system. If pupils lack familiarity with it, the actual handling
of metric measures and weights will soon remedy this. A
useful chart showing the units may be obtained of the Ameri-
can Metrological Society, 41 East Forty-ninth Street, New
York, for ten cents.

Very few of the illustrations are original. In the main they
have been selected from a wide range of standard works with
especial care to secure accuracy and clearness. Whenever
possible the source of the figure and its magnification have
been given. The attention of the teacher is invited to the
very full description which accompanies each figure. In
these explanations will be found much matter which is often
put into subordinate paragraphs in other books. I have ob-
served that students are prone merely to " look at ' ' figures,
and rarely study them. I therefore suggest that real study of
the illustrations as supplementing the text be insisted upon.
Sections are apt to be puzzling to beginners unless they are
taught how to interpret them. This can be done by requir-
ing them to sketch on paper or blackboard imaginary sections
of common objects in different planes. Articles of regular
form, such as a pencil, book, slate, ink bottle, desk, etc.,
may be " sectioned," until from sketches of sections in three
planes at right angles the student can construct a mental
image of the object.

Although divided into four parts, it has not been possible
to keep the subject matter of each wholly distinct, since
morphology, physiology and ecology are so interrelated. In-
deed it has been thought best to combine the morphology
and physiology of the reproductive organs to form Part III,
rather than to divide it between two. The teacher will do
well to see that the pupil does not neglect the abundant cross
references.

While the whole book is simply a restatement of widely

PREFACE. VI 1

known facts, for which I am mainly indebted to general
treatises, monographs and shorter papers, 1 am constrained
to acknowledge for Part IV my special indebtedness to
NVarming' s Lehrbuch dcr okologischen Pflanzengeographie and
Ludwig's Lehrbuch der Pflanzenbiologie.

C. R. B.
UNIVERSITY 01- CHICAGO,

CONTENTS.

PREFACE

PAGE

iii

PART I: THE VEGETATIVE BODY.

INTRODUCTION : THE UNIT OF STRUCTURE
CHAPTER I. SINGLE-CELLED PLANTS AND COLONIES
II. LINEAR AND SUPERFICIAL AGGREGATES

III. THE THALLUS OF THE HIGHER ALG/E .

IV. THE FUNGUS BODY OF HYPHAL ELEMENTS .

V. LIVERWORTS AND MOSSES .

VI. FERNWORTS AND SEED PLANTS

VII. THE ROOT

VIII. THE SHOOT

IX. THE STEM ....;..

X. THE LEAVES ,

8

17
26

39
49
60

65

82

96

"7

PART II : PHYSIOLOGY.
CHAPTER XL INTRODUCTION: THE UNIT OF FUNCTION. . 143

XII. THE MAINTENANCE OF BODILY FORM . . 147

XIII. NUTRITION 151

XIV. GROWTH 178

XV. THE MOVEMENTS OF PLANTS l88

PART III: REPRODUCTION.

CHAPTER XVI. INTRODUCTION : REPRODUCTIVE STRUCTURES . 209
XVII. VEGETATIVE REPRODUCTION .... 211

XVIII. SEXUAL REPRODUCTION 268

ix

CONTENTS.

PART IV : ECOLOGY.

PAGE

CHAPTER XIX. FORMS OF VEGETATION 308

XX. MESOPHYTES 312

XXI. XEROPHYTES AND HALOPHYTES . . . 318

XXII. HYDROPHYTES 327

XXIII. ADAPTATIONS TO OTHER PLANTS AS SUPPORTS 330

XXIV. SYMBIOSIS. . 333

XXV. ANIMALS AS FOOD, FOES, OR FRIENDS . . 342

XXVI. PROTECTION AND DISTRIBUTION OF SPORES

AND SEEDS ....... 352

APPENDIX I. DIRECTIONS FOR LABORATORY STUDY . . . 369
II. DIRECTIONS FOR COLLECTING AND PRESERVING

MATERIAL ........ 40!

III. APPARATUS AND REAGENTS 409

IV. REFERENCE BOOKS ...... 413

V. OUTLINE OF CLASSIFICATION .... 415

INDEX 419

PLANT LIFE.

PART I: THE PLANT BODY.

INTRODUCTION.

1. Units of structure. — An examination of any plant by
proper methods reveals the fact that it is made up of one or
more units of structure. The unit of structure of a brick
wall is the individual brick. Each has a definite shape and
relation to others, upon which the form of the wall depends.
The unit of structure of a plant is called a cell. The cells
have each a definite form and relation to others, and upon
these two factors the form of the entire plant depends.

But between the plant and the brick wall there is this im-
portant difference. The bricks, after being perfectly formed,
were put together. The cells of the plant are produced where
they lie and gradually grow to a mature form and size. The
bricks are originally disconnected ; the plant-cells are con-
nected by origin, and only as they become mature do they
separate, if at all.

2. The cell. — A plant-cell is a minute portion of living
matter, called protoplasm or plasma, generally surrounded by
a membrane, called the cell-wall (fig. i). If the brick in
the previous illustration be taken to represent the protoplasm,
the mortar may be considered as the cell-Wall.*

* This illustration must be carried no further than to show the relation
of position of these two parts of a cell.

PLANT LIFE.

3. Protoplasm.- -The protoplasm is the essential part of
the cell. It constructs the cell-wall. Rarely, if ever, is it
uniform throughout, but is differentiated into distinct mem-
bers, each having special work to do. In the most com-

pletely differentiated active cells the
greater part of the protoplasm con-
sists of a finely granular or nearly
transparent, colorless portion, called
cytoplasm. Embedded in the cyto-
plasm are the nucleus, centrospheres
(figs, i and 2), and plastids (figs.
3 to 8).

4. Cytoplasm. - • This is not a
single substance, but a mixture of
several different substances, so in-

±"'roasnpdhearCeCs°Tm The* line timatcly mixed and so unstable that

it is not possible to analyze it.

FIG. I.-A cel (the megaspore)

"io dianu- Moreover, the nature and amount

After Guignand. Qf ^ components are probably

variable. Most of the substances belong to the class of com-
pounds called proteids, so that cytoplasm responds to proteid
tests and is often spoken of as a mixture of proteids. In
addition there are frequently present other organic substances
(such as amides, carbohydrates, fats, and enzymes), and
always small quantities of mineral matters which appear as
ash when cytoplasm is completely burned. The minute
granules embedded in the cytoplasm are of various nature.
Most of them are solid substances.

5. Vacuoles. — Scarcely distinguishable from these at first
are the minute cavities, called vacuoles, filled with dilute
watery solutions of many different substances, the cell- sap.
In all but the youngest cells more or fewer of these bubbles
of water may unite to form larger ones (fig. 7). These often
increase so as to occupy the greater part of the space within

IXTRODUCTIOX. 3

the cell-wall, being separated only by plates of protoplasm.
When all vacuoles fuse into one the cytoplasm is crowded as
a thin layer against the wall, with sometimes strands of it
crossing the vacuole as the remnants of the plates at an
earlier stage (fig. T88).

6. Nucleus.- -The nucleus varies much in shape. In cells
whose diameters are nearly equal, it is generally spherical
or ovoid, but in elongated cells it may become spindle-
shaped or cylindric. It is surrounded by a very delicate
membrane, and is composed of two sorts of substances, one
of which can be readily stained by certain liquid dyes, while
the other usually remains uncolored (fig. 2). The nucleus

A B

FIG. 2. — A part of the same cell as in fig. i. but older, with the nucleus beginning to
divide. The dark thread in A, separated into pieces in £, represents the chroma-
tin of the nucleus deeply stained, the rest of the nuclear material being unstained,
a, centrospheres. Magnified 600 diam. — After Guignard.

may divide into two, a regular succession of changes in the
arrangement of the materials composing it characterizing this
process, which is commonly followed by the formation of a
partition-wall separating the cell into two parts, each con-
taining one of the daughter-nuclei.

PLANT LIFE.

7. Centrospheres. — The centrospberes are intimately re-
lated to the nucleus. They are two very minute spherical
bodies lying in contact with it (figs, i, 2). When the
nucleus is about to divide one centrosphere goes to each
pole (fig. 2, B), and the separation of the nuclear material
occurs near the nuclear equator. Just as this occurs the
centrospheres divide, forming a pair at each pole. Two
accompany each daughter-nucleus. Their purpose is not
yet fully understood.

7c

FIG.

FIG. 5.

FIG. 3. — A cell from the interior of the leaf of the oat, showing its wall, and some
inclusions of the cytoplasm, z, the nucleus; c, chloroplasts; 0, an oil-drop. Mag-
nified about 100 diam. — After Zimmermann.

FIG. 4. — A, chloroplasts from the skin of the petiole of ivy; B, from the inner leaf-
cells of morning-glory; C, from the same cells of Achyranthes. The shaded parts
are protoplasm in which are embedded starch-granules, j, and proteid crystalloids,
k. Magnified about 1000 diam. — After Zimmermann.

FIG. 5. — Leucoplasts from a young shoot of Canna. The shaded part is protoplasm,
in which are embedded starch-grains, s, and proteid crystalloids, k. Magnified
about 1000 diam. — After Schimper.

8. Plastids.--In most cells there are also other protoplas-
mic structures, the plastids. In young cells these are small,
rounded, colorless bodies. As the cell grows older they in-
crease in size and number. At maturity, in cells which lie
near the surface of green plants, they are commonly roundish
or biscuit-shaped, of spongy texture, and colored yellowish-

INTRODUCTION.

5

green by a substance known as chlorophyll. These are con-
sequently known as chloroplasts or chlorophyll-bodies (figs.
3, 4). In other cells, particularly those for the storage of
food, they may develop into smaller, denser, flattened or
roundish, uncolored bodies, called leucoplasts (figs. 5, 6, 7).
These may act either as starch-accumulators, or in case

FIG. 6.

FIG. 7.

FIG g — Part of the cell-contents of an inner cell of white potato, z, nucleus; j,
starch-grains, each having been formed by a leucoplast, /, which is still attached to
one side of the grain; £, crystalloid. Magnified abont 1000 diam. — After Zimmer-
mann.

FIG. 7. — Leucoplasts in place in a young cell of a leaf of vanilla. /, leucoplasts; z,
nucleus; e. an oil-former or elaioplast. The unshaded spaces surrounded by proto-
plasm are vacuoles. Magnified about 1000 diam. — After Wakker.

of need, in young cells, may even be converted into chloro-
plasts. In other cells, particularly in highly colored parts,
the plastids may become of most diverse form and size, and
colored red or yellow, whence they are called chromoplasts
or color-bodies (figs. 8, 9).

9. Wall.- -The cell-wall is formed by the protoplasm.
In green plants when first formed it consists chiefly of cell-
ulose, with which, as it grows older, various other substances
may be mixed.' Some of these, such as pectin, are present
even in the young wall, and may increase with age ; others

PLANT LIFE.

are characteristic of special changes which the wall may
undergo. The most noticeable changes are four: (i) Some
cell-walls contain suberin or cu/m, fat -like substances by the
presence of which water and gases are hindered from passing

FIG. 8. FIG. 9.

FIG. 8. — I, chromoplasts from flower-leaves of an orchid; II, from the root of carrot;
III, from the fruit of mountain-ash. Embedded in the protoplasmic body of the
chromoplast are sometimes proteid crystalloids, /, pigment-crystals, _/", or starch-
grains, s. Magnified about 1000 diam. — After Schimper.

FIG. 9. — Chromoplasts from the flesh-colored shoots of the horsetail, containing the
coloring matter in the form of granules embedded in colorless protoplasm. Mag-
nified 1400 diam. — After Zimmermann.

through. The cell-walls of 'bottle-cork are suberized, and
those in the skin of the apple are cutinized. (2) Some cell-
walls are lignified, as, for example, those of wood by reason of

V" **"

FIG. io.— A part of a thin slice lengthwise through the centre of the stem of garden-
balsam. The cells and vessels are elongated and are here seen from the side, show-
ing the thickened lines on the side walls of z>, z/, z/", v"1 ', z/"", and v'"" . Mag-
nified about 400 diam. — After Duchartre.

the presence of certain substances (vanillin, coniferin, etc.).
They allow the ready passage of water and gases. (3) Others
are so transformed that, in contact with water, they swell
enormously, forming a mucilage or gum. These swelling

IN TROD UCTION.

substances are produced by the alteration of the cellulose or
other constituents of the original wall. (4) An excessive
deposit of mineral matters in the
wall is known as mineralization.
Such walls may even retain their
form after all organic matter is
burned out, as in the skin of the
scouring rush or horsetail.

10. 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 Fu? "..-Cells from a liverwort

J showing thickened walls A^

uniform. When the wall grows haifaaeiat ^' art re

highly magnified; B, a cell from

thicker except at certain spots, these th.e, ^wer part of the thaiius,

with reticulate thickenings

remain as pits or pores in the (shaded); c, A rhizoids with

isolated branched thickenings.

thickening layers. When only cer- Highly magnified. - After

Sachs.

tain spots or lines grow thicker,

the wall shows projecting spikes, bands, or threads, which

give it the appearance in figs. 10, n.

CHAPTER I.

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.

Blue-green algae.

11. Fission-algae. — The simplest forms of these, the fission-
algae, have the protoplasm only slightly differentiated. The
central part becomes the nucleus, while the whole of the
remaining protoplasm is colored by the chlorophyll and a
blue coloring matter called phycocyanin, so that in mass these
algae look bluish-green or even blackish. For this reason
they are called blue-green algae to distinguish them from those
in which only the yellow-green of chlorophyll is present.

12. Gelatinous colonies.- -The cell-wall may be a thin

sheet of cellulose, 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 homo-
geneous or showing distinct stratifica-
tion. When a number of such forms
grow in company (fig. 12), this
jelly-like material blends into a single

FIG. 12.— A blue-green alga J

Single indi- mass jn which the protoplasm of the

and colonies

to be em-

viduals, A,

^~E^-f. 5f vaj,!ous afes associated plants seems

Magnified 300 diam. — After

Sachs- bedded.

13. Gelatinous filament-colonies. — In other cases, instead
of being associated only by the adhesion of the mucilaginous
portion of the cell-wall, the cells, still practically inde-
pendent the one of the other, remain connected by the

8

SINGLE-CELLED PLANTS AND COLONIES.

firmer portions of the wall into rows, forming irregularly
coiled or serpentine filaments, which are embedded in a
profuse gelatinous material (fig. 13). The essential inde-
pendence of the individual cells, even though they remain
connected, is shown by the fact that such a chain may be

il^lfe^^lf A

FIG. 13. — Nostoc. A, a gelatinous colony, irregularly lobed. Natural size. /?, a
portion of a serpentine filament with five heterocysts (one at each end by which it
\vasseparatedfromtherestof the cells composing the filament, and three inter-
mediate ones") and the jelly belonging to it. Magnified about 400 diam. — After
Thuret and Janczevvski.

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 (/*, fig. 14), called heterocysts,
whose function seems to be to break the chain into pieces,
from the growth of which independent colonies may arise.
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. 13).

14. 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. 15).
In them the cells remain connected more extensively and
more firmly, so that each is disk-shaped, and the filament is
much less easily separated into its component cells. More-

10

PLANT LIFE.

over the gelatinous part of the wall is much less prominent,
so that often it is only seen with difficulty. Even though
invisible, it may be detected by the slippery feel of the
plants when rubbed gently between the fingers.

' ^~^TJ^* i "?«"- :" ' ' "• ''

FIG. 14.

FIG. 15.

FIG. 14. — Part of a filament of Anabcena. /i, heterocyst; a-d, successive stages in
the division of a cell of the filament. Magnified 540 diam. — After Strasburger.

FIG. 15. — Oscillaria. a, the tip; b, a portion of the middle of a filament. Magnified
540 diam. — After Strasburger.

15. Feeding habits. --The feeding habits of the oscil-
larias are worth notice. They are found in permanent
puddles and ditches where organic matter is decaying. The
significance 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
(see \ 230), learned to utilize 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 consequence, they lost their color and became incapable
of existing where organic food cannot be had.

Bacteria.

16. Fission-fungi. — Along with the loss of color and
change of habit went a diminution in size. They have thus

SINGLE-CELLED PLANTS AND COLONIES.

I I

become so different that they are now known as fission -fungi,
and popularly as bacteria, bacilli, microbes, germs, etc.
These plants, probably the descendants of common ancestors
with the fission-algre, are the smallest known organisms
(figs. 1 6, 17). The diameter of many sorts does not

o o

a

OS

ooooooj e

FIG. 16. — Various bacteria, «, Micrococcus, the " blood-portent " ; <5, zoogloea form
of the same ; c, Bacterium acetz, 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.

exceed .0005 of a millimeter. That would allow 175 to
lie side by side upon the edge of the paper on which this
book is printed. In many the successive divisions are
parallel, in others they divide the cells in two planes, and in
others again in three. The cells, when they divide, separate
readily, in most sorts never cohering at all, but living as
independent cells as soon as produced. Other sorts remain
connected into two- to several-celled chains, sheet, or packets
(a, d, fig. 1 6). A few have their cells firmly coherent into

12 PLANT LIFE.

a filament. As the cells are either spherical or rod-like, the
shape of the colony depends upon the shape of the compo-
nent cells and the way in which they divide (see 1~ 24).

17. Gelatin. — In the fission-fungi, as in the fission-algae,
considerable masses of gelatinous material are produced, in
which the cells may lie embedded. The films, sometimes
smooth, sometimes wrinkled, which appear on an infusion of
organic matter, are formed by the masses of bacteria which
become embedded in the gelatinous material produced by
the alteration of their cell-walls (b, fig. 16).

18. Cilia. — Most species are furnished with locomotor
organs consisting of fine threads of cytoplasm protruded
through the wall, which, 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
lashes, called cilia, may be single at the ends of the cell
(C, fig. 17), or many at ends or sides (A, fig. 17), or the

FIG. 17. — Bacteria stained to show cilia. A, cilia tufted at one end; /?, cilia irregu-
larly 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.

whole cell may be covered with them like hairs (B, fig. 17).
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
economic relation to health and disease, decay, fermentation,
etc., which cannot be discussed here.*

'- For further information on these plants, see Frankland ' : Our
Secret Friends and Foes ; Pritdden : Story of the Bacteria, Dust and

SINGLE-CELLED PLANTS AND COLONIES.

Yellow-green algae.

19. Single-celled plants with chloroplasts. — Among the
single-celled green plants, one of the most common groups

FIG. 18. — Pleurococcus viridis. A, a single individual; B, a colony shortly after
division; C, the same after separation. Magnified 540 diam. — After Strasburger.

is that represented by fig. 18, which shows a representative
of an extensive series in which the vegetative body consists
of a single cell with its wall, cyto-
plasm, nucleus, and a few relatively
large chloroplasts. In this greater
specialization of the protoplasm, these
plants show the only advance upon
the blue-green algoe. The wall in
such as this Pleurococcus is almost
uniform and quite thin.

20. Colonies. — The cells are fre-

,1 j i FIG. 10. — Volvo.r. a colony.

quently associated in colonies, em- The individuals are repre-

, ill- -11 T<T_ sented by the minute circles,

bedded in jelly or not. Ine most between which the protopias-

., . 111 r ^t i mic strands form a network.

striking and elaborate of these colo- The large bails in the interior

,. i i TT- 7 /• r \ are daughter-colonies to be

nies is formed by Volvox (fig. 19).

In this plant the colony is a hollow
sphere, often large enough to be seen
by the naked eye as a minute green ball, composed of thou-
sands of individuals, embedded in a common jelly, arranged
in a single layer at the surface. Each is connected with its
immediate neighbors by strands of protoplasm, and two

its Dangers, Drinking-water and Ice Supplies; Ritssell : Dairy Bacteri-
ology ; Frankel (tr. by Linsley} : Bacteriology (medical).

set free upon the rupture and
death of the mother-colony.
Magnified about 45 diam. —
From Bessey.

PLANT LIFE.

cilia are protruded into the water outside. The lashing of
these rolls the whole colony about. Each vegetative in-
dividual is entirely like the others, but those connected
with reproduction become specialized.

Diatoms and desmids,

21. Shelled plants. — Other one-celled plants constitute a
group known as diatoms, found in both fresh and salt waters,

a b c d

k

FIG. 20. — Various diatoms, a, Synedra ; b, Pleurpsigma ; c, d, Grammatofihora,
side and top views ; e, colony of Gomphonema, with branched stalks attached to an
alga ; _/", g; single cells of same, more magnified, top and side views; A, colony of
Diatorna, the cells connected into a zigzag band ; z, /£, colony and individuals (top
and side views) of Frngiilaria : /, w, «, Cocconema. 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.

either attached or free-swimming (figs. 20, 21). The dia-
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

SINGLE-CELLED PLANTS AND COLONIES. I 5

or angular. They are peculiar in having the cell-wall so im-
pregnated with silica that scarcely any organic matter is left.
Indeed 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. 21). Each
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. 20). Seen in mass, as they may
often be on the sides of a glass aquarium, living diatoms
appear yellowish-brown. The chloroplasts, which are some-
times single and always few, contain a brownish pigment
(diatomin] in addition to the green chlorophyll.

A

FIG. 21.— A single diatom (Navicula amphirhynchits}. 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.

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-
zag chains, or even branched filaments (//, /, fig. 20).
Other sorts may be attached singly or in clusters by a gelati-
nous stalk (e, fig. 20). In all cases the jelly, like the rest
of the cell-wall, is a product of the protoplasm. The slow

i6

PLANT LIFE.

gliding movements of some free diatoms are due to the pro-
trusion of strands of cytoplasm through slits in the valves.

22. The desmids.- -These form another group of one-
celled green algee. 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. 22).

d

FIG. 22. — Various desmids. a, Micrasterias ; 6, Cosmarium ; c, Xanthidium ;
d, Closteriion ; e, Staurastrum ; _/, Aptogonum. Magnified about 200 diam.
— After Kerner.

Often the body of the cell is covered with warts or spine-like
projections (3, c, fig. 22), or is prolonged into horn -like or
hair-like lobes. These plants also frequently cohere into
colonies (_/", fig. 22). In that case tooth-like projections of
the cell-wall may interlock.

CHAPTER II.

LINEAR AND SUPERFICIAL AGGREGATES.

OBVIOUSLY some of the plants mentioned in the last chapter,
such as the oscillarias, are colonies of cells well on the way
to complete union into coherent filaments whose elements are
attached to each other by considerable areas of the cell-wall.
In order clearly to understand this condition, we must con-
sider the mode of origin of the individual cells composing
the row.

23. Fission. — Under conditions unknown to us, in the
course of its growth a cell may divide by a process known

FIG. 22A. — A, one of the final stages in cell-division. The daughter-nuclei are still
connected by kinoplasmic filaments, and across the equatorial plane particles of new
cell-wall material are formed. J3, the completion of cell-division; the daughter-
nuclei have rounded off and the new wall is like the lateral walls. Magnified 880
diam. — After Strasburger.

FIG 22B. — Three stages of division in the same cell of an orchid (Efipactis
palustris\. The cell is occupied in great part by vacuoles. In this case the new
wall forms first on one side between the nuclei (A), which gradually travel across
to the opposite side (£), the wall extending until it is complete (C). Magnified
about 380 diam. — After Treub.

17

i8

PLANT LIFE.

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. 2 2 A). The formation of the
partition-wall may occur simultaneously in all parts, or it may
be formed on one side first and the nuclei move across the
cell until it joins the lateral walls (fig. 226). In this way an
isolated unicellular plant of Pleurococcus (A, fig. 18) may
divide into two cells so that it consists of two hemispherical
cells, each capable of independent growth (fig. 23, A).
After a time these cells may separate from each other by the
cracking of the original wall at the line of juncture with the
new partition and the cleaving of this partition parallel to its
surfaces into two layers, one of which covers a portion of
each of the thus disconnected cells (fig. 18, C). If this
process of division and separation goes on, the result will be
the production of a number of independent cells more or less
closely associated but not connected.

24. Cell-rows, surfaces, and masses. --In many cases,
however, a second division occurs in one or both cells before

3 1

a'

a"

a"

b'

tf

3 1
B

FIG. 23. — Diagrams of cell division. A, division of a spherical cell into two hemi-
spherical cells, a, b, by the wall i. £, the same after further division in planes 2,
2, 3, parallel to i. 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 b1 ', V ', the inner of which has
elongated preparatory to a division into b" , 6", as by wall 3. C, fig. A after a
second division, by wall 2, at right angles to i.

separation; and sometimes even a third division takes place.
It is evident that the position of the later partitions deter-
mines the form of this temporary aggregate of cells, (a) If
each of the two divides in a plane parallel to the first parti-

LINEAR AND SUPERFICIAL AGGREGATES. 1 9

tion, a row of four cells will result; the two inner cells
would be disks or short cylinders, while the two outer would
be hemispheres (fig. 23, B}. (/;) Hut if (as is actually the
case in Pleurococcus, B, fig. 18) the new partitions are at
right angles with the first, the result is a cluster of four cells,
each of which is a quarter of a sphere (fig. 23, C).

Should a third division occur, it is conceivable that the
new septa might be placed parallel to those already formed,
in case a ; or parallel to one set and at right angles with
the other, in case b ; or at right angles to both, in case c.
In the first instance there would be formed a row, or filament,
of eight cells; in the second, a sheet of eight cells; or, in the
third, a mass of eight cells. This exhausts the possibilities in
the position of successive partitions. If other divisions
occur, they will necessarily be more or less nearly parallel to
some one of the first three sets.*

The structures resulting from cell-division where the cells
remain united are conveniently designated as follows: (i)
cell-rows, filaments, or linear aggregates, arising by division
in one plane; (2) cell -surf aces, or superficial aggregates,
arising by division in two planes; (3) cell-masses, or solid
aggregates, arising by division in three planes.

It is manifest that there are likely to be all degrees of union
remaining between the cells of linear and superficial aggre-
gates, and that the extent and firmness of such union will
depend largely upon the character of the wall. As in every
other case, the artificial distinction between cell-colonies and
cell-aggregates is bridged by all manner of intermediate

forms.

Filamentous algae.

There is a large number of plants in which the vegetative
body throughout life has the form of a filament. The green

*The formation of partitions at angles other than 90° or 180° to pre-
ceding ones would not affect the general result, but would only render
the form of the product, as well as of the individual cells, less regular.

20

PLANT LIFE.

plants of this sort live almost entirely in water or in wet
places, and may be conveniently designated as the filamentous
algce.

25. Spirogyra, etc. — Among these none are more beautiful
or interesting than the filamentous Conjugatae, represented in

FIG. 24.

FIG. 25.

FIG. 26.

FIG. 24. — A cell from filament of Spirogyra.

ch, chloroplast (there are three in this cell) ;

/, pyrenoids ; £, nucleus. Magnified 200

diam. — After Strasburger.
FIG. 25. — A cell from filament of Zygnema^

showing two stellate chloroplasts, in each of

which is a pyrenoid, with the nucleus between

them. Cytoplasm poorly shown. Magnified

550 diam. — After Sachs.
FIG. 26. — Two cells from filament of Zygnema,

showing the gelatinous sheath greatly swollen.

Magnified 245 diam. — After Klebs.

our waters by the genera, Spirogyra, Zygnema, Mesocarpus,
and some others.* They may be readily recognized, during
their vegetative period, by their unbranched filaments, bright

the Conjugate also belong the single- celled desmids already
described,

LIXEAR AND SUPERFICIAL AGGREGATES- 21

green color, and slippery " feel ' ' between the fingers.* Under
the microscope, they are at once distinguished from other
filamentous alg?e by the shape of their
chloroplasts. In Spirogyra these form
one or more flattish, spirally wound rib-
bons, notched on the edges, and embedded
in the protoplasm near the cell-wall (ch,
fig. 24). In Zygnema there are generally
two irregularly star-shaped chloroplasts
(figs. 25, 26) ; while in Mesocarpus a
single flat, plate-like chloroplast, nearly
as wide as the cell, traverses its center

(fig- 27). f

Embedded in the chloroplasts of these
and other algae are usually seen one or
more angular, colorless bodies, often sur-
rounded by a jacket of starch. These are
crystals of reserve proteid, known as pyre -
noids (p. figs. 24, 27). Their size depends Fl.;.27._A ceil from fiia-
upon the amount of reserve food possessed
by the plant.

In these plants there is little or no dif-
ference 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.

26. Ulothrix, etc. — But other filamentous algae show a
distinction between base and apex. In Ulothrix (fig. 301)

* 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.

f See also Ulothrix (fig. 301), which has in each cell a single chloro-
plast in the form of a thick ring.

inent of Mesocarpus.
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. 2, the nucleus.
Magnified about 200
diam. — After Zimmer-
mann.

22 PLANT LIFE.

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 portion
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. 28), as is also the thallus. In

FIG. 28. — A young plant of Vauckeria, developing from the spore. A, mature
spore ; B, the same after germination has begun ; C, plant further developed from
spore, sp, with growing apex, j, and rhizoid, w, 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.

contrast with the preceding, therefore, localization of growth,
producing branching, may be observed.

27. Branching. — A branch begins by the growth in area
of a limited portion of the cell-wall. The pressure of the
contained protoplasm upon the wall causes it to bulge out-
ward at this point, and the convexity gradually increases as
the region grows until the swelling becomes an outgrowth,
whose further lengthening constitutes a branch similar to the
main filament. Growth in length may be limited to the tip
of the filament, or to a narrow zone including one or more
cells, or it may occur indifferently in any part.

28. Coenocytes.--Many algce, while externally like others,
which are divided into true cells, have not the units of

LIiVEAR AND SUPERFICIAL AGGREGATES. 23

structure separated by cell-walls. In Vaucheria, for example,
the whole of the vegetative body forms a single chamber,
in which lies the united protoplasm, corre-

v

spending to many cells, as shown by the
numerous nuclei which are distributed through
it. The external walls of the cells are formed,
but, when the nuclei divide as growth proceeds,
the protoplasm does not divide, and the septa
or partition-walls are not formed. Such an un-
septate company of cells is called accenocy/e.

In the cladophoras (fig. 29) some of the
normal divisions are complete, while others
are only nuclear divisions. Consequently the
cladophoras seem to be a filament of true
cells, but in reality each apparent cell is a
coenocyte, as shown by the several nuclei in
each (fig. 30).

29. External segmentation. A plant
body of this construction may attain con-
siderable size and complexity, as in Caulerpa
(fig. 31) and Acetabularia (fig. 32),* even to
mimicking, upon a small scale, the form of
leafy plants. In such cases the external walls
become considerably thickened, and across FlG- 29-— A sinsle

J plant of Clado-

the protoplasm and its large vacuoles, from phora, showing

profuse monopo-

one side of the chamber to the other, run dial branching.

Natural size.

irregular bars of cellulose which act as braces After Hauck-
to prevent the collapse of the outer walls (fig. 33).

In Caulerpa, particularly, a high degree of development
as to external form is reached (fig. 31). There is a stem-
like axis, v—s, creeping in the mud, which bears green leaf-
like branches, b, on one side and clusters of colorless root-

* Note carefully the scale of the figures.

24

PLANT LIFE.

FIG. 30. FIG. 31.

FIG. 30. — One coenocyte from a branch of Clacfbphora, showing fifteen nuclei, ch,
chloroplasts ; h, pyrenoids ; rt, starch-grains; n, nuclei. Magnified 270 diarn.—
After Strasburger.

FIG. 31 — Part of a plant of Canlerpa. See text, 1 29. Two-thirds natural size.
— After Sachs.

FIG. 32. — Acetabularia. A, an entire plant, natural size — After Woronin. £, dia-
grammatic longitudinal section through the upper end of the stalk and the um-
brella-like circle of crowded branches which grow together ; «, scars left by fall of
an earlier whorl of short branches ; r, ?y, rudimentary branches ; C, the base of
stalk showing rhizoids for attachment, /, and for storage, b. Magnified 20 diam. —
After De Bary and Strasburger.

LINEAR AND SUPERFICIAL AGGREGATES. 2$

like 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.

30. The thallus. - To the loose

aggregation Of Single Cells into COlonieS FIG. 33. -Transverse section
. of axis of Caulerpa, show-

of definite form, as well as to the body ing cross-bars to stiffen wail.

Magnified about 25 diam. —

formed by their more intimate union After Murray.
in the linear and superficial aggregates just described, the
name thallus is applied. The term is most frequently applied
to those more complicated forms which constitute the vege-
tative bodies of the higher algse, which are now to be
described.

CHAPTER III.

THE THALLUS OF THE HIGHER ALG^E.

31. From linear to solid aggregates. — From the fila-
mentous algae, whose body is a linear aggregate of cells, it is
but a step to those forms whose body is a superficial aggre-
gate. When Monostroma grows from the single cell as which
it begins life, the cell-divisions, instead of occurring succes-
sively in parallel planes, are made in two planes at right
angles to each other. The result is a single sheet of cells
forming a leaf-like thallus attached to stones or other algae.
The broader forms are sometimes 20—25 cm- wide.

Ulva, a near relative, develops in much the same way,
but at least one series of divisions occurs in a third plane, at

right angles to the other two, so
that the body of the sea-lettuce con-
sists of two layers of cells. As
fig. 34 shows, it is very clearly dif-
ferentiated into rhizoid and thallus.
If two such layers separate from
each other, as they do in Enter o-
morpha, a hollow, sac -like body is
formed.

So, from the linear aggregates,
we pass through superficial to solid
aggregates of a broadly extended
form.

The transition from linear to solid aggregates of slender

26

FIG. 34. — A small plant of Ulva
lactuca, the sea lettuce, show-
ing thallus, and rhizoid for
attaching it to rocks. Natural
size. — From Bessey.

THE THALLUS OF THE HIGHER ALGsE.

form may be understood by comparing with one of the fila-
mentous algce a member of an isolated order of green fresh-
water algae, the Characece.

Characeae.

32. The order.- -These plants constitute an outlying group
of considerable antiquity, having no near relatives living, yet
showing in the vegetative body some structural resemblance
to the filamentous algre, while, as a whole, their external
form imitates quite closely that of the higher plants (figs.
35 > 36)- The species of Chara and Nitella (the two genera
which make up the bulk of this order) are found in almost
every temperate region, growing in dense masses submerged
and rooting in the mud in quiet waters. They reach a height
of 10-75 cm-

33. External form. — The plants agree in having a central
axis, at certain points of which* arise lateral outgrowths of
two kinds. One kind forms a circle of branches, nearly like
the main axis, except that their growth is limited. These
themselves bear branches of simpler structure. The primary
whorled branches are the so-called " leaves," and the second-
ary ones which these bear are the so-called " leaflets.'

Just above one of the ' ' leaves ' in each whorl is pro-
duced a branch precisely like the main axis, which has, like
it, unlimited growth.

34. The main axis. — In Nitella the axis consists of alter-
nately long and short cells, a very short cell occurring at each
point (" node") where branching occurs. The long cell
extends from one " node ' ' to another. This " internodal '

* Commonly called nodes, and the intervals internedes. These terms,
imposed from analogies with the seed-plants, are entirely misleading from
a morphological point of view, as are also the names "leaves' and
" leaflets," applied to certain divisions of the axis, but they have become
so fixed that it is difficult to avoid their use.

28

PLANT LIFE.

FIG. 35. — Upper part of a plant of Chara, showing whorled branches of limited
growth (" leaves"), and at three lower " nodes " branches of unlimited growth, the
lowest being cut off. The small bodies on the '' leaves" are " leaflets " and sex-
organs. Natural size — After Wille.

THE THALLUS OF THE HIGHER ALG&.

cell is, therefore, of an extraordinary length, as well as of
large diameter.

FIG. 36.— Upper part of a plant of Nitella. Natural size.— After \Ville.

PLANT

35. Cortex. — Nitella and Chara are much alike, except
that in Chara the main axis and all its branches are composed
of a row of large cells, surrounded by a jacket of smaller ones
(fig. 37). The walls of these outer cells are often much
thickened, and incrusted with salts of lime to such an extent
as to render the axis very brittle. Around the main axis the
cell-jacket is of much complexity ; it becomes more simple

FIG. 37.

FIG. 38.

FIG. 37.— Transverse section of the axis of Chara. a, internodal cell; Z>, cortical cells
Magnified about 30 diam. — From a drawing by C. E. Allen.

FIG. 38. — Longitudinal section of apex of axis of Chara. x, apical cell. The seg-
ment next below will divide into a nodal and an internodal cell ; the next one has
already divided and the nodal half has again divided into two internal and several
external (only 2 show) nodal cells, c, d, internodal cells ; between them a node pro-
ducing the branches (" leaves") e and/i and the cortical branches <z, a. b, a similar
branch growing up from node below, only its tip showing. Magnified 330 diam.—
After Sachs.

upon the whorled branches, and is wanting upon the ultimate
divisions.

While a cross-section of the axis shows a complete union
between the walls of the cortical cells (b, fig. 37) and the
central one (a, fig. 37), a study of their development shows
that they are originally branches of the outer cells at each
node, which likewise produce the circle of "leaves.' The

THE 7' HALL us OF THE HIGHER ALG&. 31

branches from the node above grow downward and others
from the node below grow upward until they meet and inter-
lock about the middle of the internode (fig. 38). Thus, the
cortical cells are not produced by division from the large
central cell which they cover and stiffen, but simply grow over
it and become united with it at a very early age, increasing
with its growth and undergoing division at the same time, so
that each cortical branch becomes murticellular.

36. Apical cell.- -The axis and all its branches, in both
genera, are produced by the growth of a single apical cell of
hemispherical form (x, fig. 38). The segments, successively
cut off by partition -walls from its base, each divide a second
time. One of the cells so produced increases rapidly in size,
and becomes the internodal cell, while the other, by succes-
sive divisions and differentiation, forms the node and its ap-
pendages. In those branches which show unlimited growth
the apical cell retains its hemispherical form until death ; but
in the divisions with limited growth ("leaves") it becomes
pointed and ceases to cut off segments from the base.

37. Rhizoids.- -The structures by which the Characeae are
held in place are adapted to penetrate the soft mud of the
ponds and lakes in which they grow. From the nodes near
the base of the axis arise numerous colorless rhizoids, often
of considerable strength through thickening of the cell-walls.

The thallus shows decided increase in specialization of
members. This is accomplished, however, with a minimum
of differentiation in the cells of which the body is composed.

Polysiphonia.

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

38. External form. — The body of Polysiphonia, a branch-
ing alga (fig. 39) which grows in abundance upon rocky

PLANT LIFE.

seacoasts, is not divided into nodes and internodes, and the
branches are differently arranged from those of Chara. The
axis is made up in its larger parts of five or
more rows of cells, the central or axial row
being surrounded by a jacket of at least four
others (fig. 40). But these originate by
division from the central one, and are not, as
in Chara, merely adherent to it. It is, how-
ever, only in the larger parts of the axis that

FIG. 39.

FIG. 40.

FIG. 41.

FIG. 39. — An entire plant of Polysiphonia^ showing mode of branching. Natural

size. — After Kiitzing. (See fig. 229.)
FIG. 40. — Transverse section of one of the branches of Polysiphonia, 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. 41. — Apex of a branch of Polysiphonia which has nearly ceased growing.

Magnified about 100 diam. — From a drawing by Miss Rowan.

this structure appears ; at the tips even of the main axis the
body is a linear aggregate (fig. 41). Polysiphonia, there-
fore, may be looked upon as one of the simplest forms of a
solid aggregate.

39. Apical cell. — As in Chara, growth in length is quite
definitely localized, because it is the elongated terminal cell
of either the main or secondary axes (fig. 41) which pro-
duces, by division near its base, the new cells whose subse-
quent enlargement and division give rise to the axis. In
some red algae the chambers are not cells but ccenocytes, as
shown by the several nuclei.

40. Color. — In this plant, as in very many of the marine

THE T HALL US OF THE HIGHER ALGM.

33

algse, there exists, in addition to the green of the chloro-
plasts, a special coloring matter, called phycoeryth) in. To
the naked eye, this color overpowers the green and gives the

FIG. 42. — Upper part of a plant of Fncus vesiculosus. r, midrib of thallus ; /,
bladders ; .$-, swollen tips covered by numerous elevations, in each of which is a pit
(conceptacle) which contains many sex-oryans. Two thirds natural size. — After
Luerssen.

plant a pink tinge. In other red algae it is often present in
greater quantity and variety of hue, so that brilliant reds and

34

PLANT LIFE.

purples, with shadings of brown and green, mark the more
striking species.

Fucus.

From the very simple body of Polysiphonia to the common
bladder-wrack, or Fucus vesiculosus, there are all stages of
complexity, which cannot be traced here.

41. External form. — The body of Fucus (fig. 42), is
large as compared with the plants previously described. It
is often 75-100 cm. long by 1-2 cm. broad, of greenish -

FIG. 43-— A transverse section of the thallus of Fucus, showing midrib, r ; cortex, c ;
medulla, in ; and a hair-pit,/. Magnified 10 diam.— From a drawing by Mr. C. E.
Allen.

brown color and cartilaginous consistency. Near the base
the thallus is contracted into a stalk whose extremity is
broadened into a sucker-like disk (often lobed) which at-
taches the plant firmly to the wave-
washed rocks on which it grows.
Above, the thallus is flattened, with
a thicker rib in the middle (fig.
43), and branches abundantly by
forking. These branches, though
often twisted, really lie in the same
place as the flattening. Here and
there the axis shows pairs of oval
FIG. 44.-A longitudinal section swellings, the bladders, which, by

through the apical meristem of .-, /-rmtain^ H O-QC^C crivp> rrr^a^r

FUCUS, at right angles to the tne contained gases, give greater

flattened sides of body, c, apical i.linvonrv tn \\\e* nlanrt; in thp wirpr
cell; 3, 2, i, segments succes- °> ai , Wai T.

42. Apical cell. — An examina-
tion of the structure of the thallus
shows a decided differentiation of
cells, which would be expected from the large and complex

.

?hrreeaedcyeii"eCMmagnifided
-After Rostafinski.

THE THALLUS OF THE HIGHER AIG&.

35

form. At the apex of any growing branch is found a cluster
of angular cells, thin-\valled, of nearly uniform size, with
abundant protoplasmic contents, and all in close contact.
One of these cells, lying in the center of the group, some-
what larger and of different shape from the rest (c, fig.
44), is constantly undergoing division, and thus cutting off
cells (segments) from its two inner faces (i, 2, 3, fig. 44).
The cells so produced undergo further divisions, forming
thereby all the cells of which the thallus is composed. This
group of dividing cells is present in all the higher plants.
It constitutes the " growing point ' ' or, better, the apical (or
primary) meristem. The single cell from which all proceed
in Fucus is called the initial, or apical, cell.

43. Differentiation of cells. — But if a thin section of the
thallus, from an older part, be examined (fig. 45), its cells
will be found very different from those
at the apex. The cells nearer the sur-
face are smaller and of different form
from those in the interior. They are
also close-set, whereas those in the in-
terior are no longer in contact with each
other on all sides, but have been sep-
arated by the growing of branches from
the cortical cells between them. These
filamentous branches are crossed and in-
terlaced, with wide intercellular spaces.
All of these older cells have enlarged,
and, instead of being filled with proto-
plasm, they will be found to have large
vacuoles and heterogeneous contents.
The walls, also, are no longer thin and homogeneous, but
have become thickened and differentiated into at least two
layers, the outer of which is capable of swelling enormously
in water, while the inner layer retains its usual form. There

FIG. 45. — Diagram of a por-
tion of fig. 44, magnified
about 70 diam. c.. cortex;
m, medulla. The varied
forms of the cells are due
to the different planes in
which the filaments are
cut. The clear spaces are
filled with mucilage pro-
duced by the cell-walls.
From a drawing by Mr.
C. E. Allen.

PLANT LIFE.

arises thus a cortex, as the outer dense part is called, and a
medulla or pith, as the mucilaginous and apparently isolated
central cells and filaments are called. At the bladders, the
pith becomes filled with air and other gases.

44. Special functions. — Complete examination of all parts,
the disk of attachment, the bladders, and the hair-pits (fig.

FIG. 46. — Several plants of Lessonia, showing tree-like thallus and branched rhizoids
attaching the plants to rocks. ^ natural size. — After Le Maout & Decaisne.

43) with which many species are covered, would reveal still
other modes of differentiation of cells from those of the
apical meristem. Accompanying the change of form is
always specialization of function, which we can interpret
only in a very imperfect fashion from our own standpoint.

THE T If ALL US OF THE HIGHER ALG&.

37

The compact small cells forming the surface are nutritive
and probably in part protective ; the bladders serve to in-
crease the buoyancy of the plants when the tide is in ; while
the abundant mucilage, formed in the interior from the cell-
walls, serves to retain the moisture when the plants are ex-

FIG. 47. — A plant of Sargassum, showing differentiation of thallus. Natural size. —

After Bennett & Murray.

posed by the ebbing tide \ the hair-pits are functionless, so
far as known ; and the strong, elastic cells of the 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.

45. Color. — The coloring matter in the chloroplasts of
Fucus and other brown seaweeds is chlorophyll (green) and

38 " PLANT LIFE.

phycophcein (brown). The chloroplasts exist chiefly in the
cortex, which is, therefore, the food-making tissue (see ^ 230),
while the internal tissues are used for storage of reserve food.

46. Intercalary zones of growth. — Some of the brown
seaweeds, instead of growing at the tip, grow in a zone at
the base of the flatter part of the thallus, just above the round
stalk. Such growth is called intercalary growth. There can
be no single initial cell, but at least a zone of initials.

Some species grow to great lengths. One Australian species
is said to attain a length of 200-300 meters. Still others
have the form of a tree, the stalk-like portion representing
the trunk, with a crown of flattened, frond-like branches
above (fig. 46).

The thallus in the " gulf- weed, ' : or " sea-grape ''* (fig.
47), is still further differentiated into rounded, stem-like parts
and flattened, leaf-like ones. The bladders are berry-like
enlargements in the middle of short, rounded branches, and
the form is strikingly like that of a small herb.

* This plant is of interest, also, because from its scientific name, Sar-
gassum, is derived the name of that region in the North Atlantic, in the
loop of the Gulf Stream, the Sargasso Sea, where the plants accumulate
after being torn off the tropical shores on which various species grow.

CHAPTER IV.

THE FUNGUS BODY OF HYPHAL ELEMENTS.

Fungi.

FUNGI are plants without chlorophyll, whose body is gen-
erally made up of long filaments, either loosely or densely
interwoven and united.

47. Origin. — As the bacteria, the smallest and simplest
plants, were derived from the lowest algae by slow adaptation
to a different kind of food, so, at various points in the
ascending scale of algal life, certain algae have adapted them-
selves to the use of organic food which they could secure
ready-made. These, having no use for the chlorophyll and
chloroplasts, 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 themselves to dead
or even living animals or plants in the water. The soil (con-
taining in its upper layers more or less organic matter from
the offal of plants and animals, or from their dead bodies)
and dead or living organisms furnish places of growth for a
great number of species which have adapted themselves to
other than aquatic life.

48. Hyphae. — The filaments of which the fungus body is

39

4O PLANT LIFE.

composed are called hyphae. Each is the result of growth
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. In others no partition-walls are
formed, though division of the nucleus takes place. Even
when transverse partitions are formed, they do not separate
the filaments into cells, but each chamber, or sometimes the
whole filament, is a coenocyte.

49. 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;
D 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. Com-
monly a septum 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

FIG. 48. — Reer-yeast(Saccftar0-

myces cerevisiee}. «, a full- by a small neck, and has only limited

grown plant with a branch

(bud) partially developed, b, growth in length, it is called a bud

r, colonies formed by budding,

the individuals still attached, and the process is known as budding

Magnified 750 diam. — After

Reess. (fig. 48). Such branches are usually

easily broken off, thus readily producing independent plants.
(See further under Reproduction, ^[ 302.) In some species of

THE FUNGUS BODY OF HYPHAL ELEMENTS. 4!

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

50. 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-

FIG. 49. — A single plant of Mucor Mucedo, showing the mycelium as it developed
from a single spore in an infusion of dung. It bears a single erect reproductive
branch rising above the fluid. Magnified 25 diam. — After Brefeld.

plex a web that it is impossible to follow a single hypha for
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. 49,
50). The mycelium may be formed wholly upon the sur-

PLANT LIFE.

face of the object upon which the fungus lives ; or parts of
it may be superficial, 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 ;

FIG. 50. — A section of part of the aerial body of Polyporus. j/, hyphse running at an
angle to the section, cut across ; K, crystals of oxalate of lime. Magnified about
500 diam. — After Vogl.

in others (Penicillium, etc.), the superficial hyphae become
so 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.

THE FUNGUS BODY OF HYP HAL ELEMENTS. 43

51. 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 com-
pelled 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,

sp

FIG. 51. — Young hyphae of Exobasidiuin developing from spores, sp^ entering the
air-pores of the leaf of the cranberry. Others, from sp' , sp" , penetrate the skin
directly. Magnified about 600 aiam. — After Woronin.

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 dis-
torted and useless or are even killed ; sometimes the disease
is general and is followed, slowly or quickly, by general
death of the host.

52. Infection. — These internal parasites obtain entrance

* See further ^ 222, 464.

44

PLANT LIFE.

to their hosts in various ways. Sometimes the young hypha,
growing from a special reproductive body (spore),* so minute
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 (sp, fig. 51).
These external openings are connected
with irregular spaces between most of
the cells of the softer parts, which are
also the parts in which the food-supply
is most abundant. In these, therefore,
the fungus develops, breaking out to
the surface again to form or set free its
reproductive bodies.

Or, the young hyphge may excrete
at their tips a substance which so soft-
ens or dissolves the cell-walls of the
host that they penetrate these cells
readily, not only at the surface (sp' ,
sp" y fig. 51), but in the interior. f They
then branch freely, often growing in
the spaces between the cells, often
passing through the cells themselves

FIG. 52 — Hyphae of Tra- r

metes Pini perforating the /fjcr C2).
walls of a wood-cell (at c) of V o' 3 )'

Scotch pine and destroying Plants are often attacked when mere

the primary wall of the cell.

d, e< holes made by hyphae. seedlings. Either from a bit of my-

Magnmed about 800 diam.

—After R. Hartig. celium or a spore which has survived

the winter or the dry season, a hypha grows, which, almost
as soon as the seedling emerges from the seed, penetrates it.
The fungus, in these cases, may develop quickly and kill the

* See \ 304 and the following.

f It is not improbable that the penetration of cell-walls is assisted by
such pressure as the growing hypha can exert, but the relative action of
enzymes and pressure has not been determined.

THE FUNGUS BODY OF HYPHAL ELEMENTS. 4$

young plant (as in the "damping off" disease in green-
houses), or it may develop slowly and not reach maturity
until the host is mature.

53. Haustoria.- -Those fungi which grow upon the sur-
faces of living plants (and those which grow in the internal
air-spaces) often have special branches for fastening them-
selves to the host or absorbing food from it. In the surface

FIG. 53. — Epidermis and a few cortical cells of cowberry with mycelium of Calyp-
tospora 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. «, club shaped hyphje which produce spore-mother-
cells, <r, in the epidermis. Magnified 420 diam.— After R. Hartig.

fungi these are usually very short, disk-like or lobed
branches which do not penetrate the cells of the host. In
other cases they are branches of minute diameter, which
enter the cells, and either enlarge into a knob (fig. 53) or
branch profusely (fig. 54).

54. 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

PLANT LIFE.

occur, and a section of the resulting structure has much the
appearance of a section of the tissues of a higher plant (fig.
55). These changes are particularly apt to occur among the
superficial parts of the more massive structures among the
fungi, where they are necessary to impart firmness, rigidity,
or durability. For example : in the ergot, a fungus common
upon certain grasses, a portion of the mycelium is to survive
the winter and grow again the next season. This portion

rn

FIG. 54. FIG. 55-

FIG. 54. — Branching haustoria of Peronospora. m, m, the hypha traversing an
intercellular space of the host ; z, z, two haustoria penetrating two cells of
the host and branching therein. The other contents of host-cells not shown.
Magnified about 400 diam. — After De Bary.

FIG. 55. — A section through the mycelium of a lichen showing hyphse near upper sur-
face, a, and lower surface, b, fused into a false tissue ; only in central region are the
filaments recognizable. The dark spheres are imprisoned algae. Magnified 650 diam.
—After Bornet.

replaces the young ovulary of the flower (see 1~ 335), and,
as it matures, becomes a dark-colored mass, as firm and re-
sistant as the grain itself (fig. 56).

The interweaving and fusion of the hyphae sometimes pro-
duce cord-like or strap-like structures of considerable size.
The mycelia of the higher fungi frequently form them, and

THE FUNGUS BODY OF HYTHAL ELEMENTS. 47

they may be found in the leaf-mold of forests or in rotten
stumps or between boards in wet places.

a

FIG. 56. — a, compact mycelium of ergot in the form of a grain-like body, replacing
grain of rye ; i>, the same germinating to form reproductive bodies. Natural size. —
After Tulasne.

54a. Lichens. — The body of lichens is a mycelium woven
about isolated unicellular algae, colonies, or filaments,

48 PLANT LIFE.

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 may be broad and thin (fig. 225),
or slender and shrub-like. In texture it may be tough and
leathery, with the hyphae near the surface fused into a false
tissue (at t>, fig. 55). When gelatinous algae, such as Nostoc
(see f 13) are imprisoned, the body may be gelatinous.
In all cases the algae supply the fungus with food, and are in
turn supplied with water absorbed by the spongy mycelium.
(See further If 195, 223, 462.)

* Rarely about other small green plants.

CHAPTER V.

LIVERWORTS AND MOSSES.

55. 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 reproduc-
tive cells, or gametes (see ^[ 369), the egg and sperm,
whence it is called the sexual phase, or the gametophyte. The
other is characterized by the formation of non -sexual repro-
ductive cells, the spores (see T 304), whence it is called the
non-sexual phase, or sporophyte. These two phases alternate
with each other, the sexual reproductive cells of the game-
tophyte producing, under suitable conditions, the sporophyte,
whose non-sexual reproductive cells give rise to the game-
tophyte. To this regular sequence of the two phases the
phrase alternation of generations has been applied.*

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 gametophyte carries on the
greater part of it. To this phase, therefore, attention is
first given.

Liverworts.

56. The thallus. — The form and structure of the vegeta-
tive body of the simplest liverworts is scarcely different from

* Rather obscure suggestions of the alternation of generations are to be
found among the algae 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.

49

PLANT LIFE.

that of some of the green algse. The body is a thallus with
rhizoids (fig. 57). The rhizoids are usually linear aggregates

FIG. 57. — A, plants of Riccia sorocarpa, on the ground. Gametophyte phase. Nat-
ural size. .#, a vertical section of one of the thick lobes of the thallus, showing
nearly uniform structure. The thallus has nearly covered over two young sporo-
phytes which appear as though in the interior. Rhizoids arise from the ventral side
and flanks. Magnified about 25 diam. — After Bischoff.

of cells having thin walls and little protoplasm, arising from
the under side and flanks of the thallus. They serve to

\a

FIG 58. — Portion of a vertical section of the thallus of Lunularia cruciata. a,
dorsal, 6, ventral epidermis; c, an air-pore; e, air-chamber, from whose floor rise
cell-filaments, d ; /, partition between adjoining air-chambers; g, colorless cells
containing starch, some showing net-like thickenings of the walls, others with oil-
bodies, k; /, a ventral scale ; /, a rhizoid. Magnified no diam. — After Nestler.

fasten the thallus to the substratum, — an adaptation to the
terrestrial mode of life. The thallus is usually flat and

LITER WORTS AND MOSSES.

expanded in a horizontal plane, though sometimes much
crisped. The simpler ones consist of several layers of uniform
cells *(B, fig. 57).

57. The dorsiventral thallus. — In other forms there is a
more decided difference between the upper and under sides
of the thallus. The upper cells contain chloroplasts,
while the under ones have none or very few. In the Mar-
chantia family there are large air-chambers in the upper part
of the thallus, from the floor of which arise filaments or
cactus-like rows of chlorophyll-bearing cells (fig. 58). On
the under side, also, are frequently found scale-like out-
growths (superficial aggregates), as in fig. 58, i.

A part which shows constant
differences between an upper (dor-
sal) and an under (ventral) side is
said to be dorsiventral, and the
state of being thus different is
termed dorsiventrality.

58. 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. Some-
times special branches, instead of
remaining horizontal, grow upright

FIG. 59. — Lunulana critciata,
and develop intO peculiar forms showing horizontal thallus and

rhizoids with two erect branches
adapted tO producing the SeXUal (one young, one mature), for

carrying sex-organs. Natural

reproductive organs (fig. 59). size. -After Bischoff.

59. The growing point of the thallus is usually in a notch
at the apex (fig. 60). There is a single apical cell of wedge
shape (rarely tetrahedral), from whose inner faces segments
are cut off (fig. 61). These, by division and growth,

*Ccenocytes rarely appear in the vegetative bodies of this or any
higher group.

PLANT LIFE.

produce the whole thallus. The center of the thallus is
generally thicker than the wings, and forms a sort of central
rib (£, fig. 60).

60. The shoot. --In the greater number of liverworts the
mature vegetative body is a shoot, which is differentiated

FIG. 61.

FIG. 60. — Surface view of growing apex of thallus of Metzgeria furcata just after
forking. «, primary apical cell; <5, secondary apical cell of branch; <r, the wing-
tissue between axis and branch outgrowing the apices. £, the midrib. Magnified
160 diam. — After Kny.

FIG. 61. — Diagram showing origin of branch in Metzgeria furcata. a, primary
apical cell from which the segments right and left bounded by heavy lines have
been cutoff. All have undergone further division. In the right-hand one the latest
cell-walls have been so placed as to form a wedge-shaped cell, ^, which becomes
the apical cell of a branch. Its early formation gives the (false) appearance of
dichotomy. — After Kny.

into stem and leaves (figs. 62, 63). Even in such a body
the dorsiventral character is well marked. The stem is a
filiform axis of uniform cells, bearing three (rarely more or
fewer) rows of leaves, of which the two dorsal rows
are the larger, while the under leaves are much smaller, even
to being inconspicuous or wanting. These leaves are super-
ficial aggregates, consisting 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 always sessile and are usually crowded so closely as to
overlap each other more or less, and hide the axis com-
pletely (fig. 63).

LIVERWORTS AND MOSSES.

53

61. The origin of the leaves will be apparent upon com-
paring figures 64, 65, and 66. In Blasia (fig. 64) the thallus
is lobed, i.e., the edge has not grown equally, but continued
growing longer at certain
points. In Fossombronia (fig.
65) the flattened tballoid
form is still evident, but the
lobing has become so deep

FIG. 62.

FIG. 63.

FIG. 62. — Gametophyte of Bazzania Novce-Hollandice. Besides the ordinary

branches there are slender ones (flagella) with sparse minute leaves. Natural size.

— After Lindenberg and Gottsche.
FIG. 63. — A, dorsal view; £, ventral view of a piece of fig. 62, 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.

that the almost separate parts are usually called leaves.
In Noteroclada (fig. 66) the central axis is still more com-
pact, and has lost its flat form, becoming a rounded stem
from whose flanks arise regular outgrowths, the leaves, each
of which corresponds to one of the lobes of the thallus in the
other forms.

Mosses.

In the mosses the complexity of the mature vegetative body
is somewhat greater. Tt is always developed as a shoot differ-
entiated into stem and leaves.

62. Rhizoids. — The shoot is anchored, as in the liver-

54

PLANT LIFE.

FIG. 64.

FIG. 65.

FIG. 64.— Part of a plant of Blasia pusilla. The flattened lobed thallus is the

gametophyte; the stalked capsules (one young, one bursted) are two sporophytes

attached to it. Magnified 4 diam.— Alter Schiffner.
FIG. 65. — Gametophyte and sporophyte of Fossombronia cristata. The thallus is

so deeply lobed that the divisions are usually called leaves. Magnified 15 diam.—

After Schiffner.

FIG. 66.— A, a gametophyte of Noteroclada, with a sporophyte attached. Natural
size. B, a part of the stem and a single leaf of the same, magnified about 10 diam.
— After Hooker.

LIVERWORTS AND MOSSES.

55

worts, by numerous usually much branched rhizoids (A, fig.
67; iv, fig. 68). Similar filaments may be produced, often
in great numbers, along the stem and especially in the 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.

FIG. 67. — A, gametophyte of Polytrickum commit ne, with rhizoids below. />,
Rametophyte of Hylocomiinn splendens, bearing three sporophytes near top.
Natural size. — After Kerner.

63. The stem is usually cylindrical and covered by the
crowded leaves. In structure it generally shows an advance
upon that of the liverworts in having the whole of the outer
region occupied by a distinct mass of mechanical tissue com-
posed of thick-walled cells, and, near the center, a strand of
elongated small cells, known as "conducting tissue' (fig.
68), though it is doubtful whether it conducts anything.

PLANT LIFE.

FIG. 68. — Transverse section of the stem of Bryum roseum. In the center the
small cells make a central strand, the "conducting tissue"; the surface cells form
an epidermis; the next three rows within also have thick walls and strengthen the
stem; w, rhizoids arising from epidermis. Magnified 50 diam. — After Sachs.

FIG. 69.

FIG. 70.

FIG. 69. — 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. 70. — Tip of leaf of a moss (Oligotricku-m aligerutii)^ 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.

LIVER IVOR TS A XD MOSSES.

57

64. The leaves are also more highly developed than in
liverworts. They are always sessile and are arranged in two
(rarely), three, or more vortical ranks along the stem, and
consist usually of a single sheet of chlorophyll-bearing cells,
the blade (figs. 69, 70), and a central rib running from base
to apex (frequently wanting), which is composed of elongated
conducting and strengthening cells (figs. 69, 70). In some
the amount of green tissue is increased by the formation of
vertical plates similar to the blade (fig. 70).

65. Branching.- -The stem branches, often very profusely,
by the formation of lateral growing

points beneath the developing leaves.
Sometimes the growth of the lateral
branches, as of the original main
axis, is checked by the formation
of sexual organs. In that case a
new branch is likely to arise some
distance below the apex, so that the
stem is a succession of lateral
branches, called a sympodium (fig.
71). This mode of branching is
termed 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 FlG 7I._Axis of a moss (Ortko.

/-olUrl -nirMnhnrlinl Oft^n rVip» trichniii) showing sympodial

Called monOpOaial. tne branching. .S VV.ja, S«,succes-

,1 r .1 i i j c. sive clusters of sexual organs,

growth ot the lateral axes is den- produced at apex which check

-.1 i- •, j j ,1 j i the growth of axis. Beneath

nitely limited and their develop- each" a lateral growing point

i r • develops, producing successively

ment regular, forming a pinnate the b«nces /-', ** ^. Magni-

i i -rr .1 j rit-d 10 diam. Alter l'>nu-h A:

branch-system. It the secondary schimpt-r.

axes themselves branch, there is formed a bipinnate or

even tripinnate system, as in figure 67, B.

PLANT LIFE.

66. 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 prolonema^ almost
identical with the form of the filamentous algae. Upon this
protonema the leafy shoot arises as a lateral bud, which soon
outstrips it in growth and differentiates leaves. The proto-
nema may live for some months, but generally perishes after
having produced a few leafy plants.

67. Sporophyte.- -The non-sexual phase in the liverworts
and mosses has almost no vegetative functions, and a fuller

a

B

G

FIG. 72. — .-/, two capsules of Bryum ; from the right-hand one the lid has fallen,
showing the teeth. Magnified 5 chain. B, four gametophyte shoots of Splachnum
ampullaceum, bearing four sporophytes. Natural size. C, a capsule of one of
the same sporophytes, showing enlarged apophysis, a, below the sporangium, j.
Magnified 10 diam. D, capsule of Splachnum liiteuin, with umbrella-like apo-
physis, «, below sporangium, j. Magnified 2 diam.

study of its structure is left for Part III. It consists at
maturity of a yellowish or brown spherical or cylindrical case
(fig. 72), which is sessile or raised upon a short or long
stalk and contains (a few or) hundreds or thousands of
reproductive cells called spores. The base of this stalk
constitutes an organ called the "foot,' which is embedded
in the gametophyte (f, fig. 73).

68. 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,

LIVERWORTS AND MOSSES.

59

for these are great on account of its rapid growth and the

supply required as reserve for

each spore. The foot, being in

close contact with the tissue of

the gametophyte, acts as an

absorbing organ, receiving food

solutions from it. The sporo-

phyte thus lives, in part at least,

as a parasite upon the gameto-

phyte.

In some mosses there is a ten-
dency to increase the nutritive
work of the sporophyte by de-
veloping at the top of the stalk,
below the spore-case, a mass of
green tissue. In Bryum (A, fig.
72) this gives the capsule a pear-
shape, while in Splachnum (£,
C, D, fig. 72) it is so far de-
veloped as to exceed the spo-
rangium. In some species it is

expanded into a miniature urn- FIG. 73.— Young sporophyte of

ciiiii cHspidatitm. c, columella ; J\
brella which, One Can imagine, foot, embedded in gametophyte stem;

s, seta (cells not shown); sfis, spo-
might readilv become Segmented ran.n-uim; .?/, spore-mother-cells.

Magnified 80 diam. — After Kienitz-

into leaves. Gerioff.

The intimate attachment of sporophyte to gametophyte
continues throughout the life of the former. Sometimes the
gametophyte 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.

CHAPTER VI.

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/11 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.

69. The gametophyte.- -The vegetative body of this phase

of the fernworts in its best developed forms
is a small, flattened, green body of oblong,
orbicular, or cordate outline, commonly
less than half a centimeter in diameter,
rnrely as much as 2 cm. (fig. 74). It is
strikingly like a thallose liverwort in

f^ J

general form, being distinctly dorsiventral
and having rhizoids on its under side,

FIG. 74. —Ventral side of . . . . , c , .

the gametophyte of a which fasten it 111 plaCC. (BCCaUSC OI thlS

fern, Asple niitni. The ,,,.,,.

notched end is the an- thalloid form and DCCaUSC it SCCmed to

terior. Rhizoids near . .

posteriorend. The small precede the 'real plant — a popular

circles show position of . .

male organs; the chim- phrase meaning the sporophyte — it was

ney-likeprojectionsnear , ,.. /~v i ,1

anterior end the female called a promauuim.) Only the central

organs. Magnified 10 . . r

diam.— After Kerner. part oi the gametophyte consists ot more
than one layer of cells. On the under side of this central

60

FERNWORTS A XI) SEED-PLANTS.

61

"cushion,'1 as it is called, are produced the sexual organs.
(See further under Reproduction, Part III.)

70. Reduction of garnet ophyte.- -In a few of the fern worts
the gametophyte is filamentous, or tul)erous, and more or less

FIG. 75. — Sporophyte of a fern, rolyp^dimn 7' allure, showing horizontal underground
stem, bearing secondary roots and leaves. Natural size. — From Bessey.

completely subterranean and colorless. Such prothallia 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
the sexual organs. These reduced forms grow by the use of

62

PLANT LIFE.

food stored in the spore from which they originate. The
gametophyte of such species has lost wholly its vegetative
character, and is restricted in function to the production of
the sexual organs.

71. The sporophyte. — In contrast with the smallness and
simplicity of the gametophyte is the relatively large size and

9

f

FIG. 76. — Embryo of Pteris aquilina, and a small part of the gametophyte, £-, in
which its foot,_/~, is embedded, r, the primary root ; .?, primary stem ; /, primary
leaf. Induced growth of the gametophyte about the foot is shown by small size and
number of cells. Much magnified. — After Hofmeister.

FIG. 77. — Section through embryo and gametophyte of maidenhair fern (Adiantiini
Capillus-Veneris}. The embryo is older than that in fig. 76. /,/, gametophyte;
//, rhizoids, among which are two spermaries. The eggs in three ovaries failed to
develop ; the other formed the embryo, E. a, primary stem, only slightly de-
veloped (compare j, fig 76) ; ^, primary leaf ; w, primary root. The part embedded
in the gametophyte is the foot. Magnified about 10 diam.~ After Sachs.

complexity of the sporophyte (fig. 75). It is always differ-
entiated into stem and leaves, and, with rare exceptions,
roots also. This great advance in the development of the
sporophyte of the fermvorts, as contrasted with its form in
their nearest of kin below, the liverworts and mosses, suggests
that the fernworts are a very old group ; a hint which is con-
firmed by the antiquity of their fossil remains. It is also
noteworthy that, as compared with mossworts, the chief work

'TS AND SEED-PLANTS.

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.

72. The embryo.- -The fertilized egg, from which the
sporophyte arises, develops while still embedded in the
gametophyte in which it is formed. Consequently the
embryo sporophyte is, as in the mossworts, at first surrounded
by the gametophyte (figs. 76,
77). The part of the gamet-
ophyte adjacent to the embryo
grows under the stimulus of its
presence, but the growth of the
embryo is more rapid, and it
consequently spreads apart the
gametophyte (see figs. 76, 77).
A portion of the embryo de-
velops a temporary organ, the
foot, which remains embedded
the gametophyte until the

in

first root, stem, and leaf have
been formed (fig. 78). Soon
thereafter the gametophyte per-
ishes and the foot, no longer
useful, disappears.

73. 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

FIG. 78.— The same as fiff. 77, older.
The gametophyte, /, seen from be-
low, with rhizoids; the sporophyle
still attached but with primary leaf, /.
developed into blade and stalk ; /. the
primary root: .?, a secondary root,
arising from the juncture of leaf-stalk
and stem. Magnified about 4 diam.—
After Sachs.

64 PLANT LIFE.

of the seed-plants that thay will be discussed in connection
with them.

Seed-plants.

Among the highest plants, those which produce seeds, the
differentiation of the body is essentially the same. 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 remarked 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 sexual organs
which it produces, and one or more cells which are, perhaps,
the rudiments of its vegetative body. The sporophyte, con-
sequently, is the only phase of the seed-plant visible to the
unaided eye. The relation of the gametophyte to it will be
explained in Part III.

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. To a
discussion of the vegetative members of the fernworts and
seed- plants we now turn.

CHAPTER VII.

THE ROOT.

74. Analogous members. — 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
sometimes called by the same 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 homologous with the roots of the higher plants, but as
merely analogous with them. In the plants whose vegetative
body is a thallus the gametophyte is the prominent 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, there-
fore, only among fernworts 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 produce
some organ capable of holding it in place, or of absorbing
materials from the outside, or of doing both. The organ
developed to meet this need is the root.

75. Primary roots.- -In accordance with their origin,
roots are either primary or secondary. Primary roots are
those which are developed directly from the egg from which
the entire plant takes its rise. The spherical egg in most
of the fernworts begins its development by a division into
hemispheres. The hemispheres divide into quadrants ; each
of the quadrant cells divides into two, forming octants of the
original egg. Division continues and the fundaments of
primary root, foot, stem, and one or more leaves appear

65

66

PLANT LIFE.

(see fig. 76). In many of the seed -plants the egg divides

several times in parallel planes, forming a
short filament, the suspensor (figs. 79—82).
The terminal cell of this row may then
give rise to an embryo, as just described,
or this terminal cell and an adjacent one
may take part in forming the embryo. In
this case the terminal cell, bv its divisions,

' -•

either produces the primary leaf or leaves,
Flemb7ry7VthI IS. or it: Produces the primary stem and
sor- °Jn «° VhcefisSfrom leaves \ while the second cell gives rise to
ve^fs^liirHaEt the Primary stem and root, or to the
fied. -After Sachs. primary root alone (see figs. 80-82).
The two primary members formed
from the root hemisphere of fernworts
are not always permanent. The foot is

FIG. 80. FIG. 81.

FIG. 80.— A very young embryo of shepherd's-purse. Suspensor, j, j. just completed,
and first four cells of embryo formed by division of terminal one ; the second cell,
l>, is to produce part of the root. Highly magnified. — After Hanstein

FIG. 81.— An older stage of the same. E, embryo; b1 ', 6", two cells resulting from
division of b. fig. 80 ; j, .?. suspensor. The shaded cells produce the skin and the
vascular bundles Highly magnified.— After Hanstein.

FIG. 82.— An older embryo of same. £, embryo; /, /, primary leaves: sf. apex of
stem ; r, primary root ; re, first layer of root-cap; s, suspensor. Cells shown only
in part. Less magnified than preceding. — After Hanstein.

THE XOOT. 67

always temporary, disappearing as the embryo becomes
larger. It is sometimes wanting from the first. 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, however, the primary root persists throughout
the life of the plant.

76. Secondary roots. — Secondary roots, on the contrary,
are those 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. 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 ^[ 119.) 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. Secon-
dary roots often arise in regular succession toward the grow-
ing apex of the stem, particularly in plants which have creep-
ing or subterranean stems.

77. Growing point. --Primary and secondary roots do
not differ materially in their structure. The early divisions
of the quadrant cell which produces the primary root in fern-
worts are so arranged that a cell shaped like a four-sided
pyramid is produced. This cell becomes the apical, or

68

PLANT LIFE.

e/i

fc.

initial, cell. It is situated with one face directed toward the
apex of the root (see fig. 83), and the other three faces
within it. Parallel to the three inner faces partitions are
constantly formed in regular succession dividing this apical
cell into two unequal portions, so that the smaller is looked
upon as a segment cut off from the larger portion. If these
inner faces be numbered respectively i, 2, 3, the segments

are constantly produced in the
order of the numbers. These
segments themselves divide to
form other cells, and thus give
rise to all the tissues of the root.
This mass of actively dividing
cells is the primary meristem or
growing point of the root (com-
pare ^[101). As the older cells
of the primary meristem enlarge,
divide, and differentiate, they
are constantly pushing the apical
cell further away from the older
part. Not only are segments
cut from the three inner faces of

/* l **(,

the apical cell, but, at less fre-

FIG. 83. — Median longitudinal section

£rou.K.h the extremity of a root of quent intervals, partitions paral-

Marsiha. 1 he large triangular cell

near center of figure is the apical ^ to tne outer face form sjmi_

cell. I he segments from the inner

faces may be readily traced back- }ar seorments. The division of

ward; thus the dotted line ec points

to the fourth, c to the sixth segment fVvpcp Qpcrmpntt; crivpt; ri^p tn ^

from the posterior right-hand face of >C&U

apical cell. */, root-cap (epidermis); structure COVerinfiT the VCIT tip
ec. cortex; c. stele; <?«, endodermis

(pfart ,°f CMrtex^i; '/' Perlcyde H-part of the root, and connected with

of stele). Magnified about 100 diam.

-After Van f ieghem. jt for a s}lort distance Only. It

J

receives, therefore, the appropriate name of root-cap (ep, fig.
83). Since the cells of the surface of the root-cap are older
and firmer than the inner segments and the initial cell, and
lie in front of them, they serve to protect the more delicate

THE ROOT.

69

cells as the growth of those behind constantly pushes the
apex forward through the soil.

In seed-plants, the segments of the egg which produce the

FIG. 84. — Transverse section of a young root grown in soil, showing root-hairs with
adherent soil-particles, the cortex, and the stele. Magnified about 20 diam. — After
Frank.

root do not divide so as to form a single apical cell, but a
group of initial cells, which retain the power of rapid division
and constitute a primary meristem or growing point. In all
other respects the development of the root from this group
of initials is similar to that already described.

PLANT LIFE.

In both cases, the differentiation of cells produced at the
growing point results in the formation of three characteristic
parts of the root, namely, (i) an outer layer or layers, the
epidermis ; (2) an inner region, the stele ; (3) between these,
the cortex.

78. i. The epidermis usually becomes many-layered.
At the apex it constitutes the root-cap (ep, fig. 83). 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
innermost as the covering of the cortex.

79. (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 (fig.
84). These root-hairs are
branches of the superficial

A

n

B

cells (fig. 85), and may be
looked upon as simple ex-
tensions 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. 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

FIG. 85. — Two root-hairs showing structure
and relation to superficial cells of root ;
grown in water and therefore not distorted
as in fig. 84. A, the younger; B, older,
nearly mature. «, nucleus embedded in
cytoplasm; vacuole single and very large.
Highly magnified. — After Frank.

THE ROOT. 71

root, therefore, is without root-hairs because' of their death.
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 produced and
the older ones are dying at an equal rale, so that a zone
of hairs is found only upon the younger parts of the roots.

80. (b) The root-cap, serving to protect the tenderer por-
tion of the root behind, is itself constantly exposed to injury.
The outer and older cells of the root-cap are, therefore, either
torn away through mechanical contact, having become gradu-
ally loosened from each other with age; or, losing their
active contents, they degenerate and break down into a
slightly mucilaginous material which facilitates the passage of
the root through the substratum. This degeneration or the
mechanical wear is repaired constantly by the formation of
new cells in the growing point. The thickness of the root-
cap, therefore, is maintained throughout its existence without
considerable change. It rarely becomes more than a few cell-
layers thick. Since its tissue is produced only by the division
of the apical cell or cells, it is organically connected with the
root only at the very tip; but it usually extends backward over
the root, by reason of its growth, for a considerable distance.
If the finger be supposed to represent 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.

81. 2. The stele. — Occupying the center of the root, and
surrounded on all sides by the cortex, is an aggregate of
tissues called the central cylinder, or stele (figs. 84, 86, 89).
The outermost layer of its cells is the pericycle (figs. 86 88,
89). Within this are found strands of elongated cells or
cell-fusions,* called vascular bundles, or strands. These

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

PLANT LIFE,

bundles are of two kinds, xylem bundles and phloem bundles,
so placed that they alternate with each other about the
periphery of the stele (figs. 86, 88, 89). The xylem bundles
may be in contact with one another in the center, or the
center of the stele may be occupied by a pith (figs. 86, 89).

FIG. 86. — Transverse section of the stele and a portion of the surrounding cortex of the
root of calamus, s, s, innermost layer of cortex, the endodermis, adjoining outermost
layer of stele, the pericycle; /, xylem bundles; ph, phloem bundles. The shaded ele-
ments of xylem bundles are the primary xylem ; the large ones, g, are secondary. In
the center of the stele and between the bundles is conjunctive tissue. Highly magnified.
—After Sachs.

The tissues of the xylem are usually lignified (see *\\ 9)
and, when abundant, make up what is called the wood. They
are the chief water-conducting elements of the older parts of
the root.

The tissues of the phloem are usually not lignified, and the
most important ones are the sieve-tubes, which conduct proteids
from above to the growing regions of the root.

THE ROOT. 73

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
figs. 86, 89.)

82. 3. The cortex generally consists of large thin-walled
cells which have become partially separated from each other,
leaving larger or smaller intercellular spaces (figs. 86, 89).
Its innermost layer, bordering the stele, is usually quite
different from the rest, and is recognizable by its wavy, radial
walls, which are suberized (^| 9). This layer is called the
endodermis (figs. 86, 88, 89).

83. Duration.- -Even when the primary root persists
throughout the entire life of the plant secondary roots often
appear. \Yhen 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 tran-
sient. 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.

84. 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 secondary
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.

85. i. External secondary changes. --In some cases the
older roots differ from the younger in scarcely more than the

74

PLANT LIFE.

loss of the external layer of cells, from which the root-
hairs arose. The sloughing off of this layer of cells 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 altera-
tion proceeds further, so that they become almost or quite
incapable of being penetrated by 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 certain tissues become thick-walled, so
that the root is also strengthened.

In a few instances, the root-cap is cast off from the tip.
This, however, only occurs when the growth in length of the
root is permanently stopped.

86. 2. Internal secondary changes. — In a large number

of roots, especially those
' ' of dicotyledons and gym-
nosperms, the secondary
changes result in increasing
the diameter, sometimes
very greatly. Increase in
diameter comes about by
the formation of concentric
layers of new tissue in two
or more regions. The new

FIG. 87. — Transverse section of the periphery of 11 j j • i

the root of Clusia, showing the formation of cells ai"G produced 111 each

periderm. cc, cells of cortex; /?/, the super- • i , i

ficial cells of the root (suberized) ; AT, the region by the resumption

periderm, its inner cells (opposite fier) actively r «.• J- • • • i

dividing by tangential walls, Us two outer layers, OI active division 111 a layer

//, suberized, its innermost layer, ///.the phello- r n 1-1 i j i

derm. Highly magnified.— After Van Tieghem. OI Cells Which had bed!

temporarily inactive. This region is then called the cambiu?n
or secondary meristem (see ^j 77). The divisions which ensue
in these cells are in the main parallel to the surface of

V

£C

THE ROOT.

the root, that is, they are
Uvi^cntuil divisions.

The outer growing layer
or cork cambium is in the
great majority of plants
formed from the cells of the
pericycle, but it may be
produced by some of the
cells of the cortex. In any
case the tissues which arise
from this division are of
such a nature as to protect
the parts within. They con-
stitute the/£ 'rider m (fig. 87),

-4-J UJ -'I

P

X

FIG. 88. — Transverse section of two bundles
from the periphery of the stele of root of broad
bean (I'tcia Faba) at the beginning of secon-
dary thickening. The xylein bundle, g, is
shaded; the phloem bundle unshaded. ?>, the
stelar cambium; /, the pericycle, also showing
tangential divisions in parts ; s, the endoder-
mis. Highly magnified. — After Haberlandt.

I

FIG. 89. — Transverse section of the stele of root of bean (Phascolus multijlorus) shortly
after secondary thickening has begun, s, endodermis; /r, pericycle; /', phloem bundles;
/, primary xylem bundles; g, g' , secondary xylein; c, stelar cambium; J7, central pith.
Compare with fig. 90. Highly magnified. — After Sachs.

76

PLANT LIFE.

and are ordinarily cork-like, i.e., thin-walled and impervious
to water. Those cells which lie outside 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
xylem and inside the phloem
bundles (fig. 88). As a result
of tangential divisions in this
region, tissues similar to those
already existing in the stele are
produced. On the outer side
the cells differentiate mainly
into the tissues of the phloem,
and on the inner side mainly

FIG. go.-Transverse section of the older intO those of the Xylem, often

part of the main root of bean (Phase- frkrrn:ricr n npirlv nnhrnVfn
olus multi-floras) after secondary lOrmmg a lieaily UnD
thickening has progressed consider- r i (f.ac 8r> r>r>\

ably. Compare with fig. 89, which is ( Vn§s- °9> 9°)-

about five times as highly magnified. r~1ntlVo amnnnf nf trip
6, 6, 6, 6, four primary phloem bundles; ]

6', secondary phloem produced by f- whirh rmkf» nn

stelar cambium, as are the four wedges L*^ucs

" PsSwn"' TheySeS^ bundles goes for to determine

the character of the mature root.
87. (a) Woody roots. — If mechanical tissues predominate,
particularly in the xylem, the root will become strong and
rigid, as in the case of trees and shrubs. When the root is
long-lived, the activity of this stelar cambium is usually
resumed with each season, a layer of tissue being thereby
added to the outside of the xylem region, and a thinner layer
to the inside of the phloem. The woody part, especially,
shows in cross-section concentric rings indicating the yearly
additions. Since the material produced by the stelar cam-
bium usually greatly increases the diameter of the root, the
outside parts become fissured lengthwise. Thus, in an old
and much-thickened root of the woody type, the periderm

THE A'OOT.

77

and the phloem region, with the cortex between them, if
anything is left of it, constitute a bark, which becomes fur-
rowed lengthwise, like the bark of the stems of many trees..
Such secondary thickening finally produces in the roots a

FIG. 91. — A, diagram of primary structure. /?, C, diagrams showing the results of
secondary thickening from the stelar cambium in the two extreme forms c, cortex;
ed, endodermis ; /, pericycle ; /, primary phloem ; /', secondary phloem; />, primary
xylem ; />', secondary xylem ; .i,-, stelar cambium; r, secondary pith-rays; /;/, pith. —
After Van Tieghem.

structure which is almost identical with that of stems which
have undergone secondary thickening. (Compare ^j 133.)

88. (b) Fleshy roots. — But if thin-walled cells are the
predominant products of the stelar cambium, 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. The thin-walled
cells which are produced in such volume may belong to the
phloem region, as in the carrot and parsnip, or to the xylem,
as in the radish and turnip. This thickening for storage
purposes may affect either the primary or secondary roots,
or both. Other plants may develop the cortex (orchids) or
the pith (daffodils) to an extraordinary degree, forming
fleshy roots which also function as storehouses.

89. (c) Float roots. --In plants which grow in water or
in very wet swamps, roots are sometimes modified to serve as
floats. In these cases, the voluminous cortex consists of large

7 8 PLANT LIFE.

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.

90. (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
suitable size, and thus assisting the plant to climb ; in some
instances 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.

91. Branching". --Both primary and secondary roots may
branch. The mode of branching is of two sorts, either by
dichotomy, or by the production of lateral branches.

92. (a) Dichotomy occurs only in a few fern worts, whose
roots possess a single initial cell. In this case, however,
the single initial cell (*[[ 77) is not divided into two equal
parts by a partition-wall, as in true dichotomy (see ^| 103),
but the initial of the new branch arises from a very young
segment as in Metzgeria (see fig. 61). The result is a fork-
ing which cannot be distinguished from a true dichotomy.

93. (b) Monopodial branching. --In the common mode
of branching, the monopodial, 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 behind the apical growing
point. But sometimes branches appear out of this regular
order. Such are called adventitious roots. (See *f[ 76.)

94. Position. --Whether regular or adventitious, the posi-
tion of the growing points is determined by the vascular
bundles in the stele, since they originate opposite the xylem
bundles, or with definite relation to them. (See figs. 92,
93.) The number of vertical ranks of branches can, there-
fore, be predicted with some certainty from the structure of

ROOT.

79

the root. While the angular 'diver-
gence is thus quite regular, the longi-
tudinal intervals at which the branches
will be formed, which determines
their distribution along the length of
the root, are unequal (fig. 92).

When secondary roots arise from

j

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 pro-
duced either opposite a leaf, or in
pairs, right and left of the base of the
leaf.

95. Origin. --The origin of root-
branches and of secondary roots is
rarely exogenous ; that is, the root is
not commonly produced by the divi-
sion of cells which lie upon the sur-
face of a member. In the great
majority of cases the origin of the
roots is endogenous ; that is, the for-
mation of the root is begun by the
division of cells lying in the interior
of the member producing it. In most
cases these divisions begin very near
to the surface of the stele, either just
without it, in the endodermis, or just
within it, in the pericycle. Soon a
growing point is formed (fig. 93).
The rootlet is thus in its early stage
completely hidden, being buried

FIG. 92. — Seedling pea, showing
three vertical ranks of branch-
es along the main root. These
are numbered i, 2, 3. Natural
size.— After Frank.

8o

PLANT LIFE.

beneath the cortex, through which it gradually makes its way
by the destruction of the tissues ahead of it, partly through
disorganization of the tissues by pressure, and, probably,
partly through actual digestion and absorption of the material
of these cells. When the rootlet reaches the surface it
emerges, therefore, from a distinct rift in the cortex (fig. 94).

FIG. 93.

FIG. 93. — Transverse section of a root of a fern (Pteris cretica), passing through the
axis of a rootlet which has not yet emerged. Only the stele and three rows of cortex
shown. «, apical cell of rootlet, forming anteriorly the root-cap, ej>, and posteriorly
the body of the root, ec, e, c, pd; b, binary xylem bundles; /, phloem bundle with its
fellow opposite; />e, pericycle; en, endodermis; /, temporary digestive pouch, in
course of disorganization and digestion; d, cells of cortex, which will be disorgan-
ized as rootlet advances. Highly magnified. — After Van Tieghem.

FIG. 94. — The same as fig. 93, 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;
</, disorganized cells of cortex, ec' , of parent root; b' , secondary xylem; other letters
as in fig. 93. — After Van Tieghem.

96. External conditions. --Branching of the root is often
profuse, and is dependent very largely for its character upon
the conditions under which it takes place. In those roots
which penetrate the soil, it is profoundly modified by the

THE ROOT. 8 1

character of the soil itself and the amount of moisture and
organic matter in it.

97. 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 ^[ 101). Whether formed
as a result of injuries or normally, they are known as adven-
titious buds. They arise in the same places and develop in
the same way as lateral roots ; that is, they are endogenous,
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 posi-
tion of the root, being brought about in some potted plants
by turning them upside down.

CHAPTER VIII.

THE SHOOT.

98. The gametophyte shoot. --If plants could be examined
in the order of their development, it would be discovered
that the shoot has been evolved earlier than the root. It
makes its appearance first in the leafy liverworts and in the
mosses, in which the gametophyte and sporophyte each form
a stem. The gametophyte differentiates its secondary shoot
into a stem and leaves. This stem in liverworts is a slender
cylindrical body of very simple structure, upon whose flanks
arise leaves which consist of a single layer of cells only.
(See ^ 60.) Neither the stem nor the leaves are homologous
with the stem and leaves of the higher plants. In the stem
itself one finds all the cells practically alike, so that little
differentiation of tissues has yet occurred. In mosses, how-
ever, the gametophyte stem shows some advance, in that its
tissues are clearly differentiated, the outer being transformed
into thick-walled cells, in order to give mechanical rigidity
to the stem, while the innermost, remaining slender, are
much elongated and serve the purpose, it may be, of con-
duction. (See ^| 63.) This differentiation is naturally more
marked in those mosses which are erect and whose bodv

j

becomes largest, since in these the need for rigidity and con-
duction of food materials from one part to the other becomes
greater. In both groups the branching of the gametophyte
shoot is like that of the sporophyte shoot of some of the
higher plants, except that the branches never stand in the
same relation to the leaves. (See ^| 65.)

82

THE SHOOT. 83

99. The sporophyte shoot.- -The shoot developed by the
sporophyte of mosses and liverworts forms no leaves, but
develops as a slender cylindrical stalk, at the distal end of
which the capsule containing the spores is formed (figs. 64,
73). It is rather difficult to see in this cylindrical stalk the
homologue of the leafy stem developed by the sporophyte of
the fernworts ana other plants.

The simultaneous performance of the work of nutrition and
of sexual reproduction proved impracticable, as shown by the
development of the liverworts and mosses, which are all
humble plants. The fernworts, originating probably at an
early period from the same ancestors as the liverworts, sep-
arated the two functions and laid the chief work of nutrition
upon the sporophyte. The advantage thus gained enabled
the extinct fernworts to develop into plants of tree-like size,
and to become the ancestors of all the seed plants.

The gametophyte shoot was, comparatively, a failure; the
sporophyte shoot was a marked success. It has become
adaptable to many conditions and many functions. To
accomplish this its members have been extensively modified
in form and structure in various plants. The development
and mode of branching, together with the various forms
which the shoot assumes, are now to be discussed, to be fol-
lowed by an account of the two members, stem and leaf, into
which it is usually differentiated.

100. Primary shoot.- -The shoot which develops from the
fertilized egg is called the primary shoot. A very few excep-
tional plants are found in which no primary shoot develops,
although there are a number of cases in which the primary
shoot becomes early aborted, and its place taken by secondary-
shoots arising from the root. The primary shoot normally
arises in fernworts from the anterior half of the egg. The
anterior hemisphere usually divides into two quadrants, one
of which develops into the primary leaf, and the other into

84

PLANT LIFE.

the primary stem. The stem quadrant, by repeated divisions,
quickly specializes a central cell, which becomes the apical
cell of the new shoot. Ordinarily it takes the form of a
three-sided pyramid, whose base forms the extreme tip of the
developing shoot (j, fig. 76, /, fig. 95). From the three inner
faces, as described for the root (^j 77), segments are constantly
formed, whose further divisions produce all the tissues which
constitute the members of the mature shoot, i.e., the stem
and the secondary leaves. In some fernworts and in the seed
plants, the posterior hemisphere resulting from the first divi-
sion of the egg grows into a filament called the suspensor,
and the primary shoot develops from the anterior hemisphere.
(See fig. 80.) In these plants ordinarily two or more cells
at the apex of the primary shoot are specialized as the initial
cells, and from their segmentation arise the tissues of the
whole shoot, as in the fernworts.

FIG. 95. — Median longitudinal section through the apex of a shoot of the horsetail
(Equisetum arvense), showing primary meristem and the form of the growing point.
/, apical cell, from which a segment, .S', has just been cut off by wall/. ^", a seg-
ment previously cutoff, has divided by wall in. f, f',f", successively older leaf
fundaments; g, the initial cell of a branch. Magnified 160 diam.— After Strasburger.

101. Primary meristem. --Whether the tip of the shoot
be occupied by a single initial cell or by a group of initials,
the apical region, in which the formation of new cells is

THE SHOOT.

taking place, is called the primary mcristem (fig. 95). This
primary meristem has no definite limit below, but passes
insensibly into the permanent tissues. The tip of the shoot
may be either a sharp cone or a low dome. Between these
forms a complete series of gradations exists. 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
fundaments may appear the fundaments of the lateral shoots.

FIG. 96. — Diagram of a section through a bud. I', the apex; 1,2, 3, 4, successively older
leaf fundaments; a, b, c, successively older branch fundaments; </, e, vascular bundles.
—After Hansen.

The older leaves upon the sides of the axis outgrow the
younger ones and the developing 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 protect the younger, and particu-
larly the primary meristem (fig. 96). From the terminal
bud arise all the members of the primary shoot.

102. Differences from root. — From what has been said of
the origin of the shoot, it will be observed that it is dis-

86

PLANT LIFE.

\

tinguished from the root by not forming through segmenta-
tion from the outer faces of the initial cell or cells a many-
layered epidermal cap. In further contrast with the root,
which often has no true epidermis except the root-cap, the
shoot is characterized by possessing an uninterrupted epider-
mis over its entire surface, consisting always at first of a
single layer of cells. This epidermis persists 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 axis by subsequently
formed protective layers. (See ^[ 134.)
103. Branching. - Branches of the
shoot arise from lateral buds, which are in
all respects similar to the terminal buds
just described. If, for any reason, the
terminal bud of the stem becomes de-
stroyed, or its growth arrested, a branch,
developing from a lateral bud near by,
may assume the position and habit of
the main axis, its own normal mode of
development being altered. In many
plants the death or arrest of the ter-
minal bud recurs at regular intervals.
In such plants, therefore, the main axis
is really a succession of lateral branches,
FiG.97.-shootofaiinden and the branching js said to be sympo-

dial (fig. 97). In some plants, e.g.,
Hlac, two lateral buds standing at the
the same level may develop, if the terminal
one fails. In this case the shoot seems
to divide into two equal branches. This,
however, is not true, but false, or sym-
podial, dichotomy. True dichotomy, like true dichotomy of
the root, occurs only in those plants in which the axis has

.

be

THE SHOOT, 87

a single initial cell. The initial in these cases divides into
two equal parts, each of which becomes the initial of a new
branch. Ordinarily, however, the terminal bud develops
without interruption. In case it is more vigorous than any of
the lateral 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 monopodial. These two
types of monopodial branching and the sympodial type are
all illustrated in the forms attained by common forest trees.
(See frontispiece.)

104. Inflorescence. — Especially profuse branching com-
monly occurs in the parts of the seed plants where flowers are
produced. Such clusters of branches bearing flowers constitute
an inflorescence. Each sort has received a special name which
not only indicates the type of branching, whether sympodial
or monopodial, but also the relative length of the branches.

If the branching is monopodial and each lateral shoot is
unbranched, the inflorescence is a raceme. If the lateral
shoots are very short, it is a spike. If the main axis also is
very short, it is a head. If the main axis is short and the
lateral axes long, it is an umbel. If the lateral axes are of
unequal length, so as to bring the flowers to about the same
level, it is a corymb. If the branching is sympodial, various
forms of the cyme result. Several combinations of these
inflorescences are possible, f

105. Axillary buds. --Lateral buds are ordinarily formed
in definite relation to the leaves. They stand usually in the

* 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 further discussion see Gray: "Structural Botany," p. 144;
Goebel : " Outlines of Classification," p. 407.

PLANT LIFE.

upper angle formed by the leaf with the stem. This angle
is known as the axil of the leaf, and such buds are said to

bl

FIG. 98.

FIG. 98. — 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. 99. — A, twig of red maple with ac-
cessory buds in addition to axillary bud.
B, twig of butternut, with leaf-scar, «, small
axillary bud, />, and larger accessory buds,

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

FIG. 100. — A bit of stem of a honeysuckle
(Lonicera xylosteinn} bearing large axillary
and smaller superposed accessory buds
above the axils of the scars, n >t, from
which leaves have fallen. Natural size.—
After Frank.

FIG. 100.

be axillary (fig. 98). Ordinarily a single bud arises in the
axil of each leaf. Its origin is always subsequent to that of
the leaf- fundament (figs. 95, 96),

/•///<; SHOOT. 89

There are many rases in which the lateral buds are not
found precisely in the axils of the leaves, but slightly to one
side, or at a greater or less distance above the axil (figs. 99,
100).

106. Extra-axillary buds. — Buds are frequently formed
without any relation whatever to the leaf-axil, and even on
the leaf itself (fig. 293). Sometimes these extra-axillary
buds are produced without the action of any extraordinary
cause, but more commonly injury of one sort or another
seems to act as a stimulus to the production of such buds.
Buds which do not originate in acropetal succession on the
parent shoot are called adventitious buds.

107. Adventitious buds may arise upon stems, leaves, or
roots. They are most commonly and abundantly produced
upon stems and roots. In the willows their ready production
is utilized for obtaining young, vigorous, aud pliable shoots
to be used in basket-work. The few plants which produce
adventitious buds upon leaves, as well as the many which
produce them on stems, are often propagated in this way.
(See m 364.)

108. Dormant buds. — Many buds continue to grow with-
out 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
with adventitious buds. In case they have been buried by
the growth of tissues over them, the shoot which they pro-
duce 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 endogenous origin of roots.

PLANT LIFE

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, since many buds are produced which
never develop into branches, this relation is often obscure
and difficult to see.

109. 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 (^[ 236), while its leaves are so reduced as to be scarcely
recognizable. Such a shoot is known as 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 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 corm are them-
selves rhizomes or corms. 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. 297). Offsets and stolons (figs. 296, 369) are similar
branches likewise adapted to propagation (^j 366).

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.

110. (0) 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-

THE SHOOT.

mon among the cone-bearing trees. In these plants the
short branches carry the clusters of needle leaves (figs. 101,

FIG. 101. — 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.

102, 358). After the death of the leaves the branches
themselves drop off. Somewhat similar short branches are

PLANT LIFE.

to be recognized among many deciduous trees, and, in the
apple, the so-called fruit spurs are
not dissimilar (fig. 103).

111. (b) 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

FIG. 102. FIG. 103.

FIG. 102. — 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. 103. — Twig of apple, bearing fruit spurs. .4, points at which fruit was detached
the preceding year ; //', leaf scars. Natural size. — After Hardy.

some of them are highly colored (fig. 104). Commonly
these flower branches are deciduous.

a

FIG. 105.
s, sepal; /, petal; s/, stamen; c, carpel. Mag-

FIG. 104.

FIG. 104. — Flower of Seilmti acre.

nified 3 diam. — After Baillon.

FIG. 105.- 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.

112. (c) Cladophylls. — A few plants have developed
shoots which replace leaves in function and resemble them

7 •///•: SHOOT. 93

in form. These cladophylls may be either l)road and flat-
tened, as in the " smilax ' of the greenhouses, or they
may be slender and needle-like, as in the common garden
asparagus (fig. 105). In any case, since they replace leaves
in function, they are abundantly supplied with green color-
ing matter for manufacturing food.

113. (//) Bulblets. — Other branches remain undeveloped
as buds, but their leaves become thick and fleshy. These
bulblets are easily detached and serve for propagation. (See
^[ 364.) They are to be found in many plants. In the
tiger-lily they occupy the axils of the leaves (fig. 294),
and are modified lateral buds, while in the garden onion
they usually replace the flowers.

114. (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. 106).

115. (/") Tendrils. — Some shoots take the form of slender,
leafless, sensitive tendrils, which assist the plant in climbing
by coiling about suitable objects (fig. 107).

116. (£•) Thorns. --Many plants produce defensive shoots,
which are leafless, rigid, short, and sharp, called thorns,
which may be either simple or branched (fig. 108). The
honey-locust furnishes an excellent example of branched, or
compound, thorns.

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 members will reveal their true

94

PLANT LIFE.

nature. If shoots, they will usually be subtended 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.

117. Duration. — Shoots are
either annual, biennial, or per-
ennial. If the entire shoot dies

A

\

FIG. 106.

B

FIG. 107.

FIG. 106. — A, upper part of a plant of Polygonum •vi-viparum^ 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. 107. — A portion of the stem of white bryony, fi, from which a tendril, ?^_r, arises
near the leaf stalk, b, and the bud, k. u, 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 w and iv' . Nearly natural size. — After Sachs.

this generally involves the death of the whole plant, though
new adventitious shoots may arise from the roots, as in
sweet potatoes. In many plants, in which the shoot seems

THE SHOOT.

95

to die at the close of the growing season, an underground
portion really survives, and sends tip 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.

FIG. 108. — Shoots of Vella spinosa, showing thorns. Natural size. — After Kerner.

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
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.

CHAPTER IX.

THE STEM.

118. 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 out-
growths, or branches, of it. These two members cannot be
accurately defined, but are in most cases readily distinguish-
able. Leaves commonly differ from the stem in internal
structure, and in their flattened form, limited growth, and
position, subtending the lateral shoots. (See further p. 117.)

119. Nodes and inter/nodes. --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 development
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
elongation. The amount of elongation, however, varies
greatly in different plants, and even in different parts of the
same plant. In many cases the internodes are considerably
and uniformly elongated ; the leaves are then distributed
along the stem at considerable and regular intervals. In other
cases the internodes remain very short, and the leaves are,

96

y •///•• STEM.

97

therefore, crowded. They may be so crowded as to completely

envelop the stem and hide it

from view. This is well seen

in the scale-like leaves of such

plants as the pines (fig. 101),

cedars, and arbor vita) (fig. 109).

Or, certain of the internodes

may elongate, while others

remain undeveloped. For

example, in the shepherd' s-

purse, the first internodes

remain short, so that the lower

leaves are Crowded into a tuft FlG- 109-— A shoot of arbor vita; or white

cedar, showing scale leaves covering
Or rOSette; the following inter- stem- Natural size.- -After Kerner.

nodes are elongated, the corresponding leaves being scattered
at regular intervals ; while, still higher, the internodes are
again shortened and the leaves brought into close clusters in
the flowers.

120. The consistence of the stem depends upon the relative
amount of mechanical tissues which it contains. Stems may
be designated as woody, solid, or fleshy, terms which need no
further definition.

121. The shape of the stem varies extremely in different
plants. Very commonly the stem as a whole is looked upon
as cylindrical, but, if carefully considered, it will be seen that
the diameters of successive internodes at first become gradually
greater, and, after maintaining this maximum for a time, grow
gradually less. The stem is, therefore, a cylinder with more
or less conical ends. If the attainment of the maximum
diameter is sudden, and the diminution similarly sudden, the
resulting stem will have the shape of a double cone. The
modification of such a form into the spherical is not difficult
to imagine. Striking illustrations of these extreme forms are
to be found among the cactuses ( fig. no).

PLANT LIFE.

122. A section of the stem commonly presents an irregu-
larly circular outline (fig. in). Occasionally the surface of
the stem is fluted or channeled, 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.

123. Habit. — As to habit, stems are commonly erect when
enough mechanical tissue is developed to render them suffi-
ciently rigid to carry not only their own weight, but that of

FIG. no. — Cactuses, showing form. A, Cereus dasyacanthus. B, Echinocactus
korizontalis. In both the clusters of spines arise from tubercles on the stems.
Reduced. — After Kerner.

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 deter-
mined largely by the relation of the plant to gravity and light
as stimuli. (See ^[ 285, 287.) Other stems rise into the

THE STEM.

99

air, not by their own rigidity, but by the development of
special members for climbing purposes, such as recurved
spines, tendrils, sensitive leaf stalks, or even by recurved
normal branches. (See ^[H 115, 158.) Others wrap them-
selves about objects of suitable size, and are called twining
stems. (See ^[291.) The direction of twining varies with
different plants, but most commonly corresponds to the
movement of the hands of a watch, the support being sup-
posed to be in the center.

124. Primary structure.- -The origin of the stem-tissues
has already been described. (See ^] 100.)

In following the stem from apex to base it is readily
observed that the structure changes as the parts grow older.
It is possible, however, to select a point at which the stem in

FIG. in. FIG. 112.

FIG. in. — Diagram of a transverse section of stem of Iberis amara, showing outline,
and paired vascular bundles. The black is the xylem bundle ; the gray is the phloem
bundle. The outer line represents the epidermis ; a circle including the bundles would
mark the limits of the stele, with its central pith ; the cortex lies between the epidermis
and stele. — After Na'geli.

FIG. 112. — Diagram of a transverse section of a palm stem. The epidermis is represented
by the outer line ; the endodermis by the inner one, with the narrow cortex between
them ; the stele, with numerous bundles scattered through the pith, is within the
endodermis. — After Frank.

all cases attains a definite development. This point is at the
internode which has just reached its full length. The struc-
ture of the stem at this point may be designated as its primary
structure. If a thin section be cut from such an internode,

IOO PLANT LIFE.

three definite regions may be distinguished, viz. : (i) the
epidermis; (2) the cortex; (3) the stele (figs, in, 112).

125. i. The epidermis.- -This is a single layer of cells
forming the extreme edge of the section, being, therefore, the
layer which covers the surface of the stem. Here and there
maybe observed intercellular spaces, which permit communi-
cation between the outside air and similar spaces in the deeper
tissues of the cortex. These openings are usually bordered
by t\vo specialized cells, and are called stomata. The
epidermal cells may be furnished with green chlorophyll
bodies, or these may be entirely absent.

126. 2. The cortex.- -This region consists of several
rows of cells, usually thin-walled and not in close contact, and
hence abundantly provided with intercellular spaces. These
cells usually contain many chlorophyll bodies, to which the
green color common to stems is due.

The innermost layer of the cortex abutting upon the stele,
whose radial walls are suberized (^[ 9), is usually specialized
to form a distinct layer of cells. This layer is the endodermis
(fig. 118).

127. 3. The stele. --The central region is called the
stele. It consists, as in the root, ordinarily of three parts.
Its outer layer of cells is known as the pericycle (fig. 118).
Within the pericycle are clusters of smaller cells, the cut ends
of the vascular bundles. Occupying the space between the
vascular bundles is the pith (figs, in, 112).

These regions of the stem are subject to various modifica-
tions.

128. i. The epidermis. --While the epidermis is usually
a single layer of cells, it is sometimes increased to two or
three layers. Stomata may be entirely lacking. This is
especially the case in those underground and submerged
stems in which the stomata would be useless. The cells of
the epidermis are often prolonged into outgrowths of various

THE STEM.

IOI

shapes, such as hairs, scales, and the like (figs. 113, 114;
see also figs. 361-365).

129. 2. The cortex. --In some plants the cortex under-
goes an enormous development, forming in some tubers the

greater part of the massive stem.
In other plants the cortex under-
goes such reduction that it con-
sists only of two or three layers of
cells. It very commonly enters
with the epidermis into the for-

FIG. 113.

Fir,,

FK;. 113. — Forms of hairs from Plectranthus. a, simple pointed hair; /<, stalked
glandular hair; c, sessile glandular hair with secretion covering the two glandular
cells. Highly magnified. — After De Bary.

FIG. 114. — T-shaped hair of the wall-flower (Cheiranthus). e, epidermis. Highly
magnified. — After De Bary.

mation of outgrowths, which are then known as e?nergences.
These emergences may take the form of rounded elevations,
producing a warty stem, or they may be sharp pointed
and either straight or curved, forming prickles (figs. 115,
116); or the emergence may be produced along a con-
tinuous line, giving rise to wings upon the stem ; or the
stem may be more or less covered with large pointed or
angular elevations, called tubercles, as in some cactuses
(fig. no). Very frequently the intercellular spaces of the
cortex are greatly enlarged, forming air passages of con-
siderable size. These passages may arise by mere separation
of the cells of the cortex, or by the destruction of those in
certain regions, or by a combination of these causes
(fig. 117). In other cases the cortical cells, instead of

IO2

PLANT LIFE.

remaining thin-walled, may become greatly thickened in
certain regions, or even throughout the cortex. These

FIG. 115.

FIG. 116.

FIG. 115. — Prickles on the stem of a rose. Natural size. — After Prantl.

FIG. 116. — A longitudinal section through a rose prickle in a young stage, showing how
the sub-epidermal (cortical) tissues enter into the structure of the emergence. Magni-
fied 200 diam. — After Rauter.

FIG. 117. — Transverse section of the stem of Elatine, showing intercellular canals, c.

Magnified about 15 diam. — After Reinke.

mechanical cells are likely to be aggregated in clusters or
strands, and serve an important purpose in strengthening

THE STEM.

103

the tissues (fig. 118). In some cases vascular bundles are
found in the cortex outside the stele, when they are known
as cortical bundles.

FIG. 118. — Transverse section of the stem of a ground pine (Lycopodium complana-
tion). The stele is enclosed by the endodermis, en; p, pericycle; x, xylem bundle;
ph, phloem bundle; cc', cortex, c', mechanical tissue with thickened walls; ep, epi-
dermis. In the cortex a branch stele passing out to a leaf on the right is cut across.
Magnified 100 diam. — After Sachs.

130. 3. Stele, (a) Pericycle. — The pericycle is rarely
wanting. It is much more frequently increased from one to
several layers of cells. In this case it commonly differ-
entiates into regions of mechanical cells with thick walls and
small cavities and a region of thin-walled cells. These
mechanical cells are either aggregated in strands opposite to
the vascular bundles of the stele, or they constitute a com-
plete zone 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. 119).

131. (b) Vascular bundles. --In any section of the stem
the number of vascular bundles in the central cylinder varies
greatly, not only in different plants, but even in different
parts of the same plant. The bundles are commonly arranged

IO4

PLANT LIFE.

in pairs, a phloem (bast) bundle and a xylem (wood) bundle
being placed side by side, the xylem occupying the side next

FIG. IIQ. — Portion of a transverse section of the stem of flax, m, pith; h, secondary
xylem forming a woody cylinder; ///, phloem : />, bundles of mechanical tissue (fibers)
among the thin-walled cells, the two sorts making up the cortex; ep, the epidermis.
Magnified about 25 diam. — After Frank.

FIG. 120. — Transverse section of a bundle pair from the stem of a begonia. The shaded
part is the xylem bundle; the small irregular cells above are the phloem bundle;
between them is a zone of generating tissue (secondary meristem), the stelar cambium,
which extends also right and left of the bundle pair. The radius of the section passes
through C/'; C, next the center. Magnified 150 diam. — After Haberlandt.

the center of the stem, and the phloem the side next the
surface (figs, in, 120). The number and position of these

7V//-: STEM.

105

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 in the fern \vorts
(fig. 12 1). Sometimes independent phloem bundles are

FIG. 121. — Transverse section of Selaginclla^ showing three steles, each composed
of a xylein bundle surrounded by phloem. /, /, intercellular spaces in cortex,
separated from the steles only by the large-celled endodermis. The cells underlying
the epidermis are thickened to form mechanical tissue. Magnified 150 diam. — After
Sachs.

found with which are associated no xylem bundles. In
the phloem certain cells may develop into fibers, which
are not to be confused with the fibers occurring in the
pericycle. Some of these, also, are valuable in the textile
industries.

io6

PLANT LIFE.

The paired vascular bundles within the stele occupy various
positions, and for purpose of location may be spoken of as
though single. If transverse sections of the stem are ob-
served, they may be seen either in a single row, roughly
parallel with the surface of the stem (fig. in), or in several
concentric rows (fig. 122), or they may be irregularly dis-
posed throughout it (fig. 112). No one method of arrange-

FIG. 122. — Transverse section of the aerial stem of an onion (A Ilium Schoenoprasuni).
e, epidermis; c/i, chlorophyll-bearing tissue of cortex; r, colorless tissue of cortex;
g-, g' , vascular bundles (xylem bundles black, phloem bundles dotted); sr, mechanical
tissues connected into a cylinder; m, pith; h, pith canal formed by destruction of
cells. Magnified 30 diam. — After Sachs.

ment is confined to any of the larger groups of plants,
although the first is characteristic of most dicotyledons,
while both the second and third methods are common among
the monocotyledons.*

* So many exceptions are found to these last statements that it is best
not to indicate the arrangement of the bundles by the terms dicotyle-
donous or monocotyledonous, as has been commonly done ; nor is it
possible to maintain the terms exogenous and endogenous, which have
long since become obsolete because misleading.

THE STEM.

107

132. (c) Pith. --The pith likewise varies greatly in
different plants according to different conditions of
growth. It is frequently found enormously developed
in those parts of the stem which are used by the plant
for storing its reserve food, as in some tubers, such as
the white potato and the yam. In other plants, particularly
those growing in water, it

suffers 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 cor-
responding 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
bundles, forming a strand
closely adherent to their inner
faces, or they may extend to
the flanks of the bundles, thus
forming an arc embracing
each. Sometimes the thickened region becomes extended
between the bundles and joins the corresponding mechanical
tissues in the pericycle, or even those of the cortex, so as to
enclose completely the individual bundles (fig. 123). In
other plants the pith dies early and shrivels up. Very large
canals may thus be formed through it, or it may even dis-
appear entirely (fig. 122). Such early disappearance of the
pith produces the hollow stem characteristic of the grasses,
the sedges, and the various members of the sunflower family.

133. Secondary structure. — Some stems retain throughout
their entire existence the primary structure which has just

FIG. 123. — Transverse section of a bundle-
pair of Indian corn. z», phloem bundle;
•*> £> £"> s> r-> xylem bundle; /, pith; /,
an intercellular space formed by the
tearing of some of the xylem tissues.
The bundle pair is surrounded by a
sheath of thick-walled mechanical
tissues. Magnified 235 diam. — After
Sachs.

io8

PLANT LIFE.

7c

s

si

been described, undergoing only slight changes in the char-
acteristics of the individual
tissues which compose it.
Thus, with age, there may be
a thickening of the tissues so
as to impart greater rigidity ;
or the waterproofing of the
exterior may be made more
perfect. These and similar
changes do not, however,
materially alter the structure.
This permanence of primary
structure is particularly fre-
quent in the stems of mono-
c cotyledonous plants. It has
been observed also in some
m-kf dicotyledonous plants; for ex-
, ample, in the white water lily.
But the stems of the great
majority of dicotyledonous
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

transverse Section of first formed tisSUCS (fig. I24).

134. Secondary meristem. -

dermis; k, cork cambium; /;/;-, cortex; T-I • j'.c »• r ii

s, gum-resin tubes in cortex; .^.primary ^ hlS modification of the StrilCt-

phloem bundle: <r, stelar cambium: sr.h, c i\ J i • a

secondary xylem; mk, pith rays; m, Ure °f the Stem 1S dUC chiefly

pith. The tissue between s/> and c is ,1 r .• r

secondary phloem. Highly magnified.- tO the formation Of One Or two

After Tschirch. c ,- -i j- -j-

layers of actively dividing

cells, which constitute secondary meristem or cambium,
roughly parallel to the surface. When there are two, one of

FIG. i.-

THE STEM.

IO9

the layers of cambium arises nearer the center, the other
nearer the periphery of the stem. They are formed from
existing cells which resume their power of active growth
and division. The development of the tissues from the ex-
ternal meristem, or cork cambium, results in the formation
of the peridenn, while the tissues arising from the internal
meristem, or stelar cambium, form the secondary xylem and
phloem (fig. 124).

135. i. The formation of secondary cortex. — As the
cells of the external meristem divide, sometimes the outer
segments and sometimes the inner ones differentiate into
permanent tissues, while the other segment remains as an
initial for the next division. Some of the secondary tissue
thus produced lies outside of the generating layer, and some
inside (fig. 127). The secondary tissues, as a whole, con-
stitute the periderm.

k

^.^;:j'fr^3??&

TTS^C*
^•/<

FIG. 125.

FIG. 126.

FIG. 125. — A bit of a transverse section of a young stem of Scutellaria splendens at

the beginning of the formation of periderm. <•, epidermis, some of its cells divided by
tangential walls, c, cortex. See fig. 126. Highly magnified. — After Haberlandt.
FIG. 126. — Same as 125 but older, e, outer half of epidermal cells ; A-, cork cells formed
by tangential divisions of inner half of epidermal cell (fig. 125) which has become ///,
the cork cambium; c, cortex. Highly magnified. — After Haberlandt.

136. Periderm.- -The tissues formed inside the cambium
(phelloderm) are usually similar to the cells of the primary
cortex. They form intercellular spaces, and retain their
living contents, among which chloroplasts are often present.
With the thickening of the outer tissues, however, these
usually disappear.

110

PLANT LIFE.

The outside tissues of the periderm rarely remain living,
No intercellular spaces arise between the flat cells, which
early lose their contents, while the walls become waterproof.
Such a tissue is known as cork (fig. 128). Other cells may
be altered into mechanical tissues by the thickening of their
walls and the death of the protoplasm. Zones of cork often
alternate in the periderm with zones of mechanical tissues
Since no water solution can pass through a cork zone, it is
evident that all parts lying outside of one are cut off from a
supply of nourishment, and must therefore perish sooner or
later.

137. Location of cork cambium. — How much will thus be
killed depends upon the position of the layer of cells which

v 0

FIG. 127.

FIG. 128.

FIG. 127. — Part of a transverse section through the cork cambium and the tissues it pro-
duces in the European elm. k, cork cells, the innermost layer still with some proto-
plasmic contents; ph, cork cambium; pd, secondary cortex. Highly magnified. —
After Haberiandt.

FIG. 128. — Part of a transverse section of young stem of cherry, showing formation of
periderm. e, epidermis; k, cork; ///, cork cambium, with one row of secondary
cortex below; c, cortex. Highly magnified. — After Haberiandt.

becomes the generating layer. It may be formed in one
of three places : (a) It is sometimes in the epidermis itself
(fig. 125), in which case only the outer half of the epidermal

THE STEM. Ill

cells will be sloughed off.* (b) In a majority of cases the
generating layer of the periderm is formed in the cortex,
either immediately under the epidermis (fig. 128) or in one
of the deeper layers (fig. 127). (c) In other instances the
generating layer is formed in the pericycle. If the pericycle
is more than one layer of cells thick, it may be formed in
the innermost or in any one of the external parts. In this
case, therefore, there will be killed all the tissues of the
cortex and any of the stelar tissues which lie outside the
portion of the pericycle from which the generating layer is
formed.

138. Perennials. — Plants which live for a single year have
usually but a small amount of periderm formed, or sometimes
none at all. In those, however, which are perennial, peri-
derm is formed not only during the first year's growth, but
the activity of the generating layer is resumed at the begin-
ning of succeeding seasons, so that annual additions are
made to it. In the cork oak, for example, there is an extraor-
dinary development of cork, which becomes so thick and
is so resistant to the passage of water that it serves for the
manufacture of stoppers. In the bottle-cork mechanical
tissues occur, not in zones, but in isolated patches, forming
the gritty masses in poor corks.

139. Secondary periderm.- -The dead tissues which accu-
mulate from year to year upon the outside of perennial stems
constitute a large part of what is known as the bark. In the
bark of most trees one or more generating layers form in
addition to the first, giving rise thus to secondary periderm
(fig. 129). The secondary periderm may be either concentric
with the first, in which case the outer parts of the bark will
be made of concentric layers which separate readily from
each other ; or the new generating layer may intersect the

*The epidermis sometimes continues to grow for many years, while a
secondary cortex is formed under it. In this case no sloughing off occurs.

112

PLANT LIFE.

outer one, so as to isolate a mass of tissues of greater or less
size. When this mass is killed by the formation of a sheet
of cork on its inner face it gradually dries up and ultimately
breaks away in the form of a scale or flake (fig. 129). Bark
of this sort, such as that of the hickory, sycamore, or apple,

FIG. 129. — 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.

is known as scaly bark. In other trees the dead outer por-
tions are persistent, and are only gradually worn away by
the action of the weather. Such persistent parts become
seamed or deeply furrowed lengthwise by the increased size
of the stem within and the constant drying and shrinking
of the dead parts. Such bark is called furrowed or ridgy
bark.

THE STEM.

140. Lenticels. — In steins in which the generating layer
of the periderm is formed from the epidermis or the cortex
adjacent to it, the cork cells
produced show certain modi-
fications at points correspond-
ing to the stomata of the
epidermis. Here the cork
cells become rounded and
loosened from one another
(figs. 130, 131). The epider-
mis under the strain ruptures ,

v IG. 130. — A bit of a transverse section of the

first at the Stoma, and exposes cortex of elder, showing a very young stage

in the formation or a lenticel. I he cortical
cells under a stoma have divided tangen-
tially and are forming a loose tissue which
has already torn apart the guard cells.
(See fig.[i3i.) Magnified izodiam. — After
Stahl.

this poxvdery mass of cells
through a usually biconvex
rift, whose shape suggested
for the structure the name lenticel.

Lenticels are formed

either beneath single stomata, or, when the stomata are not

FIG. 131. — Transverse section through a mature lenticel of elder, s, the cork cambium.
Compare fig. 130. Magnified So cliani. — After Stahl.

uniformly distributed, beneath the clusters of stomata. When
the generating layer of cork is deep-seated the lenticels pro-
duced are without relation to the position of the stomata.
141. 2. The formation of secondary wood and bast.-
The position of the internal generating layer (the stelar cam-
bium) is not subject to the same variations as the external

114

PLANT LIFE.

one. In stems of the few monocotyledonous plants which
undergo secondary increase in diameter, the internal generat-
ing layer arises from the pericycle. Upon division the inner
segments, chiefly, differentiate, and from them arise new
isolated bundle pairs (in which the xylem bundle surrounds
the phloem bundle) and new pith (fig. 132).

FIG. 132. — Portion of a transverse section of a stem of Dracaena, in process of secondary
thickening, e, epidermis ; h , periderm ; r, cortex, in which a bundle-pair b is passing
out to a leaf ; x, stelar cambium ; g, g, vascular bundles ; ///, primary pith ; st, secon-
dary pith. The amount of secondary thickening is shown by the radial arrangement
of cells of secondary pith. Magnified about 50 diam. — After Sachs.

In the many dicotyledons whose stems increase in diam-
eter, the stelar cambium arises between the xylem and the
phloem bundles of each pair, and extends across the pith
rays which intervene, thus forming a complete zone nearly

THE STEM.

concentric with the surface of the stem (figs. 120, 124, 133^).
As its cells divide, sometimes their inner, sometimes their
outer segments differentiate into the tissues which they then

FIG. 133. — Diagrams of transverse sections of stems illustrating modes of secondary
thickening. In all ec, cortex ; ed, endodermis ; /, pericycle ; /, primary phloem ;
/', secondary phloem; g, stelar cambium; l>, primary xylem ; b' , secondary xylem ;
r, primary pith rays ; r' , secondary pith rays. — After Van Tieghem.

adjoin. Inside the generating layer between the bundles
there arises, therefore, secondary xylem which becomes
wood ; outside it, secondary phloem, or bast. Each bundle
is thus increased in its radial dimension (fig. 124).

142. Pith rays. — The generating layer in the pith rays
arises from the pericycle or from some part more deep-
seated, but in any case it connects directly with the generat-
ing layer between the adjacent bundles (fig. 124). In this
portion of the generating layer two distinct modes of develop-
ment are to be observed : either the tissues produced by the
division of the cells differentiate into pith tissue (It, fig. 133),
or they form secondary wood and bast coresponding to that
produced between the adjacent bundles. In the latter case,
therefore, a complete zone or ring of secondary wood and
bast is formed, so that the pith occupies the center. Upon
the ring of secondary wood thus produced the primary wood
bundle projects into the pith, and upon the ring of secon-
dary bast the primary bast bundle projects into the cortex

(c, fig. 133).

I 1 6 PLAN 'T LIFE.

Intermediate between these two methods, it is common to
have new bundles produced by the differentiation of the
secondary tissues formed in the pith rays, these bundles
remaining separated by pith rays. In this case a xylem
bundle is usually first formed, followed shortly by a phloem
bundle outside (D, fig. 133).

The secondary bundles thus formed can, of course, have
no connection with those which enter the leaves. In this
they differ from the primary bundles, branches from which
enter each leaf. (See % 163.)

143. 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 generating layer
forms a line of weakness, especially when dividing rapidly,
and the parts outside separate readily from the wood. They
constitute the bark.

144. 3. The bark. — As has been already shown, the
outer part of the bark consists 'of the dead, dry, shriveled
tissues of the periderm lying outside the cork cambium. The
inner portions of the bark are composed of the tissues which
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 (depending upon the place of origin of the peri-
derm), the pericycle, and the primary and secondary bast.
As the tree grows older, the secondary generating layers of
the periderm invade the cortex and the bast, until, with
weathering, the bark may come to consist wholly of secondary
bast. It attains considerable thickness only \vhen the loss
from this cause is slow.

CHAPTER X.

THE LEAVES.

145. Primary leaves. --Leaves are distinguishable into
primary and secondary. The primary leaves arise directly
from the first cells produced by division of the egg. In the
fernworts two of the octants into which the egg divides
produce the primary leaf. This is entirely unlike the secondary
leaves, which arise upon the sides of the stem. In seed
plants, one, two, or more leaves develop as members of the
embryo, only a few plants (and those probably degenerate in
this respect) not forming leaves before the embryo enters its
resting stage.

The primary leaves of seed plants are called cotyledons
(figs. 134, 135). They are usually transient, and not rarely
so distorted by acting as storage places for reserve food that
they do not function 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.

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

147. Development. — If the apex of the shoot is examined,
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 the apex (fig.
95). These swellings are the fundaments of the leaves, into
which they become transformed by further development.
Similar swellings appear later just above the leaf fundaments,

PLANT LIFE.

which are at first not distinguishable from them, except by
position (fig. 96). These become the branches. Both leaf
and branch have their origin usually in the outer layers of the
shoot, and can only be distinguished by the later course of
development. The growth of the branch is commonly
indefinite, while that of the leaf is generally limited ; the

A B

FIG. 134. FIG. 135.

FIG. 134. — 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. 135. — Seedlings, showing primary leaves. A, a fir (Abies orientalis); J3, the dog-
rose ; C, a morning-glory. Natural size. — After Kerner.

branch usually develops leaves and often buds as lateral out-
growths, 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 dorsiventral. In most cases,
also, the leaf subtends the branch. Both leaf and branch
mark those points of the stem known as the nodes.

THE LEAVES. I 1 9

148. 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, succes-
sive 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 section of a
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.

149. 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 abundant
form of secondary leaves is foliage leaves. These may be
very simple, as the " needles " of the pines, or differentiated
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 produced each
season, as in many ferns, the mature form may not appear for
several years.

150. Foliage leaves. — A well-developed foliage leaf may
usually be divided into two equal parts by a plane passing
through its base and the axis of the stem to which it is

120

PLAi\T LIFE.

attached, i.e., it is bilateral. Moreover, the upper and under

surfaces are usually different, i.e., it

is dorsiventral. It has three parts,

the base, the stalk, the blade (fig.

136). The leaf base is always

present, but either the leaf stalk or

the leaf blade or both maybe absent.

The leaf blade is ordinarily winged ;

indeed it is for this reason that it

r/

FIG. 136. FIG. 137.

FIG. 136. — Leaf of Ranunculus Ficaria. b, leaf base; /, petiole, or leaf stalk; /,

lamina or leaf blade. Natural size. — After Prantl.
FIG. 137. — 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 ; _/, blade ; /, the ligule, an outgrowth

from the surface. Natural size. — After Frank.

received the name " blade.' Either the stalk or the base or
both may also be winged.

151. i. The leaf base. - -The leaf base is generally en-
larged so as to form a sort of cushion by which it is attached
to the stem. When a broad base is attached over a consider-
able arc of the circumference of the stem, so that it encircles
it more or less, the base is said to be sheathing (fig. 136).
In grasses, for example, the leaf base is attached over the
entire circumference of the stem, and enwraps it completely
for a considerable distance above the node (fig. 137).

THE LEAVES.

121

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

FIG. 138. — A growing shoot of a thorn (Cratcegus punctata). n, leaves developed as
bud scales which protected the parts above when in the bud ; S, stipules. Natural
size. — After Reinke.

tened 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. 139), or they may be united with one another so as to
form a sort of sheath encircling the stem (fig. 140). When
the leaf base is winged, the wings extend downward as lobes
more or less encircling the stem. In many cases the leaf is
said to be clasping (fig. 141). These lobes may even unite
on the other side of the stem, so that the stem seems to
penetrate the base of the blade. (See fig. 142.) When two
leaves occur at the same node, corresponding lobes of the

122

PLANT LIFE.

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. (See fig. 143.)

FIG. 139. — A young flowering shoot of dog-rose, showing various forms of leaves and
transition from one to the other. «'-;/5, scale leaves ; /!-/3, foliage leaves ; /z1-/*3,
bracts; the flower leaves not clearly shown. The scale leaf, «J, shows a leaf base,
winged by stipules b, 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.

153. 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
the petiole is flattened in a vertical plane, as in aspen poplars.

THE LEAVES.

123

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. 144). Not infrequent-
ly, the petiole is winged, as in the orange.
It may be entirely wanting, in which
case the blade arises directly from the

base, as in most grasses

(ng. 137).

154. 3. The leaf
blade.- -To this part of
the leaf the word " leaf '
itself is frequently ap-
FIG. i4i. plied. In general, the

FIG. 140.— Stipules of Polygonum forming a i r IJo^p jc cO hrnaHlv

sheath, o, above the sheathing leaf base s, of the 1Cai

cut-off leaf y; cc, the stem; ca, an axillary winge(J as to be thjn

shoot. Natural size. — After Jbrank.
FIG 141 -Leaf of 77^,// with clasping base. flt b t R

Natural size.— After Prantl.

FIG. i4o.

FIG. 142. FIG. 143.

FIG. 142. — Shoot of Uvularia, showing pcrfoliate leaves below. About half natural

size. — After Gray.
FIG. 143. — A shoot of wild honeysuckle, showing upper leaves connate-perfoliate.

About half natural size.— After dray.

124

PLANT LIFE.

exist between such forms and those that are much folded or
crumpled, thick and fleshy, or even cylindrical.

FIG. 144. — 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.

If a thin blade be held between the eve and the li<rht, two

j O /

parts become evident : (i) a green tissue (mesophyll), more
or less opaque; and (2) translucent "nerves" or "veins." *
The larger of these, usually called the " ribs," * frequently
form ridges upon the under surface, f

155. 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.

* These words must not be thought to indicate any resemblance in func-
tion to the same parts in animals, but only similarity of position or ap-
pearance.

f For further account of structure see \ 168.

TlfE LEAl'KS.

125

145). More profound branching is evident in divided or
parted leaves (fig. 146). In
some blades the branching
is so extensive and complete

ABC

FIG. 145. FIG. 146.

FIG. 145. — Diagrams of slight leaf branching. A, leaf with crenate edge; B, leaf with

dentate edge ; C, leaf with serrate edge. — After Bessey.
FIG. 146. — Leaf of A inorphophallus, showing sympodial branching. The successive

lateral axes are numbered in order. The extent of branching makes the blade divided.

Reduced. — After Sachs.

that the green tissue no longer fills the intervals between the
larger ribs, but the blade is made up of a series of independ-
ent 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 called simple leaves. (See figs. 136, 138, 141, 142, 145,
146.) Those which are segmented into leaflets are called
co mpound leaves. (See figs. 139, 144, 147, 148, 149.)

156. Venation. — The mode of branching of the blade is
indicated by the main ribs which occupy the axes of growth.
(See ^[ 169.) Study of distribution of the ribs and veins of
the blade, that is, of its venation or nervation, shows that
monopodial branching (€[ 93) is the common mode, sympo-
dial branching occurring rarely (fig. 146). The arrangement
of the larger ribs may be reduced to two main types.* (i)

* Compare mode of branching of shoot, \ 103.

126

PLANT LIFE.

There may be a main rib, from whose flanks arise at regular
intervals a series of lateral branches which may themselves

FIG. 148. FIG. 149.

FIG. 147. — A palmately branched (compound) leaf of horse chestnut. About one-fifth

natural size. — After Bessey.

FIG. 148. — A palmately branched (compound) leaf. — After Bessey.
FIG. 149. — Leaflets of maidenhair fern showing dichotomous branching of veinlets,

which end free. Natural size. — After Ettingshausen.

again be branched in various ways. Such a leaf is said to be
pinnately veined (figs. 138, 151, 153). Or (2) from the top
of the petiole several large ribs of almost equal strength may
be given off. Such venation is palmate (figs. 150, 152).
These may be parallel (fig. 150) or radiate (fig. 152).

The distribution of the small veins or nerves shows three
types. They may either (i) connect with each other so as
to form an irregular meshed network (fig. 151); or, (2) leav-
ing a rib nearly at right angles, they may run parallel with
each other to join another large vein ; or (3) they may leave

THE LEAVES.

127

the large vein and end free (fig. 149). In the first type the
finest branches of the veins, too delicate to be seen without
the microscope, often end free in the meshes formed by the
next larger branches (fig. 164). Near the margin of a blade

FIG. 150. FIG. 151.

FIG. 150. — Parallel venation of leaf of Polygonatum latifolium. Natural size. —

After Ettingsliausen.

FIG. 151. — Pinnately netted venation of leaf of a willow. Natural size. — After Ettings-

hausen.

the larger veins are often so connected with each other as to
form one or more series of arches whose convex side is
directed toward the margin. These form a sort of selvedge
and protect the leaf against tearing (fig. 153).

128

PLANT LIFE.

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

FIG. 152. — Palmately veined and branched leaf of Norway maple. About half natural
size. — After Kerner.

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. 154). Such
plants are called leaf-climb-
ers.

FIG. 154.

FIG. 153. — Pinnately veined leaf of buckthorn, with looped ribs forming a selvedge.—
After Kerner.

FIG. 154. — Portion of a plant of the dwarf garden-nasturtium (Trofeeolum mimts).
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, axillary branch. Natural size. — After Sachs.

TllE LEATES.

129

Some plants develop their leaves into the form of sacs or
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. 155) ; or

FIG. 155. — Pitcher-plant (Sarracenia f>nrpurea). Leaf above A cut off to show
trumpet form. One-third natural size. — After Gray.

petioled, as in Utricularia (figs. 383, 384) ; or the petiole
may be winged to serve for foliage, as in Nepenthes (fig.
382). A few plants have their leaves modified so as to serve
as traps, which, by their sudden movements, capture small
animals (figs. 386, 387, 388).

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 :

130

PLANT LIFE.

158. (i) Tendrils.- -The leaf blade alone, or some of its
branches, or the petiole and blade, may develop as a cylin-
drical body, without wings and sensi-
tive, known as a tendril. In the pea,
the stipules become very large, and
take the function of the reduced blade
(fig. 156). In other plants the base
may be broadly winged for the same
purpose.

FIG. 156.

FIG. 157.

FIG. 156. — Portion of shoot of pea, with a pmnately 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. 157. — Piece of the stem of locust {Robinia Pseudacacza), showing stipules in the
form of thorns. Natural size. — After Kerner.

159. (2) Thorns.- -The leaves may develop into slender
conical and sharp-pointed thorns or spines, either branched
or unbranched (fig. 390). Sometimes the stipules alone
become thorns, as in locust and acacia (fig. 157). Neither
tendrils nor thorns can be distinguished structurally from
similar forms of the shoot.

160. (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. 101, 102, 105, 109, 138, 139,

THE LEAVES. \^\

358). These scales may represent the sheathing base only;
they may be the base with the stipules (fig. 139) ; or they
may represent the leaf base and the blade. The petiole in
all cases is wanting. In addition to the modification of
form, scales, especially those that are protective, have their
tissues firmer and more resistant to cold and unfavorable
external conditions. Not infrequently the scales are covered
with secreting hairs, or possess glands sunk beneath their
surfaces, whose function is to produce and excrete resins and
similar materials. The inner protective scales of buds (fig.
98) are often covered with an abundant coating of woolly
hairs, which serve to prevent rapid change of temperature in
the interior of the bud,

161. (4) Flower leaves and bracts. — On certain parts of
the stem, leaves are commonly profoundly modified to carry
the spore cases. They are called sporophylls (c, s/, fig. 104).
(See ^[329.) Adjacent to these are others which may be
highly colored and adapted in form to protect the sporo-
phylls, and to facilitate the visits of insects (s, p, fig. 104).
A shoot whose leaves are thus clustered and specialized con-
stitutes 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 x> 2> 3, fig. 139). (See also ^| 359. )

162. (5) Storage leaves. — Other leaves are utilized for
purposes of storage. For this purpose the ribs are reduced in
number and size, while the softer tissues of the leaf are often
enormously developed, and serve as the receptacles of the
reserve food. The primary leaves of the seed plants (coty-
ledons) 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.
(See also ^| 109.) The leaves of buds are sometimes thick-
ened by the deposit of food material, and when such buds

132 PLANT LIFE.

loosen from the plant they may produce a ne\v plant, as in
the tiger-lily (see *[[ 361-364). 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.

163. Structure.- -Three regions in each part may be dis-
tinguished, as in the root and stem : (i) the epidermis ; (2)
the cortex ; both continuous 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 con-
tains a single stele.

164. (a) The petiole.- -The structure of the petiole agrees
in all essentials with that of the stem (see *\ 124 ff. ). The
epidermis forms the outer surface, frequently with hairs or
emergences (see ^[128, I29)- ^ne cortex consists of
rounded or cylindrical thin-walled cells, the outer layers
containing chlorophyll, and frequently with angles much
thickened for strength. Mechanical tissues forming strands
or bands are also frequently present in the cortex. In water
plants, e.g., in water-lilies, large intercellular chambers,
often forming extensive canals, are present. There may be
a single stele, surrounded by an endodermis and containing
several or many vascular bundles (£, fig. 158); or there may

A B

FIG. 158. — Diagrams of transverse sections of petioles showing two most common
structures. A , petiole with several steles. B, petiole with one stele, containing a
number of bundle pairs, ec, cortex; ed, endodermis; /, pericycle ; f, bundle pair;
m, pith ; r, pith rays. The letters A, B stand on the upper or ventral side of petiole.
— After Van Tieghem.

be several steles, each surrounded by a special endodermis
and consisting of little more than a pair of vascular bundles

THE LEAl'ES.

133

, fig. 158). In transverse section the vascular bundles
are variously placed, being irregularly scattered, or disposed
in one or several groups. The single group is most common,
with the paired bundles placed so as to form a crescent, or
even a complete ring, which is flattened above or triangular.
The largest pair is generally median and dorsal (fig. 158),
with smaller ones right and left.

165. (b) The blade. --In broad leaves, the epidermis of
the blade is made up of tabular cells, often with wavy lateral
walls (fig. 159). In narrow leaves the epidermal cells are

c t

FIG. 159. — Surface view of epidermis from under side of leaf of bracken fern (Pteris),
showing wavy cells, except over veins, 7>, where they are elongated, s/, stomata.
The dot in each cell represents the nucleus. Highly magnified. — After Sedgwick and
Wilson.

longer than wide (fig. 160). Over the veins the cells are
elongated parallel with the vein. The epidermal cells are
generally free from chloroplasts. The epidermis usually
consists of one layer, but in some plants becomes several-
layered, either to serve as additional protection against eva-
poration or for use as a water-storing tissue. (See ^| 441.)

134

PLANT LIFE.

Hairs of many sorts, plain, stinging and glandular, and
of various sizes, arise from the epidermis (figs. 361-365).
They are essentially like similar structures on the stem (figs.
113, 114).

166. Stomata. — Numerous intercellular spaces bounded
by a pair of specialized cells, called guard cells, penetrate

FIG. 161.

FIG. 160.

FIG. 162.

FIG. 160. — Surface view of epidermis from the leaf of oat, showing elongated cells (more
elongated over vein, ;/, >i) and stomata arranged in lines. Moderately magnified. —
After F'rank.

FIG. 161. — Perspective view of a stoma from the under epidermis of the beet leaf, show-
ing the sloping sides of the slit, the crescentic guard cells with chloroplasts. Highly
magnified. — After Frank.

FIG. 162. — 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 magnified. — After Frank.

the epidermis. The whole apparatus is called a stoma (.$•/,
fig. 159, 1 60). The guard cells are crescentic, sometimes
with enlarged ends (fig. 160, like curved dumb-bells then),

THE LEAVES. 135

and are sensitive to various external conditions, especially
light, so as to control the size of the slit-like space between
them by changes in their curvature (fig. 162). This slit is
formed, like most intercellular spaces, by the partial splitting
apart of the cells. It communicates with extensive intercel-
lular spaces in the interior.

The stomata are very numerous. In different plants, in

the space here enclosed

sq. cm.

, the numbers usually vary

from 4000 to 30,000, sometimes, however, reaching as much
as 60,000 to 70,000 in 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 in-
ternal intercellular 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 sides of
floating leaves. In some plants they are found in clusters,
in others uniformly distributed.

167. Cortex.- -The cortex of leaves is called the meso-
phyll. It consists of thin-walled, active cells, for the most
part richly supplied with chloroplasts. In thick leaves the
internal cells are without them. In some leaves the cells of
the mesophyll are nearly uniform, but in most those near the
upper surface are more elongated and close set, forming one
or two rows, with their ends outward, while cells near the
lower surface are irregular in form, with large intercellular
spaces. These tissues are known as the palisade and spongy
parenchyma (fig. 163).

About the steles, the cortex forms the usual endodermis
(gs, fig. 163), and often develops along the larger into one
or two strands or a sheath of mechanical tissues. These
tissues, together with a stele, constitute the rib or vein, often
so massive ns to project beyond the other parts in thin leaves.

136

PLANT LIFE.

168. Steles. — The steles are numerous and ramify through
the blade. Their structure is essentially as described for the

FIG. 163. — Diagrammatic vertical section of a leaf, e, e, epidermis, with cuticle c, c,
and stomata s/>, s/>. Between upper and lower epidermis lies the mesophyll, with cells
abundantly supplied with chloroplasts. The upper row of elongated cells is the pali-
sade parenchyma ; the rest form the spongy parenchyma, both with many intercellular
spaces a, /, ?', communicating with outside air through stomata. In the mesophyll lies
a small vein, here cut across, composed of a ventral xylem bundle g, a dorsal phloem
bundle s, surrounded by the endodermis gs, and the pericycle (between £ and £.$•).—
After Sachs.

stem (*[[ 127). Each of the smaller consists of little more
than a single pair of vascular bundles. The xylem bundles
alone form the last branches (fig. 164), the phloem disappear-
ing earlier. The larger ribs may form one or t\vo strands or
a complete sheath of mechanical tissues by the development
of the pericycle, and the bundles proper may be increased
by the development of secondary wood and bast. (See

THE LEAVES.

137

169. Growth.- -The growth of the leaf is at first apical.
In fern-worts its tissues are produced by the continued divi-

FIG. 164. — A few meshes of the finest veins of a leaf of A nthyllis. tii, main vein ; b, 6,
branches ; a, a, a, a closed mesh ; c, ends of the finest veins within the mesh. The
drawing shows only the xylem bundles ; the phloem bundles accompanying them and
the mesophyll cells filling the meshes are not shown. Moderately magnified. — After
Sachs.

sion of a single apical cell, and the further division of each
of the segments so produced (/, fig. 76). The branches of
such leaves, therefore, arise in acropetal succession. In most
seed plants, instead of a single apical cell, there is a cluster
of such cells. Growth at the apex often ceases early, and is
replaced by growth throughout the whole extent of the leaf.
This intercalary growth is sometimes localized between the
fundament of leaf base and blade, producing the petiole
when one is formed. In elongated leaves without distinct
petiole, as in grasses and many other monocotyledons, a zone
of growth occupies the entire base of the blade. By the
division of these cells, chiefly at right angles to the length

'38

PLANT LIFE.

of the blade, its tissues are produced. In such plants apical

growth ceases so early that it can
be observed only in the youngest
stages.

170. Of branched leaves. —
When the leaf is to become much
branched, two or more new growing-
points develop, so that each of the
branches has at its apex a growing-
point (fig. 1 66). These growing-
points may arise from the apical
growing-point, or from the basal
one, or sometimes from both. The
branches will appear accordingly

FIG. 165 -Ending of "a vein in the in acropetal or basipetal succession,
^•cA"tf'S or even in both as they do in the
fists ;mrShycdif Osf1he leaves of yarrow. The limits of the

growing.point are even more in-

Magnified 23odiam.

definite than in the stem. The cells of which the leaf is
composed are produced very rapidly, and at a very early
stage division ceases.

171. Wintering. — In those plants which live from year to
year, producing new leaves each spring, the unfolding of
these from the winter buds is due chiefly to the enlargement
of cells 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 may be flat,
but broad leaves are commonly folded or rolled in various
ways.

172. Growth limited. — The growth of the leaves is ordi-
narily limited, rarely extending over a single season. In a few
ferns and coniferous plants the leaves continue to grow for a
longer time. Indeed, in the curious Welwitschia (fig. 167),

THE LEAVES.

139

the basal growth of a single pair of persistent secondary
leaves is continued throughout the long life of the plant,
while the tips die and are frayed out.

173. 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 comparatively

FIG. 166. — Development of the pinnately compound leaf of the locust (Robinia Pseud-
acacia). A, young stage, snowing on one flank the first lateral growing-points,
which is to produce the lowest leaflet. />', an older stage with the fifth growing-point
x just showing. A sixth is still to be developed. The hairs in A and />' are on the
back (under side) of the leaf, and drop off early. C, nearly mature leaf. A, />',
magnified; c, about i natural size. — After Frank.

limited. Roots arise from leaves in precisely the same way
as lateral roots arise from stems (^[ 95), that is, they are en-
dogenous in their origin, and develop always near the surface
of the steles.

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

174. Secondary changes. — Leaves, like stems and roots,
undergo certain secondary changes, but these are neither so

I4O

PLANT LIFE.

common nor so extensive as in the other two members. The
formation of several to many layers of cork cells upon the
surface of scale leaves is not uncommon. Occasionally simi-
lar layers of cork are formed upon the petioles of ordinary

FIG. 167. — Wehvitschia mirabilis, a coniferous plant of Africa, showing two leaves
which grow at base and continue to develop throughout the many years which the
plant lives. The tips are dead, and become worn and frayed by winds. ^ natural
size. — After Hooker.

foliage leaves. In some cases the large vascular bundles
occupying the main ribs undergo changes similar to those de-
scribed for the bundles of the stem (^[ 141), by which sec-
ondary wood and bast are produced.

175. Leaf fall. — 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 layer of secondary meristem across
the leaf base at or near the point where it joins the stem.
The cells at this point, with the exception of those constitut-
ing the vascular bundles, begin a series of divisions at right
angles to the axis. A transverse plate of cells is thus formed,
some of which cells may become transformed into cork, mak-
ing 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

THE LEAVES.

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

PART II: PHYSIOLOGY.

CHAPTER XI.

INTRODUCTION.

176. 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 various stages of development requires only the examina-
tion 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 which
plants do and 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
increasing complexity by differentiation into tissues and
members.

Nutrition, respiration, growth, movement, and reproduction
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.

177. Physiology and ecology. — Physiology proper treats
of the plant at work, discussing the different functions and

M3

144 PLANT LIFE.

the way in which these are affected by external forces. In
its broadest sense it also treats of the relation of the plant as
a whole to external forces and to other living beings, both
plants and animals. But it is convenient to separate the
latter from physiology proper as ecology * (See Part IV.)

The study of physiology proper necessitates methods of
controlling these external forces, carefully planned and re-
peated experiments, and cautious inferences.

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

178. Chemical and physical forces. — The functions of a
plant may be divided for the sake of convenience into nu-
trition, 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 phenomena of the living plant.
Moreover, the peculiar manifestation of these forces which
we call life occurs only in connection with the substance
which we call protoplasm.

179. The unit of function. — The functions performed by
the entire plant are necessarily a sum of the functions per-
formed by the physiological units of which it is composed.
As the unit of structure is the plant cell, so the unit of
function is the protoplasmic body of that cell. Although
only a portion 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.

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

IN TROD UCTION. 1 4 5

180. The fundamental powers of protoplasm are four ; it

is metabolic, irritable, contractile, and reproductive.

181. Metabolism. --Protoplasm is metabolic, that is, it is
capable of initiating a series of chemical changes in itself and
in substances 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 may be destructive, i.e.,
they may break down complex substances into simpler, so
setting free the energy necessary for the work of the pro-
toplasm. The substances broken down may be repaired in
whole or in part, i.e., may take part in constructive me-
tabolism. 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.

182. 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
organism. 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.

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

184. Reproduction. — Protoplasm is reproductive, that is,
it is capable of so directing the chemical and physical forces

146 PLANT LIFE.

inherent in it that a new organism similar to that of which it
forms part may be produced.

185. Adaptation. — -The interrelation of these powers,
their harmonious coworking and their variation to suit the
varying conditions of the surrounding media (air, water, soil,
etc.), result in the proper performance of all the functions of
the plant. By means of these powers it is brought into re-
lation to the world about it, being adapted to other organisms
in whose company it lives, and enabled to withstand 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.)

186. Physical conditions set limits upon the discharge of
its functions. Varying amounts of light, of heat, of moisture,
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 maximum,
and to a lower limit, the minimum, above or below which
the performance of the function in question is impossible.
Between these limits there lies some point at which it pro-
ceeds most rapidly and effectively. This point is known as
the optimum.

CHAPTER XII.

THE MAINTENANCE OF BODILY FORM.

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

187. Naked cells. — If the plant consists of a single mass
of naked protoplasm, it may assume a spherical or ovoid
shape (fig. 1 68). In attaining this form the physical forces

FIG. 168. — Zoospores of various forms, swimming in water by means of one or more
cilia. A, Botrydiunt ; B, Drafarnaldia ; C, Coleochtete ; D, CEdogonium.
Highly magnified. — After Kerner.

constituting surface tension play a part, but the form is deter-
mined chiefly by internal forces inherent in the protoplasm.
This is particularly well shown when such organisms extend
delicate protoplasmic threads, the cilia, and maintain these

i47

148

PLANT LIFE.

in active motion (fig. 168), or when they extend a portion of
the body as a pseudopodium (fig. 169).

FIG. 169. — Plasmodia, creeping bits of naked protoplasm, showing varied shapes as
parts are protruded or withdrawn. Highly magnified. — After Kerner.

188. 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 proto-
plasm. In the interior of the protoplasm there exist one or
more water chambers, the vacuoles (^[5). 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 dimin-
ished, the protoplasm shrunken away from the wall, and
remeasurement will show that the cell has diminished both in
length and diameter. In its normal condition, therefore, the
wall was stretched by the pressure of the contents within. If
a cell which has been thus shrunken by immersion in a solu-
tion of salt be again placed in water, it may regain, in the
course of a few hours, its original condition, that is, it may
again become turgid. This would be brought about by the
entrance of water into the vacuoles to replace that withdrawn
when the cell was placed in the solution 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

THE MAINTENANCE OF BODILY FORM. 149

diameter and length slightly, and gains, at the same time, a
condition of rigidity greater than in its unstretched condi-
tion. 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.

189. 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 of thin- walled
cells may, by the united tension of its component 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 ^[ 259.)

190. 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
tissues. These mechanical tissues are so distributed within
the body as to afford frequently the maximum resistance to
bending and breaking strains. In the accompanying dia-
grams the position of the mechanical tissues is indicated in
transverse sections of a number of different stems (fig. 170).
It will be seen that they illustrate well-known mechanical
principles in their distribution. The hollow column (£} and
the I-beam (A, B, C), two of the most rigid mechanical con-
structions, are frequently imitated in plants.

150

PLANT LIFE,

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

C D E

FIG. 170. — Diagrams showing the arrangement of mechanical tissues and vascular
bundles in the cross-section of various stems. The mechanical tissue is gray; the
vascular bundles black, with white dots. A , linden (young) ; B, a mint ; (.', a sedge ;
D, a bamboo ; A", a grass. — After Kerner.

a solid column occupying the center of the body. Those
plants which are supported by the medium in which they
live, such as the aquatic plants, are usually without mechan-
ical tissues.

CHAPTER XIII.

NUTRITION.

191. 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, therefore,
neither repair nor growth is possible. To understand 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.

192. 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 per cent, of solid matter. The solid material, left after
driving off the water at a temperature of 110° C., is found to
consist chiefly of three elements, carbon, hydrogen, and
oxygen. The most abundant element in addition to these is
nitrogen. If the dry substance be burned these four elements
are driven off in gaseous forms, and there remains a white
material which crumbles under pressure, the ash. An analy-
sis of the ash reveals the presence of sulfur and phosphorus
in considerable amounts, and also smaller quantities of the
following elements: calcium, magnesium, potassium, iron,

152 PLANT LIFE.

sodium, chlorine, and silicon. Of these seven, the first four
are found in the ash of all plants, and the remaining three
are very 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.

193. 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 con-
tinue 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 con-
ditions of life. Water is the great solvent by which materials
of various kinds are carried into the plant body, and by
which a still greater variety within it are transported from
place to place. Before discussing the food of plants, there-
fore, the relation of water to the plant may be examined.

194. 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 algas, 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 normally have the root system
and sometimes a portion of the stem buried in the soil, con-
tinually or intermittently in contact with liquid water, while
the shoot system is occasionally sprayed by rain. Such may
be called land plants.

195. Solutions in water. — In no case, however, is the
water in which plants are immersed, or with which they

NUTRITION. 153

are sprayed, pure water. It always holds in solution sub-
stances derived from the atmosphere or from the soil with
which it has come in contact. These substances are either
organic or inorganic, and they enter the plant, along with
the water, through those organs which are adapted to ab-
sorption.

196. 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 re-
vival of a wilted plant by spraying seems to be due more
largely to checking the loss of water by evaporation than to
the slight absorption which may occur. The root system of
the land plants is developed in contact with the soil.

197. 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 organic material derived from the offal of
plants or animals. When decaying plant offal predominates,
the soil is known as vegetable mold or humus, which natu-
rally forms the upper layer of the soil of forests. To garden
or field soils, not naturally rich in organic matter, this is

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

154

PLANT LIFE.

frequently added artificially. Both manures and artificial
fertilizers (the latter consisting usually of dried and ground
animal offal) are added chiefly for the purpose of supplying
compounds of nitrogen and phosphorus.

198. Soil water. — No matter how fine the soil may be, the
rock particles are not in close contact, but, on account of
their angular outline, leave spaces of greater or less size to be
occupied by other materials. If a soil be examined immedi-
ately after a heavy rain-fall, these spaces will be found com-
pletely occupied by rain-water. If the soil be so situated as

FIG. 171. — Diagram of a portion of soil penetrated by root hairs, k, k', arising from
root, e. At s, j, j' the hair has grown into contact with some of the soil particles, T,
which are surrounded by water films (shaded by parallel lines), /3, a, T. The white
spaces are air bubbles, 6, 6', y, y' . When water enters the hair at a, the thickness of
the film a, £, 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.

to be naturally drained, considerable quantities 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. 171).

199. Salts dissolved.- -The water which thus filters
through the soil dissolves and retains certain of its constitu-
ents. As the rain passes through the atmosphere it also dis-

NUTRITION. 155

solves certain substances found therein, notably minute quan-
tities of ammonia and nitrous acid. l>y this means compounds
containing nitrogen are constantly being brought to the soil
In the rain.

200. Root absorption. --The structure of the root system
has been explained (^[ 78-82). 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. 171). So close does the contact of the
root hairs and soil grains become that many particles of the
soil are imbedded in the walls of the root hairs (fig. 84).
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. 171). They are thus in a position for
absorbing water from the adjacent films.

201. Limit of absorption. — Not only is the water im-
mediately in contact with the root a source of supply, but
even that in the deeper 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 to
equalize again the surface tensions. 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 1 2 per cent of water unavailable
for the plant.

202. 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, especially carbonates of lime and
magnesia (limestone), which could not be dissolved by the
water alone, may be brought into solution.

Water enters the root hairs by the physical process known

156 PLANT LIFE.

as osmosis, the cell-wall and protoplasm together acting as
the membrane, and the cell sap of the vacuole as the denser
fluid of the osmotic pair. (See Physics.)

203. The development of the root system is related to
the character of the soil and to the amount and distribution
of water and organic matter within it. Branching of the
root system is much more profuse in the moister parts of the
soil, as well as in those which contain more organic matter.

204. 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
the largest loss of water by evaporation (^[ 209). From the
root hairs the water passes inward through the cells of the
cortex, and reaches the stele. The forces which determine
this movement and its direction are not fully understood,
though osmosis probably plays a chief part. They are com-
prehended under the general phrase root pressure.

205. Root pressure.- -The action of root pressure may be
demonstrated by severing a suitable stem close to the ground
and observing the water which flows out, after a short time,
from the cut end. Careful examination of the cut surface
will show that the water oozes out chiefly from the woody
parts of the stele. The force with which water is extruded
may be measured by attaching to the stump, by means of a
rubber tube, a manometer (fig. 172). In this way it may be
ascertained that in woody plants, such as the birch, the
pressure sometimes becomes equal to that of five or six
atmospheres.

206. Route to the leaves. — After entering the xylem
bundles of the roots, the water is thence transferred along the
stem in the same tissues, which are continuous with those of
the root. Since the xylem bundles form an unbroken line to
the most remote parts of the leaves, passing out in the ribs

NUTRITION.

157

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 filled with

water. The water is broken into short

columns by numerous gas-bubbles, and

in ascending to any considerable height

must traverse many cell -walls.

207. 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 evapo-
ration from the leaves, i.e., when the
greatest supply is needed, root pres-
sure becomes almost or quite negative.
Capillarity is also inadequate. The
diameter of the largest ducts is too small
and the friction of the water against
their sides consequently too great to
permit the movement, by this means, of
a sufficient amount of water to supply
Moreover, the interruption of the water

FIG. 172. — Apparatus for
measuring root pressure.
To the stump of a plant
a T-tube, R, is attached by
a piece of rubber tubing,
?'. The other openings are
closed by rubber corks, /r,
through one of which
passes a small glass tube,
r, bent into two unequal
legs, containing mercury.
Through the upper should
pass a short piece of glass
tubing drawn out to a fine
point, to be sealed off in a
flame after fi is filled with
water. At the beginning of
the experiment the inert ury
is about at the same level
in both legs. As water is
forced from the stump into
A by root pressure the mer-
cury rises in the arm </'
and falls correspondingly
in q, — After Sachs.

the evaporation,
columns by gas-
bubbles produces surface tensions which quite overcome that

158 PLANT LIFE.

of capillarity. It has been found that the bubbles of gas
here mentioned often exist under negative pressure, as shown
by the fact that a stem cut under mercury allows the mercury
to ascend for some distance within the vessels. This negative
pressure of the gases is due to the evaporation of water from
the leaves, and the most recent researches point to this as a
very important or even the chief factor in lifting the water.
That the movement is not a function of living cells is shown
by experiments in which stems of plants have been subjected
to poisonous agents, or heated for many hours to a degree
sufficient to kill all the living cells, yet without materially
affecting the supply of water.

208. The loss of water. — Water is constantly evaporating
from the whole surface of the plant exposed to the air. Since
this loss is probably more or less modified by the vital activ-
ity of the plant, it has received the special name, transpira-
tion.

209. 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. The leaves,
affording the largest exposure, are especially organs of trans-
piration. After they have become fully expanded no appre-
ciable amount of water is lost directly from their surfaces.

210. 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 water
and movements of the air affect profoundly the rapidity of
transpiration. Hence arises the need of regulation by the
plant, to prevent excessive loss. The guard cells of the
stomata are irritable, so that external conditions affect their

NUTRITION, 1 59

turgor. If both are turbid, they become curved away from
each other so as to increase the si/.e of the opening between
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 (figs. 161, 162). 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. 357), or
revolution (fig, 359), have a decided effect upon the rate of
transpiration, and may be adapted to regulate it. (See

B. Foods in general.

211. Foods. — In addition to an adequate supply of water,
food is required. Materials consumed by plants as food are
either organic or inorganic. Organic materials are those
which have been produced in nature by the chemical changes
occurring within living bodies. Inorganic materials are those
formed in nature by chemical reactions not occurring in con-
nection with a living body. A very few of the simplest plants
(bacteria) have been grown by the use of inorganic materials
alone ; only the minutest quantities of such substances are
utilized by most plants as food ; but large amounts are used
by all green plants for the manufacture of organic foods.

Organic foods are of three kinds, carbohydrates, fats, and
proteids.

212. Carbohydrates are substances consisting of carbon,
hydrogen and oxygen, so proportioned that there are 6
carbon molecules (or some multiple of 6) while the two latter
elements are combined in the ratio of two parts of hydrogen
to one of oxygen. Well-known examples are sugars and
starch.

l6o PLANT LIFE.

213. Fats.- -These are likewise combinations of the same
three elements, but in them the hydrogen and oxygen do not
exist in the ratio of two to one, the oxygen being much less
in proportion. Some are solid at ordinary temperatures,
while others are fluid. They are combinations of free fatty
acids and glycerin. Upon the addition of an alkali, the fatty
acids combine with it to form soap and other compounds of
less amount while the glycerin is set free. Commercial ex-
amples of plant fats are olive oil, linseed oil, and cacao butter.

214. Proteids are foods consisting of at least five and
generally of six elements, namely, carbon, hydrogen, oxygen,
nitrogen, sulfur, and (ordinarily) phosphorus. These elements
are complexly combined in varying proportions. Proteids
are generally recognizable by their property of coagulation
upon the application of heat, acids, or other agents. Well-
known examples are the proteids forming the " white of egg. '
Examples from the vegetable kingdom are less familiar.

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 manu-
facturing it out of inorganic materials taken into the plant
body from without. They are the only organisms, so far as
known, which have the power of building up organic material
from inorganic. They are, therefore, the ultimate source of
the food supply of the world.

215. Metabolism. — After suitable foods become available
to plants, whether by manufacture or by absorption ready-
made, they suffer various chemical changes both before and
after becoming a part of the body. The changes by which
foods are manufactured and assimilated and those by which
the products of waste are gotten rid of are all comprehended
under the term metabolism.

NUTRITION. l6i

C. Nutrition of colorless plants.

216. 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 devoid 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,'1 in which reds, yellows, pur-
ples, and browns are common. (See also ^|^| n, 40, 45.)

Colorless plants necessarily live either upon the decomposi-
tion products of dead organisms, or in company with living
organisms. Those which live upon dead bodies, whether
these have lost their 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.) Some symbionts are
antagonistic and stand in the relation of parasite and host,
the name parasite being applied to the organism which
depends for its food upon the supporting organism, called the
host.

217. Saprophytes and parasites may be either obligate or
facultative. Obligate parasites or saprophytes are those which
can exist only upon living or upon dead organisms, respec-
tively. Facultative parasites or saprophytes are those which
can pass a portion of their existence upon decaying or upon
living organisms, respectively. They are not able, however,
to complete their life cycle except upon their appropriate
substratum.

218. Saprophytes. — Saprophytic bacteria live immersed
in solutions of organic material, or surrounded by films of

1 62 PLANT LIFE.

fluid on the surface or in the interior of the organic material
upon which they flourish. Saprophytic fungi either form
their mycelium upon the surface of the organic matter, or,
more commonly, they penetrate it more or less extensively
by a profusely branched system of submerged hyphae. A few
saprophytic seed plants form at the base of the stem an en-
larged, tuber-like mass from whose surface great numbers of
profusely branched roots arise. These penetrate the decay-
ing material in all directions, and act as absorbing organs.
A few have abundantly branched underground stems and
have no permanent roots.

219. 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 foods with which they are in contact.
This is brought about either by a direct action of the proto-
plasm of the living plant, or by means of enzymes (*| 237)
excreted by it. Such chemical changes, by means of which
insoluble solid materials are transformed into soluble ones
and are dissolved, are quite like those which occur in the di-
gestive tract of the higher animals, and, therefore, may be
properly termed digestion.

220. 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.*

221. Fermentation and putrefaction. — Some saprophytes
produce changes in the material upon or in which they grow,
other than those described above. The more important
changes may be comprehended under the two terms fermen-
tation and putrefaction. Between these there is no sharp

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

NUTRITION. 163

line of demarcation. Popularly the term putrefaction is ap-
plied to the changes in nitrogenous substances which are ac-
companied by offensive odors. Fermentation is commonly
applied to the chemical changes occurring in sugary solutions,
such as fruits, expressed juices, infusions, etc. Many bacteria
and a number of fungi, notably those known as yeasts, are
capable of producing fermentation in such solutions. The
chemical changes produced are more extensive than those
required for obtaining food. Ordinary brewer's yeast, for
example, utilizes about 5 per cent of the sugar present in the
solution for food, but breaks up the remaining 95 per cent
into carbon dioxide, alcohol, and some other less important
by-products. In putrefaction the by-products are commonly
offensive gases, among which hydrogen sulfid (H.,S) predomi-
nates. Various other materials may be formed, among which
not infrequently are virulent poisons. These are well known
in certain putrefactive changes of milk, meat, etc.

222. 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 mis-
tletoe, which seem to obtain from their hosts chiefly the
water and salts which they have absorbed. These materials
they themselves elaborate into food. (See further ^[ 465.)

D. Nutrition of green plants.

223. Raw materials. — In order that the green plants may
be able to manufacture their food, they require certain raw

164 PLANT LIFE.

materials, which are obtained from the medium by which
they are surrounded. These substances are a weak watery
solution of various mineral salts, and a gas, carbon dioxide.

224. 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 Lfood may be dissolved by the water and be taken
up by the plant. To this extent the plant will live as a sapro-
phyte, 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 calcium and magnesium,
which are present in all soils, in greater or less quantity,
usually in the form of nitrates, phosphates, and sulfates.
Compounds of two other indispensable elements, namely,
iron and potassium, are dissolved in soil waters. In the
same way at least seven additional elements are obtained by
plants. Besides these, other compounds to a considerable
number, of no use in forming food, are taken in. Silicon,
for example, which is found in the ash of almost all plants, is
of no value either as a food, or fur the manufacture of food,
although it plays an important role in increasing the rigidity
of certain plants, and in protecting others from injury.

225. Selective action. — Compounds of these elements
exist in the water in various, though small, amounts. But
they are not taken into the plant in the same proportions as
they exist in the water. For each substance presented to the
plant there is a certain degree of concentration at which its
solutions are absorbed with greater rapidity than at any other.
Substances which are utilized by the plant and which, there-
fore, disappear as such within it by having their chemical com-
position altered or by being stored up in a different form
and so removed from solution, will enter the plant contin-

NUTRITION. 165

uously so long as the supply outside exists. Substances ab-
sorbed by the plant and not utilized accumulate, and their
solutions soon attain the same degree of saturation within the
plant as outside, when they cease to be absorbed. It is for
this reason that two plants growing upon the same soil may
contain very unequal quantities of any important material.
Plants thus exert a sort of selective action, but this selection
is dependent upon purely physical laws, and is not directly
under the control of the plant.

226. Carbon dioxide. — Carbon dioxide, as such, is not
found in nature. It instantly combines with water to form
a gas known as carbonic acid gas, and this is ordinarily
meant when carbon dioxide is spoken of. This gas exists in
small quantities in the atmosphere, rarely exceeding one part
in twenty-five hundred, except in secluded spaces. 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. In a
soil containing carbon compounds it is constantly being pro-
duced by decomposition. 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.

227. Absorption. — Water plants readily absorb the dis-
solved gas by such surfaces as are exposed to the water.
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 carbonic acid, do not take up appreciable quan-
tities 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
intercellular spaces free communication with the outside air,
are important organs, not only in regulating transpiration,

1 66 PLANT LIFE.

but also in permitting the absorption of this gas. Its con-
tinued absorption depends upon its continuous removal from
the cell sap in the manufacture of carbohydrates.

228. Anabolism. — By this term are designated the con-
structive processes of metabolism, by which complex sub-
stances are produced from simple ones. These materials
belong chiefly to two classes, (a] carbohydrates, (£) proteids.

229. i. Carbohydrates.- -The process by which carbo-
hydrates are produced is called photosyntax. The conditions
under which photosyntax occurs are three : (#) the presence
of chlorophyll, ($) the action of light, and (c) the presence
of potassium salts.

230. (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 struc-
tures, the chlorophyll bodies. The real work of forming the
carbohydrate depends, therefore, upon the protoplasm of the
chlorophyll body. The purpose of the chlorophyll is to
absorb certain portions of the light which falls upon it. If
the light which has been passed through a green leaf, or a
solution of chlorophyll, be examined with a spectroscope,
seven dark bands appear in place of certain of the colored
rays, because these have been stopped by the chlorophyll
(fig. 173). One absorption band lies between the red and the
orange (3— 9 of scale, fig. 173), another in the orange (11—14),
the third, faint, in the yellow (17—20), the fourth at the
edge of the green (30—32), while the fifth (53—73), sixth
(75—93), and seventh (94—100) bands occupy most of the
blue and violet. These last three blend into one extremely
broad band, except when the light passes through very small
quantities of chlorophyll.

231. (b) Light. --The light absorbed by the chlorophyll
furnishes the energy necessary to carry on the work of taking
apart the carbonic acid and rearranging the molecules into a

NUTRITION.

167

more complex substance. This energy cannot be supplied
by the plant itself. An external source of energy is therefore
necessary. What this source is is unimportant, provided the

ff C

tco

II III

IV

VI

VII

FIG. 173. — The absorption spectrum of an alcoholic solution of chlorophyll. A beam
of sunlight passed through a prism is broadened into a strip, called the spectrum,
which shows different colors, according to the length of the light waves, the longest
appearing red and the shortest violet. Some of the light waves are stopped by
absorption, and at these places- black lines appear (Fraunhofer lines), the more im-
portant being those below the letters B, C, etc. When the sunlight passes through an
alcoholic solution it absorbs those parts of the light corresponding to the dark bands
I to VII. These absorption bands are made visible by spreading out the light ray into
a spectrum. The bands are located by the Fraunhofer lines, or by the artificial scale,
or roughly by the colors. — After Kraus.

energy be sufficiently intense. The light of an electric arc
serves the purpose as well as sunlight, if its intensity be
equal.

232. (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
presence is essential to the formation of the carbohydrate.

233. The product of photosyntax.- -The steps in the
process of the building of carbohydrates are not thoroughly
known. Present indications are that the material first pro-
duced by the rearrangement of the molecules of carbon,
hydrogen, and oxygen, derived from the carbonic acid, is a
molecule of the simplest carbohydrate, formaldehyde, CH2O.
Several of these are then built up (by condensation and
polymerization) into one of the more complex carbohydrates,
such as cane sugar. Starch is generally the first visible prod-
uct and appears as minute granules in the interior of the

1 68 PLANT LIFE.

chlorophyll bodies, but is probably a transformation product
from a sugar, to which it is closely akin chemically.

234. 2. Proteids.- -The formation of proteids is even
more obscure. Apparently at some point in the series of
changes following the formation of formaldehyde, molecules
of nitrogen are added to form an amid. Amids, especially
asparagin, leucin, and tyrosin, are common in plants. They
may also be produced by the use of carbon, hydrogen, and
oxygen from complex carbohydrates by katabolism (*] 238).
They are soluble in water, crystallizable, and, hence, can be
carried by osmosis from cell to cell. From these, by the
addition of sulfur and phosphorus, proteids are formed, but
neither the steps in the process nor its conditions are well
understood. Apparently the formation of amids occurs in
green tissues and under the influence of light. It is probable
that even among the green plants the formation of proteids
takes place in other parts than the green tissues, as it is
certain that this occurs also among the colorless plants. The
proteids which are built up from the amids are used directly
in the repair of protoplasm. Since carbohydrates are neces-
sary to the formation of proteids, and since they can be
manufactured only by the green plants under the influence of
light, it will be seen how essential these plants are for the
world's food supply.

E. Storage and translocation of food.

235. Storage and transfer. — Both in the colorless and
green plants it is necessary that the foods made or absorbed
should be transferred from one point to another where they
are to be used. The larger the plant, the more important
does this transfer become. 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.

NUTRITION

169

236. Storage. — In the higher plants storage places are
secured by the enlargement of roots, stems or leaves, to form

a

y

FIG. 174. — Reserve starch. A, two cells of a potato, showing enclosed starch grains
The other contents not shown. £, 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.

reservoirs. Similar specialization of parts of lower plants
occurs. Carbohydrates are sometimes transformed into fats
for storage purposes, but carbo-
hydrate and proteid reserve food
is usually solid. Reserve car-
bohydrates usually occur in the
form of starch, sugar, cellulose,
gum, etc. Reserve proteids are
usually in the form of aleurone
grains. The starch is deposited in
the form of large rounded or oval
grains (sphere-crystals), which often

Fie;. 175. — Aleurone (proteid) grains.

sllOW layers Of different Composition /, from seed of peony. «, from

the outer, />, from the middle, c,

and density (fig. 174). FatS OCCUr from the inner layers. //, from

seed of castor bean, a, in alcohol ;

ill liquid form as droplets Of van- />, after treatment with iodine solu-
tion and alcohol. In both, t;, glo-

OUS Size, and are Only rarely SOlld. boid; £, crystalloid. Very highly

magnified. — After Zimmermann.

Aleurone grains are really vacuoles

filled with reserve proteids. Some of the proteids often

't, c

& ogo

O0 O

a

PLANT LIFE.

crystallize (producing a crystalloid), and other materials are
frequently present, which form the globoid (fig. 175).

237. Intracellular digestion. — When solid foods, insol-
uble in water, are to be moved from one part of the plant to
another it must be done by altering them into soluble sub-
stances. This is accomplished by means of enzymes of differ-
ent 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 called maltose. Enzymes fitted
to transform proteids are also found in considerable amounts.
When the foods have thus been brought into a soluble condi-
tion, they dissolve in the water present and move from one
part of the plant to another, chiefly by osmosis. As any
given material is used up in growth or repair, or is altered
into another substance, a constant stream of molecules of
this material moves toward the point at which it is disappear-
ing. 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.

F. Katabolism.

238. Destructive changes. — Coincident with the processes
which result in the formation of complex organic substance
out of simpler ones are those which result in its destruction.
The constructive processes are grouped under the term anab-
olism, and the destructive ones are designated as katabolism.
In the green plants the anabolic changes predominate (be-
cause of extensive photosyntax), with the result that the plant
accumulates organic matter ; while in colorless plants kata-
bolic processes predominate, 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 con-

NUTRITION. 171

structive and destructive changes go on at the same time
and without conflict.

239. Respiration. — A series of katabolic 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 dioxide.
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
dioxide. The processes by which oxygen is obtained and
carbon dioxide excreted constitute respiration.

240. Respiratory ratio. --The ratio between the amount
of oxygen consumed and carbon dioxide 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 dioxide produced is approx-
imately equal to the volume of oxygen consumed, and the

CO2
ratio may be expressed thus : -— i.

241. Respiration and photosyntax. — In the green plants
respiration is masked in daylight by photosyntax. When-
ever the green parts are sufficiently illuminated, the carbon
dioxide produced by their respiration is consumed in the
formation of carbohydrates for food. But when these parts
are not adequately illuminated, the process of photosyntax
is interrupted, and respiration can be 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.

242. Aeration. — The oxygen consumed comes from the
atmosphere, or from the molecules of this gas dissolved in
water. Certain plants are adapted to aerial respiration, while
others are adapted to aquatic respiration, but in either case

1 72 PLANT LIFE.

the gas used is the same. In the smaller and simpler plants
the protoplasm absorbs oxygen directly through the cell wall.
In multicellular plants, however, especially when these be-
come large and complex, only the superficial cells 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
osmosis through other cells. In large plants, therefore,
intercellular spaces are provided, communicating with the
external air, and through these oxygen diffuses. In the
land plants the intercellular spaces are continued through the
epidermis, in which, with the guard cells, they constitute
the stomata (^| 166). On the older parts of woody plants
which have begun to form a periderm the stomata are replaced
by lenticels, through which the internal intercellular spaces
communicate with the outer air (^[ 140). In the absence of
stomata or lenticels, however, the oxygen may pass through
any part of the surface of the plant. In submerged water
plants, very large intercellular spaces are formed (fig. 117),
permitting the existence of an internal atmosphere of con-
siderable amount, within whose limits gaseous exchanges may
occur. Oxygen may reach these intercellular spaces from
the water through the superficial cells.

243. 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
organic matter of the plant itself. Such respiration has there-
fore been called intramolecular respiration. It can exist at
most for a few hours 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 respira-
tory supply. Such plants have adapted themselves to grow
in the absence of free oxygen, which, instead of facilitating

NUTRITION. 173

their life processes, really checks them. They are known as
anaerobic plants.

244. Excretion.- -The carbon dioxide produced by res-
piration, when not used for photosyntax, is gotten rid of by
the reverse of the methods described for the absorption of
oxygen.

245. Release of energy.- -The purpose of respiration is
to set free energy required for growth and movement. While
plants are capable of utilizing radiant energy of the sun for
photosyntax, they 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 rotation of the
protoplasm, or mass movements, such as those of leaves and
other members, or movements of locomotion, such as those
of swarm pores and sperm cells. (See ^| 276 ff.) The re-
quired energy is set free by the decomposition of organic
matter.

246. 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
replaced by the formation of new protoplasm from the pro-
teids, and these again are replaced, as already described, by
the use of carbohydrates and nitrogenous compounds. Ulti-
mately, therefore, respiration results in a diminution of the
reserve food, especially of the carbohydrates.

247. A vital function. — Respiration is a function of the
protoplasm, and does not occur simply because oxidizable
substances are present in the plant and oxygen is brought

174 PLANT LIFE.

into contact with them. On the contrary, the oxygen seems
to enter into loose combination with protoplasm, forming
an extremely unstable compound which under unknown con-
ditions breaks down into simpler substances, setting free
energy. Some of these materials are again used in building
protoplasm, while others break down still further, ultimately
into water and carbon dioxide. The supply of oxygen is so
necessary that if a plant cannot obtain oxygen from without,
it will secure it by the destruction of part of its own sub-
stance for a time, as shown by intramolecular respiration.

248. Heat. — While this decomposition of the protoplasm
in ordinary respiration is not a true oxidation, it nevertheless
results, as oxidation 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. Anything
which prevents the radiation 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. Fermentative changes, which also
occur under the same conditions, add to the evolution of
heat.

249. Light. — A few plants also produce light. This light
is like that seen when phosphorus is exposed to the air in
darkness, or when the end of a match is lightly rubbed.
Phosphorescence occurs only in some bacteria and fungi.
When it is seen upon decaying meat, fish, or wood, it is
because these organisms are present. It does not arise from
the decaying substance itself. Several of the larger fungi, as
certain toadstools, have a mycelium capable of emitting this
phosphorescent light.

NI'TKITION. 175

250. Contrast between respiration and photosyntax. -

Since the processes of respiration and photosyntax in green
plants are so frequently confused, a contrast is here drawn
between them.

Respiration. Photosyntax.

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 dioxide. Consumes carbon dioxide.

Consumes oxygen. Produces oxygen.

Sets free energy. Accumulates energy.

251. Other katabolic changes. — Besides those constitut-
ing respiration, a considerable number of other katabolic
changes occurr, which are not so closely connected with
the vital functions of the plant. They result in the produc-
tion of substances which are of no further use in nutrition
and only of incidental value for any purpose. Such sub-
stances may be stored in some out of the way place, or in
such parts as are transient, and by the loss of these parts the
useless materials are gotten rid of; or they may be excreted
directly. The waste materials are either nitrogenous or
non -nitrogenous.

252. Non-nitrogenous by-products. — Among the non-
nitrogenous materials the most important are the carbon
acids, such as oxalic, malic, etc., the tannins, the resins, the
gums and the volatile oils. These substances are either by-
products of photosyntax, or they arise in the course of the
assimilation of foods. Oxalic acid is usually gotten rid of by
being combined with lime to form calcic oxalate, which
crystallizes either in the form of squarish crystals or as long
needles, the form depending upon the amount of water of

176

PLANT LIFE.

crystallization (fig. 176). The resins, usually dissolved in
an oil, are generally excreted into' special intercellular spaces

III

FIG. 176. Crystals found in plants. I, calcium carbonate; II-V, calcium oxalate ;
II, octahedron with blunt ends ; III, compound crystals from the nectary of a mallow;
IV, a, b, needle crystals (raphides) from leaf of fuchsia; V, cell from the fruit-flesh
of a rose showing a crystal, k, embedded in an outgrowth of the cell-wall, c. All highly
magnified. — After Behrens.

(fig. 177). Volatile oils are secreted by glandular hairs

(c, fig. 113); or are formed
in the epidermis itself, as in
flowers ; or are produced in
chambers near the surface,
the cells which produce the
oil being disorganized to
form the cavity in which

FIG. 177. — Transverse section of an inter-

cellular receptacle for gum-resin from the the drops lie (fig- I?")'
fruit of fennel. The secretion has been

dissolved out by alcohol. The shaded cells Other materials, Slicll aS
lining the tube are the secretory tissue.
Moderately magnified.— After Tschirch. salts of lime, are SOmetimCS

excreted upon the surface of the plant. From glands in
the flower, nectar, which is a solution of sugar, is excreted
(figs. 179, 180). The loss of this food is compensated for
by its attractiveness for insects, which incidentally serve for
the transfer of pollen from one flower to another. Caout-

NUTRITION.

177

chouc and gutta-percha occur in the milky juice of certain
plants.

253. Nitrogenous by-products. — Among the nitrogenous
waste materials the most important are the alkaloids, such as

FIG. 178. — Section through oil-receptacles in rind of orange, a, structure at the beginning
of the disorganization of the oil-producing cells; /', final condition, with two drops of
oil occupying the cavity. Moderately magnified. — After Tschirch.

I II

FIG. 179. FIG. 180.

FIG. 179. — A flower of the red currant cut in half. The roughened surface of the cup, »,

secretes nectar. Magnified 5 diam. — After Kerner.
FIG. 180. — I, a petal from the flower of a buttercup (Ranunculus acris), showing the

nectary, n. Magnified 3 diam. II, diagram of a longitudinal section of the same

through the nectary n. The tissue lining the pouch of the petal, /', secretes the drop

of -nectar, t. Magnified 8 diam. — After Behrens.

quinine, morphine, strychnine, nicotine, etc., which occur in
the seeds, bark, or leaves, and arc gotten rid of when these
are dropped.

CHAPTER XIV.

GROWTH.

254. 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.

255. Formation of new parts. — Each new cell originates
in the division of some previously existing cell by a partition-
wall.* 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 attain 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, the primary meristem (^| 77,
101). Permanent tissue which resumes active division is
called secondary meristem (^| 86, 134). It will be seen,
therefore, that every cell of a plant has been at some time in
an undeveloped or embryonal condition.

256. Phases of cell development. — The characteristics of
this embryonal condition are the nearly uniform and small
size of the cells, the relatively large nuclei, and the absence
or small size of the vacuoles (A, fig. 181). As the cells which
are destined to become the permanent tissues grow older

* To this there are only unimportant exceptions.

178

GROWTH.

179

they pass gradually from the embryonal stage into a second
phase of development, the stage of elongation. This stage is
marked by the rapid increase of the cells in size and a much
less marked increase in the mass of protoplasm present. In
order to maintain the turgor of the cells, there is a great in-
crease in the volume of water, which accumulates in one or

FIG. 181. — Cells from young and mature fruit of snowberry (Sy>///>horicar/>us), seen in
section. A, three young cells, very small, walls thin, nuclei relatively large, vacuoles
very minute; £, two, somewhat older, larger, walls thicker, nuclei smaller, vacuoles
several. 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. The volume of
C is more than 1500 times one of the cells in A . h, cell-wall ; /, protoplasm ; k, nu-
cleus; kk, nucleolus; s, vacuole. — After Prantl.

more large vacuoles (C, fig. 181). If the organ in question
has an elongated form, such as the stem or the root, growth of
the cells takes place chiefly in the direction of its long axis,
although an increase also occurs in the transverse directions.
During this phase the cells may attain a hundred or even a
thousand times their former volume. Growth in length can

i8o

PLANT LIFE.

be studied by direct observation with a microscope, but more
conveniently by magnifying the growth by mechanical means,
so as to observe the movements of a pointer over a scale.
Such an instrument is an auxanometer. Those forms of it
which secure a continuous record automatically are of the

FIG. 182. — Golden's auxanometer. The instrument consists of two parts, a multiplying
pulley and two recording rods turned by a clock. A thread from the plant passes
through a bent glass tube and makes one turn around the small pulley to which it is
then fastened. Another thread makes one turn around large pulley and descends
to carry a pointer which slides on two guide rods. As the plant grows the thread
from it slackens and the pointer descends at a magnified rate by its own weight. Two
glass rods, blackened in a smoky gas-flame, are rotated by a clock to whose hour-
spindle the frame carrying them is attached. As they pass the pointer a mark is made
on the smoked surface. The distance of the successive marks shows the amount of
growth as magnified. Permanent record may be made by means of blue prints, using
the rods (which are removable) as negatives. — After Arthur.

most service (fig. 182). By imperceptible gradations these
cells pass into the third and final stage of growth, which is

GROWTH.

181

characterized by permanent and usually irregular thickenings
of the wall (figs. 10, n, 52, 58).

257. Grand period of growth.- -The entire duration of
growth of an organ is known as its grand period of growth.
Corresponding precisely to the phases in cell development,
there are three phases in the development of the organ as a
whole. Its growth 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 entirely. The
earliest phase, the embryonal, results in so little elongation
that it is scarcely possible to have it recorded by the auxanom-
eter. The last phase, that of internal differentiation, is not

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x

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S

s,

z

s

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8 13 16 2

FIG. 183. — Curve representing the rate of growth of an internode of crown imperial for
each day during the grand period — in this case 20 days. The height of 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.

marked by any elongation. The accompanying curve (fig.
183) therefore represents only the duration and course of the
phase of elongation.

258. Growing region.- -The part of any one of the multi-
cellular 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 centimeter in length. In

182

PLANT LIFE.

stems, however, the elongating part may measure twenty or even

fifty centimeters, and in rare cases
much more. Figure 184 shows a
root, Af upon whose surface marks
were made i mm. apart. Twenty-
four hours later the root presents
the appearance of B. Only the
tissues in the first five spaces were
capable of elongation. The others
had passed into the third phase.
Hie second and third millimeters
grew most in length. The growing
regions of stems may be deter-
mined in the same way.

259. Tension of tissues.- -The
different tissues in any organ usu-
ally do not grow at an equal pace,
and consequently certain tissues
are under strain, while others are
compressed. The curled and
crinkled leaves or the curved cap-
sules of mosses illustrate this in-

tic. 184. — A , a young root ot the pea

marked with fine lines of Chinese equality. It may be present, ho\V-
mk into 13 spaces ot i millimeter

each. B, the same root, 24 hours ever without manifesting itself in

later, showing elongation only in

terminal 5 millimeters The rate of external form. This general con-

growth is greatest in the 20 and 3d

millimeters and slow in the ist 4th, ditioil is kllOWll as the tension of
and 5th. Magnified 2 diam. — After J

Frank- tissues. 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 inner and outer tissues of a young
elder shoot and carefully measuring them shows that the
inner tissues elongate and the outer actually shorten. The
experiment, therefore, shows that the inner tissues really
grew more rapidly than the outer, but were compressed in

GRO WTH. 1 83

the uncut stem, while the outer ones were slightly stretched.
The strains thus set up are spoken of as longitudinal tissue
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 the longitudi-
nal and transverse tensions may be exaggerated if the parts
be placed for a few moments in water.

260. Conditions of growth. — That plants may grow cer-
tain conditions are prerequisite, (i) There must be an ade-
quate supply of constructive materials. These may be derived
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 oxy-
gen 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 maintain a minimum turgor
of the cells, without which growth cannot take place. (4)

'A suitable temperature is required. The range of temperature
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 10° 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.

261. External conditions exercise a very important in-
fluence upon the rate or character of growth by reason of the
irritability of the protoplasm. (See further ^[ 418.) Many
of these conditions act upon members of the plant so as either

1 84

PLANT LIFE.

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 therefore discussed in the chapter on Move-
ments. Those conditions which act more generally and
uniformly upon a large number of plants have a tonic effect
and serve to determine the form and mode of development of
members.

262. Light.- -The tonic effect of light is different upon
different plants and even different members of the same plant.

FIG. 185. — Part of the transverse sections of the stem of rye. A, from a plant grown
fully exposed to light; £, from a "laid" plant imperfectly exposed to light, a,
epidermis ; b, c, mechanical tissues ; d, thin-walled tissues. Highly magnified. — After
Koch.

In general light retards growth in length. Stems grown in
darkness usually become excessively elongated. Those
which under normal illumination have internodes very

GROWTH.

185

short, 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. In diminished light the cell walls do not thicken
normally, and mechanical tissues are weakened. " Laying"
of oats and such grasses is mainly due to this cause (fig. 185).
In weak illumination the palisade tissue of the leaves (^j 167)
is poorly developed.

263. 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

J

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0,5
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579 11 1 3579 11 1 3 5 7 9 It I

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3 5

FIG. 1 86.— 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 joined. 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.

minor fluctuations in temperature, as well as the generally
higher temperature during the day and lower during the night,

1 86

PLANT LIFE.

introduce variations in the rate of growth, which obscure, but
do not counteract, the retarding influence of light. (See fig.
1 86.) This daily period is so impressed upon the constitu-
tion of the plant that it maintains it for a considerable time
even when kept in complete darkness. Stems of sunflower,
after two weeks in complete darkness, still showed distinctly
the daily period. A similar daily period is apparent in

the tension of tissues which depends
on growth.

264. Moisture and oxygen. — The
amount of moisture and oxygen pres-
ent in the medium surrounding a
plant profoundly affects its form.
Amphibious plants, that is, those
which are capable of growing either
on land or in water, often show this
FIG. 187.— A shoot of water in a striking way. When grown sub-

crowfoot {Ranunculus , , n /• i

aquatnis}. The lower leaves merged, the leaves are usually finely

have developed under water ,..,-• •, ., ,

and are branched into many divided, while the Same IcaVCS, II

narrow divisions ; the two , - . . ,

upper leaves have developed allowed to develop 111 the air, have

in air and at maturity float , , .. .

on the surface of the water, broad blades scarcely more than lobed

About half natural size. -

After Frank. (fig-

265. Mechanical pressures or strains also exert an in-
fluence upon the rate and mode of growth. Compression of
tissues retards their growth ; strains accelerate it. Thus,
stems enclosed 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.

266. Variations in rate.- -There are not only variations
in growth in the course of each day throughout the growing

GROWTH. 187

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
variations, also, occur in various organs, particularly in the
tendrils of climbing plants, and in the leaves of flowers and
buds. These regular variations, which affect different sides
of bilateral 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 described under movements. (See ^| 283.)

267. 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, provided they are affected by
suitable stimuli. Thus, the leaf cells which have long since
ceased to divide may resume the power of division in the
neighborhood of a wound, and by division and the growth
of new cells may form a callus covering the wound. The
stimulus following fertilization also induces growth in parts
adjacent to the egg, as is most strikingly shown in the
formation of fruits of the seed plants. (See ^f 404, 409.)

CHAPTER XV.

THE MOVEMENTS OF PLANTS.

268. Irritability. — Among the fundamental properties of
protoplasm are irritability and automatism. We know practi-
cally nothing of the nature of either of these properties,
though upon them depend all the movements executed by
plants. Automatism is the name given to the power in
virtue of which protoplasm is able to initiate internal changes
without the action of any external force. Irritability ex-
presses the power of the protoplasm to respond or react to
the influence of an external change.

269. 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 upon plants. In
order that they may act as stimuli, therefore, a relatively
sudden change in intensity or direction must occur. Some-
times, however, a slow change will still produce a reaction.
For example, the gradual withdrawal of light may cause
movements of leaves. (See ^[ 297.)

270. Conditions limiting irritability. --Protoplasm is ir-
ritable only under certain conditions, which coincide in the
main with those that promote the general well-being or life
of the organism. The limits of temperature, moisture, 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

188

THE MOVEMENTS OF PLANTS. 189

may persist under such conditions for a long time. Irritabil-
ity may also be lost through fatigue, as when, after repeated
reaction, no response occurs to even a greatly increased
stimulus. Upon the return of suitable conditions, or after
sufficient rest, irritability may be regained.

271. 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.

272. Reaction time.- -The reaction does not follow in-
stantly upon stimulation. The interval, which is known as
the reaction time, is ordinarily much longer in plants than in
the higher animals. In extreme cases no reaction may be
manifest until several hours after stimulation. In other cases,
however, as in the well-known sensitive plant, the move-
ments of the leaves follow almost instantly upon stimulation.

273. 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 (Ampe-
/opsis) 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.

274. 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

PLANT LIFE.

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. 386, 205.)

275. Transmission of stimuli. — 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. Much uncertainty exists as to how this is ac-
complished. In some cases it is doubtless done by means of
the connecting threads of the protoplasm from cell to cell,
after the analogy of a diffuse nerve. In other cases it may
be transmitted through certain strands of tissue by the altera-
tion of the hydrostatic pressure in the interior of the cells.

The movements of plants may be conveniently considered
as (i) movements of locomotion by single cells; (2) move-
ments of protoplasm within a cell-wall; or (3) mass move-
ments of multicellular members of the higher plants.

I. Locomotion of single cells.

276. 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 or ciliary movements. Amoe-
boid movements are slow creeping movements brought about
by the protrusion of a portion of the protoplasm (a pseudo-
podium), toward which the remainder gradually flows (fig.
169). 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. 168).
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.

277. Cells with a wall. — Movements of locomotion in
plants possessed of a cell wall are either ciliary or creeping.

THE MOVEMENTS OF PLANTS.

The latter are usually due to the protrusion of processes from
the protoplasm through slits in the wall, as in many diatoms
(fig. 20). The filaments of the water slimes bend from side
to side, and so creep over wet surfaces very slowly (fig. 15).
Bacteria (fig. 17) and some diatoms move by means of cilia.

II. Movement of protoplasm within a wall.

278. Streaming. — In multicellular 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 layer next the
wall, with threads or ribbons extending across
it (fig. 188). When currents start along the
wall and through the strands, the motion is
designated as the streaming of the protoplasm.
These currents along any particular portion of
the protoplasm may run side by side and in
opposite directions.

279. Rotation. --When the protoplasm sur-
rounds a single large vacuole and thus occupies
only the periphery of the cell (fig. 181, C),
the whole mass may rotate, usually in the direc-
tion of its long axis. The portion immediately
in contact with the wall is motionless, and there

must necessarily be a strip between the half FIG. iss.— A single

cell from a hair of

moving up and the half moving down the Cheiidonium.

The arrows show

cell, which is also quiet. Such movements are the direction of

movement ot the

called rotation of the protoplasm. It is not protoplasm in the

peripheral layer

known whether either streaming or rotation and in the bands

which separate the

has any immediate relation to the well-being vacuoles. «, the

nucleus, with nu-

Of the Cell. cleolus. Highly

magnified. — After

280. Cell organs. — In addition to the mass
movements of the protoplasm, the smaller protoplasmic bodies

1 92 PLANT LIFE.

within the cell, such as the nucleus and the chloroplasts, are
capable of moving about. Under moderate illumination
chloroplasts accumulate upon the sides of the cells most di-
rectly reached by the light. Under very strong illumination
they retreat to the walls least illuminated, or may even pile
up in the angles of the cell so as to shade each other (fig.
189).

FIG. 189. — Cells from the spongy parenchyma of the leaf fo wood sorrel (Oxalis), seen
from the direction in which light falls on the leaf, a, position of the chloroplasts in
diffuse light ; 6, position after short exposure to direct sunlight ; r, position after longer
exposure. Highly magnified. — After Stahl.

III. Movements of multicellular members.

281. Forces. — The movements of multicellular parts may
be brought about either by special organs known as motor
organs, or by the growth of the immature parts. Motor or-
gans 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 lose their tur-
gidity, 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 dis-
tinguish movements due to growth and movements due to
variation in turgor.

282. (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 ingrowth

THE MOVEMENTS OF PLANTS. 1 93

is produced by internal causes, called spontaneous move-
ments, and (2) those in which the variation in growth results
from stimulation by external agents, called paratonic move-
ments.

283. i. 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 bilateral one. The opening of all flower and leaf buds illus-
trates 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-
veloped 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 acceleration of growth travels irregularly 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 re-
mainder into a double spiral, are paratonic movements in-
duced by contact. The rotating movements by which twin-
ing plants climb are also paratonic and not spontaneous.

284. 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 peculiar states
in which a plant or an organ exists when it can respond to

194

PLANT LIFE.

the different stimuli have received different names, and those
names indicate the nature of the stimulus. A plant or an
organ is heliotropic when it reacts to the direction of the
rays of light falling upon it ; geotropic, when it reacts to the
force of gravity ; thermotropic, when it reacts to the presence
of a warm body ; hydrotropic, when it reacts 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 direc-
tion of the stimulus. These reactions are to a certain extent

\

FIG. 190. — Diagrams representing the transverse heliotropism of leaves of the garden
nasturtium (rrofxfolutii). 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.

related to one another, and it will be convenient, 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 dorsiventral (such as leaves). Organs are
sometimes physiologically dorsiventral, even though they
possess a radial structure ; for example, some sterns behave as
dorsiventral organs, although they are perfectly radial in
structure.

285. (a) Heliotropism. — Heliotropism is the state of a plant
or organ when it is irritable to the direction of light rays.

THE MOl'EMENTS OF PLANTS.

'95

Light thus plays an important part in determining the position
of organs. As a rule radial organs are either positive!) heli-
otropic, as the stems and leaf-stalks, or negatively heliotropic,
as the roots. Dorsiventral organs, such as leaves, are all
transversely heliotropic, assuming a position at right angles
to the incident rays, which is the most favorable position
possible for the manufacture of food by the green parts (fig.
190). Intense light, however, may bring about a different
reaction, so that the leaves set themselves edgewise to the

FIG. 191. — Leaf mosaic formed by a horizontal shoot of Norway maple. The lengthen-
ing of the petioles of individual leaves to avoid shading of the blade is marked.
About one-third natural size. — After Kerner.

direction of the rays. 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. 191 to 193). The leaves
of window plants also exhibit these movements very strikingly,

196

PLANT LIFE.

because usually illuminated from one side. Plants kept in
darkness have their leaves irregularly placed.

286. (b~) Combined movements due to variations in the

FIG. 192. — A shoot of thorn-apple or " jimson " weed, showing imperfect leaf mosaics
of tall plants formed upon the same plan as in rosettes (lag. 193). One-seventh natural
size. — After Kerner.

amount of light or heat or both are especially exhibited by flow-
ers, whose opening and closing are frequently determined

FIG. 193. — A rosette of leaves of a bellflower (Campanula fusilla), showing length-
ening of petioles of lower leaves so as to carry blades from under upper leaves.—
After Kerner.

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

THE MOVEMENTS OF PLANTS. 1 97

15° to 2on. The flowers of the white water-lily (Nymphaea)
and of the dandelion open in sunlight and (lose in shade.
By marking upon their leaves a series of equidistant parallel
lines with Chinese ink, and subsequently measuring the dis-
tances 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 the proper discharge of the functions is secured
by these movements, which must not be confounded with
those due to the direction of light or heat rays.

'287. (c) Geotropism. — Geotropism is the state of a plant
or an organ when it is irritable to the action 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
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
direction 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
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

198

PLANT LIFE.

successive moment (fig. 194). If the wheel upon which
such seedlings are grown be rotated at a high speed, the cen-

FIG. 194. — Seedling mustard plants grown on a cube of peat, T, 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 m^ aerial
hyphs of a mold have taken direction as far from the repellant moist surfaces as pos-
sible. One half natural size. — After Sachs.

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 stem will be controlled by a com-
bination of the force of gravity and the centrifugal force (the
latter predominating if the speed is great), and will grow in-
ward and upward, while the roots will grow downward and
outward (fig. 195).

288. Transverse geotropism. — Not all stems, however,
are negatively geotropic, nor all roots positively geotropic.

THE MOVEMENTS OF PLANTS.

I99

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 perfectly transversely geotropic. What-

FIG. 195. — Part of centrifuge, a, the axle, rotated at a high speed by water or electric
motor, to which is attached the circular metal plate, r, r, carrying a disk of cork, k.
To the latter are attached two seedling beans, A , £, by means of pins ; st, the primary
stem; /i, the primary root. Over the seedlings the cover, g, 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 half natural size. — After Sachs.

ever 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
curvatures 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.

289. Grasses. — In only a few cases do the maturer parts
of plants regain their power of growth under the stimulus of
gravity. The basal portion of the internodes of grasses,
however, remain for a long time capable of growth ; hence,

2OO

PLANT LIFE.

when grasses are blown down or trampled their stems erect
themselves by the geotropism of this basal growing zone
(fig. 196).

FIG. 196. — 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.

FIG. 197. — Root-cage. On the lower edge of a sheet of zinc a little larger than the panes
of glass selected is formed a water-tight trough of the same material. Two panes of
glass of suitable size are clamped together, with a piece of wood i cm. thick on three
edges to keep them separate. Seeds are sown in fine soil evenly packed between the
panes ; these are set with the lower edge in the water-trough and a sheet of zinc is
used to keep out light. The cage should be slightly inclined, as shown, so as to keep
roots against the glass. — From a drawing by J. C. Arthur.

THE MOVEMENTS OF PLANTS.

2O I

\

290. Root-cage. --Experiments upon the response of root-
lets to the stimulus of gravity upon altering their position
may be carried on by means of a root-cage, shown in figure
197. It consists essentially of two panes of glass placed close
together, 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 198, in
which the dark portion of the
rootlets represents the growing
parts while the cage was in-
verted. They then took about
the same angle with the horizon
as when in normal position.

Many dorsiventral organs,
such as leaves, are transversely
geotropic, just as leaves are
transversely heliotropic.

291. 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 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 rota-
tion the stem comes in contact with a nearly erect support
the free part continues to rotate, growing longer at the same
time, and encircles the support. The part below the point

FIG. 198. — 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.

2O2

PLANT LIFE.

of contact now becomes negatively geotropic, and its growth

on all sides is equally accel-
erated. The coils are thereby
straightened until the stem
clasps the support very closely,
from which it is often prevented
from slipping by angles or out-
growths of various kinds, which
roughen the surface (fig. 199).

While gravity thus plays a
large part in determining the
position of both aerial and sub-
terranean organs, it must be
remembered that it works con-
jointly with many other stimuli.

FIG. 199. — A, a bit of the stem of the J

hop, showing the six angles, each The position of the members

carrying a row of emergences, crowned

by a branched rigid hair with very sharp js therefore, a resultant of the

points. Magnified 3 diam. JS, three

emergences more highly magnified.- reactions tO the Various external
Alter Kerner.

forces which stimulate it.

292. (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 200, the roots which pass into the air,
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

THE MOVEMENTS OF PLANTS. 203

of the wire gauze. Since only one-sided action of a stimulus
determines direction of movement, if the air be saturated
they continue to react to the stimulus of gravity alone.

293. (c) 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

<t

FIG. 200. — Apparatus for demonstrating hydrptropism. 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, /z, /, k, in, first descend into the air but soon turn
toward the damp sawdust again, in has threaded itself in and out of the netting.—
After Sachs.

continued contact (or pressure) in the case of some twining
plants. But in many plants lateral axes in the form of ten-
drils (H^l 115, 158) and leaf- stalks (^| 157) are irritable to
contact, even to a degree far surpassing that of our nerves of
touch.

If the tip of a tendril (^j 266), while still capable of growth,
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 opposite sides. Finally this effect

2O4 PLANT LIFE.

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, ac-
companied by a twisting of the tendril on its axis (fig. 107).
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 series of spiral springs.

Other tendrils do not nutate, but are negatively heliotropic,
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. 154).

294. (B) Movements of turgor. - -The movements just
described are confined to members which are growing either
throughout or in some part. As turgor can affect only tis-
sues whose cell-walls are elastic (^[ 188), the movements
•produced directly by variation in turgor can occur in such
mature members only as are provided with special motor
organs. In almost all cases these are leaves. Stimuli which
regulate growth (^| 284) may also affect motor organs, pro-
ducing like curvatures. But elongation of any part of a motor
organ by increased turgor is reversible, not permanent, (cf.

II 254).

295. Motor organs.- -The motor organ in leaves is usually

the leaf base (^| 151) or a modified portion of the petiole,
sometimes greater but generally less in diameter than the
rest. Its cortex consists of large, rather thick-walled, pa-
renchyma cells, and the stele occupies a relatively small part
of the transverse section. In other parts of the petiole the
stele is much larger, or there may be several steles distributed

THE MO T EVENTS OF PLANTS.

205

about the center. (See ^| 164.) In figure 201, .1 and />'
show the contrast. If the leaf
be a compound one, there are
usually secondary motor or-
gans at the base of the leaf-
lets, as in the leaf of the bean
(fig. 202). Variation in the
turgor of the cells of the cor-
tex upon one side or the other
produces a sharp curvature of

FIG. 201. FIG. 202.

FIG. 201. — Transverse sections through petiole of scarlet runner. A, through the rigid
portion; U, through the motor organ. Cr, g, vascular bundles; c, cortex; in, pith ;
r, deep channel along ventral side of petiole. Magnified about 10 diam. — After Sachs.

FIG. 202. — 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, P1,
P^. 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.

the motor organ, which alters the position of the leaf or leaflet
(fig. 202). The concave surface of the motor organ is always
deeply wrinkled transversely, while the convex surface is
smooth.

206 PLANT LIFE.

296. Spontaneous movements. — Only a few plants exhibit
spontaneous movements through the motor organs. The lat-
eral leaflets of the telegraph plant (j, fig. 203), under normal

conditions of rather high temperature (at
least 22° C.), show jerky movements of
such direction that their tips describe an
irregular ellipse, which is completed in
i to 3 minutes. The leaflets of the
clovers and oxalis show much slower
movements (of a few hours period),
which are usually obscured by the light
movements described in the next para-

FIG. 203. — Leaf of Desmo- crr,,nV1
dium gyrans. Two giapn.

thirds natural size. ^QIQ commonly the turgor movements

are induced. The most common stimuli are light and con-
tact, although many others suffice to induce them.

297. Photeolic movements. — Movements produced by the
withdrawal of light have long been known as "sleep move-
ments ;" more properly, photeolic movements — that is, move-
ments induced by variation of light. They are best observed
upon the leaves of the bean family, though many other plants
exhibit them. Figure 204 shows the positions assumed by
various leaves toward nightfall. It will be seen that in
compound leaves the leaflets sometimes rise, so as to apply
their outer faces to each other ; others sink, so that the un-
der surfaces are in contact ; others become folded in various
ways. This position is maintained throughout the night.
Upon the increase of light in the morning, the day position
is assumed. The cutting off of light artificially from any of
these plants causes them within a short time to assume the
nocturnal position. Darwin suggested that the nocturnal
position prevents the loss of heat by radiation and consequent
injury from light frosts. But it is not by any means certain
that this is its real purpose.

THE MOVEMENTS OF PLANTS.

207

298. Contact movements. — Some organs are sensitive to
contact, as the leaves of Venus' fly-trap and other related
plants. The motor organ in the Venus' fly-trap (figs. 386,
205) is the cushion of tissue running along the dorsal side of
the leaf between the two lobes. By the sudden variation in

a

FIG. 204. — Photeolic movements, a, leaf of a mimosa in day position ; a', the same in
night position. 6, leaf of Coronilla varia in day position ; />', the same in night po-
sition, c, leaf of A morpha fruticosa in day position ; c' , the same in night position.
d, leaf of Tetragonolobus in day position ; d' ' , same in night position. — After Kerner.

turgor of some of these cells the two halves ot the leaf are
thrown quickly together when one of the six bristles upon its
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

208

PLANT LIFE.

normally expanded is shown in figure 206, and their position
after stimulation by figure 207. The stamens (^[ 344) of
some flowers and the stigmas (^j 336) of others are sensitive

FIG. 206. FIG. 207.

FIG. 205. — Part of a transverse section of a leaf of Venus' fly-trap, in, 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. 206. — A leaf of the sensitive plant fully expanded. Natural size. — After Duchartre.

FIG. 207. — 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.

to a touch, shortening, elongating, or bending in such a way
as to promote pollination (^[ 358).

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

H

PART III: REPRODUCTION.

CHAPTER XVI.

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 the reproductive organs and the functions by
which a succession of similar individuals is insured.

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 sep-
arated, organs being specialized for each, so that the func-
tions may be more certainly and efficiently performed.

299. Reproductive structures. — Any part capable of grow-
ing 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-aggre-
gates, they are generally called brood buds or ge?nmce, to dis-
tinguish them from ordinary buds. In both cases it is neces-
sary that the cells to be separated from the parent should be
capable of growth — that is, in the condition known as the
embryonic phase (^[ 256). The reproductive organs pro-

209

2IO PLANT LIFE.

duced by some plants are exceedingly complex and varied,
while others form reproductive bodies in very direct ways.
The reproductive bodies themselves are generally very simple.
In addition to complex reproductive organs, there are some-
times accessory parts by which the plant adapts its reproduc-
tive 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.

300. 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.

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.

CHAPTER XVII.

VEGETATIVE REPRODUCTION.

I. Fission and budding.

301. Fission. — In single-celled plants cell division and
reproduction are practically identical, since shortly after divi-
sion occurs the two cells so produced separate and lead an
independent existence (C, fig. 18). Such a method of repro-
duction evidently interferes little with the processes of nutri-
tion, which probably are scarcely even suspended during the
process of reproduction.

302. 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. 48). Across this neck the partition wall is
formed in the usual way. This becomes mucilaginous, ren-
dering 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.

303. 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 ^[13, and figs. 13,
14), there are specialized cells whose function seems to be

211

212 PLANT LIFE.

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.

II. Spores.

304. Sexual and non-sexual spores. — A spore is a single-
celled body capable of producing a new plant. Spores may
be formed either by a process of growth or by a sexual act —
i.e., 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.

305. Structure. — While a spore is generally composed of
one cell, the term is extended to include two- to many-celled
bodies which are formed in the same way as the simpler
ones. In fact, no clear distinction in form or structure can
be drawn between spores and brood-buds. (See 1" 361.)

306. 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 algse and aquatic
fungi. They are usually pear-shaped and furnished with one
or more cilia, by means of which they swim about (fig. 168).
When locomotion was supposed to be a distinctive power of
animal bodies they were called zoospores, a name still re-
tained. They are also called swarm-spores.

I'EGE TA TI I 'E REP ROD UCTION.

213

When zoospores possess chlorophyll -bodies, as they fre-
quently do, they are aggregated at
the larger end, leaving the pointed
end to which the cilia are attached
colorless. Zoospores are formed
either in a general body-cell, not
visibly different from the other
body-cells, or in a cell specialized
in form and structure. In either
case the cell in which they are pro-
duced is called a zoosporangium.
The entire contents of the zoospo-
rangium may form a single zoospore,
or it may divide into several or
many. In the latter case the nu-
cleus divides into two or more, each
of which gathers about itself a por-
tion of the protoplasm. The zoo-
spores are set free by the rupture of
the wall of the sporangium or by
the solution of a portion of the wall
(fig. 208). They may begin to
move before the rupture of the wall,
in accomplishing which their activ-
ity may materially assist. They

then WOrk their Way OUt and Swim Fir»- 208.— Development and escape

of zoospores of an aquatic fungus

freely in the water. After a time (Saproiegnta lactea). The ends

of two hyphas are shown, the ter-
minal cells being zoosporangia.
In/7, the protoplasm is aggregat-
ing about the numerous nuclei (not
shown). From b many of the zo-
ospores have escaped through the
perforation in the wall near the

off, come to rest, and begin to grow
into a new plant.

307. Non • motile spores are

formed by all classes of land plants without exception. They

of movement they usually lose their
cilia, either withdrawing them into
the protoplasm or dropping them

upper end of the cell. From c all
have escaped but one, which is just
slipping through the opening (here
in profile). Magnified 300 diam. —
After Kerner.

2I4

PLANT LIFE.

are often produced in great profusion, especially by the fungi,
the mosses, the ferns, and the seed plants.

308. Form and structure.- -Their form is exceedingly
various. Many are spherical or ovoid, while some are cylin-
drical or even needle-shaped (figs. 213, 228, 271). Irregular
forms, also, are not uncommon.

In structure spores are usually only single cells, specialized.
Each is a nucleated mass of protoplasm surrounded by
a cell-wall which may be either thin or thick, according
as the spore is destined to immediate growth, or, as a
resting spore, to endure for a time unfavorable conditions.

In some cases the wall of even the
thin-walled spores has two layers, a
condition which is almost universal
among resting spores. When the
wall is so differentiated the inner
layer is delicate, rarely thickened,
extensible, and composed of more or
less unaltered cellulose. The outer
layer is often irregularly thickened,
so that its surface is covered with

FIG. 2o9.-Section of a mature ridgCS, WartS, Spines, Or boSSCS of

spore of Pilu lar ia glob t< lifer a • cnrrc; ( fiox ? T n ?/l8 9 *7 T

A, the cavity of the cell (contents VanOUS SOrtS Vn&S> 2IO> 245, 2yi,

- It is brittle, as compared
the inner coat, and is usually

have a prismatic structure. Mag- rn_r,k or i~cc oUPrpH in rnrrmrKitinn
nified about 50 diam. — After more Or

from its original cellulose nature.

A third layer (the epispore) is sometimes present, but this
is not produced by the cell which it surrounds. It is added
from the outside, being derived from the protoplasm sur-
rounding the spores after they are formed * (fig. 209). This
form of spore is common among the fern allies.

* This protoplasm often comes from the disorganization of some of the
cells around the chamber in which the spores lie.

V EG ETA TIVE RE PROD UCTION.

215

309. Food. --In almost all cases there is a supply of reserve
food within the spore. This reserve food varies in amount
with the conditions under which the spores are formed. It
is ordinarily greater in resting spores than in those intended
for immediate growth. Spores may contain chlorophyll, but
generally do not ; even the spores of green plants are mostly
without it. Its presence seems to indicate an active condition
of the protoplasm, and the vitality of such spores is usually
of short duration. It is of course absent from the spores of
colorless plants, such as the fungi.

FIG. 210. — Part of a vertical section of a leaf of a willow, attacked by a fungus (Melainp-
sora. salicinn). eo, epidermis of upper side lifted by the young teleuto spores; t, de-
veloping from the spore-bed above the ends of the palisade parenchyma, p<ir ; eu,
epidermis of the under side, broken through spore-bed from which spring uredo-
spores, st, and paraphyses, /. eo will also finally be ruptured to set free t. Magni-
fied 260 diam. — After Prantl.

310. Growth. — Spores germinate by absorbing water, thus
bursting the more rigid layer or layers of the cell-wall. The
inner layer then grows in area to accommodate the increas-
ing protoplasm, which so controls the regions of growth and
the mode of cell division as to produce a plant of definite

2l6

PLANT LIFE.

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.
Variety of bodily form is common among the fungi, in which
it is called pleomorphism. Among plants showing well-de-
fined alternation of generations (*[^[ 55, 320), the non-
sexual spores are produced by one form only, and always
give rise to the other.

311. Origin. --Non-motile spores are either free, being
produced at the ends of branches specialized for that purpose,
or enclosed in a case called a sporangium. Often the same
plant forms spores by both methods at different stages in its
development.

a

FIG. 211. — Diagrams showing the formation of an acropetal spore-chain by budding.
a, the spore-producing hypha ; b, its terminal cell showing a bud which in c has ma-
tured into a spore ; d, the spore c has budded, and so on, until in It five spores have
been formed, numbered in order of their development. — After Zopf.

312. 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 aggregated at
certain points, forming a spore-bed (fig. 210). 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

EG ETA TJVE REPRODUCTION.

217

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. 210).

313. Spore-chains. — Spores maybe produced either singly
at the ends of the branches or in chains. When produced in
chains, the youngest spore may be at the base or at the apex
of the chain. The first method is much more common than
the second. In the second case each spore must arise as a
bud upon an older spore, budding itself to form a younger one
(fig. 2 1 1 ) . The spores in such a chain are limited in number.
They develop rapidly, and all are loosened at about the same
time. Those chains which have the oldest spore at the apex

FIG. 212.

FIG. 213.

FIG. 212. — An outline showing the formation of a basipetal spore-chain of the blue-green
mold (Penicillium glaucuin). £, 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. 213. — Longitudinal section through the edge of a gill of a mushroom (Co/riiins)
after spore-formation is completed. /, interwoven hyphie of the gill, branching to
form the hymenium, composed of the paraphyses, /, the cystidia, c, and the ba-
sidia. />. 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.

are produced by the continued division of the branch by
transverse partitions, usually preceded by budding of the
apex, often described as constriction ( />, fig. 212). Beneath

218

PLANT LIFE.

the first spore so formed another spore is produced as the first
grows older ; and this process continues as long as the
plant is able to furnish material for the making of spores.
In such cases, often the oldest spores are liberated while
new ones are being produced at the base of the chain.

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 tip into a single spore, so that the main branch appears
to carry two to eight spores upon slender stalks. Such a
spore-producing branch is called a basidium (fig. 213). It is
the characteristic form in the higher fungi, which produce
conspicuous fructifications.

A

FIG. 214. — A, a puffball (Octaviana) halved, showing the internal chambers (shaded
dark) lined by hymenium (the narrow white border). The intervening spaces, g,
and the unshaded outer part are formed of interwoven hypha?. Magnified 5 diam.
B, a bird's-nest fungus (Crucibzthtw) halved. The similar internal chambers have
been loosened by the disappearance of the intervening hyphae immediately about the
hymenium (represented by radiating lines) and a wavy stalk by which each remains
loosely attached. Magnified 4 diam. — After Luerssen.

314. Fructifications. — In the higher fungi whose myce-
lium is developed within a dead substratum many branches
are aggregated to constitute a reproductive structure or fructi-
fication, which is the only conspicuous part of the fungus.
(For an account of the vegetative parts, see *\\^\ 50, 54.)

VEGE TA TI I 'E REP ROD UCTION.

219

The body of the fructification is made up of hyphse, 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, called in these plants the
hymenium (fig. 213). The hymenium consists of the enlarged

FIG. 215.

FIG. 215. — A fructification of Clavaria
a urea. The hymenium covers the
upper p^rt of the branches. Natural
size. — After Kerner.

FIG. 216.

FIG. 216. — A fructification of a mushroom, Amanita fhalloides. /, the cap or pileus ;
v, 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 hymenium. Most mushrooms showing a distinct volva are poisonous.
Natural size. — After Kerner.

free ends of the hyphae, which are set at right angles to the
surface. Some, the basidia, develop 2-8 slender branches
each of which produces at the tip a single spore. The hyme-
nium may be formed upon the outer surface of the fructifica-
tion or in internal chambers (fig. 214). In the latter case

22O

PLANT LIFE.

these chambers rupture at the maturity of the spores, or even
earlier.

The fructification may be irregularly lobed, sessile and
gelatinous, or much branched and cylindrical or flattened,

FIG. 217. — Fructification of Hydnuni imbricatuut.
The surface of the projecting spines on the under
side of the cap are covered with the hymenium.
Natural size. — After Kerner.

with the hymenium covering the
whole or the upper part of the body,
as in Clavaria (fig. 215) ; or it may
form an umbrella-like, stalked cap,
as in toadstools, with the hymenium
extending over radiating plates on
the under side of the cap, as in Agari-
cus (fig. 216), or over spine-like pro-
jections in the same region, as in
Hydnum (fig. 217) ; or it may be

. . FIG. 218. — Trunk of an ash tree,

a semicircular, sessile body projecting showing fructifications of roiy-

ponis ignarius. After a pho-

irom the substratum like a shelf or tograph by Von Tubeuf .
bracket, with the hymenium lining innumerable minute

VEGE TA 7V I 'E REP ROD UCTION.

221

tubes on the under face, as in Poly /writs (fig. 218) ; or it may
take the form of a ball, the hymenium arising as a lining
upon the walls of regular or irregular internal chambers,
which may occupy most of the interior, as in puff balls and
their kin (figs. 214, 219).

315. Sporangia. — Spores are also formed in the interior
of cells which are either free or covered by a jacket of other

FIG. 219. — Fructification of a puffball (Geaster hygrometricus) ; A, young; B, mature,
the outer layer split open and recurved, the inner also broken to allow escape of
spores. Natural size. — After Corda.

cells. The entire structure is called a sporangium. In the
first case the sporangium is said to be simple. Its wall is the
wall of the mother cell in which the spores are produced,
and they are set free by its rupture (fig. 220). In the second
case the sporangium is said to be compound. The mother
cells of the spores (rarely only one mother cell) are sur-
rounded by others forming a jacket of greater or less thick-
ness. In the mother cells, which are differentiated from the
investing cells, the spores are formed as in simple sporangia.
As the spores mature the walls of the mother cells burst or
are disorganized, leaving the spores still surrounded by the
layer or layers of investing cells (fig. 221). This jacket is
ruptured sooner or later and the spores, thus set free, are
distributed in various ways. (See T 475- )

222

PLANT LIFE.

316. Simple sporangia.- -The simple sporangium may
be like the general body-cells, or it may be specialized in

FIG. 220.

FIG. 220. — Longitudinal section of the simple sporangium of a mold (Mucor). The
aerial hypha, /i, has partitioned off a cell, -r, within which spores are produced. The
walls of this sporangium are studded with needle crystals of calcium oxalate. The par-
tition protrudes far into the end cell. Magnified 260 diam. — After Kerner.

FIG. 221. — Longitudinal section of the stem, j, of a moss gametophyte, bearing leaves,
b. Embedded in the stem is the sporophyte, consisting of a stalk, -y/1, and a compound
sporangium, of which tv is the wall, formed ot a sheet of cells, enclosing the spores,
j/ (contents not shown). Magnified 100 diam. — After Hofmeister.

form as well as in function. It may be spherical, sac-like,
or linear. The elongated sporangium produced by the en-
largement of the end of a hypha in certain fungi has received
a special name, ascits. The number of spores formed within
a simple sporangium may be two or more, up to several
hundred. The spores are formed like the zoospores de-
scribed in ^[ 306, with the difference that a wall is secreted
by each spore before it escapes.

The rupture of the cell-wall, which sets the spores free,
is brought about by the increase of the spores in size, or by
the swelling of the surplus protoplasm left after their forma-
tion. Preparatory to bursting, the wall is frequently altered
so as to be mucilaginous, or it becomes brittle. In some
cases a certain area is thin, which furnishes a starting-point
for the rupture.

y EG ETA TIVE REP ROD UCTION.

223

317. Arrangement. — Simple sporangia may occur singly
or they maybe aggregated. When
aggregated, they usually stand side
by side, and constitute a layer,
called the hymenium (figs. 222,
226). (Compare ^[ 314.) When
thus aggregated (and even when
single) they may be enclosed by
a jacket formed by the coalescence
of sterile filaments, as in the mil-
dews, in which the whole structure
constitutes a fructification (figs.
223, 224, 337). In the lichens the
hymenium, during its earlier stages,
is partially enveloped by sterile
filaments forming a cup-like apo-
thecium (figs. 225, 226). In the
cup fungi (fig. 222) the fructifica-
tion, which is the only part of the
fungus above the substratum, is a
single apothecium, whose whole

. . FIG. 222. — A cup fungus (Peziza

inner race is the hymenium. In aumntta). A, three fructifica-

tions, about natural size. The

an allied form, the morels (fig. inner surface of the cup is covered

with a hymenium, a bit of which
is shown at />' in section at right
angles to surface. />, paraphyses ;
a, an ascus bursting to allow
escape of spores. Highly magni-

enlarged head marked by narrow fied.— After Kemer.
ridges separating broad shallow pits. The hymenium extends
over the surface of these depressed areas. In other fungi,
the sporangia are sunk in deep, narrow-mouthed pits with
which the outer part of the fructification is filled (fig. 228).

The simple sporangia of some of the red seaweeds show a
transition to the compound type in being formed by an in-
ternal cell of the thallus (fig. 229). The adjacent cells, how-
ever, do not constitute a special wall, nor are they neces-

227), the fructification is differ-
entiated into a stalk carrying an

224

PLANT

LIFE.

sarily ruptured to permit the escape of the spores, being
often displaced in the development of the sporangium, so
that at maturity it is partially free.

FIG. 223. — A mildew (Erysiphe cotnmunis), showing the mycelium ramifying over a
bit of leaf, with erect spore-bearing branches and globular fructifications, containing
asci. Magnified about 175 diam. — After Tulasne.

318. Compound sporangia. — Simple sporangia occur only
among the lower plants. In the higher plants, including

the mossworts, fernworts, and seed
plants, the sporangium is always
compound.

319. Development. — Compound
sporangia may be developed either
from superficial or from internal
FIG. 224.— A cluster of asci from cells. As a consequence, the mature

the interior of the fructification

of a m\te<x(Erysif>he Heraciei\ sporangia will be either free or more

similar to those shown in fig. 223.

Each ascus contains four spores. or Jess enclosed withill the tJSSUCS of

Magnified 200 diam. — After De-

Bary. the organ by which they are borne.

A superficial cell may enlarge so as to protrude from the
surface, and divide into two parts, of which the upper cell
develops into the sporangium proper, and the lower cell into
its stalk. According to this method of development the
sporangium is a surface appendage, and may be looked upon

VEGE TA TI VE REP ROD UCTION.

225

as homologous with a hair. Sometimes the sporangia,
although really free, are overgrown by adjacent parts, so that

FIG. 225. — A lichen (Parmelia co n spersa) growing on a stone, showing the leaf-like
thallus (mycelium*, with many fructifications (apothecia). The older ones are more
or less irregular and large with a narrow rim ; the younger are nearer the margin, cir-
cular, and nearly closed over at top. Natural size. — After Frank.

FIG. 226. — A vertical section of an apothecium of a lichen (Anaptychia ciliaris). //,
the hymenium ; y, the subhymenium, a layer of densely interwoven hyphae ; t, t, the
sterile hyphae which partially enclose the hymenium ; »i, the loosely woven hyphae of
the thallus ; a, the algae enslaved by the fungus. Magnified about 50 diam. — After
Sachs.

they are enclosed in a chamber, whence the spores escape
after they are set free by the bursting of the sporangium.

226

PLANT LIFE.

The other mode of development produces enclosed spo-
rangia. One or more internal cells differentiate and become
the mother cells of the spores. The spores, when mature,

FIG. 227.

FIG. 228.

FIG. 227. — A fructification of the morel (Morchella esculenta). The hymenium occu-
pies the surface of the depressed areas. Natural size. — After Kerner.

FIG. 228. — A small bit of a section through the fructification of the ergot (Claviceps
purpurea), showing one of the deep, narrow-mouthed pits, /'land part of another),
enclosing the asci. From the broken ascus at the right thread-like spores are escap-
ing. Highly magnified. — After Tulasne.

will therefore be enclosed by the adjacent cells of the plant,
which may became altered so as to form a sort of special wall
more or less different from the tissue which lies farther off.

VEGE TA TIVE REP ROD UCTION.

227

320. The sporophyte. — Among the mossworts, fermvorts,
and seed plants reproduction by non-sexual spores has be-
come so fixed and important that

one stage in the plant is devoted
especially to producing them.
This phase is different from that
producing sexual cells, the differ-
ence becoming greater the more
complex the plant. The stage set
apart for spore production is called
the sporophyte. In the moss-
worts the sporophyte has very
little green tissue, and therefore
carries on little nutritive work,
but depends for its supply of food
chiefly upon the sexual stage, with
which it is connected throughout
its entire existence (^j 68). In
the fernworts and seed plants,
however, the sporophyte possesses
extensive nutritive tissues, the
leaves, stems, and roots belonging
entirely to this stage. Sporangia
in these plants may be formed
either upon the stem or the leaves
— never upon the roots.

321. Liverworts. — In the
liverworts the sporangium is gen-
erally produced at the upper end
of a short or long stalk. It is
either spherical, ovoid, or short-
cylindrical (figs. 64, 65). The

spore-producing tissue occupies the greater part of the
interior, the wall being formed usually by a single layer of

FIG. 229. — A branch of a red sea-
weed \Polysif>honia o/>aca), show-
ing tetraspores, /, formed by an
internal cell of the thallus. Mag-
nified about joodiam. — After Kiitz-
ing.

228

PLANT LIFE.

cells. Mixed with the spore-producing cells, however, are
many sterile cells, which become gradually elongated, and

ch

nt

FIG. 230. FIG. 231.

FIG. 230. — The sporophyte of a peat moss, (Sphagnum actitifoliuni) with adjacent parts
of the gametophyte. The sporophyte consists of a capsule, .r.v, and a broad foot, sg' . At
the stage shown in B it is still completely enclosed in the tissues of the gametophyte,
viz., c, the enlarged ovary which forms the calyptra or hood, and ?', the vaginule or
sheath surrounding the foot, ar is the neck of the ovary. (Compare fig. 331.) The
arc over the large-ceiled central tissue (columella) is the sporangium, ps, the false
stalk, produced by the gametophyte, which raises the sporophyte. In A, the calyptra
has broken, only a fragment remaining, exposing the capsule. </, the lid, by whose fall
the sporangium is exposed and the spores escape, ch, leaves of the gametophyte : </s,
the false stalk. Compare figs. 67, 72, 73, in which the stalk is part of the sporophyte.
A magnified 13 diam.: />, 32 diam — After Schimper.

FIG. 231. — Longitudinal section of the young capsule of a true moss (Bryiou). s, spo-
rangium. At this stage the mother cells of the spores, sf»n, have become free (only a
few are shown still enclosing the spores) ; siu, the wall of the sporangium, lined by
the remains of another layer of cells now disorganized ; c, the columella, of partly col-
lapsed cells ; is, intercellular space ; cu>, wall of the capsule ; an, the annulus, a ring
of cells which pries off the lid, at whose edge they develop ; ot, the outer, m, the inner,
peristome, formed by the thickening of parts of the walls of certain rows of cells ; nt,
nutritive tissue, with chloroplasts and intercellular spaces. Magnified 25 diam. — Orig-
inal.

rEGETATITE REPRODUCTION. 22g

in many species thicken their walls along one or more spiral
lines. These sterile cells are called elaters (fig. u, A, A'}.
They serve to entangle the spores in clusters when they are
set free. The sporangium opens at maturity by splitting at
the apex, sometimes into two, commonly into four or more,
parts (fig. 64).

322. Mosses. --In most mosses the sporangium is developed
within the enlarged upper part of the sporophyte, to which
the name capsule is given. In the peat mosses it is cap- or
thimble-shaped (fig. 230), while in most of the true mosses
it is a hollow cylinder (fig. 231). It opens by the falling off
of the sterile upper end of the capsule, which separates as a
lid and thus allows the spores to escape from the upper'
end of the cylindrical sporangium. By the time the spores
are mature, the sterile central tissue of the capsule, which
forms the columella (c, fig. 231), shrivels and often almost
disappears, so that the capsule seems to be a cup or urn, filled
with loose spores. In the younger stage (fig. 232) the orig-
inal form is shown.

323. Ferns. — In the ferns the sporangia are usually nu-
merous, stalked, free, and often associated in clusters
called sori. They are either produced upon the under sur-
face of the foliage leaves or upon specialized leaves.* The
sori are often arranged in elongated clusters or lines
(fig. 233). Each sorus, or a cluster of them, may be pro-
tected by a special outgrowth from the cells in its neighbor-
hood, called an indusium (figs. 233, 234). Each sporangium
consists of a stalk composed of two or four rows of cells ex-
panding above into a body composed of a single outer layer
enclosing the spore-producing cells, and at maturity the
spores themselves. The walls of a row of cells more or less
completely encircling the body of the sporangium become

* It must be remembered that the entire plant, consisting of root, stem,
and leaves, is the homologue of the capsule and stalk of the mossworts.

230

PLANT LIFE.

irregularly thickened (see fig. 401). The strains caused by
the unequal absorption and loss of water burst the sporangium

at some definite point. This
line of dehiscence is often
between a pair of large sad-
dle-shaped cells (fig. 401).

324. Sporophylls. In
many of the ferns the leaves
which produce sporangia are
not different from the foliage

FIG. 232.

FIG. 233.

FIG. 232. — Diagram of a longitudinal and transverse section of the very young capsule
of a true moss (Bryiuii). The transverse section is taken along the line A B. a, the
mother cells of the spores ; c, the columella ; is, intercellular space. The constriction
at the top marks the limit of the lid. The part below the sporangium is the neck, with
nutritive tissues. — Original.

FIG. 233. — A leaflet of a fern (Aspidiu-m) seen from the back. Eight sori are shown,
each covered by its own indusium, z. Magnified 2 diam. — After Sachs.

leaves. In others, certain leaves are so specialized for
bearing the sporangia that they lose their nutritive function
in part or entirely. To such specialized leaves the name
sporophyll is applied.

325. Horsetails. — In the horsetails the sporangia have the
form of sacs, varying in number from six to twelve. They
arise upon the lower face of a shield-shaped sporophyll (figs.
235, 236). These sporophylls are aggregated in a close
cluster at the upper end of the axis, constituting what

VEGETAJ^IVE REPRODUCTION.

may be called, properly enough, a flower.* The wall of the
sporangium when young is formed by three layers of cells,
but consists at maturity of one layer only, which, having its
cell-walls thickened in an irregular manner (fig. 238), tears
open the sporangium, usually along a vertical line. The wall
of the spore consists of three layers, the outer one splitting
into narrow strips and remaining lightly attached to the spore
at one point (fig. 239). To these parts of the cell-wall the
name elaters has also been given. ( Compare ^f 321.) Their

FIG. 234. — Vertical section through the leaflet shown in fig. 233, passing through the cen-
ter of a sorus. e, ventral epidermis; e', dorsal epidermis; between them the meso-
phyll, showing 3 veins cut across ; over the central one is a cushion of tissue from
whose surface arise the stalked sporangia s, s. i, z, the indusium. Magnified about 30
diam. — After Sachs.

purpose seems to be to entangle the spores so that they may
not be too sparingly distributed.

326. Club-mosses. --In club-mosses the sporangia are sac-
like outgrowths upon the upper surface of the leaf near its
base, or occasionally of the axis itself just above the leaf.
Sometimes the leaves bearing them are the ordinary foliage
leaves ; in other species they are specialized and crowded
into a terminal cluster or spike (fig. 240).

327. Differentiation of spores. — Among the higher fern-
worts the spores are of two sizes : large ones, known as mega-

* This term is not generally applied to these sporophylls. But see defi-
nition of a flower, ][ 329, and compare fig. 237 of a " flower" of Zatnia.

232

PLANT LIFE.

spores, and much smaller ones, known as microspores (fig.
241). Each kind, when it germinates, produces a sexual
plant, or gametophyte (^| 377), upon which, however, only

FIG. 235.

FIG. 236.

FIG. 235. — Part of two sporophytes of a horsetail (Equisetum arvense). A, the
spring shoots, with sheath-like whorls of leaves below and crowded sporophylls above.
/>', summer shoots, much branched, with inconspicuous leaves ; nutritive work all
done by stems of these shoots. Two thirds natural size. — After Kerner.

FIG. 236. — Three sporophylls from the flower of a horsetail (Eguisetuin telitniteia),
seen in different positions, s, the shield-shaped sporophyll ; sf, its stalk attached to
the center of dorsal face ; sg, sporangia. Magnified about 10 diam. — After Sachs.

one sort of sexual organs is borne. The megaspores give rise
to plants bearing female organs only, the microspores to

VEGE TA TIVE RETROD UC TION.

233

those bearing male organs only. A similar separation of
sexes in the gametophytes frequently occurs when the spores
are equal in size, as in Marchantia and horsetails, but it

FIG. 238.

FIG. 237.

FIG. 239.

FIG. 237. — A, the "flower" of a seed plant (/.ainia tnuricata). It is composed of
crowded sporophylls, of which one is represented in />' as seen from the side. It has
a stalk capped by a hexagonal top, s, with numerous sporangia, x, on the under side.
A, natural size. A, magnified about 6 diam. — After Karsten.

FIG. 238. — A bit of a section of the wall of a sporangium of a horsetail. The cells of
the outer layer thicken their walls along spiral lines. The two inner layers of cells, /,
become disorganized at maturity of the sporangium. Magnified 250 diam. — After
Campbell.

FIG. 239. — Two spores of a horsetail (Eguisetuin arvenseY, one showing the elaters
open, as when dry, the other with them coiled, as when moist. Magnified 25 diam.—
After Kerner.

234

PLANT LIFE.

always occurs when they are unequal. A corresponding dif-
ference in size is often found between the sporangia con-
taining small spores (inicrosporangia) and those containing
large spores (megasporangia} (figs. 241, 242).

The sex terms, male and female, applicable primarily to
the sex cells, are applied also to the organs and to the plants

FIG. 240.

FIG. 241.

FIG. 240. — Sporophyte of a club-moss {Lycopodiitm clavatum). The horizontal stem
is densely covered with leaves ; those on the erect branch become small and few for a
space ; these are succeeded by broader leaves, the sporophylls, crowded in a dense
spike, j. Half natural size. — After Prantl.

FIG. 241. — Section through three sori of an aquatic fernwort (Salvinia. natans).
Each is covered by a double indusium. /, /', two sori consisting of sporangia con-
taining microspores isee fig. 242); «, a sorus consisting of sporangia, each containing
one megaspore. Magnified 10 diam. — After Sachs.

which bear them, so that the microspores are said to produce
male plants, and the megaspores female plants. For a fur-
ther account of the gametophyte, see *\\ 386, 394, 393.

328. Seed plants. — In the seed plants this differentiation
of the spores is always found. The microspores are called

VEGE TA 7V / TE REP ROD UCTION.

235

pollen, and the mcgaspores are called embryo-sacs* The mi-
crosporangia and megasporangia, 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 sporo-
phylls perform nutritive work ; they are always specialized.
Those leaves which bear microsporangia are called stamens,
and the leaves which produce the megasporangia are called

c

FIG. 242. — A , a microsporangium of Salvinia seen from the outside. It contains 64
microspores. B, four spores from A, surrounded by hardened frothy mucilage. C,
median longitudinal section of a megasporangium, showing structure of wall at matu-
rity, and the single spherical megaspore, with its proper wall (black line) and a thick
frothy epispore (IT 308). A and C magnified 55 diam. />, magnified 250 diam. — After
Strasburger.

carpels* (figs. 245, 250, 251). In spite of these special
names, it must be carefully borne in mind that the sporangia
and sporophylls of the seed plants are not different from those
of the fern worts or mossworts in any essential particular.

329. The sporophylls of the seed plants are usually aggre-
gated by the failure of the internodes of the axis to lengthen
as much as between the foliage leaves. Very often, also, the

* 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 rela-
tion 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.

236

PLANT LIFE.

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 sporophylls and
accessory leaves is called a floiver (*[ 330). As a similar
aggregation of the sporophylls occurs in horsetails and many
club-mosses (figs. 235, 240), it is evident that the flower is
not distinctive of the seed plants, though it attains the highest
specialization among them.*

The parts and functions of the flower of seed plants are
now to be discussed.

The Flower.

330. A flower, in its simplest form, may consist of an axis
bearing only a single sporophyll (fig. 243). A flower usually
consists of a shortened axis, the torus, bearing several sporo-
phylls and several accessory floral leaves (figs. 104, 244).

A

FIG. 243. FIG. 244.

FIG. 243. — A , a single flower ; B, a portion of the flower cluster of A risannn vnlgare.

The flower is composed of one stamen only. Magnified slightly. — After Engler.
FIG. 244. — A flower of linden, halved ; showing a pestle-like pistil. Magnified about 3

diam. — After Kerner.

The sporophylls 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

* It is for this reason that the term seed plants is preferred io flowering
plants.

I'EGETA TH'E REPRODUCTION. 237

include both sorts of sporophylls. The perianth may be com-
posed of one or two kinds of leaves, often bright-colored. If
there are two sorts, those next the sporophylls are generally
highly colored, and constitute the corolla. Each leaf of the
corolla, when distinct, is a petal. The leaves below the co-
rolla are often green. They constitute the calyx, and each,
when distinct, is a sepal.

331. Carpels.- The leaves (sporophylls) bearing the
ovules (megasporangia) are called carpels. They may be
flattened ; or so curved that in the course of their develop-
ment 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. 244).
A flower whose only essential organs are pistils is called pis-
tillate. The sporangia 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 communicates with the outside air.

332. Ovules. — Among seed plants the sporangia 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 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.

333. 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

238

PLANT LIFE.

within this case, by which they are protected until mature, or
longer.

These two methods of seed production form the basis for
the separation of the seed-bearing plants into two great groups,
one known as gymnosperms, or plants with naked seeds, the
other as the angiosperms, or plants with encased seeds.
Open carpels 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.

334. The simplest form of carpel occurs in Cycas (fig.
245), in which the ovules are borne on the edges near the
bases of leaves which somewhat resemble the foliage leaves,
and form a whorl between preceding and succeeding whorls
of foliage leaves upon the main axis. The carpel of most

gymnosperms is a scale from
whose upper surface arises a
similar fleshy scale, the pla-
centa, bearing two ovules
upon its ventral (upper or in-

FIG. 245. FIG. 246.

FIG. 245. — An ovule-bearing leaf or carpel of Cycas revoluta, showing 4 ovules near
base, replacing the branches. On the right above, a young seed. About one quarter
natural size. —After Sachs.

FIG. 246. — A young cone-scale (placenta) of Scotch pine showing the two ovules ; the
latter halved parallel to the scale, showing the body of ovule and the prolonged integ-
ument forming the micropyle, in. The scale is attached at b. Magnified about 8
diam. — After Kerner.

I'EGE TA TI I 'E REPKOD UCTION.

239

ner) face (fig. 246). In such cases the carpels are generally
aggregated in close spirals near the end of a thickish axis,
and finally ripen into a cone (figs. 341, 358), which gives
the name to one of the largest orders of gymnosperms, the

FIG. 247. — A , shoot of the yew ( Ta.rus baccata*} with three ripe seeds, each surrounded
by a fleshy aril. Natural size. B, ovule with its tip projecting from the scale leaves
of the shoot it terminates. C, the same, halved, showing the body of ovule (sporan-
gium) and the long tube-like integument. D, young seed of same, witli aril partly
formed. E, mature seed, halved. The central (white) body is the embryo ; around
it (dotted) the food ; then the seed coat; then the aril (white). B, C, D, E, slightly
magnified. — After Kerner.

Coniferae. (See further ^f 404. ) The ovules of some gym-
nosperms are not borne by carpels, but each terminates an
axis, as in the yew (fig. 247).

335. The closed pistils of angiosperms are usually distin-

24O

PLANT LIFE.

guishable into (i) an enlarged basal part, the ovulary* con-
taining the ovules, surmounted by (2) a slender part of vari-
able length, the style, which is terminated by (3) a rough,
sticky, or branched part, the stigma. (See figs. 250, 258.)

336. 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 exten-

sions (figs. 248, 283), 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.

337. The style may be thick or
slender, long or short, branched or un-
branched, hollow or solid. It is fre-
quently wanting, so that the stigma is
said to be sessile upon the ovulary.

338. Simple and compound pistils.
FTrom4Ve°ns?ig0mfa *? com —When several carpels are present in

one flower they may form as many
separate simple pistils as there are car-
- Pels' If numerous, the axis will be
After strasburger. enlarged or elongated to accommodate

them. (See ^| 360.) Instead of forming separate pistils,

* 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
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 ^ 403, 407. ) To avoid confusion with the true ovary (<[ 388),
in which the real egg is produced (^j 387), I here suggest the name ovu-
lary — 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 con-
fusion.

VEGE TA TIVE REP ROD UCTION.

241

the carpels may be united to form a single compound pistil.
This union is commonly brought about (i) by the actual
growing together of the parts in a very young stage, so that
the cells interlock and become partially or completely united;
or (2) the carpels develop, not as separate parts, but as a
ring of tissue growing up from the surface of the axis; or,
(3), a portion of each carpel develops separately, and later
these distinct parts may be lifted by the growth of the ring
of tissue beneath them (fig. 249).

339. The union * of the carpels may be only *at the base ;
or it may involve the entire ovulary, leaving the styles free ;

FIG. 249. FIG. 250. FIG. 251.

FIG. 249. — Pistil of white hellebore (Veratrum album} showing three carpels separate
above only. Magnified about 6 diam. — After Berg and Schmidt.

FIG. 250. — Calyx and pistil of the manna ash (Fraxinus omits) 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. 251. — 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.

or the union may be complete, with the exception of the
stigmas, or it may involve even them (fig. 250). Union may
take place in such a way that the edge of each carpel meets
its fellow and the edges of neighboring carpels in the center
of the compound pistil (fig. 251). In this case the ovulary

* This phrase may be used for convenience in all cases, even of those
pistils in which the carpels were at no time separate.

242

PLANT LIFE.

is divided into as many chambers as there are component
carpels, and the partition by which the chambers are sepa-
rated represents the adjacent parts of the two carpels. Or
the carpels may unite with each other at their edges only, so

that the line of union is at the outside
of the pistil. In this case the ovulary
will have a single chamber. In both these

FIG. 252. — A transverse _ , , , c

section of the capsule of methods of union the normal number ot

shepherd's purse. The . . . , ,

pistil consists of two chambers in the ovulary may be increased

carpels, at whose united , _ , 1,1

edges two placenta; are by outgrowths from the carpels tnem-

formed carrying the _ . f ,

ovules (now seeds i. The selves, as in figure 252, where irom the

partition from one pla- . . . r •

centato the other is an united edges of the carpels a plate ot tis-

outgrowth (false parti- .

tiom and not part of the sue has grown out to meet a correspond-

carpel. Magnified about

6 diam.— After Bessey. ing one from the other side, so that what
should be a one-chambered pistil has become two-chambered.
(Compare also fig. 276.) Even simple pistils are subject to
such subdivision of their interior (fig. 253).

FIG. 253. FIG. 254.

FIG. 253. — Lower half of the pistil of Astragalus canadensis. It consists of only one
carpel, but is divided into two chambers by a false partition, an outgrowth from the
midrib of the leaf. Magnified several diam.— After Gray.

FIG. 254. — Two stages in the development of the ovule of the currant. A, a median
longitudinal section of a young ovule ; n, the sporangium ; it, inner integument be-
ginning to develop as a ring at base of n ; ai, the fundament of the outer integument ;
•m, the mother cell of the megaspores ; B, a similar section of the sporangium alone,
older, showing in', m", m'", the daughter cells of in ; m'", only becomes a perfect
spore ; m' and m" do not develop further and become destroyed. Contents of cells
not shown. Magnified 350 diam.— After Warming.

340. Ovules. — An ovule consists of a megasporangium
partially enveloped by one or two outgrowths from beneath.

VEGETATIVE REPRODUCTION. 243

The sporangium forms the body of the ovule (fig. 254). In
the interior the mother cells of the megaspores are differen-
tiated early, the outer tissues forming the wall of the sporan-
gium (fig. 254). In a few ovules as many as 20 to 40 mega-
spores 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 perfection ; the remainder disappear
almost completely.

341. Indehiscence. — The megaspore never escapes from
the sporangium ; a condition which necessitates many adapta-
tions. (See further ^j^[ 358, 414). The protection of the
megaspore by the sporangium renders a thick wall unneces-
sary. For this reason the megaspore looks more like a cavity
in the ovule than like a spore. Because an embryo appears
later inside this apparent cavity, the megaspore of seed plants
has long been called the embryo-sac.

342. Integuments. — The sporangium is surrounded by
one or two integuments. These arise as outgrowths from
the tissues adjacent. If the spo-
rangium 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. 255).

FIG. 255. — Two- very young ovules

These integuments, as well as the of the California poppy (Esck-

scholtzia), seen from the outside.

Sporangium, Often grOW imsym- B, somewhat older than A. nc,

the sporangium ; jc, the inner in-

metriCally, SO that at the maturity tegument; /r, the outer integu-
ment ; f>i, the stalk. Magnified

Of the megaspore the OVUle IS Often 140 diam.— After Duchartre.

variously curved (figs. 254, 255, 256). The megaspore it-
self may be distorted by this means so as to lose still more
its likeness to a spore.

343. Location. — Ovules are borne either upon the axis
itself or upon the carpels. When they are borne upon
the axis they may be either uncovered, as in the yew

244

PLANT LIFE.

among gymnosperms (fig. 247), or the carpels* may form
a covering, as in angiosperms. In these plants the ovule
may terminate the axis, as in sunflower and buckwheat
families (fig. 257) ; or the ovules may be lateral upon
the surface of an enlargement of the axis within the ovulary,
as in pinks and primroses (fig. 258).

It is usual, however, for the ovules to arise upon a carpel,
either singly or in clusters which occupy definite portions of
its surface. The cushion or ridge from which the ovules
arise is called the placenta. In the pines the placenta is a

FIG. 256. — Diagrams of median longitudinal sections of three sorts of ovules to show
curvatures due to unsymmetric growth. A, a straight, />', an inverted, C, a bent ovule.
In all: f, the stalk; k, the sporangium; //, the inner integument; ai\ the outer in-
tegument; w, the micropyle ; f, the base of the sporangium where the integuments
arise (called the chalaza) ; r, the ridge (rhaphe) formed by the union of stalk and outer
integument ; em, the megaspore. As C develops further e in may become sharply bent
on itself. — After Prantl.

scale-like outgrowth from the upper surface of the carpel,
bearing two ovules (fig. 246), and as the cones mature these
gradually outgrow the carpels and constitute the main por-
tion of the ripened cone. To such placentas the ovules are
attached by one side ; they are therefore entirely sessile. The

* Although the enclosing leaves in this case do not bear the sporangia,
and are, therefore, not strictly sporophylls, their similarity in form renders
it convenient to retain the name carpel even for those pistils in which
they are a mere roof over a convex or hollowed axis bearing the ovules.
(See fig. 258.)

V EG ETA TIVE REP ROD UCTION.

245

placenta in angiosperms commonly consists of a cushion of
tissue usually at the united edges of the carpel or carpels. 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. 252),
or aggregated at its center
(fig. 251). Occasionally the
ovules arise upon the entire
inner face of the carpels, as in
the gentians.

FIG. 257.

FIG. 258.

FIG 257.— A median longitudinal section through the flower of Rheum undulatum.
s, a sepal; /, a petal; a, a, a, anthers; «, stigma; f, ovulary; kk, sporangium,
which, with the two integuments over it, forms the single ovule terminating the axis;
dr, nectary. Magnified about 10 diam.— After Sachs.

FIG. 258. — Pimpernel (Anagallis ari>ensis}. A, median longitudinal section of a
young flower-bud ; /, sepal ; c, corolla, just beginning to develop ; n, anther; A' car-
pels growing over S, the apex of the axis. B, median longitudinal section of the
pistil. c, the carpels, forming a roof over vS", the axis on which ovules are beginning
to develop, and growing up to form a columnar style at whose apex is the stigma, «.
C, the same, older. ^', the enlarged apex of the axis showing six ovules, SK, in sec-
tion ; £••-, the style ; «, the stigma, on which are lodged pollen grains, /. All magni-
fied.—After Sachs.

344. Stamens. — A stamen is a leaf (sporophyll) of the
seed plants which bears the microsporangia, or pollen sacs.
The flowers whose essential organs are all stamens are said to

246

PLANT LIFE.

be staminate. Rarely a single stamen constitutes a flower.
Except for the crowding, 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 filament, bearing an enlarged portion, called the
anther.

345. The filament may be long or short, slender or thick,
rounded or flattened. It may be entirely wanting, in which
case the anther is sessile.

346. The anther is usually larger than the filament and
commonly two-lobed, having the sporangia located in the
thicker parts. The sterile tissue between the sporangia is
called the connective (fig. 262). This appears usually as a
mere continuation of the filament, but sometimes is prolonged
beyond the body of the anther, as an appendage (fig. 259).

a

FIG. 259.

FIG. 260.

FIG. 261.

FIG. 259. — Anther of the sweet violet (I'iola odorata), showing the connective pro-
longed into a triangular tip. Magnified about 5 diam. — After Kerner.

FIG. 260. — Anther of thyme ( Thymus serpyllum), showing broad connective. Magni-
fied about 5 diam. — After Kerner.

FIG. 261. — Anther of the sage (Salina ojftcinalis). Opposite a the filament proper is
jointed to the elongated connective which has one perfect anther-lobe on the upper
end ; on the other the sporangia do not develop. Magnified about 5 diam.— After
Kerner.

It is sometimes broad, so that the sporangial lobes are widely
separated (fig. 260), and may even be so long and slender as
to seem a part of the filament (fig. 261).

VEGE TA TI VE REPR OD UC TION.

247

347. Sporangia.- -The anther bears from 1-12 micro-
sporangia upon its surface, or wholly or partly sunk in its

P

FIG. 262. — Transverse section of the anther of thorn-apple (Datura Stramonium).
c, connective, with a small stele embedded in parenchyma; a, ft, <•*,/, the four spo-
rangia, arranged in pairs showing pollen grains. When the sporangia break, the walls
rupture at the groove between a and /. Magnified about 25 diam. —After Frank.

tissues. In most anthers the sporangia are either 2 or 4
(fig. 262). When there are four they are often paired, and
each pair may become confluent by
the absorption of the portion of the
anther tissue between them (fig. 263).
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. In those which contain

Only tWO Sporangia, the tWO may Open FIG. 263. -Transverse section of

bursted anther of a lily (Bu-

mdependently, or they may become tomustimi>eiiatus).$von&ri&

. have ruptured at z, so that the

COnfllient, SO that at maturity they two pairs have each formed a

single cavity. The connective
may Seem tO Constitute a Single is relatively small; in the center

a single stele. Magnified about
chamber. 20 diam.— After Sachs.

348. Dehiscence.- -The opening of the chambers occurs in
one of three ways : by pores, by slits, or by valves, (i) A small
area of the outer wall is absorbed or breaks away so that the

248

PLANT LIFE.

pollen spores sift out through the pore so formed (fig. 264) ;
or (2) a crack begins at one point and extends lengthwise of
the sporangium, in which case the anther is said to open by
slits (figs. 259, 260, 261) ; or (3) the break occurs along a
line considerably curved, and the flap (valve) thus loosened
curls up or lifts so as to allow the escape of the spores (fig.
265). All three methods are dependent upon some special

FIG. 265.

FIG. 264. — Anther and pollen of a Rhododendron. A, the anther, opening by pores at
the end and allowing the pollen to escape. Magnified 8 diam. />', 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. Mag-
nified 50 diam. — After Kerner.

FIG. 265" — 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.

structure of the wall of the sporangium at the lines of rup-
ture.

349. Union. --The stamens are not infrequently united
with each other or with some of the neighboring leaves of
the flower. They may be united to each other by their fila-

V EG ETA TITE REP ROD UCTION.

249

ments only, or by their anthers only, or throughout their
whole length. Union with the pistil or pistils is rather un-
common, but union with the corolla or calyx is very frequent.
The union of stamens may be real or apparent. They may
develop independently and later
cohere by their adjacent edges
(fig. 266). Or they may begin
development separately and be
subsequently raised by the growth
of a ring of tissue of the torus
(^[360), so that the free portions
arise from the top of a shorter or
longer tube. When the stamens
and corolla, arising independently,
are carried up together by the
growth of such a zone of the axis,
the stamens appear to arise from
the surface of the corolla (fig.
267).

350. Branching. - The sta-
mens frequently branch, and this
is difficult to distinguish from the
displacement by basal growth just
described, except by studying
their development. When sta-
mens branch a single fundament appears, on which later arise
smaller knob-like elevations, the fundaments of the branches,
each with its own growing point. (See figs. 268, 269, 270;
also 1} 171 and figs. 146, 166 on branching of leaves, of
which this is only a special case. )

351. Pollen grains. — The microspores produced in the
sporangia of the stamen are at maturity single cells. Their
forms and walls are various, being round, ovoid, or even
angular, with the surface smooth, grooved, or roughened with

FIG. 266. — The stamens of one of the
sunflower family (Cosmos bif>in-
natus). A, stamen tube formed by
five stamens coherent by their an-
thers around the style ; the fila-
ments with a tuft of hairs about the
middle. B, the same, but stamens
only ; the tube has been slit along
one side and opened out flat ; seen
from the ins'de. Connective pro-
longed ; dehiscence by slits. Mag-
nified about 7 diam. — After Baillon.

250

PLANT LIFE.

few or many bosses, points, or ridges, as in other spores
(A-D, fig. 271). In the pines the outer layer of the wall

FIG. 267. FIG. 269.

FIG. 267. — Corolla of Alcanna tinctoria slit and laid open, showing almost sessile
stamens united with corolla above the middle of tube, j, scale-like outgrowth from
corolla. The tube between j and the notches at edge of corolla result from the growth
of a ring of tissue beneath the five fundaments of the corolla which produce the five
corolla lobes c. Having grown so far, a ring of tissue inside, on which the stamen fun-
daments were developing, became involved in this upward growth, and thus the sta-
mens were carried up and arise just above .$•. Magnified 4 diam. — After Berg and
Schmidt.

FIG. 268. — Very young flower of Hypericum fierforatum, seen from above, showing
s, sepals; /, fundaments of petals ; a,a,n, fundaments of the three stamens, each al-
ready with two lateral growing points, the fundaments of branches, appearing ; g, fun-
daments of 3 carpels. Compare with figs. 269 and 270. Magnified about 50 diam. —
After Frank.

FIG. 269. — An older stage of fig. 268, showing only the fundaments of stamens, a, and
of carpels, g. On the latter at the angles appear the fundaments of the three styles.
Many branches of a have begun. Compare fig. 270. Magnified about 50 diam.
—After Frank.

forms two bladdery swellings which make the spore relatively
lighter (E, fig. 271). The pollen spores arise in the spo-
rangia in fours in each mother cell, as described in ^| 306.
(See also fig. 264.) They are either dry and powdery when

VEGE 7"A TIVE KEPROD I 'CTION.

251

the sporangia burst, or arc moist and sticky, adhering to

each other in larger or smaller

clusters (fig. 264). Sometimes,

as in orchids and milkweeds, they

are all held together in one mass

by the remnants of the mother

cells in which they were formed,

and are attached to a part of the

tissue of the anther which carries

the mass as a stalk or handle (figs.

272, 273). Dry spores are usually FlG 270 _ Ma*re condition of the

adapted to distribution by wind ;

while the adherent spores are

adapted to carriage by small ani- L

mals, especially insects. (See further ^f 481.)

352. Germination in place. — By the time the sporangia

about 3 diam'

B

Fir,. 271.— Pollen grains. A, white water lily (Xymphtpa alba}. B, a thistle (Cirsimii
nemorale). C, a mallow (Hibiscus ternatus}. D, dandelion (Taraxacum offi-
cinale}. Magnified 200 diam. — After Kerner. /•;, pine, showing bladdery enlarge-
ments, /», b, of the outer layer of the cell-wall. The central portion is the body of the
spore filled with protoplasm with a large nucleus. From it is separated a lenticular
cell,/, the rudiment of the gametophyte. Magnified 400 diam. — After Strasburger.

are old enough to release the spores, the latter have already
germinated and begun to form a new sexual plant, the male
gametophyte. Thus the spores of the non-sexual plant give

252

PLANT LIFE.

rise to a plant of the other or sexual phase ; the sporophyte
produces the gametophyte. (For a description of the plant
thus formed see ^[ 385.)

353. Perianth.- -The perianth is not present in any

FIG. 272. — A, hanging flower of milkweed, seen from the side. The petals are sharply
reflexed. Natural size. B, the upper part of same, magnified about 2^ diam., with
two of the appendages, a, of the stamens cut off and the front of the anther wall dis-
sected away to show its two pollen masses. C, two pollen masses from neighboring
anthers connected to a clip, by which they may be attached to the foot of an insect.
Magnified about 8 diam. D, foot of an insect with pollen masses attached. In Cand
D the pollen masses are inverted as compared with their position in A and B.— After
Kerner.

gymnosperms (^j 333), except in a rudimentary form in a
few species of the highest order. In angiosperms the
perianth, which is rarely wanting, is primarily for the
protection of the sporophylls. As in all cases where leaves
are produced rapidly and in close proximity on a short
axis, they grow during their early stages more rapidly
upon the outer face than the inner. They are, therefore,
concave inward and closely pressed together, forming a bud.
At a certain stage the growth upon the two faces of the

n

VEGETATIVE REPRODUCTION. 253

perianth becomes equal, and later is more rapid upon tin-

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 g ^^^ cd

growth are often repeated, the stimulus

being light or heat or both, when it is Fi<;773.-Poiienmassfroin

necessary to protect the spores against ^rs

unfavorable weather. Such flowers open gj

and close several times before their leaves

wither. (See also f 286.)

354. Calyx and corolla.— The leavesof

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.

355. The calyx.- -The calyx leaves, or sepals, are generally
green and possess 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 in the
manner already described for the stamens, 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 undivided, remains throughout the entire development
of the flower, and often of the fruit.

356. The corolla.- -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 petals
may be sessile or have a short or long stalk (fig. 274). The
corolla may develop a cup or tube, as described for the calyx,
with teeth or lobes representing the petals (c, c, fig. 267). It

254

PLANT LIFE.

»

(M \

may be lifted on a common tube with the calyx from which

it then seems to arise ; or it- may be raised
with the stamens, which then seem to be
attached to it, as in figure 267 ; or stamens,
corolla, and calyx may be lifted together
(figs. 288, 355). The corolla is ordinarily
not persistent, usually falling or withering
shortly after the microspores have been
lodged upon the stigma.

357. Irregularity. - - Both corolla and

FIG. 274.— Outline of a calyx are often radially symmetrical — i. e.,

petal of Lychnis,

showing long stalk the parts surrounding the center of the

and an outgrowth, u, TIM i

the liguie. Compare stem are of equal size and like shape,

fig. 137— After Luers- i j- -j j • ivi i i

sen. and may.be divided into several like halves

by radial planes (figs. 275, 276). But often the symmetry
of the calyx, and still more frequently that of the corolla,

FIG. 275. FIG 276.

FIG. 275.— A flower of the flax, halved ; showing radial symmetry. See fig. 276. Magni-
fied 2 diam. — After Bessey.

FIG. 276. — 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.

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,

VEG E TA TIVE REP ROD UCTION.

255

planes; or it may even be entirely unsymmetrical. This
unlikeness in the size and shape of the accessory leaves not
infrequently extends to the sporophylls (figs. 277, 278).

The irregular form and color of the perianth (when other
than green), including the variegation of the ground color
by lines and spots, seem to be dependent upon the relation of
the flower to insects. (See further ^[ 484.)

FIG. 277.

FIG. 278.

FIG. 277. — An unopened flower of the sweet pea, halved ; showing bilateral symmetry

(irregularity). Slightly enlarged. — After Bessey.
FIG. 278. — 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, i separate ; center, one carpel. Only one plane will divide this

flower into halves. — After Bessey.

358. Pollination. — Since the megaspore is enclosed per-
manently by the ovule, and in angiosperms the ovules are
again enclosed by the pistil, it is necessary that the male plant
growing from the pollen spores be developed in the neighbor-
hood of the ovule whose megaspore produces a female plant.
(See TT 341, 386.) To insure this a portion of the pistil
forms a receptive surface, the stigma, upon which the pollen
spores may be readily lodged. It is advantageous, also, to
have the pollen spores of one flower lodged upon the stigma
in another flower of the same sort rather than upon the
stigma of the same flower. The process of 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
cross-pollination.* To secure pollination, and especially

* Since fertilization of the egg is the ultimate object of pollination and

256

PLANT LIFE.

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 development of stamens and
stigma, etc. For an account of these see ^[^[ 477-482.
359. Bracts. — In the immediate neighborhood of the

perianth the leaves are usually modi-
fied at least in form and size, and
not infrequently in color. The
leaves in whose axils the flowers
arise are called bracts, as are also
those which subtend branches of the
inflorescence (h\ h*, h*, fig. 139).
The axis of the flower, when
elongated beneath it, usually bears
one or more bractlets.

The bract is sometimes large and
surrounds the entire inflorescence,
as in Indian turnip (fig. 279) and
the calla, when it may be vari-
ously colored. Highly colored
bracts occur in the scarlet sage

FIG. 279.— Inflorescence of Indian and, with inCOHSpicUOUS flowers,
turnip (a spadix), surrounded

by a large striped and mottled in poillSCttia and Daillted CUD,
bract, the spathe. Natural size.

-After Gray. while the four large whitish bracts

of dogwood are the only conspicuous part of the inflores-
cence (fig. 280).

Bracts are aggregated to form an involucre beneath a head
(^[ 104), as in the sunflower family (figs. 281, 409), or an
umbel (•[" 104), as in the parsnip. The perianth may be
almost or quite wanting, and the bracts and bractlets may
be the only protective leaves for the sporophylls, as in the

generally its final result, the terms close- or self-fertilization and cross-
fertilization were formerly used. The word pollination is preferable.

VEGE TA 77 VE RE PROD UCT10N.

257

FIG. 280. — Inflorescence of the dogwood (Cormts _ftorida), showing four white bracts
below it, giving the whole cluster the aspect of a single flower. Two thirds natural
size. — After Baillon.

-ra

Fir,. 281. — Inflorescence of yarrow (A ch illea millefolium). A, seen from above: P,
in longitudinal section, t, bracts, forming the involucre; e/, bracts in whose axils the
flowers stand; ra, the ray flowers; »/, the disk flowers; c, corolla ;_/, ovulary ; ti,
stigmas; r, the common torus. A magnified about b diam. ; B, about 15 diam. — "After
Prantl.

258

PLANT LIFE.

grasses (fig. 282). Bractlets sometimes form a sort of second
calyx beneath the true calyx, as in hollyhock. In the straw-
berry and its kin, the somewhat similar extra whorl of leaves

FIG. 282.

FIG. 283.

FIG. 284.

FIG. 282. — A single flower of wheat, showing two chaffy bracts, b, 7>, which protect it.
For the parts of the flower see fig. 283. Magnified about 5 diam. — After Luerssen.

FIG. 283. — The flower of wheat with bracts removed, showing two fleshy bractlets, c, c,
the lodicules, which at time of blossoming swell and open the bracts. Three stamens,
and a carpel with two styles and feathery stigmas constitute the flower proper. Magni-
fied about 5 diam. — After Luerssen.

FIG. 284. — Outline of the flower of strawberry, seen from beneath, c, corolla; k, calyx;
k1 ', epicalyx, formed by the union of the stipules of the sepals. Slightly reduced.—
After Luerssen.

belongs to the calyx, being the stipules of the calyx leaves
united in the course of development (fig. 284).

The " cup ' ' of the acorn, the "shuck ' of the beechnut,
and the ' ' bur ' ' of the chestnut represent late-developed out-
growths beneath the flower or the flower cluster, which be-
come scaly or spiny as the nut develops, and serve to protect
the forming fruits.

360. 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-
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 sur-
face, with close-set scars left by their bases (fig. 285). When

V 'EG ETA TIVE REP ROD UCTION.

259

a great number of sporophylls are to be borne, the torus is
elongated, as in the mousetail (fig. 286); or greatly enlarged,

FIG. 285. FIG. 286.

FIG. 285. — 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. 286. — Flower of mousetail (Myositrus »iininius\, halved; showing s, spurred
sepal ; st, stamen ; st', 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. Mag-
nified several diam.— After Engler.

FIG. 287. — Flower of the strawberry, halved ; showing elongated and thickened torus.
Magnified about 3 diam. — After Bessey.

as in the strawberry (fig. 287); or transformed into a cup, as
in the rose (fig. 288).

When flowers in large numbers are very closely associated,

260

PLANT LIFE.

as in a head (*f 104), the receptacles are joined to form a
large common receptacle, as in the sunflower and its allies
(fig. 281). The receptacle in such plants may be a cone,
a dome (fig. 409), or a more or less flattened disk. In the

FIG. 288. FIG. 289.

FIG. 288. — Flower of sweetbrier rose, halved; showing urn-shaped torus. Compare fig.

139. Natural size. — After Bessey.
FIG. 289. — The inflorescence of 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.

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. 289).

III. Brood buds, etc,

361. Definition. — Single-celled spores pass without any
sharp distinction into the multicellular bodies known as brood
buds. For convenience, however, brood buds may be de-
fined as multicellular (sometimes unicellular) bodies capable
of producing a new plant of the same phase as that from
which they arise. Since this is a distinction for conve-
nience merely, it is not desirable to distinguish brood buds

VEGE TA TI I 'E KEF ROD UCTION.

26l

from spores until the mossworts are reached, in which the
alternation of phase is well marked. In their simplest form
such buds consist of a single cell, though more commonly
they are two- to several-celled. Some or all of their cells are
in the embryonic stage (^f 256). Like spores, they are sup-
plied with reserve food.

362. Simple forms.- -The form of brood buds is various.
When not differentiated into distinct organs, they are club-
shaped, lenticular, or spherical. In some thalloid liverworts
(Marchantia and Lunularia) they are produced on the surface
of the thallus, surrounded wholly or on one side by an out-
growth from the surface forming a cup or a crescentic ledge
(figs. 59, 290, 291). In some mosses brood buds arise from

FIG. 290. — Thallus of Marchantia, seen from above, showing the cups containing brood
buds. See fig. 291. Natural size. — After Kerner.

the apex of the stem, either in cup-like clusters of leaves or
exposed (A, A' ', fig. 292) ; in others they are smaller and
simpler and are developed upon the leaves (J3, B' , fig. 292).
In all the mossworts they belong to the gametophyte.

363. Shoots. --In fern worts and seed plants the brood buds
belong to the sporophyte. In the latter they are especially
abundant, and often reach considerable size and complexity
before being separated from the parent, usually consisting of
a short axis with a growing point and at least rudimentary

262

PLANT LIFE.

A'

A
FIG. 291. FIG. 292.

FIG. 291. — Six stages in the development of a brood bud of Marchantia ; all seen from
side. I, very young, the originally single cell projecting from bottom of cup (fig. 290)
divided into a stalk ceil and terminal cell. II, older, terminal cell divided trans-
versely. Ill, IV, V, successively older stages. VI, mature, cells not shown; two
growing points localized on right and left edges. I-V, magnified about 250 diam.;
VI, about 25 diam. — After Sachs.

FIG. 292. — Brood buds of mosses. A, upper part of the stem of A ulaconininiu andro-
gynuin, 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 Syrrhopodon sender (magnified about 10
diam.) showing brood buds ; B' . some more enlarged (about 40 diam.). — After Kerner.

A B

FIG. 293. — Young plants developing from adventitious buds on leaves of a fern (Asple-
nium bulbiferum\, from which they readily separate to form new plants. A, natural
size. B, magnified 2 diam. — After Kerner.

VEGETATIVE REPRODUCTION.

263

leaves. They generally arise upon the stem, more rarely

from the leaves or the root. Upon

the stem they usually take the place of

shoots of other forms, developing from

axillary buds (figs. 294, 296). If

formed on leaf or root it is always from

adventitious buds (fig. 293).

Every possible gradation exists, from
the simplest to those with well-de-
veloped members, constituting a plant
of some size. They may be artificially
grouped as follows :

364. (a) Buds. — In these the axis
is short and the leaves scale-like. When
most highly developed the quantity of
reserve food is considerable and the

FIG. 295. — Pond weed ( Potamoffeton crispus). Detachmentof special shoots, hibernac-
ula, which are to hibernate under water. The plant A has one of these shoots at the
tip ; B has just loosened one, //, which is sinking to the bottom. Two thirds natural
size. — After Kerner.

264

PLAATT LIFE.

parts of the bud are often distorted
by the enlargement of the tissues
to contain the food. The fleshy

j

buds which readily separate from
the axils of the leaves of some
garden lilies (fig. 294), and those
which replace the flowers in some
cultivated onions, are well known.
(Compare also fig. 106.)

365. (b) Hibernacula. — Some-
what similar but more highly de-

FIG. 296. — A plant of stonecrop (Sedum dasyphylluni). Offsets are produced near the
base on short branches o, o ; at the tip of longer branches, o' ; and in place of the flow-
ers, o" . Natural size. — After Kerner.

a

FIG. 297. — Formation of runners in the strawberry, a, the mother plant ; b, young plant
formed at tip of first nmner ; c, plantlet at tip of second ; a third has put out from c.
Slightly reduced. — After Seubert.

V EG ETA TIVE REP ROD UCTION.

265

veloped brood buds are formed at the approach of winter
about the base of the stem in many perennials with her-
baceous 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.

295)-
366. (c) Offsets, etc. -

Some plants produce special
branches, either underground
or aerial, which develop at
their extremities new plants or
special structures for their for-
mation. The house -leek or live-
forever (fig. 369) and stonecrop
(fig. 296) reproduce themselves
by offsets. These are short
branches with a rosette of
leaves at the tip which is read-
ily detached and rolls away,
to take root at the first oppor-
tunity and establish a new
plant. The strawberry and FIG.' 298.— A plant of eel-grass

riii s/>ir<tlis) forming new plants, a, b, at

eel-gl"aSS form lOllg leafless tips of runners, arising from axils of lower

leaves. One third natural size. — After

branches which take root at the Schmzlein.

tip and produce new plants, the slender runner subsequently
perishing (figs. 297. 298). 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 is connected with

266

PLANT LIFE.

the main axis perishes at the end of the growing season
(fig. 299).

367. (d) Cuttings or scions. — Closely related to this

mode of reproduction is that by the separation of fleshy

FIG. 299. — 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, jf, 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, r', The tips of these brandies, when
illuminated, bear foliage leaves,./' ; but usually they thicken into tubers,/1^, which
have scale leaves, e'c', in whose axils buds, br, are formed, the so-called " eyes " of
the tuber. Natural size. — After Duchartre.

members, upon which are subsequently developed adventi-
tious buds, which give rise to new plants. The thick leaves
of Bryophyllum are often blown off by storms, and produce
new plants from buds formed at the teeth along the edge.

VEGE TA TIVE REP ROD tJCTION.

267

Some species of Kleinia, natives of Cape Colony, have fleshy
stems, jointed 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 severed parts to form
adventitious roots and shoots in the artificial propagation of
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.

368. Branching. — A further modification of this method
of reproduction is to be ob-
served in the formation of
new individuals through pro-
gressive death of the older
parts. If a plant, dying thus,
be a branching one, death will
sever the branches as it reaches
them sooner or later, and
each branch then becomes an
independent plant. This is
seen in its simplest form in
those plants which have a hori-
zontal branching thallus whose D
base dies as the apex elongates Fir,. 300.— Outline of a thaiius of

chantia geminata. The base D is
(fig'. 1OO). It IS COUimon in dying as "the apices are growing and

branching. When deatli reaches the
plants with Underground CTeep- first fork there will be two independent

plants ; at the second there will be four,

ing stems which send up aerial and so on.

leaves or shoots annually, as do the ferns of temperate regions

and many grasses and mints.

CHAPTER XVIII.

SEXUAL REPRODUCTION.

369. 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 gamete and
the female gamete. The essential step in their union is the
coalescence of the nuclei. The cell thus formed is capable
of developing into a new plant under suitable conditions,
and is, consequently, a spore. Such sexually produced spores
must not be confounded with non-sexual spores (see ^| 304).

370. Origin. — It is scarcely to be doubted that the earliest
methods of reproduction were vegetative, and that sexuality
has been acquired by a gradual modification of cells previ-
ously devoted wholly to ordinary processes of growth. The
probable history of the origin of sexual cells and sex organs
can only be inferred from the fact that the simplest plants
show no sexuality, others show imperfect sexuality, and still
others complete sexuality. The data are very imperfect, but
they enable us to form at least an intelligent idea of how
sexuality may have been acquired.

Theory of sexuality.

371. Rejuvenescence. — Among the processes of growth
in the simpler plants, especially the fission-algae (^[ n), one
of the most striking is that known as rejuvenescence. In this
process the protoplasm of the cell escapes from the cell-wall,
and acquires special motor organs known as cilia, which en-

268

SEXUAL REPRODUCTION. 269

able it to swim rapidly, but apparently aimlessly, through the
water. In this form it is essentially a zoospore. (See ^ 306.)
After having moved about for a variable time and perhaps
increased its volume by growth, it loses its cilia, surrounds
itself again with a cell-wall, and resumes its ordinary mode of
life. In filaments of some multicellular algae a similar process
occurs. The contents of any cell may escape by the solution
of the cell-wall and become a zoospore. After swimming
about for a time the zoospore may come to rest, secrete a
cell-wall, and by repeated divisions in one plane produce an
individual similar to the parent. (See ^[ 24.) It is evident
that such a method would give rise economically to a con-
siderable number of individuals. The process is essentially
the separation of the filament into pieces, each being the
contents of a single cell.

372. Conjugation. — In other filamentous algae the cell-
contents, instead of escaping as a single zoospore, divide into
two or more zoospores. If, while these are still active, two
accidentally collide, the possibility of their adherence and
and the fusion of the two into one is conceivable. Such
fusion actually occurs among the zoospores of algae, and is
called conjugation. But in observed cases it follows a definite
method, and is not merely accidental. It is probable, how-
ever, that the first occurrence of conjugation was accidental,
and that it has become fixed and definite because those indi-
viduals in which it occurred with most certainty and regular-
ity thereby produced the most vigorous offspring.

373. Imperfect sexuality. --In the alga Ulothrix, we have
a plant in which many of the processes just described still
occur. It produces zoospores of two kinds : (i) large ones,
with four cilia (C, fig. 301), formed in pairs in each cell (B] ;
(2) small ones, having two (rarely four) cilia, and arising
eight or sixteen from each mother cell (D). Both these sorts
of zoospores will grow, after a period of swimming, into new

270

PLANT LIFE.

plants, though the small ones produce very slender, weak fila-
ments (fig. 302). Beside the zoospores, Ulothrix produces,
under certain conditions, gametes, which are precisely like

FIG. 301. — Ulothrix zonata. A, a young filament with rhizoid cell, r, at base. B, bit
of a filament from whose cells large zoospores are escaping through a pore in the side-
wall. C, a single large zoospore. D, bit of a filament from whose cells small zoo-
spores lor gametes) are escaping. £, small zoospores (or gametes . F, gametes con-
jugating. G, same, conjugation complete. //, zygote, before formation of wall to
become a resting spore. Magnified 482 diam. — After Dodel-Port.

the small zoospores in appearance. But their behavior is
different. They usually conjugate freely in pairs and produce
resting spores. If, however, they do not conjugate, each

SEX UA L RE PR OD UC 7 'ION.

271

a

may round itself off and, alone, become a resting spore.
These resting spores, after a dormant period, germinate and
develop into new plants.

In Ulothrix, therefore, the gametes are imperfectly sexual.
Failing to conjugate, as many do, they may still develop into
new individuals. A con-
sideration of the appearance
and behavior of the gametes
leaves little doubt that they
are merely small zoospores
which have acquired imper-
fectly the habit of conjuga-
tion and retained partially
the power of independent
growth.

374. Further develop-
ment.— The perfecting of
reproductive methods fol-
lowed the two lines just sug-
gested. On the one hand,
complete sexuality was ac-

. . Fir,. 302. — Sporelings of Ulothrix zonata.

quired by Certain Cells, while «, a young plant from a large zoospore.

b, young plants from small zoospores which
Others Were more Completely germinated without leaving the motker cell.

Magnified 482 diam.— After Dodel-Port.

specialized as non-sexual re-
productive bodies. The latter have already been discussed

Tracing now only the line of sexual development, it is
probable that the first step in this differentiation was the
failure of some of the zoospores to escape from the cell pro-
ducing them. From this point two lines of development
diverge.

375. i. Isogamy. — Along one of these lines, the zoo-
spores ceased to form cilia, and became non-motile sex
cells, in some cases similar in form and function, and in others

2/2

PLANT LIFE.

\ 1

like in form but unlike in behavior. This leads to the com-

pletest form of conjugation, as seen
in Mesocarpus, Spirogyra, and othei
Conjugatae. (See ^[ 25.) In these
the contents of one cell of a filament
enter those of another either by a
partial solution of the partition-wall
between them or by the formation of
a tube-like outgrowth from one or
both of the cells concerned, so that
when these tubes come in contact and
have their ends absorbed the contents
of one cell passes over into that of
the other (fig. 303). The cells con-
jugating in this way may be either
neighboring cells of the same fila-
ment or cells of different filaments
brought into proximity by acccident.

FIG. 303-— Conjugation of Spiro-

gyraquinina. The cells ,a, a' \\\ the COlirSC OI development 111 thlS
are just forming the conjugat- _ %

ing tube; the contents not yet direction conjugation reaches its

fully reorganized as gametes.

The body protoplasm is not highest perfection, being secured with

shown in these two cells,

though it is in the others such certainty that non-sexual methods

(compare fig. 25, of another ••,-,•,

species of Spirogyra). The are almost entirely abandoned.

cells b, b' have completed the

tube ; the ends have been dis- 376. 2. HeterOgamy.- -The SCCOnd

solved and the contents of b

is passing over into b1 . This line of development was followed by

process is nearly completed in

ceils c, c1. z, z, zygotes, with other alsrae. and the method proved so

protecting wall, thereby pre-
pared to become resting spores, efficient that it became the dominant

Magnified 150 diam. — After

Strasburger. one in the plant kingdom. Among

these algse there occurred a differentiation of the zoospores.
The first step in this differentiation was an increase in size
of one of the sex cells, so that they differed both in action
and in form. To distinguish one from the other the larger
sex cell is called the female cell, or egg, and the smaller, the
male cell, or sperm. A further difference arose in the com-

SEX UA L REPR OD UCTION.

273

plete loss of motility by the female cell (fig. 304). When
these differences exist in the sex cells their union is no
longer called conjugation, but fertilization, the active male
cell being said to fertilize the quiescent female cell.

377. Sex organs. — A further stage in the development of
sexuality is reached when the cells producing the sperms or

FIG. 304. — Differentiation of gametes in some marine algae, a, like gametes of Ecto-
carpus. />, sperm, c, egg of /.anardinia. The egg loses its cilia and rounds itself
before fertilization which is about to occur in d. e, sperm, f, egg of Fucns. This is
the extreme of difference in size in gametes. All magnified equally (about 700 diam.).
— After Mobius.

the eggs are differentiated. The cell or the organ producing
the egg has been known by various names in different groups
of plants. An appropriate general name for it, without refer-
ence to its structure, is the ovary. (See further ^f 335.)

2/4 PLANT LIFE.

The male organ was called the antheridium, from the idea
that it was like the anther of seed-plants, which was once
supposed to be the male organ of the flower. There is no
special objection to the name, but a more appropriate one for
it is the spermary, since these male cells are known as the
spermatozoids or, briefly, the sperms.

The final step in the development of sexuality is the restric-
tion of the formation of sex organs to a certain phase in the
life history of the plant, which is therefore known as the
sexual phase, or gametophyte, the remaining phase or phases
being called, for the sake of distinction, non-sexual, and con-
stituting the sporophyte. The gametophyte alternates with
the sporophyte, giving rise to the phenomenon known as the
"alternation of generations.' (See ^| 55.)

378. Directive agents. — To secure the union of the male
and female cells, the male gamete must be directed to the
female. By what means this is accomplished is not fully
known. Organic acids and sugar exercise such an influence
on certain sperms that they swim towards the source of these
substances. The wide distribution of such compounds sug-
gests that probably their presence in the female gamete may
render it attractive. If this is true, the sperms exhibit a spe-
cial irritability towards these materials, whose diffusion acts
as a stimulus.

Isogamy.

Sexual reproduction, as developed among existing plants,
shows two main types, known as isogamy and heterogamy,

379. Isogamy is that mode of sexual union in which the
size and form of the gametes is alike. In some cases the
behavior also of both male and female is alike, while in others
the male shows a greater power of movement. When both
are equally motile and escape from the cell, conjugation occurs
wherever they happen to come in contact. The form is usually

SEXUAL REPRODUCTION,

275

ssswgr :-
•?Wi"

pear-like (E, fig. 301). The protoplasm at the narrower end
is more transparent and bears two or more
cilia ; while the larger end is occupied by
the reserve food and particularly the chloro-
plasts, if present. Union of free motile
gametes occurs by gradual coalescence, be-
ginning at the pointed, transparent end (Ft
fig. 301). When the conjugation is com-
plete the resulting spore (zygote) usually
acquires a spherical form, soon secretes about
itself a wall, and either begins to grow at
once into a new plant or thickens the wall
and becomes dormant for a time as a resting
spore. In other cases the form of the
gametes is determined only by the shape of
the cell, from which they do not escape. The
entire cell contents constitutes the gamete
(figs. 303, 304). In such plants both
gametes may be equally motile and meet
in a branch, the conjugating tube, to form a
spore, as in Mesocarpus (fig. 304) ; or the
male gamete may be motile and migrate from the cell in
which it is produced, through the conjugating tube into the
cell containing the female gamete, with which it fuses, as in
Spirogyra (fig. 303).

The spore thus formed may be a resting spore, in which
case it secretes about itself a thick wall, and remains dormant
for several weeks or months. In the plants just referred to,
the spores, formed in early summer, with the remnants of the
parent cell-walls about them, sink to the bottom of the water,
and do not germinate till the next spring.

mulating in the con-
jugating tube to form
a zygote, which is
complete in the
lower tube. Magni-
fied about 150 diam.
—After DeBary.

PLANT LIFE.

Heterogamy.

Heterogamy is that mode of sexual union in which the sex
cells are unlike, being differentiated into sperms and eggs.

380. The sperms.- -The body of the sperm is the cell
nucleus, surrounded by a small amount of protoplasm which is
often extended into one or more cilia (fig. 306). The more
complete the differentiation of the sperm the smaller, as a
rule, is the amount of body protoplasm. Whether or not the
sperm is motile depends upon the conditions to which it has
become adapted. Whenever motile, fertilization must occur
in the presence of water of amount sufficient to permit the
sperm to swim to the egg.

FIG. 306. — Sperms of various plants, showing variety of form, i, Volvox aureus ;
2, Vaucheria synandra ; 3, Cknrafragilis ; 4, Fucus serratus ; 5, Ularchantia
polymorfiha ; 6, Equisetum Telmateia ; j, I\Iarsilia -vestita. Magnified 1000
diam.— After Mobius.

The spermary may produce only one sperm (fig. 307), or
its contents may divide into many (fig. 310), When single,

SEXUAL REPRODUCTION.

277

the form of the sperm is usually that of the cell in which it
is produced. If it is set free, it may become globular, and
have slow amoeboid movements, or it may be entirely im-
motile. In the latter case it must depend upon the move-
ments of the water into which it escapes for transference to
the vicinity of the egg. The sperm may be ovoid and fur-
nished at the end with one or more cilia; or elongated and
bent or coiled one or more times. The elongated forms
have almost invariably two to many cilia (fig. 306).

381. The spermary.- -The organ in which the sperms are
produced is the spermary or antheridium. It is either simple
or compound. A simple spermary consists of a single cell
whose contents is transformed into one or more sperms.
Simple spermaries occur only in algre and fungi, and by
reduction among seed-plants. (See ^[
385.) If more than one sperm is to be
formed, the nucleus, originally single,
becomes divided into as many parts as
there are to be sperms (sometimes into
more than become mature). The total
number of sperms produced by a plant is
related somewhat to the number of eggs,
but particularly to the chances of the
sperms reaching the egg.

• . . FIG. 307. -The sex organs

If there is but a single sperm formed of i\-ronosf>ora. k,

hypha which has devel-

by each spermary, either the number 01 oped at the end the

ovary, c, containing a

spermaries is great or some adaptation single egg (the central

dark sphere). //', hypha

exists for the certain transfer of the sperm which has developed the

. spermary, //, whose pro-

to the egg. In Cystopus and its allies, toplasm, constituting a

single sperm, is passing

for instance, a branch of the spermary through the fertilizing

tube (a branch of the
grOWS into the OVarV, through which the spermary) into the egg.

Magnified 350 diam.—
Sperm passes to the egg (fig. 307). After DeBary.

A simple spermary arises either by the differentiation of
one of the ordinary cells, or of a special lateral branch, as in

h1

2/8

PLANT LIFE.

the filamentous

algae

and fungi

(figs. 307, 308). In the

thallus of multicellular algae it may be the terminal cell of a

A

7)

-2.

*»~&

- °0.0/°/«0o VcT0'";^
D^-^o'Vj-yo.o-

o^p° ? qV

;6V

-Qik.

FIG. 308. — Sex organs of \\ater flannel (I'aucJieria sessilis). A, a portion of filament
with two lateral branches, a, og. In a the spermary has already been divided from
the body cavity by a partition wall. In og, a partition will form at juncture with main
axis (see fig. B), when og becomes the ovary. />', the ovary, mature, having opened
and extruded si, a portion of the protoplasm. What remains is the egg. The chloro-
plasts have accumulated, leaving a clear receptive spot opposite entrance of ovary. C ',
sperms, which escape at maturity from A, a. D, ovary with egg about to be fertil-
ized; the sperms have collected at the opening. A, B, D, magnified about 100 diam.
C, magnified much more (about 350 diam. ?). A, D, after Sachs ; B, C, after Prings-
heim.

branch or, in the leaf-like forms, a cluster of surface cells.
In Fucus the spermaries (figs. 309, 310) are terminal cells
of much-branched hairs which

develop from the surface cells
of a narrow -mouthed pit like

FIG. 309.

FIG. 310.

FIG. 309. — A portion of a branched hair from a conceptacle of bladder wrack (Fucus
vesiculosus). The darker cells are the spermaries. Magnified 160 diam. — After
Thuret.

FIG. 310. — Spermaries of Fucus vesiculosus, showing the escape of the sperms. Magni-
fied 350 diam. — After Thuret,

SEXUA 1. REPROD UCTIOX.

279

that for the ovaries (fig, 326). (See also fig. 42.) The
sperms are set free by the rupture of the wall of the spermary.
382. A compound spermary consists of one or more cells
in which the sperms are to be produced (each corresponding
to a simple spermary), surrounded by a wall formed of a
single layer of cells (rarely more). Compound spermaries
are found only in Characeae, mossworts, and higher plants.
The spermary is a spherical or elongated sac, raised upon a
stalk, or sessile ; free upon the surface of the plant, or sunk
in a pit (fig. 311). The cell in which each sperm is formed

n

FIG. 311. — A, a longitudinal section ot a male head of Marchantia. t, portion of
thallus ; ha, enlarged head or receptacle; a, spermaries, sunk in pits opening at o.
Magnified about 15 diam. />, compound spermary. ?c, its wall, surrounding the
immense number of minute regularly arranged sperm mother cells ; st, its stalk.
Magnified about 80 diam. — After Sachs.

is called a "sperm mother cell.' Each contains a single
nucleus which enlarges to form the sperm of that cell (fig.
312). The sperms are set free by the breaking down of the
walls of the mother (-ells at about the same time that the
outer wall of the spermary is ruptured by the destruction of
one or more of its cells.

The form of the vegetative body of the gametophyte in all

280

PLAN

T LIFE.

but the seed plants was described in Part I. The forms of
the spermaries are as follows :

383. Chara. — The compound spermary of Chara (fig.
313) consists of a spherical case composed of four triangular,
plate-like cells ; from the inner face of each projects a
handle-like cell to whose end are attached 24 filaments, each
composed of 100-200 disk-shaped cells. Each of these con-

FIG. 312. — Development of a sperm of a liverwort (Pellia epiphylla\. a, mother cell
with nucleus, the latter approaching the wall ; l> to /i, nucleus elongating and curving
into an arc, and finally a spiral coil ; e, an edge view, showing origin of cilia from
peripheral protoplasm ; /, also an edge view ; k, mature sperm, free. Magnified 1000
diam. — After Guignard.

tains a sperm; so that each spermary produces 20,000-
40,000 sperms.

384. Mossworts and fernworts. - -In the moss worts the
spermary is a stalked body, whose internal cells are the sperm
mother cells, the outer layer forming the spermary wall (fig.

311)-

In the fernworts the spermary is sessile and the number of
mother cells is much smaller (fig. 314), corresponding to the
reduction in size of the gametophyte (see ^[ 395). When
the gametophyte is greatly reduced, as in the club-mosses,
a single spermary only is formed, which is even larger
than the rest of the gametophyte (fig. 315).

385. Seed plants. — In the seed plants the male gameto-
phyte begins to be formed before the microspore leaves the
sporangium. In gymnosperms the spore divides into two to
six cells, one or two of which represent the vegetative part

SEXUAL REPRODUCTION.

28l

of the gametophyte and the others the spermary (fig. 316).
In angiosperms the vegetative part seems to have vanished
and the two cells which are formed constitute the spermary,
the smaller representing
the sperm cells and the
larger the wall cells (fig.
317; compare fig. 315).
Sometimes, indeed, the
smaller cell is only repre-
sented by a nucleus, no
partition wall being pres-
ent. Thus, the spermary
in allseed plants has almost
become a simple one again
by reduction from the com-
pound spermary of their
ancestors.

reduction of the male game-
tophyte, that is, to a sex
organ alone, almost all trace
of resemblance to a plant
has been lost, and it is diffi-
cult to think of the pollen-
grain (microspore) as pro-
ducing a real plant. This
male plant, though ex-
tremely small and simple
even when mature, is the
exact homologue of the
larger male plant produced
by the spores of the mosses, ferns, horsetails and selaginellas.
386. Pollen tube. — The maturity of the male gametophyte
is reached only after the microspore has been caught by the
moist surface (fluid in the micropyle or on the stigma) pro-

By this extreme FIG. 313.— A, part of a "leaf" of Chara, bear-
ing sexual organs. />, leaf; )3, undeveloped
"leaflets"; J8', leaflet; |3", leaflets of the
branch, sc ; the dark oval body is the ovary
containing the fertilized egg ; s, five cortical
cells which have grown spirally around the
ovary proper and become adherent to it ;
they terminate in c, the five crown cells, be-
tween which the sperm makes its way to the
egg; a, the spermary, showing four of the
8 toothed plates of which its wall is composed,
and the center of each to which on the inside
the handle cell is attached. Magnified 33
diam. />', longitudinal section through young
"node " of a " leaf " of Chara, showing origin
and young stage of sexual organs. / and iv
stand in the corners of the adjacent internodal
cells ; between them is the thin nodal cell
from which arise // and the sexual organs sk
and a ; br, cortical cells covering /, 7c. .vX-
is the young ovary not yet overgrown by the
cortical cells at its sides, a, the spermary,
shows four wall cells outside, from which
their handle cells have just been divided ;
all too young to show relative sizes or shapes.
Magnified 240 diam. — After Sachs.

282

PLANT LIFE.

vided to receive it. The wall cell remains undivided and
grows to form an unseptate filament, called the "pollen
tube" (figs. 317, 318, 319, 321, 322, 323). In gymno-

FIG. 314.

FIG. 314. — Vertical median section of the mature spermary of a fern (Adiantinn
capillus-veneris). p, adjacent cells of gametophyte (figs. 74, 77) ; a, spermary, show-
ing wall composed of three cells, the two lower (above and below letter a) being ring-
like. The chloroplasts have accumulated on the inner face. The interior cell, origi-
nally single, has divided into a number, the sperm mother cells, which at this stage are
loosened and contain each a fully developed coiled sperm. Magnified 550 diam.—
After Sachs.

FIG. 315. — A vertical median section of the gametophyte of Selaginella stolonifera.
/, a single cell representing the vegetative part of the gametophyte (compare figs. 74,
314) ; 71', the cells forming the wall of the spermary ; .$•, the mother cells of the sperms,
each containing one sperm and now loosened from each other. The gametophyte with
its single spermary scarcely exceeds the size of the microspore which produces it and
therefore only just bursts the outer wall of the spore. The solution of the wall cells
iv allows the sperms to escape. Magnified 640 diam. — After Strasburger.

FIG. 316. — Diagram of the gametophyte of the larch (Lari.v Enro/>ePii), formed in the
microspore. /, the vegetative cell ; sf, two stalk cells of the spermary ; s, cell whose
nucleus subsequently divides to form two sperms (the walls of the mother cells not
forming) ; m, the wall of the spermary which remains undivided. Compare fig. 315.

sperms this penetrates the megasporangium (ovule body) and
reaches the female gametophyte on whose surface are formed
the ovaries (figs. 319, 320, 321, 322). In the course of its
development the sperm cell loosens itself and migrates down
the tube. Its nucleus is set free by the disorganization of the
wall of the cell (if formed) and usually undergoes division,
thus making two or more sperms (figs. 321, 322). These
escape through the ruptured wall of the end of the tube,
pass between the neck cells of the ovary and so fertilize the

egg HI 393> fig- 320-

In angiosperms, in order that the sperm may reach the

egg, the pollen tube must grow through the tissues of the
stigma and style, or pass down the style canal to the interior

SE X UA L

V C 7 'ION.

283

of the ovulary, then through the micropyle (fig. 323), and
finally penetrate the megasporangium. The sperm nucleus
then fuses with the egg nucleus (see ^f 369).

P

FIG. 317.

FIG. 319.

FIG. 317.— Gametophyte of the pinesap {Monotropa Hypof>itys). a, microspore show-
ing two cells ; the smaller being the sperm cell and the larger corresponding to the
wall of the spermary, undivided. />, the same, 6 hours later, showing the pollen tube
developed from the larger cell. The smaller one has become disorganized and its
nucleus (still undivided into sperms) and that of the larger cell have migrated into the
tube. Magnified 600 diam. — After Strasburger.

FIG. 3 18. — One stage in the fertilization of the egg of an orchid (Orc/i is latifolia). The
pollen tube, /, has entered the narrow micropyle, nt, of an ovule, and reached the
megaspore e, the upper half of which only is shown with three eggs (two imperfect).
In the pollen tube, just above and below the entrance of the micropyle, are the two
sperms, j, s' . Magnified 360 diam. — After Strasburger.

FIG. 319. — Longitudinal section through the ovule of the larch and the placental scale
to which it is attached. _/", placental scale ; _v, vascular bundles ; «, megasporangium ;
/, integument ; e, female gametophyte inside megaspore whose limit is shown by oval
line ; a, ovary;/, pollen-tube. Magnified 14 diam. — After Strasburger.

The growth of the spermary as a tube within which the
sperms may migrate to the egg is necessary because the female
gametophyte is forced to develop within the megaspore,
which is not released from the sporangium. In angiosperms
the further enclosure of the megasporangia in the sporophyll
(carpel) makes it necessary for the tube to be sufficiently long

284

PLANT LIFE.

to traverse the pistil. Pollen tubes may, therefore, grow
10-15 cm. in length. Usually the older part of the tube dies

•nu

FIG. 321.

FIG. 322.

FIG. 320.— Anterior fourth of female gametophyte of spruce (Picea excetsa}, showing
two ovaries, e, tissue of gametophyte (endosperm); a, egg; k. nucleus of egg; h,
neck of ovary (the line does not reach the neck, which is situated in a depression of the
plant below h ; the shading shows the side of this slope); kz, neck canal cell. See fig.
321. Magnified 50 diam.— After Strasburger.

FIG. 321.— A portion of the ovary of the spruce, seen as in fig. 320, but magnified 165
diam. The cell kz of fig. 320 has become disorganized to make way for the pollen
tube, /, which has pushed between the neck cells and reached the egg, e, into which
one of the sperms in its tip is about to enter, g, tissue of the female gametophyte.—
After Strasburger.

FIG. 322. -Upper part of ovule of red cedar, with integument removed. HH, mega-
sporangium ; al, female gametophyte with three ovaries of a cluster of six ; /, pollen
tube. Each ovary shows an elongated egg and above the small neck cells. The left-
hand pollen tube has two sperms about to pass between neck cells into an egg. Magni-
fied 67 diam.— After Strasburger.

as the tip advances. The food needed is chiefly derived
from the cells of the stigma and style which it disorganizes.

SEXUAL REPRODUCTION.

285

387. The egg.- -The egg is larger than the sperm, usually
non-motile and fixed. In aquatic algae the egg is sometimes

FIG. 323. — Diagram of a longitudinal section of a pistil with one ovule, s, stigma, on
which are lodged two pollen grains; g, style; <?, oyulary; f, », ai, ii, together form
the ovule ; f, stalk ; n, megasporangium ; ai, outer integument ; zY, inner integument ;
e, megaspore, with nucleus which is to develop later into vegetative part of female
plant; />, antipodal cells; k, egg, and near by another ; ;//, micropyle ; /, pollen tube
entering it and reaching egg.— After Luerssen.

free, escaping from the ovary in which it is produced, and
being fertilized by the sperms, which are likewise free in the
water, as in Fucus (fig. 324). Sometimes the egg itself is
ciliated and hence motile. In these cases it meets the motile
sperms in the water.

The form of the egg is much less variable than that of the

286

PLANT LIFE.

sperm. It is almost always ovoid or globular. The small
amount of body protoplasm of the sperm may be looked upon
as merely accessory. That of the egg, however, is usually
abundant and well supplied with reserve food, and it takes
part after fertilization in the formation of the new plant.

388. The ovary. --The organ in which the egg is produced
is the ovary (oogonium, carpogonium, or archegonium).
Usually but one egg is produced in each ovary, though as
many as eight are formed in the Fucacese

(fig. 327). The ovary is either simple
or compound.

389. A simple ovary consists of a
single cell, the bulk of whose proto-
plasm becomes one egg (or several).

FIG. 324-

FIG. 325.

FIG. 324. — Egg of Fucns as it floats in sea-water, surrounded by many sperms, one of
which eventually plunges into it, unites with its nucleus and so fertilizes it. Magnified
350 diam. — After Thuret.

FIG. 325. — Portion of two ovaries of an alga (Sphceroplea annnlina). The upper part
contains two eggs, and a number of sperms which have entered through the pore at
the side. The lower egg of the two shows the receptive spot above. A sperm is
partially imbedded in the protoplasm of this part in process of fertilization. The
egg in the lower ovary has been fertilized and has secreted a thick wall, thus becom-
ing a resting spore. Magnified 500 diam. — After Cohn.

A portion of the protoplasm of the ovary is almost invariably
excluded from the egg (-B, fig. 308). The sperms reach the
egg either through an opening formed in the wall of the
ovary (D, fig. 308, 325), or through a tube formed by the
spermary, which penetrates the ovary (fig. 307).

SEXUAL REPRODUCTION.

28;

Simple ovaries occur only in the algae and fungi, where they
are known as oogonia or carpogonia. They are either pro-
duced by the modification of one of the cells of a filament
(fig. 325), or they are the terminal cell of a special branch
(fig. 308). Usually the ovary is decidedly larger than the or-
dinary vegetative cells. The fertilized egg often becomes a
resting spore (fig. 325).

In the higher algae, especially the marine algae, the ovaries
are often aggregated in special pits, the conceptacles, as in

FIG. 326.— A section through a female conceptacle of bladder wrack (Fucus vesiculo-
s?ts) ; showing form of pit, the numerous hairs with which it is lined, and ovaries in
various stages of development. In the tissue about the pit note the cortex of densely
placed cells and the loose network of filaments in the interior. Magnified sodiam. —
After Thuret.

Fucus (figs. 42, 326). Here the ovary is formed by the en-
largement of the terminal cell of a two-celled outgrowth from
the surface (fig. 327). The eight eggs are set free and are
fertilized in the water by the motile sperms (fig. 324). They
grow at once into new plants.

The simple ovary is surrounded in Chara (fig. 313) by a
jacket of spirally coiled cells, which grow up from beneath it
and make it look as though it were compound (*[ 390).

288

PLANT LIFE.

The most highly developed simple ovary (the carpogonium)
occurs in the red algae, in which it is often differentiated into
the ovary proper (which does not always form a distinct egg)
and a long branch, the receptive apparatus, or trichogyne,
to which the sperm adheres and through which its nucleus

FIG. 327.

FIG. 328.

FIG. 329.

FIG. 327.— Ovary of bladder wrack (Fieci/s resiculosHs), with some of the hairs. The
ovary is raised on a stalk cell ; it contains 8 eggs, of which 6 are shown. Magnified
160 diam. — After Thuret.

FIG. 328. — The ovary of a red alga (Wemalion multifidmn}. A, in process of ferti-
lization, no, egg nucleus (a dark chromoplast lying near); sp, sperm which has ad-
hered to the trichogyne t and caused the absorption of the wall there ; ns, the sperm
nucleus on the way down the trichogyne. B, a later stage, no and ns about to unite.
Magnified about 600 diam. — After Wille.

FIG. 329.— A branch of a red seaweed (Polysipkonia opaca) bearing cystocarps (the
black dots). See fig. 330. Natural size. — After Kiitzing.

travels to the ovary proper (fig. 328). The result of fertiliza-
tion is the production, often by a very complicated process
of growth, of a spore-producing body, the cystocarp (figs.
329, 330). The cystocarp is, in part, the homologue of the
sporophyte phase of higher plants. From its interior non-

SEX UA L RE PR OD UC TION.

289

sexual spores arise (fig. 330), which produce the gametophyte

again.

390. A compound ovary consists of a central row of cells
(each of which is homologous with a simple ovary) surrounded

FIG. 330. — y4,abit of a red seaweed bearing a mature cystocarp ; seen from the side.
The spores show through the translucent wall. B, a diagram of a section through the
same, showing spores as enlarged terminal cells of twigs arising from a basal cell of the
cystocarp. The shaded parts arise from the fertilized egg (= a sporophyte), the case
developing by induced growth. Magnified 25 diam. — After Falkenberg.

by a wall composed of one or more layers of cells. Of the
central cells only the lowest produces an egg. The upper
ones break down into mucilage, by the swelling of which the
ovary is opened, and by its escape in whole or part a canal is
formed leading to the egg (fig. 332). Down this canal the
sperms make their way, and one fertilizes the egg.

The compound ovary is known as an archegonium. When
best developed, it is a flask-shaped structure (fig. 331) con-
sisting of a body and a neck. In the body is the cell con-
taining the egg. Compound ovaries may be stalked, sessile,
or sunk in the tissues of the gametophyte. They are found
only in mossworts, fernworts, and seed plants. In the latter,
however, they are simplified out of all likeness to the form
described.

391. Mossworts. —When the gametophyte is differentiated
into stem and leaves, as in mossworts alone, they are formed
upon the stem. Usually several are developed in the same
neighborhood, when they are generally protected by over-

2QO

PLANT LIFE.

arching leaves (fig. 331). In the same cluster there may be
spermaries, or these may be on a different part of the same
plant, or on another plant.

FIG. 331. — Longitudinal section through the tip of a shoot of a moss (Funaria hygro-
metrica). st, stem ; b, leaves protecting the ovaries a. Magnified 100 diam. — After
Sachs.

FIG. 332. — A vertical section of the gametophyte of a fern ( Pteris serrulata). g, vege-
tative tissue of gametophyte, with chloroplasts ; e, body of ovary sunk in gameto-
phyte, surrounding the spherical egg; n, neck projecting and curved; w, mucilage
formed by disorganization of canal cells and escaping, having pushed apart terminal
cells of neck. Magnified 260 diam. — After Strasburger.

392. Fernworts and seed plants. — When the gametophyte
is a thallus, as in fernworts and seed plants, the ovaries are
borne on the surface of the thallus, partially or wholly sunk
in its tissue. In the ferns, they arise upon the under surface,
near the anterior end (fig. 74), and have the neck only pro-
jecting (fig. 332). In the horsetails the ovary is still more
deeply sunk. In the selaginellas the gametophytes are male
and female, the male arising from the microspores (fig. 315)
and the female from the megaspores (fig. 333). Both are
small, scarcely larger than the spores in which they grow.
The ovary is completely sunk in the female gametophyte and

SEXUAL REPRODUCTION.

291

is much simplified, the neck-cells and the egg being the only
distinct parts of maturity.

393. Gymnosperms. — In the gymnosperms the female
gametophyte is not large enough to burst the megaspore which

spm,

FIG. 333.— Longitudinal section of the female gametophyte of Selaginella Martensii.
d, d, d, the body of gametophyte; r,r, rhizoids (rudimentary) on its surface; a, an
ovary whose egg failed of fertilization ; e, embryo developed from fertilized egg ; its
cell-structure is not shown, but the various members are begun ; s, suspensor ; st, stem;
/, /, primary leaves ; rt, root; /, foot ; e1 , a younger embryo, with cell-structure shown,
the letter standing in large suspensor cell ; spin, wall of megaspore. Magnified 125
diam.— After Pfeffer.

remains enclosed in the sporangium. Upon its surface are
formed several ovaries, each reduced to an egg and two to four
tiers of neck-cells (figs. 320, 321).

394. Angiosperms.--In the angiosperms the female gam-
etophyte is so simplified that it is represented only by a few
cells, among which may be recognized at least one egg (e,
fig. 334), and possibly two others, s, s. The ovary has been
reduced to nothing but an egg, and the full development of
the gametophyte seems to be delayed until after the egg is

292

PLANT LIFE.

fertilized. In these plants, therefore, we return to a con-
dition which is scarcely an alternation of sexual and spore-
producing phases, because the >
sexual phase is nearly obliterated
by reduction.

395. Relative size of gameto-
phyte and sporophyte. --The ac-
companying diagram (fig. 335) may «
roughly illustrate the history of

f

d

c

a

FIG. 334.

FIG. 335.

FIG. 334. — End of megaspore of Polygonum divaricatum. e, egg; s, s, synergi-
dae, probably sterile eggs. Below e the nucleus from whose divisions arise the cells
of the belated gametophyte. Magnified 540 diam. — After Strasburger.

FIG 335 — Diagram representing the reduction of gametophyte and increase in sporo-
phyte from lower to higher plants, a, green algae; />, red algs ; c, liverworts ; d,
mosses; e, ferns;./", club-mosses; g, gymnosperms ; Ji, angiosperms. — Original.

development of these phases in the vegetable kingdom.

The gametophyte phase is represented by the dotted area.
It has its greatest development in the lower algce and fungi,
where it constitutes the whole, diminishes at first slowly and
then rapidly. After the fernworts are passed it constitutes a
relatively inconsiderable part of the plant and almost disap-
pears among angiosperms. Of the sporophyte, represented
by the white area, the reverse is true. The lines crossing
the diagram at various levels show by their length in the
white and black areas the relative importance of the two
phases in the groups indicated.

SEX UA L RE PR OD UC T10N.

293

Loss of sexuality.

396. Among fungi.- -Though descended from ancestors
possessing sexual organs, certain groups of plants have lost this
mode of reproduction and rely wholly upon non-sexual
methods. Such are the higher
fungi. The lower forms only
have sexual organs. These fungi
show their relation to algae by
retaining in part or wholly aqua-
tic habits. In Cystopus, for ex-
ample, at a certain stage zo-
ospores are produced ; and these
are generally characteristic of
aquatic plants, though Cystopus
has become a parasite upon land
plants. Many aquatic fungi are
known, most of which grow
upon dead plants or animals
(especially insects) which have
fallen into the water. Not only
do many of these lower forms
produce zoospores, but the form
of their sex-organs and mode
of union remind one immedi-
ately of similar structure and
action in common algae. Com-
pare, for example, the sex- organs
in Vaucheria (fig. 308) and those of Achlya (fig. 336).

Some fungi possess sex-organs which are functionless,
although the egg develops as though it had been fertilized (fig.
336). But in most, all trace of sexual organs has disappeared,
though many produce spore-bearing structures, the fructifica-

B A

FIG. 336. — A. Functionless sex-organs
of a fungus (Achlya lignicola).
Ovaries globular, with 2-4 eggs;
spermaries from branches of same
hypha form fertilizing tube which re-
mains closed. B, eggs which have
become resting spores without ferti-
lization. Magnified 265 diam. — After
Sachs.

PLANT LIFE.

tions (T 314) which are homologous with those known to arise
from the fertilized egg and adjacent parts. In all these cases
the fructification may be considered the homologue of the
sporophyte of higher plants, for, even though its origin is
now purely vegetative, this has come about by reduction from
more perfect ancestors.

397. Apogamy. — In certain of the higher plants sexual re-
production is sometimes replaced by a process of budding,
which differs from reproduction by brood buds (^[ 361 ff.)
in giving rise to the other phase from that on which the bud
arises. Some ferns, for example, regularly produce upon the
gametophyte a bud which grows into a sporophyte, the sex-
organs being functionless. This process is called apogamy.

398. Polyembryony. — Among the seed-plants a budding
of the megasporangium, instead of the fertilization of the egg,
may produce an embryo. Except that the embryo so pro-
duced suspends its growth and becomes a part of a seed, such
reproduction is in no w^ay different from that by brood buds
(^[ 361 ff.) It is common in the orange, and often results in
the formation of more than one embryo in the seed.

Results of sexual union.

The immediate result of the coalescence of a male and a
female gamete is the formation of a cell capable of producing
a new plant, i.e., a spore. The first step toward this is the
formation of a wall about the spore. It may then grow at
once into a new plant, or it may remain dormant for a longer
or shorter time.

399. Resting spores. — In the latter case it is called a
"resting spore.' To protect itself, it thickens its wall, often
very greatly. It may then escape from the parent by the
breaking of the ovary in which it lies, but more commonly it
remains enclosed until set free by the death of the parent

SEX UA L REPR OD UC 7 'ION.

295

and the decay of the ovary. Such are the resting spores of
Spirogvra, ]\Iucor, Cystopus, and Char a.*

400. Embryo. — In the other case the sexually produced
spore develops at once. Except in the brown seaweeds,
whose eggs are ejected into the water before fertilization, the
spore remains enclosed in the ovary, within which it begins
to form an embryo.

401. Induced growth. — As a consequence of this develop-
ment, growth is induced in the ovary itself and the parts
adjacent. In the mildews the ovary produces one or more
asci (fig. 224), while the hyphae near by branch profusely and
cover the developing internal parts with a thick false tissue
(figs. 223, 337), the whole constituting a fructification. In

FIG. 337. — Formation of the " fruit" in a mildew (Erysiphe Cichoriacearum), a,
threads of mycelium ; b< spermary ; c, ovary ; d, the ovary after fertilization, show-
ing the branches from hypha beneath ovary covering it ; e, later stage, snowing
these branches coalescent and dividing by partitions to form a false tissue. (Com-
pare fig. 223.) Highly magnified. — After (Ersted.

red seaweeds the ovary and adjacent parts finally form the
cystocarp (fig. 330). In mosses the ovary grows extensively
(fig. 338), but is finally torn loose and carried up on the
embryo and becomes the loose hood, which is usually lost
early. The stem also enlarges beneath the ovary and forms
a sheath around the embryo (fig. 338), which grows down-
ward into the parent though not organically connected with

* It should be remembered that thick-walled "resting spores" are also
formed vegetatively. See *[[ 308.

296

PLANT LIFE.

it. At the same time the neighboring leaves are stimulated
to increased growth.

In fermvorts the sexual plant is stimulated by the growth
of the embryo within it, and enlarges considerably.
But it is soon outgrown by the young sporophyte,
to which it supplies nourishment until leaves are
produced and it is able to feed itself (figs. 76, 77,
78).

402. Seed. — In all but the seed plants the de-
velopment of the embryo is uninterrupted until

a mature sporophyte is
formed. In seed-plants
the embryo develops to a
certain stage, and then

FIG. 338. — Development of the embryo sporophyte of a moss (Funaria hygro-
metrica). A, longitudinal section of the ovary, b, b, h, shortly after fertilization
of egg which has developed into the embryo, of which _/is the apical growing point
and f the b.isal, or foot ; b, b. body of ovary ; /z, the base of the neck. B, longi-
tudinal section through apex of stem and leaves. Two ovaries are seen ; one has
failed of fertilization ; the other, c, has enlarged to accommodate the embryo, _/, de-
veloping inside it ; h, its neck, now withered. C, longitudinal section of same, older;
fi the embryo has grown downward into the apex of stem ; the ovary, c, has still
further enlarged and indeed outgrown the embryo, forming a bladdery case around
its base and elsewhere a close sheath for it ; h, the neck. Around the embryo, where
it enters the stem, the latter has grown up as a sheath to whose edge the base of
ovary is still attached. A little later the ovary will be torn off at this point and will
be lifted on the elongating sporophyte as a dry membranous sheath, the calyptra.
A, magnified 500 diam. ; B and C about 65 diam. — After Sachs,

SEX I '.1 L RETROD { 'CY'/OW.

2Q7

ceases to grow. With suitable protection and food-supply
it is then cast off as a seed (see further ^j 408), and usu-
ally alter a dormant period continues its development until
mature.

403. In gymnosperms.- -The growth of the embryo from
the egg in the gymnosperms stimulates the whole gameto-
phyte. This gro\vs as rapidly as the embryo, which pushes
its way into it and remains completely surrounded by it (fig.
339). The whole ovule is also stimulated to growth. The
sporangium increases for a time, but is so crowded between
the growing gametophyte within and the hardening integu-
ment without that it is mostly absorbed (fig. 339). The in-
tegument grows for a time
to accommodate the struc-
tures within, but its tissues
finally become in whole or
in part thick- walled, form-
ing the seed -coat. In a few
gymnosperms (Cycas} its

FIG. 339. FIG. 340.

FIG. 339. — Longitudinal section of the seed of silver fir (Abies pectinata), showing
straight embryo with several primary leaves in center of the endosperm (dotted) ;
;«, the micropyle. The integument has become the testa (shaded with radial lines).
Between the testa and endosperm are the remains of the sporangium. Magnified
about 5 diam. — After Kerner.

FIG. 340. — Longitudinal section of seed of Cycas circinalis. It , hilum (scar of attach-
ment) ; jn, micropyle ; z, outer fleshy layer of integument ; it and ///, two hard
layers of same ; s, thin cap-like remnant of sporangium • /, gametophyte enlarged
forming the endosperm ; c>, eggs which failed of fertilization ; e»i, embryo produced
by a fertilized egg. Two thirds natural size. — After Luerssen.

outer parts become fleshy, and the seed looks like a large
cherry. In the yew a second fleshy integument (an aril)
grows up around the hard seed (fig. 247). At maturity the
seed of gymnosperms thus consists of the embryo within
(fig. 340, ew) surrounded by the gametophyte, p, whose cells

298

PLANT LIFE.

become filled with reserve food, constituting then the so-called
endosperm; around .this is the remnant of the sporangium,
when more than a mere membrane, likewise stored with food,
and called \hepeHsperm; while over all is the hardened in-
tegument or lesta, often of unlike layers, i, ii, in.

404. Fruit. — In the conifers the sporophylls bearing the
ovules and the axis from which they arise also grow. As the
ovule is becoming the seed each sporophyll enlarges, but

especially the placental out-
growth (see ^[ 334), and the
whole number, together with
the enlarged axis, form the
cone (fig. 341, 358). Some-
times (as in the junipers) the
sporophylls become fleshy and
adherent, forming a berry-like
body.

FIG. 341.

FIG. 342.

FIG. 341. — A mature cone of a pine (Pinus sylvestrzs), the upper quarter cut away.
sq, sg', the placental scales ; g, seeds ; em, embryo in a seed. Just below the pla-
cental scale which bears the lower seed g, may be seen part of the carpellary scale
in section. Magnified about 2 diam. — From Bessey.

FIG. 342. — A placental scale of pine (P. sylvestris) seen from above ; showing two
winged seeds in place. M, micropyle ; ch, limit of seed ; the parts beyond are flat
wings, formed by the splitting off of a layer of tissue from the surface of the scale.
Magnified about 3 diam. — From Bessey.

SEXUAL REPRODUCTION. 2gg

When firm at maturity the cone scales open on drying, and
the seeds, each with a wing attached, split off from the scale
(fig. 342) and are shaken out.

405. In angiosperms the development of the embryo
stimulates the belated female plant to complete its growth,
and the megaspore (embryo-sac) is soon entirely filled by it.
This late-forming gametophyte is called endosperm, as in the
pines.

406. Endosperm.- -The growing endosperm and the
embryo sporophyte, which it surrounds, crowd upon the
sporangium. This may, therefore, partly or wrholly dis-
appear. If, when the full size of the endosperm is reached,
the embryo continues to grow, it may crowd upon the endo-
sperm until a part or all of it is absorbed. The embryo
sooner or later passes into a resting stage and ceases to en-
large. In this dormant condition it remains for a time whose
duration is chiefly determined by external conditions.

407. Food. — The tissue of the endosperm is utilized by
the parent sporophyte as a storehouse of food for the use of
the embryo sporophyte when it resumes growth. If the
embryo displaces the endosperm, it absorbs the reserve food
therein, consisting of starch, oil, or aleurone grains (^[ 236).
In case any tissue belonging to the sporangium remains, this
also is utilized for storage. To distinguish it from the endo-
sperm it is called perisperm. It is only occasionally present
in any amount in this group of plants.

408. The integuments of the ovule at the same time en-
large, and finally become differentiated in such fashion as to
constitute the seed-coats. The ripened seed, therefore, con-
sists of the following parts: (i) in the interior, occupying
various positions and of exceedingly variable relative size, the
embryo; (2) immediately around this, the endosperm or peri-
sperm, or both ; but either or both may be so shrunken
and emptied as to be recognizable only by microscopic ex-

PLANT LIFE.

animation ; (3) upon the exterior, one or two integuments
more or less readily distinguishable from each other (figs.

343> 344. 345)-

PC

FIG. 343. — Longitudinal section of fruit of black pepper, containing' a single seed, pc,
pericarp, showing two layers (the outer unshaded, the inner shaded by radial lines);
sc, seed-coats ; em, embryo, surrounded by en, the endosperm ; p, perisperm. Mag-
nified about 5 diam. — After Baillon.

FIG. 344. — Seed of pansy, entire and halved, the latter showing the straight embryo,
the endosperm (white and dotted), the seed-coats ; m, micropyle. Magnified about
10 diam. — After Baillon.

409. Fruit. --The growth of the embryo
excites not only the tissues of the ovule to
further development, but also the sporophylls
(carpels) bearing the ovules, and not infre-
quently even more remote parts. The carpels
and their contents and adherent parts, when
fully developed, constitute the fruit. The car-
pels are then known as the pericarp. The
changes which the parts undergo are chiefly
of two sorts — an increase in size and an altera-
tion of texture. The increase in size requires
no special explanation. The carpels may be-
come dry at maturity, or may thicken and become soft and
fleshy, 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 line
of demarcation.

410. Dry fruits. --If the pistil contain only one or two

FIG. 345. — Seed
of pokeberry
( Phytolacca
de c a ndr a) ,
halved ; show-
ing curved em-
bryo next the
two seed-coats
and nearly sur-
rounding the
endosperm .
Magn. about 10
diam. — After
Baillon.

SEXUA L RETROD I 'C7VOJV.

301

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 carpel
becomes adherent at an early stage to the surface of the
ovule, and at maturity the pericarp is so firmly attached that
it can scarcely be distinguished from the seed-coats them-
selves. Such a change takes place in the fruit of most grasses,
and the grain so formed is ordinarily mistaken for a seed
(fig. 346). When dry fruits are one-seeded and indehiscent

12 34

FIG. 346. — A small portion from the margin of a transverse section of grain of oats,
i, 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. 174)3!
7 richer in gluten, with less starch. Magnified about 325 diam. — After Han:.

the pericarp usually bears whatever special contrivances are
necessary for the distribution of the seeds. (See further *[
489 ff.) If, however, the pericarp contains many seeds, it
generally breaks at maturity to allow the loosened seeds to
escape. The extent and position of the opening into the
seed chamber or chambers are extremely various. In some
cases the openings are so small as to be mere slits or pores
(fig. 347). In others a more or less circular line of breakage
forms a little door or valve which opens and closes with

302

PLANT LIFE.

changes of moisture (fig. 348). In other cases the pericarp
splits lengthwise into two or more pieces (fig. 349), or, less

FIG. 347.

FIG. 348.

FIG. 347. — Ripe capsules of a wintergreen (Pyrola chlorantha}, showing dehiscenee
by pores. The opening is a short split at the middle of the base of each carpel.
Natural size. — After Kerner.

FIG. 348. — Ripe capsules of a bellflower {Campanula rapunculoides), showing
small reflexed valves. Natural size. — After Kerner.

FIG. 349. — A, capsule of violet split open at maturity, the seeds still attached to the
parietal placenta;. j9, three pods of Lotus corniculatus ; a, just beginning to
crack; £, split throughout, with the pieces somewhat twisted ; c, empty of seeds, the
two pieces fully dried and twisted. Natural size. — After Baillon.

SEX UA L REPR OD U CTION.

303

often, cracks transversely so as to loosen a lid (fig. 350). In
the former case, if it is composed of two or more carpels,
(i) the carpels may separate from each other along their
original line of coalescence. If these carpels so separated
contain only one or two seeds, they may remain indehiscent
and behave like the simple pistils previously described ; but

B

FIG. 350.

FIG. 351.

FIG. 350. — Ripe capsule of pimpernell (Anag-allis arvensis), opening by a lid.
Magnified several diam. — After Baillon.

FIG. 351. — Diagrams showing three modes in which capsules break as seen in trans-
verse sections. A, septicidal dehiscence ; J5, loculicidal dehiscence ; C, septifragal
dehiscence. Modified from Prantl.

if they contain several to many seeds, they also break along
their inner edges (A, fig. 351). Or, (2) the carpels may
split along the middle, and also at the center of the ovulary
if it is more than one-chambered (It, fig. 351 ; A, fig. 349).
Or, (3) the outer parts of the carpel may split away from the
placentae, thus exposing the seeds (C, fig. 351).

411. Fleshy fruits. — The changes which produce fleshy
fruits consist in the transformation of certain parts of the
pericarp 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
hardness, while the outer portion becomes soft and juicy. Such

304

PLANT LIFE.

m

cot

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 com-
-en pletely usurped by the stone (fig.
352). In other cases, while the
inner face becomes stony, the outer
becomes fibrous, tough, and dry, as
in the almond, walnut, and hickory
nut. The outer part in the last even

FIG. 352.— Fruit of the cherry, breaks regularly into four pieces.

halved, e, epidermis of peri- ,

carp; m, fleshy layer of Such fruits furnish a transition from

pericarp ; en, stony layer of

pericarp; s, seed; cot, one the lllOSt perfect flCShy frllltS tO the

of the pair of thickened seed- .

leaves of embryo. Natural dry fruits. In other cases the placentas

size. — After Focke. .

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.

412. Accessory fruits. --Parts adjacent to the carpels,
either flower leaves or axis or both, stimulated to growth,
frequently enter into the formation of
fleshy fruits. These may be accompanied
by either a fleshy or a dry pericarp. In
the wintergreen berry the calyx grows
thick and fleshy and surrounds a dry peri-
carp, which cracks at maturity (fig. 353).
In the strawberry (fig. 287) the torus be- FIG. 353- — Fruit of

wintergreen (Gaul-

comes greatly enlarged and fleshy, while tkeria proctim-

. bens), halved, show-

the minute, one-seeded, dry fruits are ing thin (dry) peri-
carp, surrounded by

scattered over its surface, imitating small thickened fleshy

calyx. Magnified

seeds. i he fig has the same parts, with about 2 diam.— After
the torus concave, instead of convex (fig.
289). The apple consists of a fleshy torus carrying at its
free end the withered calyx and enclosing the tough, thin

SEXUAL REPRODUCTION.

305

pericarp (fig. 354). In the blackberry the receptacle be-
comes fleshy, and each pistil forms a minute fruit like a

FIG. 354. — Fruit of the apple. A, halved longitudinally; B, halved transversely. _/",
pericarp, enclosing seeds ; g~, vascular bundles of the fleshy torus entering /£, the
calyx leaves. One half natural size. — After Focke.

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. 355).

413. Multiple fruits. --If the flowers form a crowded in-
florescence, either dry or fleshy fruits 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

355-

FIG. 356.

FIG. 355. — Vertical section of a flower of raspberry (Ritbus itfteus), 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 Kcrner.

FIG. 356. — A, pistillate flower cluster of white mulberry; />', multiple fruit from same.
Natural size.— After Baillon.

306 PLANT LIFE.

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. 356) with such an
aggregate fruit as the blackberry, in which each section is
one pistil out of the many belonging to a separate flower (fig.
355). 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 gen-
erally grows and becomes stronger, to carry the fruit, espe-
cially if large. The minute bractlets sometimes become
highly developed beneath the fruit. The cup of the acorn
and the husk of the hazelnut originate in this way as the
nuts form. The similar husk of the beechnut and chestnut
encloses more than one fruit.

414. Distributive arrangements. — Since the seed plants
abandoned the distribution of the megaspores and form both
the gametophyte and the new sporophyte within the tissues
of the old, it became necessary to adopt some other method
whereby the young can be so scattered as to prevent them
from coming into sharp competition with the parents. This
distribution occurs at the time of maturity of the seed, i.e.,
when the embryo has become dormant, and the food store
and protective 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.
Thus, one-seeded, indehiscent fruits must be scattered by the
structures arising upon the surface of the pericarp or its ad-
herent parts. On the contrary, seeds which escape from the
pericarp have the distributive structures developed by the
seed coats themselves. For distribution plants adapt them-
selves so as to employ the agency of the wind, water, and
animals, or they develop special mechanisms for casting off
the seed as a projectile. A consideration of these adapta-
tions belongs to ecology. (See Chap. XXVI.)

PART IV: ECOLOGY.

415. 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 rela-
tions of the plant to the forces and beings of the world about
it, as distinguished from physiology proper, which treats
of the relation 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 ; consequently it is quite impossible to draw a sharp dis-
tinction between 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 surroundings and to other living beings can
be given.

307

I. NUTRITIVE ADAPTATIONS,

§ I. ADAPTATIONS OF FORM AND STRUCTURE

TO ENVIRONMENT.

CHAPTER XIX.

FORMS OF VEGETATION.

416. 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 substratum
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 themselves to the places in which they grow. This
compulsion is on pain of death.

417. The struggle for existence. — The competition be-
tween plants is intense. Only a very small portion of the
seedlings wrhich start in any particular area can come to
maturity. Far the greater number will be killed by being
robbed of light and of water by the overshadowing leaves
and interlacing roots of their companions. Since such com-
petition exists, it is evident that only those best suited to the
conditions 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
species better suited to the conditions of that region.

308

FORMS OF }'EGETATION. 309

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 a differ-
ent environment 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 as well as or better than the occupants
it finds in possession. In the beginning it was probably by
competition between species that water plants were gradually
adapted to an amphibious life, and then to a terrestrial 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 occupied
even the deserts ; plants loving the shade adapted themselves
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.

418. 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
ordinary land plant. A portion of such a plant is imbedded
in the soil, and the remainder rises into the air. The sub-
terranean 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 night, from day to day, and from season to season. It is

310 PLANT LIFE.

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 com-
pletely 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 in-
jurious 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 precipitation are likely to be as-
sociated. It is possible, in a somewhat arbitrary way, to
recognize four general sets of conditions to which plants must
adapt themselves, in each of which the water supply is the
predominant factor. It should be understood clearly, how-
ever, that these sets of conditions pass into each other im-
perceptibly. Corresponding 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 possible to distinguish four forms of vegetation
corresponding to the four sets of external conditions.

419. The first set of conditions consists of those charac-
terized by no extremes. Both the air and the soil are moder-
ately moist ; the precipitation is distributed through the
year, or at least through the growing season ; there is no ex-
cess 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 to people in the fertile regions of temperate

FOAMS OF VEGETATION. 311

climates. These may be reckoned as the average, or mean,
plants, and are therefore called technically mesophytes.

420. A second set of conditions is characterized by de-
ficient 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.

421. 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 sodium chloride
(NaCl, common salt), gypsum (CaSO4), and magnesium
chloride (MgCl). Plants which can live under these condi-
tions are known as salt plants, or halophytes.

422. A fourth set of conditions is characterized by an
excess of water. The plants grow wholly or partly surrounded
by water, or their roots are imbedded 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.

CHAPTER XX.

MESOPHYTES.

423. 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.

424. 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 sulphurous acid. Whatever special adaptations are found
are internal, since only the very simplest plants find it pos-
sible to live in such conditions.

The movements of the air, however, influence profoundly

312

MESOPHYTES. 313

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 reduced
temperature ; but probably none of these causes is to be
looked upon as so efficient as the drying brought about by
the prevalent wind.

425. 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 clays' 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) The
form of plant parts is directly influenced by light. Plants accus-

3H PLANT LIFE.

tomed 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 internal structure,
also, there are decided differences, particularly in the leaves.
(See ^[ 167, 438.) The leaves of light plants usually have a
thick epidermis, often shiny, with lateral walls straight; the
stomata are frequently confined to the under side and often
sunk ; the palisade cells are elongated, sometimes forming
two or three layers and occasionally appearing on both faces
of the leaf. The shade plants, on the contrary, have a thin
epidermis, often containing chlorophyll, with lateral walls
often very wavy ; the stomata are produced on both sides of
the leaves, and the palisade tissues are poorly developed.
Light plants frequently have red cell-sap, especially in the
epidermis of smooth plants, and their colors are always
deeper, especially in the plants of high latitudes. Shade
plants, on the other hand, are usually pale, rarely high-
colored.

426. 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 "con-
sequently 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 maybe determined. (See ^j 186, 263.) The

MESOPHYTES. 315

variations in temperature to which plants arc subjected require
special adaptations.

427. (</) Protection against changes of temperature. -
These adaptations are to be found in the presence of special
cell-contents, such as oils or resins, which reduce the liability
of those cells to freezing ; in the reduction of the amount of
water in cells so that less damage results from freezing ; and,
finally, in the presence of poor conductors of heat, such as
scale-leaves and hairs in profusion, 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.

428. (6) 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 rudiments
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.

429. (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.

430. (d The rate of development is strikingly influenced
by variations in the temperature of the soil. The soil heat is
derived from the sun and from the decomposition of organic
matter within it. The sun is far the most important source.
The amount of heat absorbed varies with the exposure of the
soil, its color, porosity, amount of water, and the duration of

PLANT LIFE.

the sun's rays. The influence of the temperature of the soil
is mainly indirect, acting through its effect on the water
supply of the plant.

431. (e) 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
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 ^[ 196.) 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 adjusting the
direction of their leaves to it so that a heavy, splashing rain
strikes them at an acute angle. Others, by a movement 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 rainfall.

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

IfESOPHYTES. 31/

even in the midst of snow, putting forth their leaves and
blossoms while still surrounded by melting snow.

432. (_/) 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 reason
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
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.

CHAPTER XXL

XEROPHYTES AND HALOPHYTES.

433. 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 algae, 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.

434. 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.
Perennial plants with perennial snoots may drop their leaves

318

XEROTHYTES AND HALOPHYTES.

3'9

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. 357) and mosses.

435. 2. The constant reduc-
tion of exposed surface. --This
may be secured among the leaves
by reducing them either in area
or in number or both, or by much
branching, with little green tissue.

FIG. 357. — Transverse sections of a grass leaf {Lasiagrostis). 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.

Plants with bristle-shaped or needle-shaped leaves (figs. 101,
358), those with permanently rolled leaves (fig. 359), or
those with scale-like leaves (fig. 109) 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 ^[ 112);
or the branches may be thick, rigid, and fleshy (fig. 360) ;
or they may be thread-like or needle-shaped, as in the aspara-
gus (fig. 105) ; or the stems themselves may reduce their area
by becoming fleshy and cylindrical, prismatic, or spheroidal,
as in the various forms of Cereus and melon cactuses (fig.
no).

436. 3. Movements of parts to reduce the illumina-
tion.— Certain leaves are adapted to a permanent profile
position, that is, with the edges turned toward the sky,,

320

PLANT LIFE.

instead of the surfaces. (See ^j 285.) Others assume a

profile position when the illu-
mination becomes too intense.
These positions, by placing the
leaf surface oblique to the di-
rection of the light rays, reduce
the amount of evaporation very
considerably.

437. 4 Coverings, consist-
ing of living or dead scale-
leaves, stipules, leaf-bases or
entire leaves, reduce transpira-
tion by obstructing the free ex-
change of air, or by holding
water and so keeping moist the
surfaces they cover.

438. 5. Structural modifi-
cations. — These may occur
either in the epidermis or some
internal tissues. (<?) The epi-
dermis may greatly reduce evap-
oration by the formation of
hairs in such profusion as to
form a cover for the surface

358. — Shoot of larch, with ripe
cone; showing needle-shaped leaves (figs. 761-^64). Hairs

nn Hwarr hranrhpc • era p IpavPS on V O »_> >J '/

on dwarf branches ; scale leaves on

Ill-

main axis ; carpellary scales just peep- tended to protect from evap-
ing from between placental scales or

cone. Natural size.— After Kemer. oration 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. 365). Further
adaptations of the epidermis are to be found in the pres-
ence of a thick cuticle (fig. 367); the water-proofing of
the whole of the outer wall of the epidermis; the develop-

XEROPHYTES AND HALOPHYTES.

321

ment of two or more layers of epidermal cells (fi^. 370) ; or
the excretion of wax or of varnish upon the surface of the epi-

FIG. 359. — Transverse section of a leaf of a heath (Tylanthus ericoides), showing
revolute form. The stomata are on the under (concave) surface among the hairs,
which still further impede the transpiration. Magnified 130 diam. — After Kerner.

dermis. The latter often becomes very thick, giving to the
leaves a shiny appearance. Wax is usually in the form of a

FiTTT

FIG. 361.

FIG. 360.

KK;. 362.

FIG. 360. — Prickly pear (;~>/>untia Tulwar is) with flattened jointed stem and no

leaves. About one fourth natural size. — After Frank.

FIG. 361. — Multicellular hairs of edelweiss. Magnitn d about 50 diam. — After Kerner.
FIG. 362.— Silky unicellular hairs <>t ( nn7'<:/7> H/I/S Cut-ormii. Magnified about 50

diam. — After Kerner.

322

PLANT LIFE.

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 cab-
bage, or the stalk of sugar-
cane (fig. 366). The in-
terior layers of the wall of
the epidermis are some-
times converted into mu-
cilage, which retards the
evaporation of water.
The sinking of the sto-
mata below the general

FIG. 364.

FIG. 363. — Stellate hairs oiDraba
Thomasii, seen from above.
Magnified about 50 diam. —
After Kerner.

FIG. 364. — T-shaped hairs of Ar-
temisia tnutellina. Magnified
about 50 diam. — After Kerner.

FIG. 365. — Shieldlike scales of an
oleaster {Eleeagnus angusti-
folia), seen from above. Mag-
nified about 50 diam. — After
Kerner.
FIG. 365.

level (fig. 367), their arrangement in pits (fig. 368) or in
grooves (fig. 357), and their restriction to the under side of
the leaf (fig. 359) may be looked upon as further epidermal

XEROPHYTES AND HALOPHYTES.

323

adaptations to reduce evaporation. In the leaves of some
xerophytes the guard cells of the stomuta are motile only
when young, becoming thick-walled and fixed when the leaf
is mature. The stoma itself sometimes becomes closed, also.

-Of

FIG. 366.

FIG. 367.

FIG. 366. — 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. 367.— Transverse section of a portion of the margin of a leaf of Aloe socotrina.
c, thick cuticle ; below <r, cutinized layers of wall of epidermis, ep ; /, parenchyma
cells with chloroplasts ; cr, a crystal cell with needle crystals of oxalate of lime ; sp,

fuard cells of stoma, sunk below surface ; a, intercellular space.under stoma. Magni-
ed about 175 diam. — After Tschirch.

(b] The internal tissues of the leaves may be more compact.
This reduces transpiration by restricting the area of the air
passages. Such dense structure is secured by multiplying
the number of the palisade layers and by the more regular
form of the spongy parenchyma (fig. 359 and ^| 167).

B. Adaptations for taking up water.

439. Absorption.--i. Some plants are adapted to im-
mediate 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

324

PLAN T LIFE.

moss. 3. Other plants adapt aerial roots to the absorption of
moisture from the air, as well as falling water. (See ^ 196.)
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 struc-

FIG. 368. — Portion of a vertical section of leaf of oleander. c/>, epidermis of upper
face ; e/>', same of lower face with stomata, .y, in deep pits with numerous hairs, £/
/«/, palisade parenchyma in two layers; j/, spongy parenchyma; /i, //', hypoderma
adapted to water storage. Chloroplasts shown only in left-hand side of figure.
Magnified about 175 diam. — After Van Tieghem.

tures, acting as water receptacles, from which it can be
absorbed as required. Such adaptations occur chiefly in
epiphytes. (See ^454.) 5. Many xerophytes develop ex-
ceedingly long tap roots, which penetrate the soil deeply
to a permanent water supply,

XEROPHYTES AXD HALOPHYTES.

325

C. Adaptations for storing water.

440. i. Special cell contents. --The simplest of these adap-
tations is the presence of mucilage in the cells, arising from
the cell-wall or developed in the cell -sap of various parts.
(See ^| 5.) The presence of acids, tannins, and salts perhaps
aids in the retention of water.

441. 2. Water-storing tissues. — (a) Fleshy plants, or
succulents, are those which thicken their parts by the develop-
ment of an unusual amount of parenchyma, which contains
a large quantity of cell-sap, and usually much mucilage.
These thin- walled, mucilage-containing tissues form a reser-
voir for the storing of water. In such plants the epidermis
is very strongly water-proofed ; the stems are thick, cylin-
drical, prismatic or spheroidal ; the leaves are wanting, or they
are thick and fleshy, cylindrical or broad (fig. 369), and
arranged in rosettes.

In non-succulents,
the epidermis itself may
be greatly developed as
a water-storing tissue,
or it may form great
numbers of bladdery
hairs which are richly
supplied with water, as FlG. 36g._A plant of houseleek ^fmpervivum

in the well-known " "^- tect<n •«"')• showing fleshy leaves arranged in a

plant,' on which
hairs glisten like ice.

In the first case, the epidermis, 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.
370). The cells immediately under the epidermis sometimes
become transformed into a water-storing tissue, as in the
oleanders (fig. 368); or strips of tissue extending from the

rosette, with offsets formed at the ends of speciai
branches. These become detached and form in-
dependent plants. About one half natural size.—
After Gray.

326

PLANT LIFE.

upper to the lower side of the leaf may act as reservoirs

of water.

442. 3. Tubers and bulbs. — These forms of the shoot

in which the parenchyma is
abundant and richly supplied
with water may also be
counted, in part at least, as an
adaptation for water-storage.
443. III. Halophytes. -
The salt-loving plants are,
in most of their characters,
strikingly similar to the xero-
phytes. This similarity is to
be explained probably by the
difficulty of securing a suita-
ble 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 halophy tes
are trees and shrubs, with
leathery leaves, but almost all

ciirriilpnrs Tn rnhi'f tVi^r
al liaDlt Hey

cr^n^ralK' lo\v nfr^n ^r^r->
ai 3U > C eP'

• -^ fT,:,,!- flpchv and

H5> AV1 -K> nv ai

.. i i , . -i

Ol less tiailslllCent leaves

FIG. 370. — Strip from a vertical section of
leaf of Pepcroinia trichocarpa. A, from
a fresh leaf ; 7c, water-storing tissue, com-
posed of the multiple epidermis of the
upper side ; #, chlorophyll-bearing cells ;
s, spongy parenchyma with sparse chloro-
plasts and much water. />', the same after
four days' transpiration at 18-20° C. The
tissue w is much collapsed, the walls being
plaited; * also shrunken/but a as before alld Stems ; the Cells large and

"After Haber" thin-walled, containing com-
paratively little chlorophyll and abundantly supplied with
water, with few and small intercellular spaces and the surface
generally smooth.

CHAPTER XXII.

HYDROPHYTES.

444. 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 thin -walled
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 dioxide and the manufacture of sufficient

327

328 PLANT LIFE.

food by means of the weak light in a situation where there is
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 weight.

445. 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 hundred
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.

446. 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.*

447. 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

* The minimum temperature of the deeper water is usually stated as 4°
C. , but many observations upon Lake Mendota by Birge have shown that
in winter it falls nearly to zero, even at a depth of eighteen meters.

HYDROPHYTES. 329

alg;e, 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.

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
reaction in the mode of growth.

448. 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 percent.
In fresh waters the differences in kind and amount of dis-
solved salts are chiefly due to differences in the soils which
the streams drain.

§ II. ADAPTATIONS TO OTHER PLANTS.

449. Plant associations. — Each set of external conditions
brings about the association of certain plants with each other,
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 each
other, 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.

450. i. Climbing plants. — Climbing plants are those
which develop lateral organs, sensitive to contact, which be-
come recurved or coil about a support of suitable form and

330

ADAPTATIONS TO OTHER PLANTS. 331

size, or ionn adhesive disks by means of which they cling to
rough surfaces. These lateral organs are forms either of
leaves or lateral shoots, and are known as tendrils (figs. 107,
156). (For their form see ^[ 115, 158; for their action,
^| 266, 293.)

451. 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. 115) may serve these purposes.

452. 3. Twining plants are those which have adapted
their shoots to winding about a support of suitable size. (See
1 291.)

453. 4. Root climbers have adapted their aerial roots to
attaching the plant to rough surfaces. (See ^[ 90.) All of
these organs are structures belonging to the sporophyte, and,
therefore, are found only in fernworts and seed plants.

454. 5. Epiphytes. — This name is rather loosely applied
to those plants which are attached to others for mechanical
support, and do not derive food from them. All kinds of
plants have representatives in this group. Algae, diatoms,
and other small water plants attach themselves to other alga?
and the higher water plants. Lichens, liverworts, mosses,
ferns, orchids, bromelias, etc., are abundant upon trees.
Epiphytes are attached by hair-like rhizoids, or by hold-fasts,
which apply themselves to the roughnesses or even penetrate
the outer dead parts, but do not absorb from the living tis-
sues of the supporting plant either water or food materials.
The water supply is provided for (i) by adaptations for ab-
sorbing rain or dew, mists, or even dampness, instantly, either
by the surface, as inalgae, mosses, and lichens, or by means of
hairs, as in the Spanish moss and other seed plants; (2) by
adaptations to catch the water in living or dead leaves and
hold it, either by capillarity or as a vessel, long after pre-
cipitation has ceased. Many of the simpler epiphytes are

33 2 PLANT LIFE.

adapted to become dry without injury, while the larger ones
are inhabitants of moist tropical regions, where the danger
of drying is avoided and it is possible to obtain an adequate
water supply. Their food materials are derived entirely
from the air and the water which falls upon them, while the
mineral salts are obtained 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 debris about the base of the epiphyte. Or-
ganic 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.

CHAPTER XXIV.

SYMBIOSIS.

455. 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 mulualistic 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 ^[^[ 51, 52, 53,
222.)

A. Mutualism.

456. i. Between plants of the same species. — Mutual-
ism may occur between individuals of the same species.
Illustrations of this are to be seen in the massing of the
lower algce into colonies, in some of which certain individuals
may be differentiated from others for the purpose of carrying
on a function of advantage to the colony. (See 12, 13,

333

334 PLANT LIFE.

20.) In a somewhat similar way certain bacteria are found
always massed into colonies, constituting a sort of thallus of

a

FIG. 371. — A, serpent-like colonies of Chondromyces serpens, composed of numerous
rod-shaped individuals, B, a, which multiply by fission, b, and secrete a mass of jelly
which holds them together. A magnified 45 diam.; B, 750 diam. — After Thaxter.

characteristic outline (fig. 371). In the higher fungi, also,
the mycelium may be looked upon as a thallus formed by the
aggregation of many individuals ; for, while it is possible to
have a mycelium produced from the development of a single
spore, it is not common. The mycelium is generally the
result of the union of hyphse (see ^[ 50) arising from many
spores. Even in such cases the mycelium may constitute
a single body, and may give rise to a single fructification.

457. 2. Between plants of different species. - -Mutual-
ism is more common between plants of different species. It
takes the following forms:

458. (a) Lodgers.- The higher plants often shelter
various species of lower ones within their intercellular cham-
bers, 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 intercellular
spaces of liverworts and duck-weeds, in the cortex of the
roots of some land plants, and in the bladdery 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 epiphytic (see ^[ 454)
is shown by the fact that certain species are found only upon
certain other species, while they do not grow upon other

Y MB 10 SIS,

335

plants which would furnish them similar external conditions
(fig-

A B

FIG. 372. FIG. 373.

FIG. 372. — A portion of a filament of an alga {Ectocarpus\ showing at a another alga
(Entodenna \\~ittrockii) which has embedded itself in the cell-wall. Magnified 480
diam.— After Wille.

FIG. 373. — A , a tuft of rootlets of white poplar forming mycorhiza. Natural size. B,
a portion of a transverse section of one of these rootlets, showing the mantle of fungus
mycelium and the growth of the hyphae also in some of the outer cells of the root.
Magnified 480 diam. — After Kerner.

459. (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
forms a jacket over the outside of the root (figs. 373, 374),
taking the place and work of the root hairs by means of
strands of hyphse extending from the surface of the fungus
jacket (fig. 374) ; or it grows inside the cells of the cortex
and epidermis, forming knotted masses (fig. 375) ; 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 number of herbaceous plants. The second form belongs

336

PLANT LIFE.

chiefly to the heaths and orchids. The third form grows
upon alders, bayberry, etc.

460. (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. 376). The presence of these

FIG. 374.

FIG. 375.

FIG. 374. — Tip of a rootlet of beech (Fagus sylvatica) with fungus mantle, the loose
hyphz acting as absorbing organs in place of root hairs. Magnified 100 diam. — After
Frank.

FIG. 375.— Mycorhiza of orchids. A, diagram of a longitudinal section of a root ; p, p,
the cells of cortex filled with hyphs of fungus ; j, stele. Magnified about 20 diam.
B, a bit of longitudinal section of root of Neottia, near the tip. e, epidermis ; /, a
series of cortical cells filled with fungus. Into the cell a (nearer the tip of root) the
hyphs are just entering ; in the cells above /, recently entered, they have only formed
a small knot about the nucleus. Magnified about 200 diam. — After Frank.

bacteria, in a way yet unexplained, certainly enables the plant
to use free nitrogen from the atmosphere, while other plants
are required to obtain it in combination from the soil. The
enrichment of the soil by growing clover and similar crops
upon it and plowing them tinder is explained by their ability
thus to accumulate nitrogen from the air.

461. 3. Between plants and animals. — Mutualism also

337

? — I

occurs between plants and animals. Various species of plants
attach themselves to ani-
mals by which they are
carried about. The plant
is thus aided in obtaining
the materials for food,
and not infrequently the
plant conceals the animal
from another which seeks
it as prey. In this way
certain fish are hidden by
algae attached to them.
One of the most striking
cases of protective mimicry
is that in which an Aus-
tralian fish has acquired
surface outgrowths which
imitate almost precisely the
appearance of brown sea-
weeds, SO that, when quiet, FIG. 376.— A young clover plant, showing tuber-
cles, /, on the roots. Natural size. — After

it looks like a stone to Goff.

which seaweeds had attached themselves. In this it imitates

other species which have real seaweeds at-
tached to them.

B. Helotism.

462. i. Fungi and algae. — Helotism
exists between fungi and algee, constituting
3* the bodies known as lichens, in which the
{nveifpin(geeangaig5a; fungus is the master and the alga the slave.
~l*L (See 1| 54<z, and fig. 377.) The same
fungus may be found enslaving more than
one species of algae even within the same mycelium. The
protonema of mosses or even the leaves of some small

338

PLANT LIFE.

jvsd*

plants may be surrounded by a mycelium. The enslaved
green plants are generally unicellular or filamentous algae. If
the latter are the species whose colonies produce voluminous
gelatine, the texture of the lichen body is gelatinous ; other-
wise it is tough and leathery. Some
of the fungi which ordinarily associ-
ate themselves with algae to form
lichens may exist free as sapro-
phytes. The alga itself influences
the form of the thallus more or less
profoundly according to its relative
amount. The same fungus associ-
ated with different algae produces
lichens which are described as dif-

FIG. 378. — A radiolarian (Litho-

cercus annular is\ one of the ferent species, or even as different

microscopic single-celled animals
with a siliceous skeleton, 5,
formed by the outer portions of
the protoplasm, J£, which is sep-
arated from the internal proto-
plasm, 7, by a perforated cap-
sule, c \ nu, nucleus ; fsd,
threadlike protrusions of the
protoplasm. Embedded in the

outer protoplasm , E, are numer- such as infusoria, hydras, SteiltOl'S,

ous "yellow cells," z, each with

its own cell-wall, nucleus, and

chloroplasts. These are an alga,

called Zooxanthella, nutricola.

Highly magnified. - - After

Biitschli.

genera.

463. 2. Animals and algse. —

Helotism exists between animals
and algae. Various simple animals,

sponges, echinoderms, and worms,
enclose algae in their bodies and
utilize the products of their food
manufacture. The algae thus enslaved are all minute uni-
cellular forms which multiply within the animal body by
division (fig. 378).

C. Parasitism.

464. i. 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

S YMBWSIS.

339

general, according to the circumstances. Many animals are

FK;. 379. — Roots of a yellow Gerardia, C, 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.

thus preyed upon by bacteria and fungi. Most communi-
cable diseases, such as typhoid fever, diphtheria, and tuber-

B A

FIG. 380. — A , European dodder twining about a hop stem. All but the uppermost coils
show the groups of \\artlike swellings from which haustoria penetrate the host stem.
Natural size. />', Germination of same. The various stages are arranged in order
from right to left. In the last stage the seedling has (omul 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.

340

PLANT LIFE.

culosis, 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 bacterial diseases
among plants is relatively small, for comparatively few bacteria
have been able to adapt themselves to living in the acid cell-
sap of plants. The number of diseases of plants due to
parasitic fungi, on the contrary, is very large. (For the mode
by which parasitic fungi gain entrance to the bodies of their
hosts, see If 52.)

465. 2. Seed plants. — A few seed plants have adapted
themselves to a parasitic life upon others. Some may be

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. 379). Other semi-
parasites, such as the mistletoe, at-
tach themselves to the host above
ground, and have no true roots of
their own. Some parasitic seed
plants twine about their hosts, into
which they send absorbing organs
by means of which they derive all
their food from the host. Such is
the yellow parasitic vine, known as
dodder (fig. 380, 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.
380, B]. Some root parasites begin to germinate upon the

FIG. 381. — A twig infested with a
parasitic seed plant (A poda ti-
thes) whose body is hidden un-
der the bark of the host, through
which a short branch bearing a
few scale leaves and a single
flower bursts. Natural size. —
After Kerner.

341

ground, but do not pass beyond the first stages of develop-
ment unless in contact with the root of the host by which
they are normally sustained. Under these conditions they
then form a cone-like enlargement, which unites with the
cortex of the host root and penetrates to the stele. 1'Yom
this conical stem arise the aerial shoots. Other parasites
form a network or even a complete 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. 381).

§ III. ADAPTATIONS TO ANIMALS.

CHAPTER XXV.

ANIMALS AS FOOD, FOES, OR FRIENDS.

I. Carnivorous plants.

466. 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 sup-
ply. Some plants solve the problem by entrapping animals,
deriving 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

467. i. By pitfalls and traps. — (#) 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. 382 ; see also fig. 155). 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

342

ANIMALS AS FOOD, FOES, OR FRIENDS. 343

foothold to an insert 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 cap-
tives 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
digestive enzymes or bac
teria quickly dissolve the
softer parts of the insect
bodies, and the soluble
portions are absorbed by
the leaf.

(/;) The bladderwort,
which abounds in quiet
pools, furnishes an ex-
cellent illustration Of traps Fir- 382 —A, trumpet-shaped sessile leaf of Sar-

raccnia r'.« rwlans, showing thin nienibran-

^nO"S l82 ^84.) TJpOn ous windows in the meshes of the veins of

•J "' «J the hood which arches over the mouth of the

the leaves are numerous trumpet. A1, cup-shaped petioled leaf of Ne-
penthes villosa, with elevated lid and margin
minute bladders each ribbed. One-third natural size.-- After Kerner.

with a small opening about which divergent hairs serve as
guides to the entrance. The entrance is lightly closed by a
flap of membrane, 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
materials.

344

PLANT LIFE.

468. 2. By adhesive surfaces. — Animals are also cap-
tured by adhesive surfaces. These surfaces are covered by a

b1

FIG. 383. — A bladderwort (Utricularia 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, />, and others the large bladders,
/>'. See fig. 384. A shoot of a smaller species is shown at a, 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

ANIMALS AS FOOD, FOXS, OX FRIENDS. 345

cases the softer parts of the insect bodies are digested and
absorbed. It should be noted, however, that adhesive sur-

FIG. 384. B FIG. 385. A

FIG. 384. — A 'bladder of Utricitlaria. vul^aris, halved lengthwise, with an imprisoned
crustacean, Cyclops, a to />, opening, witli hairs, //, /, about it; b to c, cushion-like
rim, 6-c part cut through, d-e surface on which the flap,/, rests, opening inwards only ;
v, wall of bladder set with absorbing hairs within and glandular hairs without ; k, the
stalk (secondary petiole). Magnified 20 diam.— After Cohn.

FIG. 385. — Two leaves of sun-dew ( n rostra rotundi folia). A, in expanded position
showing the tentacles. />', 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
2i diam. — After Kerner.

faces are also merely protective against the visits of unwel-
come guests, who steal nectar or pollen. (See ^[ 488.)

469. 3. By move-
ments of traps and
adhesive surfaces. -
Somewhat more
complex methods of
capture are exhibited
by leaves which have
special movements
connected with traps
or sticky surfaces.

r
I he Sundew OI Our

T .1 j

swamps has the edges

and surface of the leaves covered with many outgrowths,

FIG. 386. —Cluster of leaves at the base of flower stalk
Of Venus' fly-trap (/?/*««« iiiHscifHtti). One-half
natural size.— Alter I )rude.

346

PLANT LIFE.

each of which is tipped by a large gland (fig. 385). The
clear, glistening fluid, a large drop of which is secreted

by each gland, is sticky enough
to entangle even insects of con-
siderable size, which alight upon
the leaves. The viscid secretion
envelops the struggling insect, and
at the same time the branches 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
contains ferments
which soon digest
the softer parts of the

FIG. 387. FJG 388.

FIG. 387. — A, blooming plant of Aldrovandia vesicnlosa. Natural size. — After
Drude. B, a single circle of leaves seen from the center above, showing stalk and
two semicircular lobes. Magnified ij diam. — After Caspary.

FIG. 388. — 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
B, fig. 387. Magnified 20 diam. — After Caspary.

body. These are absorbed, and play an important part in
the nutrition of the plant.

Dioncea (fig. 386) and its water mate, Aldrovandia (fig.
387), have leaves whose blades are somewhat like a spring

ANIMALS AS FOOD, FOES, OK J-'KIENDS. 347

trap. The blade is two-lobed, with a hinge along the middle
(figs. 205, 388). 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 Dioiiica to catch the slow-flying insect, or, in Aldrovandia,
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 nitrogenous
materials follow.*

II. Herbivorous animals.

470. 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
protection, therefore, may be looked upon as a protection
against extermination rather than against injury. As pro-
tective adaptations against browsing animals are usually
reckoned :

471. i. Armor, in the form of hard, leathery, sharp-
edged, woolly, bristly, or sticky parts, especially leaves
(figs. 361, 362, 364, 389); or thorns (figs. 157, 390), prickles
(fig. 115), or stinging hairs (fig. 391).

* Travesties upon these strange methods of nutrition appear periodically
in newspapers, and plants of remarkable size and forbidding aspect are
represented as capturing birds, animals, and even men, that venture into
their neighborhood. It should be noted, therefore, that in all cases the
plants which capture animal food entrap only the smaller animals, scarcely
any of them, except those caught by the pitcher plants, larger than the
common house-fly.

348

PLANT LIFE.

472. 2. Distasteful or injurious substances, such as
volatile oils, camphors, acids, tannins, alkaloids, etc. The
milky juice of plants like milkweeds, which c

often contain acrid substances, may also be
protective.

473. 3. Mimicry. — Certain plants which
are not distasteful or disagreeable have
adopted the same form of leaves and stem
and the general habit of those which graz-
ing animals have found distasteful. This

mimicry causes them to be
avoided, as well as the really
hurtful ones which they imitate.

a

FIG. 389.

FIG. 390.

FIG. 391.

FIG. 389. — Edge of a leaf of a sedge (Career strzcta), showing alternate epidermal cells
pointed and underlaid by two layers of mechanical cells. Magnified 200 diam. — After
Kerner.

FIG. 390. — 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. 391. — A stinging hair of the nettle (Urtica), in longitudinal section. _r, emerg-
ence in which the single-celled hair abc 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.

474. 4. Ants. — In the tropics particularly, certain plants

AXIMALS AS FOOD, FOKS, OA'

349

secure themselves from the attacks both of browsing ani-

mals and leaf-cutting insects

by encouraging the presence

of colonies of warlike ants

upon them and making pro-

vision for their defenders'

wants. A very large number

of species * protect themselves

in this way. For the ants

the plants provide (a) nectar,

FIG. 392.

FIG. 393.

FIG. 392. — Bit of a section through the cushion (c, fig. 393) at base of leaf of
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 i<> diam.— After Scltimper.

FIG. 393. — Apex of the hollow stem of a young Cecropia. >/,the thin spot above a
leaf, which at b has been gnawed through' by the ants to make their nest in the cavity
of the stem ; c, the cushion at base of leaf stalk where food bodies grow. See fig. 392.
Two-thirds natural size. — After Schimper.

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. 392), often of
peculiar form, richly supplied with nutritive substances,

More than three thousand are listed by Delpino.

350

PLANT LIFE.

growing from special parts of the surface, which are regularly
eaten by the ants and grow again, so that a constant supply is
at hand ; (c] divellings 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. 393). In others, portions of the
internodes are much enlarged 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. 394). In some acacias the stipules are developed
as massive thorns, which the ants inhabit.

475. Domatia. — Somewhat sim-
ilar dwelling places, though less
perfect, are provided by many
plants for the mites. These d \vell-

FIG. 394.

FIG. 395.

B

FIG. 394.— Under side of the base of the leaf blade of Tococa land folia, showing
bladder on each side of midrib, each with entrance at a, a. Natural size. (?) — After
Schumann.

FIG. 395.— Domatia on under side of leaves. A, between midrib and laterals of
Psychotria. B, between midrib and lateral of the linden (Tilia Europeea). Magni-
fied about 5 diam. — After Lundstrom.

ing places are in the form of minute shelters usually upon the
under side of the leaves. They are generally formed by hairs
roofing over an angle of the veins, or by various outgrowths,
folds and pits (fig. 395). Their significance is not at all
clear.

ANIMALS AS FOOD, FOES, OK FRIENDS. 351

476. 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 containing
these crystals are avoided by such animals, but will be readily
eaten by them after the crystals are removed.

II. REPRODUCTIVE ADAPTATIONS.

CHAPTER XXVI.

PROTECTION AND DISTRIBUTION OF SPORES

AND SEEDS.

THE present knowledge of reproductive adaptations among
the flowerless plants is very imperfect,, though probably many
exist. This chapter must, therefore, discuss chiefly the
adaptations in the more complicated reproductive structures
of seed plants which have been most studied, with only
incidental allusions to such arrangements in the lower plants.

I. Protection against bad weather.

477. By movements. — Spores 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. 396), 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

352

DISTRIBUTION OF SPORES AND SEEDS. 353

movements, brought about by variations in light and tem-
perature, which act as stimuli. (See ^f 286.)

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

B A B

FIG. 396. Fir.. 397.

FIG. 396. — A, flower of California poppy (Eschsckoltzia), opened in sunshine ; />, the

same, closed in wet weather. Natural size. — After Kerner.
FIG. 397 — A , aerial hypha of rilobolus crvstallinus, with sporangium. The hypha is

swollen beneath the sporangium and very turgid. B, the same with sporangium 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 :

478. i. By turgor and tension. — Among the fungi, spores
are often projected from the spore case by the pressure upon

354

PLANT LIFE,

it of neighboring cells, increasing until the sporangium
ruptures suddenly and the spores are shot out like projectiles.
In some cases the whole sporangium is thrown off in this
fashion, often to the distance of a meter or more (fig. 397).

C B A

FIG. 398.

FIG. 398. — A, a fly killed by the fly fungus (Empusa Muscce), stuck to wall by hyphae
and surrounded by a halo of the spores. Two-thirds natural size. B, hyphae projecting
into the air from the body of the fly, from whose tips spores are being shot off.
Several are shown in various stages of development. The turgor of the enlarged end
of hypha finally ruptures the attachment of the spore and it is shot off surrounded by
the mucilaginous contents which cause it to adhere to any object struck. Magnified
200 diam. (.', a spore enveloped in mucilage. Magnified 420 diam — After Kerner.

FIG. 399. — A, spore chain from a fructification (ceciifin»i) of the cranberry rust
(Calyptrospora). s, s, mature warty spores separated by an intermediate cell. ZTC,
which has arisen by the division of the spore fundament by a transverse wall into a large
upper and a small lower cell. The upper becomes the spore and the lower the inter-
mediate cell which elongates, loses its contents, and dies ; its wall becomes mucilagi-
nous and so loosens the spores. Magnified 420 diam. — After Hartig. £, three spores
at tip of an acropetal chain ; the terminal spore therefore smallest. A disjunctor, d,
has been formed between the layers of the partition wall and has forced them apart.
The white area between two lowest shows area formerly connected. «, nucleus.
Magnified 520 diam. — After Woronin.

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 excessive
turgor (fig. 398). With the spore goes the contents of the

DISTRIBUTION' OF SPORES AND SEEDS. 355

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, either
the walls of a special cell or a layer of the cell-wall between
them may act as a separator by its alteration into mucilage
(A, fig. 399). In some cases the spores are wedged apart by
the secretion, between the layers of the wall joining them, of
a cellulose plug which gradually elongates into a slender
spindle to whose tips the spores are so slightly attached that
the lightest breath carries them away (.5*, fig. 399). The
elaters of the liverworts (fig. n and ^[ 321) serve in some
cases to sling out the spores when the capsule bursts ; in other
cases, as in Marchantia, they entangle the spores, insuring
gradual and preventing too sparing distribution. The teeth
around the mouth of the capsule of mosses serve to distribute
the spores at opportune intervals, instead of having them
emptied out all at once. In some mosses the teeth are erect
or recurved when dry, but upon being moistened they arch
over the mouth, thus
forming a nearly closed
cover (fig. 400). Others
have the teeth arched
over the mouth when
dry or permanently fas-
tened together by their
tips, thus narrowing the
opening and allowing

i . c

the Spores tO Sift Ollt FlG 400>_ L-apsuics of a moss «;,-/„„„/„) after

liPfwppn tl-ipm Tn cnmp fal1 of lid- -Meeth erect when dry, leaving cap-
11 • sule widely open ; /A the same in damp weather.

cases the teeth, by their

form and hygroscopic curvatures, serve to sling out the spores

to a short distance. In many ferns the annulus of the spo-

356 PLANT LIFE.

rangium tends to straighten itself upon drying, thus rupturing
the sporangium. After bending backward for some distance
until the tear gapes wide, it suddenly straightens and hurls
the spores to a considerable distance (fig. 401).

A B C

FIG. 401.— Sporangia 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.

479. 2. By water. --In perfectly quiet water, distribution
of spores depends solely upon their own motor organs. Only
zoospores (see *f[ 306) 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 algae
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. Even such relatively heavy spores as
the resting spores of algae may be carried long distances by
water currents. The microspores (pollen) of aquatic seed
plants are sometimes carried to the stigma by water currents,
as in Vallisneria (fig. 402).

480. 3. By air currents. — Spores may be readily carried
by the air on account of their small size and their ability to

D1STKIBUTIOX OF SPOKES AXD SKF.DS. 357

withstand dryness. Most spores tloat in the air for some time
like dust particles, and the slightest current is adequate to
lift many and carry them along. Spores of most non-aquatic

Fir,. 402.— Pollination of eel-grass (Vallisneria s/>iralis\. 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.

fungi, mosses, and fern worts are distributed by air currents.
The microspores of some seed plants, especially the common
forest trees, are carried in this way.

481. 4. By animals, especially insects. --It is the seed
plants, particularly, which have adapted themselves to the
distribution of spores by this means. The development of
the male plants in this group must be completed in the
neighborhood of the female plants, for the reason explained
in T 386. The microspores must, therefore, be carried to
the ovules of gymnosperms or to the stigmas of angiosperms

PLANT LIFE.

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 ^[ 358.) Some of these may be here enumerated.

482. Adaptations for cross-pollination. — (a) The sepa-
ration of the stamens and pistils, staminate flowers and pistil-
late flowers being produced upon 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 of fertilization to occur when close-pollination
happens. In such cases the pollen is said to be impotent.
This means that the male plants are either not completely
formed by it, or that their sperms do not stimulate the egg
to development.

483. 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.

484. Adaptations to insects. — The adaptations to secure
cross pollination through the visits of insects are so numerou
and so varied, and the advantage in the number and weight
of seeds produced is so marked, that for most seed plants

DISTA'/fil'T/OX (V'' STOXES AND SEEDS. 359

cross-pollinntion must be considered the far more desirable
process. Flowers are adapted to insect visitors in the follow-
ing ways :

485. (<0 Food. --They provide for their visitors edible
substances, such as nectar and pollen,* material for nest
building, shelters, or breeding places.

486. (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
further 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 epidermis of the
petals or sepals, often curiously localized. Dusk- and night-
blooming plants often have heavy odors.

487. (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 is 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 it 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.

488. (d) Exclusion of unwelcome visitors. --In addition to

* The microspores are often produced in great excess of the plant' sown
needs.

360

PLANT LIFE.

provision for welcome guests must be enumerated the meth-
ods 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.

FIG. 403. — Flower of Cobcea scandens, halved : showing tufts 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.

(i) Various obstructions with-
in the flower may render ac-
cess to the nectar impossible
to the smaller and weaker in-
sects, while allowing others
to reach it. Such obstruc-
tions are formed by folds,
hairs, and other outgrowths
upon the flower leaves or the
essential organs (fig. 403).
(ii) Obstructions outside the
flower may exclude crawling

FIG. 404.— Flower of a saxifrage (Saxifraga insects. Slicll are Sticky SUF-
controversa), protected against invasion J

by the numerous sticky glandular hairs on faces an(J J^Jj-g /£„ 404),
the flower stalk, ovulary, and calyx. Mag-
nified several diam -After Kerner. 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 bloom-

DISTRIBUTION OF SPORES AND SEEDS. 361

ing also prevents the visits of any insects except those Hying
at that particular season.

III. Adaptations to the distribution of seeds.

489. After the ripening of the seed various devices and
forces operate to scatter them at as great a distance as pos-
sible 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 distribution
of the spores, can only be attained in seed plants by scatter-
ing the seed, because the megaspore is not set free ; the ga-

FIG. 405. — Elastic valves for slinging seeds. A, fruit of wild geranium (G. />,tlHst>-t-)
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. A", fruit of touch-me-not ( /////< iticn. v
noli-ine tiingere), one sound, the other bursted The carpels have curled up elasti-
cally from the base and slung out the seeds. Natural size. — After Kerner.

metophyte is consequently developed within the sporophyte ;
and the embryo sporophyte is likewise enclosed by the old
sporophyte. (See ^f 408.)

362 PLANT LIFE.

The methods by which distribution is secured may be
grouped as follows :

490. i. Distribution by tension and turgor. — Some plants
(e.g., witch hazel) as they ripen the pericarp, alter its tissues
in such a way that the contained seeds are compressed when
the pericarp dries, and after it opens they are pinched out
from the narrowing valves, as a wret 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 peri-
carp shorten on one side until the strain breaks them loose,
when they become suddenly elastically curled and sling

the seeds contained to a considerable distance (fig. 405).
Somewhat similar causes, i.e., curvatures due to unequal
shrinkage or swelling of the tissues, enable some fruits
with long awn or bristles to creep over the ground or to
bury themselves in it when al-
ternately moistened and dried
(fig. 406). The peri carp of the
squirting cucumber is so dis-
tended by the almost liquid
pulp surrounding the seeds that
it ejects the mass through the
opening formed by its separa-
tion from the axis.

491. 2. Distribution by
water. — In some plants this
is secured by the fact that the
fruits open only when moist-
ened. In such cases the seeds .,

r IG. 406. — Pieces into which the fruit of
may be either Washed OUt from storksbill breaks. There are five of

these each corresponding to a carpel and
the Opening pods by rain, Or arranged on the sides of a prolonged

torus as in ,-J, fig. 405. A, when dry the

may be loosened in many beak is spirally coiled; />•, when moist.

The base is hard and very sharp. Magni-

other ways. The seeds are fied about 2 diam.— After Noli.

thus set free at the time best suited to their prompt germi-

OF SPOKES AND .VAYtVJLY. 363

nation. Sonic plants, adapted to distribution by water, arc
provided with floats. These floats may consist either of the
enlarged and bladdery pericarp (or. sonic 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-loving plants are chiefly
adapted to distribution in this manner.

492. 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 incurv-
ing of the branches upon
drying, so that the uprooted
plant is more or less spheri-
cal in outline, or by the fact
that the plant is normally
spherical by the propor-
tion of the branches. Such
plants are known as ' ' tum-
ble weeds.'1 Singly or ag-
gregated in large bundles
they are rolled over plains
and prairies for long dis-
tances, shaking out their

*rU as thf>v o-n or onen- FlG- 4°7-— Seeds of an orchid (/ 'a ml a tcrc x\
C> 5°> ' with cells of seed coat bladdery and filled with

ing their fruits when moist-
ened. Another adaptation
for distribution by the
wind is the small si/e of some seeds. Those of some orchids
are so diminutive that it takes 500,000 to weigh i gram.

air. These seeds are ejected from the i -apsule
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
Keruer.

PLANT LIFE.

Such minute seeds are readily blown long distances by
the wind. Relative lightness is also secured by the con-
struction of some seeds, which are surrounded by a volu-
minous coat containing many large air spaces (fig. 407).
Outgrowths from parts of the seed coat or pericarp also secure
the same end. In such cases the fall of the fruit or seed
though 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 buoyancy is derived only from air-

FIG. 408. — 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.

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 outgrowths from the surface
(fig. 408). The center of gravity in such cases is so placed
that the plane of flattening will be nearly horizontal when the
seed falls. These fruits or seeds sink from i to 30 times as
slowly as the same bodies without the wing. Sometimes spe-
cialized persistent flower leaves, either corolla or calyx, are
used for this purpose, as in dandelion and thistle (fig. 409).

/?AV7ViV/»T77().\' OF .sV'OAV-.'.V AND SKI-'.DS. 365

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 see Is ( figs. .410, 411).

H v \vv\\V 11 'I1' ii/J» i' Ifi lllll i

fe^v'^J lr

FIG. 410.

FIG. 409.

FIG. 409. — Heads of fruits of the dandelion ; single fruits falling, exposing common

torus and involucre. Natural size. — After Kerner.
FIG. 410. — Fruits of a willow, burst, and allowing the seeds, each with a tuft of silky

hairs (coma), to escape. Natural size. — After Kerner.

493. 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 (b] 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 i. The adhesion of fruits or
seeds to animals, especially to those which are provided with

366

PLANT LIFE.

FIG. 411. — A fruit of Barbadoes cotton, open, exposing the volumindus hairs (commer-
cial cotton i which clothe the seeds. Natural size. — After Kerner.

A
FIG. 412. FIG. 413.

FIG. 412. — 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. 288.
Magnified about 8 diam.— After Baillon.

FIG. 413. — Fruit of tick trefoil {Desmodinni 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.

DISTRIBUTION OF SPORES AND SEEDS. 367

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
(figs 412, 413, 414, 415). 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 germi-
nate when voided. The seeds
of the mistletoe are separated
from the 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 germi-
nate.

The adaptation of plants to
any one of these agents of
distribution 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 the seed chance to alight upon water, or they may
suffice to entangle the seed in the fur of animals.

494. 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 transported, so that

FIG. 415.

FIG. 414. — A, cluster of fruits of Spanish
needles (Bidens bipinnata). B, a single
fruit enlarged, showing barbed awns, rep-
resenting the calyx lobes, by which it ad-
heres to animals. A , natural size ; B,
magnified 2^ diam. — After Kerner.

FIG. 415. — Fruit of cockle-bur ( \anthiian
struntarium), halved, showing two seeds,
the upper of which usually germinates a
year later than the lower. Natural size.—
After Arthur.

368 PLANT LIFE.

they may not be subject to further disturbance. Such an-
chorage 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, cling to the surface of the earth ; or by
barbed bristles and hygroscopic awns which, having become
entangled among the grass, work a pointed seed body deeper
by every change of moisture (fig. 406).

Study of plants in relation to their surroundings, therefore,
yields the conclusion that these organisms are wonderfully
plastic, responding either temporarily or permanently to
every change in conditions. It is greatly to be desired that
the too common thought of plants as only things to be clas-
sified may be replaced by the conception of them as beings at
work, to be studied alive.

APPENDIX I.

DIRECTIONS FOR LABORATORY STUDY.
Part I : Morphology.

I. ALG^E.
A. PLEUROCOCCUS.

1. Examine with a lens pieces of bark bearing Pleurococcus
and similar algae. Note the irregular distribution of the green
granular heaps of plants. Is there any similarity to the distri-
bution 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. Demonstration. Examine slide under a high power and
observe the form and color of single plants. Notice many con-
sisting of two or more cells still joined together, resulting from
cell division. (*[ 19, fig. 18.)

B. NOSTOC or RIVULARIA.

1. Observe the size and form of the colonies, and the consist-
ence of the jelly enclosing them. (^T 13.)

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. (Figs. 13, 14.)

369

37° APPENDIX.

C. OSCILLARIA.

1. Observe the color of a bit of Oscillaria; contrast it with that
of Pleurococcus. (*|[ II.)

2. With needles tease out the specimen in a drop of water on a
glass slip; observe the delicate thread-like form. (Fig. 15.)

3. Transfer a bit of living Oscillaria to -a small glass dish or
white individual butter plate with a little water; protect it from
drying up with a cover; 24 hours later observe the position of
the filaments. (^[ 14.)

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 deposited on the dish at the edge of the water.

(IF ii.)

D. SPIROGYRA.

If fresh material is available examine a few filaments in a white
dish for color. If preserved material is used, stain red by
immersing 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. 24.)
This can be readily seen only in the larger species. (^[ 25.)

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. 24.)

4. Examine conjugating specimens with a lens after staining.
Observe the conjugating tubes connecting two filaments like rungs
of a ladder (^[ 361); the zygotes or zygospores (^[365) as blackish
dots in some cells. Are they in one filament only or in both ?

5. Demonstration. Mount conjugating filaments and show
the conjugating tubes and zygospores. (^[ 375, fig. 303.)

E. CLADOPHORA.

If fresh material is at hand observe in a white dish; if pre-
served specimens are used stain for a few minutes in eosin.
I. How is the plant attached?

D IRE CTIONS FOR L A B 0 RA TORY STL'D Y. 3/1

2. Observe form and particularly the abundant branching.
Can a single main axis be traced ? How many branches arise at
one point? (Fig. 29.)

3. Demonstration. Kill and fix the protoplasm of some fila-
ments of Cliidophin-a by placing them in chrom-acetic acid
(water, 990 parts; chromic acid, 7 parts; acetic acid, 3 parts) for
i hour; wash out the acid by placing them in running water
for several hours (6-24) or in a large dish of water changed
several times in the course of 24 hours; stain by placing them in
alcoholic borax-carmine or haematoxylin for several hours.
Mount in water. Examine with high power of microscope.
Each segment of the filament will be seen to contain several
nuclei (more deeply stained than the body protoplasm and the
numerous chloroplasts), showing the segments to be ccenocytes and
not true cells. (^[ 28.)

F. STONEWORT (Chara sp.).

Place the plant in a glass dish with clean water. Set it over a
black background if preserved (and therefore colorless) material
is used. If fresh, a white dish furnishes a good background.

1. From the base of the axis carefully remove the mud by
washing. Observe the colorless rhizoids. (^[ 37.)

2. In the body of the plant observe (a) the central axis; (l>) the
whorls of lateral dwarf branches ("leaves") at intervals
("nodes"); (c) the single lateral axes arising among the
whorled dwarf branches. (If 33, fig. 35.)

3. Trace the main axis to its tip. Compare the distance be-
tween whorls toward the tip. How do they stand close to tip?
Dissect away the outer ones successively. What is within?

4. Demonstration. Prepare or obtain a longitudinal section of
the apex of the axis, and show under compound microscope the
apical cell and the differentiation and growth of its successive
segments. (H 39, fig. 38.)

5. Compare the length of the various lateral axes. Compare
the tip of any of the long lateral axes with that of the main axis.
What do the observations show as to the duration of growth of
these ?

6. Compare the length of old and young dwarf branches.
Compare their tips with those of either lateral or main axes.
What do these observations show as to the duration of growth
of the dwarf branches? Observe the form and distribution of
the branchlets. Can they continue to grow in length ?

372 APPENDIX.

7. Hold a bit of the main axis (use decalcified plants) between
the halves of a piece of pith and with a very sharp knife or a
razor cut a transverse section of the axis. Mount on a slide in
water with cover glass, and examine with lens. Observe the
central cell, surrounded by a row of cortical cells. (Fig. 37.)

8. Trace the course of the rows of cortical cells by examining
the surface of the axis with lens. Note the short projecting cells
which roughen the surface. (^[ 35.)

9. Demonstration. If fresh material is available mount a living
rhizoid in water and show the rotation of the lumpy protoplasm.

10. On the lower whorled branches observe the black ovoid
resting spores, surrounded by a paler cortex, with a crown of five
cells at the free end. Study these on successively higher and
higher branches, and observe differences in color, and finally of
shape. What is the form of the youngest (ovary) ? (^[ 389, fig.

3I3-)

11. Examine at the same time the spherical spermaries (orange

or scarlet in fresh specimens) which are found with some ovaries.
Why are they absent on older branches ? Can any trace of them
be found? (If 383, fig. 313.)

12. Demonstration. Mount young ovaries and show the central
cylindric egg; the five cortical cells, straight in the youngest,
spirally twisted in older ones, terminated by five crown cells,
between which the sperms make their way to the egg.

Mount entire spermary; also on another slide one teased out
with needles ; show the eight wall cells, united by zigzag edges,
each carrying a handle-cell on its inner face, from which arise
numerous filaments composed of disk-like cells each containing
one sperm.

G. POLYSIPHONIA (P. variegata}.

Place a plant in a glass dish over a black or white background.
Observe

1. The form of the body and the mode of branching. (Fig. 39.)

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. (If 39, fig. 41.)

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. (^[ 38, fig. 40.)

DIRECTIONS FOR LABORATORY STUDY. 373

5. On some plants observe that the smaller branches are
swollen here and there with more opaque contents at these
points. These are the tetrasporangia. Compare their size as they
are traced tip-wards. What do you infer as to their origin ?

(IT 3*7. fig- 220)

6. Demonstration. Mount tetrasporic branches and show the
tetraspores.

The sexual reproduction is so specialized that beginners should
not be perplexed with it. (See p. 288.)

H. BLADDER WRACK (Fucus vesiculosus}.

Place plant in a glass dish or a pan of water. Observe

1. The general form of the body or thallus; its mode of branch-
ing. (1[ 41.)

2. The thicker central region forming a midrib, with thinner
wings. (Figs. 42, 43.)

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 pro-
trude through an opening at the top a tuft of fine hairs. These
are the mouths of the hair pits.

8. Crowded on the receptacles, larger warts with a hole at top
and similar 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 ?

Cut thin transverse sections through the center of the recepta-

374 APPENDIX.

cles of male and female plants. If another species than Fucus
vesicttlosus is used (e.g., F. platycarpus) both sex-organs will be
found in same conceptacle. If the sexes were not collected
separately and marked they can only be recognized after cutting
sections by the descriptions and figures given. Observe

n. The form and size of conceptacles. Compare with hair
pit.

12. In male conceptacles, the crowded and tufted hairs, some
of whose terminal cells are spermaries. (U 381, figs. 309, 310.)

13. In female conceptacles, the ovaries of various sizes. The
larger ones are mature. (^T 389, figs. 324, 326, 327.)

14. Demonstration. Mount very thin sections of male and
female conceptacles or some of the teased out hairs from them
and show :

The oval spermaries, filled with rounded sperms.
The ovaries, young and old ; in the latter, the eight crowded
and therefore angular eggs, which round off on escape.*

II. FUNGI.

A. BLACK MOLD (Rhizopus nigricans}.

Before any white or black dots appear on the mold, examine
the vegetative hyphce. (^[ 48.) These are of two kinds, (a) those
running over the surface of the bread ; (6) 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, ^[ 50)
white ?

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

After mold has begun to show black dots {sporangia*} examine.

3. Determine how the branches are placed which bear the spo-
rangia. (Fig. 49.)

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

* If fresh material can be obtained demonstrate the sperms and eggs after escape from
spermary and ovary. Expose a plant with mature receptacles which has been in sea
water (or a 3 per cent, solution of sea salt) to the air for a few hours; mount in sea
water on a slide some of the orange exudation which appears at the mouths of male con-
ceptacles. The water will be found filled with spermaries from which are escaping
motile sperms. The same treatment with female plants will demonstrate the eggs. By
mixing drops of water containing sperms and eggs the process of fertilization may be
watched.

DIRECTION'S FOR LABORATORY STUDY. 375

5. Snip off a few ripe sporangia with scissors, handling them
cautiously to avoid breaking or tangling them ; mount in alcohol *
and examine. Crush (if not already broken) and observe numer-
ous dust-like particles, the spores, which escape.

6. Demonstration. Mount a full grown but immature sporan-
gium and show the structure of sporangium, with septum grown
up into it forming the columella ; the spores. (Tf 316, fig. 220.)

B. WHITE RUST ( Cystopus portulacee}.

1. Demonstration. Boil a leaf of purslane for a minute or two
in 5$ potassic hydrate. Tease apart the tissues of leaf with
needles on a slide, mount and show the mycelium of the fungus.
consisting of tangled hyphae ramifying among the cells of leaf.
(IT 5i, 52.)

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. (If 312, fig 210.)

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

4. Demonstration. Cut a transverse section through one of
these spore beds and show the close set ends of hyphae producing
the spores in chains. (^[ 313.)

5. Cut a transverse section of the leaf or stem, mount and
observe the numerous dark dots scattered through the tissues of
the host. These are the resting spores with thick opaque walls.

6. Demonstration. Show in a similar section the spermaries
and ovaries, and the various stages in the maturing of the fertil-
ized egg into the resting spore.

C. MILDEW {Microsphara Friesii, or Erysiphe communis}.

Examine dried leaf bearing mildew. Observe

1. The whitish interlacing hyphse on surface of leaf, forming
the mycelium. (^[50.)

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.

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

3/6 APPENDIX.

3. The pulverulent appearance on the younger leaves, due to
spores.

4. Demonstration. Scrape a bit of the mycelium from the sur-
face of the leaf after moistening it for a few minutes with a 5$
solution of potassic hydrate. Mount and show (a) the colorless
branching hyphae ; (&'} the erect branches bearing the spores ; (c)
the spores.

7. Examine as before one of the older leaves. Observe the
yellowish dots scattered over the mycelium, the immature fruits.
(IT 401, fig. 337.) Associated with these the black mature fruits.
These contain sporangia with spores. (^[ 317, fig. 223.)

8. Demonstration. Mount and crush under cover glass some
mature fruits ; show the sporangia (asci) and their contained
spores. (Fig. 224.)

D. CUP-FUNGUS (Peziza sp.).

1. The mycelium penetrates the earth or rotting wood on which
the fructification appears and cannot be dissected out. Only the
reproductive parts (^[ 317) are to be examined. Observe the size,
shape, and color of the cup. The red and orange cups usually
lose their color in preserved specimens.

Cut a thin section from a piece of the cup at right angles to
inner surface. Mount. Observe

2. The dense upper layer of parallel hyphae (hymenium), with
rows of black specks. The latter are the spores in the long
parallel sporangia (asci\ (H 317, fig. 222.)

3. The lower layer, less dense, of tangled hyphae.

4. Demonstration. In a very thin vertical section show (a) the
hymenium, with paraphyses, asci, and ascospores ; (b} the looser
lower layers of interwoven hyphae.

E. LICHEN (Physcia stellar is}.

Soften the plants by soaking them in water for a few minutes.
Observe

1. The mycelium, forming a connected leaf-like lobed thallus.
Compare as many other forms as are available. (*[ 540, fig. 225.)

2. Compare the color when dry and wet. In the latter condi-
tion, the mycelium is more translucent and the imprisoned green
algae show through more plainly. (Figs. 55, 377.)

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

DIRECTIONS FOR LABORATORY STUDY. 377

4. Occupying the central region on the upper surface, the
round colored disks, apothecia. Compare the form of the younger
ones nearer the margin. What change occurs as they grow
older? (*[ 317, fig. 225.)

5. Here and there, minute black specks, the mouths of sacs
sunk in the thallus, called spcrmogonia.

Cut a vertical section through an apothecium and a part of the
thallus on each side. Observe

6. The layers of the thallus; above and below, dense layers, the
upper and lower cortical layers; between them, the medullary
layer, with green alga distributed unequally through it.

7. The form of the apothecium : its broad short stalk and
rim; the convex surface of the disk. Is this more convex than
before cutting ? How shown ? Why?

8. The layers of the apothecium; the upper (hymenium) of ver-
tical parallel sporangia containing rows of black dots, the spores ;
the second (sub-kymenium) of fine, pale, tangled hyphae; the third
{medullary layer} with green alga; the lower cortical layer. (Fig.
226 )

9. Demonstration. In a very thin vertical section of apothe-
cium show the sporangia (asci) and ascospores; the paraphyses.

10. Compare apothecium with the cup of Peziza. How are
they different? Do these differences seem important? (Figs.
222, 226.)

F. MUSHROOM (Agaricus sp.).

1. The mycelium of this plant consists of rope- or ribbon-like
strands of hyphae ramifying extensively in the substratum. The
fructification only is here studied (^[ 314). Examine this part
fresh or in water. Observe in a mature one the two parts, stalk
and cap. (Fig. 216.)

2. With a sharp long-bladed knife or razor cut the cap and
stalk lengthwise through center. Is the stalk hollow through-
out? Or is the central part only of different texture from outer?
Determine differences of texture by teasing apart the hyphae with
needles.

3. Cut off stalk close under the cap. Turn the latter under side
up. Observe the radial plates (gills) extending from margin to
stalk. Do all reach the stalk ?

4. Examine the young fructifications. By cutting them length-
wise observe the formation of the chamber from whose roof the

378 APPENDIX.

gills develop; the floor becomes thinner as the chamber enlarges,
and finally ruptures, exposing the gills. Does any part of this
floor (called the veil] adhere to the stalk or the edge of cap on
mature fructifications ?

5. If fresh mature fructifications are available cut away the
stalk and place the cap on a piece of black paper,* gills down,
resting on the stump of stalk, cover with a tumbler or bell jar,
and examine after 24 hours the spore print formed by the great
number of spores which have fallen from the surface of the gills.

6. Demonstration. Cut a very thin transverse section of a gill
and show the hymenium covering the surface, with basidia carry-
ing the free spores. (Fig. 213.)

7. Compare with mushroom various other fructifications of
related fungi (Hydnum, Boletus, Polyporus, Clavaria). Observe
the various forms by which extensive surface is secured for the
hymenium. (^[ 314, figs. 215, 217, 218.)

III. BRYOPHYTES.
A. THALLOSE LIVERWORT (Marchantia polymorpha).

Examine an entire plant in water. Observe

1. The flattened horizontal body (thallus) with central line, the
midrib, and thinner wings on each side.

2. The notched apex (the apical cell is at the base of this
notch). (\ 59-)

3. The mode of branching (dichotomoui). 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. Does
the branch appear on the side of the older thallus, or are the
branches equal at first? Are they equal when older? (^[ 58.)

4. The green lens-shaped bodies (brood-buds] growing at certain
spots along the midrib, surrounded by an outgrowth which forms
a cup-like rim about the cluster. Remove a brood-bud and ob-
serve its form, especially in full grown ones the two opposite
notches, the growing points. (^[ 362, fig. 290.)

5. The air chambers (areoltz) 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 ? (T 57-)

* If the gills are light colored ; if dark colored use white paper.

DIRECTIONS FOR LABORATORY STUDY, 37Q

6. The openings into the ait chambers, in the skin over each
one.

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. ("[[ 56.)

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 remain-
ing) 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.)

12. 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 filaments of chlorophyll-bearing cells. (Fig. 58.)

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

The sexual branches are so peculiar and specialized that the
beginner ought not to be puzzled with them.

•

B. LEAFY LIVERWORT (Porella platyphylla}.

1. In what position do the plants grow with reference to the
substratum ?

Disentangle carefully a single plant.* Observe

2. The growing apex ; the dying base; the distinctly dorsiven-
tral habit. Enumerate the differences between the upper and
undersides. (^[60.)

3. The mode of branching : a central axis, with lateral
branches, themselves with lateral branches ; i.e., monopodial and
bipinnate. (^[65.)

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

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

380 APPENDIX.

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.
62, 63.)

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

7. Examine male plants* and observe the male branches:
short, abundant near the anterior end of main and lateral axes,
with crowded, closely overlapping leaves, the anterior ones often
pale.

8. Cut off a male branch ; dissect leaves carefully and observe
in the axil of each leaf a spherical yellowish body on a slender
stalk, the spermary. (1 382, fig. 311, B.}

9. Demonstration. Mount a mature but unbroken spermary
and show the single layer of cells forming a wall enclosing an
opaque mass of sperms. If fresh, the spermary may rupture on
being put into water and the sperms swim about rapidly in the
field of the microscope.

10. Examine a female plant. On the under side observe very
short lateral branches, bearing a pear-shaped tumid sac, the
perianth. How is it constructed at the free end ?

11. Examine old perianths ; observe partly projecting from
such the mature sporophyte, consisting of a brown spherical capsule
on a pale slender stalk (seta). (The capsule is often bursted ; if
so, determine into how many pieces (valves') it splits.) To what
is the stalk attached? (IF 32, figs. 64, 65.)

12. Examine successively younger female branches (to be
found toward the anterior end) and note various stages of devel-
opment of the sporophyte. Find a young sporophyte, differenti-
ated into stalk and capsule, but still enveloped by a thin mem-
brane, formed by the enlarged body of ovary and surmounted by
a brown bristle, the neck of the ovary. Determine what becomes
of this membrane (calyptra).

13. Demonstration. Select the youngest female branch with
well grown perianth, cut a median longitudinal section, or dissect
away the perianth, mount, and show the group of several ovaries ;
some with canal cells in place, others with canal cells disorgan-

* The sexual organs are borne on different plants.

DIRECTIONS FOR LABORATORY STUDY. 381

ized making an open canal to the egg, and others, perhaps, with
an embryo spor^pltyte in the enlarged body. (^[391, fig. 331.)

14. Demonstration. From a mature capsule mount and show
spores and elaters. (Fig. n, .-/.)

C. MOSS {Mnium cuspidatuni].

Examine plants with capsules attached. Observe the two
connected plants :

1. The leafy stemmed plant or gametophyte. (1 55.)

2. The slender plant attached to its tip, the sporophyte, consist-
ing of a wire-like stalk, the seta, enlarged above to form the
hanging capsule. (^[^[ 67, 322.)

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. 73.)

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 ? (^[62.)

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. (IF 63, fig. 68.)

7. The form -and structure of the foliage leaves: note midrib
of mechanical cells (test strength); lamina of one layer of cells
large enough to be visible under lens ; border of mechanical cells,
some projecting pretty regularly as teeth. (^[64, fig. 69.)

8. Smaller, scale-like leaves on part of the stem.
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. (^[322, fig. 72.)

11. About the edge of the capsule a fringe of pointed projec-
tions, 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. 72, 231.)

12. Among these, or to be pressed out of capsule, many fine
spores.

13. Demonstration. Cut off on a slide the end of the capsule as
a ring, with peristome attached. Divide this ring into halves.

APPENDIX.

Holding one half with needle cut off the peristome close to cap-
sule. This allows the teeth to float away from membrane. Turn
other half with convex side up, cover all pieces, and show the
peristome, endostome, and spores.

Examine young sporophytes of this or other mosses. Observe

14. The cylindrical form of the embryo sporophyte.

15. The hood covering its apex and carried up by it until the
developing capsule forces it off. (If 401, fig. 338.)

16. The lid which falls off to open capsule.

17. Examine on young gametophytes the sex organs. Dissect
with needles the tufts of leaves at apex of stem * and search for
(a) Transparent oval sacs, the empty spermaries ; and similar
opaque greenish or whitish ones, in which sperms are still en-
closed. (IT 384, fig. 311, j9). (£) Flask-shaped bodies, with a long
neck and short stalk, the ovaries. These may always be found,
withered somewhat, at the tip of a stem where a young sporo-
phyte is developing. (^[ 391, fig. 331.)

Numerous hairs, paraphyses, of no known function, may be
found intermixed with the sex organs.

19. Demonstration. With dissection as above, mount spermary
and ovary. Show (a) in spermary, the stalk, the wall, the sperm
cells ; (/>) in ovary, the stalk, body, neck, canal, and egg.

IV. PTERIDOPHYTES.

A. MAIDENHAIR FERN (Adiantum pedatum).

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. (IT 69.)

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

3. Compare this plant with the thallus of Afarchantia.

4. Demonstration. Mount a gametophyte underside up, and
show (a) among the rhizoids the spherical spermaries ; (b) nearer
the apex the chimney-like necks of the ovaries.

If gametophytes with young sporophytes attached are available,
observe

* In some species the male organs form at the apex of the axis disk-like clusters, sur-
rounded by leaves, the whole reminding one in form of a miniature sunflower-head,
while the female organs occur in smaller numbers (3-6) in the bud-like clusters of leaves
at the apex of other stems.

DIRECTIONS FOR LABORATORY STUDY. 383

5. That the young sporophyte is fastened to the under side of
the gametophyte. (^[ 72, figs. 76-78.)
II. The sporophyte.
Taking the underground parts in a dish of water, observe

1. The slender wire-like roots. How are they branched ? (^[ 91
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 ? (IT 79.)

2. Demonstration. Cut a longitudinal median section of a root
tip and show the tetrahedral (triangular in section) apical cell ;
the segments cut off from inner faces producing root tissues,
those from outer face producing the root-cap. (U 77, fig. 83.)

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

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

a 35.)

4. The central whitish tissue, chiefly the stele, in which the
visible openings are the larger vessels. (^[ 81.)

5. In what position does the stem naturally stand ? Observe
its occasional branching (^[ 103) ; the surface covered with chaffy
scales (U 128) ; the growing apex and dying base.

6. Its nodes and inter nodes ; the nodes are indicated by the
attachment of a single leaf at each ; the internodes are the inter-
vals between the nodes. How are the leaves placed? (^[ 119.)

Cut a transverse section of the stem and observe

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

(IF 129.)

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 (i mm.) sec-
tions, 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. (UTT 130, 131.)

Taking a perfect leaf, dried under pressure, observe

9. The stalk or petiole, with its branches. Note the mode of
branching; the petiole divides into two equal divergent branches ;
each of these forks, one branch carrying leaflets while the other
again forks, and so on. (ITU 153, 155.)

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

384 APPENDIX.

11. The leaflets. Note (a) shape, as to outline and margin,
comparing basal, median, and terminal leaflets of any branch ;
(b) the veins, containing branches of the stele ; (c) the green tissues
between the veins. (^[ 154.)

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[ 165, 166.)

13. Demonstration. Cut a very thin vertical section of a leaf
at right angles to veins, and show (a) the upper and lower layer
of cells forming the epidermis; (b) the green parenchyma cells with
intercellular spaces; (r) the section of the vein composed of the
stele with mechanical tissues above and below it. (1I^[ 167, 168.)

14. At the edges of the leaflets on the under side crescentic
brown spots, sort. (^[ 323.)

15. Boil a leaflet for a minute in water. With a needle turn
back a flap which covers the sorus, the indusium; observe that
it is a specialized portion of the edge of leaflet.

16. On the under side of the indusium, a mass of yellowish
spheroidal bodies, the sporangia. Scrape away most of them and
notice the relation of their points of attachment to the veins.

Mount some of the sporangia and observe

17. Their shape; the stalk by which they were attached. (Fig.
401.)

18. The darker ridge, annulus, which serves to burst them
when mature. (Fig. 401.)

19. 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.

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

B. HORSETAIL (Eqins'tum arvense}.

I. The gametophyte cannot be readily obtained, and differs
from that of the fern mainly in having erect branches, with the
sex organs on the upper side and always on separate plants.*

II. The sporophyte. Taking the underground parts in water,
observe

* See Goebel, Outlines of Classification, figs. 210, 211; Campbell, Mosses and Ferns,
fig. 220 ; Sachs, Physiology of Plants, figs. 425, 426.

DIRECTIONS FOR LABORATORY STUDY. 385

1. The slender roots (all secondary); their places of origin.
(* 76.) (Structure quite like ferns.)

2. The stem; its nodes and internodes; longitudinal shallow
furrows and low rn/gcs.

3. At each node a toothed sheath (representing a circle of
leaves not distinct from each other), best seen on younger region.

Cut a transverse section of the stem; mount; observe

4. A circle of large air-canals, one opposite each furrow. Trace
these lengthwise in an internode. Do they pass the node?

(1 129.)

5. Within the circle of air canals, the tissues constitute the stele.
Opposite each surface ridge, a cluster of small cells looking
denser than adjacent tissues. These are the cut ends of the
vascular bundles. (^[ 131.)

(If underground stems are lacking make out this structure in
the aerial ones, which differ mainly in being hollow.)

Examine one of the flesh-colored aerial shoots in water (fig.
235, A}. Observe

6. Similar distinction into nodes and internodes. Break the
stem by a lengthwise pull. Where does it break ? There is an
intercalary zone of growth at the base of internode. (Compare
leaves, ^[ 169.)

7. The large sheath at each node, the leaves. Each tooth
represents a scale leaf. Note relation of teeth to ridges of
stem and to those of sheath next above or below. (^[ 160.)

8. The different leaves near apex, separate, but whorled and
crowded in a cone; these are the sporophylls. (^[^[ 324, 325, fig.
235.) Note the lowermost whorl united and forming a sort of
collar.*

Dissect off several sporophylls in a small dish of water and
observe

9. Their parts, the stalk, the head ; hexagonal form of head
due to crowding.

10. The six to ten thin sacs under the head and parallel with
stalk, the sporangia. (Fig. 236.)

11. Tear open a sporangium. Leave the spores in a pile on one
slide and mount a bit of the wall on another. In the latter ob-
serve the cells with thread-like spiral thickenings on the walls;

* This may be considered a primitive perianth (U 353) and gives added reason for
calling the whole cluster a llower.

386 APPENDIX.

an arrangement to burst the sporangium when mature. (Fig.
238.)

Breathe on the dry mass of spores. Watch the squirming
movements.

12. Demonstration. Mount a few spores in water and others
dry, and show the elaters ; strips of the outer walls of spores,
loosened but wrapped around spores when moist, straightened
out when dry. (Fig. 239.)

Examine the green branched shoots (fig. 235, £}. Compare struc-
ture with other shoots, noting differences. Observe

13. Profuse branching and the arrangement of the branches and
branchlets.

14. Cut a longitudinal section through the base of a branch.
Observe that the branches arise from the stem above the origin
of leaves and burst through the sheath.

15. That the nutritive work depends on the stem, not on the
leaves, which lack green tissue.

16. The roughness of the surface. Rub branches on a metal
surface and observe that they scratch it, on account of silica in
walls of surface cells.

C. SELAGINELLA (S. rupestris}.

I. Gametophytes, male and female, are extremely reduced,
scarcely bursting the wall of the spores producing them. See
1F1384. 392, figs. 315, 333.

II. Sporophyte.

Examine in water an entire plant. (If previously dry it should
be boiled for a few minutes in water.) Observe

1. The yellow thread-like secondary roots arising at various
points from the stem. (Structure like fern.)

2. The branched shoots ; note method ; lateral branches arising
from side of mother shoot, i.e., monopodial branching.

3. The crowded foliage leaves. How arranged ? (See p. 97.)

4. The sporophylls. Search for ends of branches having leaves
in four vertical ranks. Compare form of these leaves with foliage
leaves. Observe

5. In their axils large yellow sacs, the sporangia ; some con-
taining

6. One to three large spores, the megaspores; more abundant
than similar sporangia containing

DIRECTIONS FOR LABORATORY STUDY. 387

7. Numerous small spores, the microstores. Microsporangia are
usually at tip or base of spike and are often difficult to find if
material is not collected at proper season. (^[1J 326, 327.)

V. SPERMATOPHYTES.*

A. PINE (Pinus sylvestris).

Examine a shoot showing at least the growth of present year
and that of the preceding. Observe

1. Two kinds of axes : (a) the main axis of the shoot, with un-
limited growth, now terminated by a conical bud ; (I)) the very
short lateral axes of limited growth, dwarf branches, each bear-
ing two needle-leaves. (^[ no, fig. 101.)

2. The six forms of leaves. Study the shape and structure of
each, (a) the slender green leaves, needles ; (b) the scales closely
covering the older parts of the stem, in whose axils arise the
dwarf branches carrying the needle-leaves ; (c) the thin broad
scales on the dwarf branches, enwrapping the bases of the needle-
leaves (best seen about the leaves on the young shoot) ; (d) the
scales protecting the apical bud (^[ 160) ; (e) the two forms of
sporangium-bearing leaves, sporophylls, in the two sorts of flowers
(see further 4 and 9).

3. Dissect the scales carefully from a large terminal bud and
compare the interior parts with those of the shoot which bears it.
Can you make out the corresponding members? If not, it is
because the bud is too young. Use a bud taken from the tree in
summer or autumn and these points can be seen best. What is a
bud? (p. 85.)

4. Examine the sporophylls. Observe the two kinds : (a)
Numerous oval clusters of yellowish bodies, the micro sporophylls
or stamens, about the base of the young shoots (fig. 101), now
called a staminate flower ; (b*) a single cluster of mega-sporophylls
about the apex of one or two short lateral branches arising just
below terminal bud of a young shoot and extending a little beyond
it, forming the pistillate flower. (HIT 331, 344.)

5. Study the arrangement of the staminate flowers on the axis.
Compare the position of each cluster of sporophylls (flower) with

* In this group the sporophytes only can be studied without the compound microscope.
For gametophytes see demonstration

388 APPENDIX.

that of the dwarf shoots on the upper part of the same axis.
What is a flower? (p. 236.)

6. Dissect off a single micro-sporophyll (stamen) from one of
the staminate flowers. Observe the broad short stalk ; the thin
upturned end ; the two large sacs, sporangia, on the under side.
Tear open these and observe the innumerable small spores,
microspores (or pollen grains).

7. Demonstration. Mount mature microspores in water and show

(a) the spore itself (the central body) with two bladdery enlarge-
ments of the outer wall to secure buoyancy in air ; (b) the immature
male gametophyte inside, consisting of two cells, the smaller rep-
resenting the vegetative part (a mere rudiment) and the larger the
spermary, simple by reduction. (^[ 385.)

8. Examine a pistillate flower. Observe that it shows from the
surface two kinds of leaves : (a) thin ones with toothed edge, the
so-called bracts ; (b) thick fleshy ones with a prominent point, the
carpels. These are probably two parts of one structure, the
sporophyll, which is deeply divided ; but there is wride difference of
opinion as to the exact nature of the bracts and carpels.

9. Dissect out a carpel and observe (</) the broad attachment ;

(b) the ridge on the upper side (kfel) extending into a prominent
point ; (c) the two enlargements on the upper side near the base,
the ovules, and their oblique position. The ovules consist of an
integument and a sporangium containing a single megaspore.
Note the opening in the integument (micropyle] at the end nearest
the base of the carpel, with two prolongations right and left.
(Fig. 246.)

10. Examine a year-old cone. Observe the excessive growth
of the carpels as compared with the bracts. Can you find the
latter by cutting the cone smoothly lengthwise through the cen-
ter? Note the woody texture of all parts. (1[ 404, fig. 341.)

n. Dissect out an entire carpel. Observe the obliquely placed
ovules (Fig. 342).

12. Cut a thin longitudinal section of the ovules and the carpel.
Observe the sporangium surrounded by the integument prolonged
beyond it at the orifice ; inside the sporangium a cavity, the
interior of the megaspore, now partly filled with the young female
gametophyte. (Compare fig. 319.)

13. Demonstration. In a similar section show these parts under
compound microscope, especially (a) the female gametophyte,
growing inside the spore which has not escaped from the sporan-

DIRECTIONS FOR LABORATORY STUDY. 389

gium; (/'i inicrospores lodged about the mouth of integument, the
spermary often forming a tube. (1[ 386.)

Examine a 2-year-old (mature) cone. Observe

14. The extreme woodiness of the cone, especially the carpels
which are spread apart when dry. (1 404.)

15. On the upper surface of some carpels, two thin wing-like
scales, with a seed attached.

16. Time the fall of winged seed from the extreme height to
which you can reach. Time its fall after removing wing. How
will this aid in distributing seed ? (^[ 492.)

Bisect a seed lengthwise, parallel to flatter faces. Observe

17. The firm seed-coat, which is the integument of the ovule
grown and ripened.

18. Enclosed by the coat a white tissue loaded with starch and
oil, the endosperm, which is the enlarged female gametophyte. In
the center of this the embryo sporophyte which grew from one of
the eggs produced by the female gametophyte, after the egg was
fertilized. Note that the tissues of the sporangium have disap-
peared, having been crowded and absorbed. (5[ 403.)

19. Dissect out the embryo from another seed. Observe that
it is already differentiated into a slender stem, and six primary
leaves about its apex. (Fig. 339.)

B. MARSH MARIGOLD (Caltha palustris).

1. Examine the roots. Observe (a) their surface, wrinkled
from shortening; (/>) 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 internodes are very short so that leaves are crowded;
in the middle the internodes 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. (^ 119.)

Study one of the well developed foliage leaves (^[ 150). Ob-
serve

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

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

APPENDIX.

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

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; (^r) these near
the flowers losing petiole and diminishing blade, becoming bracts;
(d) the yellow perianth leaves ; (e} next within these the yel-
lowish stamens (micro-sporophylls); (/) the flattened pod-like
green carpels (mega-sporophylls) each forming a simple pistil.
(11 160, 161.)

8. Bisect a flower 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. (1 330.)

9. Are perianth leaves similar, or of two sorts? (1 354-)

10. Dissect off a stamen. Observe the two parts: (a) the slender
stalk, filament, and (b) the enlarged part, anther. Note in the
anther the two lobes, each with a shallow groove marking the
position of the two pairs of sporangia. Tear open the sporangia
with a needle and observe the innumerable microspores (pollen
grains) which they contain. Examine a naturally bursted anther
and determine how they open. (IT 345-348-)

11. Demonstration. Cut a thin section of an anther from a bud
and show (a] the four sporangia, in pairs, entirely distinct, and
the point at which they become confluent as they burst; (b) the
pollen grains, (1 351.)

Dissect off and examine a pistil. (1 338.) Observe

12. At the apex the roughened area, the stigma (1 336), sessile

(1 337) upon

13. The enlarged part, the ovulary (1335). Observe its flat-
tened form and the groove along one edge. Split it along this
line, flatten it out carefully and note the ovules attached to the
edges. (1 343.)

14. Cut several transverse sections of the pistil and observe the
thickened edges of the carpel, forming the placenta, to which
ovules are attached. Compare sections. Are all ovules attached
to same edge ?

15. Demonstration. Prepare a longitudinal section of an ovule
of a lily and show the two integuments; the sporangium, enclos-
ing the single megaspore, or embryo sac. (H 340, 394.)

DIRECTIONS FOR I.AttORATORY STUDY. 3QI

Study and compare the flower and leaves of the sweet pea
{Lathyrus cdvratus}, apple, fuchsia, and garden lily.

For the study of primary roots and root hairs, primary stem
and primary leaves, germinate Indian corn, scarlet runner or any
bean, in clean damp pine sawdust, and grow until plants are sev-
eral inches high, watching stages of development.

For forms of stems examine white potato (tuber); onion (bulb);
Indian turnip or Cyclamen (corm); morning glory or hop (twin-
ing); white clover (creeping).

For structure of stems, study Indian corn (monocotyledon, with
no secondary thickening), cucumber or pumpkin (dicotyledon,
with no secondary thickening), and young sunflower (dicotyledon,
with secondary thickening). Compare transverse sections.

For lenticels and the formation of periderm, examine the twigs
of plum, cherry, elder or box-elder.

For buds examine large winter buds of hickory, horsechestnut,
or poplar.

Part II: Physiology.

1. To show the existence of turgor in the individual cell. (^[ 188.)
Mount a bit of Spiro-gyra 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 Trades-
cantia ; or the epidermis, filled with purple cell sap, from the
under side of the leaves of the cultivated Tradescantia^1' wander-
ing Jew"); or the hairs of geranium leaves.)

2. To show effect of turgor of cells on rigidity of young parts con-
taining no mechanical tissues. (^[ 188.)

Remove carefully a young plant with vigorous primary root
grown in sawdust or sand. Lay in water for a few minutes.
Note rigidity. Transfer to 5 per cent, salt solution for a few
minutes. Again note rigidity. What has happened? Remove
to water again for 15 min. What is the result?

3. To sho^u the existence of longitudinal tensions of tissues due to
unequal growth or turgor. (^[ 259.)

A. Cut a young internode of elder 10 cm. long, making ends
as square as possible. Measure accurately. Remove wood all
around and measure pith. Place pith in an atmosphere satu-

392 APPENDIX.

rated with moisture and measure after i hour. Compare meas-
urements. (If elder is not at hand use young shoots of grape,
wild or cultivated.)

Bo 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 solution. 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.)

4. To show the existence of transverse tensions of tissues due to
u n equal gr o wth .

A. From a piece of willow or poplar stem separate a ring of
bark I cm. 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?

5. To show the location of root hairs and especially their adhesion
to soil particles. (^[Tf 79, 200.)

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 distortion of root hairs,
and particles of sand partly embedded in them.

6. To show excretion of acid salts by roots. (*[ 202.)

Fill a wide-mouthed bottle holding 250 cc. with tap water; add
2-3 drops of ammonia and several drops of phenolphtalein.*
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
corresponding notches of such size that with a little cotton for
packing the plant will be firmly held. Place the plant with

* 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 phenolphtalein is dissolved in
alcohol.

DIRECTIONS FOR LABORATORY STUDY. 393

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 dis-
appearance of color in the solution, which will indicate when the
alkaline fluid has become 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.

7. To show the corrosion of carbonate of lime by the carbonic acid
excreted by the roots* (^j 202.)

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.

8. To show root pressure as a factor in the movement of water in
plants. (^ 205, fig. 172.)

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. 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 ?

A more satisfactory record may be reached by attaching to the
stump a J-tube as shown in fig. 172. To the horizontal arm
attach a mercury manometer. (A manometer 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 U 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 U-
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 permit the escape of air and extra water. Seal
this with 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 mercury in each leg ; measure
difference at intervals thereafter until mercury begins to fall.

394 APPENDIX.

g. To show that water is not absorbed by leaves in quantity ade-
quate to siipply evaporation. (^[ 196.)

Cut off a vigorous shoot of a plant with abundant foliage ;
close end of stem with grafting wax ; expose to sunlight until
slightly wilted ; then immerse it in water. Does the plant recover
its turgidity ?

10. To show that many leaves are not wetted by water. (^[ 2IO. )
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 surfaces of some ? What relation does this repulsion of
water have to blocking of stomata by rain ?

11. To show the loss of rvater by evaporation. (^[ 208.)

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 with a thick layer of
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 pat-
tern cut a cover for the soil from a sheet of lead ; slit the cover
from the central hole to circumference ; adjust it around plant
and cement all cracks with grafting wax.* Weigh. Weigh again
at intervals of 24 hours, for 4 days.

12. To show the variation in the rate of evaporation diie to the
difference in structure of the organ. (HIT 2O9> 438.)

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. (b) 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 under side 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.

13. To show the conditions affecting evaporation. (^]~ 2IO.)
Construct a potometer as follows : Bend the central stem of a

T-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 J-tube with

* Or the pot can be set in a tin vessel which it fits and the lead cover luted to this.

DIRECTIONS FOR LABORATORY STUDY. 395

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 between a series of equidistant marks on capillary tube.
Try the rate under various conditions of light, temperature, and
moisture acting on shoot.

14. To show the lifting power of evaporation. (1J 207.)

Cut off under water a shoot from a thrifty plant ; fasten it air-
tight in the end of a piece of glass tubing 30 cm. long, of appro-
priate diameter, by means of a piece of rubber tubing slipped
over the end of the stem, taking care not to expose the cut end 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 1-48 hours.

15. 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?

16. To show roughly the path of evaporation stream in woody
plants. (IT 206.)

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

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\ i cm. above this cut
make a similar one on the opposite side. The two must be so
placed and of such a depth that all the tissues are severed. Sup-
port 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, there-
fore, do you infer water travels to leaves?

17. To show restoration and maintenance of an interrupted evap-
oration stream.

Fit a well wilted shoot into the short arm of an unequal U-tubc
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

39^ APPENDIX.

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 ?

18. To show in what tissues food most readily travels. (^[ 235.)
Girdle as in experiment 16 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 ?

19. To show the permeability of stomata for air and their com-
munication rvith the system of intercellular spaces. (*j[^[ 167, 227.)

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
observation. Where do bubbles appear? Is there any difference
between upper and lower sides?

20. To show the depth to which light may penetrate green tissues.

(1 231.)

Take a cylindrical pasteboard or metal tube, closed at one end
and having a cover which will fit over the closed end. In the
end and in the cover cut corresponding holes I cm. in diam. Mark
side and cover when in place so that holes can be made to coin-
cide. On the bottom place a part of a leaf which will cover hole.
Slip on cover and observe whether light is transmitted through
leaf. Add successive pieces of leaf until no more light passes.
What is the color of last light seen ? The examination must be
made with direct sunlight, and light completely excluded from the
eye except that which passes through the instrument.

21. Method for detecting considerable quantities of starch in plant
organs. (J 233.)

Boil a few leaves of various plants for a few minutes. Place
in alcohol at about 60° C. until all chlorophyll is dissolved.*
Bring the leaves into a tincture of iodine, diluted to a bright
brown, for half an hour. The leaves or parts containing starch
will become bluish, dark blue, or black, according to amount of
starch present.

22. To show that manufacture of starch occurs only in cells directly
illuminated. (*[ 231.)

* Do not heat over open flame, but set bottle, loosely corked, in a vessel of hot water.

DIRECTIONS FOR LABORATORY STUDY. 397

Darken portions of some leaves of a plant previously found to
show starch in its leaves (sunflower, bean, tomato, or nasturtium)
by attaching 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, if sunny, cut off the leaves and test for starch.
What has become of starch in cells under the cork?

23. To show that oxygen is a by-product of photosyntax. (^[ 250.)
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 sunlight. When the tube is filled, test the
contents for oxygen by inserting a glowing splinter.

24. To show the effect of light and temperature on photosyntax,
ttsing the rate of evolution of oxygen as an index.

Fasten a shoot of a water plant (Elodea, Myriophyllum, or Cerat-
ophyllum) 10 cm. long to a glass rod and immerse in tap water so
that the cuf end is uppermost. Set in sunlight and observe the
bubbles rising from the end of stem.* Determine rate at which
they rise by counting the number given off in a certain short
time. Continue the observation until the rate is approximately
uniform. Shade the shoot and determine rate. Return to sun-
light and determine rate. Put a piece of ice in the water and de-
termine again.

25. To show the digestion of starch by diastase. (^[ 237.)
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 to-
gether; allow mixture to stand (with occasional stirring) one to
two hours; filter; preserve the filtrate. Take i gm. of starch
and rub it up in a dish with 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 contains 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 con-
verted ?

26. 7^o show evolution of CO -2 by respiration of leaves and
flowers. (^[[239.)

* If several bubbles arise at once, remove shoot from water, dry the cut end of stem
with filter paper and coat it with a *hin layer of grafting wax ; then perforate this wax
witli a fine needle point so as to offer one exit for gases.

398 APPENDIX.

Provide a piece of plate glass and a bell jar with ground rim,
of suitable 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 con-
tact 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?

27. To show evolution of CO? by respiration of seedlings.

Fill a wide-mouthed glass jar or bottle of i liter capacity one-
third full of peas and beans which have been swollen for a day
in water, then 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 CO2 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 CO2-

28. To show the evolution of heat during respiration. (^[248.)
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 form-
alin as above ; 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 run-
ning 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 temperature for two days.*

29. 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 spool-wheel will revolve smoothly but have no un-

* 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.

DIRECTIONS FOR LABORATORY STUDY. 3QQ

necessary play. On the board, with hole for glass tube as a
center, mark an arc of 90 degrees. The radius of the arc should
be a multiple of the radius of wheel. Divide arc into half centi-
meters. 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 observations at regular intervals determine
the rate of growth of stem for a week. What regular variation
can you discover ?

30. To show the necessity of respiration for growth. (^1^[ 242, 245.)
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 exp. 31.)

31. To determine the zone of maximum growth in roots and stems.
(11258.)

A. Observe the four seedlings of exp. 30, whose roots grew in
moist air. Which spaces grew 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.

32. To show the effect of gravity as a stimulus on roots. (^[1 287-
290.)

Arrange the marked root of a seedling bean as in exp. 30, ex-
cept that the root is horizontal, and a pin just above the extrem-
ity marks its position. After 24 hours observe curvature and
which spaces have become curved. Compare with those which
have grown most.

4OO APPENDIX.

33. To show the effect of gravity as a stimulus on growing regions
of tipright leaves and stems. (HIT 287-290.)

A. Support an onion, roots down, in a vessel of water so that
it is half immersed, until the leaves are about 10 cm. long. Then
turn it so that leaves are horizontal and observe where curvature
occurs.

B. 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
the part of the leaf-sheath in this curvature.

34. To show the effect of direction of light as a stimulus on leaves.

(IF 285.)

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 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.

35. To show effect of direction of light as a stimiilus upon stems
and roots. (^ 285.)

Grow seedlings of white mustard thus : Tie loosely over the
mouth of a jelly-glass a double piece of fine bobbinnet; fill vessel
with tap water to the net, on which place seeds ; set in dark, re-
placing water as it evaporates, 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 curva-
tures 24 hours later.

36. To show effect of intensity of light as a stimulus on certain,
leaves. (^[ 297.)

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 showing these movements. After an hour or
two, observe the position of leaflets.

37. To show effect of contact as a stimulus to tendrils. (^ 293.)
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.

APPENDIX II.

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. 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.

401

402 APPENDIX.

(See IT 25.) 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.

Chara. — Several species are common in shallow ponds and lakes,
in water 0.2-1 meter deep, rooting in the mud, often in company
with Myriophyllum and Ceratophyllum, two seed plants, the latter
of which may readily be mistaken for it by novices. But these
plants are usually bright green while Chara is dull or dirty green,
or even whitish (especially when dry) from the coating of lime,
which also renders it brittle and harsh to the touch. Careful in-
spection of its form and a section of the axis at once enables one
to recognize it. (See figs. 35, 37.) Specimens should be gathered
when the spermaries on the lower branches (" leaves ")are orange.
Pull up the plants carefully, wash off as much as possible of the
mud which clings to the delicate, colorless rhizoids. The basal
part of the axis should be put in a separate jar from the rest.
Put a few plants into 2 per cent, chromic acid, and allow them to
remain 24 hours to dissolve off lime with which they are incrusted.
After pouring off the acid and rinsing them thoroughly, soak
them in a large vessel of water for 24 hours, changing water
several times (or allow water to run over them slowly for six
hours) to remove acid. Preserve in 70 per cent, alcohol. Plants
may be preserved in formalin or 70 per cent, alcohol, in long
jars so as to entangle them as little as possible. If brittle from
alcohol (as they often are) before removing them from jar for
distribution pour off alcohol and cover with water for a few
minutes.

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.

COLLECT IXd AXD rKESERl'INC, MATERIAL.

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/ntra, 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 Fttcus vesiculosns (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
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. Microsphara grows everywhere on the leaves of
the cultivated lilac. Erysiphe is abundant on the leaves of blue
or white vervain (Verbena hastata and V. urticafolia) and many
Compositae. 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 (Capsflhi bursa-pastoris)
and another on the pigweeds (Amarantkus sp.). Any one will
answer. The species on Capsella {Cystopns candidus] only oc-

404 APPENDIX.

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.

Feziza. — The cup fungi grow on earth or fallen rotting leaves,
twigs or trunks, in woods. The fructifications may be at once
recognized by their cup-like form. The inner surface of the cup
is often bright colored, red or orange, brown or black. The
mycelium is hidden in the substratum. They may be collected in
spring and summer and preserved in formalin or 70 per cent,
alcohol.

Lichens. — Any common foliose 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 polycarfa).
These may be collected at any convenient time, and kept dry.
Besides these, collect other foliose 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.

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

COLLECTING AND PKESEKl'lXG MATERIAL.

may be recognized by flattish green body about I 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 (Coiioi-cp/inlits ci>nicns) 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
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 Bryum.

Equisetum. — The gametophytes are not readily obtainable. The
sporophytes of the common E. arvense grows on dry sandy banks,
often on railroad embankments. The underground stems send
up in spring (April-May) unbranched flesh-colored shoots 5 mm.

406 APPENDIX.

in diameter and 10-25 cm. high, with brown scale-like sheaths at
the nodes. These shoots terminate in a cone-like cluster of
sporophylls. Later in the season from the same underground
stems, grow green much branched shoots, looking somewhat like
miniature pines, the main lateral axes being produced in whorls
at the nodes. Collect both sorts of aerial shoots with under-
ground shoots and roots attached. Preserve the flesh-colored
and underground shoots and a few green shoots in alcohol or
formalin ; most of the green shoots may be dried under light
pressure between drying paper or newspaper.

Adiantum. — Gametophytes of any fern will answer. They are
flat 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.

Selaginella. — A wild species, S. rupestris, grows abundantly on
dry bare hills and rocks. It forms grayish-green, much branched
tufts, 3-8 cm. high, with narrow bristle-tipped appressed
leaves, and resembles in aspect a large rigid moss. Many
branches are terminated by a sharply quadrangular spike of
sporophylls, about i cm. long. Several exotic species are com-
monly cultivated in greenhouses and window gardens, where
they produce sporangia abundantly. Any species will answer.
Collect the wild plant about July. Specimens may be preserved
dry or in alcohol or formalin.

Pinus. — Any species will answer. The Scotch pine is so widely
planted that it is often easiest to collect. The leaves are grayish

COLLECTING AND PKf-.SI- :A' I Y.V(/ MATERIAL.

in pairs, 5-10 cm. long; cones small, about 5 cm. long,
the ends of scales bearing a conspicuous protuberance, long and
recurved on the basal scales. The Austrian pine, also widely
planted, has dark green longer leaves (10-15 cm.), larger cones,
with no recurved bosses. The flowers are of two sorts and
should be watched for in spring (May) as new shoots appear.
The staminate flowers form conspicuous yellow clusters at the
base of the young shoots, and should be collected as soon as the
sporangia begin to shed the spores. The pistillate flowers are
quite inconspicuous, small oval clusters (5-7 mm. long) pro-
jecting slightly beyond the tip of the young shoots. The tree
bearing staminate flowers usually bears few pistillate ones, and
vice -versa. Collect shoots bearing each kind of flowers, cutting
far enough back to include the leaves of the previous year. Pre-
serve in alcohol or formalin. Collect also year-old and two-year-
old cones. Preserve the former (green) in fluid; the latter
(mature) dry.

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 mm. 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. Preserve flowers and leaves in
summer in alcohol or formalin.

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, {Lupimis al-
bus}, scarlet runner (Phaseolus], broad bean (Vicia faba}, 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 accessj-

408 APPENDIX.

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 100° C.

APPENDIX III.
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 i part, water
9 parts.

Grafting wax. — Made as follows : Melt together resin (by

409

4IO APPENDIX.

weight) 4 parts, beeswax 2 parts, tallow i 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. Schools are advised to
deal only 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,

.-/ PPA RA TUS A XD RE A CENT*. 4 1 I

sharps) with the eye end set into a soft pine penholder or similar
handle. They must be kept sharp on a fine oil-stone.

Drawing materials. — A medium pencil (No. 3 or M) and a very
hard one (No. 6 or 6 H) should be used and kept sharp. Slips of
heaviest linen ledger paper (120 Ib.) cut 14 X 8 cm. are recom-
mended. Only one drawing should be put on a slip.

APPARATUS FOR PHYSIOLOGY.

Since much of the apparatus needs to be put together by the
student, the requisites are mainly tools and a good supply of tub-
ing, both glass and rubber, bottles, and bell jars. The following
will enable the foregoing experiments to be carried out.

Tools. — Hammer, fine saw, three or four chisels, assorted files,
brace and assorted bits, screw-driver, smoothing plane, with a
supply of nails (especially finishing nails) and screws will be
found most useful.

Glass tubing. — A little capillary tubing (0.5 mm. bore) will
be needed. Most used sizes are 5 mm. (3 mm. bore), 7 mm.
(5 mm. bore.) Some larger sizes (13 and 19 mm.) will also be
useful.

Rubber tubing. — 3 and 5 mm. bore mostly ; some of 10 and 15
mm. bore.

Bottles. — Wide-mouthed, various sizes, up to i liter.

Tumblers. — Jelly glasses answer well. Odd lids and glass dishes
from homes and stores can be made useful.

Corks. — Assorted sizes. Several rubber stoppers, sizes 8, 10, 12,
3-hole, are desirable.

Bell jars. — Several sizes are necessary ; 15 X 20 and 20 X 30 cm.
will be found useful ; also at least one 30 X 50 cm. All should
have ground rim and tubulure at top.

Funnels. — Glass, assorted sizes. 6, 8, and 12 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.

Thermometers. — Should be graduated in degrees, — 10° to-)- 100°
C., with milk-glass scale.

Test tubes. — 2 X 15 cm. is a convenient size.

f-tubes. — Two sizes, 5 and 10 mm. bore.

Bunsen burners. — If gas is not available, gasolene burners
should be substituted.

412 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 p^ltnp. — 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.

Tin tube. — 3 X 15 cm. See experiment 20.

Absorbent cotton. — Also a roll of cotton batting.

Sheet lead. — Light weight, used by plumbers.

Plate glass. — Cut into pieces 20, 25, and 35 cm. square.

Pine sawdust and clean sand. — For germinating seeds.

APPENDIX IV.

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.

KERNER : 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.)

BENNETT 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.

BESSEY : Botany, Advanced Cottrse. New York : Henry Holt &
Co. $2.20.

GEDDES : Chapters in modern botany. New York : Charles
Scribner's Sons. $1.25.

413

APPENDIX.

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. i. 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.

APPENDIX V.

OUTLINE OF CLASSIFICATION.

In the foregoing work no endeavor has been made to present
any scheme of classification, but only to develop certain principles
in logical fashion. As a supplement the following general classi-
fication, adapted mainly from Strasburger, Noll, Schenck and
Schimper's Lehrbuch der Botanik, may be useful in showing the
relationship of the more important plants named in the text and
appendices.

All classification is more or less artificial. The purpose of such
an outline is to indicate roughly the present knowledge of kinship
among plants. Even were knowledge perfect it would naturally
be impossible to do this in a linear arrangement such as is neces-
sary in a book. Moreover, knowledge is far from complete. It
is to be expected, for example, that ultimately botanists will be
able to express much more accurately the relationship between
the groups of fungi and the algae than is now possible. Then,
the various groups of fungi will be ranked alongside the green
plants to which they are most akin, as is now done in the Schizo-
phyta, instead of being constituted a class by themselves.

The following classification differs more or less from all others
in details. Like them, it is merely tentative, and will be modified
as knowledge increases. Only in the most general divisions will
all schemes be found similar.

Subkingdom I. THALLOPHYTA. Thallophytes.

Class I. Myxomycetes. Slime molds.
Class II. Schizophyta. Fission plants.

Order I. Schizophycea. Fission algae. Blue-green algae.

Nostoc. Rivularia. Oscillaria.
Order 2. Schizomycetes. Fission fungi.
Bacteria.

415

41 6 APPENDIX.

Class III. Diatomeae. Diatoms.

Class IV. Peridineae. Often ranked as animals.

Class V. Conjugatae. Brook silks and desmids.

Spirogyra. Zygnema. Mesocarpus. Desmids.
Class VI. Chlorophyceae. Green algae.
Order i. Protococcales.

Pleurococcus. Volvox.

Order 2. Confervoidahs. Confervoid algae.
Ulothrix. Cladophora. Ulva.
Order 3. Siphonales.

Vaucheria. Caulerpa. Acetabularia.
Class VII. Phaeophyceae. Brown algae.
Order I. Phaosporales,1

Lessonia.
Order 2. Fucales.1

Fucus. Sargassum.
Order 3. Dictyotales.
Class VIII. Ehodophyceae. Red algae.

Orders numerous. Polysiphonia.
Class IX. Characeae. Stoneworts.
Chara. Nitella.
Class X. Hyphomycetes. True fungi.

A. PHYCOMYCETES. Algoid fungi.

Heterogamous Series.
Sub-class I. Oomycetes.
Orders numerous. Cys-

topus.

Isogamous Series.
Sub-class II. Zygomycetes.
Orders numerous.

Mucor. Rhizopus. Em-

pusa.
B. MESOMYCETES. Intermediate fungi.

Sporangiate Series.
Sub-class III. Hemiasci.

Yeast.

Non-sporangiate Series.
Sub-class IV. Hemibasidii.
Brand fungi. Smuts.

C. MYCOMYCETES. Higher fungi.

Sporangiate Series.

Sub-class V. Ascomycetes.

Witch-broom fungus. Mil-
dews. Truffles. Penicil-
lium. Cup-fungi. Morels.

Non-sporangiate Series.
Sub-class VI. Basidiomy-

cetes.
Rusts. Cap-fungi. Poly-

porei. Puff-balls.

Class XL Lichenes. Lichens.

Physcia. Theloschistes.

1 Various larger species known as tangles, kelp, rock-weed, bladder-wrack.

OUTLINE OF CLASSIFICATION.

Subkingdom II. BRYOPHYTA. Bryophytes. Mossworts.

Class I. Hepaticae. Liverworts.
Order i. fiiidnlt-s.
Riccia.
Order 2. Alarc/mntiales. Liverworts.

Marchantia. Lunularia.

Order 3. Anthocerotalcs. Horned liverworts.
Order 4. Jungcrmanniales. Leafy liverworts. Scale mosses.

Porella.
Class II. Musci. Mosses.

Order I. Sphagnales. Peat mosses.

Sphagnum.
Order 2. Andreaales.
Order 3. Archidiales.
Order 4. Bryales. True mosses.

Bryum. Mnium. Hypnum.

Subkingdom III. PTERIDOPHYTA. Pteridophytes.

Fernworts.

Class I. Filicineae.

Order i. filicales. True ferns.

Adiantum. Pteris. Aspidium. Asplenium.
Order 2. Hydropteridales. Water ferns.
Class II. Equisetineae. ' Horsetails. Scouring rushes.

Equisetum.
Class III. Lycopodineae.

Order i. Lycopodiales. Ground pines.

Lycopodium.

Order 2. Selaginellales. Club mosses.
Selaginella.

Subkingdom IV. SPERMATOPHYTA. Seed plants.

Class I. Gymnospermae. Gymnosperms.
Order i. Cycadales. Cycads.
Cycas.

41 8 APPENDIX.

Order 2. Coniferales.

Pines, spruces, larches, firs, etc.
Order 3. G net ales.

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.

INDEX.

All references are to pages. When there are two or more references to the
same topic, figures in bold-face indicate the definition or chief discussion of the
subject. Italic figures indicate illustrations.

Absorption, carbon dioxide 165;
water 74, 153, 155, 323

Acacia, leaves 124

Acetabularia 23, ~4

Achillea, inflorescence 257

Achlya, sex organs 293

Acids, carbon 175

Adaptations 146, 308

Adiantum 382; embryo 62, 63;
leaf 126\ spermary 282

Aeration 171

Agaricus 377, 404

Agrimonia, fruit 366

Ailanthus, fruit 364

Air, distributing seeds 363; dis-
tributing spores 356; effect of
composition 312 ; effect of
moisture in 316; -plants 152

Alcanna, corolla 250 .

Aldrovandia 346

Aleurone grains 169

Algae, eggs 286, 288; fission 8;
gametes 273\ imprisoned 338,
377; in other water plants 334

Alkaloids 177

Allium, stem 106

Aloe, epidermis 3.'-:

Alternation of generations 49,
60

Amanita, fructification 219

Amorpha, sleep movement 207

Amorphophallus, leaf !..'.'>

Anabaena 10

Anabolism 166

Anagallis, fruit 3<>,j; pistil 245

Anaptychia, apothecium 225

Angiosperms 237; ovary 291;

seed 299; spermary 281
Animals, and plants 336, 338,

342; distributing seeds 365;

distributing spores 357
Anther 246

Anthyllis, venation 137
Ants and plants 348
Apical cell, Chara<?#, 31; Fucus

34; liverworts 51; Polysipho-

nia 32; root 67, 68; shoot 84
Apodanthes 340
Apogamy 294
Apparatus 409
Apple, fruit 305
Arbor vitae, shoot 97
Archegonium 289
Arisarum, flower 236
Armor, protective 347
Artemisia, hairs 3,.'.'
Ash, pistil of 241
Asparagus, branches 92
Aspidium, pinnule 230; sorus

231; sporangium 356
Asplenium, buds 263; gameto-

phyte 60
Assimilation 162
Astragalus, pistil ..'.'/:
Aulacomnium, brood buds 262
Automatism 145, 188
Auxanometer 180

Bacteria 10, .//, /.'
Bacterium aceti //
Balsam, stem 6
Barberry, thorns .l/f$

419

420

INDEX.

Bark 111, 116
Bast, secondary 113

Bazzania 53

Bean, geotropic roots 199, 201

Beech, mycorhiza 336

Beet, stoma 134

Begonia, stem bundle 104

Bellflower, fruit SOS; leaf ro-
sette 196

Bidens, fruit 367

Bird's-nest fungus 218

Blackberry 305

Bladderwort 343, 344, 345

Blade, leaf 123; structure of
leaf 133

Blasia 54

Boletus 404

Books, reference 413

Bracts 131, 236, 256

Branches, dwarf 90, 91, 92

Branching 22; of leaves 122,
124, 125, 126, 128, 138; of liv-
erworts 51; of mosses 57; re-
production by 267; of root 78;
of shoot 86; of stamens 249

Brood buds 260

Bryony, tendril 94

Bryum, capsule 58, 228, 230;
section of stem 56

Buckthorn, leaf 128

Buds, 85, 88; adventitious 89;
axillary 87; dormant 89; on
roots 81; reproductive 263;
shoot 85

Budding 40, 211, 267

Bulb 90, 326

Bulblets 93

Bundles, vascular 71, 72, 100,
103, 114, 132, 136

Butomus, anther 248

Butternut, buds 88

Cactus, forms 98

Calamus, root 72

Caltha 389, 407

Calyptospora, haustoria 45;
spores 354

Calyx 237, 253

Campanula, fruit 302; leaf ro-
sette 196

Canna, leucoplasts 4

Capsella, embyro 66; pistil 242
Carbohydrates 159; manufac-
ture 166

Carbon dioxide, absorption 165

Carex, leaf edge 348

Carnivorous plants 342

Carpels 235, 236, 237

Carpogonium 287

Carrot, chromoplasts 6

Caulerpa 23, 24, 25

Cecropia, stem 349

Cedar, gametophytes 284

Cell 1; division 17, 18; naked
147; wall 5

Centrifuge 199

Centrospheres 4

Cereus, shoot 98

Chara27, 28, 30, ^i, 402; ovary
281; spermary 280, 281

Characeae 27

Cheiranthus, hairs 101

Chelidonium, hair cell 191

Chemotaxis 274

Cherry, cork cambium 110;
fruit 304

Chlorophyll, function 166; spec-
trum 166, 167

Chloroplasts 4, 5, 21; move-
ments 192

Chondromyces, colonies 334

Chromoplasts 5

Cilia 12, 147, 190

Cinchona, bark 112; stem 108

Cinnamon, flower 248

Cladonia 377

Cladophora 22, 23, 24, 370, 402

Cladophylls 92

Classification 415

Clavaria, fructification 219, 404

Claviceps, fructification ^7, 226

Climate, relation of plants to
308

Climbers 330

Close-pollination, adaptations
for 358

Clover, root tubercles 337

Club-mosses, sporangia 231

Clusia, periderm of root 74

Cobaea, flower 360

Cockle-bur, fruit 367

Ccenocytes 22

INDEX.

421

Cohesion, carpels 241; stamens
248

Cold, protection against 315

Colonies, gelatinous 8

Color, significance 359

Conducting tissues 156

Cone, pine 298

Conifers, fruit 298

Conjugatae 16, 20

Conjugation 269, 274

Contact movements 203

Contractility 145

Convolvulus, hairs 321

Coprinus, gill 217

Cosmos, stamens 24$

Cotton, fruit 366

Cotyledons 117

Cork no; cambium no

Corm 90

Corn, stem bundles 107

Cornus, inflorescence 257

Corolla 237, 253

Coronilla, sleep movement ,.'(>7

Cortex, Chara 30; leaves 135;
root 72, 73; secondary 109;
stem 100, 109

Cranberry rust, spore chain 354

Crataegus, stipules 121

Cross-pollination 255; adapta-
tions for 358

Crucibulum 218

Crystals 175,- 176, 351

Cup fungus .-'/./

Currant, nectary 177; ovules

-4-

Cuscuta 339
Cutin 6
Cuttings 266

Cycas, carpel 238; seed 297
Cystocarps, Polysiphonia 288,

289

Cystopus 277, 375, 403
Cytoplasm 2

Dandelion, fruit 365

Datura, anther 248; leaf mo-
saic 196

Dehiscence, anthers 247; fruit
301, .102, 303

Development, phases of 178

Desmids 16

Desmodium fruit ..

Diatoms 14, 15

Dichotomy 78, 86

Digestion 162; intracellular 170

Dionaea 346; leaf ,V.s', .;'/.',

Distribution, of seeds 361; of

spores 353
Dodder it.i'.t

Dogwood, inflorescence ,.',•>/"
Domatia 350
Dorsiventrality 57
Draba, hairs 322
Dracaena, stem 114
Drosera, leaves 345
Duration, of root 73; of shoot

94

Echinocactus, shoot 98

Ecology 144, 307

Edelweiss, hairs 3..'1

Eel grass, runners 20.5

Egg* 285

Elaeagnus, scales 3;'.'

Elaters 7, 355

Elatine, stem in.'

Elder, lenticel 113

Elm, buds 88; cork cambium

110

Emergences 101, 102, 202
Embryo 02, 63, 66,239,291, 295,

296, 297, 300, 304; sac 243,

244

Empusa 354
Endodermis, root 72, 75, 77;

stem TOO, 115
Endosperm 298, 299
Energy, released by respiration

173

Entoderma in alga 335
Enzymes 162
Epidermis, adaptations 320; of

leaf 133; of root 70; of stem

100, 101

Epipactis, cell division 17
Epiphytes 331
Epispore 214
Equisetum 230, 232, 384; apical

bud 84; sporangium wall 2SS\

spores 2.i.i

Ergot, fructification ^?, .
Erysiphe 224, 375; fruit ~'.'

422

INDEX.

Eschscholtzia, ovules 243; pro-
tection of stamens 353
Excretion 173
Exobasidium 43

Fagus, mycorhiza 336

Fats 160

Fennel, resin receptacle 176

Fermentation 162

Fern, maidenhair 382, 406

Fernworts 60; ovary 290; sper-

mary 280, 282\ sporangium

229, 356

Fertilization 255, 285
Fig, inflorescence 260
Filament 246

Fir, seed 297; seedling 118
Fission 17, 211
Flax, stem 104
Flower 92, 236; leaves 131;

movements 196
Fly fungus 354
Fly trap, leaves 208, 345
Foliage 119
Food, for insects 359; insects as

342; with spores 215
Foods 159; manufacture 166,

168; storage 168; transloca-

tion 168

Fossombronia 54
Fragmentation 211
Fraxinus, pistil 241
Freezing, protection against

315
Fructifications 218

Fruits, accessory 304; adapta-
tions to distribution of seed
361; of angiosperms 300; dry
300; fleshy 303, 367; of gym-
nosperms 298; multiple 305

Fucus 33, 34, 373,403; egg 286;
ovary 287, 288; spermary 278

Funaria, leaf 56; development
of sporophyte 296; ovary 290

Function 143; limits to 146; unit
of 144

Fungi 39, 213, 216 ff., 335, 337,
338; fission 10; loss of sex-
uality 293

Fusion, of hyphae 45; of sta-
mens 249

Gametophyte 49; of fernworts
60; of liverworts 53, 54; of
mosses 55; reduction 61, 292;
of seed plants 64; shoot 82

Gaultheria, fruit 304

Gelatin 6, 12

Gemmae 260

Geotropism 197

Gerardia, parasitic 339

Germination, adaptations to
367; of pollen 251

Gloeocapsa 8

Grafting 267

Grain 301

Grasses, geotropic node 199,
200; \eafl20; rolling of leaves
319

Grimmia, capsules 355

Growth 151, 178; conditions of
183; daily period 185; dura-
tion 187; grand period 181;
induced 295; intercalary 38;
of leaves 137, 138; localiza-
tion of 22; measuring 180;
movements due to 192; of cell
wall 7; of spores 215; region
of 181; spontaneous varia-
tions in 187

Gymnosperms 237; ovary 291;
seed 297; spermary 280, 282

Hairs 320, 321. 322, 347; absorb-
ing 323; glandular 360; of
stem 101

Halophytes 311, 326

Haustoria 4o, 4$

Heat from respiration 174

Heath, rolled leaf 321

Heliotropism 194

Hellebore, pistil 2 4!

Helotism 333, 337

Heterocysts 9

Heterogamy 271, 276

Hibernacula 264

Honeysuckle, buds 88; leaves
123

Hop, emergences 202

Horse-chestnut, leaf 126

Horsetails 384, 405; sporangia
230, 232\ sporangium wall
233; spores 233

INPI-.X.

423

1 lost 161

Houseleek .

llydnum, fructification ££0, 404

Hydrophytes 311, 327

Hydrotropism 202; apparatus
SOS

Hylocomium /o

Hyphae 39; branching 40; fu-
sion 45

Indian turnip, inflorescence ..';'><:
Infection with fungi 43
Inflorescence 87
Insects, adaptations of flowers

to 358; distributing spores

357; exclusion of 359; as food

342
Integuments, of ovule 243; of

seed 299

Internodes 96; of Chara 27
Involucre 256

Irregularity 2^4; purpose 359
Irritability" 145, 183, 188, 274;

localization 189
Isogamy 271, 274
Ivy, chloroplasts 4

Katabolism 170, 175

Land plants 152, 311

Larch, gametophyte 282, 283\
shoot 320

Lasiagrostis, rolling of leaf 310

Lathyrus 407

Leaves, adaptation 314, 320;
arrangement 119; base 120;
blade 123; development 117;
fall of 140; form 119; growth
137. T38; °f mosses 57; origin
53; pine 91, 92; primary 117;
secondary 117; stalk 122;
structure 132, /."/; suppres-
sion 319; as water recepta-
cles 324

LeguminoSc'E, root tubercles 336

Lenticels 113

Leucoplasts 4< 5

Lichens 46, 47, ..'..'o, 337

Light, effect on growth 184,
185; effect on form 313; effect
on water plants 338; escaping

319; produced by plants 174;

relation to photosyntax i(>(>
Lignification 6
Lily, anther ,.V,,V; buds :<:.'
Lime, effect of 317
Linden, domatia ,i5O; shoot .v/'
Liverwort 49, 378, 379, 404, 405;

sporangium 227
Locomotion 190
Locust, development of leaf

139; stipule thorns 130
Lodgers 334
Lonicera, buds 88
Lotus, fruit 302
Lunularia 4-^ 50
Lychnis, petal 254; stigma 240
Lycopodium, stem 103

Malt 408

Maple, buds 88; fruits 324; leaf

188; mosaic !',>'>
Marchantia 378, 404; elaters 7;

rhizoids 7; spermary S79;

thallus 26? \ brood-buds 262;

thallus 261

Marigold, marsh 389, 407
Marsilia, root tip 68
Mechanical tissues 149; devel-
opment of 186
Mechanics of body 149
Megasporangium 234
Megaspore 231; of lily 2
Melampsora, spore beds 215
Meristem, primary 35; of root

68; of shoot 84; secondary 74,

108
Mesocarpus 21; conjugating

07 £

£ I O

Mesophytes 311, 312
Metabolism 145, 215
Metzgeria 52
Micrococcus 11
Microsphrera 375, 403
Micr'osporangium 234
Microspores 231
Mildew .'..'.'(, 375, 403; fruit 295
Milkweed, flowers 25:.'; pollen

mass ,.'-•"-/
Mimicry 348
Mimosa, leaves 2<>X; sleep

movement ~i>7

424

INDEX.

Mineralization 7

Mnium 381, 405

Moisture, effect on growth 186

Monopodial branching, of root
78; of shoot 87

Monostroma 26

Monotropa, pollen tube 283

Morchella, fructification 226

Morning glory, chloroplasts 4',
seedling 118

Mosaic, leaf 105, 196

Mosses 53, 381; brood buds 26 J;
sporangium 229; teeth 355;
sporophyte 222

Moss worts, ovary 289; sper-
mary 280

Motor organs 192, 295

Mountain ash, chromoplasts 6

Mousetail, flower 259

Movements 188; combined 196;
contact 203, 207; for entrap-
ping animals 345; of water,
effect on plants 328; para-
tonic 193; photeolic 206; spon-
taneous 193, 206; to protect
spores 352

Mucor.^, 403; sporangium 222

Mulberry 306; flower and fruit
305

Mushroom 377, 404; gill 317

Mustard seedlings, geotropic 198

Mutualism 333

Mycelium 41

Mycorhiza 335, 336

Myosurus, flower 259

Nectar 176; guides to 359

Nectaries 177

Nemalion, ovary 288

Nettle hair 348

Nitella 27, 29

Nitrogen, supply 342

Nodes 96; of Chara 27

Nostoc 9, 369, 401

Noteroclada 54

Nucleus 3

Nutation 193

Nutrition 151; of Oscillaria 10

Oats, cell from leaf 4', epider-
mis 134.

Odor, cause 176; purpose 359

Offsets 90, 265

Oils 176

Oleander, leaf 324

Oleaster, scales 322

Oligotrichum, leaf 56

Onion, embryo 56; stem 106

Oogonium 287

Opuntia 321

Orange, oil receptacle 177

Orchid, chromoplast 6; light
seeds 363 ; mycorhiza 3o6 ;
pollen tube 283

Organ 143

Origin of roots 79

Orthotrichum, branching 57

Oscillaria 10, 370, 401

Osmosis 156

Ovary 240, 273, 286

Ovulary 240

Ovules 237, 242, 243, 244; dia-
grams 285

Oxalis, cells 192

Oxygen, effect on growth 186;
supply 171

Pansy, seed 300

Parasites 43, 161, 163

Parasitism 333, 338

Parmelia, thallus 225

Pea, flower 255; growth of root
182 ; leaf tendrils 130 ; root
branches 79; sweet 407

Pellia, sperms 280

Peperomia, water storing 326

Pepper, fruit 300

Perennials in

Perianth 236, 252

Pericarp 300 ; adaptations to
distribution of seeds 362

Pericycle, root 71 ; stem 100,
103

Periderm, root 74, 751 second-
ary in; stem 109

Perisperm 298, 299

Peronospora, haustoria 4G\ ?ex
organs 277

Petal 237

Petiole 122; scarlet runner 105;
sensitive 128; structure 132

Peziza 223, 376, 404

IXHEX.

425

Phascum, sporophytc !~>9
Phaseolus, motor organs 205;

stele of root 75, '*,*'>
Phelloderm 109
Phloem, bundle of root 72 ;

secondary 109
Photosyntax 166; product 167;

and respiration 171, 175
Phycocyanin 8
Phycoerythrin 33
Phycophaein 38
Phyllodia 124
Phyllotaxy 119
Physcia 376, 404
Physiology 143; apparatus 411;

experiments 391
Phytolacca seed 300
Pilobolus, abjection of sporan-
gium J5J

Pilularia, megaspore 214
Pimpernel, fruit 303; pistil 245
Pine 387, 406; carpel 238; cone

29S ; shoot 91 ; wood, pene-
trated by hyphae 44
Pineapple 306
Pinesap 283
Pistil 237; diagram 285; simple

and compound 240
Pitcher plants 129, 342, 343
Pitfalls 342

Pith, rays 115; stem 107
Placenta 244
Plasmodia 148
Plastids 4

Plectranthus, hairs 101
Pleurococcus 13, 369, 401
Pokeberry, seed 300
Pollen, grains 249, 250 ; tube

S4V, 281, 283, 284, 285
Pollination 255, 358
Polyembryony 294
Polygonatum, leaf 127
Polygonum, megaspore 292 ;

stipules 123; tubers i>4
Polypodium 61
Polyporus 4~ \ fructification

220, 404
Polysiphonia 31. 32, 372, 402;

cystocarps 288, 28'J ; tetra-

spores 227
Polytrichum 55

Pondweed, hibernacula ..'<'>.:

Poplar, mycorhiza 335

Poppy, ovules .'/-/; protection

of stamens .!'<•>'
Porella 379, 405
Potassium salts, relation to

photosyntax 167
Potato, pistil 241 ; starch -•> ;

seedling 266
Pressure, effect on growth 186;

root 156

Prickles 101, 102, 347
Proteids 160; grains 169; manu-
facture 168
Prothallium 60
Protonema, mosses 58
Protoplasm 2; movements 191;

naked 147; powers 145
Psychotria, domatia 350
Pteris, embryo 62 ; origin of

root 80; ovary 290
Puffball 214, 221
Putrefaction 162
Pyrenoids 21
Pyrola, fruit 802

Radiolarian and algse 338
Rainfall, adaptations to 316
Ranunculus, leaf 120} nectary

Raspberry 305

Reaction 189

Reagents 409

Rejuvenescence 268

Repair 151

Reproduction 145, 209; adapta-
tions 352; sexual 268; vegeta-
tive 211

Resins 176

Respiration 171; intramolecular
172

Rheum, flower 245

Rhizoids 22; Chara 31; liver-
worts 50; mosses 53

Rhizome 90

Rhizopus 374, 403

Rhododendron, anthers and
pollen 249

Riccia 50

Rigidity, how secured 149

Rings, annual, of stem 116

426

INDEX.

Rivularia 369, 401

Robinia, thorns 130

Root 65; adaptations 156; ad-
ventitious 267 ; aerial 324 ;
cage 200, 201; cap 68, 70, 71;
climbers 331 ; differences
from shoot 85 ; fleshy 77 ;
float 77; hairs 69, 70; hairs
and soil 154', hairs, solvent
action 155; origin from leaves
139 ; parasitic 389 ; pressure
156; pressure, apparatus for
157; primary 65; secondary
67 ; tap 324 ; tendrils 78 ;
thorns 78 ; tubercles 336 ;
woody 76

Rose, flower 260; leaves 122 ;
prickle 102; seedling 118

Rotation of protoplasm 191

Runner 90, 265

Rye, daily period of growth
185; stem 184

Sage, anther 247

Salts in water 154, 164

Salvinia, sporangium 235

Saprolegnia, zoospores 213

Saprophytes 161

Sarcina 11

Sargassum 37, 38

Saxifrage, flower 360

Scales 320, 322; leaf 130

Scarlet runner, motor organs
205

Scions 266

Scutellaria, cortex 109

Secretion receptacles 176, 177

Sedge, leaf edge 348

Sedum, flower 92, 259; offsets
264

Seed 296, 407; in angiosperms
299; distribution 306, 361; in
gymnosperms 297

Seed plants, ovary 290 ; para-
sitic 340 ; spermary 280 ;
spores and sporangia 234

Selaginella 386, 406 ; female
gametophyte 291 ; male ga-
metophyte 282; stem 105

Selection, power of 164

Sempervivum 325

Sepal 238, 253

Sex organs 273

Sexuality, imperfect 269; loss
of 293; origin 268

Shepherd's purse, embryo 66;
pistil 242

Shoot 82; differences from root
85; from leaves 139; liver-
worts 52; primary 83

Sleep movements 206

Soil 153; effect of temperature
of 315 ; effect of physical
characters 317; limits of ab-
sorption from 155 ; salts in
154; water in 154

Solutions, water 152

Spadix 256

Spathe 256

Spermary 274, 277

Sperms 276

Sphaeroplea, gametes, 286

Sphagnum, sporophyte 228

Spirogyra 20, 370, 401 ; conju-
gating 272

Splachnum, capsules 58

Sporangia 216, 221; of anther
247; of fern 356

Spore 212; chains 217; diagram
216; germinating ^J ; non-
sexual 212; of Penicillium^/;
of Pilularia 214; protection
352; resting 294; sexual 268

Sporophylls 131, 230

Sporophyte 49, 227, 292; fern-
worts 62; mosses 58, 59, 222;
shoot 83; seed plants 64

Spruce, ovaries 284

Stamens 235, 236, 245

Starch, manufacture 167 ; re-
serve 169

Stem 96; climbing 99; erect 98;
forms of xerophytic 319; of
mosses 55, 56; prostrate 98;
sections 99, 102, 103, 104, 105,
106, 10S, 114; shape 97; struc-
ture 99; twining 99

Stele, of leaves 136; of root 71;
of stem 100, 103

Stigma 240

Stimulus 188; transmission of
190

INDEX.

427

/

Stipules 121

St. John's wort, stamens 860,

'

Stolon 90

Stomata 134; sunken 322

Stonecrop, flower :.''>' >\ offsets

964

Storage 107; of foods 168, 169;

in leaves 131; in roots 77
Strawberry, flower 258, 259 ;

runners 264

Streaming of protoplasm 191
Style 240
Suberin 6
Sugar, manufacture 167 ; re-

serve 169

Sugar cane, epidermis 323
Sundew, leaves 3J/5
Suspensor 66, 291
Symbionts 161
Symbiosis 161, 333
Symphoricarpus, fruit cells 179
Sympodial branching, in moss

57; in shoot of seed plants 86
Syrrhopodon, brood buds 262

Telegraph plant, leaf 206
Temperature, effect on growth

185; on form 314; on water

plants 328
Tendril, of bryony 94', leaf 130;

movement of 203; shoot 93
Tension, distributing seeds

362; distributing spores 355;

of tissues 149, 182
Tetragonolobus, sleep move-

ments :.'07
Tetrasporangia, of Polysi-

phonia 227
Thallus 22, 25; of Fucus 34; of

liverworts 49
Thickening, secondary, of root

74, 77; of stem 107, 115
Thlaspi, leaf 123
Thorn apple, anther 2J+8
Thorns 347; leaf 130; shoot 93;

of Vella 95
Thyme, anther 247
Tococa, base of leaf 350
Torus 236, 258
Traction, effect on growth 186

Tramcirs / /
Transfer of foods 168
Transpiration 158; adaptations

for reducing 318
Traps 343

Trefoil, fruit of tick o<">>'>
Tropjeolum, leaf /.'.v
Tubers 93, 326
Turgor 148; distributing seeds

362; distributing spores 353;

movements 204
Twiners 201, 331
Tylanthus, leaf 321

Ulothrix 21 ; reproduction 270,

271; zoospores 269
Ulva ..'<!
Uncinula 403
Urtica, hair 848
Utricularia 343, .,'44, 345
Uvularia, leaves 1 .'•!

Vacuoles 2, 179

Vallisneria, distribution of

spores 356, 357; runners 265
Vanda, light seeds 363
Vanilla, leucoplasts ~>
Varnish, on epidermis 321
Vascular bundles 71, 7;', 100,

103, 114, 132, 136
Vaucheria 22, 23 ; sex organs

278

Vella, thorns 95
Venation, leaves 125, 1..'7, A-7,

138

Veratrum, pistil ;','/!
Vicia, vascular bundles of root

75
Violet, anther S4G\ fruit-/".'

Water, absorption 153, 323 ;
distributing seeds 362; dis-
tributing spores 356 ; effect
of composition 329; effect of
movements 328; force raising
157; loss 158; movement 156;
necessity 152 ; path of 156 ;
percentage 151 ; -plants 152,
327; salts in 164; storing 325

Waste products 175

Wax, on epidermis 321

428

INDEX.

Weight, loss of 173
Welwitschia 140
Willow, fruit 365; leaf 127
Wind, distributing seeds 363;

distributing spores 356; effect

on form 313
Wings to fruits 364
Wintergreen, fruit 302, 304
Wheat, flower 258 ; geotropic

stem 200; seedling 118
Wood, in root 71; secondary 113

Xanthium, fruit 367

Xerophytes 311, 318
Xylem bundles, of root 72; sec
ondary 109

Yarrow, inflorescence 257

Yeast, beer 40

Yew ovule and fruit 239

Zamia, flower 233
Zea, stem bundles 107
Zoospores 147, 212
Zygnema 20, 401

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