Plants; a text-book of botany

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TWENTIETH CENTURY TEXT-BOOKS

EDITED BY
A. F. NIGHTINGALE, Pu. D.
SUPERINTENDENT OF HIGH SCHOOLS, CHICAGO
AND
CHARLES H. THURBER, A. M.

ASSOCIATE PROFESSOR OF PEDAGOGY IN THE UNIVERSITY
OF CHICAGO

TWENTIETH CENTURY TEXT-BOOKS

gd Oe ts Me

A TEXT-BOOK OF BOTANY

BY
JOHN M. COULTER, A.M., Pu. D.

HEAD OF DEPARTMENT OF BOTANY
UNIVERSITY OF CHICAGO

NEW YORK
D. APPLETON AND COMPANY
1900

(@
GRY]
CO

|4 00

CopyRiGHT, 1899
By D. APPLETON AND COMPANY

Citi)

Pipe NES
A TEXT-BOOK OF BOTANY

PREFATORY NOTE

AutHoven Plant Relations and Plant Structures have
been prepared as independent volumes, chiefly to meet the
needs of those schools which can give but one half year to
Botany, they form together a natural introduction to the
science. With this in view, the simple title Plants seems
suitable, with the understanding that this volume is an
introduction to the study of plants.

. Either part of this combined volume may be used first,
according to the views or needs of the teacher. In many
cases it may be wise not to observe the order of the book,
but to organize laboratory work as seems best, and to assign
the appropriate readings wherever they may occur in the
volume. The author isa stickler for independent teaching,
and would not presume to prescribe an order or a method
for teachers. His purpose is simply to offer those facts and
suggestions which may be helpful to them in organizing
and presenting their work. He would urge that intelligent
contact with plants is the essential thing; that a clear
understanding of a few large facts is better than the collec-
tion of numerous small ones; and that “ getting through”
should never sacrifice the leisure needed for digestion.

The two parts of this work are indexed separately, and
references to indexes are to be made at the end of each part.

JouHn M. Counter.

Tue University or Cutcaco, November, 1899.

TWENTIETH CENTURY TEXT-BOOKS

PLANT RELATIONS

A FIRST BOOK OF BOTANY

BY
JOHN M. COULTER, A.M., Px.D.

HEAD PROFESSOR OF BOTANY
UNIVERSITY OF CHICAGO

NEW YORK
D. APPLETON AND COMPANY

1900

COPYRIGHT, 1899,
By D. APPLETON AND COMPANY.

PREFACE,

THE methods of teaching botany in secondary schools
are very diverse, and in so far as they express the experience
of successful teachers, they are worthy of careful considera-
tion. As the overwhelming factor in successful teaching
is the teacher, methods are of secondary importance, and
may well vary. It is the purpose of the present work to
contribute another suggestion as to the method of teach-
ing botany in secondary schools. The author does not
intend to criticise other methods of teaching, for each
teacher has his own best method, but it may be well to
state the principles which underlhe the preparation of this
work,

The botany is divided into two parts, each representing
work for half a year. The two books are independent,
and opinions may differ as to which should precede. The
first book, herewith presented, is dominated by Ecology,
and also contains certain fundamentals of Physiology that
are naturally suggested. The second book will be domi-
nated by Morphology, but plant structure, function, and
classification will be developed together in an attempt to
trace the evolution of the plant kingdom. In the judg-
ment of the author Ecology should precede Morphology,
but this order brings to Ecology no knowledge of plant
structures and plant groups, which is of course unfortu-
nate. The advantages which seem to overbalance this dis-
advantage are as follows:

1. The study of the most evident life-relations of

plants gives a proper conception of the place of plants in
1*

vi PREFACE.

nature, a fitting background for subsequent more detailed
studies.

2. Such a view of the plant kingdom is certainly of the
most permanent value to those who can give but a half
year to botany, for the large problems of Ecology are con-
stantly presented in subsequent experience, when details
of structure would be forgotten.

3. The work in Ecology herein suggested demands Lht-
tle or no use of the compound microscope, an instrument
il adapted to first contacts with nature.

The second book will demand the use of the compound
microscope, and those schools which possess such an equip-
ment may prefer to use that part first or exclusively.

In reference to the use of this part something should
be said, although such cautions are reiterated in almost
every recent publication. .A separate pamphlet containing
“Suggestions to Teachers” who use this book has been
prepared, but a few general statements may be made here.
This book is intended to present a connected, readable
account of some of the fundamental facts of botany, and
may serve to give a certain amount of information. If it
performs no other service in the schools, however, its pur-
pose will be defeated. It is entirely too compact for any
such use, for great subjects, which should involve a large
amount of observation, are often merely suggested. It is
intended to serve as a supplemeut to three far more im-
portant factors: (1) the teacher, who must amplify and
suggest at every point; (2) the laboratory, which must
bring the pupil face to face with plants and their strue-
tures; (3) field-work, which must relate the facts observed
in the laboratory to their actual place in nature, and must
bring new facts to notice which can be observed nowhere
else. Taking the results obtained from these three fac-
tors, the book seeks to organize them, and to suggest
explanations. It seeks to do this in two ways (1) by
means of the tect, which is intended to be clear and un-

PREFACE. vii

technical, but compact ; (2) dy means of the illustrations,
which must be studied as carefully as the text, as they are
only second in importance to the actual material. Espe-
cially is this true in reference to the landscapes, many of
which cannot be made a part of experience.

Thanks are due to various members of the botanical
staff of the University, who have been of great service in
offering suggestions and in preparing illustrations. In
this first book I would especially acknowledge the aid of
Professor Charles R. Barnes and Dr. Henry C. Cowles.

The professional botanist who may critically examine
this first book knows that Ecology is still a mass of incho-
ate facts, concerning which we may be said to be making
preliminary guesses. It seems to be true, nevertheless,
that these facts represent the things best adapted for pres-
entation in elementary work. The author has been com-
pelled to depend upon the writings of Warming and of
Kerner for this fundamental material. From the work of
the latter, and from the recent splendid volume of Schim-
per, most useful illustrations have been obtained. The
number of original illustrations is large, but those obtained
elsewhere are properly credited.

Joun M. COULTER.
Tae University oF Curcaco, /ay, 1899.

CONTENTS.

CHAPTER, PAGE.
I.—INTRODUCTION . é : : ‘ , 1
TI.—FouiaGr LEAVES: THE LIGHT-RELATION : 6

If{]..—FoulaGr LEAVES: FuNcTION, STRUCTURE, AND PROTECTION 23

IV.—Snoots 53
V.—Roors 80
VI.—REPRODUCTIVE ORGANS 109
VIT.—FLoweERS AND INSECTS 123
VIIL.—AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS 188
IX.—THE STRUGGLE FOR EXISTENCE 142
X.—THE NUTRITION OF PLANTS 149
XI.—PLANt’ SOCIETIES: ECOLOGICAL FACTORS ‘ 162
ATI.—HypRopPHYTE SOCIETIES : 170
XIII.—XeEROPHYTE SOCIETIES g 193
NIV.—MesopoHyre sSocreTIES . 230
XV.—HALOPHYTE SOCIETIES : 3 249

InDEX : ) ‘

BOTANY
PART I.—PLANT RELATIONS

CHAPTER I.
INTRODUCTION.

1. General relations.—Plants form the natural covering
of the earth’s surface. ‘So generally is this true that a land
surface without plants seems remarkable. Not only do
plants cover the land, but they abound in waters as well,
both fresh and salt waters. They are wonderfully varied in
size, ranging from huge trees to forms so minute that the
microscope must be used to discover them. They are also
exceedingly variable in form, as may be seen by comparing
trees, lilies, ferns, mosses, mushrooms. lichens, and the
green thready growths (a/g@) found in water.

2. Plant societies—One of the most noticeable facts in
reference to plants is that they do not form a monotonous
covering for the earth’s surface, but that there are forests in
one place, thickets in another, meadows in another, swamp
growths in another, ete. In this way the general appear-
ance of vegetation is exceedingly varied, and each appear-
ance tells of certain conditions of hving. These groups of
plants living together in similar conditions, as trees and
other plants ina forest, or grasses and other plants in a
meadow, are known as plunt societies, These societies are as

2 PLANT RELATIONS.

numerous as are the conditions of living, and it may be said
that each society has its own special regulations, which ad-
mit certain plants and exclude others. The study of plant
societies, to determine their conditions of living, is one of
the chief purposes of botanical field work.

3. Plants as living things—Before engaging in a study
of societies, however, one must discover in a general way
how the individual plant lives, for the plant covering of the
earth’s surface is a living one, and plants must always be
thought of as living and at work. They are as much alive
as are animals, and so far as mere living is concerned they
live in much the same way. Nor must it be supposed that
animals move and plants do not, for while more animals than
plants have the power of moving from place to place, some
plants have this power, and those that do not can move cer-
tain parts. The more we know of living things the more is
it evident that life processes are alike in them all, whether
plants or animals. In fact, there are some living things
about which we are uncertain whether to regard them as
plants or animals.

4, The plant body.—Every plant has a body, which may
be alike throughout or may be made up of a number of
different parts. When the green thready plants (a/g@), so
common in fresh water, are examined, the body looks like
a simple thread, without any special parts ; but the body of
a lily is made up of such dissimilar parts us root, stem,
leaf, and flower (see Figs. 75, 144, 155, 168). The plant
without these special parts is said to be stmple, the plant
with them is called complex. The siniple plant lives in
the same way and does the same kind of work, so far as
living is concerned, as docs the complex plant. The differ-
ence is that in the case of the simple plant its whole body
does every kind of work; while in the complex plant
different kinds of work are done by different regions of the
body, and these regions come to look unlike when differ-
ent shapes are better suited to different work, as in the

INTRODUCTION. 3

case of a leaf and a root, two regions of the body doing
different kinds of work.

5. Plant organs—These regions of the plant body thus
set apart for special purposes are called organs. The sim-
plest of plants, therefore, do not have distinct organs,
while the complex plants may have several kinds of organs.
All plants are not either very simple or very complex, but
beginning with the simplest plants one may pass to others
not quite so simple, then to others more complex, and so
on gradually until the most complex forms are reached.
This process of becoming more and more complex is known
as differentiation, which simply means the setting apart of
different regions of the body to do different kinds of work.
The advantage of this to the plant becomes plain by using
the common illustration of the difference between a tribe
of savages and a civilized community. The savages all do
the same things, and each savage does everything. In the
civilized community some of the members are farmers,
others bakers, others tailors, others butchers, etc. This is
what is known as “ division of labor,” and one great advan-
tage it has is that every kind of work is better done. Ditf-
ferentiation of organs in a plant means to the plant just
what division of labor means to the community ; it results
in more work, and better work, and new kinds of work.
The very simple plant resembles the savage tribe, the com-
plex plant resembles the civilized community. It must be
understood, however, that in the case of plants the differ-
entiation referred to is one of organs and not of individuals.

6. Plant functions—Whether plants have many organs,
or few organs, or no organs, it should be remembered that
they are all at work, and are all doing the same essential
things. Although many different kinds of work are being
carried on by plants, they may all be put under two heads,
nutrition and reproduction. Every plant, whether simple
or complex, must care for two things: (1) its own support
(nutrition), and (2) the production of other plants like

4 PLANT RELATIONS.

itself (reproduction). To the great work of nutrition many
kinds of work contribute, and the same is true of repro-
duction. Nutrition and reproduction, however, are the
two primary kinds of work, and it is interesting to note
that the first advance in the differentiation of a simple
plant body is to separate the nutritive and reproductive
regions. In the complex plants there are nutritive organs
and reproductive organs ; by which is meant that there are
distinct organs which specially contribute to the work of
nutrition, and others which are specially concerned with
the work of reproduction. The different kinds of work are
conveniently spoken of as functions, each organ having one
or more functions.

7. Life-relations—In its nutritive and reproductive work
the plant is very dependent upon its surroundings. It
must receive material from the outside and get rid of waste
material ; and it must leave its offspring in as favorable
conditions for living as possible. As a consequence, every
organ holds a definite relation to something outside of it-
self, known as its life-relation. For example, green leaves
are definitely related to light, many roots are related to
soil, certain plants are related to abundant water. some
plants are related to other plants or animals (living as
parasites), etc. A plant with several organs, therefore,
may hold a great variety of life-relations, and it is quite a
complex problem for such a plant to adjust all of its parts
properly to their necessary relations. The study of the
life-relations of plants is a division of Botany known as
Ecology, and presents to us many of the most important
problems of plant life.

It must not be supposed that any plant or organ holds
a perfectly simple life-relation, for it is affected hy a great
variety of things. A root, for instance, is affected by light,
gravity, moisture, soil material, contact, etc. Every or-
gan, therefore, must adjust itself to a very complex set of
life-relations, and a plant with several organs has so many

INTRODUCTION. 5

delicate adjustments to care for that it is really impossi-
ble, as yet, for us to explain why ull of its parts are placed
just as they are. In the beginning of the study of plants,
only some of the most prominent functions and life-rela-
tions can be considered. In order to do this, it seems bet-
ter to begin with single organs, and afterwards these can
be put together in the construction of the whole plant.

CHAPTER II.
FOLIAGE LEAVES: THE LIGHT-RELATION.

8. Definition.—A foliage leaf is the ordinary green leaf,
and is avery important organ in connection with the work
of nutrition. It must not be thought that the work done by
such a leaf cannot be done by green plants which have no
leaves, as the algw, for example. A leaf is simply an or-
gan set apart to do such work better. In studying the
work of a leaf, therefore, we have certain kinds of work
set apart more distinctly than if they were confused with
other kinds. For this reason the leaf is selected as an in-
troduction to some of the important work carried on by
plants, but it must not be forgotten that a plant does not
need leaves to do this work ; they simply enable it to work
more effectively.

9. Position It is easily observed that foliage leaves
grow only upon stems, and that the stems which bear them
always expose them to light; that is, such leaves are aerial
rather than subterranean (see Figs. 1, 75,169). Many
stems grow underground, and such stems either bear no
foliage leaves, or are so placed that the foliage leaves are
sent above the surface, as in most ferns and many plants of
the early spring (see Figs. £5, 46, 144).

10. Color.—Another fact to be observed is that foliage
leaves have a characteristic green color, a color so universal
that it has come to be associated with plants, and espe-
cially with leaves. It is also evident that this green color
holds some necessary relation to light, for the leaves of
plants grown in the dark, as potatoes sprouting in a cellar,

FOLIAGK LEAVES: THE LIGHT-RELA'TION. 7

do not develop this color. Even when leaves have devel-
oped the green color they lose it if deprived of light, as is
shown by the process of blanching cclery, and by the effect
on the color of grass if a board has lain upon it for
some time. It seems plain, therefore, that the green color
found in working foliage leaves depends upon light for its
existence.

We conclude that at least one of the exseutial life-rela-
tions of a foliage leaf is what may be called the light-rela-
fion. his seems to explain satisfactorily why such leaves
are not developed in a subterranean position, as are many
stems and most roots, aud why plants which produce them
do not grow in the dark, asin caverns. The sume green,
and hence the sume light-relation, is observed in other
parts of the plant as well, and in plants without leaves, the
only difference being that leaves display it most conspicu-
ously. Another indication that the green color is con-
nected with light may be obtained from the fact that it is
found only in the surface region of plants. If one cuts
across a living twig or into a cactus body, the green color
will be seen only in the outer part of the section. The con-
clusion is that the leaf is a special organ for the lght-re-
lation. Plants sometimes grow in such situations that it
would be unsafe for them to display leaves, or at least large
leaves. Insuch a case the work of the leaves can be thrown
upon the stem. .\ notable illustration of this is the cactus
plant, which produces no foliage leaves, hut whose stem dis-
plays the leaf color.

11. An expanded organ.—Another general fact in refer-
ence to the foliage leaf is that in most cases it is an expanded
organ. This means that it has a great amount of surface
exposed in comparison with its mass. As this form is of
such common occurrence it is safe to conclude that it is in
some way related to the work of the leaf, and that whatever
work the leaf doves demands an exposure of surface rather

than thickness of body. It is but another step to say that
2

8 PLANT RELATIONS.

the amount of work un active leaf can do will depend in
part upon the amount of surface it exposes.

THE LIGHT-RELATION,

12. The general relation —'The ordinary position of the
foliage leaf is more or less horizontal. This enables it to
receive the direct rays of light upon its wpper surface. In

Fig. 1. The leaves of this plant (Wiews) are
in general horizontal, but it will be seen
that the lower ones are directed down-
ward, and that the leaves hecome more
horizontal as the stem is ascended. It
will also be seen that the leaves are so
broad that there are few vertical rows.

this way more rays of
light strike the leaf sur-
face than if it stood ob-
liquely or on edge. It is
often said that leaf blades
are so directed that the
flat surface is at right
angles to the ieident
rays of light. While this
may be true of horizon-
tal leaves in a_ general
way, the observation of
almost any plant will
show that it is a very
general statement, to
which there are numerous
exceptions (see Fig. 1).
Leaves must be arranged
to receive as much light
as possible to help in
their work, but too much
light will destroy the
green substance (chloro-
phyll), which is essential
to the work. The adjust-
ment to light, therefore,
is a delicate one, for
there must be just enough

FOLIAGE LEAVES: THE LIGHT-RELATION. 9

and not too much. The danger from too much light is
not the same in the case of all leaves, even on the same
plant, for some are more shaded than others. Leaves also
have « way of protecting themselves from too intense light
by their structure, rather than by a change in their posi-
tion. It is evident, therefore, that the exact position which
any particular leaf holds in relation to ight depends upon
many circumstances, and cannot be covered by a general
rule, except that it seeks to get all the light it can without
danger.

13. Fixed position.— Leaves differ very much in the power
of adjusting their position to the direction of the light.

Fie, 2. The day and night positions of the leaves of a member (Amicia) of the pea
family.—After STRASBURGER.

Most leaves when fully grown are in a fixed position and
cannot change it, however unfavorable 1t may preye to he,
except as they are blown about. Such leaves are said to
have fized light positions. This position is determined by
the light conditions that prevailed while the leaf was grow-
ing and able to adjust itself. If these conditions continue,
the resulting fixed position represents the best one that can
be secured under the circumstances. The leaf may not
receive the rays of light directly throughout the whole
period of daylight, but its fixed position is such that it
probably receives more light than it would in any other
position that it could secure.

10 PLANT RELATIONS.

14. Motile leaves—There are leaves, however, which
have no fixed light position, but are so constructed that
they can shift their position as the direction of the light
changes. Such leaves are not in the same position in the
afternoon as in the
forenoon, and their
night position may be
very different from
either (see Figs. 2, 3,
3b, £). Some of the
common house plants
show this power. In
the cause of the com-
mon Qralis the night

Fie. 3a. The day position of the leaves of redbud position of the leaves
(Cervix). —After ARTHUR. is remarkably different

from the position in light.
If such a plant is exposed
to the light ina window and
the positions of the leaves
noted, and then turned
half way around, so as to
bring the other side to the
light, the leaves may be
observed to adjust them-
selves gradually to the
changed light-relations. Fic. 3b, The night position of the leaves
15. Compass plants.—.\ of redbud (Cervés),—After ARTHUR.

striking illustration of a

special light position is found in the so-called * compass
plants.” The best known of these plants is the rosin-weed
of the prairie region. Growing in situations exposed te
intense light, the leaves are turned edeewise, the flat faces
being turned away from the intense rays of midday, and
directed towards the rays of less intensity ; that is, those of

FOLIAGE LEAVES: THE LIGHT-RELATION. 11

.
bY
N
N
\
N
\¥

we
ST” y

Fig. 4. Two sensitive plants, showing the motile Jeaves. The plant to the left has its
leaves and numerous leaflets expanded ; the one to the right shows the leaflets
folded together and the leaves drooping.— After KERNER,

the morning and evening (see Fig. 165). As a result, the
apex of the leaf points in a general north or south direction.
It is a significant fact that when the plant grows in shaded
places the leaves do not assume any such position. It
seems evident, therefore. that the position has something
to do with avoiding the danger of too intense light. It

12 PLANT RELATIONS.

must not be supposed
that there is any ac-
curacy in the north or
south direction, as the
edgewise position
seems to be the signifi-
cant one. In the ros-
in-weed probably the
north and south direc-
tion is the prevailing
one; but in the prickly
lettuce, a very common
weed of waste grounds,
and one of the most
striking of the compass
plants, the edgewise
position is frequently
assumed without any
special reference to the
north or south direc-
tion of the apex (see
Fig. 5).

16. Heliotropism.—
The influence of light
upon the positions of
leaves and other or-
gans is known as /eli-
otropism, and it is one
of the most important
of those external influ-
ences to which plant
organs respond (see
Figs. 6, 43).

Fie, 5. The common prickly lettuce (Lactuca It should be under-

Scariola), showing the leaves standing edge- : ‘ :
wise, and in a general north and south plane, stood cl early that. this

—After AnrHUR and MacDouea. is but a slight glimpse

FOLIAGE LEAVES: THE LIGHT-RELATION, 13

Tia. 6. These plants are growing near a window. It will be noticed that the stems
bend strongly towards the light, and that the leaves face the light.

of the most obvious relations of foliage leaves to light, and
that the important part which heliotropism plays, not only
in connection with foliage leaves, but also in connection
with other plant organs, is one of the most important and
extensive subjects of plant physiology.

RELATION OF LEAVES TO ONE ANOTHER.

A. On erect stems.

In view of what has been said, it would seem that the
position of foliage leaves on the stem, and their relation to
one another, must be determined to some extent by the
necessity of a favorable light-relation. It is apparent that
the conditions of the problem are not the same for an erect
as for a horizontal stem.

17. Relation of breadth to number of vertical rows.—
Upon an erect stem it is observed that the leaves are usu-

14 PLANT RELATIONS.

ally arranged in a definite number of vertical rows. It is
to the advantage of the plant for these leaves to shade one
another as little as possible. Therefore, the narrower the
leaves, the more numerous may be the vertical rows (see
Figs. 7, 8); and
the broader the
leaves the fewer
the vertical rows
(xee Fig. 1). A
relation exists,
therefore, be-
tween the breadth
of leaves and the
number of verti-
cal rows, and the
meaning of this
becomes plain
when the light-re-
lation ix consid-
ered.

18. Relation of
length to the dis-
tance between
Fic. 7. An Easter lily, showing narrow leaves and leaves of the same

numerous vertical rows. row.—The leaves

in a vertical row

may he close together or far apart. If they should be close
together and at the same time long, it is evident that they
will shade each other considerably, as the light cannot well
strike in between them and reach the surface of the lower
leaf. Therefore, the closer together the leaves of a verti-
cal row, the shorter are the leaves; and the farther apart
the leaves of a row, the longer may they be. Short leaves
permit the light to strike hetween them cyen if they are
close together on the stem; and long leaves permit the
same thing only when they are far apart on the stem, A

FOLIAGE LEAVES: THE LIGHT-RELATION. 15

relation is to be observed, therefore, between the length
of leaves and their distance apart in the same vertical row.

The same kind of relation cun be observed in reference
to the breadth of leaves, for if leaves are not only short but
narrow they can stand very close together. It is thus seen
that the length and breadth of leaves, the number of ver-
tical rows on the stem, and the distance between the leaves

Fig. 8. A dragon-tree, showing narrow leaves extending in all directivus, and numer-
ous vertical rows.

of any row, all have to do with the light-relation and are
answers to the problem of shading.

19. Elongation of the lower petioles—There is still
another common arrangement by which an effective light-
relation is secured by leaves which are broad and placed
close together on the stem. In such a case the stalks
(petioles) of the lower leaves become longer than those
above and thus thrust their blades beyond the shadow (sce
Fig. 9). It may be noticed that it is very common to

16 PLANT RELATIONS.

find the lowest leaves of a plant the largest and with the
longest petioles, even when the leaves are not very close
together on the stem.

It must not be supposed that by any of these devices
shading is absolutely avoided. This is often impossible and
sometimes undesirable. It simply means that by these

Fie. 9. A plant (Sein(paulic) with the lower petioles elongated, thrusting the blades
beyond the shadow of the upper leaves. A loose rosette.

arrangements the most favorable light-relation is sought by
avoiding too great shading.

20. Direction of leaves—Not only is the position on the
stem to be observed, but the direction of leaves often shows
a definite relation to light. It is a very common thing to
find a plant with a cluster of comparatively large leaves at
or near the lase, where they are in no danger of shading
other leaves, and with the stem leaves gradually becoming

FOLIAGE LEAVES: THE LIGHT-RELATION. 17

smaller and less horizontal toward the apex of the stem
(see Figs. 10, 13). The common shepherd's purse and the
mullein may be taken as illustrations. By this arrange-
ment all the leaves are very
completely exposed to the
light.

21. The rosette habit.—
The habit of producing a
cluster or rosette of leaves
at the base of the stem is
called the rosette habit.
Often this rosette of leaves
at the hase, frequently lying
flat on the ground or on the
rocks, includes the only fo-
liage leaves the plant pro-
duces. It is evident that a
rosette, in which the leaves
must overlap one another
more or less, is not a very
favorable light arrange-
ment, and therefore it must
be that something is being

Fie. 10. A plant (Echereria) with fleshy

provided for besides the leaves, showing large horizontal ones
light-relation (see Figs. 1a; at base, endo thsits becomine, smaller

‘ . feo ‘ and more directed upward as the
12, 13). What this is will ators is-necerdad.

appear later. but even in

this comparatively unfavorable light arrangement, there is
evident adjustment to secure the most ight possible under
the circumstances. The lowest leaves of the rosette are
the longest, and the upper (or inner) ones become gradu-
ally shorter, so that all the leaves have at least a part
of the surface exposed to light. The overlapped base of
such leaves is not expanded as much as the exposed apex,
and hence they are mostly narrowed at the base and broad
at the apex. This narrowing at the base is sometimes

18 PLANT RELATIONS.

carried so far that most of the part which is covered is
but a stem (petiole) for the upper part (blade) which is
exposed.

In many plants which do not form close rosettes a gen-

Hie, 11. A eroup of live-for-evers, illustrating the rosette habit and the light-relation.
In the rosettes it will be observed how the leaves are fitted together and diminish
in size inwards, so that excessive shading is avoided. The individual leaves also
become narrower where they overlap, antl are broadest where they are exposed to
light. In the background is a plant showing leaves in very definite vertical rows.

eral rosette arrangement of the leaves may be observed by
looking down upon them from aboye (sce Fig. 9), ax in some
of the early buttercups which are so low that the large
leaves would seriously shade one another, except that the
lower leaves have longer petioles than the upper, and so
reach beyond the shadow.

FOLIAGE LEAVES: THE LIGHT-RELATION. 19

Fic. 12. Two clumps of roscttes of the house leek (Semperrirum), the one to the
right showing the compact winter condition, the one to the left with rosettes more
open after being kept indoors for several days.

22. Branched leaves.—Another notuble feature of foliage
leaves, which has something to do with the light-relation,
is that on some plants the blade does not consist of one
piece, but is lobed or even broken up into separate pieces.
When the divisions are distinct they are called leaflets, and
every gradation in leaves can be found, from distinct leaf-
lets to lobed leaves, toothed leaves, and finally those whose
margins are not indented at all (ev/irc). This difference
in leaves probably has
more important rea-
sons than the light-
relation, but its sig-
nificance may be ob-
served in this connec-
tion. In those plants
whose leaves are un-
divided, the leaves
generally either di-
minish in size toward
the top of the stem,
or the lower ones de- Fie. 18. The leaves of a bellflower (Campanula),

velop longer petioles. showing the rosette arrangement. The lower

Bs tg Peri petioles are successively longer, carrying their
In this Case the Celt blades beyoud the shadow of the blades above.
eral outline of the —After Kernen,

dangerous shading, It will be seen that the larger blades or less-branched leaves
are towards the bottom of the group,

FOLIAGE LEAVES: THE LIGHT-RELATION. 21

plant is conical, a form very common in herbs with entire
or nearly entire leaves. In plants whose leaf blades are
broken up into leaflets (compound or branched leaves),
however, no such diminution in size toward the top of the
stem is necessary (see Fig. 17), though it may frequently

Be x %
2 y at

Fig. 15. A plant showing much-branched leaves, which occur in great profusion with-
out cutting off the light from one another.

occur. When a broad blade is broken up into leaflets
the danger of shading is very much less, as the light can
strike through between the upper leaflets and reach the
leaflets below. On the lower leaves there will be splotches
of light and shadow, but they will shift throughout the
day, so that probably a large part of the leaf will receive
light at some time during the day (see Fig. 14). The

22 PLANT RELATIONS.

general outline of such a plant, therefore, is usually not
conical, as in-the other case, but cylindrical (sce Figs. 4,
15, 16, 22, 45, 83, 96, 155, 162, 169 for branched leaves).
Many other factors enter into the light-relation of foli-
age leaves upon erect stems, but those given may suggest

Fie. 16. A cycad, showing much-branched leaves and palm-like habit.

observation in this direction, and serve to show that the
arrangement of leaves in reference to light depends upon
many things, and is by no means a fixed and indifferent
thing. The study of any growing plant in reference to this
one relation presents a multitude of problems to those who
know how to observe.

B. On horizontal stems.

23. Examples of horizontal stems, that is. stems exposed
on one side to the direct light, will be found in the ease of
many branches of trees, stems prostrate on the ground, and

FOLIAGE LEAVES: THE LIGHT-RELATION. 23

stems against a support, as the ivies.

It is only necessary

to notice how the leaves are adjusted to Lght on an erect

stem, und then to bend the
stem into a horizontal posi-
tion or against a support, to
realize how unfavorable the
sume arrangement would
be. and how many new ad-
justments must be made.
The leaf blades must. all be
brought to the light side of
the stem, so far as possible,
and those that belong to
the lower side of the stem
must be fitted imto the
spaces left by the leaves
which belong to the upper
This may be brought
about by the twisting of
the stem, the twisting of
the petioles, the bending of
the blade on the petiole,
the lengthening of petioles,
or in some other way.
Every horizontal stem has
its own special problems of
leaf adjustment which may
be observed (see Figs. 18,
50).

Sometimes there is not
space enough for the full
development of every blade,
and smaller ones are fitted

side.

into the spaces left by the larger ones (see Fig. 21).

Fig. 17.
lobed leaves, the rising of the petioles
to adjust the blades to light, and the
general cylindrical habit.

A chrysanthemum, showing

This

sometimes resultsin what are called unequally paired leaves,
where opposite leayes develop one large blade and one small

24 PLANT RELATIONS.

one. Perhaps the most complete fitting together of leaves
is found in certain ivies, where a regular layer of angular
interlocking leaves is formed, the leaves fitting together like

as SB TRL REL EE — — ss eee

Fie. 18. A plant (Pellionia) with drooping stems, showing how the leaves are all
brought to the lighted side and fitted together.

the pieces of a mosaic. In fact such an arrangement is
known as the mosate arrangement, and involves such an
amount of twisting, displacement, elongation of petioles,

“SUIPLYS ploav 07 JYIA50) payy are Lay] MOY SUTMOYS ‘saaval BIUOseg Jo o1vsoUl Y “EL “OMT

26 PLANT RELATIONS.

Fre. 20. A spray of maple, showing the adjustment of the leaves in size and position
of blades and length of petioles to secure exposure to light on « horizontal stem.—
After KEnNER.

etc., as to give ample evidence of the effort put forth by
plants to secure a favorable light-relation for their foliage

= SASS Ss ~ = =
Fig. 21. Two plants showing adjustment of Jeaves on a horizontal stem. The plant
to the left is nightshade, in which small blades are fitted into spaces left by the
large ones. The plant to the right ix Sclaginella, in which small leaves are dis-
tributed along the sides of the stem, and oticrs are displayed along the upper sur-
face.—After Kerner.

FOLIAGE LEAVES: THE LIGHT-RELATION. OW.

leaves (see Figs. 19, 22). In the case of ordinary shade trees
every direction of branch may be found. and the resulting
adjustment of leaves noted (see Fig. 20).

Looking up into a tree in full foliage, it will be noticed
that the horizontal branches are comparatively bare be-

Fic. 22. A mosaic of fern (Adiantum) leaflets.

neath, while the leaf blades have been carried to the upper
side and have assumed a mosaic arrangement.

Sprays of maidenhair fern (see Fig. 22) show a remark-
able amount of adjustment of the leaflets to the light side.
Another group of fern-plants, known as club-mosses, has
horizontal stems clothed with numerous very small leaves.
These leaves may he seen taking advantage of all the space
on the lighted side (see Fig. 21).

CHAPTER III.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, AND PROTEO-
TION.

A. Functions of foliage leaves.

24, Functions in general We have observed that foliage
leaves are light-related organs, and that this relation is an
important one is evident from the various kinds of adjust-
ment used to secure it. We infer, therefore, that for some
important function of these leaves light is necessary. It
would be hasty to suppose that light is necessary for every
kind of work done by a foliage leaf, for some forms of work
might be carried on by the leaf that light neither helps nor
hinders. Foliage leaves are not confined to one function,
but are concerned in « variety of processes, all of which
have to do with the great work of nutrition. Among the
variety of functions which belong to foliage leaves some of
the most important may he selected for mention. It will
be possible to do little more than indicate these functions
until the plant with all its organs is considered, but some
evidence can be obtained that various processes are taking
place in the foliage leaf.

25. Photosynthesis—The most important function of the
foliage leaf may be detected by a simple experiment. If
an active leaf or a water plant be submerged in water ina
glass vessel, and exposed to the hght, bubbles may be seen
coming from the leaf surface and rising through the water
(see Fig. 23). The water is merely a device by which the
bubbles of gas may be seen. If the leaf is very active the

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETc. 29

bubbles are numerous. That this activity holds a definite
relation to light may be proved by gradually removing the
vessel containing the leaf from the light. As the light
diminishes the bubbles diminish in number, and when a

Fig. 23. An experiment to illustrate the giving off of oxygen in the process of photo.
synthesis.

certain amount of darkness has been reached the bubbles
will cease entirely. If now the vessel be brought back
gradually into the light. the bubbles will reappear, more
and more numerous as the light increases. That this gas
being given off is oxygen may be proved by collecting the

30 PLANT RELATIONS.

bubbles in a test tube, as in an ordinary chemical experi-
ment for collecting gas over water, and testing it in the
usual way.

Some very important things are learned by this experi-
ment. It is evident that some process is going on within
the leaf which needs light and which results in giving off
oxygen. It is further evident that as oxygen is eliminated,
the process indicated is dealing with substances which
contain more oxygen than is needed. The amount of
oxygen given off may be taken as the measure of the work.
The more oxygen, the more work; and, as we have observed,
the more light, the more oxygen; and no light, no oxygen.
Therefore, light must be essential to the work of which the
elimination of oxygen is an external indication. That this
process, whatever it may be, is so essentially related to
light, suggests the idea that it is the special process which
demands that the leaf shall be a light-related organ. If so,
it is a dominating kind of work, as it chiefly determines
the life-relations of foliage leaves.

The process thus indicated is known as photosynthesis,
and the name suggests that it has to do with the arrange-
ment of material with the help of ight. It is really a pro-
cess of food manufacture, by which raw materials are made
into plant food. This process is an exceedingly important
one, for upon it depend the lives of all plants and animals.
The foliage leaves may be considered, therefore, as spectu/
organs of photosynthesis. They are special organs, not ex-
clusive organs, forany green tissue, whether on stem or fruit
or any part of the plant body, may do the same work. It
is at once apparent, also, that during the night the process
of photosynthesis is not going on, wnd therefore during the
night oxygen is not being given off.

Another part of this process is not so easily observed, but
is so closely related to the elimination of oxygen that it
must be mentioned. Carbon dioxide occurs in the air to
which the foliage leaves are exposed. It is given off from

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 81

our lungs in breathing, and also comes off from burning
wood or coal. It is a common waste product, being a com-
bination of carbon and oxygen so intimate that the two
elements are separated from one another with great dif-
ficulty. During the process of photosynthesis it has been
discovered that carbon dioxide is being absorbed from the
air by the leaves. As this gas is absorbed chiefly by green
parts and in the light, in just the conditions in which oxy-
gen is being given off, it is natural to connect the two, and
to infer that the process of photosynthesis involves not only
the green color and the light, but also the absorption of
carbon dioxide and the elimination of oxygen.

When we observe that carbon dioxide is a combination
of carbon and oxygen, it seems reasonable to suppose that
the carbon and oxygen are separated from one another in
the plant, and that the carbon is retained and the oxygen
given back to the air. The process of photosynthesis may
be partially defined, therefore, as the breaking up of carbon
dioxide by the green parts of the plants in the presence of
light, the retention of the carbon, and the elimination of
the oxygen. The carbon retained is combined into real
plant food, in a way to be described later. We may con-
sider photosynthesis as the most important function of the
foliage leaf, of which the absorption of carbon dioxide and
the evolution of oxygen are external indications ; and that
light and chlorophyll are in some way essentially connected
with it.

26. Transpiration.—One of the easiest things to observe
in connection with a working leaf is the fact that it gives
off moisture. .A simple experiment may demonstrate this.
If a glass vessel (bell jar) be inverted over a small active
plant the moisture is seen to condense on the glass, and
even to trickle down the sides. A still more convenient way
to demonstrate this is to select a single vigorous leaf with
a good petiole ; pass the petiole through a perforated card-
board resting upon a tumbler containing water, and invert

32 PLANT RELATIONS.

a second tumbler over the blade of the leaf, which projects
above the cardboard (see Fig. 24). It will be observed that
moisture given off from the surface of the working leaf is
condensed on the inner surface of the inverted tumbler.
The cardboard is to shut off evaporation from the water
in the lower tumbler.

When the amount of water given off by a single leaf is
noted, some vague idea may be formed as to the amount ot
moisture given off by a great mass of vegetation, such as a
meadow or a forest. It is evident that green plants at
work are contributing a very large amount of moisture to
the air in the form of water vapor, moisture which has been
absorbed by some region of the plant. The foliage leaf,
therefore, may be regarded as an organ of transpiration,
not that the leaves alone are engaged in transpiration, for
many parts of the plant do the same thing, but because the
foliage leaves are the chief seat of transpiration.

The important fact in connection with transpiration is
not that moisture is given off by active foliage leaves,
but that this escaping moisture is the external indication
of some work going on within the leaf. Transpiration,
therefore, may not be regarded so much as work, as the
result, and hence the indication of work. In case the
leaves are submerged, as is true of many plants, it is evi-
dent that transpiration is practically checked, for the
leaves are already bathed with water, and under such cir-
cumstances water vapor is not given off. The same is true
of green water plants without leaves (such as alge). It is
evident that under such circumstances leaf work must be
carried on without transpiration.

2%. Respiration ——.\nother kind of work also may be de-
tected in the foliage leaf, but not so easily described. In
fact it escaped the attention of hotanists long after they
had discovered photosynthesis and transpiration. Itis work
that goes on so long as the leaf is alive, never ceasing day
or night. The external indication of it is the absorption

Fra. 24. Experiment illustrating transpiration.

34 PLANT RELATIONS.

of oxygen and the giving out of carbon dioxide. It will be
noted at once that this is exactly the reverse of what takes
place in photosynthesis. During the day, therefore, carbon
dioxide and oxygen are both being absorbed and evolved.
It will also be noted that the taking in of oxygen and the
giving out of carbon dioxide is just the sort of exchange
which takes place in our own respiration. In fact this pro-
cess is also called respiration in plants. It does not depend
upon light, for it goes on in the dark. It does not depend
apon chlorophyll, for it goes on in plants and parts of plants
which are not green. It is not peculiar to leaves, but goes
on in every living part of the plant. A process which goes
on without interruption in all living plants and animals
must be very closely related to their living. We conclude,
therefore, that while photosynthesis is peculiar to green
plants, and only takes place in them when light is present,
respiration is necessary to all plants in all conditions, and
that when it ceases life must soon cease. The fact is,
respiration supplies the energy which enables the living
substance to work.

Once it was thought that plants differ from animals
in the fact that plants absorb carbon dioxide and give off
oxygen, while animals absorb oxygen and give off carbon
dioxide. Tt is seen now that there is no such difference,
but that respiration (absorption of oxygen and evolution of
carbon dioxide) is common to both plants and animals.
The difference is that green plants have the added work of
photosynthesis.

We may also call the foliage leaf, therefore, an organ of
respiration, because so much of such work is done hy it,
but it must be remembered that respiration is going on in
every living part of the plant.

This by no means completes the list of functions that
might he made out for foliage leaves, but it serves to
indicate both their peculiar work (photosynthesis) and
the fact that they are doing other kinds of work as well.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 85

B. Structure of foliage leaves.

28. Gross structure.—It is evident that the essential part
of a foliage leaf is its expanded portion or blade. Often the
leaf is all blade (sce Figs. 7,
8, 18) ; frequently there is a
longer or shorter leaf-stalk
(petiolv) which helps to put

ia
CUE
iegeaaey

sh
sy
:

QS

A

Fie. 25. Two types of leaf venation. The figure to the left is a leaf of Solomon’s
seal (Polygonatum), and shows the principal veins parallel, the very minute cross
veinlets being invisible to the naked cye, being a monocotyl type. The figure to
the right is a leaf of a willow, and shows netted veins, the main central vein (mid-
rib) sending out a series of parallel branches, which are connected with one another
by a network of veinlets, being a dicotyl type.—After ErrINGsHAUSEN.

the blade into better light-relation (see Figs. 1, 9,17, 20,
26); and sometimes there are little leaf-like appendayes (stip-
ules) on the petiole where it joins the stem, whose func-
tion is not always clear. Upon examining the blade it
is seen to consist of a green substance through which a

36 PLANT RELATIONS,

framework of veins is variously arranged. The large veins
which enter the blade send off smaller branches, and these
send off still smaller ones, until the smallest veinlets are

Fic. 26. A leaf of hawthorn, showing a short petiole, and
a broad toothed blade with a conspicuous network of
veins. Note the relation between the veins and the
tecth.— After SrRASBURGER.

invisible, and the
framework is a
close network of
branching veins.
This is plainly
shown bya ‘‘skel-
eton” leaf, one
which has been so
treated that all
the green sub-
stance has disap-
peared, and only
the network of
veinsremains. It
will be noticed
that in some
leaves the veins
and yeinlets are
very prominent,
in others only
the main veins
are prominent,
while in some it
is hard to detect
any veins (see
Figs. 25, 26).

20. Significance
of leaf veins,—It
is clear that the

framework of veins is doing at least two things for the
blade: (1) it mechanically supports the spread out green sub-
stance ; and (2) if conducts material to and from the green
substance. No complete is the network of veins that this

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 37

support and conduction are very perfect (see Fig. 27). It
is also clear that the green substance thus supported and
supplicd with material is the important part of the leaf, the
part that demands the light-relation, Study the various
plans of the vein systems in Figs. 3, 4, 13, 18, 19, 20, 21,

2d, 20, d1, 70, 76, 52, 83, 92, 161.

Hs
; ees guia

CONS

Fie. 27. A plant (Fittonia) whose leaves show a network of veins, and also an adjust-
ment to one another to form a mosaic.

30, Epidermis.—If a thick leaf be taken, such as that
of a hyacinth, it will be found possible to peel off from
its surface a delicate transparent skin (epidermis). This
epidermis completely covers the leaf, and generally shows
no green color. It is a protective covering, but at the same
time it must not completely shut off the green substance
beneath from the outside. It is found, therefore, that
three important parts of an ordinary foliage leaf are: (1)

38 PLANT RELATIONS.

a network of veins; (2) a green substance (mesophyll) in
the meshes of the network ; and (3) over all an epidermis.

31. Stomata.—If a compound microscope is used, some
very important additional facts may be discovered. The
thin, transparent epidermis is
found to be made up of a layer of
cells which fit closely together,
sometimes dovetailing with each
other. Curious openings in the
epidermis will also be discovered,
sometimes in very great numbers.
Guarding each opening are two
crescent-shaped cells, known as
Hi Ba alk oP eae guard-cells, and between them a

of Maranta, showing the Slit-like opening leads through the
interlocking walls, and a enidermis. The whole apparatus
stoma (s) with its two guard-,
cells. is known as a stoma (plural
stomata), Which really means
“mouth,” of which the guard-cells might he called the
lips (see Figs. 28, 29). Sometimes stomata are found only
on the under side of the leaf, sometimes only
on the upper side, and sometimes on both
sides.

The important fact about stomata is that
the guard-cclls can change their shape, and
so regulate the size of the opening. Itis not
certain just how the guard-cells change their
shape and just what stomata do for leaves.
They are often called ‘breathing pores,”
but the name is very inappropriate. Stomata Fi. 29. A single

: . ‘ stoma from the
are not peculiar to the epidermis of foliage epidermis of a
leaves, for they are found in the cpidermis lily leat, show-
of any green part, as stems, young fruit, ae on
ete. It is evident, therefore, that they hold of chlorophyl,
an important relation to green tissue which Tee
is covered by epidermis. Also, if we examine between,

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 39

foliage leaves and other green parts of plants which live
submerged in water, we find that the epidermis contains
no stomata. Therefore, stomata hold a definite relation
to green parts covered by epidermis only when this epider-
mis is exposed to the air.

It would seem that the stomata supply open passage-
ways for material from the green tissue through the epider-
mis to the air, vr from the air to the green tissue, or both.
It will be remembered. however, that quite a number of
substances are taken into the leaf and given out from it,
so that it is hard to determine whether the stomata are
specially for any one of these movements. For instance,
the leaf gives out moisture in transpiration, oxygen in
photosynthesis, and carbon dioxide in respiration ; while it
takes in carbon dioxide in photosynthesis, and oxygen in
respiration. It is thought stomata specially favor transpira-
tion, and, if so, “‘ breathing pores” is not a happy phrase,
for they certainly assist in the other exchanges.

32. Mesophyll.—If a cross-section be made of an ordi-
nary foliage leaf, such as that of a lily, the three leaf
regions can be secn in their proper relation to cach other.
Bounding the section above and below is the layer of trans-
parent epidermal cells. pierced here and there by stomata,
marked by their peculiar guard-cells. Between the epi-
dermal layers is the green tissue, known as the mesophyll.
made up of cells which contain numerous small green
bodies which give color to the whole leaf, and are known as
chlorophyll bodies oy chloroplasts.

The mesophyll cells are usually arranged differently in
the upper and lower regions of the leaf. In the upper
region the cells are elongated and stand upright, present-
ing their narrow ends to the upper leaf surface. forming
the palisade tissue. In the lower region the cells are irreg-
ular, and so loosely arranged as to leave passageways for air
between, forming the spongy tissue. The air spaces among
the cells communicate with one another, so that a system of

4

40 PLANT RELATIONS.

air chambers extends throughout the spongy mesophyll.
It is into this system of air chambers that the stomata
open, and so they are put into direct communication with
the mesophyll or working cells. The peculiar arrangement
of the upper mesophyll, to form the palisade tissue, has to
do with the fact that that surface of the leaf is exposed to
the direct rays of light. This light, so necessary to the
mesophyll, is also dangerous for at least two reasons. If

Oy st

Fig. 30. A section through the leaf of lily, showing upper epidermis (we), lower cpi-
dermis (Ze) with its stomata (sé), mesophyll (dotted cells) composed of the palisade
region (p) and the spongy region (sp) with air spaces among the cells, and two
veins (v) cut across.

the light is too intense it may destroy the chlorophyll, and
the heat may dry out the cells. By presenting only nar-
row ends to this direct light the cells are less exposed to
intense light and heat. Study Fig. 30.

33. Veins,—In the cross-section of the leaf there will
also be seen here and there, embedded in the mesophyll,
the cut ends of the veinlets, made up partly of thick-
walled cells, which hold the leaf in shape and conduet
material to and from the mesophyll (see lig. 30).

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 41

C. Leuf protection.

34. Need of protection—Such an important organ as
the leaf, with its delicate active cells well displayed, is ex-
posed to numerous dangers. Chief among these dangers
are intense light, drought, and cold. ATI leaves are not
exposed to these dangers. For example, plants which grow
in the shade are not in danger from intense light ; many

rater plants are not in danger
from drought ; and plants of
the tropical lowlands are in no

“Zs.

Fig. 31. Sections through leaves of the same plant, showing the effect of exposure to
light upon the structure of the mesophyll. In both cases os indicates upper surface,
and ws under surface. In the section at the left the growing leaf was exposed to
direct and intense sunlight, and, as a consequence, all of the mesophyll cells have
assumed the protected or palisade position. In the section at the right the leaf was
grown in the shade, and none of the mesophyll cells have organized in palisade
fashion.—After STAHL.

danger from cold. The danger from all these sources is be-
cause of the large surface with no great thickness of body,
and the protection against all of them is practically the
same. Most of the forms of protection can be reduced
to two general plans: (1) the development of protective
structures between the endangered mesophyll and the air ;
(2) the diminution of the exposed surface.

35. Protective structures—The palisade arrangement of
mesophyll may be regarded as an adaptation for protection,

42 PLANT RELATIONS.

but it usually occurs, and does not necessarily imply ex-
treme conditions of any kind. However, if the cells of the
palisade tissue are unusually narrow and elongated, or

C. LY yyy
: Sas Oh ae ti Ge

Fie. 82. Section through a portion of the leaf of the yew (7axus), showing cuticle
(c), epidermis (e), and the upper portion of the palisade cells (p).

form two or three layers, we might infer the probability of
exposure to intense light or drought. The accompanying
illustration (Fig. 31) shows in a striking way the effect of
light intensity upon the structure of the mesophyll, by
contrasting leaves of the same plant exposed to the extreme
conditions of ight and shade.

The most usual structural adaptations, however, are
connected with the epidermis. The outer walls of the epi-
dermal cells may become thickened, sometimes excessively
so; the other epidermal
walls may wlso become
more or less thickened;
or even what seems to
be more than one epi-
dermal Javer is found
protecting the meso-
phyll. If the outer

Fig. 33. Section through a portion of the leaf of walls of the epidermal
carnation, showing the heavy cuticle (ew) HELLS ti
formed by the outer walls of the epidermal eclls continue to

eclls (ep). Through the cuticle a pussageway thicken, the outer re-

leads to the stoma, whose two guard-cells are ane

secu lying between the two epidermal cells Son of the thick wall
shown in the figure. Below the epidermal loses its structure
cells some of the palisade cells (pad) are shown e ie
containing chloroplasts, and below the stoma and forms the cuticle,
is seen the air chamber into which it opens. which is one of the

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 48

Fie. 34. A hair from the leaf
of Potentilla. It is seen
to grow out from the epi-
dermis,

best protective substances (see Fig.
32). Sometimes this cuticle be-
comes so thick that the passage-
ways through it leading down to
the stomata become regular canals
(see Fig. 33).

Another very common protective
structure upon leaves is to be found
in the great variety of hairs de-
veloped by the epidermis. These
may form but «a slightly downy
covering, or the leaf may be cov-
ered by a woolly or felt-like mass
so that the epidermis is entirely
concealed. The common mullein
is a good illustration of a felt-
covered leaf (see Fig. 36), In cold
or dry regions the hairy covering
of leaves is very noticeable, often

giving them a brilliant silky white or bronze look (see
Figs. 34, 35). Sometimes, instead of a hair-like cover-
ing, the epidermis develops scales of various patterns,
often overlapping, and forming an excellent protection
(see Fig. 37). In all these cases it should be remembered
that these hairs and scales may serve other purposes also,
as well as that of protection.

36, Diminution
of exposed surface.—
It will be impossible
to give more than a
few illustrations of
this large subject.
In very dry regions
it has always been
noticed that the
leaves are small and

Fie, 35. A section through the leaf of bush clover
(Lespedeza), showing upper and lower epidermis,
palisade cells, and cells of the spongy region.
The lower epidermis produces numerous hairs
which bend sharply and lie along the leaf surface
(appressed), forming a close covering.

44 PLANT RELATIONS.

Fig. 36. A branching hair from the leaf of common mullein. The whole plant has a
felt-like covering composed of such hairs.

comparatively thick, although they may be very numerous
(see Figs. 4, 167). In this way each leaf exposes a small

Fie. 37. A scale from the leaf of Shepherdia. These
scales overlap and form a complete covering.

surface to the dry-
ing air and intense
sunlight. In our
southwestern dry
regions the cactus
abounds, plants
which have reduced
their leaves so much
that they are no
longer used for
chlorophyll work,
and are not usually
recognized as leaves.
In their stead the
globular or eylin-
drical or flattened
stems are green and

do leaf work (Figs,

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[volayds [[etus ov PUNOIS ayy UO Yor puL qs oy YB ! sulsoy snyovo TVUWULOD OIG Taj}UId OY NT ‘saavat YoryI Asda UTA
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Fic. 89, A group of cactus forms (slender cylindrical, columnar,
and globular), all of them spiny and without leaves ; an agave in
front ; clusters of yucca flowers in the background.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 47

38, 89, 40, 185, 186, 187, 188). In the same regions the
agaves and yuccas retain their leaves, but they become so
thick that they serve as water reservoirs (see Figs. 38, 39,

A
Fig. 40. A globular cactus, showing the ribbed stem, the strong spines, and the entire
absence of leaves.

189). In all these cases this reduced surface is supple-
mented by palisade tissue, very thick epidermal walls, and
an abundant cuticle.

37. Rosette arrangement.—The rosette arrangement of
leaves is a very common method of protection used by

48 PLANT RELATIONS.

small plants growing in exposed situations, as bare rocks
and sandy ground. ‘he cluster of leaves, flat upon the
ground, or nearly so, and more or less overlapping, is very
effectively arranged for resisting intense light or drought
or cold (see Figs. 11, 12, 48).

3x. Protective positions—In other cases, a position is
assumed by the leaves which directs their flat
surfaces so that they are not exposed to the
most intense rays of light. The so-called “‘ com-

Fie. 41. A leaf of a sensitive plant in two conditions. In the figure to the left the
leaf is fully expanded, with its four main divisions and numerous leaflets well
spread. In the figure to the right is shown the same leaf aftcr it has been
“‘shocked”? by » sndden touch, or by sudden heat, or in some other way. The
leaflets have been thrown together forward aud upward ; the four main divisions
have been moved together; and the main leaf-stalk has been directed sharply
downward. The whole change has very much reduced the surface of exposure.—
After DUCHARTRE.

pass plants,” already mentioned, are illustrations of this,
the leaves standing elgewise and receiving on their surface
the less intense rays of light (see Figs. 5, 165). In the
dry regions of Australia the leaves on many of the forest,
trees and shrubs have this characteristic edgewise position,
known as the profile posi/ion, giving to the foliage a very
curious appearance.

Some leaves have the power of shifting their position
according to their necds, directing their flat surfaces to-
ward the light, or more or less inchning them, according

|
Q

Fie. 42. The telegraph plant (Desmodium gyrans). Each leaf is made up of three
leaflets, a large terminal one, and a pair of small lateral ones. In the lowest figure
the large leaflets are spread out in their day position ; in the central figure they are
turned sharply downward in their night position. The name of the plant refers to
the peculiar and constant motion of the pair of lateral leaflets, each one of which
describes a curve with u jerking motion, like the second-hand of a watch, as
indicated in the uppermost figure.

50 PLANT RELATIONS.

to the danger. Perhaps the most completely adapted
leaves of this kind are those of the ‘‘sensitive plants,”
whose leaves respond to various external influences by
changing their positions. The common sensitive plant
abounds in dry regions, and may be taken as a type of
such plants (see Figs. 4, £1, 166). The leaves are divided
into very numerous small leaflets, sometimes very small,
which stretch in pairs along the leaf branches. When
drought approaches, some of the pairs of leaflets fold to-
gether, slightly reduc-
ing the surface expo-
sure. As the drought
continues, more leaflets
fold together, then still
others, until finally all
the leaflets may be
folded together, and the
leaves themsclyes may
Fig. 43. Colyledons of squash seedling, show- bend. aginst the stem.
darkness Gight Ngure)—Atter Arkanon. It i8 like a sailing vessel
gradually tuking in sail
as a storm approaches, until finally nothing is exposed,
and the vessel weathers the storm by presenting only bare
poles. Sensitive plants can thus regulate the exposed sur-
face very exactly to the need.

Such motile lewves not only behave in this manner at the
coming of drought, but the positions of the leaflets are
shifted throughout the day in reference to light, and at
night a very characteristic position is axsumed (sce Pigs. 2,
3, 42), once called a “sleeping position.” The danger from
night exposure comes from the radiation of heat which
oceurs, which may chill the leaves to the danger point.
The night position of the leaflets of Ovel/x hag heen re-
ferred to already (see $14). Similar changes in the direc-
tion of the leaf planes at the coming of night may be
observed in most of the Leyuminose, even the common

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 51

white clover displaying it. It can be observed that the
expanded seed leaves (codyledons) of many young germinat-
ing plants shift their positions at night (see Fig. 43), often
assuming a vertical position which brings them in contact
with one another, and also covers the stem bud (pluie).

Certain leaves with well-developed
protective structures are able to en-
dure the winter, as in the case of
the so-called evergreens. In the
case of juniper, however, the winter
and summer positions of the leaves
are quite different (see Fig. 44). In
the winter the leaves le close against
the stem and overlap one another;
while with the coming of warmer
conditions they become widely
spreading.

39. Protection against rain.—It is

also necessary for leaves to avoid Fis: 44 Two twiss of junt-
‘ per, showing the effect of

becoming wet by rain. If the water heat and cold upon the
is allowed to soak in there is danger positions of the leaves.

Sree 7 = The ordinary protected
of filling the stomata and interfering qintee osition “of the
with the air exchanges. Hence it leaves is shown by 4;
i ] Newel that ay aed ane while in B, in response to
will be noticed that most leaves are varmer sconditious) the
able to shed water, partly by their leaves have spread apart

and have become freely ex-

positions, partly by their structure. Sa Se

In many plants the leaves are so ar-

ranged that the water runs off towards the stem and so
reaches the main root system: in other plants the rain is
shed outwards, as from the eaves of a house.

Some of the structures which prevent the rain from
soaking in are a smooth epidermis, a cuticle layer, waxy
secretions. felt-like coverings, ete. Interesting experi-
ments may be performed with different leaves to test their
power of shedding water. If a gentle spray of water is
allowed to play upon different plants, it will be observed

52 PLANT RELATIONS.

that the water glances off at once from the surfaces of
some leaves, runs off more slowly from others, and may be
more or less retained by others.

In this same connection it should be noticed that in
most horizontal leaves the two surfaces differ more or less
in appearance, the upper usually being smoother than the
lower, and the stomata occurring in larger numbers, some-
times exclusively, upon the under surface. While these
differences doubtless have a more important meaning than
protection against wetting, they are also suggestive in this
connection.

CHAPTER IV.
SHOOTS.

40. General characters.—The term shoot is used to include
both stem and leaves. Among the lower plants, such as
the alge and toadstools, there is no distinct stem and leaf.
In such plants the working body is spoken of as the thallus,
which does the work done by both stem and leaf in the
higher plants. These two kinds of work are separated in
the higher plants, and the shoot is differentiated into stem
and leaves.

41. Life-relation—In seeking to discover the essential
life-relation of the stem, it is evident that it is not neces-
sarily a light-relation, as in the case of the foliage leaf,
for many stems are subterranean. Also, in general, the
stem is not an expanded organ, as is the ordinary foli-
age leaf. his indicates that whatever may be its essential
life-relaution it has little to do with exposure of surface.
It becomes plain that the stem is the great leaf-hbearing
organ, and that its life-relation is a leaf-relation. Often
stems branch, and this increases their power of producing
leaves.

In classifying stems, therefore, it seems natural to use
the kind of leaves they bear. From this standpoint there
are three prominent kinds of stems: (1) those bearing foli-
age leaves ; (2) those bearing scaly leaves ; and (3) those
bearing floral leaves. There are some peculiar forms of
stems which do not bear leaves of any kind, but they need
not be included in this general view.

b4 PLANT RELATIONS.

A. Stems bearing foliage leaves.

42. General character.—.\s the purpose of this stem is to
display foliage leaves, and as it has been discovered that the
essential life-relation of foliage leaves is the light-relation,
it follows that a stem of this type must be able to relate its
leaves to light. Itis, therefore, commonly aerial, and that
it may properly display the leaves it is generally elongated,
with its joints (xodes) bearing the leaves well separated (see
Figs. 1, 4, 18, 20).

The foliage-bearing stem is generally the most conspicu-
ous part of the plant and gives style to the whole body.
Qne’s impression of the forms of most plants is obtained
from the foliage-bearing stems. Such stems have great
range in size and length of life, from minute size and very
short life to’ huge trees which may endure for centuries.
Branching is also quite a feature of foliage-bearing stems ;
and when it occurs it is evident that the power of displiuy-
ing foliave is correspondingly increased. Certain promi-
nent types of foliage-bearing stems muy be considered.

+5. The subterranean type.—It may seem strange to in-
clude any subterranean stem with those that bear foliage,
as such a stem seems to be away from any light-relation.
Ordinarily subterranean stems send foliage-bearing branches
above the surface, and such stems are not to be classed as
foliage-bearing stems. But often the only stem possessed
by the plant is subterranean, and no branches are sent to
the surface. In such cases only foliage leaves appear above
ground, and they come directly from the subterranean stem.
The ordinary ferns furnish a conspicuous illustration of
this habit, all that is seen of them above ground being the
characteristic leaves, the commonly called ++ stem” being
only the petiole of the leaf (see Figs. 45, £6, 144). Many
seed plants can also be found which show the same habit,
especially those which flower early in the spring. This
cannot be regarded as avery favorable type of stem for

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Fig. 45. A fern (Aspidium), showing three large branching leaves coming from a hori-
zontal subterranean stem (rootstock) ; growing leaves are also shown, which are
gradually unrolling. The stem, young leaves, and petioles of the large leaves are
thickly covered with protecting hairs. The stem gives rise to numerous small roots
from its lower surface. The figure marked 3 represents the under surface of a
portion of the leaf, showing seven groups of spore cases; at 5 is represented a
section through one of these groups, showing how the spore cases are attached and
protected by a flap ; while at 6 is represented a single spore case opening and dis-
charging its spores, the heavy spring-like ring extending along the back and over
the top.—After WossIDLo,

5

56 PLANT RELATIONS.

leaf display, and as a rule such stems do not produce
many foliage leaves, but the leaves are apt to be large.

Fie. 46. A common fern, showing the underground stem (rootstock), which sends the
few large foliage leaves above the surface.—After ATKINSON.

The subterranean position is a good one, however, for
purposes of protection against cold or drought, and when
the foliage leaves are killed new ones can be put out by

SHOOTS. 57

the protected stem. This position is also taken advantage
of for comparatively safe food storage, and such stems are
apt to become more or less thickened and distorted by this
food deposit.

44. The procumbent type.—In this case the main body
of the stem lies more or less prostrate, although the advanc-
ing tip is usually erect. Such stems may spread in all
directions, and become interwoven into
a mat or carpet. They are found
especially on sterile and exposed soil,

G
Fie. 47. A strawberry plant, showing a runner which has devel-
oped a new plant, which in turn has sent out another run-
ner.—After SEUBERT.

and there may be an important relation between this fact and
their habit, as there may not be sufficient building material
for erect stems, and the erect position might result in too
much exposure to light, or heat, or wind, etc. Whatever
may be the cause of the procumbent habit, it has its advan-
tages. As compared with the erect stem, there is economy
of building material, for the rigid structures to enable it to
stand upright are not necessary. On the other hand, such
a stem loses in its power to display leaves. Instead of
being free to put out its leaves in every direction, one side
is against the ground, and the space for leaves is diminished
at least one-half. All the leaves it bears are necessarily
directed towards the free side (see Fig. 18).

We may be sure, however, that any disadvantage com-
ing from this unfavorable position for leaf display is over-
balanced by advantages in other respects. The position is

58 PLANT RELATIONS.

certainly one of protection, and it has a further advantage
in the way of migration and vegetative propagation. As
the stem advances over the ground, roots strike out of the
nodes into the soil. In this way fresh anchorage and new
soil supplies are secured ; the old parts of the stem may

Fie. 48. Two plants of a saxifrage, showing rosette habit, and also the numerous
runners sent out from the base, which strike root at tip and produce new plants.
—After Kerner.

die, but the newer portions have their soil connection and
continue to live. So effective is this habit for this kind of
propagation that plants with erect stems often make use of
it, sending out from near the base special prostrate branches,
which advance over the ground and form new plants.
A very familiar illustration is furnished by the straw-
berry plant, which sends out peculiar naked ‘ runners”
to strike root and form new plants, which then become

SHOOTS. 59

independent plants by the dying of the runners (see Figs.
ae,

45. The floating type.—In this case the stems are sus-
tained by water. Numerous illustrations can be found in
small inland lakes and slow-moving streams (see Fig. 41).
Beneath the water these stems often seem quite erect, but

Fie, 49. A submerged plant (Ceratophyllum) with floating stems, showing the stem
joints bearing finely divided leaves.

when taken out they collapse, lacking the buoyant power
of the water. (irowing free and more or less upright in
the water, they seem to have all the freedom of erect stems
in displaying foliage leaves, and at the same time they
are not called upon to build rigid structures. Economy
of building material and entire freedom to display foliage
would seem to be a happy combination for plants. It must
be noticed, however, that another very important condition
is introduced. To reach the leaf surfaces the light must
pass through the water, and this diminishes its intensity so

60 PLANT RELATIONS.

greatly that the working power of the leaves is reduced.
At no very great depth of water a limit is reached, beyond
which the light is no longer able to be of service to the
leaves in their work. Hence it is that water plants are

Fig. 50. A vine or liana climbing
the trunk of a tree. The leaves
are all adjusted to face the light
and to ayoid shading one an-
other as far as possible,

restricted to the surface of the
water, or to shoal places ; and in
such places vegetation is very
abundant. Water is so serious
an impediment to light that very
many plants bring their working
leaves to the surface and float
them, as seen in water lilies, thus
obtaining light of undiminished
intensity.

46. The climbing type.—Climb-
ing stems are developed especially
in the tropics, where the vegeta-
tion is so dense and overshadow-
ing that many stems have learned
to climb upon the bodies of other
plants, and so spread their leaves
in better light (see Figs. 50, 55,
98, 201). Great woody vines
fairly interlace the vegetation of
tropical forests, and are known
as ‘‘lianas,” or ‘‘lianes.*” The
same habit is noticeable, also, in
our temperate vegetation, but it
is by no means so extensively dis-
played as in the tropics. There
are a good many forms of climb-
ing stems. Remembering that
the habit refers to one stem de-
pending upon another for
mechanical support, we may in-
clude many hedge plants in the

SHOOTS. 61

list of climbers. In this case the stems are too weak to
stand alone, but by interlacing with one another they may
keep an upright position. There are stems, also, which
climb by twining about their support, as the hop vine and

Fie, 51. A cluster of smilax, showing the tendrils which enable it to climb, and also
the prickles.—After KERNER.

morning glory : others which put out tendrils to grasp the
support (see Figs. 51, 52), as the grapevine and. star
cucumber ; and still others which climb by sending out
suckers to act as holdfasts, as the woodbine (see Figs. 53,
54). In all these cases there is an attempt to reach towards

62 PLANT RELATIONS.

the light without developing such structures in the stem
as would enable it to stand upright.

47. The erect type—This type seems altogether the
best adapted for the proper display of foliage leaves. Leaves

Piece Ee aes a ae

Fig. 52. Passion-flower vines climbing supports by means of tendrils, which may be
seen more or less extended or coiled, The two types of leaves upon a single stem
may also be noted.

can be sent out in all directions and carried upward to-
wards the light ; but it is at the expense of developing an
elaborate mechanical system to enable the stem to retain
this position. There is an interesting relation between
these erect bodies and zones of temperature. At high alti-

SHOOTS.

st

Fie. 538. Woodbine (.4

mpelopsis) in a deciduous forest. The tree trunks are almost

covered by the dense masses of woodbine, whose leaves are adjusted so as to form
compact mosaics. A lower stratum of vegetation is visible, composed of shrubs
and tall herbs, showing that the forest is somewhat open.—After SCHIMPER.

tudes or latitudes the subter-
ranean and prostrate types of
foliage-bearing stems are most
common ; and as one passes to
lower altitudes or latitudes the
erect stems become more nu-
merous and more lofty. Among
stems of the erect type the tree
is the most impressive, and it
has developed into a great vari-
ety of forms or ‘‘ habits.” Any
one recognizes the great differ-
ence in the habits of the pine
and the elm (see Figs. 56,
57, 48, 59), and many of our

Fig. 54. A portion of a woodbine
(Ampelopsis). The stem tendrils
have attached themselves to a
smooth wall by means of disk-like
suckers.—After STRASBURGER.

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Fie. 56.

A tree of the pine type (larch), showing the continuous central shaft and
the horizontal branches, which tend to become more upright towards the top of
the tree. The general outline is distinctly conical.
such trees in periodically shedding its leaves,

The larch is peculiar among

Fie. 57. A pine tree, showing the central shaft and also the bunching of the
needle leaves toward the tips of the branches where there is the best exposure
to light.

SHOOTS. 67

common trees may be known, even at a distance, by their
characteristic habits (see Figs. 60, 61, 62). The difficulty
of the mechanical problems solved by these huge bodies
is very great. They maintain form and position and en-
dure tremendous pressure and strain.

Fie. 58. An elm in its winter condition, showing the absence of a continuous central
shaft, the main stem soon breaking up into branches, and giving a spreading top.
On each side in the background are trees of the pine type, showing the central
shaft and conical outline,

68 PLANT RELATIONS.

48, Relation to light.—As stems bearing foliage leaves
hold a special relation to light, it is necessary to speak of
the influence of light upon the direction of growth, an

the spreading top.

influence known as heliotropism, already referred to under
foliage leaves. In the case of an erect stem the tendency
is to grow towards the source of light (see Figs. 1, 64).

SHOOTS. 69

This has the general result of placing the leaf blades at
right angles to the rays of light, and in this respect the
heliotropism of the stem aids in securing a favorable leaf
position (see Figs. 63, 63a). Prostrate stems are differently
affected by the light, however, being directed transversely
to the rays of light. The same is true of many foliage

se

Fic. 60. An oak in its winter condition, showing the wide branching. The various
directions of the branches have been determined by the light-relations.

branches, as may be seen by observing almost any tree in
which the lower branches are in the general transverse posi-
tion. These branches generally tend to turn upwards when
they are beyond the region of shading. Subterranean
stems are also mostly horizontal, but they are out of the
influence of light, and under the influence of gravity,
known as geotropism, which guides them into the trans-
verse position, The climbing stem, like the erect one,

70 PLANT RELATIONS.

et

Fie. 61.

habit, and the tendency to grow in groups.

grows towards the light, while floating stems may be
either erect or transverse.

B. Stems bearing scale leuves.

49, General character.—.A scale leaf is one which does
not serve as foliage, as it does not develop the necessary
chlorophyll. This means that it does not need such an
exposure of surface, and hence scale leaves are usually much
smaller, and certainly are more inconspicuous than foliage
leaves. A good illustration of scale leaves is furnished hy
the ordinary scaly buds of trees, in which the covering of
overlapping scaly leaves is very conspicuous (see Fig. 65).
As there is no development of chlorophyll in such leayes,

SHOOTS. 71

they do not need to be exposed to the light. Stems bearing
only scale leaves, therefore, hold no necessary light-relation,
and may be subterranean as well as aerial. For the same

Fie. 62. A group of weeping birches, showing the branching habit and the peculiar
hanging branchlets. The trunks also show the habit of birch bark in peeling off
in bands around the stem.

reason scale leaves do not need to be separated from one
another, but may overlap, as in the buds referred to.

Sometimes scale leaves occur so intermixed with foliage
6

a <a

Fia. 63. Sunflowers with the upper part of the stem sharply bent towards the light,
giving the leaves better exposure.—After SCHAFFNER.

SHOOTS. 73

leaves that no peculiar stem type is developed. In the
pines scale leaves are found abundantly on the stems which
are developed for foliage purposes. In fact, the main stem
axes of pines bear only scale leaves, while short spur-like
branches bear the characteristic needles, or foliage leaves,
but the form of the
stem is controlled
by the needs of the
foliage. Some very
distinct types of
scale-bearing stems
may be noted.

50. The bud type.
—TIn this case the
nodes bearing the
leaves remain close
together, not sepa-
rating, as is neces-
sary in ordinary
foliage-bearing
stems, and the
leaves overlap. In J
a stem of this char- Fie. 63a. Cotyledons of castor-oil bean ; the seedling
acter the later joints to the left showing the ordinary position of the
may become s epa- cotyledons, the one to the right showing the curva-

j . ture of the stem in response to light from one
rated and bear foli- side.—After ATKINSON.

age leaves, so that
one finds scale leaves below and foliage leaves above on
the same stem axis. This is always true in the case of
branch buds, in which the scale leaves serve the purpose
of protection, and are aerial, not because they need a
light-relation, but because they are protecting young foli-
age leaves which do.

Sometimes the scale leaves of this bud type of stem do
not serve so much for protection as for food storage, and
become fleshy. Ordinary bulbs, such as those of lilies, etc.,

Fie. 64. An araucarian pine, showing the
central shaft, and the regular clusters of
branches spreading in every direction and
bearing numerous small leaves. The low-
ermost branches extend downwards and
are the largest, while those above become
more horizontal and smaller. These dif-
ferences in the size and direction of the
branches secure the largest light expo-
sure,

74 PLANT RELATIONS.

are of this character ;
and as the main pur-
pose is food storage
the most favorable
position is a subter-
ranean one (see Fig.
66). Sometimes such
scale leaves become
very broad and not
merely overlap but en-
wrap one another, as
in the case of the
onion.

51. The tuber type.
—The ordinary potato
may be taken as an il-
lustration (see Fig.
67). The minuie scale
leaves. to be found at
the ‘‘eyes” of the
potato, do not overlap,
which means that the
stem joints are farther
apart than in the bud
type. The whole form
of the stem results
from its use as a place
of food storage. and
hence such stems are
generally subterra-
nean. Food storage,
subterranean position,
and reduced scale
leaves are facts which
seem to follow each
other naturally.

SHOOTS.

52. The rootstock type.—This is prob-
ably the most common form of subter-
ranean stem. It is elongated, as are foli-
age stems, and hence the scale leaves
are well separated. It is prominently
used for food storage, and is also admirably
adapted for subterranean migration (see
Fig. 68). It can do for the plant, in the
way of migration, what prostrate foliage-
bearing stems do, and isinamore protected
position. Advancing beneath the ground,
it sends up a succession of branches
to the surface. It is a very efficient
method for the “‘spreading” of plants,
and is extensively used by grasses in coy-
ering areas and forming turf. The persist-
ent continuance of the worst weeds is often
due to this habit (see Figs. 69, 70). It
is impossible
to remove
all of the
indefinitely
branching
rootstocks
from the soil,

75

Fie. 65. Branch buds

of elm. Three buds
(k) with their over-
lapping scales are
shown, each just
above the scar (d)
of an old leaf.—
After BEHRENS.

Fie. 66. A bulb, made up of overlap-
ping scales, which are fleshy on
account of food storage. — After
Gray.

and any fragments that remain
are able to send up fresh crops
of aerial branches.

53. Alternation of rest and
activity.—In all of the three
stem types just mentioned, it
is important to note that they
are associated with a remark-
able alternation between rest
and vigorous activity. From
the branch buds the new leaves

76

Fie. 67. A potato plant, showing thesubterranean tubers.—

After STRASBURGER.

be covered suddenly with young vegetation.

PLANT RELATIONS.

emerge with
great rapidity,
and trees be-
come covered
with new foliage
in a few days.
From the sub-
terranean stems
the aerial parts
come up so
speedily that the
surface of the
ground seems to
This sudden

change from comparative rest to great activity has been
well spoken of as the ‘“‘awakening ” of vegetation.

C. Stems bearing floral leaves.

54. The flower.—The so-called
“flowers” which certain plants
produce represent another type of
shoot, being stems with peculiar
leaves. So attractive are flowers
that they have been very much
studied; and this fact has led
many people to believe that flowers
are the only parts of plants worth
studying. Aside from the fact
that a great many plants do not
produce flowers, even in those
that do the flowers are connected
with only one of the plant pro-
cesses, that of reproduction.
Every one knows that flowers are
exceedingly variable, and names

Fig. 68. The rootstock of Solo-
mon’s seal; from the under side
roots arc developed ; and on the
upper side are seen the scars
which mark the positions of the
successive aerial branches which
bear the leaves. The advanc-
ing tip is protected by scales
(forming a bud), and the posi-
tions of previous buds are in-
dicated by groups of ring-like
scars which mark the attach-
ment of former scales. Advanc-
ing in front and dying behind
such a rootstock may give rise
to an indefinite succession of
acrial plants.—After Gray.

SHOOTS. vue

have been given to every kind of variation, so that their
study is often not much more than learning the definitions
of names. However, if we seek to discover the life-rela-
tions of flowers we find that they may be stated very simply.

55. Life-relations—The flower is to produce seed. It
must not only put itself into proper relation to do this, but

Fic. 69. The rootstock of a rush (Juncus), showing how it advances beneath the
ground and sends above the surface a succession of branches. The breaking up
of such a rootstock only results in so many separate individuals.—After CowLes.

there must also be some arrangement for putting the seeds
into proper conditions for developing new plants. In the
production of seed it is necessary for the flower to secure a
transfer of certain yellowish, powdery bodies which it pro-
duces, known as pollen or pollen-grains, to the organ in
which the seeds are produced, known as the pisti/. This
transfer is called pollination. One of the important things,
therefore, in connection with the flower, is for it to put

78 PLANT RELATIONS.

Fie. 70. An alpine willow, showing a strong rootstock developing aerial branches
and roots, and capable of long life and extensive migration.—After SCHIMPER.

itself into such relations that it may secure pollination.

Fig. 71. A flower of peony, showing the four sects of
floral organs: 4, the sepals, together called the
calyx ; c, the petals, together called the corolla ;
u, the numerous stamens; g, the two carpels,
which contain the ovules.—After STRASBURGER.

Besides pollination,
which is necessary
to the production of
seeds, there must be
an arrangement for
seed distribution.
It is always well for
seeds to he scattered,
so as to be separated
from one another
and from the parent
plant. The two
great external prob-
lems in connection
with the flower,
therefore, are polli-

SHOOTS.

nation and seed-distribution.
It is necessary to call attention
to certain peculiar features of
this type of stem.

56. Structures.—The joints
of the stem do not spread
apart, so that the peculiar
leaves are kept close together,
usually forming a rosette-like
cluster (see Fig. 71). These
leaves are of four kinds: the
lowest (outermost) ones (indi-
vidually sepals, collectively
calyx) mostly resemble small
foliage leaves ; the next higher
(inner) set (individually petals,
collectively corolla) are usually
the most conspicuous, delicate
in texture and brightly col-
ored; the third set (stamens)
produces the pollen; the
highest (innermost) set (car-
pels) form the pistil and pro-
duce the ovules, which are to
become seeds. These four sets
may not all be present in the
same flower; the members of
the same set may be more or
less blended with one another,
forming tubes, urns, etc. (see
Figs. 72, 78, 74); or the dif-
ferent members may be modi-
fied in the greatest variety of
ways.

Another peculiarity of this

type of stem is that when the ©

79

Fie.72. A group of flowers of the rose

family. The one at the top (Poten-
tilla) shows three broad sepals,
much smaller petals alternating
with them, a group of stamens, and
a large receptacle bearing numer-
oussmall carpels. The central one
(Alchemilla) shows the tips of two
small sepals, three larger petals
united below, stamens arising from
the rim of the urn, and.a single pe-
culiar pistil. The lowest flower (the
common apple) shows the sepals,
petals, stamens, and three styles,
all arising from the ovary part of
the pistil.—After Focke.

80 PLANT RELATIONS.

Fie. 73. <A flower of the tobacco plant: u, a complete flower, showing the calyx with
its sepals blended below, the funnelform corolla made up of united petals, and the
stamens just showing at the mouth of the corolla tube ; 6, acorolla tube split open
and showing the five stamens attached to it near the base ; ¢, a pistil made up of
two blended carpels, the bulbons base (containing the ovules) being the ovary, the
long stalk-like portion the style, and the knob at the top the stigma.—After
STRASBURGER.

last set of floral leaves (carpels) appear, the growth of the
stem in length is checked and the cluster of floral leaves

a €

Fie. 74, A group of flower forms: a, a flower of harebell, showing a bell-shaped
corolla composed of five petals ; }, a flower of phlox, showing a tubular corolla
awith its five petals distinct above and sharply spreading ; c, a flower of dead-nettle,
showing an irregular corolla with its five petals forming two lips above the funnel-
form base ; d, a flower of toad-flax, showing a two-lipped corolla, and also a spur
formed by the base of the corolla; e, a flower of the snapdragon, showing the two
lips of the corolla closed.—After Gray,

SHOOTS. 81

appears to be upon the end of the stem axis. It is usual,
also, for the short stem bearing the floral leaves to broaden

4 1} j
~%® y A
= ——_

Lip \ LX
X

Fie. 75. The Star-of-Bethlehem ( Ornithogalum), showing the loose cluster of flowers
at the end of the stem. The leaves and stem arise from a bulb, which produces a
cluster of roots below.—After STRASBURGER.

at the apex and form what is called a receptacle, upon which
the close set floral leaves stand. __
Although many floral stems are produced singly, it is

82 PLANT RELATIONS.
very common for them to branch, so that the flowers appear

in clusters, sometimes loose and spray-like, sometimes com-
pact (see Figs. 75, 76, 77). For example, the common

AS
TRY

Fie. 76. A flower cluster from a walnut tree.—After STRASBURGER.

dandelion ‘“ flower” is really a compact head of flowers.
All of this branching has in view better arrangements for
pollination or for seed-distribution, or for both.

The subject of pollination and seed-distribution will be
considered under the head of reproduction.

SHOOTS. 88

STRUCTURE AND FUNCTION OF THE STEM.

57. Stem structure—The aerial foliage stem is the most
favorable for studying stem structure, as it is not distorted
by its position or by being a depository for food. If an
active twig of an ordinary woody plant be cut across, it will

Fie. 77. Flower clusters of an umbellifer (Sitz2).—After STRASBURGER.

be seen that it is made up of four general regions (see Fig.
78): (1) an outer protecting layer, which may be stripped
off as a thin skin, the epidermis ; (2) within the epider-
mis a zone, generally green, the cortez ; (3) an inner zone
of wood or vessels, known as the vascular region; (+4) a
central pith.

58. Dicotyledons and Conifers—Sometimes the vessels

84 PLANT RELATIONS.

Fie. 78. Section across a young twig of box
elder, showing the four stem regions: e,
epidermis, represented by the heavy bound-
ing line ; ¢c, cortex ; w, vascular cylinder ;
D, pith.

are arranged in a hollow
cylinder, just inside of
the cortex, leaving what
is called pith in the
center (see Fig. 78).
Sometimes the pith dis-
appears in older stems or
parts of stems and leaves
the stem hollow. When
the vessels are arranged
in this way and the stem
lives more than a year, it
can increase in diameter
by adding new vessels
outside of the old. In

the case of trees these additions appear in cross-section like
a series of concentric rings, and as there is usually but one
growth period during the year, they are often called annual
rings (see Fig. 79), and the age of a tree is often estimated

by counting them.
This method of ascer-
taining the age of a
tree is not absolutely
certain, as there may
be more than one
growth period in some
years. In the case of
trees and shrubs the
epidermis is replaced
on the older parts by
layers of cork, which
sometimes hecomes

very thick and makes Fie. 79, Section across a twig of box elder three
years old, showing three annual rings, or growth

up the outer part of rings, in the vascular cylinder. The radiating
what is commonl y lines (7m) which cross the vascular region (2¢) rep-

resent the pith rays, the principal ones extending
called bark. from the pith to the cortex (c).

SHOOTS. 85

Stems which increase in diameter mostly belong to the
great groups called Dicotyledons and Conifers. To the
former belong most of our common trees, such as maple,
oak, beech, hickory, etc. (see Figs. 58, 59, 60, 61), as
well as the great majority of common herbs; to the latter
belong the pines, hemlocks, etc. (see Figs. 46, 57, 192,
193, 194). This annual increase in diameter enables the
tree tc put out an increased number of branches and
hence foliage leaves each year, so
that its capacity for leaf work be-
comes greater vear after year. A
reason for this is that the stem is
conducting important food sup-
plies to the leaves, and if it in-
creases in diameter it can conduct
more supplhes each year and give
work to more leaves.

59. Monocotyledons—In other
stems, however, the vessels are
arranged differently in the central Fis. 80. A corn-stalk, showing

Gj : cross-section and longitudinal

region. Instead of forming a hol- esilon, Wheat mpneeat
low cylinder enclosing a pith, they the scattered bundles of ves-
are scattered through the central Bi paced ey
region, as may be seen in the cross- fiber-like strands.
section of a corn-stalk (see Fig.
80). Such stems belong mostly to a great group of plants
known as Monocotyledons, to which belong palms, grasses.
lilies, etc. For the most part such stems do not increase in
diameter. hence there is no branching and no increased
foliage from year to year. A palm well illustrates this
habit, with its columnar, unbranching trunk, and its crown
of foliage leaves, which are about the same in number from
year to vear (see Figs. 81, 82).

60. Ferns,—The same is true of the stems of most fern-
plants, as the vessels of the central region are so arranged
that there can be no diameter increase, though the ar-

Fig. 81. A date palm, showing the unbranched columnar trunk covered with old leaf
bases, and with a cluster of huge active leaves at the top, only the lowest portions
of which are shown, Two of the very heavy fruit clusters are also shown,

SHOOTS. 87

rangement is very different from that found in Monocotyle-
dons. It will be noticed how similar in general appearance
is the habit of the tree fern and that of the palm (see Fig.
83).

61. Lower plants.—In the case of moss-plants, and such
alge and fungi as develop stems, the stems are very much

ONO Was |

Pa a festa, PIAS Bey all as ns mn mi Pt
Fie, 82. A palm of the palmetto type (fan palm), with low stem and acrown of large
leaves.

simpler in construction, but they serve the same general
purpose.

62. Conduction by the stem.—Aside from the work of
producing leaves and furnishing mechanical support, the
stem is a great conducting region of the plant. This sub-
ject will be considered in Chapter X., under the general

head of ‘‘ The Nutrition of Plants,”
7

Fig. 83. <A group of tropical plants. To the left of the center is a tree fern, with its
slender columnar stem and crown of large leaves. The large-leaved plants to the
right are bananas (monocotyledons).

CHAPTER V.

ROOTS.

63. General character—The root is a third prominent
plant organ, and it presents even a greater variety of rela-
tions than leaf or stem. In whatever relation it is found
it is either an absorbent organ or a holdfast, and very often
both. For such work no light-relation is necessary, as in
the case of foliage leaves ; and there is no leaf-relation, as
in the case of stems. Roots related to the soil may be
taken as an illustration.

It is evident that a soil root anchors the plant in the
soil, and also absorbs water from the soil. If absorption is
considered, it is further evident that the amount of it will
depend in some measure upon the amount of surface which
the roots expose to the soil. We have already noticed that
the foliage leaf has the same problem of exposure, and it
solves it by becoming an expanded organ. The question
may be fairly asked, therefore, why are not roots expanded
organs? The receiving of rays of light, and the absorbing
of water are very different in their demands. In the former
case a flat surface is demanded, in the latter tubular pro-
cesses. The increase of surface in the root, therefore, is
obtained not by expanding the organ, but by multiplying
it. Besides, to obtain the soil water the roots must burrow
in every direction, and must send out their delicate thread-
like branches to come in contact with as much soil as pos-
sible. Furthermore, in soil roots absorption is not the only
thing to consider, for the roots act as holdfasts and must
grapple the soil, This is certainly done far more effectively

90 PLANT RELATIONS.

by numerous thread-like processes spreading in every direc-
tion than by flat, expanded processes.

It should also be noted that as soil roots are subterra-
nean they are used often for the storage of food, as in the
case of many subterranean stems. Certain prominent root
types may be noted as follows :

64, Soil roots—These roots push into the ground with

great energy,

and their ab-
sorbing sur-
eat {iy ——~y_ faces are en-

ol eee tirely covered.
Only the voung-
est parts of a
root system
absorb actively,
the older parts
transporting
the absorbed
material to the
stem, and help-
ing to grip the

5 mm _
Fie. 84. Root tips of corm, showing root hairs, their position soil. The soil
in reference to the growing tip, and the effect of the root is the most

surrounding medium upon their development : 1, in soil ;
2, in air; 3, in water. common root

type. being
used by the great majority of seed plants and fern plants,
and among the moss plants the very simple root-like pro-
cesses are mostly soil-related. T'o such roots the water of
the soil presents itself either as free wafer—that is, water
that can be drained away—or as films of water adhering to
each soil particle, often called water of adhesion. To come
in contact with this water, not only does the root system
usually branch profusely in every direction, but the youngest
branches develop abundant absorbing hairs, or root hairs
(see Fig. 84), which crowd in among the soil particles and

ROOTS.

91

absorb moisture from them. By these root hairs the absorb-
ing surface, and hence the amount of absorption, is greatly

Fie. 85. Apparatus to show the influence of
water (hydrotropism) upon the direction of
roots. The ends (a) of the box have hooks
for hanging, while the box proper is a cylinder
or trough of wire netting and is filled with
damp sawdust. In the sawdust are planted
peas (g), whose roots (h, i, 4, m) first descend
until they emerge from the damp sawdust,
but soon turn back toward it— After Sacus.

increased. Individual
root hairs do not last
very long, but new
ones are constantly ap-
pearing just behind the
advancing root tips,
and the old ones are
as constantly disap-
pearing.

(1) Geotropism and
hydrotropism. — Many
outside influences affect
roots in the direction
of their growth, and
as soil roots are espe-
cially favorable for ob-
serving these influ-
ences, two prominent

ones may be mentioned. The influence of gravity, or the
earth influence, is very strong in directing the soil root.

Fie. 86. Araspberry plant, whose stem has been bent down to the soil and has ‘‘ struck
root.”—After BEAL.

92 PLANT RELATIONS.

As is well known, when a seed germinates the tip that is to
develop the root turns towards the earth, even if it has
come from the seed in some other direction. This earth
influence is known as geotropism. Another directing in.
fluence is moisture, or the water influence, known as hydrot-

Fie. 87. A section through the leaf-stalk of a yellow pond-lily (Vuphar), showing the
numerous conspicuous air passages (s) by means of which the parts under water
are aerated ; h, internal hairs projecting into the air passages; v, the much
reduced and comparatively few vascular bundles.

ropism. By means of this the root is directed towards the
most favorable water supply in the soil.

Ordinarily, geotropism and hydrotropism direct the root
in the same general way, and so reinforce each other ; but
the following experiment may be arranged, which will
separate these two influences. Bore several small holes in
the bottom of a box (such as a cigar box), suspended as in-
dicated in Figure 85, and cover the bottom with blotting
paper. Pass the root tips of several germinated seeds

ROOTS. 93

through the holes, so that the seeds rest on the paper, and
the root tips hang through the holes. If the paper is kept
moist germination will continue, but geotropism will pull
the root tips downwards, and hydrotropism (the moist
paper) will pull them upwards. In this way they will
pursue a devious course, now directed by one influence
and now by the other.

If a root system be examined it will be found that when
there is a main axis (tap
root) it is directed
steadily downwards,
while the branches are
directed differently.
This indicates that all
parts of a root system
are not alike in their
response to these influ-
ences. Several other
influences are also con-
cerned in directing soil

S Soe leae nee
roots, and the path of conn. eatsses 0s:
any root branch is a Fie. 88. Asection through the stem of a water-
result of all of them. wort (Elatine), showing the remarkably large
; and regularly arranged air passages for root
How variable they are aeration. The single reduced vascular bundle
may be seen by the is central and connected with the small cor-
: ; f tex by thin plates of cells which radiate like
numerous directions the spokes of a wheel.—After ScHENCK.

which the branches
travel, and the whole root system preserves the record of
these numerous paths.

(2) The pull on the stem.—Another root property may
be noted in connection with the soil root, namely the pull
on the stem. When a strawberry runner strikes root at
tip (see Fig. 47), the roots, after they obtain anchorage in
the soil, pull the tip a little beneath the surface, as if they
had gripped the soil and then slightly contracted. The
same thing may be observed in the process known as

94 PLANT RELATIONS,

“layering,” by which a stem, as a bramble, is bent down
and covered with soil. The covered joints strike root, and
the pulling follows (see Fig. 86). A very plain illustration
of the same fact can be obtained from many crevice plants.
These plants send their root systems into the crevices of
rocks, and spread a rosette of leaves against the rock face.
In the next year a new rosette of leaves, developed further

Fie. 89. Section through the leaf of a quillwort (Zsoetes), showing the four large air
chambers («), the central vascular region (b), and the very poorly developed
cortex.

up the stem, is also found against the rock face. It is
evident that the stem has been pulled back into the crevice
enough to bring the new leaves against the rock, and this
pulling has been effected by the new roots, which have
laid hold of the crevice soil, or walls.

(3) Soil dangers.—In this connection certain soil dan-
gers und the response of the roots should be noted. The
soil may become poor in water or poor in certain essential
materials, and this results in an extension of the root sys-

ROOTS. 95

tem, as if seeking for water and the essential materials.
Sometimes the root system becomes remarkably extensive,
visiting a large amount of soil in order to procure the
necessary supplies. Sometimes the soil is poor in heat, and
root activity is interfered with. In such cases it is very
common to find the leaves
massed against the soil, thus
slightly checking the loss of
heat.

Most soil roots also need free
air, and when water covers the
soil the supply is cut off. In
many cases there is some way
by which a supply of free air
may be brought down into the
roots from the parts above Fre. 90. Longitudinal section

? ti a fle through a young quillwort leaf,
water ; sometimes y farge am showing that the four air cham-

passages in leaves and stems bers shown in Fig. 89 are not con-
‘ tinuous passages, but that there

y) P _ ges,
(see iE igs. 87, 88, 89, 90) » some are four vertical rows of promi-
times by developing special root nent chambers. The plates of
structures which rise above the Cells separa tines the! chambers
. a vertical row very soon become
water level, as prominentl dead and full of air. In addition

? y

shown b the cypress in the to the work of aeration these air
y y ; chambers are very serviceable in
development of knees. These enabling the leaves to float when
knees are outgrowths from roots _ they break off and carry the com-

paratively heavy spore cases.
beneath the water of the cypress

swamp, and rise above the water level, thus reaching the
air and aerating the root system (see Fig. 91). It has been
shown that if the water rises so high as to flood the knees
for any length of time the trees will die, but it does not
follow that this is the chief reason for their development.
65. Water roots.—A very different type of root is devel-
oped if it is exposed to free water, without any soil relation.
If a stem is floating, clusters of whitish thread-like roots
usually put out from it and dangle in the water. Ifthe water
level sinks so as to bring the tips of these roots to the mucky

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ROOTS. 97

Ef ms Poy

Fie. 92. A tropical aroid (Anthurium), showing its large leaves, and bunches of
aerial roots.

soil they usually do not penetrate or enter into any soil re-
lation. Such pure water roots may be found dangling from
the under surface of the common duck weeds, which often
cover the surface of stagnant water with their minute,
green, disk-like bodies.

98 PLANT RELATIONS. F

Plants which ordinarily develop soil roots, if brought
into proper water relations, may develop water roots. For
instance, willows or other stream bank plants may be so
close to the water that some of the root system enters it.
In such cases the numerous clustered roots show their water

van

Fic. 93. An orchid, showing aerial roots,

character. Sometimes root systems developing in the soil
may cuter tile drains, when water roots will devclop in such
clusters as {o choke the drain, The same bunching of water
roots may he noticed when a hyacinth bulb is grown in a
vessel of water.

60, Air roots—In certain parts of the tropics the air is
so moist that it is possible for some plants to obtain sufti-

ROOTS. 99

cient moisture from this source, without any soil-relation or
water-relation. Among these plants the orchids are most
notable, and they may be observed in almost any green-
house. Clinging to the trunks of trees, usually imitated
in the greenhouse by nests of sticks, they send out long
roots which dangle in the moist air (see Digs. 93, 94).
It is necessary to have some special absorbing and condens-
ing arrangement, and in the
orchids this is usually pro-
vided by the development of
a sponge-like tissue about the
root known as the velamen,
which greedily absorbs the
moisture of the air. Examine
also Figs. 92, 95, 96, 7.

67. Clinging roots.—These
roots are developed to fasten
the plant body to some sup-
port, and do no work of ab-
sorption (see Fig. 98). Very
common illustrations may be
obtained from the ivies, the
trumpet creeper, etc. These
Hoots Gag to-vanous puppets, Beat danerciad, sowie world
stone walls, tree trunks, etc., rooisand thicie. leaves.
by sending minute tendril-
like branches into the crevices. The sea-weeds (alga)
develop grasping structures extensively, a large majority
of them being anchored to rocks or to some rigid support
beneath the water, and their bodies floating free. The
root-like processes by which this anchorage is secured are
very prominent in many of the common marine sea-weeds
(see Fig. 157).

68. Prop roots—Some roots are developed to prop
stems or wide-spreading branches. In swampy ground, or
in tropical forests, it is very common to find the base of

or

#1e. 95. Astughorn fern (Platycerium), an aerial plant of the tropics. About it is a

Fig. 96. Selaginella, showing dangling aerial roots und nuely divided leaves.

Fig. 97. Live oaks, in the Gulf States, upon which are growing masses of long moss
or black moss (Ti//andsia), a common aerial plant.

like holdfasts developed by certain

showing the cord

which pass around the tree trunks like ti

KERNER.

a)

Fie. 98. A tropical forest.

ghtly bound ropes.—After

lianas,

ROOTS. 103

tree trunks buttressed by such roots which extend out over
and beneath the surface, and divide the area about the tree
into a series of irregular chambers (see Fig. 100). Some-

x oe ee. ——s <= h LEW a i e-. 4
Fie. 99. A screw-pine (Pandanus), from the Indian Ocean region, showing the
prominent prop roots put out near the base.

times a stem, either inclined or with a poorly developed

primary root system, puts out prop roots which support

it, as in the screw-pine (see Fig. 99). A notable case is
8

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106 PLANT RELATIONS.

that of the banyan tree, whose wide-spreading branches
are supported by prop roots, which are sometimes very
numerous (see Fig. 101). The immense banyans usually

Fie. 102. A dodder plant parasitic on a willow twig. The
leafless dodder twines about the willow, and sends out
sucking processes which penetrate and absorb,—After
STRASBURGER.

illustrated are
especially culti-
vated as sacred
trees, the prop
roots being as-
sisted in pene-
trating the soil.
There is record
of such a tree in
Ceylon with 350
large and 3,000
small prop roots,
able to cover a
village of 100
huts.

69. Parasites,
—Besides roots
related to soil,
water, air, and
various mechani-
cal supports,
there are others
related to hosts.
A host is a liv-
ing plant or
animal upon
which some
other plant or
animal is living
as a parasite,

The parasite gets its supplies from the host, and must be
related to it properly. If the parasite grows upon the
surface of its host, it must penetrate the body to obtain

ROOTS.

food supplies.
Therefore, pro-
cesses are devel-
oped which pene-
trate and absorb.
The mistletoe and
dodder are seed-
plants which have
this habit, and
both have such
processes (see Figs.
102, 103). This
habit is much more
extensively devel-
oped, however, in
a low group of
plants known as
the fungi. Many

107

Fic. 103. A section showing the living connection
between dodder and a golden rod upon which it is

of these parasitic growing. The penetrating and absorbing organ (/)

fungi live upon
plants and animals,

has passed through the cortex (c), the vascular
zone (6), and is disorganizing the pith (yp).

common illustrations being the mildews of lilac leaves and
many other plants, the rust of wheat, the smut of corn, ete.

Fic. 104. Section through the thallus of a liver-
wort (Marchantia), showing the hair-like pro-
cesses (rhizoids) which come from the under
surface and act as roots in gripping and ab-
sorbing. In the epidermis of the upper surface
a chimney-like opening is seen, leading into
a chamber containing cells with chloroplasts.

70. Root structure.
—In the lowest groups
of plants (alge, fungi,
and moss-plants) true
roots are not formed,
but very simple struc-
tures, generally hair-
like (see Fig. 104). In
fern-plants and seed-
plants, however, the
root is a complex
structure, so different
from the root-like pro-

108 PLANT RELATIONS.

cesses of the lower groups that it is regarded as the only
true root. It is quite uniform in structure, consisting of a
tough and fibrous central axis surrounded by a region of
more spongy structure. The tough axis is mostly made
up of vessels, so called because they
conduct material, and is called the
vascular axis, The outer more spongy
region is the cortez, which covers
the vascular axis like a thick skin
(see Fig. 105).

One of the peculiarities of the
root, in which it differs from the
stem, is that the branches come from
the vascular axis and burrow through
the cortex, so that when the latter
is peeled off the ranches are left
attached to the axis, und the cortex
ees ase - ‘anew aaaal shows the holes through which they

section through the root passed. It is evident that when such
tip of shepherd’s purse, 4 root is absorbing, the absorbed ma-
showing the central vas- e ‘ é
cularaxis(p ),surroundea terial (water with various materials
by the cortex (p), outside in solution) is received into the
of the cortex the epi- 2 .

dermis (e) which disap. Cortex, through which it must pass
pears in the older partsof {to the vascular axis to be conducted
the root, and the promi- Pete shar

nent root-cap (¢).

Another pecuharity of the root
is that it elongates only by growth at the tip, while the
stem usually continues to elongate some distance behind
its growing tip. In the soil this delicate growing tip is
protected by a little cap of cells, known as the root-cap
(see Fig. 105).

ep pt

fe Leas

a

i

CHAPTER VI.

REPRODUCTIVE ORGANS.

Ir will be remembered that nutrition and reproduction
are the two great functions of plants. In discussing
foliage leaves, stems, and roots, they were used as illustra-
tions of nutritive organs, so far as their external relations
are concerned. We shall now
briefly study the reproductive
organs from the same point
of view, not describing the
processes of reproduction, but
some of the external relations. f Fa

71. Vegetative multiplica- f) 3
tion Among the very lowest
plants no special organs of

reproduction are developed, B

Fic. 106. A group of spores: 4.
but most plants have them. spores: fem. Common old a
There is a kind of reproduc- fungus), which are so minute and
: : : light that they are carried about by
tion by which a portion of the air ; B, two spores from a com-

the parent body is set apart to mon alga (Ulothrix), which can
. swim by means of the hair-like
produce anew plant, as when processes; ’, the conspicuous dotted
a strawberry runner produces cell is a spore developed by a com-
a mon mildew (a fungus), which is
n r i) a
i HEY strawber ty pla t, e carried about by currents of air,
when a willow twig or a grape
cutting is planted and produces new plants, or when a potato
tuber (a subterranean stem) produces new potato plants, or
when pieces of Begonia leaves are used to start new Begonias.
This is known as vegetative multiplication, a kind of repro-

duction which does not use special reproductive organs.

110 PLANT RELATIONS.

72. Spore reproduction.—Besides vegetative multiplica-
tion most plants develop special reproductive bodies,
known as spores, and this kind of reproduction is known
as spore reproduction. These spores are very simple
bodies, but have the power of producing new individuals.
There are two great groups of spores, differing from each
other not at all in their powers, but in the method of their
production by the parent plant. One kind of spore is
produced by dividing
certain organs of the
parent; in the other
case two special bodies
of the parent blend
together to form the
spore. Although they
are both spores, for
convenience Wwe may
call the first kind
spores (see Figs. 106,

Fic. 107. Fragments of « common alga (Spi-
rogyra). Portions of two threads are shown,
which have been joined together by the grow- 109), and the second

ing of connecting tubes. In the upper thread la - =
four cells are shown, three of which contain kind eggs (see ue 1g.

eggs (z), while the cell marked g, and its mate 107). * The two special
of the other thread each contain a gamete, a .
the lower one of which will pass through the bodies which blend to-
tube, blend with the upper one, and form gether to form an egg
another!eee. are called gametes (see
Figs. 107, 108, 109). These terms are necessary to any
discussion of the external relations. Most plants develop
both spores and eggs, but they are not always equally con-
spicuous. Among the alge, both spores and eggs are prom-
inent; among certain fungi the same is true, but many
fungi are not known to produce eggs ; among moss-plants
the spores are prominent and abundant, but the eve is
concealed and not generally noticed. What has been said
* Tt is recognized that this spore is really a fertilized egg, but in
the absence of any accurate simple word, the term egg is used for con-
venience,

REPRODUCTIVE ORGANS.

of the moss-plants is still more true
of the fern-plants; while among
the seed-plants certain spores (pol-
len grains) wre conspicuous (see
Fig. 110), but the eggs can be ob-
served only by special manipulation
in the luboratory. Seeds are neither
spores nor eggs, but peculiar repro-
ductive bodies which the hidden
egg has helped to produce.

73. Germination,— Spores and
eggs are expected to germinate ;
that is, to begin the development
of a new plant. This germination
needs certain external conditions,
prominent among which are defi-
nite amounts of heat, moisture,
and oxygen, and sometimes light.
Conditions of germination may be
observed most easily in connection
with seeds. It must be understood,
however, that what is called the
germination of seeds is something

111

Fie. 108.

A portion of the
body of a common alga

(Gdogonium), showing
gametes of very unequal size
and activity; a very large
one (0) is lying in a globular
cell, and a very small one is
entering the cell, another
similar one (s) being just
outside. The two small
gametes have hair-like pro-
cesses and can swim freely.
The small and large gam-
etes unite and form an egg.

Fie. 109. A group of swim-
ming cells: A, a spore of
Edogonium (an alga);
B, spores of Ulothrix (an
alga); C, a gamete of
Equisetum (horse-tail or
scouring rush).

very different from the germination
of spores and eggs. In the latter
cases, germination includes the very
beginnings of the young plant. In
the case of a seed, germination begun
by an egg has been checked, and
seed germination is its renewal. In
other words, an egg has germinated
and produced a young plant called
the ‘‘embryo,” and the germination
of the seed simply consists in the
continued growth and the escape of
this embryo.

112 PLANT RELATIONS.

It is evident that for
the germination of seeds
light is not an essential
condition, for they may
germinate in the ght or
in the dark ; but the need
of heat, moisture, and
oxygen is very apparent.
The amount of heat re-
quired for germination

varies widely with different
Fo 210A pollen gain pore\from te seeds, some germinating
in its transportation by currents of air. at much lower tempera-
tures than others. Every
kind of seed, or spore, or egg has a special temperature
range, below which and above which
it cannot germinate. The two limits
of the range may be called the
lowest and highest points, but be-
tween the two there is a best point
of temperature for germination. The
same general fact is true in reference
to the moisture supply.

V4. Dispersal of reproductive bodies,
—Among the most striking external
relations, however, are those con-
nected with the dispersal of spores,
gametes, and seeds. Spores and
seeds must be carried away from the
parent plant, and separated from
each other, out of the reach of
rivalry for nutritive material ; and
gametes must come together and ee ne ee eee
blend to form the eggs, Conspicuous (Epilobiun) opening and
among the means of transfer are the —°XPosing its plumed seeds

7 which are transported by
following. the wind.—After Brat.

REPRODUCTIVE ORGANS. 118

75. Dispersal by locomotion.—The common method of
locomotion is by means of movable hairs (cilia) developed
upon the reproductive body, which propel it through the

water (see Fig. 109).
Swimming spores are
very common among
the alga, and at least
one of the gametes
in alge, moss-plants,
and fern-plants has
the power of swim-
ming by means of
cilia.

76. Dispersal by
water,—It is very
common for repro-
ductive bodies to be
transported by cur-
rents of water. The
spores of many water
plants of all groups,
not constructed for
locomotion, are thus
floated about. This
method of transfer is
also very common
among seeds. Many
seeds are buoyant, or
become so after soak-
ing in water, and
may be carried to
great distances by

Fie. 112. The upper figure to the left isan opening
pod of fireweed discharging its plumed seeds.
The lower figure represents the seed-like fruits
of Clematis with their long tail-like plumes.—
After KERNER.

currents. For this reason the plants growing upon the
banks or flood-plains of streams may have come from a
wide area. Many seeds can even endure prolonged soak-
ing in sea-water, and then germinate. Darwin estimated

114 PLANT RELATIONS.

that at least
fourteen per
cent. of the
seeds of any
country can re-
tain their vital-
ity in sea-water
for twenty-
eight days. At
the ordinary
rate of move-
ment of ocean
currents, this
length of time
would permit
such seeds to
be transported

Fic, 113. A ripe dandelion head, showing the mass of
plumes, a few seed-like fruits with their plumes still over a thou-
attached to the receptacle, and two fallen off.—After gand miles,
KERNER.

thus making
possible a very great range in distribution.

77. Dispersal of spores by air.—This is one of the most
common methods of transport- ies
ing spores and seeds. In most 4a 4
cases spores are sufficiently ee ST
small and light to be trans-
ported by the gentlest move-
ments of air. Among the
fungi this is a very common
method of spore dispersal (see
Fig. 106), and it is extensively
used in scattering the spores
of moss-plants, fern-plants (see
Fig. 45), and seed-plants.
Among seed-plants this is one Fis 14. Seed-like fruits of Senecio

. 2 with plumes for dispersal by air.—
method of pollination, the After KERNER.

REPRODUCTIVE ORGANS. 115

ae SN

Fie. 115. A winged seed of Bignonia.—After STRASBURGER.

spores called pollen grains being scattered by the wind,
and occasionally
falling upon the
right spot for
germination.
With such an
agent of transfer
the pollen must
be very light and
powdery, and
also very abun-
dant, for it must
come down al-
most like rain to be certain of reaching the right places.
Among the gymno-
sperms (pines, hem-
locks, ete.) this is the
exclusive method of
pollination, and when a
pine forest is shedding
pollen the air is full of
the spores, which may
be carried to a great

Nee distance before being
Fig. 117. Winged fruit of Ptelea.—After a 7
KERNER. deposited. Occasional

Fic. 116. Winged fruit of maple.—After KERNER.

116

Fie. 118. Winged fruit of
Ailanthus.—After Krer-
NER.

PLANT RELATIONS.

reports of ‘‘ showers of sulphur” have
arisen from an especially heavy fall of
pollen that has been carried far from
some gymnosperm forest. In the case
of pines and their near relatives, the
pollen spores are assisted in their dis-
persal through the air by developing a
pair of broad wings from the outer
coat of the spore (see Fig. 110). This
same method of pollination—that is,
carrying the pollen spores by currents
of air—is also used by many mono-
cotyledons, such as grasses; and by
many dicotyledons, such as our most

common forest trees
(oak, hickory, chest-
nut, ete.).

78. Dispersal of
seeds by air,—Seeds
are very rarely light
enough to be carried
by currents of air
without some special
adaptation. Wings
and plumes of very
many and often very
beautiful patterns
are exceedingly com-
mon in. connection
with seeds or seed-
like fruits (see Figs.
15, Wb. Ta as:
119). Wings are de-
veloped by the fruit
of maples and of
ash, and by the seeds

Fie. 119. Fruit of basswood (7%lia), showing the
peculiar wing formed by a leaf.—After Kerner.

REPRODUCTIVE ORGANS. 117

Fie. 120. A common tumbleweed (Cycloloma).

of pine and catalpa. Plumes and tufts of hairs are devel-
oped by the seed-like fruits of dandelion, thistle, and very
many of their relatives, and by the seeds of the milkweed
(see Figs. 111, 112,113, 114). On plains, or level stretches,
where winds are
strong, a curious
habit of seed dis-
persal has been de-
veloped by certain
plants known as
““tumbleweeds ” or
‘‘field rollers.”
These plants are
profusely branching

ith a small
annuals Ww % Fie. 121. The 3-valved fruit of violet discharging
root system in a ita seeds.—After Brat.

Fig. 122. A fruit of witch
hazel discharging its
seeds.— After BEAL.

PLANT RELATIONS.

light or sandy soil (see Fig. 120).
When the work of the season is over,
and the absorbing rootlets have
shriveled, the plant is easily blown
from its anchorage by a gust of wind,
and is trundled along the surface like
a light wicker ball, the ripe seed ves-
sels dropping their seeds by the way.
In case of an obstruction, such as a
fence, great masses of these tumble-
weeds may often be seen lodged
against the windward side.

79. Discharge of spores.—In many
plants the distribution of spores and
seeds is not provided for hy any of

the methods just mentioned, but the vessels containing
them are so constructed that they are discharged with

more or less violence and are some-
what scattered.

Many spore cases, especially those,

of the lower plants, burst irregularly,
and with sufficient violence to throw
out spores. In the liverworts pecu-
har cells, called eaters or ** jumpers,”
are formed among the spores, and
when the wall of the spore case is
ruptured the elaters are liberated,
and by their active motion assist in
discharging the spores.

In most of the true mosses the
spore case opens by pushing off a
lid at the apex, which exposes a
delicate fringe of teeth covering the
mouth of the urn-like case. These
teeth bend in and out of the open
spore case as they become moist or

Fie. 123. A pod of wild bean
bursting, the two valves
violently twisting and dis-
charging the seeds.—After
Brat.

REPRODUCTIVE ORGANS. 119

dry, and are of considerable service
in the discharge of spores.

In the common ferns a heavy
spring-like ring of cells encircles
the delicate-walled spore case.
When the wall becomes dry and
comparatively brittle the spring
straightens with considerable force,
the delicate wall is suddenly torn
and the spores are discharged (see
Fig. 45).

Even in the case of the pollen-
spores of seed-plants, a special layer
of the wall of the pollen-sac usually
develops as a spring-like layer, which
assists in opening widely the sac

{ i
Fie. 125. A fruit of
beggar ticks,
showing the two
barbed append-
ages which lay
hold of animals.
—After BEAL.

9

5 é a
when the wall be- Fig. 124. Fruits of Spanish
needle, showing barbed ap-

gins to yield along pendages for grappling.

the line of break- The figure to the left is one
i of the fruits enlarged.—
ing. After KERNER.

80. Discharge of
seeds,— While seeds are generally carried
away from the parent plant by the agency
of water currents or air currents, as al-
ready noted, or by animals, in some in-
stances there ix a mechanical discharge
provided for in the structure of the seed-
case. In such plants as the witch hazel
and violet, the walls of the seed-vessel
press upon the contained seeds, so that
when rupture occurs the seeds are pinched
out, as a moist apple-seed is discharged
by being pressed between the thumb and
finger (see Figs. 121, 122). In the touch-
me-not a strain is developed in the wall
of the seed-vessel, so that at rupture it

120 PLANT RELATIONS.

suddenly curls up and throws the seeds (see Fig. 123). The
squirting cucumber is so named because it becomes very
much distended with water, which is finally forcibly ejected
along with the mass of seed. An *‘ artillery plant” common
in cultivation discharges its
seeds with considerable vio-
lence ; while the detonations
resulting from the explosions
of the seed-vessels of Hura
crepitans, the ‘‘monkey’s din-
Fig. 126. The fruit of carrot, showing Neer bell,” are often remarked

the grappling appendages.—After by travelers in tropical

BEAL.

forests.

81. Dispersal of seeds by animals—Only a few illustra-
tions can be given of this very large subject. Water birds
are great carriers of seeds which are contained in the mud
clinging to their feet and legs. This mud from the borders
of ponds is usually completely filled with seeds and spores
of various plants. One has no conception of the number
until they are actually com-
puted. The following ex-
tract from Darwin's Origin
of Species illustrates this
point :

“T took, in February, three 2 a .
tabl fuls of d:from thr Fig. 127. The fruit of cocklebur, showing
ablespoontuls OF Mud trom three the grappling appendages.—After BEAL.

different points beneath water,

on the edge of a little pond. This mud when dried weighed only 64
ounces ; I kept it covered up in my study for six months, pulling up
and counting each plant as it grew; the plants were of many kinds,
and were altogether 537 in number; and yet the viscid mud was all
contained in a breakfast cup!”

Water birds are generally high and strong fliers, and the
seeds and spores may thus be transported to the margins of
distant ponds or lakes, and so very widely dispersed.

In many cases seeds or fruits develop grappling append-

REPRODUCTIVE ORGANS. 121

ages of various kinds, which lay hold of animals brushing
past, and so the seeds are dispersed. Common illustrations
are Spanish needles, beggar ticks, stick seeds. burdock, etc.
Study Figs. 124, 125, 126, 127, 128, 129, 130.

Fie. 128. Fruits with grappling appendages. That to the left is agrimony ; that to
the right is Galiwm.—After KERNER.

In still other cases the fruit becomes pulpy, and attrac-
tive as food to certain birds or mammals. Many of the
seeds (such as those of grapes) may be able to resist the
attacks of the digestive fluids and escape from the alimen-
tary tract in a condition to germinate. As if to attract the
attention of fruit-eating animals, fleshy fruits usually
become brightly col-
ored when ripe, so that
they are plainly seen
in contrast with the
foliage.

82. Dispersal of pol-
len spores by insects.—

The transfer of pollen,
the name applied to Fic. 129. Fruits with grappling appendages.

; The figure to the left is cocklebur ; that to the
certain spores of seed- right is burdock.—After KERNER.

122 PLANT RELATIONS,

plants, is known as pollination, and
the two chief agents of this transfer
are currents of air and insects. In
$77 the transfer by currents of air
was noted, such plants being known
as anemophilous plants. Such plants
seldom produce what are generally
recognized as true flowers. All those
seed-plants which produce more or
less showy flowers, however, are in
some way related to the visits of
oa cee ae insects to bring about pollination,

grappling appendages— and are known as entomophilous

eee plants. This relation between in-
sects and flowers is so important and so extensive that it
will be treated in a separate chapter.

CHAPTER VII.

FLOWERS AND INSECTS.

83. Insects as agents of pollination The use of insects
as agents of pollen transfer is very extensive, and is the pre-
vailing method of pollination among monocotyledons and
dicotyledons. All ordinary flowers, as usually recognized,
are related in some way to pollination by insects, but it
must not be supposed that they are always successful in
securing it. This mutually helpful relation between flow-
ers and insects is a very wonderful one, and in some cases
it has become so intimate that they cannot exist without
each other. Flowers have been modified in every way to be
adapted to insect visits, and insects have been variously
adapted to flowers.

84. Self-pollination and cross-pollination.—The advantage
of this relation to the flower is to secure pollination. The
pollen may be transferred to the carpel of its own flower,
or to the carpel of some other flower. The former is known
as self-pollination, the latter as cross-pollination. In the
case of cross-pollination the two flowers concerned may be
upon the same plant, or upon different plants, which may
be quite distant from one another. It would seem that
cross-pollination is the preferred method, as flowers are so
commouly arranged to secure it.

85. Advantage to insects.—The advantage of this relation
to the insect is to secure food. This the flower provides
either in the form of nectar or pollen ; and insects visiting
flowers may be divided roughly into the two groups of
nectar-feeding insects, represented by butterflies and moths,

124 PLANT RELATIONS.

and pollen-feeding insects, represented by the numerous
bees and wasps. When pollen is provided as food, the
amount of it is far in excess of the needs of pollination.
The presence of these supplies of food is made known to
the insect by the display of color in connection with the
flowers, by odor, or by form. It should be said that the
attraction of insects by color has been doubted recently, as
certain experiments have suggested that some of the com-
mon flower-visiting insects are color-blind, but remarkably
keen-scented. However this may be for some insects, it
seems to be sufficiently established that many insects rec-
ognize their feeding ground by the display of color.

86. Suitable and unsuitable insects.—It is evident that
all insects desiring nectar or pollen for food are not suit-
able for the work of pollination. For instance, the ordi-
nary ants are fond of such food, but as they walk from plant
to plant the pollen dusted upon them is in great danger of
being brushed off and lost. The most favorable insect is
the flying one, that can pass from flower to flower through
the air. It will be seen, therefore, that the flower must not
only secure the visits of suitable insects, but must guard
against the depredations of unsuitable ones.

87. Danger of self-pollination.—There is still another
problem which insect-pollinating flowers must solve. If
cross-pollination is more advantageous to the plant than
self-pollination, the latter should be prevented so far as
possible. As the stamens and carpels are usually close to-
gether in the sume flower, the danger of self-pollination is
constantly present in many flowers. In those plants which
have stamen-producing flowers upon one plant and carpel-
producing flowers upon another, there is no such danger.

88. Problems of pollination.—In most insect-pollinating
flowers, therefore, there are three problems: (1) to prevent
self-pollination, (2) to secure the visits of suitable insects,
and (3) to ward off the visits of unsuitable insects. It
must not be supposed that flowers are uniformly successful

FLOWERS AND INSECTS.

in solving these problems.

125

They often fail, but succeed

often enough to make the effort worth while.
80. Preventing self-pollination—It is evident that this
danger arises only in those flowers in which the stamens

and carpels are associ-
ated, but their separa-
tion in different flowers
may be considered as
one method of prevent-
ing self-pollination. In
order to understand the
various arrangements to
be considered, it is nec-
essary to explain that
the carpel does not re-
ceive the pollen indif-
ferently over its whole
surface. There is one
definite region organ-
ized, known as the
stigma, upon which the
pollen must be deposited
if it is to do its work.
Usually this is at the
projecting point
of the carpel, very often
at the end of a stalk-
like prolongation from
the ovary (the bulbous
part of the carpel),
known as the style;

most

Fig. 131. Parts of the flower of rose acacia
(Robinia hispida). In 1 the keel is show n pro-
jecting from the hairy calyx, the other more
showy parts of the corolla haying been re-
moved. Within the keel are the stamens
and the carpel, asseen in3. The keel forms
the natural Janding place of a visiting bee,
whose weight depresses the kee] and causes
the tip of the style to protrude, as shown in
2. This style tip bears pollen upon it,
caught among the hairs, seen in 3, and as it
strikes the body of the bee some pollen is
brushed off. If the bee has previously visited
another flower and received some pollen, it
will be seen that the stigma, at the very tip
of the style, striking the body first, will very
probably receive some of it. The nectar pit
is shown in 3, at the base of the uppermost
stamen.—After Gray.

When

sometimes it may run down one side of the style.
the stigma is ready to receive pollen it has upon it a
sweetish, sticky fluid, which holds and feeds the pollen.
In this condition the stigma is said to be mature: and the
pollen is mature when it is shedding, that is, ready to fall

126

PLANT RELATIONS.

out of the pollen-sacs or to be removed from them. The
devices used by flowers containing both stamens and carpels
to prevent self-pollination are very numerous, but most
of them may be included under the three following heads :

Fie. 132. A portion of
the flower of an iris,
or flag. The single
stamen shown is
standing between the
petal to the right and
the petal-like style to
the left. Near the
top of this style the
stigmatic shelf is
seen extending to the
tight, which must
receive the pollen
upon its upper sur-
face. The nectar
pit is at the junc-
tion of the petal and
stamen. While ob-
taining the nectar the
insect brushes the
pollen-bearing part
of the stamen. and
pollen is lodged upon
its body. In visiting
the next flower and
entering the stamen
chamber the _ stig-
matic shelf is apt to
be brushed.—After
GRAY,

(1) Pos/tion.—In these cases the
pollen and stigma are ready at the same
time, but their position in reference to
each other, or in reference to some con-
formation of the flower. makes it un-
likely that the pollen will fall upon the
stigma. The stigma may be placed
above or beyond the pollen sacs, or the
two may be separated by some mechan-
ical obstruction, resulting in much of
the irregularity of flowers.

In the flowers of the rose acacia and
its relatives, the several stamens and
the single carpel are in a cluster, en-
closed in the keel of the flower. The
stigma is at the summit of the style,
and projects somewhat beyond the
pollen-sacs shedding pollen. Also there
is often a rosette of hairs, or bristles,
just beneath the stigma, which acts as
a barrier to the pollen (see Fig. 131).

In the iris, or common flag, each
stamen is in a sort of pocket between
the petal and the petal-like style, while
the stigmatic surface is on the top of a
flap, or shelf, which the stvle sends out
asa roof to the pocket. With such an
arrangement, it would seem impossible
for the pollen to reach the stigma un-
aided (see Fig. 132).

In the orchids, remarkable for their
strange and beautiful flowers, there are

FLOWERS AND INSECTS. 127

usually two pollen-sacs, and stretched between them is the
stigmatic surface. In this case, however, the pollen grains
are not dry and powdery, but cling together in a mass, and
cannot escape from the sac without being pulled out (see
Fig. 133). The same sort of pollen is developed by the
milkweeds.

(2) Consecutive maturity.—In these cases the pollen and

Fie. 183. A flower of an orchid (Habenaria). At 1 the complete flower is shown,
with three sepals behind, and three petals in front, the lowest one of which has
developed a long strap-shaped portion, and a still longer spur portion, the opening
to which is seen at the base of the strap. At the bottom of this long spur is the
nectar, which is reached by the long proboscis of a moth. The two pollen sacs of
the single stamen are seen in the centre of the flower, diverging downwards, and
between them stretches the stigma surface. The relation between pollen sacs and
stigma surface is more clearly shown in 2. Within each pollen sac is a mass of
sticky pollen, ending below in a sticky disk, which may be seenin 1 and 2. When
the moth thrusts his proboscis into the nectar tube, his head is against the stig-
matic surface and also against the disks. When he removes his head the disks
stick fast and the pollen masses are dragged out. In 3 a pollen mass (q@) is
shown sticking to each eye of a moth. Upon visiting another flower these pollen
masses are thrust against the stigmatic surface and pollination is effected.—After
GRAY.

128 PLANT RELATIONS.

stigma of the same flower are not mature at the same time.
It is evident that this is a very effective method of prevent-
ing self-pollination. When the pollen is being shed the
stigma is not ready to receive, or when the stigma is ready
to receive the pollen is not ready to be shed. In some
cases the pollen is ready first, in other cases the stigma,
the former condition being called protandry, the latter
protogyny. This is a very common method of preventing
self-pollination, and is com-
monly not associated with
irregularity.

The ordinary figwort may
be taken as an example of
protogyny. When the flowers
first open, the style, bearing
the stigma at its tip, is found
Fie, 134. Flowers of fireweed (Zpi- protruding from the urn-like

lobium), showing protandry. Inithe flower, while the four
stamens are thrust forward, and the
style is sharply turned downward and stamens are curved down
backward. In 2 the style is thrusts into the tube, and not ready
forward, with its sigmiatic branches to shed their pollen. At
spread, An insect in passing from 1
to 2 will almost certainly transfer po- some later time the style
nea ai ha ltothestig bearing the stigma wilts,
and the stamens straighten
up and protrude from the tube. In this way, first the
receptive stigma, and afterwards the shedding pollen-sacs.
occupy the same position.

Protandry is even more common, and many illustrations
can be obtained. For example, the showy flowers of the
common fireweed, or great willow herb, when first opened
display their eight shedding stamens prominently, the style
being sharply curved downward and backward, carrying
the four stigma lobes well out of the way. Later, the
stamens bend away, and the style straightens up and ex-
poses its stigma lobes, now receptive (see Fig. 154).

(3) Difference in pollen.—In these cases there are at

FLOWERS AND INSECTS. 129

least two forms of flowers, which differ from one another
in the relative lengths of their stamens and styles. In the
accompanying illustrations of Housfonta (see Fig. 135) it
is to be noticed that in one flower the stamens are short
and included in the tube, and the style is long and pro-
jecting, with the four stigmas exposed well above the
tube. In the
other flower the
relative lengths
are exactly re-
versed, the
style being
short and in-
cluded in the
tube, and the
stamens long
and projecting.
It appears that
the pollen from
the short sta-
mens is most
effective upon

the stigmas of Fic. 135, Flowers of Houstonia, showing two forms of
the sl tatvles flowers. In 1 there are short stamens and a long style ;
CS ORES TTS: in 2 long stamens and short style. An insect visiting 1
and that the will receive a band of pollen about the front part of its
"5 body ; upon visiting 2 this band will rub against the

pollen from the stigmas, and a fresh pollen band will be received upon

long stamens 1s the hinder part of the body, which, upon visiting another

g P

most effective flower like No. 1, will brush against the stigmas.—
After GRayY.

upon the stig-
mas of the long styles; and as short stamens and long
stvles, or long stamens and short styles, are associated in
the same flower, the pollen must be transferred to some
other flower to find its appropriate stigma. This means
that there is a difference between the pollen of the short
stamens and that of the long ones.

In some cases there are three forms of flowers, as in one

130 PLANT RELATIONS.

of the common loosestrifes. Each flower has stamens of
two lengths, which, with the style, makes possible three
combinations. One flower has short stamens, middle-length
stamens, and long style ; another has short stamens, middle-
length style, and long stamens; the third has short style,
middle-length stamens, and long stamens. In these cases
also the stigmas are intended to receive pollen from stamens

Fic. 136. Yueca and Pronuba. In the lower figure to the right an opened flower
shows the pendent ovary with the stigma region at its apex. The upper figure to
the right shows the position of Pronuba when collecting pollen, The figure to the
left represents a cluster of capsules of Yucca, which shows the perforations made
by the larvee of Pronuba in escaping.—After RibEyY and TRELEASE.

of their own length, and a transfer of pollen from flower to
flower is necessary.

90, Self-pollination.—In considering these three general
methods of preventing self-pollination, it must not be sup-
posed that self-pollination is never provided for. It is pro-
vided for more extensively than was once supposed. — It is
found that many plants, such as violets, in addition to the
usual showy, insect-pollinated flowers, produce flowers that
are not at all showy, in fact do not open, and are often not
prominently placed. The fact that these flowers are often
closed has suggested for them the name cletstogamous

FLOWERS AND INSECTS. 131

flowers. In these flowers self-pollination is a necessity, and
is found to be very effective in producing seed.

91. Yueca and Pronuba.—There can be no doubt, also,
that there is a great deal of self-pollination effected in
flowers adapted for pollination by insects, and that the in-
sects themselves are often responsible for it. But in the
remarkable case of Yucca and Pronuba there is a definite
arrangement for self-pollination by means of an insect (see
Fig. 136). Yuccais a plant of the southwestern arid regions
of North America, and Pronuba is a moth. The plant and
the moth are very dependent upon each other. The bell-
shaped flowers of Yucca hang in great terminal clusters, with
six hanging stamens, and a central ovary ribbed lengthwise,
and with a funnel-shaped opening at its apex, which is the
stigma. The numerous ovules occur in lines beneath the
furrows. During the day the small female Pronuba rests
quietly within the flower, but at dusk becomes very active.
She travels down the stamens, and resting on the open
pollen-sac scoops out the somewhat sticky pollen with her
front legs. Holding the little mass of pollen she runs to
the ovary, stands astride one of the furrows, and _pierc-
ing through the wall with her ovipositor, deposits an egg
in an ovule. After depositing several eggs she runs to the
apex of the ovary and begins to crowd the mass of pollen
she has collected into the funnel-like stigma. These actions
are repeated several times, until many eggs are deposited
and repeated pollination has been effected. As a result of
all this the flower is pollinated, and seeds are formed which
develop abundant nourishment for the moth larve, which
become mature and bore their way out through the wall of
the capsule (Fig. 136).

92. Securing cross-pollination—In very many ways flow-
ers are adapted to the visits of suitable insects. In ob-
taining nectar or pollen as food, the visiting insect receives
pollen on some part of its body which will be likely to
come in contact with the stigma of the next flower visited.

Fie. 137. A clump of lady-slippers (Cypripedium), showing the habit of the plant
and the general structure of the flower.—After Gipson.

FLOWERS AND INSECTS. 1838

Illustrations of this process may be tuken from the flowers
already described in connection with the prevention of
self-pollination.

In the flowers of the pea family, such as the rose acacia
(see Fig. 151), it will be
noticed that the stamens
and pistil are concealed
within the keel, which
forms the natural land-
ing place for the bees
which are used in pol-
lination. This keel is
so inserted that the
weight of the insect de-
presses it, and the tip
of the style comes in
contact with its body.
Not only does the
stigma strike the body,
but by the glancing
blow the surface of the
style is rubbed against
the insect, and on this

style, below the stigma, : 7

x Fig. 188. Flower of Cypripedium, showing the
the pollen has been de- flap overhanging the opening of the pouch,
posited and is rubbed into which a bee is crowding its way. The
off against the insect small figure to the right shows a side view of

the flap; that to the left a view beneath the
At th e next fl ower flap, showing the two dark anthers, and be-
visited the stigma is oS ae ann
ikely to strike the pol-

len cptained from the previous flower, and the style will
deposit a new supply of pollen.

In the flower of the common flag (see Fig. 132) the nectar
is deposited in a pit at the bottom of the chamber formed
by each style and petal. In this chamber the stamen is
found, and more or less roofing it over is the flap, or shelf,

134 PLANT RELATIONS.

upon the upper surface of which the stigma is developed.
As the insect crowds its way into this narrowing chamber,
its body is dusted by the pollen, and us it visits the next
flower and thrusts aside the stigmatic shelf, it is apt to
deposit upon it some of the pollen previously received.

The story of pollination in connection with the orchids
is still more complicated (see Fig. 133). Taking an ordi-
nary orchid for illustration, the detailsare as follows. Each
of the two pollen masses terminates in a sticky disk or
button ; between them extends the concave stigma sur-
face, at the bottom of which is the opening into the long
tube-like spur in which the nectar is
found. Such a flower is adapted to
the large moths, with long probosces
which can reach the bottom of the
tube. As the moth thrusts its pro-
boscis into the tube, its head touches
the sticky button on each side, so that
when it flies away these buttons stick

to its head, sometimes directly to its

arcs rn a eyes, and the pollen masses are torn

away) of Cypripedium. out. These masses are then carried

a to the next flower and are thrust
against the stigma in the attempt to get the nectar.

In the lady-shpper (Cypripedium), another orchid, the
flowers have « conspicuous pouch (see Fig. 137), in which
the nectar is secreted. A peculiar structure, like a flap,
overhangs the opening of the pouch, beneath which are the
two anthers, und between them the stigmatic surface (see
Fig. 138). Into the pouch a bee crowds its way and be-
comes imprisoned (see Fig. 139). The nectar which the
bee obtains is in the bottom of the pouch (see Fig. 140).
When escaping, the bee moves towards the opening oyer-
hung by the flap and rubs first against the stigmatic sur-
face (see Fig. 141), and then against the anthers, receiving
pollen on its back (see Fig. 142). A visit to another flower

FLOWERS AND INSECTS, 135

will result in rubbing some of the pollen upon the stigma,
and in receiving more pollen for another flower.

In cases of protandry, as the common figwort, flowers
in the two condi-
tions will be visited
by the pollinating
insect, and as the
shedding stamens
and receptive stig-
mas occupy the

same relative posi- SSE
tion, the pollen Fie. 140. A bee obtaining nectar in the pouch of
5 Cypripedium.—After Gipson.

from one flower
will be carried to the stigma of another. It is evident that
exactly the same methods prevail in the case of protogyny,
as the fireweed (see Fig. 134).

The Houstonia (see Fig. 135), in which there are sta-
mens and styles of different lengths, is visited by insects
whose bodies fill
the tube and pro-
trude above it. In
visiting flowers of
both kinds, one re-
gion of the body
receives pollen
from the short sta-

Fic. 141. A bee escaping from the pouch of Cypri- mens, and another
pedium, and coming in contact pale the stigma. region from the
Advancing a little further the bee will come in con-
tact with the anthers and receive pollen.—After long stamens, In

Cieeon this way the insect
will carry about two bands of pollen, which come in con-
tact with the corresponding stigmas. When there are three
forms of flowers, as mentioned in the case of one of the
loosestrifes, the insect receives three pollen bands, one for
each of the three sets of stigmas.

93. Warding off unsuitable insects——Prominent among
10

136 PLANT RELATIONS,

the unsuitable insects, which Kerner calls ‘‘ unbidden
guests,” are ants, and adaptations for reducing their visits
to a minimum may be taken as illustrations.

(1) Hatrs.—A common device for turning back ants,
and other creeping insects, is a barricr of hair on the stem,
or in the flower cluster, or in the flower.

(2) Glandular secretions.—In some cases a sticky
secretion is exuded from the surface of plants, which
effectively stops
the smaller creep-
ing insects. In
certain species of
catch-fly a sticky
ring girdles each
joint of the stem.

(3) Lsolation.—
The leaves of cer-
tain plants form
water reservoirs
about the stem.
To ascend such a
stem, therefore, a
_ creeping insect
Fia. 142. A bee escaping from the pouch of Cypri- must cross a series

pedium, and rubbing against an anther.—After of such reservoirs.
GIpson.

Teasel furnishes a
common illustration, the opposite leaves being united at
the base and forming a series of cups. More extensive
water reservoirs are found in Bilbergia, sometimes called
‘“‘traveler’s tree,” whose great flower clusters are pro-
tected by large reservoirs formed by the rosettes of leaves,
which creeping insects cannot cross.

(4) Later.—This is a milky secretion found in some
plants, as in milkweeds. Caoutchoue is a latex secretion
of certain tropical trees. When latex is exposed to the
air it stiffens immediately, becoming sticky and _ finally

FLOWERS AND INSECTS. 137

hard. In the flower clusters of many latex-secreting
plants the epidermis of the stem is very smooth and deli-
cate, and easily pierced by the claws of ants and other
creeping insects who seek to maintain footing on the
smooth surface. Wherever the epidermis is pierced the
latex gushes out, and by its stiffening and hardening glues
the insect fast.

(5) Protective forms.—In some cases the structure of
the flower prevents the access of small creeping insects to
the pollen or to the nectar. In the common snapdragon
the two lips are firmly closed (see Fig. 74), and they can be
forced apart only by some heavy insect, as the bumble-bee,
alighting upon the projecting lower lip, all lighter insects
being excluded. In many species of Pentstemon, one of
the stamens does not develop pollen sacs, but lies like a bar
across the mouth of the pit in which the nectar is secreted.
Through the crevices left by this bar the thin proboscis of
a moth or butterfly can pass, but not the whole body of a
creeping insect. Very numerous adaptations of this kind
may be observed in different flowers.

(6) Protective closure.—Certain flowers are closed at
certain hours of the day, when there is the chief danger
from creeping insects. For instance, the evening prim-
roses open at dusk, after the deposit of dew, when ants are
not abroad ; and at the same time they secure the visits of
moths, which are night-fliers.

Numerous other adaptations to hinder the visits of
unsuitable insects may be observed, but those given will
serve as illustrations.

CHAPTER VIII.
AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS.

For the purpose of summarizing the general life-rela-
tions detailed in the preceding chapters, it will be useful to
apply them in the case of a single plant. Taking a com-
mon seed-plant as an illustration, and following its history
from the germination of the seed, certain general facts
become evident in its relations to the external world.

‘4, Germination of the seed.—'The most obvious needs of
the seed for germination are certain amounts of moisture
and heat. In order to secure these to the best advantage,
the seed is usually very definitely related to the soil, either
upon it and covered by moisture and heat-retaining debris,
or embedded in it. Along with the demand for heat and
moisture is one for air (supplying oxygen), which is essen-
tial to life. The relation which germinating seeds need,
therefore, is one which not only secures moisture and heat
advantageously, but permits a free circulation of air.

45. Direction of the root.—The first part of the young
plantlet to emerge from the seed is the tip of the axis
which is to develop the root system. It at once appears to
be very sensitive to the earth influence (geotropisim) and
to moisture influence (hydrotropism), for whatever the
direction of emergence from the seed, a curvature is devel-
oped which directs the tip towards and finally into the soil
(sce Fig. 143). When the soil is penetrated the primary
root may continue to grow vigorously downward, showing
a strong geotropic tendency, and forming what is known
as the tap-root, from which lateral roots arise, which are

AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS. 189

much more influenced in direction by other external
causes, especially the presence of moisture. As a rule,
the soil is not perfectly uniform, und contact with different
substances induces curvatures, and as a result of these and
other causes, the root system may become very intricate,
which is extremely favor-
able for absorbing and
gripping.

9. Direction of the stem.
—as soon as the stem tip
is extricated from the seed, h
it exhibits sensitiveness to
the light influence (hel¢ot-
ropism), being guided in
a general way towards the
light (see Fig. 145¢).
Direction towards the
light, the source of the in-
fluence, is spoken of as
positive heliotropism, us
distinguished from direc-
tion away from the light,
called negative heliotro-

Fie. 143. Germination of the seed of
arbor-vite (Y7huja). B shows the
emergence of the axis (7) which is to
develop the root, and its turning to-
wards the soil. (‘shows a later stage,
in which the root (7) has been some-
what developed, and the stem of the

pism. If the main axis
continues to develop, it
continues to show this posi-
tive heliotropism strongly,
but the branches may show

embryo (2) is developing a curve pre-
paratory to pulling out the seed leaves
(cotyledons). 2 shows the young plant-
let entirely free from the seed, with its
root (7) extending into the soil, its stem
(hk) erect, and its first leaves (¢) hori-
zontally spread.—After STRASBURGER.

every variation from positive to /ransverse heliotropism ;
that is, a direction transverse to the direction of the rays
of light. In some plants certain stems, as stolons, run-
ners, etc., show strong transverse heliotropism, while other
stems, as rootstocks, etc., show a strong transverse geot-
ropism.

97. Direction of foliage leaves—The general direction of
foliage leaves on an erect stem is transversely heliotropic ;

140 PLANT RELATIONS.

if necessary, the parts of the leaf or the stem itself twisting
to allow the blade to assume this position. The danger of
the leaves shading one another is reduced to a minimum by
the elongation of internodes, the spiral arrangement, short-
ening and changing direction upwards, or lobing.

This outhnes the general nutritive relations, the roots

Fie. 143a. Germination of the garden bean, showing the arch of the seedling stem
above ground, its pull on the seed to extricate the cotyledons and plumule, and
the final straightening of the stem and expansion of the young leaves.—After
ATKINSON.

and leaves being favorably placed for absorption, and the
latter also favorably placed for photosynthesis.

WS. Placing of flowers——The purposes of the flower seem
to be served best by exposed positions, and consequently
flowers mostly appear at the extremities of stems and
branches, a position evidently favorable to pollination and
seed dispersal. The flowers thus exposed are very com-
monly massed, or, if not, the single flower is apt to be large
and conspicuous. The various devices for protecting nec-
tar and pollen against too great moisture, and the more

AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS. 141

delicate structures against chill ; for securing the visits of
suitable insects, and warding off unsuitable insects; and
for dispersing the seeds, need not be repeated.

99. Branch buds—If the plant under examination be a
tree or shrub, branch buds will be observed to develop at
the end of the growing season (see Fig. 65). This device
for protecting growing tips through a season of dangerous
cold is very familiar to those living in the temperate
regions. The internodes do not elongate, hence the leaves
overlap ; they develop little or no chlorophyll, and become
scales. The protection afforded by these overlapping
scales is often increased by the development of hairs. or
by the secretion of mucilage or gum.

CHAPTER IX.
THE STRUGGLE FOR EXISTENCE.

100. Definition. The phrase “struggle for existence”
has come to mean, so far as plants are concerned, that it is
usually impossible for them to secure ideal relations, and
that they must encounter unfavorable conditions. The
proper light and heat relations may be difficult to obtain,
and also the proper relations to food material. It often
happens, also, that conditions once fairly favorable may be-
come unfavorable. Also, multitudes of plants are trying
to take possession of the same conditions. <All this leads
to the so-called “struggle,” and vastly more plants fail
than succeed. Before considering the organization of plant
societies, it will be helpful to consider some of the possible
changes in conditions, and the effect on plants.

101. Decrease of water.—This is probably the most com-
mon factor to fluctuate in the environment of a plant.
Along the borders of streams and ponds, and in swampy
places, the variation in the water is very noticeable, but the
same thing is true of soilsin general. However, the change
chiefly referred to is that which is permanent, and which
compels plants not merely to tide over a drought, but to
face a permanent decrease in the water supply.

Around the margins of ponds are very commonly seen
fringes of such plants as bulrushes, cat-tail flags, reed-
grasses, etc., standing in shoal water. As these plants
grow close together, silt from the land is entangled by them,
and presently it accumulates to such an extent that there
is no more standing water, and the water supply for the

THE STRUGGLE FOR EXISTENCE. 148

bulrushes and their associates has permanently decreased
below the favorable amount. In this way certain lake
margins gradually encroach upon the water, and in so
doing the water supply is permanently diminished for many
plants. By the same process, smaller lakelets are gradually
being converted into bogs, and the bogs in turn into drier
ground, and these unfavorable changes in water supply are
a menace to many plants.

The operations of man, also, have been very effective in
diminishing the water supply for plants. Drainage, which
is so extensively practiced, while it may make the water-
supply more favorable for the plants which man desires, cer-
tainly makes it very unfavorable for many other plants.
The clearing of forests has a similar result. The forest
soil is receptive and retentive in reference to water, and is
somewhat like a great sponge, steadily supplying the streams
which drain it. The removal of the forest destroys much
of this power. The water is not held and gradually doled
out, but rushes off in a flood; hence, the streams which
drain the cleared area are alternately flooded and dried up.
This results in a much less total supply of water available
for the use of plants.

102. Decrease of light.—It is very common to observe
tall, rank vegetation shading lower forms, and seriously
interfering with the light supply. If the rank vegetation
is rather temporary, the low plants may learn to precede or
follow it, and so avoid the shading ; but if the over-shading
vegetation is a forest growth, shading becomes permanent.
In the case of deciduous trees, which drop their leaves at the
close of the growing season and put out a fresh crop in the
spring, there is an interval in the early spring, before the
leaves are fully developed, during which low plants may
secure a good exposure to light (see Fig. 144). In such
places one finds an abundance of ‘‘spring flowers,” but later
in the season the low plants become very scarce. This
effective over-shading is not common to all forests, for

Fie. 144. A common spring plant (dog-tooth violet) which grows in deciduous
forests. The large mottled leaves and the conspicuous flowers are sent rapidly
above the surface from the subterrancan bulb (see cut in the left lower corner),
where are also seen dissected out some petals and stamens and the pistil.

THE STRUGGLE FOR EXISTENCE. 145

there are ‘light forests,” such as the oak forest, which
permit much low vegetation, as well as the shade forests,
such as beech forests, which permit very little.

In the forest regions of the tropics, however, the shad-
ing is permanent, since there is no annual fall of leaves.
In such conditions the climbing habit has been extensively
cultivated.

103. Change in temperature.—In regions outside of the
tropics the annual change of temperature is a very im-
portant factor in the life of plants, and they have previded
for it in one way or another. In tracing the history of
plants, however, back into what are culled ** geological
times.” we discover that there have een relatively per-
manent changes in temperature. Now and then glacial
conditions prevailed, during which regions before temperate
or eyen tropical were subjected to arctic conditions. It is
very evident that such permanent changes of temperature
must have had an immense influence upon plant life.

104. Change in soil composition.—One of the most ex-
tensive agencies in changing the compositious of soils in
certain regions has been the movement of glaciers of vonti-
nental extent, which have deposited soil material over very
extensive areas. Areas within reach of occasional floods,
also, may have the soil much changed in character by the
new deposits. Shifting dunes are billow-like masses of
sand, developed and kept in motion hy strong prevailing
winds, and often encroach upon other areas. Besides these
changes in the character of soil by natural agencies. the
yarious operations of man have been influential. Clearing,
draining, fertilizing, all change the character of the soil,
both in its chemical composition and its physical properties.

105. Devastating animals.—The ravages of animals form
an important factor in the life of many plants. For example,
grazing animals are wholesale destroyers of vegetation. and
may seriously affect the plant life of an area. The various
leaf feeders among insects have frequently done a vast

146 PLANT RELATIONS.

amount of damage to plants. Many burrowing animals
attack subterranean parts of plants, and interfere seriously
with their occupation of an area.

Various protective adaptations against such attacks have
been pointed out, but this subject probably has been much
exaggerated. The occurrence of hairs, prickles, thorns,
and spiny growths upon many plants may discourage the
attacks of animals, but it would be rash to assume that
these protections have been developed because of the danger
of such attacks. One of the families of plants most com-
pletely protected in this way is the great cactus family,
chiefly inhabiting the arid regions of southwestern United
States and Mexico. In such a region succulent vegetation
is at a premium, and it is doubtless true that the armor of
thorns and bristles reduces the amount of destruction.

In addition to armor, the acrid or bitter secretions of
certain plants or certain parts of plants would have a
tendency to ward off the attacks of animals.

106. Plant rivalry.—It is evident that there must be
rivalry among plants in occupying an area, and that those
plants which can most nearly utilize identical conditions
will be the most intense rivals. For example, a great many
young oaks may start up over an area, and it is evident
that the individuals must come into sharp competition with
one another, and that but few of them succeed in establish-
ing themselves permanently. This is rivalry between in-
dividuals of the same kind ; but some other kind of trees,
as the beech, may come into competition with the oak, and
another form of rivalry will appear.

As w consequence of plant rivalry, the different plants
which finally succeed in taking possession of an area are
apt to be dissimilar, and a plant society is usually made up
of plants which represent widely different regions of the
plant kingdom. It is sometimes said that any well de-
veloped plant society Is an epitome of the plant kingdom.

A familiar illustration of plant rivalry may be observed

THE STRUGGLE FOR EXISTENCE. 147

in the case of what are called ‘‘ weeds.” Every one is fa-
miliar with the fact that if cultivated ground is neglected
these undesirable plants will invade it vigorously and seri-
ously affect the development of plants under cultivation.

107. Adaptation—When the changes mentioned above
occur in the environment of plants to such an extent as
to make the conditions for living very unfavorable, one
of three things is likely to occur, adaptation, migration,
or destruction.

The change in conditions may come slowly enough, and
certain plants may be able to endure it long enough to
adjust themselves to it. Such an adjustment may involve
changes in structure, and probably no plants are plastic
enough to adjust themselves to extreme and sudden changes
which are to be comparatively permanent. There are
plants, such as the common cress, which may be called
amphibious, which can live in the water or out of it without
change of structure, but this is endurance rather than
adaptation. Many plants, however. can pass slowly into
different conditions, such as drier soil, denser shade, etc.,
and corresponding changes in their structure may be noted.
Very often, however, such plants are given no opportunity
to adjust themselves to the new conditions, as the area is
apt to be invaded by plants already better adapted. While
adaptation may be regarded as a real result of changed con-
ditions, it would seem to be by no means the common one.

108. Migration —This is a very common result of
changed conditions. Plants migrate as truly as animals,
though, of course, their migration is from generation to
generation. It is evident, however, that migration cannot
be universal, for barriers of various kinds may forbid it.
In general, these barriers represent unfavorable conditions
for living. Ifa plant area with good soil is surrounded by
a sterile area, the latter would form an efficient barrier to
migration from the former. Plants of the lowlands could
not cross mountains to escape from unfavorable conditions.

148 PLANT RELATIONS.

To make migration possible, therefore, it is necessary for
the conditions to be favorable for the migrating plants in
some direction. In the case of bulrushes, cat-tail flags,
etc., growing in the shoal water of a lake margin, the
building up of soil about them results in unfavorable con-
ditions. As a consequence, they migrate further into the
lake. If the lake happens to be a small one, the filling up
process may finally obliterate it, and a time will come when
such forms as bulrushes and flags will find it impossible to
migrate.

In glacial times very many arctic plants migrated south-
ward, especially along the mountain systems, and many
alpine plants moved to lower ground. When warmer con-
ditions returned, many plants that had been driven south
returned towards the north, and the arctic and alpine plants
retreated to the north and up the mountains. The history
of plants is full of migrations, compelled by changed con-
ditions and permitted in various directions. It must be
remembered, also, that migrations often result in changes
of structure.

109. Destruction.—Probably this is by far the most com-
mon result of greatly changed conditions. Even if plants
adapt themselves to changed conditions, or migrate, their
structure may be so changed that they will seem like quite
different plants. In this way old forms gradually disappear
and new ones take their places.

CHAPTER X.
THE NUTRITION OF PLANTS.

110. Physiology.—In the previous chapters plants have
been considered in reference to their surroundings. It
was observed that various organs of nutrition hold certain
life-relations, but it is essential to discover what these rela-
tions mean to the life of the plant. The study of plants
from the standpoint of their life-relations has been called
Ecology ; the study of the life-processes of plants is called
Physiology. These two points of view may be illustrated
by comparing them to two points of view for the study of
man. Man may be studied in reference to his relation to
his fellow-men and to the character of the country in which
he lives ; or his bodily processes may be studied, such as
digestion, circulation, respiration, etc. The former cor-
responds to Ecology, the latter is Physiology.

All of the ecological relations that have been mentioned
find their meaning in the physiology of the plant, for life-
relations have in view life-processes. The subject of plant
physiology is a very complex one, and it would be impossi-
ble in an elementary work to present more than a few very
general facts. Certain facts in reference to plant move-
ments. an important physiological subject, have been men-
tioned in connection with life-relations, but it seems neces-
sary to make some special mention of nutrition.

111. Significance of chlorophyll—Probably the most im-
portant fact to observe in reference to the nutrition of
plants is that some plants are green or have green parts,
while others, such as toadstools, do not show this green

150 PLANT RELATIONS.

color. It has been stated that this green color is due to
the presence of a coloring matter known as chlorophyll
(see §12). The two groups may be spoken of, therefore,
as (1) green plants and (2) plants without chlorophyll.
The presence of chlorophyll makes it possible for the plants
containing it to manufacture their own food out of such
materials as water, soil material, and gases. For this
reason, green plants may be entirely independent of all
other living things, so far as their food supply is concerned.

Plants without chlorophyll, however, are unable to
manufacture food out of such materials, and must obtain
it already manufactured in the bodies of other plants or
animals. or this reason, they are dependent upon other
living things for their food supply, just as are animals. It
is evident that plants without chlorophyll may obtain this
food supply either from the living bodies of plants and ani-
mals, in which case they are called parasites, or they may
obtain it from the substances derived from the bodies of
plants and animals, in which case they are called sapro-
phytes. For example, the rust which attacks the wheat,
and is found upon the leaves and stems of the living plant ;
is a parasite, while the mould which often develops on stale
bread is a saprophyte. Some plants without chlorophyll
can live either as parasites or saprophytes, while others are
always one or the other. By far the largest number of
parasites and saprophytes belong to the group of low plants
called fungi, and when fungi are referred to, it must be
understood that it means the greatest group of plants with-
out chlorophyll.

112. Photosynthesis.—The nutritive processes in green
plants are the same as in other plants, and in addition there
is in green plants the peculiar process known as photoxyn-
thesis (see §25). In plants with foliage leaves, these are
the chief organs for this work. It must be remembered,
however, that leaves are not necessary for photosynthesis,
for plants without leaves, such as alge, perform it. The

THE NUTRITION OF PLANTS. 1651

essential thing is green tissue exposed to light, but in this
brief account an ordinary leafy plant growing in the soil
will be considered.

As the leaves are the active structures in the work of
photosynthesis, the raw materials necessary must be brought
to them. Ina general way, these materials are carbon di-
oxide and water. The gas exists diffused through the
atmosphere, and so is in contact with the leaves. It also
occurs dissolved in the water of the soil, but the gas used
is absorbed from the air by the leaves. The supply of
water, ou the other hand, in soil-related plants, is obtained
from the soil. The root system absorbs this water, which
then ascends the stem and is distributed to the leaves.

(1) Ascent of water.—The water does not move up-
wards through all parts of the stem, but is restricted to a
certain definite region. This region is easily recognized as
the woody part of stems. Sometimes separate strands of
wood, looking like fibers, may be seen running lengthwise
through the stem ; sometimes the fibrous strands are packed
so close together that they form a compact woody mass, as
in shrubs and trees. In the case of most trees new wood is
made each year, through which the water moves. Hence
the very common distinction is made between sap-wood,
through which the water is moving, and heart-wood, which
the water current has abandoned. Just how the water
ascends through these woody fibers, especially in tall trees,
is a matter of much discussion, and cannot be regarded as
definitely known. In any event, it should be remembered
that these woody fibers are not like the open veins and
arteries of animal bodies, and no ‘‘ circulation ” is possible.
These same woody strands are seen branching throughout
the leaves, forming the so-called vein system, and it is evi-
dent, therefore, that they form a continuous route from
roots to leaves.

It is easy to demonstrate the ascent of water in the

stem, and the path it takes, by a simple experiment. If
11

152 PLANT RELATIONS.

an active stem be cut and plunged into water stained with
an aniline color called eosin,* the ascending water will stain
its pathway. After some time sections through the stem
will show that the water has traveled upwards through it,
and the stain will point out the region of the stem used in
the movement.

In general, therefore, the carbon dioxide is absorbed
directly from the air by the leaves, and the water is ab-
sorbed by the root from the soil, and moves upwards through
the stem into the leaves. An interesting fact about these
raw materials is that they are very common waste products.
They are waste products because in most life-processes they
cannot be taken to pieces and used. The fact that they
can be used in photosynthesis
shows that it is a very re-
markable life process.

(2) Chloroplasts.—Maving
obtained some knowledge of
the raw materials used in
Fig. 145. Some mesophyll cells from photosynthesis, and their

the leaf of Fitlonia, showing chloro- SOUTCCS, it 1s necessary to

piaste: consider the plant machinery
arranged for the work. In the working leaf cells it is
discovered that the color is due to the presence of very
smiull green bodies, known as chlorophyll bodies or chloro-
plasts (see Fig. 145). These consist of the living substance,
known as protoplasm, and the green stain called chloro-
phyll; therefore, each chloroplast is a living body (plastid)
stained green. It is in these chloroplasts that the work of
photosynthesis is done. In order that they may work it
is necessary for them to obtain a supply of energy from
some outside source, and the source used in nature is sun-
light. The green stain (chlorophyll) seems to be used in
absorbing the necessary energy from sunlight, and the

* The commoner grades of red ink are usually solutions of eosin.

THE NUTRITION OF PLANTS. 153

plastid uses this energy in the work of photosynthesis. It
is evident, therefore, that photosynthesis goes on only in
the sunlight, and is suspended entirely at night. It is
found that any intense light can be used as a substitute
for sunlight, and plants have been observed to carry on
the work of photosynthesis in the presence of electric
light.

(3) Result of photosynthesis.—The result of this work
can be stated only in a very general way. Carbon dioxide
is composed of two elements, carbon and oxygen, in the
proportion one part of carbon to two parts of oxygen.
Water is also composed of two elements, hydrogen and oxy-
gen. In photosynthesis the elements composing these sub-
stances are separated from one another, and recombined in
anew way. In the process a certain amount of oxygen is
liberated, just as much as was in the carbon dioxide, and a
new substance is formed, known as a carbohydrate. The
oxygen set free escapes from the plant, and may be re-
garded as waste product in the process of photosynthesis.
It will be remembered that the external changes in this
process are the absorption of carbon dioxide and the giving
off of oxygen (see §25).

(4) Carbohydrates und proteids.—The carbohydrate
formed is an organic substance; that is, a substance made
in nature only by life processes. It is the same kind of
substance as sugar or starch, and all are known as carbohy-
drates ; that is, substances composed of carbon, and of hy-
drogen and oxygen in the same proportion as in water.
The work of photosynthesis, therefore, is to form carbohy-
drates. The carbohydrates, such as sugar and starch, rep-
resent but one type of food material. Proteids represent
another prominent type, substances which contain carbon,
hydrogen, and oxygen, as do carbohydrates, but which also
contain other elements, notably nitrogen, sulphur, and
phosphorus. The white of an egg may be taken as an ex-
ample of proteids. They seem to be made from the carho-

154 PLANT RELATIONS.

hydrates, the nitrogen, sulphur, and other necessary
additional elements being obtained from soil substances
dissolved in the water which is absorbed and conveyed
to the leaves.

113. Transpiration.—The water which is absorbed by the
roots and passes to the leaves is much more abundant than
is needed in the process of photosynthesis. It should he re-
membered that the water is not only used as a raw material
for food manufacture, but also acts as a solvent of the soil
materials and carries them into the plant. The water in
excess of the small amount used in food manufacture is
given off from the plant in the form of water vapor, the
process being already referred to as (ranspiration (sev $26).

114. Digestion. —Carbohydrates and proteids may be re-
garded as prominent types of plant food which green
plants are able to manufacture. These foods are trans-
ported through the plant to regions where work is going on,
and if there is a greater supply of food than is needed for
the working regions, the excess is stored up in some part
of the plant. Asa rule, green plants are able to manufac-
ture much more food than they use, and it is upon this ex-
cess that other plants and animals live. In the transfer of
foods through the plant certain changes are often neces-
sary. For example, starch is msoluble, and hence cannot
be carried about in solution. It is necessary to transform
it into sugar, which is soluble. These changes, made to
facilitate the transfer of foods, represent digestion.

115. Assimilation—When food in some form has reached
a working region, it is organized into the living substance
of the plant, known us protoplasm, and the protoplasin
builds the plant structure. This process of organizing the
food into the living substance is known is axsimilation.

116. Respiration —The formation of foods, their diges-
tion and assimilation are all preparatory to the process of
respiration, which may be called the use of assimilated
food. The whole working power of the plant depends

THE NUTRITION OF PLANTS. 155

upon respiration, which means the absorption of oxygen by
the protoplasm, the breaking down of protoplasm, and the
giving off of carbon dioxide and water as wastes. The im-

Fic. 146. The common Northern pitcher plant. The hollow leaves, each with a hood
and a wing, form a rosette, from the center of which arise the flower stalks,—
After KERNER,

portance of this process may be realized when it is remem-
bered that there is the same need in our own living, as it
is essential for us also to ‘‘ breathe in” oxygen, and asa
result we ‘** breathe out” carbon dioxide and water. This
breaking down or ‘‘ oxidizing * of protoplasm releases the

156 PLANT RELATIONS.

power by which the work of the plant is carried on (see

$27).

117. Summary of life-processes—T'o summarize the nu-
tritive life-processes in green plants, therefore, photosyn-

Fie. 147, The Southern pitcher
plant, showing the funnelform
and winged pitcher, and the
overarching hood with translu-
cent spots.—After KERNER.

thesis manufactures carbohydrates,
the materials used being carbon
dioxide and water, the work being
done by the chloroplast with the
aid of light ; the manufacture of
proteids uses these carbohydrates,
and also substances containing
nitrogen, sulphur, etc.; digestion
puts the insoluble carbohydrates
and the proteids into a soluble
form for transfer through the
plant; assimilation converts this
food material into the living sub-
stance of the plant, protoplasm ;
respiration is the oxidizing of the
protoplasm which enables the
plant to work, oxygen being ab-
sorbed, and carbon dioxide and
water vapor being given off in
the process.

118. Plants without chlorophyll.
—Remembering the life-processes
described under green plants, it is
evident that plants without chlo-
rophyll cannot do the work of
photosynthesis. This means that
they cannot manufacture carbo-
hydrates, and that they must de-

pend upon other plants or animals for this important food.

Mushrooms, puff-balls,

molds, mildews, rusts, dodder,

corpse plants, beech drops, etc., may be taken as illustra-

tions of such plants.

THE NUTRITION OF PLANTS, 157

Although plants without chlorophyll cannot manufac-
ture carbohydrates, the other processes, proteid manufac-
ture, digestion, assimilation, and respiration, are carried on.
It is true, however, that in obtaining carbohydrates from

other plants and ani-
mals, proteids are ob-
tained also, so that
proteid manufacture
is not go prominent as
in green plants.

119. “ Carnivorous”
plants.—This name has
been given to plants
which have developed
the curious habit of
capturing insects and
using them for food.
They are green plants
and, therefore, can man-
ufacture carbohydrates.
But they live in soil
poor in nitrogen com-
pounds, and hence pro-
teid formation is inter-
fered with. The bodies
of captured insects sup-
plement the proteid
supply, and the plants
have come to depend
upon them. Many, if
not all of these carniy-
orous plants, secrete a
digestive substance
which acts upon the

Fie. 148. The Californian pitcher plant (Darling-
tonia), showing twisted and winged pitcher,
the overarching hood with translucent spots,
and the fish-tail appendage to the hood
which is attractive to flying insects.—After
KERNER.

bodies of the captured insects very much as the diges-
tive substances of the alimentary canal act upon proteids

158 PLANT RELATIONS.

swallowed by animals. Some common illustrations are as
follows :

(1) Pitcher plants.—In these plants the leaves form
tubes, or urns, of various forms, which contain water, and
to which insects are attracted and drowned (see Fig. 146).
A pitcher plant common throughout the Southern States
may be taken as a type (see Fig. 147). The leaves are
shaped like slender, hollow cones, and rise in a tuft from
the swampy ground.
The mouth of this
conical urn is over-
arched and shaded
by a hood, in which
are translucent spots,
like small windows.
Around the mouth
of the urn are
glands, which se-
crete a sweet hquid
(nectar), and nectar
drops form a_ trail
down the outside of
Ky theurn. Inside, just
below the rim of the
at 3 : urn, is a glazed zone,

‘ TAS so smooth that insects

LE NRE cannot walk wpon it.

Fie. 149. A sun-dew, showing rosette habit of Below the glazed zone

the insect-catching leayes. is unother zone Pi

thickly set with stiff,

downward-pointing hairs, and below this is the liquid in
the bottom of the urn.

If a fly is attracted by the nectar drops upon this curious
leaf, it naturally follows the trail wp to the rim of the urn,
where the nectar is abundant. If it attempts to descend
within the urn, it slips on the glazed zone, and falls into

THE NUTRITION OF PLANTS. 159"

the water, and if it attempts to escape by crawling up the
sides of the urn, the thicket of downward-pointing hairs
prevents. If it seeks to fly away from the rim, it flies
towards the translucent spots in the hood, which look like
the way of escape, as the direction of entrance is in the
shadow of the hood. Pounding against the hood, the fly
falls into the tube. This Southern pitcher plant is known

Bile
Ce
rs
a
gd

aoe

Silke
a

Fie. 150. Two leaves of a sun-dew. The one to the right has its glandular hairs
fully expanded ; the one to the left shows half of the hairs bending inward, in the
position assumed when an insect has becn captured.—After KERNER.

as a great fly-catcher, and the urns are often well supplied
with the decaying bodies of these insects.

A much larger Californian pitcher plant has still more
elaborate contrivances for attracting insects (see Vig. 148).

(2) Drosera.—The droseras are commonly known as
“‘sun-dews,” and grow in swampy regions, the leaves form-
ing small rosettes on the ground (see Fig. 149). In one
form the leaf blade is round, and the margin is beset by
prominent bristle-like hairs, each with a globular gland at
its tip (see Fig. 150). Shorter gland-bearing hairs are

160 PLANT RELATIONS.

scattered also over the inner surface of the blade. These
glands excrete a clear, sticky fluid, which hangs to them in
denies like dew-drops. If a small insect becomes entangled

Fic. 151. Plants of Dionwa, showing the rosette habit of the leaves with terminal
traps, and tbe erect flowering stem,—After KERNER.

in the sticky drop, the hair begins to curve inward, and
presently presses its vietim down upon the surface of the
blade. In the case of larger insects, several of the marginal
hairs may join together in holding it, or the whole blade
may become more or less rolled inward.

THE NUTRITION OF PLANTS. 161

(3) Dionea.—This is one of the most famous and re-
markable of fly-catching plants (see Fig. 151). It is found
only in swamps near Wilmington, North Carolina. The
leaf blade is constructed like a steel trap, the two halves
snapping together, and the marginal bristles interlocking
like the teeth of a trap (see Fig. 152). A few sensitive
hairs, like feelers, are
developed on the leaf
surface, and when one
of these is touched by
a small flying or hover-
ing insect, the trap
snaps shut and the in-
sect is caught. Only
after digestion does the
trap open again.

There are certain
green plants, not called
carnivorous plants,
which show the same
general habit of sup-
plementing their food
supply, and so reduc-
ing the necessity of
food manufacture. Fie. 152. Three leaves of Dionwa, showing

Site ig
* Bo
vai

i hee RK

Taal

‘a

The istletoe is the details of the trap in the leaves to right
ners k : and left, and the central trap in the act of
green plant, growing capturing an insect.

upon certain trees, from
which it obtains some food, supplementing that which it
is able to manufacture.

In rich soil, the organized products of the decaying
bodies of plants and animals are often absorbed by ordinary
green plants, and so a certain amount of ready-made food
is obtained.

CHAPTER NI.
PLANT SOCIETIES: ECOLOGICAL FACTORS.

120. Definition of plant society.—From the previous
chapters it has been learned that every complex plant is
a combination of organs, and that each organ is related in
some special way to its environment. It follows, therefore,
that the whole plant, made up of organs, holds a very com-
plex relation with its environment. The stem demands
certain things, the root other things, and the leaves still
others. To satisfy all of these demands, so far us possible,
the whole plant is delicately adjusted.

The earth’s surface presents very diverse conditions in ref-
erence to plant life, and as plants are grouped according to
these conditions, this leads to definite associations of plants,
those adapted to the same general conditions being apt to
live together. Such an association of plants living together
in similar conditions is a plant society, the conditions for-
bidding other plants. It must not be understood that all
plants affecting the same conditions will be found living
together. For example, a meadow of a certain type will not
contain all the kinds of grasses associated with that type.
Certain grasses will be found in one meadow, and other
grasses will be found in other meadows of the same type.

Very closely related plants generally do not live in the
same society, as their rivalry is apt to be intense. Closely
related plants are likely to occur, however, in different
socicties of the same type. A plant society, therefore, may
contain a wide representation of the plant kingdom, from
plants of low rank to those of high rank.

PLANT SOCIETIES: ECOLOGICAL FACTORS. 163

Before considering some of the common societies, it is
necessary to note some of the conditions which determine
plant societies. ‘Those things in the environment of the
plant which influence the organization of a society are
known as ecological factors.

121. Water.—Water is certainly one of the most im-
portant conditions in the environment of a plant, and has
great influence in determining the organization of societies.
If all plants are considered, it will be noted that the amount
of water to which they ure exposed is exceedingly variable.
At one extreme are those plants which are completely
submerged; at the other extreme are those plants of arid
regions which can obtain very little water ; and between
these extremes there is every gradation in the amount of
available water. Among the most striking adaptations of
plants are those for living in the presence of a great amount
of water, and those for guarding against its lack.

One of the first things to consider in connection with
any plant society is the amount of water supply. It is not
merely a question of its total annual amount, but of its
distribution through the year. Is it supplied somewhat
uniformly, or is there alternating flood and drought? The
nature of the water supply is also important. Are there
surface channels or subterranean channels, or does the
whole supply come in the form of rain and snow which
fall upon the area ?

Another important fact to consider in connection with
the water supply has to do with the structure of the soil.
There is what may be called a water level in soils, and it is
important to note the depth of this level beneath the sur-
face. In some soils it is very near the surface ; in others,
such as sandy soils, it may be some distance beneath the
surface.

Not only do the amount of water and the depth of the
water level help to determine plant societies, but also the
substances which the water contains. Two areas may have

164 PLANT RELATIONS.

the same amount of water and the same water level, but
if the substances dissolved in the water differ in certain
particulars, two entirely distinct societies may result.

122. Heat.—The general temperature of an area is im-
portant to consider, but it is evident that differences of
temperature are not so local as differences in the water
supply, and therefore this factor is not so important in the
organization of the local associations of plants, called socie-
ties, as is the water factor. In the distribution of plants
over the surface of the earth, however, the heat factor is
probably more important than the water factor. The range
of temperature which the plant kingdom, as a whole, can
endure during active work may be stated in a general way
as from 0° to 50° C.; that is, from the freezing point of
water to 122° Fahr. There are certain plants which can
work at higher temperatures, notably certain alge growing
in hot springs, but they may be regarded as exceptions. It
must be remembered that the range of temperature given
is for plants actively at work, and does not include the tem-
perature which many plants are able to endure in a specially
protected but very inactive condition. For example, many
plants of the temperate regions endure a winter tempera-
ture which is frequently lower than the freezing point of
water, but it is a question of endurance and not of work.

It must not be supposed that all plants can work equally
well throughout the whole range of temperature given, for
they differ widely in this regard. Tropical plants, for in-
stance, accustomed to a certain limited range of high tem-
perature, cannot work continuously at the lower tempera-
tures. Tor each kind of plant there is what may be called
a zero point, below which it is not in the habit of working.

While it is important to note the general temperature
of an arca throughout the year, it is also necessary to note
its distribution. Two regions may have presumably the
same amount of heat through the year, but if in the one case
it is uniformly distributed, and in the other great extremes

PLANT SOCIETIES: ECOLOGICAL FACTORS. 165

of temperature occur, the same plants will not be found in
both. It is, perhaps, most important to note the tempera-
ture during certain critical periods in the life of plants,
such as the flowering period of seed-plants.

Although the temperature problem may be compara-
tively uniform over any given area, the effect of it may be
noted in the succession of plants through the growing sea-
son. In our temperate regions the spring plants and summer
plants and autumn plants differ decidedly from one another.
It is evident that the spring plants can endure greater
cold than the summer plants, and the succession of flowers
will indicate somewhat these relations of temperature.

It should be remarked, also, that not only is the tem-
perature of the air to be noted, but also that of the soil.
These two temperatures may differ by several degrees, and
the soil temperature especially affects root activity, and
hence is a very important factor to discover.

At this point it is possible to call attention to the effect
of the combination of ecological factors. For instance, in
reference to the occurrence of plants in any society, the
water factor and the heat factor cannot be considered each
by itself, but must be taken in combination. For example,
if in a given area there is a combination of maximum heat
and minimum water, the result will be a desert, and only
certain specially adapted plants can exist. It is evident
that the great heat increases the transpiration, and tran-
spiration when the supply of water is very meager is pe-
culiarly dangerous. Plants which exist in such conditions,
therefore, must be specially adapted for controlling tran-
spiration. On the other hand, if in any area the combina-
tion is maximum heat and maximum water, the result will
be the most luxuriant vegetation on the earth, such as grows
in the rainy tropics. It is evident that the possible com-
binations of the water and heat factors may be very numer-
ous, and that it is the combination which chiefly affects
plant societies.

166 PLANT RELATIONS.

123. Soil—The soil factor is not merely important to
consider in connection with those plants directly related
to the soil, but is a factor for all plants, as it determines
the substances which the water contains. There are two
things to be considered in connection with the soil, namely,
its chemical composition and its physical properties. Per-
haps the physical properties are more important from the
standpoint of soil-related plants than the chemical com-
position, although both the chemical and physical nature
of the soil are so bound up together that they need not be
considered separately here. The physical properties of the
soil, which are important to plants, are chiefly those which
relate to the water supply. It is always important to de-
termine how receptive a soil is. Does it take in water
easily or not ? It is also necessary to determine how re-
tentive it is; it may receive water readily, but it may not
retain it.

For convenience in ordinary field work with plants,
soils may be divided roughly into six classes: (1) rock,
which means solid uncrumbled rock, upon which certain
plants are able to grow ; (2) sand, which has small water
capacity, that is, it may receive water readily enough, but
does not retain it ; (3) l’me soil ; (4) clay, which has great
water capacity ; (5) humus, which is rich in the products
of plantand animal decay ; (6) salé sotl, in which the water
contains various salts, and is generally spoken of as alka-
line. These divisions in a rough way indicate both the
structure of the soil and its chemical composition. Not
only should the kinds of soil on an area be determined,
but their depth is an important consideration. It is
very common to find one of these soils overlying another
one, and this relation between the two will have a very
important effect. For instance, if a sand soil is found
lying over a clay soil, the result will be that the sand soil
will retain far more water than it would alone. If «humus
soil in one area overlies a sand soil, and in another area

PLANT SOCIETIES: ECOLOGICAL ‘ACTORS. 167

overlies a clay soil, the humus will differ very much in the
two cases in reference to water.

The soil cover should also be considered. The common
soil covers are snow, fallen leaves, and living plants. It
will be noticed that all these covers tend to diminish the
loss of heat from the soil, as well as the access of heat to
the soil. In other words, a good soil cover will very much
diminish the extremes of temperature. All this tends to
increase the retention of water.

124. Light—It is known that light is essential for the
peculiar work of green plants. However, all green plants
cannot have an equal amount of light, and some have
learned to live with a less amount than others. While
no sharp line can be drawn between green plants which
use intense light, and those which use less intense light,
we still recognize in a general way what are called light
plants and shade plants. We know that certain plants
are chiefly found in situations where they can be exposed
freely to light, and that other plants, as a rule, are found
in shady situations.

Starting with this idea, we find that plants grow in
strata. In a forest society, for example, the tall trees rep-
resent the highest stratum ; below this there may be a
stratum of shrubs, then tall herbs, then low herbs, then
forms like mosses and lichens growing close to the ground.
In any plant society it is important to note the number of
these strata. It may be that the highest stratum shades
so densely that many of the other strata are not represented
at all. An illustration of this can be obtained from a
dense beech forest.

125. Wind.—It is generally known that wind has a dry-
ing effect, and, therefore, it increases the transpiration of
plants and tends to impoverish them in water. This factor
is especially conspicuous in regions where there are pre-
vailing winds, such as near the sea-coast, around the great

lakes, and on the prairies and plains. In all such regions
12

168 PLANT RELATIONS.

the plants have been compelled to adapt themselves to this
loss of water ; and in some regions the prevailing winds are
so constant and violent that the force of the wind itself has
influenced the appearance of the vegetation, giving what is
called a characteristic physiognomy to the area.

These five factors have been selected from a much larger
number that might be enumerated, but they may be re-
garded as among the most important ones. It will be
noticed that these factors may be combined in all sorts
of ways, so that an almost endless series of combinations
seems to be possible. This will give some idea as to the
possible number of plant societies, for they may be as
numerous as are the combinations of these factors.

126. The great groups of societies.—It is possible to re-
duce the very numerous societies to three or four great
groups. For convenience, the water factor is chiefly used
tor this classification. It results in a convenient. classitica-
tion, but one that is probably more or less artificial. The
selection of any one factor from among the many for the
purpose of classification never results in a very natural
classification when the combination of factors determines
the group. Ilowever, for general purposes, the usual
classification on the basis of water supply will be used.
On this basis there are three great groups of societies,
as follows :

(1) Hydrophytes.—The name means ** water plants,” and
suggests that such societies are at that extreme of the water
supply where it is very abundant. Such plants may grow
in the water, or in very wet soil, but in any event they are
exposed to a large amount of water.

(2) Yerophytes.—The name means ** drought plants,”
and suggests the other extreme of the water supply. True
xerophytes are exposed to dry soil and dry atmosphere.

(3) Mesophytes.—Between the two extremes of the water
supply there is a great middle region of medium water
supply, and plants which occupy it are known as meso-

PLANT SOCIETIES: ECOLOGICAL FACTORS. 169

phytes, the plants of the middle region. It is evident that
mesophytes gradually pass into hydrophytes on the one
side, and into xerophytes on the other; but it is also evi-
dent that mesophyte societies have the greatest range of
water supply, extending from a large amount of water to
a very small amount.

It should be understood that these three groups of socie-
ties, which are distinguished from one another by the amount
of the water supply, are artificial groups rather than natural
ones, for they bring together unrelated societies, and often
separate those that are closely related. For example, a
swampy meadow is put among hydrophyte societies by this
classification ; and it may shade into an ordinary meadow,
which belongs among the mesophytes. Probably the largest
fact which may be used in grouping plant societies is that
certain societies are so situated that they seek for the most
part to reduce transpiration, and that others are so situated
that they seek for the most part to increase transpiration.

However, the factors which determine societies are so
numerous that they cannot be presented in an elementary
book, and the simpler artificial grouping given above will
serve to introduce the societies to observation.

Upon a different basis another great group of socicties
has been suggested as follows :

(4) Halophytes.—The word means “salt plants.” The
basis of classification here depends not so much upon the
water supply as upon the fact that the water contains
certain salts which make it impossible for most plants to
live. Such societies may be found near the sea-coast,
around salt springs, on alkaline flats, or wherever the soil
contains these characteristic salts.

CHAPTER NII.
HYDROPHYTE SOCIETIES.

127. General character.— Hydrophytes are related to
abundant water, either throughout their whole structure
or in part of their structure. It is a well-known fact that
hydrophytes are among the most cosmopolitan of plants,
and hydrophyte societies in one part of the world look
very much like hydrophyte societies in any other region.
It is probable that the abundant water makes the condi-
tions more uniform.

It is evident that for those plants, or plant parts, which
are submerged, the water affects the heat factor by dimin-
ishing the extremes. It also affects the light factor, in so
far as the light must pass through the water to reach the
chlorophyll-containing parts, as light is diminished in
intensity by passing through the water. Before consider-
ing a few hydrophyte sucieties, it is necessary to note the
prominent hydrophyte adaptations.

128. Adaptations——In order that the illustration may be
as simple as possible, a complex plant completely exposed
to water is selected, for it is evident that the relations of a
swamp plant, with its roots in water and its stem and leaves
exposed to air, are complicated. A number of adaptations
may be noted in connection with the submerged or floating
plant.

(1) Thin-walled epidermis.—In the case of the soil-re-
lated plants, the water supply comes mainly from the soil,
and the root system is constructed to absorb it. In the
case of the water plant under consideration, however, the

HYDROPHYTE SOCIETIES. 171

whole plant body is exposed to the water supply, and there-
fore absorption may take place through the whole surface
rather than at any particular region such as the root. In
order that this may be done, however, it is necessary for
the epidermis to have thin walls, which is usually not the
case in epidermis exposed
to the air, where a certain
amount of protection is
needed in the way of
thickening.

(2) Roots much reduced
or wanting.—-It must be
evident that if water is
being absorbed by the
whole free surface of the
plant, there is not so
much need for a special
root region for absorp-
tion. Therefore, in such
water plants the root sys-
tem may be much re-
duced, or may even disap-
pear entirely. It is often
retained, however, to act
as a holdfast, rather than
as an absorbent organ, for

Fie. 153. Fragment of a common seaweed

most water plants anchor (Fucus), showing the body with forking

themselves to some sup- branching and bladder-like air cavities.—
After LUERSSEN.

port.

(3) Reduction of water-conducting tissues.—In the ordi-
nary soil-related plants, not only is an absorbing root sys-
tem necessary, but also a conducting system, to carry the
water absorbed from the roots to the leaves and elsewhere.
It has already been noted that this conducting system takes
the form of woody strands. It is evident that if water
is being absorbed by the whole surface of the plant, the

172 PLANT RELATIONS.

work of conduction is not so extensive or definite, and
therefore in such water plants the woody bundles are not
so prominently developed as in land plants.

(4) Reduction of mechanical tissues.—In the case of
ordinary land plants, certain firm tissues are developed so

Fig. 154. Gulfweed (Sargassum), showing the thallus differentiated into stem-like and
leaf-like portions, and also the bladder-like floats.—After BENNETT and MURRAY.

that the plant may maintain its form. These supporting
tissues reach their culmination in such forms as trees,
where massive bodies are able to stand upright. It is evi-
dent that in the water there is no such need for rigid sup-
porting tissues, as the buoyant power of water helps to
support the plant. This fact may be illustrated by taking

HYDROPHYTE SOCIETIES. 173

out of water submerged plants which seem to be upright,
with all their parts properly spread out. When removed they
collapse, not being able to support themselves in any way.
(5) Development of air cavities.—The presence of air in
the bodies of water plants is necessary for two reasons: (1),

Fig. 155. Bladderwort, showing the numerous bladders which float the plant, the
finely divided water leaves, and the erect flowering stems. The bladders are also
effective ‘‘insect traps,’ Utricularia being one of the ‘carnivorous plants.”
—After KERNER.

to aerate the plant ; (2), to increase its buoyancy. In most
complex water plants there must be some arrangement for
the distribution of air containing oxygen. This usually
takes the form of air chambers and passageways in the
body of the plant (see Figs. 87, 88, 89, 156). Of course
such air chambers increase the buoyancy of the body.
Sometimes, however, a special buoyancy is provided for
by the development of regular floats, which are bladder-

174 PLANT RELATIONS.

like bodies (see Figs. 153, 154). These floats are very
common among certain of the seaweeds, and are found
among. higher plants, as the utricularias or bladderworts,
which have received their name from the numerous blad-
ders developed in connection with their bodies (see Fig.
155).

Such adaptations as the above may be regarded as the
most prominent general adaptations. There are many
other special ones in connection with certain groups of
water plants which will be mentioned in considering the
societies.

A. Free-swimming societies.

120. Definition.—In these societies there is the largest
exposure to water, and no relation at all to the nutrient or
mechanical support of the soil, the plants being completely
supported by the water. In such plants all of those mate-
rials which lund plants obtain from the water of the soil are
obtained from the water in which they are submerged ; and
in the case of completely submerged plants the materials
usually obtained from the air are also supplied by the
water. Free swimming plants may be either submerged
or floating, and they are free to move either by locomo-
tion or by water currents. Two prominent societies are
selected as types.

130. The plankton.—This term is used to designate the
minute organisms, both plants and animals, which are
found in the water. The plankton is composed of indi-
viduals invisible to the naked eye, but taken together they
represent an enormous organic mass. The plankton socie-
ties are especially well represented in the colder oceanic
waters, but they are not absent from any waters. Among
the most prominent plants in these societies are the dia-
toms. Diatoms are minute plants of various forms, and all
have a wall very full of silica. This makes their bodies

HYDROPHYTE SOCIETIES. 175

extremely enduring, and therefore diatoms are often found
in great deposits in the rocks, in some cases forming the
whole mass of rock. Associated with the diatoms are
numerous other plant and animal forms.

131. Pond societies—The word pond is used to indicate
stagnant or slow-moving waters. In such waters free-
swimming plants of all groups are associated. Of course
the alge are well represented, but even the highest plants
are repre-
sented by the
duckweeds,
which are very
commonly
seen in the
form of small
green disks
floating on the
surface of the Fig. 156. A section through the body of a duckweed (Lemna),
water, which showing the air spaces (@) which make it buoyant, the
they frequent- origin (7) of the simple dangling root, and the pockets

(s and Z) from which new plants bud out. and in which
ly cover with flowers are developed.

great masses

(see Fig. 156). It should be observed that the floating and
submerged positions result in a difference in light-relations.
The floating forms may be regarded as light forms, being
exposed to the greatest amount of light. The submerged
forms are shade plants, and the shading becomes greater
as the depth of the water is greater. It must not be sup-
posed that submerged plants can live at any depth, for
soon a limit is reached, beyond which the light is not
intense enough to enable plants to work.

It has been noticed that this complete water habit has
affected plants in many ways. For instance, the duck-
weeds are related to land plants with root, stem, and leaves,
but they have lost the distinction between stem and leaf,
and the body is merely a flat leaf-like disk floating upon

176 PLANT RELATIONS.

the water, with a few roots dangling from the under side,
or with no roots at all (see Fig. 156). This same duck-
weed also shows some interesting modifications in its hab-
its of reproduction. Althongh related to plants which pro-
duce flowers and make seed, the duckweeds have almost
lost the power of producing flowers, and when they do
produce them, seeds are very seldom formed. In other
words, the ordinary method of reproduction employed
by flowering plants has been more or less abandoned.
Replacing this method of reproduction is a great power
of vegetative propagation. From the disk-like body of
the plant other disk-like bodies bud out, and this bud-
ding continues until a large group of disks, more or
less connected with each other, may be formed. These
plants also form what are known as winter buds—well
protected bud-lke bodies which sink to the bottom of
the pond when the floating plants are destroyed, and
remain protected by the mucky bottom until the waters
become warm again in the next growing season.

In examining the pond societies, therefore, attention
should be paid to the floating forms and the submerged
forms, and also to the varying depths of the latter. It will
also be noted that the leaves of floating forms are com-
paratively broad, while those of submerged forms are
narrow.

B. Pondweed societies.

132. Definition.—These are societies fixed to the soil but
with submerged or floating leaves. In this case there is
still great exposure to water, but there is also a definite soil
relation. 'T'wo prominent societies are selected from this
group for illustration.

133. Rock societies—The term rock is used in this con-
nection in a very general way, meaning simply some firm
support beneath the water ; it is just as likely to be a stick

HYDROPHYTE SOCIETIES, 177

as a stone. Probably the most prominent group of plants
affecting these conditions are alge, both fresh water and
marine. In the fresh waters very many of the alge will be

Fie. 157. A group of marine seaweeds (Laminarias). Note the various habits of the
plant body and the root-like holdfasts.—After KERNER.

found anchored to some support. The largest display of
such forms, however, is found among the marine alge,
which abound along all seacoasts (see Fig. 157). It will

Fic. 158. A natural, but nearly overgrown lily pond, The lily pads may be seen
rising more or less above the water where they are thickest. The forest growth in
the background is probably a tamarack (larch) swamp. It is to be noticed that as
the lily pond loses its water it is being invaded by the coarse sedge and grass
growth of a swamp-moor, Between the lily pond and the forest is a swamp-
thicket. At least four distinct societies are represented in this view, A fifth is
probably represented in the form of plants of the reed-swamp type, which form a
transition between the lily pond and the swamp-thicket.

HYDROPHYTE SOCIETIES. 179

be noticed that the habit of anchorage demands the
development of special organs of attachment, which usu-
ally take the form of root-like structures, often associated
with sucker-like disks. Associated with the anchoring
structures is often a development of floats, which is es-
pecially characteristic of seaweeds, enabling the working
body to float freely in the water (see Figs. 153, 154). It is
evident that while free-swimming forms may be suitable
for stagnant waters, anchored forms are better adapted for
moving waters. Therefore, where there are currents of
water, or wave action, the anchored forms predominate.
The ability to live in moving waters, and often in those
that become violently agitated, has its advantage to the
plant in the more rapidly renewed food material. In such
a situation free-swimming forms would soon be stranded
or disposed of in quieter waters.

In the case of the marine seaweeds there is an interest-
ing relation between the depth of the water and the color
of the plants. While the fresh water algee are prevailingly
green, it will be remembered that the prevailing colors of
the alge of the seashore are brown and red. The brown
often passes into some shade of yellow, and the red may
merge into purple or violet, but in general the two types of
color may be called brown and red. It has been noticed
that the brown forms are found at less depth than the red
forms, so that ina general way there are two zones of dis-
tribution in relation to depth, the red zone being the lower
one and the yellow zone the upper. Just what this means
in the economy of the plants is not clear, but it has been
suggested that the yellow and the red colors assist the
chlorophyll in its work, which is more or less interfered
with by the diminished intensity of the light passing
through sea water.

134. Loose soil societies —This phrase is used merely to
contrast with rock societies, referring to the fact that the
anchorage is not merely for mechanical support, but that

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HYDROPHYTE SOCIETIES. 181

there is a definite relation to soil in which roots or root-like
structures are embedded. Societies of this type contain
the greatest variety of plants of all ranks. In these soci-
eties are found alge, mosses, fern plants, pondweeds,
water lilies, etc. (see Figs. 158, 159, 160, 161). Pondweeds
and water lilies may be taken as convenient types of high
grade plants which grow in such conditions.

In the first place, it will be noticed that they are in-
clined to social growths, great numbers of individuals
growing together and forming what are known as lily
ponds or pondweed beds, although in the small lakes of
the interior where pondweeds abound in masses, they are
more commonly known as “ pickerel beds.” If the petiole
of a lily pad be traced down under the water, it will be
found to arise from an intricate mass of thick, knotted
stems. So extensively do these stems (rootstocks) in the
mucky bottom branch that they are able to give rise to
close set masses of leaves.

Water lilies and pondweeds may ulso be compared, to
show the effect of the floating habit in vontrast with the
submerged habit. The leaves of water lilies float on the
surface, and therefore are broad ; and being exposed to light
are a vivid green, indicating the abundant development of
chlorophyll. Many of the pondweeds, however, are com-
pletely submerged. As one floats over one of these “ pick-
erel beds,’ the leafy plants may be seen, at considerable
depths, and have a pallid, translucent look. It will be
seen that in these causes the leaf forms are narrow rather
than broad, often being ribbon-like, or in some submerged
plants even cut up into thread-like forms. It is evident
that such narrow leaf forms can respond more easily to
water movements than broad forms. The pallid look of
these submerged leaves indicates that there has not been
an abundant development of chlorophyll. Some pondweeds,
however, have both types of leaves, some being submerged
and others floating. In these cases it is interesting to notice

Fie. 160.—A group of pondweeds, The stems are sustained in an erect position by
the water, and the narrow leaves are exposed to a light whose intensity is dimin-
ished by passing through the water.—After KERNER,

HYDROPHYTE SOCIETIES. 183

the corresponding change of form; on the same individual
the submerged leaves are very narrow, or divided into
very narrow lobes, while the floating ones are broad
(see Fig. 162). The relation of the plant to the water,
therefore, has determined the leaf form. The advantage
of the floating habit of leaves is not merely a better rela-
tion to light, but the carbon dioxide used in photosynthesis
and the oxygen used in respiration may be obtained freely
from the air, rather than from the water. It will also be
noticed that these water plants usually send their flowers
to the surface, indicating that such a position is more fav-
orable for the work of the flower than a submerged position.
Any society of this type will furnish abundant material for
observation, and it is, perhaps, the most valuable type of
society for study that has been mentioned so far.

C. Swamp societies.

135. Definition.—In swamp societies the plants are rooted
in water, or in soils rich in water, but the stems bearing
the leaves rise above the surface. Among the hydrophytes,
swamp plants are least exposed to water, and as the stem
and its leaves are exposed to the air, there is no such reduc-
tion of the root system and of conducting and mechanical
tissues as in the other hydrophytes. Also the epidermis is
not thin, and there is no development of floats to increase
the buoyancy. However, the root must be aerated, and
hence air chambers and passageways are abundant. This
aeration of the root system reaches a very high develop-
ment in such swamp trees as the cypress. In cypress swamps
the so-called ‘‘ knees” are abundant, and they are found to
be special growths from the root system, which rise above
the surface of the water, both for bracing and to admit air
to the roots (see Fig. 91). It has been shown that if such
swamps are flooded above the level of the knees, many of
the trees are killed. In ordinary cases the air is admitted

13

Fie. 161. Eel grass (Vallisneria), a common pondweed plant. The plants are
anchored and the foliage is submerged. The carpel-bearing flowers are carried to
the surface on long stalks which allow a variable depth of water. The stamen-
bearing flowers remain submerged, as indicated near the lower left corner, the
flowers breaking away and rising to the surface, where they float and effect pollina-
tion,—After KERNER.

HYDROPHYTE SOCIETIES. 185

through openings in the epidermis of the stem and leaves,
and so enters the air passageways and reaches the roots.
Another habit of swamp plants is called turf-building,
which means that new individuals arise from older ones,
and so a dense mat of roots and rootstocks is formed. Very
prominent among these turf-building swamp plants are

Fic. 162, Two leaves of a water buttercup, showing the difference in the forms of
submerged and aerial leaves on the same plant, the former being much more
finely divided.—After STRASBURGER.

the sedges. Some of the prominent swamp societies may be
enumerated as follows :

136, Reed swamps.—The reed-swamp plants are tall wand-
like forms, which grow in rather deep, still water (see Fig.
163). Prominent as types are the cat-tail flag, bulrushes,
and reed grasses. Such an assemblage of forms usually
characterizes the shallow margins of small lakes and ponds.
In such places the different plants are apt to be arranged
according to depth, the bulrushes standing in the deepest
water, and behind them the reed grasses, and then the

186 PLANT RELATIONS.

cat-tails. This regular arrangement in zones is so often

interfered with, however, that it is not always evident.
The reed-swamp societies have been called ‘‘ the pioneers

of land vegetation,” for the detritus collects about them,

% if: BY 2

Tic. 168. A reed swamp, fringing the low shore of a lake or a sluggish stream. The
plants are tall and wand-like, and all are monocotyls. Three types are prominent,
the reed grasses (the tallest), the cat-tails (at the right), and the bulrushes(a group
standing out in deeper water near the middle of the fringing growth). The plant
in the foreground at the extreme right is the arrow-leaf (Sagitlaria), recognized
by its characteristic leaves.—After Kerner.

the water becomes more and more shallow, until finally
the reed plants are compelled to migrate into deeper water
(see §108). In this way small lakes and ponds may be
completely reclaimed, and become converted first into
ordinary swamps, und finally into wet meadows. Instances

HYDROPHYTE SOCIETIES. 187

of nearly reclaimed ponds may be noticed, where bulrushes,
cat-tail flags, and reed grasses still occupy certain wet
spots, but are shut off from further migration. The social
growth of these plants, brought about by extensive root-
stock development, is especially favorable for detaining
detritus and building a land surface.

Reed-swamp plants also have in general a tall and un-
branched habit of body. They may be bare and leafless,
with a terminal cluster of flowers, as in the bulrushes; or
the wand-like stems may bear long, linear leaves, us in the
cat-tails; or the stem may be a tall stalk with two rows
of narrow leaves, as in the reed grasses. No more charac-
teristic group of forms is found in any socicty. Of course,
associated with these forms are also free and fixed hydro-
phytes, which characterize the other societies.

137. Swamp-moors.—The word moor is used to designate
the meadow-like expatses of swampy ground. Here belong
the ordinary swamps, marshes, bogs, etc. There is less
water than in the case of the reed swamps, and often very
little standing water. One of the peculiarities of the
swamp-moor is that the water is rich in the soil materials
used in food manufacture, notably the nitrates from which
nitrogen is obtained for proteid manufacture. In such
conditions, therefore, the vegetation is dense, and the soil
is black with the humus derived from the decaying plant
bodies.

Typical swamp-moors border the reed swamps on the
land side, and slowly encroach upon them as the reed
plants build up land. Probably the most characteristic
plant forms of the swamp-moor are the sedges. and asso-
ciated with them are certain coarse grasses. These give
the meadow-like aspect to the swamp, although these grass-
like forms are very coarse. Along with the dominant
sedges and grasses are numerous other plants adapted to
such conditions, such as some of the buttercups. It would
be impracticable to give a list of swamp-moor plants, as the

188 PLANT RELATIONS.

forms associated with sedges and grasses may vary widely
in different societies.

In almost all swamp-moors there is a lower stratum of
vegetation than that formed by the sedges. This lower
stratum is made of certain swamp mosses, which grow in
very dense masses. Towards the north, where the temper-
ature conditions are not so favorable for the sedge stratum,
it may be lacking almost entirely, and only the lower moss
stratum left. In these cases the swamp-moor becomes
little more than a great bed of moss. It is in such con-
ditions that peat may be formed, a coal-like substance
formed by the dead plant bodies which have been kept
from complete decay by submergence in water.

138. Swamp-thickets—Swamp-thickets are very closely
associated with swamp-moors, and are doubtless derived
from them. If aswamp-moor, with its sedge stratum and
moss stratum, be invaded by shrubs or low trees, it be-
comes a swamp-thicket. This means that the general con-
ditions of food supply which belong to the swamp-moor
also favor certain shrubs and trees. It will be noticed that
these shrubs and trees are of very uniform type, being
mainly willows, alders, birches, etc. Such willow and alder
thickets are very common in high latitudes.

139. Sphagnum-moors.—The sphagnum-moor is a very
peculiar type of swamp society. It is sonamed because the
common bog or peat moss, known as sphagnum, gives a
peculiar stamp to the whole area. Sphagnums are large,
pale mosses, whose lower parts may die, and whose upper
parts continue to live and put out new branches, so that a
dense turf is formed. In walking over such a bog the moss
turf seems springy, and sometimes trembles so as to sug-
gest the name “‘ quaking bog.” These are the great peat-
forming bogs. It is interesting to know what conditions
keep the swamp-moor plants out of the sphagnum-moor.
The plants of the sphagnum-moor seem to be entirely dif-
ferent from those of the swamp-moor, although the amount

UYDROPHYTE SOCIETIES. 189

of water is approximately the same. Not only are the
plants different in the sphagnum-moor, but they are not so
numerous, and, with the exception of the moss, do not
grow so densely. It is to be noticed that creeping plants
are abundant, and also many forms which are known to
obtain their food material already manufactured, and there-
fore are saprophytes. Certain kinds of sedges and grasses
are found, but generally not those of the swamp-moor,
while heaths and orchids are especially abundant. It is in
these sphagnum-moors, also, that the curious forms of car-
niyorous plants are developed, among which the pitcher
plants, droseras, and dionwas have been described. In
considering this strange collection of forms, it is evident
that there must be some peculiarity in the food supply, for
the heaths and orchids are notorious for their partial sap-
rophytic habits, and the carnivorous plants are so named
because they capture insects to supplement their food sup-
ply. The fact, also, that the peculiar sphagnum mosses,
rather than the mosses of the swamp-moor, are the prevalent
ones, indicates the same thing.

It has been discovered that the water of the sphagnum-
moor is very poor in the food materials which are abundant
in the water of the swamp-moor. There is a special lack
of the materials which are used in the manufacture of pro-
teids. and hence this process is seriously interfered with.
It is necessary. therefore, to obtain proteids already formed
in animals. or in other plants. This will account for the
necessity of the saprophytic habit, and of the carnivorous
habit, and for the sphagnum mosses which can endure such
conditions. Of course, it also accounts for the exclusion
of the characteristic plants of the swamp-moor.

Another peculiarity in connection with the sphagnum-
moor, aside from its poverty in food material, is the lack
of those low plant forms (dacteria) which induce decay.
Bacteria are very minute plants, some of which are active
agents in processes of decay, and when these are absent

190 PLANT RELATIONS.

decay is checked. As a consequence, the sphagnum-moor
waters are strongly antiseptic; that is, they prevent decay
by excluding certain bacteria, It is a well-known fact that
bodies of men and animals which have become submerged
in sphagnum-hogs may not decay, but have been found
preserved after a very long period. This will also indicate
why such bogs are especially favorable for peat formation.

These two types of moors, therefore, may be contrasted
as follows: The swamp-moor is rich in plant food, and is
characterized chiefly by grassy plants ; the sphagnum-moor
is poor in food material, and is characterized chiefly by
sphagnum moss. It will be noted that peat may be formed
in connection with both of these moors, but in the swamp-
moor the plant forms cannot be distinguished in the peat,
as they have been more or less disorganized through decay,
while in the peat of the sphagnum-moor the plant forms
are well preserved. The peat of the swamp-moor, also,
yields a great amount of ash, for the swamp-moor is rich
in soil materials, while the peat of the sphagnum-moor
yields very little ash.

140. Swamp forests.—It was noted that the special types
of shrub or tree growth associated with the swamp-moor
conditions are willows, alders, birches, etc. In the same
way there is a peculiar tree type associated with the
sphagnum-moor. It is very common to have a sphagnum
area occupied by trees, and the area becomes a swamp
forest, rather than a sphagnum-moor. The chief tree
type which occupies such conditions is the conifer type,
popularly known as the evergreens. The swamp forests,
therefore, with a sphagnum-moor foundation, are made up
of larches, certain hemlocks and pines, junipers, ete., and
towards the south the cypress comes in (sce Fig. 164).
The larch is » very common swamp tree of the northern
regions, where such an area ig commonly called a “ tama-
rack swamp’ (see Fig. 158). The larch forests are apt to
be in the form of small patches, while the larger swamp

‘B9SSOUI JO WINILI}S U SSA[}QNOp SI a0} T}.Mows.o9pun
at) MOfa_ “SUJOs PUT SQNAYS Jo YJMOISIOpuN osuap at[} pUL ‘sidJTWOO Jo SyuNIP aBIe] Moy B Uoos aq ABUT YI ul ysadoj dures Y “POT “SLA

192 PLANT RELATIONS.

forests are made of dense growths of hemlocks, pines, etc.
In the densest of these forests the shade is so complete
that there may be very few associated plants occurring
in strata between the sphagnum moss and the trees. In
the larch forests, however, the undergrowth may be very
dense.

CHAPTER NII.
XEROPHYTE SOCIETIES.

141. General character.—Strongly contrasted with the
hydrophytes are the xerophytes, which are adapted to dry
air and soil. The xerophytic conditions may be regarded
in general as drouth conditions. It is not necessary for
the air and soil to be dry throughout the year to develop
xerophytic conditions. These conditions may be put under
three heads: (1) possible drouth, in which a season of
drouth may occur at irregular intervals, or in some seasons
may not occur at all; (2) pertodic drouth, in which there
is a drouth period as definite as the winter period in cer-
tain regions ; (3) perennial drouth, in which the dry con-
ditions are constant, and the region is distinctly an arid
or desert region.

However xerophytic conditions may occur, the problem
of the plant is always one of water supply, and many strik-
ing structures have been developed to answer it. Plants
in such conditions must provide, therefore, for two things:
(1) collection and retention of water, and (2) prevention of
its loss. It is evident that in these drouth conditions the
loss of water through transpiration (see $26) tends to be
much increased. This tendency in the presence of a very
meager water supply is a menace to the life of the plant.
It is impracticable to stop transpiration entirely, for it
must take place in connection with a necessary life-process.
The adaptations on the part of the plant, therefore, are
directed towards the regulation of transpiration, that it

194 PLANT RELATIONS,

may occur sufficiently for the life-processes, but that it
may not be wasteful.

The regulation of transpiration may be accomplished
in two general ways. It will be remembered that the
amount of transpiration holds some relation to the
amount of leaf exposure or exposure of green tissue.
Therefore, if the amount of leaf exposure be diminished,
the total amount of transpiration will be reduced. Another
general way for regulating transpiration is to protect
the exposed surface in some way so that the water does
not escape so easily. In a word, therefore, the general
method is to reduce the extent of exposed surface or to
protect it. It must be understood that plants do not differ
from each other in adopting one or the other of these
methods, for both are very commonly used by the same
plant.

aldaptations.

142. Complete desiccation Some plants have a very re-
markable power of completely drying up during the drouth
period, and then reviving upon the return of moisture.
This power is strikingly illustrated among the lichens and
mosses, some of which can become so dry that they may be
crumbled into powder, but revive when moisture reaches
them. <A group of club mosses, popularly known as ‘ res-
urrection plants,” illustrates this same power. The dried
up nest-like bodies of these plants are common in the
markets, and when they are placed in a bowl of water they
expand and may renew their activity. In such cases it can
hardly be said that there is any special effort on the part of
the plant to resist drouth, for it seems to yield completely
to the dry conditions and loses its moisture. The power
of reviving, after being completely dried out, is an offset,
however, for protective structures.

143. Periodic reduction of surface—In regions of periodic

XEROPHYTE SOCIETIES.

drouth it is very com-
mon for plants to
diminish the exposed
surface in a very de-
cided way. In such
cases there is what
may be called a peri-
odic surface decrease.
For example, annual
plants remarkably
diminish their ex-
posed surface at the
period of drouth by
being represented
only by well-pro-
tected seeds. The
whole exposed sur-
face of the plant,
root,stem,and leaves,
has disappeared, and
the seed preserves the
plant through the
drouth.

Little less remark-
able is the so-called
geophilous habit. In
this case the whole of
the plant surface ex-
posed to the air dis-
appears, and only
underground parts,
such as bulbs, tubers,
etc., persist (see Figs.
45, 46, 66, 67, U8, 69,
70, 75, 144, 164a,
1642). At the re-

195

: one )
SS
| i aah (hi (eas
| ON
| NAAN An
| \ Hey of Ne }
| Cesta WI } TiS
ay \P,
Mm | | \ { |)
HH \ \ | \Y
Nl .
\\
\ "
SSS
KS ee
\ Sa aA
Sa
TSS)
“ re - es I,
eA ve
i a Ie
ee
(CA
SAG
/
Fie. 164a. The bloodroot (Sanguinaria), showing

the subterranean rootstock sending leaves and
flower above the surface.—After ATKINSON.

196

Fic, 164, The spring
beauty ( Claytonia),
showing subterranean
tuber-like stem sending leaf and flower-bearing
stem above the surface.—After ATKINSON.

PLANT RELATIONS.

turn of the moist season
these underground parts
develop new exposed
surfaces. In such cases
it may be said that at
thecoming of the drouth
the plant seeks a sub-
terranean retreat.

A little less decrease
of exposed surface is
shown by the deciduous
habit. It is known that
certain trees and shrubs,
whose bodies remain
exposed to the drouth,
shed their leaves and
thus very greatly reduce
the amount of exposure ;
with the return of mois-
ture, new leaves are put
forth. It will be re-
marked, in this connec-
tion, that the same
habits serve just as well
to bridge over a period
of cold as a period of
drouth, and perhaps
they are more familiar
in connection with the
cold period than in con-
nection with the drouth
period.

144. Temporary reduc-
tion of surface.—While
the habits above have to
do with regular drouth

XEROPHYTE SOCIETIES. 197

periods, there are other habits by which a temporary re-
duction of surface may be secured. For instance, at the
approach of a period of drouth, it is very easy to observe
certain leaves rolling up in various ways. As a leaf be-
comes rolled up, it is evident that its exposed surface is
reduced. ‘The behavior of grass leaves, under such cir-
cumstances, is very easily noted. .\ comparison of the grass
blades upon a well-watered lawn with those upon a dried-up
lawn will show that in the former case the leaves are flat,
and in the latter more or less rolled up. The same habit
is also very easily observed in connection with the larger-
leaved mosses, which are very apt to encounter drouth
periods.

145. Fixed light position.—In general, when leaves have
reached maturity, they are unable to change their position
in reference to light, having obtained what is known as a
fixed light position. During the growth of the leaf, how-
ever, there may be changes in direction so that the fixed
light position will depend upon the light direction during
growth. The position finally attained is an expression of
the attempt to secure sufficient, but not too much light
(see §13). ‘The most noteworthy fixed positions of leaves
are those which have been developed in intense light.
A very common position in such cases is the profile posi-
tion, in which the leaf apex or margin is directed upwards,
and the two surfaces are more freely exposed to the morn-
ing and evening rays—that is, the rays of low intensity—
than to those of midday.

Illustrations of leaves with one edge directed upwards
can be obtained from the so-called compass plants. Prob-
ably most common among these are the rosin-weed of the
prairie region, and the prickly lettuce, which is an intro-
duced plant very common in waste ground (see Fig. 165).
Such plants received their popular name from the fact that
many of the leaves, when edgewise, point approximately
north and south, but this direction is very indefinite. It is

198 PLANT RELATIONS.

evident that such a position avoids exposure of the leaf
surface to the noon rays, but obtains for these same sur-
faces the morning and evening rays. If these plants are
developed in the shade, the ‘‘ compass” habit does not

Fie. 165. Two compass plants. The two figures tothe left represent the same plant
(Silphium) viewed from the east and from the south. The two figures to the right
represent the same relative positions of the leaves of Lactuca.—After KERNER.

appear (see $15). The profile position is a very common
one for the leaves of Australian plants, a fact which gives
much of the vegetation a peculiar appearance. All these
positions are serviceable in diminishing the loss of water,
which would occur with exposure to more intense light.
146. Motile leaves—Although in most plants the mature

XEROPHYTE SOCIETIES. 199

leaves are in a fixed position, there are certain ones whose
leaves are able to perform movements according to the need.
Mention has been made already of such forms as Oralis
(see §14), whose leaves change their position readily in
reference to light. Motile leaves have been developed most
extensively among the Leguminose, the family to which

Fic. 166. Two twigs of asensitive plant. The one to the left shows the numerous
small leaflets in their expanded position ; the one to the right shows the greatly
reduced surface, the leaflets folded together, the main leaf branches having
approached one another, and the main leaf-stalk having bent sharply downwards.
—After STRASBURGER.

belong peas, etc. In this family are the so-called ‘‘sen-
sitive plants,” which haye received their popular name
from their sensitive response to light as well as to other
influences (see Fig. 166). The acacia and mimosa forms
are the most notable sensitive plants. and are especially
developed in arid regions. The leaves are usually very
large, but are so much branched that each leaf is com-
posed of very numerous small leaflets. Each leaflet has
14

200 PLANT RELATIONS.

the power of independent motion, or the whole leaf may
move. If there is danger from exposure to drouth, some
of the leaflets will be observed to fold together ; in case

the danger is prolonged, more leaflets will fold together ;
and if the danger persists, the surface of exposure will be
still further reduced, until the whole plant may have its
leaves completely folded up. In this way the amount of

XEROPHYTE SOCIETIES. 201

reduction of the exposed surface may be accurately regu-
lated to suit the neud (see $3s).

147. Reduced leaves—In regions that are rather per-
manently dry, itis observed that the plants in general pro-
duce smaller leaves than in other regions (see Fig. 1s),
That this holds a direct relation to the dry conditions is

Fic. 168. Leaves from the common basswood (Zilia), showing the effect of environ-
ment; those at the right being from a tree growing in ariver bottom (mesophyte
conditions) ; those at the left being from a tree growing upon a dune, where it is
exposed to intense light, heat, cold, and wind. Not only are the former larger,
but they are much thinner. The lcaves from the dune tree are strikingly smaller,
much thicker, and more compact.—After CowLEs.

evident from the fact that the same plant often produces
smaller leaves in xerophytic conditions than in moist con-
ditions. One of the most striking features of an arid
region is the absence of large, showy leaves (see Fig. 167).
These reduced leaves are of various forms, such as the
needle leaves of pines, or the thread-like leaves of certain
sedges and grasses, or the narrow leaves with inrolled
margins such as is common in many heath plants. The

202 PLANT RELATIONS.

at.
es

St
wt

Fic. 169. Two species of Achillea on different soils. The one to the left was grown
in drier conditions and shows an abundant development of hairs.— After
SCHIMPER,

extreme of leaf reduction has been reached hy the cactus

plants, whose leaves, so far as follage is concerned, have
disappeared entirely, and the leaf work is done by the

XEROPHYTE SOCIETIES. 2038

surface of the globular, cylindrical, or flattened stems (see
§36).

14s. Hairy coverings.—A covering of hairs is an effective
sun screen, and it is very common to find plants of xerophyte
regions character-
istically hairy (see
§35). The hairs
are dead struc-
tures, and within
them there is air.
This causes them
to reflect the light,
and hence to ap-
pear white or
nearly so. This
reflection of light
by the hairs dimin-
ishes the amount
which reaches the
working region of
the plant (see Fig.
169).

149. Body habit.
—Besides the ya-
rious devices for
diminishing ex-
posure or leaf sur-
tes, aril ence ee, ee
loss of water, unbranched one having grown in normal mesophyte
enumerated abore, conditions ; the short, bushy branching, more slender

k form having grown on the dunes (xerophyte condi-
the whole habit of tions).—After CowLEs.

the plant may em-

phasize the same purpose. In dry regions it is to be observed
that dwarf growths prevail. so that the plant as a whole
does not present such an exposure to the dry air as in
regions of greater moisture (see Fig. 170). Also the pros-

2.04 PLANT RELATIONS.

trate or creeping habit is a much less exposed one in such
regions than the erect habit. In the same manner, the very
characteristic rosette habit, with its cluster of overlapping
leaves close against the ground, tends to diminish loss of
water through transpiration.

One of the most common results of xerophytic conditions
upon body habit is the development of thorns and spiny

Fie, 171. Young plants of Huphorbia splendens, showing a development of thorns
characteristic of the plants of dry regions,

processes. Ax 2 consequence, the vegetation of dry regions
is characteristically spiny. In many cases these spiny pro-
cesses Cun be made to develop into ordinary stems or leaves
in the presence of more favorable water conditions. It is
probable, therefore, that such structures represent reduc-
tions in the growth of certain regions, caused by the unfavor-
able conditions. Incidentally these thorns and spiny pro-
cesses ure probably of great service as a protection to plants
in regions where vegetation is peculiarly exposed to the

XEROPHYTE SOCIETIES. 205

ravages of animals (see §105). Examine Figs. 171, 172,
173, 174, 175, 176.

150. Anatomical adaptations—It is in connection with
the xerophytes that some of the most striking anatomical
adaptations have been
developed. In such
conditions the epider-
mis is apt to be coy-
ered by layers of
cuticle, which are de-
veloped by the walls
of the epidermal cells,
and being constantly
formed beneath the
cuticle, may become
yery thick. This
forms a very efficient
protective covering,
and has a tendency to
diminish the loss of
water (see §35). It is
also to be observed
that among xerophytes
there is a strong de-
velopment of palisade

tissue. The working Fie. 172. Two plants of common gorse or furze

Ils of the 1 <t (Ulex), showing the effect of environment : }
Cells 0 ne leaves Nex is a plant grown in moist conditions; a is a

to the exposed surface plant grown in ary conditions, the leaves and
are elongated, snd are anehehving em amos etry develope
directed endwise to

the surface. In this way only the ends of the elongated
cells are exposed, and as such cells stand very closely to-
gether, there is no drying air between them. In some
cases there may be more than one of these palisade rows
(see §32). It has been observed that the chloroplasts in
these palisade cells are able to assume various positions in

206 PLANT RELATIONS.

Fig. 173. A branch of Cytisus, showing the
reduced leaves and thorny branches.—After
KERNER.

regulation of transpiration, but also to the
storage of water, as it is received at rare inter-
vals. It is very common to find a certain re-
gion of the plant body given over to this work,
forming what is known as water tissue. In

the cell, so that when
the light is very intense
they move to the more
shaded depths of the
cell, and when it be-
comes less intense they
moye to the more exter-
nal regions of the cell
(see Fig. 177). The
stomata, or breathing
pores, which are devel-
oped in the epidermis,
are also great regulators
of transpiration, as has
been mentioned already
(see §31).

151. Water reservoirs.
—In xero-
phytes at-
tention
must be
given not
only to the

many leaves this water tissue may be distin-
guished from the ordinary working cells by
being a group of colorless cells (see Figs. 178,
179, 180). In plants of the drier regions leaves
may become thick and fleshy through acting
as water reservoirs, as in the case of the agave,
sedums, etc. Fleshy or ‘succulent ” leaves
are regarded as adaptations of prime impor-

Fie. 174. A
leaf of traga-
canth, show-
ing the re-
duced leaf-
lets and the
thorn-like
tip.—After
KKERNER.

XEROPHYTE SOCIETIES. 207

tance in xerophytic conditions. In
the cactus plants the peculiar stems
have become great reservoirs of
moisture. The globular body may
be taken to represent the most com-
plete answer to this general problem,
as it is the form of body by which
the least amount of surface may be
exposed and the greatest amount of
water storage secured. In the case
of fleshy leaves and fleshy bodies it
has long been noticed that they not
only contain water, but also have a

Fie. 176. Twig of com-
mon locust, showing
the thorns.—After
KERNER.

berry, showing the thorns.
—After KERNER.

great power of re-
taining it. Plant
collectors have found great difficulty in
drying these fleshy forms, some of which
seem to be able to retain their moisture in-
definitely, even in the driest conditions.

152. Xerophytic structure.—The adap-
tations given above are generally found
in plants growing in drouth conditions,
and they all imply an effort to diminish
transpiration. It must not be supposed,
however, that only plants living in
drouth conditions show these adapta-
tions. Such adaptations result in what
is known as the xerophytic structure,
and such a structure may appear even
in plants growing in hydrophyte condi-
tions. For example, the bulrush grows
in shallow water, and is a prominent
member of one of the hydrophyte socie-
ties (see §136); and yet it has a remark-
ably xerophytic structure. This is prob-
ably due to the fact that although it

208 PLANT RELATIONS,

stands in the water its stem is exposed
to a heat which is often intense.

The ordinary prairie (see $163) is
included among mesophyte societies
on account of the rich, well-watered
soil; and yet many of the plants are
very xerophytic in structure, probably
on account of the prevailing dry winds.

The ordinary sphagnum-bog (see
$139), or ‘‘peat-bog,” is included
among hydrophyte societies. It has
an abundance of water, and is not ex-
posed to blazing heat, as in the case
of the bulrushes, or to drying wind,
as in the case of prairie plants; and
yet its plants show uw xerophytic struc-

Fig. 177. Cells from the leaf
of a quillwort (Jsoetes).
The light is striking the
cells from the direction of
one looking at the illus-

tration. If it be some- 7
ture.

what diffuse the chloro-
plasts distribute them-
selves through the shal-
low cell, as in the cell to
the left. If the light be
intense, the chloroplasts
move to the wall and as-
sume positions less ex-

This is found to be due, proba-
bly, to a lack of certain important soil
materials.

It is evident, therefore, that xero-
phytic structures are not necessarily
confined to xerophytic situations. It

posed, as in the cell to

: is probably true that all societies which
the right. =

show xerophytic structures belong to-
gether more naturally
than do the societies
which are grouped ac-
cording to the water

supply.

Societies.

No attempt will be
made to classify these
very numerous socie-
ties, but a few prom-

Fie. 178, Asection through a Begonin leaf, show-
ing the epidermis (ep) above and below, the
water-storage tissue (ws) above and below, and
the central chlorophyll region (as).

XEROPHYTE SOCIETIES. 209

inent illustra-
tions will be
given.

153. Rock
societies. — Vari-
ous plants are
able to live up-
on exposed rock
surfaces, and \
therefore form

Fie. 179. A section through a fleshy leaf (Clinia), show-

distinct associa- ing the chlorophyll region on the outside (shaded and
tions of xero- marked as), and the large interior water-storage region
(ws).

phytes. In gen-
eral they are lichens, mosses, and crevice plants (see Fig.
181). The crevice plants are those
which send their roots into the rock
crevices and so gain a foothold.
The crevice plants also commonly
show a rosette habit, the rosette of
overlapping leaves being against the
rock face, and therefore in the most
favorable position for checking loss
of water.

154. Sand societies—In general
sand societies may be roughly grouped
as beach societies, dune societies, and
sandy field societies. These three
hold a certain definite relation to
one another. This natural relation-
Fig. 180. Asectionthrough = ship appears on the borders of the

a leaf of an epiphyte,

showing avery large de. large lakes, and on seacoasts. The
pee oe tissue heach is nearest the water, the dunes
dermis and the chloro, are next, and behind them stretch
phyll region, which is the sandy fields. When the three
restricted nies types are thus associated. the plants

under surface of the leaf.
—After ScHmmrEn. of the different areas pass gradually

210 PLANT RELATIONS.

into one another. It is very common to find the dunes
omitted in the series, and to have the beaches pass gradu-
ally into the sandy fields.

The beach society is usually quite characteristic, and in
general it is a poor flora, the beach being characteristically
bare. ‘The plants which grow in such conditions are apt to
occur in tufts, or are creeping plants. It is evident that

Fie. 181. A rock covered with lichens.

while the water may seem to be abundant, it disappears
quickly, so that plants must adapt themselves to a dry
condition of the soil, which is poor and with little or no
accumulation of humus. At the same time, the exposure
to intense light is extreme. This combination results in a
poor display of individuals and of species. Here and there
along beaches, where special conditions have favored the
accumulation of humus, dense vegetation may spring up,
but it should not be confused with the ordinary beach type.

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212 PLANT RELATIONS.

The dune societies are subjected to very peculiar con-
ditions. Dunes are billows of sand that have been devel-
oped by prevailing winds, and in many cases they are con-
tinually changing their form and are frequently moving

ae Pay ae : ey ty

ae a ae kes DOW ec ae ma eer a MSc

Fie. 183. A sandy field type, showing the development of vegetation upon an old
beach. The vegetation is low, often tufted and heath-like, being composed chiefly
of grasses, bearberry (Arctostaphylos) and Hudsonia. In the background to
the right is a conifer forest, and between it and the old beach is seen a dense mass
of bearberry, a very characteristic heath plant, and forming here what is called a
transition zone between the beach and the forest.—After CowLEs.

landward (see Fig. 182). The moving dunes should be
distinguished from the fixed ones, where the billow form is
retained, but the dunes have ceased their motion. In the
case of the active dunes a peculiar type of vegetation is de-
manded, As is to be expected, the flora is very scanty, and

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214 PLANT RELATIONS.

has two remarkably developed characters. The plants are
what are known as ‘‘ sand-binders,” that is, the underground
structures become extremely developed, reaching to great
distances horizontally and vertically, so that one is always
surprised at the extent of the underground system. This
wide searching for water results in giving the plants a deep
anchorage in the shifting soil, and at the same time helps
to prevent the shifting. As soon as enough of the sand-
binders have established themselves, a shifting dune becomes
a fixed one. Another characteristic that must be strongly
developed by these plants is the ability to grow up through
the sand after they have been engulfed. The plants of the
shifting dunes are often buried as the dune shifts, and
unless the burial has been too deep, they are able to continue
their development until leaves may be exposed to the air.
In this way plants have often developed a length of stem
which is far beyond anything they attain when growing in
ordinary conditions.

The sandy field societies are represented by a much
more abundant flora than the beach or the dune societies,
the general character being tufted grasses and low shrubby
growths (see Fig. 183).

155. Shrubby heaths—The shrubby heaths are very
characteristic of the more northern regions, and are closely
related to the sandy field societies. The heath soil is apt
to be a mixture of coarse sand, or gravel and rock, with
an occasional deposit of humus, and would be regarded
in general as a sterile soil. The flora of the shrubby
heaths shows well-marked strata, the upper one being the
low shrubby plants of the heath family, most prominent
among which are huckleberries and bearberries (see Fig.
167). The lower stratum is made up of mosses and l-
chens. A branching lichen, usually spoken of as the
“reindeer moss,” often occurs in immense patches on
such heaths. While these shrubby heaths occur most
extensively towards the north, small areas showing the

MUA KIHON LO]PYsnjouy avod-SpYOU Oy} WLM posoroo ‘umd yo "GRE “bi

216 PLANT RELATIONS.

same general character are common in almost all temper-
ate regions.

156. Plains.—Under this head are included great areas
in the interior of continents, where dry air and wind
prevail. The plains of the United States extend from
about the one hundredth meridian westward to the foot-
hills of the Rocky Mountains. Similar great areas are
represented by the steppes of Siberia, and in the interior of
all continents. These regions have been regarded as semi-
desert areas, but they are found for the most part to be
far from the real desert conditions. They are certainly
areas of comparative dryness, on account of the dry winds
which prevail.

Taking the plains of the United States as a type, a very
characteristic plant physiognomy is presented (see Fig.
184). In general, there is a meadow-like expanse, but the
vegetation is much more sparse than in meadows, and is
much more dense than in deserts. The two characteristic
plant forms are the bunch grasses, that is, grasses which
grow in great tufts; and low grayish shrubs, predomi-
nantly ‘‘sage brush.” Under the shelter of the sage brush
or other bush forms, many low herbs succeed in growing.
In such areas the growing scasou is very short, during
which time the vegetation looks vigorous and fresh; but
during the rest of the year it is very dull. In some parts
the plain is dry enough to permit the growth of the prickly-
pear cactus (Opuntia), which may take possession of ex-
tensive areas (see Fig. 185).

Usually there are two rest periods during the year,
developed by the summer drouth and the winter cold. As
a consequence, the plants of the area are partly spring
plants, which are apt to he very brilliant in flower; and
partly the later, deep-rooted forms. Over such areas the
transportation of seeds by the wind is very prominent, as
the force of the wind and the freedom of its sweep make
possible very wide distribution. It is in such areas that

Siccerabrars)
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FUMoys Yaasop smyovo YW “98T ‘DIyg

Fie. 187. Two plants of the giant cactus. Note the fluted, clumsy branching, leaf-
less bodies growing from the rocky, sterile soil characteristic of cactus deserts,
Certain dry-ground grasses and low, shrubby plants with small leaves may be seen
in the foreground,

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220 PLANT RELATIONS.

the tumbleweed habit is prominently developed. Certain
low and densely branching plants are lightly rooted in
the soil, so that at the close of their growing period they
are easily uprooted by the wind, and are rolled to great

Fira. 189. Tree-like yuccas from the arid regions of Africa, showing the very numer-
ous thick and pointed, sword-like leaves.

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D929: PLANT RELATIONS.

distances. Where some barrier, such as a fence, lies across
the track of the wind, these tumbleweeds may accumulate
in great masses. This tumbling over the surface results
in an extensive scattering of seeds (see Fig. 120).

The prairies, so characteristic of the United States, are
regarded by some as belonging to the plains. They cer-
tainly are closely related to them in origin, but can hardly
be regarded as being included in xerophyte conditions, as
the conditions of water supply and soil are characteristically
mesophyte, under which head they will be considered.

157. Cactus deserts—In passing southward on the
plains of the United States, it is to be noted that the con-
ditions become more and more xerophytic, and that the
bunch grasses and sage brush, peculiar to the true plains,
gradually merge into the cactus desert, which represents
a region whose conditions are intermediate between true
plains und true deserts (see Fig. 186). In the United States
this characteristic desert region begins to appear in West-
ern Texas, New Mexico, Arizona, and Southern California,
and stretches far down into the Mexican possessions. This
yast arid region has developed a pecuhar flora, which con-
tains most highly specialized xerophytic forms. The va-
rious cactus forms may be taken as most characteristic,
and associated with them are the agaves and the yuccas.
Not only are the adaptations for checking transpiration
and for retaining water of the most extreme kind, but
there is also developed a remarkable armature. It is eyi-
dent that such succulent bodies as these plants present
might speedily disappear through the attacks of animals,
were it not for the armor of spines and bristles and rigid
walls. Study Pigs. 38, 39, 40, 187, 18s. 189.

15s. Tropical deserts —In such areas xerophyte con-
ditions reach the greatest extreme in the combination of
maximum heat and minimum water supply. It is evident
that such a combination is almost too difficult for plants
to endure. That the very scanty vegetation is due to lack

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224 PLANT RELATIONS.

of water, and not to lack of proper materials in the soil, is
shown by the fact that where water does occur oases are
developed, in which luxuriant vegetation is found.

The desert which extends from Egypt across Arabia may
be regarded as a typical one. It is to be noted that the
vegetation is so scanty that the soil is the conspicuous
feature, and really gives the characteristic physiognomy
(see Fig. 191). Accordingly the appearance of the deserts
will depend upon whether the desert soil is rocky, or of
small stones, or gravel (as in the Desert of Sahara), or of
red clay, or of the dune type. As is to be expected, such
vegetation as does occur is of the tuft and bunch type, as
developed by certain grasses, or of the low irregular bush
type (see Fig. 190).

In the South African deserts certain remarkable plants
have been noted which have attained a certain amount of
protection through mimicry, rather than by means of armor,
as in the case of the cactus forms. Some of these plants
resemble the ordinary stones lying about upon the desert.
With the tropical deserts should not be confused such
areas as those about the Dead Sea, or in the Death’s Valley
in Southern California, as the barrenness of these areas is
due to the strongly alkaline soils, and therefore they belong
to the halophyte areas.

159. Thickets.—The xerophyte thicket is the most
strongly developed of all thicket growths. Mention has
been made of willow and alder thickets in hydrophyte con-
ditions, but these are not to be compared in real thicket
characters with the xerophyte thickets. These thickets
are especially developed in the tropics and subtropies, and
may be described as growths which are scraggy. thorny,
and impenetrable. Warming speaks of these thickets as
‘the unsuccessful attempt of Nature to form a forest.”
Hvidently the conditions are not quite favorable for for-
est development, and un extensive thicket is the result.
Such thickets are well developed in Texas, where they are

Fig. 192., A xerophyte conifer forest in the mountains. The peculiar conifer habit
of body is recognized, the trees finding foothold in the crevices of rocks or in
areas of rock débris,

22.6 PLANT RELATIONS.

spoken of as ‘‘ chaparral.” These chaparrals are nota-
bly composed of mesquit bushes, acacias and mimosas of
various sorts, and other plants. Similar thickets in Af-
rica and Australia are frequently spoken of as ‘* bush ™ or
‘scrub.’ In all of these cases the thicket has the same
general type, and probably represents one of the most for-
bidding areas for travel.

160. Forests—The xerophyte forest societies may be
roughly characterized under three general heads :

(1) Contferous forests.—These forests are very common
in xerophyte conditions to the north, and also in the more
sterile regions towards the south (see Figs. 192, 193, 194).
They are generally spoken of as evergreen forests, although
the name is not distinctive. These forests are of several
types, such as true pine forests, in which pines are the
prevailing trees and the shade is not dense; the fir and
hemlock forests, which are relutively dark ; and the mixed
forests, in which there is a mingling of various conifers.
In such forests the soil is often very bare, and such under-
growth as docs occur is largely composed of perennial
plants. Many characteristic shrubs with fleshy fruits oc-
cur, such as huckleberries, bearberries, junipers, ete. It
will be noted that in these forests a characteristic adapta-
tion to xerophyte conditions is the development of needle
leaves, which are not only narrow, thus presenting a small
exposure of surface, but also have heavy walls, which
further prevents excessive transpiration.

(2) Foliage foresis.—These are more characteristic of
tropical and subtropical xerophyte regions. Illustrations
may be obtained from the eucalyptus, a characteristic
Australian forest tree, the live oaks, oleanders, ete. It
will be noticed that in these cases the leaves are not so
narrow as the needles of conifers, but are generally lance-
shaped, and stiff and leathery, indicating heavy walls to
reduce transpiration. :

(3) Leafless forests.—In Java and other oriental regions

Fie. 193. A pine forest, showing the slender, tall, continuous trunks and compara-
tively little undergrowth.—After ScHIMPER,

“APANIHON Joy V—"punossor10J om uy stayed oyowyed Jo YyArors v YI ‘sould WioYyyNOY Jo aAoas Y “FOT “OL

KEROPHYTE SOCIETIES, 229

areas of dry naked soil are sometimes occupied by forest
growths which show no development of leaves, the tree-like
forms appearing continually bare. ‘The oriental leafless
tree form is mostly a Casuarina. Bordering the Gulf of
California, both in Mexico proper and in Lower California,
there are leafless forests composed of various kinds of
giant cactus (see Fig. 187), known as the ** cardon forests.”
These leafless forests represent the most extreme xerophyte
conditions occupied by plant forms which may be regarded
as trees.

CHAPTER XIV.
MESOPHYTE SOCIETIES.

161. General characters.— Mesophytes make up the com-
mon vegetation of temperate regions, the vegetation most
commonly met and studied. The conditions of moisture
are medium, precipitation is in general evenly distributed,
and the soil is rich in hunus. The conditions are not ex-
treme, and therefore special adaptations, such as are neces-
sary for xerophyte or hydrophyte conditions, do not appear.
This may be regarded as the normal plant condition. It
is certainly the arable condition, and most adapted to the
plants which men seek to cultivate. When for purposes
of cultivation xerophyte areas are irrigated, or hydrophyte
areas are drained, it is simply to bring them into mesophyte
conditions.

In looking over a mesophyte area and contrasting it
with a xerophyte area, one of the first things evident is that
the former is far richer in leaf forms. It is in the meso-
phyte conditions that foliage leaves show their remarkable
diversity. In hydrophyte and xerophyte arcas they are apt
to be more or less monotonous in form. Another contrast
is found in the dense growth over mesophyte areas, much
more so than in xerophyte regions, and even more dense
than in hydrophyte areas.

Among the mesophyte societies must be included not
merely the natural ones, but those new societies which
have been formed under the influence of man, and which
do not appear among xcrophyte and hydrophyte societies.

Fic. 195. Alpine vegetation, showing the low stature, dense growth, and conepicu-
ous flowers.-—After KERNER.
16

232 PLANT RELATIONS.

These new societies have been formed by the introduction
of weeds and culture plants.

162. The two groups of societies—Two very prominent
types of societies are included here under the mesophytes,
although they are probably as distinct from one another as
are the mesophyte and xerophyte societies. One group is
composed of low vegetation, notably the common grasses
and herbs ; the other is a higher woody vegetation, com-
posed of shrubs and trees. The most characteristic types
under each one of these divisions are noted as follows.

A. Grass and herb societies.

It should not be inferred from this title that most
grasses are not herbs, but it is convenient to consider
grasses and ordinary herb forms separately.

163. Arctic and alpine carpets.—These are dense mats of
low vegetation occurring beyond forest growth in arctic
regions, and above the tree limit in high mountains. These
carpet-like growths are a notable feature of such regions.
In such positions the growing season is very short, and the
temperature is quite low at times, especially at night. It
is evident. therefore. that there must be provision for rapid
growth, and also for preventing dangerous radiation of
heat, which might chill the active plant below the point of
safety. It is further evident that the short season and the
low temperature form a combination which prevents the
growth of trees or shrubs, or even tall herbs, because the
season is too short for them to reach a protected condition,
and their more exposed young structures are not in a posi-
tion to withstand the daily fall of temperature.

These carpets of vegetation are notably fresh-looking,
indicating rapid growth ; green, indicating an abundance
of chlorophyll and great activity; thick, as they are
mostly perennials, developed from abundant underground
structures ; low, on account of the short season and low

Fic. 196. Two plants of a rock-rose (J/elianthemum), showing the effect of low
ground and alpine conditions. The low-ground plant (@) shows an open habit,
and elongated stems with comparatively large and well-separated leaves. The
same plant in alpine conditions is drawn to the same scale in 6, and magnified in
c, the very short and compact habit being in striking contrast with that of the low-
ground form.—After BoNNIER.

234 PLANT RELATIONS.

temperature ; and soft, the low stature and short life not
involving the development of specially rigid structures for
support or resistance. In such conditions, as would be
expected, annuals are in the minority, the plants being
mostly perennial and geophilous. Geophilous plants are
those which have the habit of disappearing underground
when protection is needed. This is probably the best adap-
tation for total disappearance from the surface and for rapid
reappearance (see $143). In such conditions, also, rosette
forms are very common, the overlapping leaves of the rosette
closely pressed to the ground diminishing the loss of heat
by radiation. It has also been noticed that these arctic and
alpine carpets show intense color in their flowers, and often
a remarkable size of flower in proportion to the rest of the
plant. Wherever the area is relatively moist, the carpet is
prevailingly a grass mat; in the drier and sandier spots
the herbs predominate (see Fig. 1115).

In the case of plants which can grow both in the low
ground and in the alpine region, a remarkable adaptation
of the plant body to the different conditions may be noted.
The difference in appearance is sometimes so great that it
is hard to realize that the two plants belong to the same
species (see Fig. 196).

164. Meadows.—This term must be restricted to natural
meadow areas, and should not be confused with those arti-
ficial areas under the control of man, which are commonly
called meadows. The appearance of such an area hardly
needs definition, as it is a well-known mixture of grasses
and flowering herbs, the former usually being the pre-
dominant type. Such meadow-like expanses are common
in connection with forest areas, and it is an interesting
question to consider what. conditions permit forest growth
and meadow growth side by side (see Fig. 197).

The greatest meadows of the United States are the well-
known prairies, which extend from the Missouri castward
to the forest regions of Illinois and Indiana (see Fig. 198).

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236 PLANT RELATIONS.

The prairie is regarded by some as a xerophyte area, and this
is a natural conclusion when one examines only the struc-
tures of the plants which occupy it. It is certainly a tran-
sition area between the plains of the West and the true
mesophyte areas of the Hast. However, an examination of
the soil reveals a deep, rich humus, with the water sup-
ply decidedly greater than that which characterizes a true
xerophyte area. On the other hand, the prevailing winds
are dry. There is a mixture, therefore, of mesophyte con-
ditions in the soil and xerophyte conditions in the air,
which leads to a peculiar association of structures.

The vegetation of the prairies in general is composed
of tufted grasses and perennial flowering herbs. Unfortu-
nately, most of the natural prairie has disappeared, to be
replaced by farms, and the characteristic prairie forms are
not easily seen, The flowering herbs are often very tall
and coarse, but with brilliant flowers, such as species of
aster, goldenrod, rosin-weed, indigo plant, Inpine, bush
clover, etc. The most characteristic of these forms show
their xerophyte adaptations by their rigidity and roughness.

It has long been a vexed question as to the absence of
trees in a soil which seems to be most suitable for their
development. Probably the most ancient explanation was
the occurrence of prairie fires, but it seems evident that
some general natural condition rather than an artificial one
is responsible for such an extensive area. <A possible
explanation is as follows: The extensive plains of the
West develop the strong and dry winds which prevail over
the prairie region, and this brings about extremes of heat
and drouth, in spite of the character of the soil. In such
conditions a tree in a germinating condition could not
establish itself. The prairies, therefore, represent a sort
of broad beach between the Western plains and the East-
ern forests. The eastward limit of the prairie has proba-
bly depended upon the limit of the dry winds, which
are gradually modified as they move eastward, until they

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238 PLANT RELATIONS.

cease to be unfavorable to forest growth. The forest does
not begin abruptly upon the eastern limit of the prairie,
but appears first as clumps of trees, with interspersed
meadows, and finally as a dense forest mass. Of course, the
forest display of the eastern border of the prairie has been
immensely interfered with by man.

165. Pastures,—This term is applied to areas drier than

very dense, excluding all other vegetation, and the grass or pasture areas are too
dry to form real meadows.—After CowLEs.

natural meadows, and includes the meadows formed or con-
trolled by man (see Fig. 199). They may be natural, or
derived from natural meadow areas, or from forest clear-
ings; therefore they are often maintained in conditions
which, if not interfered with, would not produce a meadow.
In general, the pasture differs from the natural meadow in
being drier, a fact often due to drainage, and in develop-
ing lower and more open vegetation. Naturally the plant

MESOPHYTE SOCIETIES. 239

forms are prevailingly grasses, and their cultivation is the
purpose of the artificial pasture, but the meadow tendency
is shown by the coming in of perennial weeds. The inva-
sion of pastures by weeds suggests many interesting ques-
tions. Are the weeds natives or foreigners? Are they
annuals or perennials ? What is the relative success of the
different invaders, and why are some more successful than
others? <A study of pastures will also reveal the fact that
there is great difference in the vegetation of mowed and
grazed pastures. The same effects are noted when natural
meadows are used for grazing.

B. Woody societies.

These societies include the various shrub and tree as-
sociations of mesophyte areas, associations entirely distinct
from the grass and herb societies.

166. Thickets—The mesophyte thickets are not so abun-
dant or impenetrable as the xerophyte thickets. They seem
to be developed where the conditions are not quite favor-
able for forests. An illustration of this fact may be ob-
tained by noting the succession of plants which appear
on a cleared area. After such an area has been cleared of
its trees, by cutting or by fire, it is overrun by herbs which
develop rapidly from the seed. Sometimes these herbs
are tall and with showy flowers, as the so-called fire-weed
or great willow herb. Following the herb societies there
is a gradual invasion of coarser herbs and shrubby plants,
forming thickets, and finally a forest growth may appear
again.

In arctic and alpine mesophyte regions the willow is the
great thicket plant, often covering large areas. In tem-
perate regions willow thickets are confined to stream banks
and boggy places, the plants evidently needing moist and
cool soil. Although the willow may be regarded as the
characteristic mesophyte thicket plant, there are other

240 PLANT RELATIONS.

well-known thicket plants, such as hazel, birch, alder, etc.
Although pure thickets frequently occur, that is, thickets
in which willow, or hazel, or alder, is the prevailing type,
mixed thickets are probably more common. One who is
familiar with mesophyte thickets will recognize that the
ordinary mixed thickets are composed of various kinds of
shrubs, brambles, and tall herbs.

167. Deciduous forests—Deciduous forests are especially
characteristic of temperate regions. The deciduous habit,
that is, the habit of shedding leaves at a certain period, is
an adaptation to climate. In the temperate regions the
adaptation is in response to the winter cold, when a vast
reduction of delicate exposed surface is necessary. Instead
of protecting delicate leaf structures from the severe cold
of winter, these plants have formed the habit of dropping
them and putting out new leaves when the favorable season
returns.

It is instructive to notice how differently the conifers
(pines, etc.) and the deciduous trees (oaks, maples, etc.)
have answered the problem of adaptation to the cold of
winter. The conifers have protected their leaves, giving
them a small surface and heavy walls. In this way pro-
tection has been secured at the expense of working power
during the season of work. Reduced surface and thick
walls are both obstacles to leaf work. On the other hand,
the deciduous trees have developed the working power of
their leaves to the greatest extent, giving them large sur-
face exposure and comparatively delicate walls. It is out
of the question to protect such an amount of surface dur-
ing the winter, and hence the deciduous habit. The coni-
fers are saved the annual renewal of leaves, but lose in
working power; the deciduous trees must renew their
leaves annually, but gain greatly in working power.

It should be remarked that leaves do not fall because
they are broken off, but that in a certain sense it is a
process of growing off. Often at the base of the leaves,

MESOPHYTE SOCIETIES. 241

where the separation is to occur, a cleavage region is gradu-
ally developed until the leaf is entirely separated from the
stem except by a woody strand or two, which is easily
broken (see Fig. 200). In this way the scar which remains
has really been formed before the leaf falls.

In this process of sloughing off leaves, the plant cannot
afford to lose the living substance
present in the working leaves.
This substance, during the prep-
aration for the fall, has been graid-
ually withdrawn into the perma-
nent parts of the plant.

It will be noticed that in
general deciduous leaves are thin,
exceedingly variable in form, and
in a general horizontal position,
nor do they have the firm, leathery
texture of the xerophyte leaves.
All this indicates great leaf ac-
tivity, for, the necessity of pro-
tection being removed, the leaf is
not impeded in its work by the
development of protective struc-

Fie, 200. A section through the
base of a leaf of horse-chest-
nut preparing to fall off at
the end of the growing sea-
son. A cleavage plate (s) has

tures.

One of the most prominent
features associated with the de-
ciduous habit is the autumnal col-

developed between the woody
bundle (0) and the surface.
Presently this reaches the
surface, and only the woody
strand fastens the leaf to the

* aoe % stem.
oration. The vivid colors which

appear in the leaves of many trees, just before the time of
falling, is a phenomenon which has attracted a great deal of
attention, but although it is so prominent, the causes for
it are very obscure. It will be noticed that this autumnal
coloration consists in the development of various shades of
two typical colors, yellow and red. These colors are often
associated together in the same leaf, and sometimes a leaf
may show a pure color.

242 PLANT RELATIONS,

The two colors hold a very different relation in the leaf
cell. It is known that the yellow is due to the break-
ing down of chlorophyll, so that the chloroplasts, which
are green when active, become yellow when disorganizing,
and finally bleach out entirely. That yellow may indicate
a post mortem change of chlorophyll may be noticed in con-
nection with the blanching of celery, in which the leaves
and wpper part of the stem may be green, the green may
shade gradually into yellow, and finally into the pure
white of complete blanching.

The red shades, however, do not seem to hold any such
relation to the disorganization of chlorophyll. The red
coloring matter appears as a stain in the cell sap, so that
what might be called the atmosphere of the active cell is
suffused with red. Certain experiments upon plant colors
have indicated that the presence of the red color slightly
increases the temperature by absorbing more heat. This
has suggested that the red color may be a slight protec-
tion to the living substance, which has ceased working
and which is in danger of exposure to cold. If this be
true, it may he that the same explanation will cover the
case of the red flush so conspicuous in buds and young
leaves in the early spring. It must not be supposed that
the need of protection has developed the color, but that
since it is developed it may be of some such service to the
plant. The whole subject, however, is too indefinite and
obscure to be presented in any other form than as a bare
suggestion.

Even the conditions which determine autumnal colora-
tion have not been made out certainly. To many the an-
tumnal coloration is associated with the coming of frost,
which simply means a reduction of temperature ; others
associate it with diminishing water supply: still others
associate if with the change in the direction of the rays of
light, which are more oblique in autumn than during the
active growing season. It is certainly true that the colors

MESOPHYTE SOCIETIES. 243

are far more brilliant in certain years than in others, and
that the coloration must be connected in some way with
the food relations of the plants. Recent experiments have
shown that the red coloration is largely dependent upon
low temperature, which affects certain of the food-stuffs,
and the red stain is one of the products.

The autumnal colors are notably striking in American
forests on account of the fact that in these forests there
is the greatest display of species, and hence not only are
more colors produced, but they are usually strikingly
associated.

Not only is protection during the cold period secured
by deciduous forests through the falling of leaves, but the
development of scaly buds is an adaptation to the same
end. By means of these overlapping. often hairy, and
even varnished structures, delicate growing tips are pro-
tected during the cold season. The development of cork,
also, on the older parts, is a measure of protection.

As in the case of thickets, deciduous forests may be
pure or mixed. A very common type of pure forest is the
beech forest, which is a characteristic dark forest. The
wide-spreading branches of neighboring beeches overlap
each other, so as to form dense shade. As a consequence,
ina pure beech forest there is little or no undergrowth ;
in fact, no lower strata of vegetation until the lowest
ones are reached, made up of grasses and mosses. An-
other type of pure forest, which belongs to the drier re-
gions, is the oak forest, which forms a sharp contrast to
the beech, in that it isa Lght forest, permitting access of
light for lower strata of plants. lence in such a forest
there is usually more or less undergrowth, consisting of
shrubs, etc., which may develop regular thickets. The
typical American deciduous forest, however, is the great
mixed forest, made up of many varieties of trees, such as
beech, oak, elm, walnut, hickory, gum, maple, etc. These
great mixed forests, with their remarkable autumnal

244 PLANT RELATIONS.

coloration, reach their culmination in the Central West,
in Southern Illinois, Central and Southern Indiana, Ohio,
and Kentucky.

168. Evergreen foliage forests—The word foliage is in-
troduced to distinguish these forests from the ordinary
evergreen forests which are coniferous, and which do not
display broad leaves. The evergreen foliage forests are
chiefly characteristic of tropical regions, but occasionally
they are represented in temperate regions, notably of South
America. The conditions which especially favor them are
abundant precipitation and great heat. These rainy forests
of the tropics may be regarded, as Warming says, ‘‘as the
climax of the world’s vegetation,” for the conditions in
which they are developed favor constant plant activity at
the highest possible pressure. Such great forest growths
are found within the region of the trade winds, where
there is heavy rainfall, great heat, and rich black soil. So
abundant is the precipitation that the air is often saturated
and the plants drip with moisture. In such conditions
pure forests may occur, characterized by such tree forms as
the tree ferns, palms, or bamboos. Only the great mixed
tropical forest will be considered. The main characteris-
tics are as follows :

(1) Absence of simultaneous pertodicity.—Perhaps the
most. striking feature, in contrast with the deciduous
forests, is that there is no regular period for the develop-
ment or fall of leaves. Leaf activity is possible through-
out the year, and there is no time of bare forest, or of
forests just putting out leaves. This does not mean that
the leaves persist indefinitely, but that there is no regular
time for their fall and formation. Leaves are continually
being shed and formed, but the trees always appear in full
foliage.

(2) Density of growth.—Such an arca is remarkably
filled with vegetation, stratum after stratum occurring,
resulting in gigantic jungles. The higher strata may be

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246 PLANT RELATIONS.

made up of trees of different heights, below them are
shrubs of varying heights, then tall and low herbs, and
finally mosses and liverworts. Among these close-set
standing forms, great vines or lianas climb and bind the

Ll aah.

Fie. 202. A group of aerial plants (epiphytes) from a tropical forest. Note the vari-
ous habits of the epiphytes attached to the tree-trunks, and the dangling roots.—
After ScHimpER.

standing vegetation into an inextricable tangle (see Figs.
55, 201). In addition to these, hosts of aerial plants find
lodging places upon the tree-trunks and vines (sce Fig.
202). These rainy forests of the tropics furnish the very
best conditions for the development of the numerous epi-
phytic orchids, bromelias, etc. In such conditions also

MESOPHYTE SOCIETIES. 247

numerous saprophytes occur. Such an assemblage of vege-
tation is to be found nowhere else.

(3) Mumber of species.—Not only is there an immense
number of individuals, but an extraordinary number of
species occur. <A list of
plants growing in these
forests would show a re-
markable representation of
the plant kingdom.

(+) Forms of trees.—
The dense vegetation re-
sults in straight leafless
tree-trunks, so that the
leaves of trees are mainly
clustered at the tops of
high branches. The shade
is so dense and the inter-
ference is so great that
the development of low
branches is impossible. It
is common, also, for the
larger trees to develop a
system of buttresses near
the base, and also fre-
quently to send out prop
roots (see Figs. 100, 101).

(5) Absenceofbud scales.
—In the deciduous forest
bud scales are necessary to Fie. 203. A gutter-pointed leaf from a

; tropical plant.—After ScHimpER.
protect the tender growing
tips during the period of ccld. The same device would be
sufficient to protect against a period of drouth. In the
tropical forest there is danger neither from cold nor drouth,
and in such conditions bud scales are not developed, and
the buds remain naked and unprotected.

(6) Devices against too abundant rain.—The abundance

VG

248 PLANT RELATIONS.

of rain is in danger of checking transpiration, and as this
process is essential to plant activity, there are often found
devices to prevent the leaves from becoming saturated.
Many leaves have cuticles so smooth and glazed that the
water glances off without soaking in; in other cases a
velvety covering of hairs answers the same purpose; in
still other cases leaves are gutter-pointed, that is, the tip
is prolonged as asort of gutter, and the veins are depressed,
the whole surface of the leaf resembling a drainage system,
so that the rain is conducted rapidly from the surface (see
Fig. 203). These are only a few illustrations of many
devices against dangerous wetting.

CHAPTER XV.
HALOPHYTE SOCIETIES.

169, General characters——The hydrophytes, xerophytes,
and mesophytes are distinguished from one another by the
amount of water accessible. This classification must be
regarded as largely artificial, often resulting in the natural
separation of closely related societies. For example, the
sphagnum-moor is a well-marked hydrophyte society, but
it holds a very close relation to the shrubby heath, which
is a xerophyte society. These two societies, however, are
kept separate on the basis of the water supply, but they
are brought together by similarity in the food material sup-
plied by the water. It becomes evident, therefore, that a
natural classification properly depends not so much upon
the amount of water, as upon what the water contains.
However, the three groups of societies already considered
have been used for the sake of simplicity.

The halophytes, however, are characterized in a very
different way, for the condition which determines them
is not the amount of water supply, but the fact that the
water contains certain salts, notably common salt, gypsum,
and magnesia. The water may be abundant enough to rep-
resent hydrophyte conditions, or it may be scanty enough
to represent xerophyte conditions, but if.these salts are
present in the soil in sufficient abundance to strongly
affect the water, the plants are halophytes. Such soils
are recognized in popular language as salt soils or alkaline
soils.

Such areas occur in various positions: (1) in the

250 PLANT RELATIONS.

vicinity of the seashore, where there are salty beaches, and
swamps and meadows ; (2) the margins of salt lakes, such
as the Great Salt Lake, the Dead Sea, or Caspian Sea, and
a host of smaller lakes: (3) about saline springs, which are
common among the numerous medicinal springs of water-
ing places ; (4) certain interior arid wastes, which probably
mark the position of old sea basins. An extensive area of
this last kind is known as the Bad Lands, which stretch
over certain portions of Nebraska and Dakota. In these
Bad Lands the waters are strongly alkaline.

Comparatively few plants wre able to endure such con-
ditions. The family which has been able to develop
most halophyte forms is the family of chenopods, which
contains such prominent halophyte forms as the sam-
phire, seablight, saltwort, greasewood, etc. Associated with
these chenopods are certain portulacas, spurges, sedges,
grasses, etc. Such plants do not seem to be very sensitive
to climate, for the same hulophyte species are found
everywhere, in all latitudes and at all altitudes. Probably
the so-called Russian thistle, which is not a thistle at all,
may be cited as a notable illustration of a chenopod which
ranges through all climates.

Halophyte vegetation is very open, and the ground
rarely seems to be covered. If the soil is always moist,
some plants which are not true halophytes may grow in
connection with the halophyte plants. If the soil dries
up easily, even a small percentage of salt presently be-
comes very conspicuous, and from such places every other
plant is driven out but the pure halophytes.

There are many great families of plants which are never
known to grow in halophyte conditions, as for example the
great groups represented by oaks, hickories, walnuts, etc.,
the nettle family, the rose family. the heath family, and
the whole display of mosses and lichens. On the other
hand, halophytes often grow outside of halophyte condi-
tions. To be wv halophyte does not mean that other condi-

— = St Se LE

|

|

HALOPHYTE SOCIETIES. 261

tions are not possible, but that halophytes are plants which
have succeeded in living in halophyte conditions. If they
find other conditions, they may grow with even greater
vigor.

Halophytes are mostly succulent plants, with the leaves
thick and often translucent. This indicates the presence
of water reservoirs, and also the fact that the plants are
poor in chlorophyll. The succulent habit is common also

Fic. 204. A mangrove forest advancing into the water.—After SCHIMPER.

among xerophytes, a group which halophytes further re-
semble in the small leaves and often prostrate habit. If
halophytes with such adaptations are transplanted into
more favorable conditions, as into a mesophyte area, the
plants become taller and thin-leaved.

The evidence seems to show that the presence of the
salts in the soil, at least in the amount in which they
occur, interferes with the nutritive work of the plant.
Certainly the plant seems to make food with difficulty, a

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HALOPHYTE SOCIETIES. 253

difficulty that means impossibility to all but the compara-
tively few forms that have succeeded in living in halophyte
conditions.

Numerous halophyte societies have been recognized, but
attention is called only to a few.

170. Mangrove swamps.—This is certainly the most vigor-
ous of the halophyte societies. Mangrove swamps occur
along flat tropical sea coasts, where the waters are quiet.
The mangrove is a tree of curious habit, which advances
slowly out into the water and extends back landwards as
low woods or thickets (see Figs. 204. 205). The whole
surroundings appear forbidding, for the water is sluggish
and mucky, covered with scum, rich in bacteria, and with
bubbles constantly breaking upon the surface from decay-
ing matter beneath the water. The mangrove has the pe-
culiarity of germinating its seeds while still upon the
tree, so that embryos hang from the trees. and then drop
like plumb-bobs into the muck beneath, where they stick
fast and are immediately in a condition to establish them-
selves. In these mangrove swamps the species are few, and
the adaptations chiefly in the way -of developing various
kinds of holdfasts for anchoring in the uncertain soil, and
also various devices for carrying air to the submerged parts.

171. Beach marshes and meadows.—The salt marshes and
meadows near the seacoast are very well known. They
lie beyond the reach of ordinary flood tide, but the waters
are brackish. In these marshes and meadows occur certain
characteristic halophyte grasses and sedges. Such forms
being the dominant type give the general appearance of
a coarse meadow. The difference between a marsh and
meadow is simply a question of the amount of water.

172. Salt steppes—These areas are often large in extent,
and belong to the interior of continents (see Fig. 206).
So far as water supply is concerned, they hold the same
relation to other halophyte societies as do the plains to
mesophyte societies. In the United States one of the most

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HALOPHYTE SOCIETIES. 255

extensive of the salt steppes is the Great Salt Lake basin.
It is here that the halophyte chenopod forms are especially
developed, and there is a rich display of greasewoods,
seablights, samphires, etc. The Bad Lands, already re-
ferred to, represent another such area.

173. Salt and alkaline deserts.—In these areas the water
supply reaches its minimum, and therefore the water be-
comes saturated with the characteristic salts of the soil.
No worse combination for plant activity can be imagined
than the combination of minimum water and maximum
salts. In consequence, such areas are almost, if not abso-
lutely, devoid of vegetation. As illustrations, the exten-
sive desert of the Dead Sew region and the Death’s Valley
may be cited. Death's Valley is an area in Southern Cali-
fornia upon the borders of Arizona, in the general region of
the cactus desert. The soil is so strongly impregnated with
the so-called alkaline salts, and the water supply is so scanty,
that the surface of the soil is covered by a thick crust of
salt. In such conditions vegetation becomes impossible.

INDEX TO PLANT RELATIONS.

(The italicized numbers indicate that the subject is illustrated on the page cited.
In such case the subject may be referred to only in the illustration, or it may be

referred to also in the text.]

A

Acacia, 199.

Achillea, 202.

Adaptation, 147.

Adiantum, 27,

Aeration, 92, 93, 95, 188.

Agave, 45, 47. :

Agrimony, 121.

Ailanthus, 116.

Air, 95, 98, 114, 122, 138.

Air cavities, 171, 172, 178, 176.

Air passages, 92, 93, 94, 95.

Air plants, 97, 98, 99, 100, 101,
246.

Air roots, 97, 98, 99, 100.

Alchemilla, 79.

Alge, 1, 2, 87, 99, 107, 109, 110,
111, 118, 150, 171, 172, 177.

Alkaline deserts, 255.

Alpine plants, 148, 291, 282, 233.

Amicia, 9.

Ampelopsis, 63,

Anemophilous, 122.

Animals, 119, 121, 122, 128, 145,
205.

Annual habit, 195.

Annual rings, 84.

Anthurium, 97.

Apple, 79.

Araucaria, 74.

Arbor vite, 139.

Arctic plants, 148, 232.
Arrow-leaf, 186.
Artillery plant, 120.
Ash, 116.

Aspidium, 55.
Assimilation, 154, 156,
Autumn coloration, 241.

B

Bacteria, 189.
Banana, 88.

Banyan, 105, 106.
Barberry, 207.

Bark, 84.

Basswood, 116, 201.
Beach, 209, 210.
Beach marshes, 253.
Beach meadows, 253
Beach pea, 118.

Bean, 140.

Bearberry, 212, 214.
Beech drops, 157.
Beech forest, 145, 243.
Beggar ticks, 119, 121.
Begonia, 25, 208.
Bellflower, 19, 80.
Bidens, 719.
Bignonia, 715.

258

Bilbergia, 136.

Birches, 71.

Black moss, 96, 101.
Bladderwort, 173.

Blade, 35

Bloodroot, 195.

Bogs, 148.

Box elder, 84.

Bramble, 94.

Branched leaves, 19, 20, 21, 23.
Buds, 70, 73, 75, 141, 248, 247.
Bulbs, 73, 75, 81.

Bulrush, 142, 148, 185, 186, 207.
Burdoek, 121, 122.

Bush, 226.

Bush clover, 43.

Buttercup, 185.

Buttresses, 108, 104, 247.

C

Cactus deserts, 277, 222.

Cactus forms, 45, 46, 47, 146, 202,
218, 219,

207,

222,
Calyx, 78, 79, 80, 128.
Campanula, 19, 80.
Caoutchoue, 186.
Carbohydrates, 153, 156.
Carbon, 153.
Carbon dioxide, 30, 151, 153.
Cardon forests, 229.
Carnation, 42.

215, 216, 217,

Carnivorous plants, 155, 156, 157,

1738, 189,
Carpel, 78, 79, 80, £25.
Carrot, 120.
Castor-oil bean, 73.
Casuarina, 229.
Catalpa, 117.
Catchfly, 186.
Cat-tail flag, 142, 148, 185, 286.

INDEX.

Cercis, 10.

Chaparral, 226.

Chenopods, 250.

Chlorophyll, 6, 8, 149, 162.

Chloroplasts, 39, 107, 152,
208, 209, 242.

Chrysanthemum, .23.

Cilia, 109, 111.

Claytonia, 190.

Cleistogamons, 130.

Clematis, 272.

Climbing stems, 60, 61, 62, 63, 64,
102, 248.

Clinging roots, 99, 10.2.

Clinia, 209.

Coeklebur, 720, 171.

Compass plants, 10, 12, 197, 198.

Compound leaves, 19, 2, 21, 23.

Conducting tissue, 171.

Conifer forests, 225, 226, 227, 228.

Conifers, 83, 190, 191, 223, 226,

Cork, 243.

Corn, 85, 90.

Corolla, 78, 79, 80.

Cortex, 88, 84, 93, 94, 107, 108.

Cottonwood, 70.

Cotyledons, 50, 51, 73, 139, 140.

Crevice plants, 94, 209.

Cuticle, 42, 205.

Cyead, 22.

Cycloloma, 177.

Cypress knees, 95, 96, 183.

Cypripedium, 132, 133, 134, 135,
156,

Cytisus, 20.

205,

D

Dandelion, 82, 774, 117.
Darlingtonia, 157.
Date palm, 87.
Dead-nettle, 80.

INDEX.

Deciduous forests, 240.

Deciduous habit, 148, 196, 240,
lel,

Deserts, 771,

Desiccation, 194.

Desmodium gyrans, 49.

Destruction of plants, 148.

Diatoms, 174.

Dicotyledons, 35, 83, 116.

Differentiation, 3.

Digestion, 154, 156.

Dionea, 160, 161.

Dodder, 106, 107, 157.

Dog-tooth violet, 244.

Dragon tree, 15.

Drainage, 143, 145.

Drosera, 158, 150.

Drouth, 193.

Duckweed, 97, 175.

Dunes, 145, 201, 209, 212, 212.

Dwarf growths, 203.

999

Nay

223, 255.

E

Easter lily, 14.

Echeveria, 17.

Ecological factors, 163.

Ecology, 4, 149.

Eel grass, 184.

Ege, 110, 111.

Elaters, 118.

Elatine, 92.

Elm, 63, 67, 68, 75.

Embryo, 111, 139.

Entomophilous, 122, 123.

Epidermis, 87. 40, 41, 42, 88, 84,
107, 170, 205, 208, 209.

Epilobium, 712, 113, 128, 185.

Epiphyte, 209.

Equisetum, 111, 203.

Erect stems, 62, 65, 66, 67, 68, 69,
70, 71.

258

Erica, 200.
Erythronium, 244.
Euphorbia, 04.

PF

Ferns, 55, 56, 85, 88, 100, 111, 118,
119.

Fertilizing, 145.

Ficus, 8.

Figwort, 128, 135.

Fireweed, 11?, 113, 128, 135, 239.

Fittonia, 37, 152.

Fixed light position, 197.

Flag, 124, 138.

Floating stems, 59.

Floats, 171. 172, 173.

Flowers, 76, 78, 140.

Foliage forests, 226, 244.

Foliage leaves, 6, 28, 139.

Forest clearing, 143. 145.

Forests, 190, 226, 240, 245.

Fruit. 173, 114, 115, 116, 117, 118,
A190, 120, 12d, D2,

Fucus, 171.

Functions, 3.

Fungi, 87, 107, 709, 110.

Furze, 25.

G

Galium, 17.

Gamete, 710, 117, 112, 113.

Geophilous habit, 55, 56, 73, 74,
Toy, PB, TT, FS OL, 108, L9G, 234:

Geotropism, 69, 91, 188.

Germination, 111, 188, 739, 140.

Gorse, 205.

Grape vine, 61.

Grass, 187, 197, 216, 236.

Gravity, 91.

Guard cells, 38.

Gymnosperms, 115.

260

H

Habenaria, 727.

Hairs, 43, 92, 136, 146, 202, 208.

Halophytes, 169, 249.

Harebell, 19, 80.

Hawthorn, 36.

Heart-wood, 151.

Heat, 112, 1388, 145, 164.

Heath plants, 189, 200, 214.

Helianthemum, 232.

Helotropism, 12, 13, 68, 72, 73,
139.

Hemlock, 190.

Horse-chestnut, 242.

Hosts, 106.

House leek, 79.

Houstonia, 729, 185.

Huckleberry, 214.

Hudsonia, 212.

Hura crepitans, 120.

Hydrogen, 153.

Hydrophytes, 168, 170, 174.

Hydrotropism, 91, 188.

ui

Insects and flowers, 123.
Tris, 126, 188.

Isoetes, 94, 95, 208.

Ivy, 99.

J

Juncus, 77.
Juniper, 51, 238,

L

Lactuca, 12, 197, 198.

Lady-slipper, 132, 183, 134, 135,
186.

Lakes, 143, 148.

INDEX.

Laminaria, 277.
Larch, 178, 190.
Latex, 136.
Leafless forests, 226.
Leaflet, 19.
Leaf-relation, 538.
Lemna, 97.
Lespedeza, 43.
Lianas, 60, 61, 62, 63, 64. 102,
245, 246,
Lichens, 194, 209, 214.
Life-relations, 4, 7, 8, 53, 77.
Light, 148, 167, 197.
Light-relation, 7, 8.
Lily, 38, 40.
Live-for-ever, 18.
Live oak, 101.
Liverworts, 118.
Locomotion, 118.
Locust, 207.
Long moss, 96, 101.
Loosestrife, 1380, 135.
Lotus, 180.

M

Mangroves, 251, 252, 253.

Maple, 26, 115, 116.

Maranta, 38.

Marchantia, 107.

Meadows, 234, 235.

Mechanical tissue, 172.

Mesophyll, 38, 39, 40, 41, 42, 152.

Mesophytes, 168, 280.

Migration, 58, 75, 147.

Mildew, 109, 157.

Milkweed, 117.

Mimosa, 199.

Mistletoe, 107.

Mold, 109.

Monocotyledons, 35, 85, 88, 116,
ISG,

Moors, 187, 188,

INDEX.

Mosaic arrangement, 25, 27, 37.

Mosses, 87, 107, 110, 118, 118, 188,
194, 209, 214.

Motile leaves, 9, 10, 11, 49, 198,
199.

Mould, 109.

Mullein, 48, 44.

Mushrooms, 157.

N

Nectar, 123, 158.
Nelumbium, 780.
Nicotiana, 80.
Nightshade, 26.
Nitrogen, 153.
Nodes, 54.

Nuphar, 92.
Nutrition, 3, 149.
Nymphexa, 178, 180.

ce)

Oak, 69, 101.
Oak forest, 145, 248.
(Edogonium, 111.
Orchids, 98, 99, 126, 127, 132, 133,
134, 185, 136, 189.
Organs, 8.
Ornithogalum, 81.
Ovary, 79, 80, 125.
Ovules, 78, 79, 80.
Oxalis, 10, 50, 199.
Oxygen, 29, 138, 158.

P

Palisade tissue, 39, 40, 42, 205.
Palms, 86, 87, 228.

Pandanus, 103.

Parasites, 106, 150.

Passion vine, 62.

Pastures, 238.

261

Pellionia, 24.

Pentstemon, 137.

Peony, 78.

Petals, 78, 79, 80.

Petioles, 15, 26, 35, 55.

Phlox, 80.

Photosynthesis, 28, 29, 150,
153, 156.

Physiology, 149.

Pickerel weed, 181, 182.

Pines, 63, 65, 66, 112, 115,
190, 227, 228.

Pirus, 79.

Pistil, 77, 79, 80.

Pitcher plant, 155, 156, 157,

Pith, 88, 84, 107.

Plains, 213, 215, 216.

Plankton, 174.

Plant body, 2.

Plant societies, 1, 146, 162,
174.

Plastid, 152.

Platycerium, 100.

Plumes, 112, 113, 114, 116, 117.

Plumule, 51, 140.

Pollen, 111,

123.

Pollination, 77, 115, 122, 123.

Polygonatum, 35.

Ponds, 142, 175, 178, 180, 184.

Pondweed, 176, 181, 25.7.

Potato, 74, 76.

Potentilla, 43, 79.

Prairies, 208, 222, 284, 237.

Prickles, 146.

Prickly lettuce, 12, 197, 198.

Primrose, 187.

Procumbent stem, 57.

Profile position, 197, 198.

Pronuba, 130, 131.

Prop roots, 99, 108, 104, 105, 106,
247.

152,

117,

158.

168,

pad
vt,

112, 115, 121,

262

Protandry, 128, 185.

Protection of leaves, 9, 10, 11, 12,
41, 42, 43, 48, 49.

Proteids, 158, 156, 189.

Protogyny, 128, 135.

Protoplasm, 154, 156.

Ptelea, 115.

Puff-balls, 157.

Q
Quillwort, 94, 95, 208.

R

Rain, 51, 247.

Ranunculus, 18.7.

Raspberry, 92.

Receptacle, 77, 81, 114.

Redbud, 0.

Reed grass, 142, 185, 186.

Reed swamps, 185.

Reproduction, 3, 109.

Respiration, 82, 154, 156.

Rhizoids, 107.

Rivalry, 146.

Robinia, 125, 126, 1238, 207.

Rock-rose, 233.

Rock societies, 209, 210.

Roots, 89, 90, 95, 98, 99, 188, 139,
AA.

Root-cap, 108.

Root-hairs, 90.

Rootstalk, 55, 56, 75, 76, 77, 78,
D6,

Rose acacia, 175, 126, 133.

Rosette habit, 76, 17, 78, 19, 47,
158, 160, 209, 234.

Rosinweed, 10, 197, 198.

Rubber tree, 74.

Runners, 57, 3.

Rusts, 157.

OA,

INDEX.

8

Sage brush, 216.

Sagittaria, 186,

Saintpaulia, 16.

Sult deserts, 255.

Salt steppes, /54.

Sand societies, 209.

Sandy fields, 209, 272.

Sanguinaria, 195.

Saprophytes, 130, 189.

Sap-wood, 151.

Sargassum, 17.

Sarracenia, 165, 156, 158.

Saxifrage, 58.

Seale leaves, 70, 78.

Scales, 141.

Scouring rush, 203.

Serew pine, 70:3.

Scrub, 226.

Seaweeds, 1, 2, 87, 99.

Sedges, 187. ;

Seed-dispersal, 22”, 118, 774, 116,
117, 118, 119, 120.

Seed-plants, 111, 119, 121.

Seeds, 111, 122, 123, 115, 138, 139,
140.

Selaginella, 20, 100, 194.

Semperviyum, 19.

Senecio, 174.

Sensitive plants, 71, 48, 50, 299.

Sepals, 78, 79, 80.

Shepherdia, 44.

Shoots, 53.

Silphium, 10, 197, 798.

Sinilax, 67.

Snapdragon, 80, 137.

soil, 90, 94, 145, 151, 166, 214
ed,

Solomon’s seal, 35, 70.

Spanish needle, 779, 121.

Sphagnum, 18s.

INDEX. 26

Sphagnum-bogs, 208.

Sphagnum-moors, 188.

Spines. 146, 204.

Spiregyra, 110.

Spongy tissue. 89, 40.

Spore cause, 55, 118, 119.

Spore-dispersal, 10, 711,112, 118,
114, 11s

Spores, 209, 110, 112. 112.

Spring beauty. 296.

Spring plants, 148, 144.

Squash seedlings, 39.

Squirting cucumber, 120.

staghorn fern, 100.

Brame, 78, 79, 80, 125,

Starch, 153.

star cucumber, 61.

Star-of-Bethlehem, 82.

Stem, 54, 85, 139.

Steppes, 216, 203.

Stigma. 80, 123.

Supules. 35.

Stomata, 8. 40, 206.

Strawberry plant, 57, 58, 98.

Struggle for existence, 142.

Style. 80, 128.

Subterranean stems, 54, 55, 56. 76,
Pip 8s

Succulent plants, 251.

Sugar, 158.

Sundew, 738, 159.

Sunflower, 72.

Swamp-forest, 190, 252.

Swamp-imoers, 187,

Swamp-thickets, 18s.

Swamps, 183.

£

Tamarack, 178, 190.
Tap root. 93.
AR 42,

axus, 4 6

qo

Teasel, 136.

Telegraph plant, 49.

Temperature, 145.

Tendrils, 62. 62, 63.

Thallus, 107.

Thickets, 188, 224, 239.

Thistle, 117.

Thorns, 146, 204. 205, 206, 207,
224.

Thuja, 209.

Tilia, 126, 201.

Tillandsia, 96, 101.

Toad-flax, 80.

Toadstools, 149.

Tobacco, 80.

Touch-me-not, 119.

Tragacanth, 206.

Transpiration, 31, 33, 154. 193,
2A,

Tropical forest. 245.

Trumpet creeper. 99.

Tubers, 74. 76. 196.

Tumbleweeds. 277, 220.

Turf-building, 185.

U

Ulex, 208.
Ulothrix, 109, 111.
Utricularia, 173, 174.

Vv

Vallisneria, 154.
Vascular bundles, 88, 84, 92, 938,
94, 107, 108, 151, 171.
Vegetative multiplication. 109.
Veins, 335, 36. 387, 40, 151.
Velamen, 99.
Venation, 33,
Victoria, 180.
Violet, 117, 119.

56, 37.

264 INDEX.

WwW Witch hazel, 118, 119.
Woodbine, 61, 62.
Walnut, 82.

Water, 90, 92, 94, 95, 118, 188, x

142, 151, 163, 193, 206, 244. 7
Water lily, 178, 180, 181, Xerophytes, 168, seed
Water reservoirs, 206, 208, 209. ERODING SRRELELIE),
Weeds, 147.
Willow, 3. 239. “
Wind, 95, 98, 114, 122, 167. Yew, 42.
Wings, 712, 115, 116. Yucea, 45, 47, 180, 131, 220.

TWENTIETH CENTURY TEXT-BOOKS

PLANT SIRUGIURES

A SECOND BOOK OF BOTANY

BY
JOHN M. COULTER, A.M., Pu. D.

HEAD OF DEPARTMENT OF BOTANY
UNIVERSITY OF CHICAGO

NEW YORK
D. APPLETON AND COMPANY
1900

Copyricut, 1899,
By D. APPLETON AND COMPANY.

PREFACE

Iy the preface to Plant Relations the author gave his
reasons for suggesting that the ecological standpoint is best
adapted for the first contact with plants. It may be, how-
ever, that many teachers will prefer to begin with the mor-
phological standpoint, as given in the present book. Rec-
ognizing this fact, Plant Structures has been made an
independent volume that may precede or follow the other,
or may provide a brief course of botanical study in itself.

Although in the present volume Morphology is the domi-
nant subject, it seems wise to give a somewhat general view
of plants, and therefore Physiology, Ecology, and Taxonomy
are included in a general way. For fear that Physiology
and Ecology may be lost sight of as distinct subjects, and
to introduce important topics not included in the body of
the work, short chapters are devoted to them, which seek
to bring together the main facts, and to call attention to
the larger fields.

This book is not a laboratory guide, but is for reading
and study in connection with laboratory work. An accom-
panying pamphlet for teachers gives helpful suggestions
to those who are not already familiar with its scope and
purpose. It is not expected that all the forms and sub-
jects presented in the text can be included in the labora-
tory exercises, but it is believed that the book will prove a
useful companion in connection with such exercises. It
is very necessary to co-ordinate the results of /aboratory
work, to refer to a larger range of material than can be
handled, and to develop some philosophical conception of

Vv

vi PREFACE

the plant kingdom. The learning of methods and the
collection of facts are fundamental processes, but they
must be supplemented by information and ideas to be of
most service.

The author does not believe in the use of technical
terms unless absolutely necessary, for they lead frequently
to mistaking definitions of words for knowledge of things.
But it is necessary to introduce the student not merely to
the main facts but also to the literature of botany. Ac-
cordingly, the most commonly used technical terms are
introduced, often two or three for the same thing, but it
is hoped that familiarity with them will enable the student
to read any ordinary botanical text. Care has been taken
to give definitions and derivations, and to call repeated
attention to synonymous terms, so that there may be no
confusion. The chaotic state of morphological terminology
tempted the author to formulate or accept some consistent
scheme of terms; but it was felt that this would impose
upon the student too great difficulty in reading far more
important current texts.

Chapters I-XII form a connected whole, presenting the
general story of the evolution of plants from the lowest to
the highest. The remaining chapters are supplementary,
and can be used as time or inclination permits, but it is the
judgment of the author that they should be included if
possible. The flower is so conspicuous and important a
feature in connection with the highest plants, that Chapter
ATII seems to be a fitting sequel to the preceding chapters.
It also seems desirable to develop some knowledge of the
great Angiosperm families, as presented in Chapter XIV,
since they are the most conspicuous members of every flora.
In this connection, the author has been in the habit of
directing the examination of characteristic flowers, and of
teaching the use of ordinary taxonomic manuals. Chap-
ter XV deals with anatomical matters, but the structures
included are so bound up with the form and work of plants

PREFACE vil

that it seems important to find a place for them even in an
elementary work. The reason for Chapters XVI and AX VII
has been stated already, and even if Plant Relations is stud-
ied, Chapter A VII will be useful either as a review or as an
introduction. In the chapter on Plant Physiology the
author has been guided by Noll’s excellent résumé in the
““Strasburger ” Botany.

The illustrations have been entirely in the charge of
Dr. Otis W. Caldwell, who for several years has conducted
in the University, and in a most efficient way, such labo-
ratory work as this volume implies. Many original illus-
trations have been prepared by Dr. Caldwell and his assist-
ants, and some are credited to Dr. Chamberlain and Dr.
Cowles, of the University, but it is a matter of regret that
pressure of work and time limitation have forbidden a still
greater number. The authors of the original illustrations
are cited, and where illustrations have been obtained else-
where the sources are indicated. The descriptions given
in connection with each illustration are unusually full,
and should be studied carefully, as frequently they contain
important material not included in the text.

The author would again call attention to the fact that
this book is merely intended to serve as a compact supple-
ment to three far more important factors: the teacher, the
laboratory, and field work. Without these it can not serve
its purpose.

Joun M. CouLter.

Tue University oF Cuica@o, Vovember, 1899.

CONTENTS

CHAPTER
I.—Iytropuction

Il.—THaLuopuytes: ALG&
III.—TueE EVOLUTION OF SEX
IV.—THE GREAT GROUPS OF ALG.E
V.—THALLOPHYTES: FUNGI
VI—THE FOOD OF PLANTS
VIL—BryYoruyteEs
VIII—THE GREAT GROUPS oF BRYOPHYTES .
IX.—PTeERIDOPHYTES
X.—THE GREAT GROUPS OF PTERIDOPHYTES
XI.—SPERMATOPHYTES : GYMNOSPERMS
XTI.—SpPERMATOPHYTES : ANGIOSPERMS
XIUL—THE FLOWER
XIV.—MonocoryLEDONS AND DICOTYLEDONS .
XV.—DIFFERENTIATION OF TISSUES
XVI.—P.LaNT PHYSIOLOGY
XVII—PuLaxt ECOLOGY
GLOSSARY

INDEX

ix

PAGE

TO ae NEY.
PART IL.—PLANT STRUCTURES

CHAPTER I

INTRODUCTION

1. Differences in structure—It is evident, even to the
casual observer, that plants differ very much in structure.
They differ not merely in form and size, but also in com-
plexity. Some plants ure simple, others are complex, and
the former are regarded as of lower rank.

Beginning with the simplest plants—that is, those of
lowest rank—one can pass by almost insensible grada-
tions to those of highest rank. At certain points in this
advance notable interruptions of the continuity are dis
covered, structures, and hence certain habits of work, chang-
ing decidedly, and these breaks enable one to organize the
vast array of plants into groups. Some of the breaks ap-
pear to be more important than others, and opinions may
differ as to those of chief importance, but it is customary
to select three of them as indicating the division of the
plant kingdom into four great groups.

2. The great groups—The four great groups may be
indicated here, but it must be remembered that their names
mean nothing until plants representing them have been
studied. It will be noticed that all the names have the

1

2 PLANT STRUCTURES

constant termination phytes, which is a Greek word mean-
ing “plants.” The prefix in each case is also a Greek word
intended to indicate the kind of plants.

(1) Thallophytes—The name means “thallus plants,”
but just what a “thallus” is can not well be explained
until some of the plants have been examined. In this
great group are included some of the simplest forms,
known as Alge and Fungi, the former represented by green
thready growths in fresh water and the great host of sea-
weeds, the latter by moulds, mushrooms, etc.

(2) Bryophytes—The name means “moss plants,” and
suggests very definitely the forms which are included.
Every one knows mosses in a general way, but associated
with them in this great group are the allied liverworts,
which are very common but not so generally known.

(3) Pteridophytes—The name means * fern plants,” and
ferns are well known. Not all Pteridophytes, however, are
ferns, for associated with them are the horsetails (scouring
rushes) and the club mosses.

(4) Spermatophytes.—The name means “ seed plants ”—
that is, those plants which produce seeds. In a general
way these are the most familiar plants, and are commonly
spoken of as “flowering plants.” They are the highest in
rank and the most conspicuous, and hence have received
much attention. In former times the study of botany in
the schools was restricted to the examination of this one
group, to the entire neglect of the other three great groups.

3. Increasing complexity.—.\t the very outset it is well
to remember that the Thallophytes contain the simplest
plants—those whose bodies have developed no organs for
special work, and that as one advances through higher
Thallophytes, Bryophytes, and Pteridophytes, there is a con-
stant increase in the complexity of the plant body, until in
the Spermatophytes it becomes most highly organized, with
numerous structures set apart for special work, just as in the
highest animals limbs, eyes, cars, bones, muscles, nerves, etc.,

INTRODUCTION 3

are set apart for special work. The increasing complexity
is usually spoken of as /ifterentiation—that is, the setting
apart of structures for different kinds of work. Hence the
Bryophytes are said to be more highly differentiated than
the Thallophytes, and the Spermatophytes are regarded as
the most highly differentiated group of plants.

4. Nutrition and reproduction.—However variable plants
may be in complexity, they all do the sume general kind of
work. Increasing complexity simply means an attempt to
do this work more effectively. It is plant work that makes
plant structures significant, and hence in this book no at-
tempt will be made to separate them. All the work of
plants may be put under two heads, nutrition and repro-
duction, the former including all those processes by which
a plant maintains itself, the latter those processes by which
it produces new plants. In the lowest plants, these two
great kinds of work, or functions, as they are called, are
not set apart in different regions of the body, but usually
the first step toward differentiation is to set apart the re-
productive function from the nutritive, and to develop
special reproductive organs which are entirely distinct from
the general nutritive body.

5. The evolution of plants.—It is generally supposed that
the more complex plants have descended from the simpler
ones; that the Bryophytes have been derived from the Thallo-
phytes, and so on. All the groups, therefore, are supposed
to be related among themselves in some way, and it is one
of the great problems of botany to discover these relation-
ships. This theory of the relationship of plant groups is
known as the theory of descent, or more generally as evo-
lution. To understand any higher group one must study
the lower ones related to it, and therefore the attempt of
this book will be to trace the evolution of the plant king-
dom, by beginning with the simplest forms and noting the
gradual increase in complexity until the highest forms are
reached.

CHAPTER II

THALLOPHYTES: ALG

6. General characters—Thallophytes are the simplest of
plants, often so small as to escape general observation, but
sometimes with large bodies. They occur everywhere in
large numbers, and are of special interest as representing
the beginnings of the plant kingdom. In this group also
there are organized all of the principal activities of plants,
so that a study of Thallophytes furnishes a clew to the
structures and functions of the higher, more complex
groups.

The word “thallus” refers to the nutritive body, or
vegetative body, as it is often called. This body does not
differentiate special nutritive organs, such as the leaves and
roots of higher plants, but all of its regions are alike. Its
natural position also is not erect, but prone. While most
Thallophytes have thallus bodies, in some of them, as in
certain marine forms, the nutritive body differentiates into
regions which resemble leaves, stems, and roots ; also cer-
tain Bryophytes have thallus bodies. The thallus body,
therefore, is not always a distinctive mark of Thallophytes,
but must be supplemented by other characters to determine
the group.

%. Alge and Fungi—It is convenient to separate Thallo-
phytes into two great divisions, known as Alge and Fungi.
It should be known that this is a very general division and
not a technical one, for there are groups of Thallophytes
which can not be regarded as strictly either Algw or Fungi,
but for the present these groups may be included.

4

THALLOPHYTES: ALGH 5

The great distinction between these two divisions of
Thallophytes is that the Alge contain chlorophyll and the
Fungi do not. Chlorophyll is the characteristic green color-
ing matter found in plants, the word meaning “leaf green.”
It may be thought that to use this coloring material as the
basis of such an important division is somewhat superficial,
but it should be known that the presence of chlorophyll gives
a peculiar power—one which affects the whole structure
of the nutritive body and the habit of life. The presence
of chlorophyll means that the plant can make its own food,
can live independent of other plants and animals. Algae,
therefore, are the independent Thallophytes, so far as their
food is concerned, for they can manufacture it out of the
inorganic materials about them.

The Fungi, on the other hand, contain no chlorophyll,
can not manufacture food from inorganic material, and
hence must obtain it already manufactured by plants or
animals. In this sense they are dependent upon other or-
ganisms, and this dependence has led to great changes in
structure and habit of life.

It is supposed that Fungi have descended from Alge—
that is, that they were once Algae, which gradually acquired
the habit of obtaining food already manufactured, lost their
chlorophyll, and became absolutely dependent and more or
less modified in structure. Fungi may be regarded, there-
fore, as reduced relatives of the Algez, of equal rank so far
as birth and structure go, but of very different habits.

ALG

8. General characters—As already defined, Alge are
Thallophytes which contain chlorophyll, and are therefore
able to manufacture food from inorganic material. They
are known in general as “ seaweeds,” although there are
fresh-water forms as well as marine. They are exceedingly
variable in size, ranging from forms visible only by means

19

6 PLANT STRUCTURES

of the compound microscope to marine forms with enor-
mously bulky bodies. In general they are hydrophytes—that
is, plants adapted to life in water or in very moist places.
The special interest connected with the group is that it is
supposed to be the ancestral group of the plant kingdom—
the one from which the higher groups have been more or
less directly derived. In this regard they differ from the
Fungi, which are not supposed to be responsible for any
higher groups.

9. The subdivisions—Although all the Alge contain
chlorophyll, some of them do not appear green. In some
of them another coloring matter is associated with the chlo-
rophyll and may mask it entirely. Advantage is taken of
these color associations to separate Algw into subdivisions.
As these colors are accompanied by constant differences in
structure and work, the distinction on the basis of colors is
more real than it might appear. Upon this basis four sub-
divisions may be made. The constant termination phycec,
which appears in the names, is a Greek word meaning “ sea-
weed,” which is the common name for Alge; while the pre-
fix in each case is the Greek name for the color which char-
acterizes the group.

The four subdivisions are as follows: (1) Cyanophycea,
or “ Blue Algve,” but usually called ‘ Blue-green Alew,” as the
characteristic blue does not entirely mask the green, and
the general tint is bluish-green ; (2) Chlorophycecw, or “ Green
Algee,” in which there is no special coloring matter associ-
ated with the chlorophyll; (3) Phaaphyceew, or * Brown
Alge”; and (4) Rhodophycee, or “ Red Alge.”

It should be remarked that probably the Cyanophycee
do not belong with the other groups, but it is convenient to
present them in this connection.

10. The plant body.—By this phrase is meant the nutri-
tive or vegetative body. There is in plants a unit of struc-
ture known as the cell. The bodies of the simplest. plants
consist of but one cell, while the bodies of the most com-

THALLOPHYTES: ALG q

plex plants consist of very many cells. It is necessary to
know something of the ordinary living plant cell before the
bodies of Alge or any other plant bodies can be under-
stood.

Such a cell if free is approximately spherical in outline,
(Fig. 6), but if pressed upon by contiguous cells may become
yariously modified in form
(Fig. 1). Bounding it there
is a thin, elastic wall, com-
posed of a substance called
cellulose. The cell wall,
therefore, forms a delicate
sac, which contains the liv-
ing substance known as pro-
toplasm. This is the sub-
stance which manifests life,
and is the only substance
in the plant which is alive.
It is the protoplasm which j
has organized the cellulose Fig. 1. Cells from a moss leaf, showing
wall about itself, and which nucleus (B) in which there is a nucle-
does all the plant work. It eens a ci
is a fluid substance which
varies much in its consistence, sometimes being a thin vis-
cous fluid, like the white of an egg, sometimes much more
dense and compactly organized.

The protoplasm of the cell is organized into various
structures which are called organs of the cell, each organ
having one or more special functions. One of the most
conspicuous organs of the living cell is the single nucleus, a
comparatively compact and usually spherical protoplasmic
body, and generally centrally placed within the cell (Fig. 1).
All about the nucleus, and filling up the general cavity
within the cell wall, is an organized mass of much thinner
protoplasm, known as cytoplasm. The cytoplasm seems to
form the general background or matrix of the cell, and the

8 PLANT STRUCTURES

nucleus lies imbedded within it (Fig. 1). Every working
cell consists of at least cytoplasm and nucleus. Sometimes
the cellulose wall is absent, and the cell then consists sim-
ply of a nucleus with more or less cytoplasm organized
about it, and is said to be naked.

Another protoplasmic organ of the cell, very conspicuous
among the Alge and other groups, is the plastid. Plastids
are relatively compact bodies, commonly spherical, variable
in number, and lie imbedded in the cytoplasm. There are
various kinds of plastids, the most common being the one
which contains the chlorophyll and hence is stained green.
The chlorophyll-containing plastid is known as the chloro-
plastid, or chloroplast (Fig. 1). An ordinary alga-cell, there-
fore, consists of a cell wall, within which the protoplasm is
organized into cytoplasm, nucleus, and chloroplasts.

The bodies of the simplest Alge consist of one such
cell, and it may be regarded as the simplest form of plant
body. Starting with such forms, one direction of advance
in complexity is to organize several such cells into a loose
row, which resembles a chain (Fig. 4); in other forms the
cells in a row become more compacted and flattened, form-
ing a simple filament (Figs. 2, 5); in still other forms the
original filament puts out branches like itself, producing
a branching filament (Fig. 8). These filamentous bodies
are very characteristic of the Alge.

Starting again with the one-celled body, another line of
advance is for several cells to organize in two directions,
forming a plate of cells. Still another line of advance is for
the cells to organize in three directions, forming a mass of
cells.

The bodies of Algz, therefore, may be said to be one-
celled in the simplest forms, and in the most complex forms
they become filaments, plates, or masses of cells.

11. Reproduction.—In addition to the work of nutrition,
the plant body must organize for reproduction. Just as the
nutritive body begins in the lowest forms with a single cell

THALLOPHYTES: ALGA 9

and becomes more complex in the higher forms, so repro-
duction begins in very simple fashion and gradually be-
comes more complex. Two general types of reproduction
are employed by the Algx, and all other plants. They are
as follows:

(1) Vegetative multiplication.—This is the only type of
reproduction employed by the lowest Alga, but it persists
in all higher groups even when the other method has been
introduced. In this type no special reproductive bodies are
formed, but the ordinary vegetative body is used for the
purpose. For example, if the body consists of one cell, that
cell cuts itself into two, each half grows and rounds off as
a distinct cell, and two new bodies appear where there was
one before (Figs. 3,6). This process of cell division is very
complicated and important, involving a division of nucleus
and cytoplasm so that the new cells may be organized just
as was the old one. Wherever ordinary nutritive cells are
used directly to produce new plant bodies the process is
vegetative multiplication. This method of reproduction may
be indicated by a formula as follows: P—P—P—P-—P, in
which P stands for the plant, the formula indicating that
a succession of plants may arise directly from one another
without the interposition of any special structure.

(2) Spores.—Spores are cells which are specially organ-
ized to reproduce, and are not at all concerned in the nutri-
tive work of the plant. Spores are all alike in their power
of reproduction, but they are formed in two very distinct
ways. It must be remembered that these two types of
spores are alike in power but different in origin.

-lserual spores.—These cells are formed by cell divi-
sion. A cell of the plant body is selected for the purpose,
and usually its contents divide and form a variable number
of new cells within the old one (Fig. 2,8). These new cells
are asexual spores, and the cell which has formed them
within itself is known as the mother cell. This peculiar
kind of cell division, which does not involve the wall of the

10 PLANT STRUCTURES

old cell, is often called internal division, to distinguish it
from fission, which involves the wall of the old cell, and is
the ordinary method of cell division in nutritive cells.

If the mother cell which produces the spores is different
from the other cells of the plant body it is called the sporan-
gium, which means “spore vessel.” Often a cell is nutri-
tive for a time and afterward becomes a mother cell, in
which case it is said to function as a sporangium. The wall
of a sporangium usually opens, and the spores are dis-
charged, thus being free to produce new plants. Various
names have been given to asexual spores to indicate certain
peculiarities. As Alge are mostly surrounded by water,
the characteristic asexual spore in the group is one that
can swim by means of minute hair-like processes or cilia,
which have the power of lashing the water (Fig. 7, ().
These ciliated spores are known as zoospores, or “animal-
like spores,” referring to their power of locomotion ; some-
times they are called swimming spores, or swarm spores. It
must be remembered that all of these terms refer to the
same thing, a swimming asexual spore.

This method of reproduction may be indicated by a for-
mula as follows: P—o—P—o—P—o-—P, which indi-
cates that new plants are not produced directly from the
old ones, as in vegetative multiplication, but that between
the successive generations there is the asexual spore.

Serual spores.—These cells are formed by cell union,
two cells fusing together to form the spore. This process
of forming a spore by the fusion of two cells is called the
sexual process, and the two special cells (sexual cells) thus
used are known as gametes (Fig. 2, (, d, e). It must be
noticed that gametes are not spores, for they are not able
alone to produce a new plant; it is only after two of them
have fused and formed a new cell, the spore, that a plant
can be produced. The spore thus formed does not differ
in its power from the asexual spore, but it differs very
much in its method of origin.

THALLOPHYTES: ALG 11

The gametes are organized within a mother cell, and if
this cell is distinct from the other cells of the plant it is

called a gametangium, which means “ gamete vessel.”
This method of reproduction may be indicated by a for-
mula as follows: P=%>0—P=%>0—P=3>07-—P,

which indicates that two special cells (gametes) are pro-
duced by the plant, that these two fuse to form one (sexual
spore), which then produces a new plant.

It must not be supposed that if a plant uses one of these
three methods of reproduction (vegetative multiplication,
asexual spores, sexual spores) it does not employ the other
two. All three methods may be employed by the same
plant, so that new plants may arise from it in three differ-
ent ways.

CHAPTER III
THE EVOLUTION OF SEX

12. The general problem.—In the last chapter it was re-
marked that the simplest Algee reproduce only by vegetative
multiplication, the ordinary cell division (fission) of nutri-
tive cells multiplying cells and hence individuals. Among
other low Alge asexual spores are added to fission as a
method of reproduction, the spores being also formed by
cell division, generally internal division. In higher forms
gametes appear, and a new method of reproduction, the
sexual, is added to the other two.

Sexual reproduction is so important a process in all
plants except the lowest, that it is of interest to discover
how it may have originated, and how it developed into its
highest form. Among the Alge the origin and develop-
ment of the sexual process seems to be plainly suggested ;
and as all other plant groups have probably been derived
more or less directly from Algewe, what has been accom-
plished for the sexual process in this lowest group was
probably done for the whole plant kingdom.

13. The origin of gametes—One of the best Alge to
illustrate the possible origin of gametes is a common fresh-
water form known as Ulothrir (Fig. 2). The body consists
of a simple filament composed of a single row of short
cells (Fig. 2, 4). Each cell contains a nucleus, and a
single large chloroplast which has the form of a thick cyl-
inder investing the rest of the cell contents. Through the
microscope, if the focus is upon the center of the cell,
an optical section of the cylinder is obtained, the chloro-

12

THE EVOLUTION OF SEX 13

plast appearing as a thick green mass on each side of the
central nucleus. As no other color appears, it is evident
that Ulothriz is one of the Chlorophycee.

Fie. 2. Ulothrix, a Conferva form. A, base of filament, showing lowest holdfast
cell and five vegetative cells, each with its single conspicuous cylindrical chloro-
plast (seen in section) inclosing a nucleus; B, four cells containing numerous
small zoospores, the others emptied; C, fragment of a filament showing one cell
(a) containing four zoospores, another zoospore (%) displaying four cilia at its
pointed end and just having escaped from its cell, another cell (¢) from which
most of the small biciliate gametes have escaped, gametes pairing (d@), and the
resulting zygotes (e); D, beginning of new filament from zoospore; #, feeble
filaments formed by the small zoospores; F, zygote growing after rest; G,
zoospores produced by zygote.—CALDWELL, except F and G, which are after
DopEL-Port.

The cells are all alike, excepting that the lowest one of
the filament is mostly colorless, and is elongated and more
or less modified to act as a holdfast, anchoring the filament
to some firm support. With this exception the cells are all
nutritive ; but any one of them has the power of organizing
for reproduction. This indicates that at first nutritive and

14 PLANT STRUCTURES

reproductive cells are not distinctly differentiated, but that
the same cell may be nutritive at one time and reproductive
at another.

In suitable conditions certain cells of the filament will
be observed organizing within themselves new calls by
internal division (Fig. 2, C, a, 0). The method of forma-
tion at once suggests that the new cells are asexual spores,
and the mother cell which produces them is acting as a
sporangium. The spores escape into the water through an
opening formed in the wall of the mother cell, and each is
observed to have four cilia at the pointed end, by means of
which it swims, and hence it is a zoospore or swarm spore.
After swimming about for a time, the zoospores “settle
down,” lose their cilia, and begin to develop a new filament
like that from which they came (Fig. 2, D).

Other cells of the same filament also act as mother cells,
but the cells which they produce are more numerous, hence
smaller in size than the zoospores, and they have but two
cilia (Fig. 2, C, ¢). They also escape into the water and
swim about, except in size and in number of cilia resem-
bling the zoospores. In general they seem to be unable to
act as the zoospores in the formation of new filaments, but
occasionally one of them forms a filament much smaller
than the ordinary one (Fig. 2, #’'). This indicates that
they may be zoospores reduced in size, and unable to act as
the larger ones. The important fact, however, is that
these smaller swimming cells come together in pairs, each
pair fusing into one cell (Fig. 2, (, d,e). The cells thus
formed have the power of producing new filaments more or
less directly.

It is evident that this is a sexual act, that the cell pro-
duced by fusion is a sexual spore, that the two cells which
fuse are gametes, and that the mother cell which produces
them acts as a gametangium. Cases of this kind suggest
that the gametes or sex cells have been derived from zoo-
spores, and that asexual spores have given rise to sex cells.

THE EVOLUTION OF SEX 15

The appearance of sex cells (gametes) is but one step in the
evolution of sex. It represents the attainment of sexuality,
but the process becomes much more highly developed.

1t. Isogamy.— When gametes first appear, in some such
way as has been described, the two which fuse seem to be
exactly alike. They resemble each other in size and activ-
ity, and in every structure which can be distinguished.
This fact is indicated by the word isogamy, which means
“similar gametes,” and those plants whose pairing gametes
are similar, as Ulothriv, are said to be isogamous.

The act of fusing of similar gametes is usually called
conjugation, which means a “yoking together” of similar
bodies. Of course it is a sexual process, but the name is
convenient as indicating not merely the process, but also an
important character of the gametes. The sexual spore
which results from this act of conjugation is called the
zygote or zygospore, meaning “ yoked spore.”

In isogamy it is evident that while sexuality has been
attained there is no distinction between sexes, as obtains in
the higher plants. It may be called a wufserual condition,
as opposed to a dixerwal one. The next problem in the
evolution of sex, therefore, is to discover how a bisexual
condition has been derived from a unisexual or isogamous
one.

15. Heterogamy.—Beginning with isogamous forms, a
series of plants can be selected illustrating how the pairing
gametes gradually became unlike. One of them becomes
less active and larger, until finally it is entirely passive and
very many times larger than its mate (Fig. 7). The other
retains its small size and increases in activity. The pairing
gametes thus become very much differentiated, the larger
passive one being the femule gamete, the smaller active one
the male gamete. This condition is indicated by the word
heterogamy, which means “ dissimilar gametes,” and those
plants whose pairing gametes are dissimilar arc said to be
heterogamous.

16 PLANT STRUCTURES

In order to distinguish them the large and passive female
gamete is called the oosphere, which means “egg sphere,”
or it is called the egg ; the small but active male gamete is
variously called the spermatozoid, the antherozoid, or simply
the sperm. In this book egg and sperm will be used, the
names of similar structures in animals.

In isogamous plants the mother cells (gametangia)
which produce the gametes are alike; but in heterogamous
plants the gametes are so unlike that the gametangia which
produce them become unlike. Accordingly they have re-
ceived distinctive names, the gametangium which produces
the sperms being called the entheridium, that producing the
egg being called the oogoniwm (Fig. 10).

The act of fusing of sperm and egg is called fertiliza-
tion, which is the common form of the sexual process. The
sexual spore which results from fertilization is known as the
oospore or “ egg-spore,” sometimes called the fertilized egg.

It is evident that heterogamous plants are bisexual, and
bisexuality is not only attained among Alge, but it prevails
among all higher plants. Among the lowest forms there is
only vegetative multiplication ; higher forms added sexu-
ality ; then still higher forms became bisexual.

16. Summary.—Isogamous forms produce gametangia,
which produce similar gametes, which by conjugation form
zygotes. Heterogamous forms produce antheridia and
oogonia, which produce sperms and eggs, which by fertiliza-
tion form oospores.

CHAPTER IV
THE GREAT GROUPS OF ALG

17. General characters—The Alge are distinguished
among Thallophytes by the presence of chlorophyll. It
was stated in a previous chapter that in three of the four
great groups another coloring matter is associated with the
chlorophyll, and that this fact is made the basis of a division
into Blue-green Algew (Cyanophycee), Green Alga (Chloro-
phycez), Brown Alge (Pheophycez), and Red Alge (Rhodo-
phycee). In our limited space it will be impossible to do
more than mention a few representatives of each group,
but they will serve to illustrate the prominent facts.

1. CyaNnoPHYcE®£ (Blue-green Alg@)

18. Gleocapsa.—These forms may be found forming
blue-green or olive-green patches on damp tree-trunks, rock,
walls, etc. By means of the microscope these patches are
seen to be composed of multitudes of spherical cells, each
representing a complete Gleocapsa body. One of the pecul-
larities of the body is that the cell wall becomes mucilagi-
nous, swells, and forms a jelly-like matrix about the work-
ing cell. Each cell divides in the ordinary way, two new
Gleocapsa individuals being formed, this method of vegeta-
tive multiplication being the only form of reproduction
(Fig. 3).

When new cells are formed in this way the swollen
mucilaginous walls are apt to hold them together, so that
presently a number of cells or individuals are found lying

17

18

PLANT STRUCTURES

together imbedded in the jelly-like matrix formed by the

wall material (Fig. 3).

Fi. 8. Gleocapsa, a blue-
green alga, showing
single cells, and small
groups which have been
formed by division and
are held together by the
enveloping mucilage.—
CALDWELL.

These imbedded groups of individ-
uals are spoken of as colonies, and as
colonies become large they break up
into new colonies, the individual cells
composing them continuing to divide
and form new individuals. This rep-
resents a very simple life history, in
fact a simpler one could hardly be
imagined.

19. Nostoc.—These forms occur in
jelly-like masses in damp places. If
the jelly be examined it will be found
to contain imbedded in it numerous
cells like those of Glevcapsa, but they
are strung together to form chains of
varying lengths (Fig. 4). The jelly in
which these chains are imbedded is the
same as that found in Glwocapsa, being

formed by the cell walls becoming mucilaginous and swollen.
One notable fact is that all the cells in the chain are not

alike, for at irregu-
lur intervals there oc-
cur larger colorless
cells, an illustration
of the differentiation
of cells. These larger
cells are known as hef-
crocysts (Fig. 4, 4),
which simply means
“other cells.” It is
observed that when
the chain breaks up
into fragments each
fragment iscomposed
of the cells between

Fi.
chain-like filameuts, and the heterocysts (.1)
which determine the breaking up of the chain,
- CALDWELL,

4. Nosfoc, a blue-green alga, showing the

THE GREAT GROUPS OF ALG.E 19

two heterocysts. The fragments wriggle out of the jelly
matrix and start new colonies of chains, each cell dividing
to increase the length of the chain. This cell division,
to form new cells, is the characteristic method of repro-
duction.

At the approach of unfavorable conditions certain cells
of the chain become thick-walled and well-protected. These
cells which endure the cold or other hardships, and upon
the return of favorable conditions produce new chains of
cells, are often called spores, but they are better called
“resting cells.”

20. Oscillaria—These forms are found as bluish-green
slippery masses on wet rocks, or on damp soil, or freely
floating. Theyare simple filaments, composed of very short
flattened cells (Fig. 5), and the name
Oscillaria refers to the fact that they
exhibit a peculiar oscillating move-
ment. These motile filaments are is-
olated, not being held together in a
jelly-like matrix as are the chains of
Vostoc, but the wall develops a cer-
tain amount of mucilage, which gives
the slippery feeling and sometimes
forms a thin mucilaginous sheath
about the row of cells.

The cells of a filament are all alike, =
except that the terminal cell has its pene uivianle ible.
free surface rounded. If a filament ae rete ey,
breaks, and a new cell surface ex- and a single filament

a more enlarged (B).—
posed, it at once becomes rounded. Oupawein
If a single cell of the filament is
freed from all the rest, both flattened ends become rounded,
and the cell becomes spherical or nearly so. These facts
indicate at least two important things: (1) that the cell
wall is elastic, so that it can be made to change its form,
and (2) that it is pressed upon from within, so that if free

90 PLANT STRUCTURES

it will bulge outward. In all active living cells there is
this pressure upon the wall from within.

Each cell of the Oscillaria filament has the power of
dividing, thus forming new cells and elongating the fila-
ment. A filament may break up into fragments of varying
lengths, and each fragment by cell division organizes a new
filament. Here again reproduction is by means of vegeta-
tive multiplication.

21. Conclusions—Taking Gleocapsa, Nostoc, and Oscil-
laria as representatives of the group Cyanophycee, or
“ oreen slimes,” we may come to some conclusions concern-
ing the group in general. The plant body is very simple,
consisting of single cells, or chains and filaments of cells.
Although in Nostoc and Osctllaria the cells are organized
into chains and filaments, each cell seems to be able to live
and act independently, and the chain and filament seem to
be little more than colonies of individual cells. In this
sense, all of these plants may be regarded as one-celled.

Differentiation is exhibited in the appearance of hetero-
cysts in .Vostoc, peculiar cells which seem to be connected
in some way with the breaking up of filamentous colonies,
although the Oscillvria filament breaks up without them.

The power of motion is also well exhibited by the group,
the free filaments of Osr//lvr‘a moving almost continually,
and the imbedded chains of \Vostoc at times moving to es-
cape from the restraining mucilage.

The whole group also shows a strong tendency in the
cell-wall material to become converted into mucilage and
much swollen, a tendency which reaches an extreme expres-
sion in such forms as Nos/oc and Gleocapsa.

Another distinguishing mark is that reproduction is
exclusively by means of vegetative multiplication, through
ordinary cell division or fission, which takes place very
freely. Individual cells are organized with heavy resistant
walls to enable them to endure the winter or other unfavor-
able conditions, and to start a new series of individuals

THE GREAT GROUPS OF ALG a1

upon the return of favorable conditions. These may be
regarded as resting cells. So notable is the fact of repro-
duction by fission that Cyanophycee are often separated
from the other groups of Alge and spoken of as “ Fission
Alge,” which put in technical form becomes Schizophycee.
In this particular, and in several others mentioned above,
they resemble the “ Fission Fungi” (Schizomycetes), com-
monly called “bacteria,” so closely that they are often
associated with them in a common group called “ Fis-
sion plants” (Schizophytes), distinct from the ordinary
Alge and Fungi.

2. CHLOROPHYCE® ((reen .tlg@).

22. Pleurococcus.—This may be taken as a type of one-
celled Green Alge. It is most commonly found in masses
covering damp tree-trunks, etc., and looking like a green
stain. These fine-
ly granular green
masses are found
to be made up
of multitudes of
spherical cells re-
sembling those of
Gleocapsa, except
that there is no
blue with the chlo-
rophyll, and the
cells are not im-

bedded in such Fie. 6. Pleurococcus, a one-celled green alga : A, show-

jelly-like masses. ing the adult form with its nucleus; B, (, D, E,

various stages of division (fission) in producing new
The cells may be cells; #, colonies of cells which have remained in
solitary, or may contact.—CALDWELL.

cling together in

colonies of various sizes (Fig. 6). Like Gleorapsi, a cell

divides and forms two new cells, the only reproduction
20

99 PLANT STRUCTURES

being of this simple kind. It is evident, therefore, that the
group Chlorophycee begins with forms just as simple as
are to be found among the Cyanophycee.

Pleurococcus is used to represent the group of Protococ-
cus forms, one-celled forms which constitute one of the
subdivisions of the Green Alge. It should be said that
Pleurococeus is possibly not a Protococcus form, but may
be a reduced member of some higher group; but it is so
common, and represents so well a typical one-celled green
alga, that it is used in this connection. It should be
known, also, that while the simplest Protococcus forms re-
produce only by fission, others add to this the other meth-
ods of reproduction.

23. Ulothrix—This form was described in § 13. It
is very common in fresh waters, being recognized easily by
its simple filaments composed of short squarish cells, each
cell containing a single conspicuous cylindrical chloroplast
(Fig. 2). This plant uses cell division to multiply the cells
of a filament, and to develop new filaments from fragments
of old ones; but it also produces asexual spores in the form
of zoospores, and gametes which conjugate and form zygotes.
Both zoospores and zygotes have the power of germination—
that is, the power to begin the development of a new plant.
In the germination of the zygote a new filament is not pro-
duced directly, but there are formed within it zoospores,
each of which produces a new filament (Fig. 2, 7, @). All
three kinds of reproduction are represented, therefore, but
the sexual method is the low type called isogamy, the pair-
ing gametes being alike.

Ulothriv is taken as a representative of the Conferva
forms, the most characteristic group of Chlorophycee.
All the Conferva forms, however, are not isogamous, as will
be illustrated by the next example.

24. Edogonium.—This is a very common green alga,
found in fresh waters (Fig. 7). The filaments are long and
simple, the lowest cell acting as a holdfast, as in Ulolhrix

Fie. 7. Edogonium nodosum, a Conferva form: A, portion of a filament showing a
vegetative cell with its nuclens (@), an oogonium (@) filled by an egg packed with
food material, a second oogonium (c) containing a fertilized egg or oospore as
shown by the heavy wall, and two antheridia (5), each containing two sperms; B,
another filament showing antheridia (a) from which two sperms (0) have escaped,
a vegetative ceil with its nucleus, and an oogonium which a sperm (c) has entered
and is coming in contact with the egg whose nucleus (@) may be seen; C, a zoo-
spore which has been formed in a vegetative cell, showing the crown of cilia and
the clear apex, as in the sperms; J. a zoospore producing a new filament, putting
out a holdfast at base and elongating; #, a further stage of development; F, the
four zoospores formed by the oospore when it germinates.—CALDWELL, except
Cand F, which are after PRINGSHEIM.

4 PLANT STRUCTURES

(§ 13). The other cells are longer than in Ulothriz, each
cell containing a single nucleus and apparently several
chloroplasts, but really there is but one large complex
chloroplast.

The cells of the filament have the power of division,
thus increasing the length of the filament. Any cell also
may act as a sporangium, the contents of a mother cell
organizing a single large asexual spore, which is a zoospore.
The zoospore escapes from the mother cell into the water,
and at its more pointed clear end there is a little crown of
cilia, by means of which it swims about rapidly (Fig. 7, C).
After moving about for a time the zoospore comes to rest,
attaches itself by its clear end to some support, elongates,
begins to divide, and develops a new filament (Fig. 7, D, /).

Other cells of the filament become very different from
the ordinary cells, swelling out into globular form (Fig. 7,
A, B), and each such cell organizes within itself a single
large egg (oosphere). As the egg is a female gamete, the
large globular cell which produces it, and which is differen-
tiated from the other cells of the body, is the oogonium.
A perforation in the oogonium wall is formed for the
entrance of sperms.

Other cells in the same filament, or in some other fila-
ment, are observed to differ from the ordinary cells in
being much shorter, as though an ordinary cell had been
divided several times without subsequent elongation (Fig.
7, .1, f, B, a). In each of these short cells one or two
sperms are organized, and therefore each short cell is an
antheridium. When the sperms are set free they are seen
to resemble very small zoospores, having the same little
crown of cilia at one end.

The sperms swim actively about in the vicinity of the
oogonia, and sooner or later one enters the oogonium
through the perforation provided in the wall, and fuses
with the egg (Fig. 7, Bc). As a result of this act of fer-
tilization an oospore is formed, which organizes a firm wall

THE GREAT GROUPS OF ALGA 95

about itself. This firm wall indicates that the oospore is
not to germinate immediately, but is to pass into a resting
condition. Spores which form heavy walls and pass into
the resting con-
dition are often
spoken of as “ rest-
ing spores,” and it
is very common
for the zygotes
and oospores to
be resting spores.
These resting
spores enable the
plant to endure
through unfavor-
able conditions,
such as failure of
food supply, cold,
drought, etc.
When favorable
conditions return,
the protected rest-
ing spore is ready

for germination. Fie. &. Cladophora, a branching green alga, a very
When the small part of the plant being shown. The branches
arise at the upper ends of cells, and the cells are

oospore of Edogo- coenocytic.—CALDWELL.

nium germinates

it does not develop directly into a new filament, but the
contents become organized into four zoospores (Fig. 7, /),
which escape, and each zoospore develops a filament. In
this way each oospore may give rise to four filaments.

It is evident that Hdogonium is a heterogamous plant,
and is another one of the Conferva forms. Conferva bodies
are not always simple filaments, as are those of UVlothrix
and Edogonium, but they are sometimes extensively branch-
ing filaments, as in Cladophora, a green alga very common

26 PLANT STRUCTURES

in rivers and lakes (Fig. 8). The cells are long and densely
crowded with chloroplasts ; and in certain cells at the tips
of branches large numbers of zoospores are formed, which
have two cilia at the pointed end, and hence ure said to be
biciliute.

25. Vaucheria—This is one of the most common of the
Green Alge, found in felt-like masses of coarse filaments in
shallow water and on muddy banks, and often called “ green

Fie. 9. Vaueheria geminata, a Siphon form, showing a portion of the ccenocytic
body (4) which has sent out a branch at the tip of which a sporangium (B)
formed, within which a large zoospore was organized. and from which (D) it is
discharged later as a large multiciliate body ((), which then beyins the develop-
ment of a new ccenocytic body (# ).—CALDWELL.

felt.” The filament is very long, and usually branches ex-
tensively, but its great peculiarity is that there is no parti-
tion wall in the whole body, which forms one long continuous
cavity (Figs. 9,11). This is sometimes spoken of as a one-
celled body, but it is a mistake. Imbedded in the exten-
sive cytoplasm mass, which fills the whole cavity, there are
not only very numerous chloroplasts, but also numerous
nuclei. As has been said, a single nucleus with some cyto-

THE GREAT GROUPS OF ALG oF

plasm organized about it is a cell, whether it has a wall or
not. Therefore the body of Vuucheria is made up of as
many cells as there are nuclei, cells whose protoplasmic
structures have not been kept separate by cell walls. Such
a body, made up of numerous cells, but with no partitions,
is called a cenocyte, or it is said to be cenarylic. Vancheria
represents a great group of Chlorophycew whose members
have coenocytic bodies, and on this account they are called
the Siphon forms.

Vaucherta produces very large zoospores. The tip of a
branch becomes separated from the rest of the body by a
partition and thus acts as a sporangium (Fig. 9, 2). In
this improvised sporangium the whole of the contents or-
ganize a single large zoospore, which is ciliated all over,
escapes by squeezing through a perforation in the wall

(Fig. 9, C), swims about for a time, and finally
develops another Vawrheria body (Figs. 9, #, 10).
It should be said that this large body, called
a zoospore and acting like one, is really a
mass of small biciliate zoospores, just as the

Fie. 10. A young Vareheria germinating from a
spore (sp), and showing the holdfast (2#).—
After Sacus.

apparently one-celled vegetative body is really composed of
many cells. In this large compound zoospore there are
many nuclei, and in connection with each nucleus two cilia
are developed. Hach nucleus with its cytoplasm and two
cilia represents a small biciliate zoospore, such as those of
Cladophora, § 24.

Antheridia and oogonia are also developed. In a com-
mon form these two sex organs appear as short special
branches developed on the side of the large ccenocytic body,

28 PLANT STRUCTURES

and cut off from the general cavity by partition walls (Fig.
11). The oogonium becomes a globular cell, which usually

Fig. 11. Vaucheria sessilis, a Siphon form, show-
ing a portion of the ceenocytic body, an an-
theridial branch (4) with an empty anthe-
ridium (a) at its tip, and an oogoninm (B)
containing an oospore (¢) and showing the
opening (/) through which the sperms passed
to reach the egg.—CaLDWELL.

develops a perforated break for
the entrance of the sperms, and
organizes within itself a single
large egg (Fig. 11, B). The an-
theridium is a much smaller cell,
within which numerous very small
sperms are formed (Fig. 11, .1, a). Fie. 12. Botrydium, one of the
The sperms are discharged, swarm penne aes

y containing

about the oogonium, and finally one continuous cavity, with
a bulbous, chlorophyll-con-

one passes through the break and uisiiniee ‘peeitOn, “amet Soak
fuses with the egg, the result be- like branches which pene-
7 trate the mud in which
ing an oospore. The oospore or- noire Sirantnernad en
ganizes a thick wall and becomes WELL.

a resting spore.

It is evident that Vaucheria is heterogamous, but all the
other Siphon forms are isogamous, of which Botrydiwm may
be taken as an illustration (Fig. 12).

26. Spirogyra.—This is one of the commonest of the
“pond scums,” occurring in slippery and often frothy
masses of delicate filaments floating in still water or about

THE GREAT GROUPS OF ALGE& 99

springs. The filaments are simple, and are not anchored by
a special basal cell, as in Ulothrix and Edogonium. The

Fic. 18. Spirogyra, a Conjugate form, showing one complete cell and portions of
two others. The band-like chloroplasts extend in a spiral from one end of the
cell to the other, in them are imbedded nodule-like bodies ( pyrenoids), and near
the center of the cell the nucleus is swung by radiating strands of cytoplasm.—
CALDWELL.

cells contain remarkable chloroplasts, which are bands pass-
ing spirally about within the cell wall. These bands may

Fie. 14. Spirogyra, showing conjugation: 4, conjugating tubes approaching each
other; B, tubes in contact but end walls not absorbed: C, tube complete and con-
tents of one cell passing through; D, a completed zygospore.—CaLDWELL.

30 PLANT STRUCTURES

be solitary or several in a cell, and form very striking and
conspicuous objects (Figs. 13, 14).

Spirogyra and its associates are further peculiar in pro-
ducing no asexual spores, and also in the method of sexual
reproduction. Two adjacent filaments put out tubular
processes toward one another. A cell of one filament sends
out a process which seeks to meet a corresponding process
from a cell of the other filament. When the tips of two
such processes come together, the end walls disappear,

Fig. 15. Spirogyra, showing some common exceptions. At .1 two cells have been
connected by a tube, but without fusion a zygote has been organized in each cell;
also, the upper cell to the left has attempted to conjugate with the cell to the
right. At B there are cells from three filaments, the cells of the central one hay-
ing conjugated with both of the others.—CaLDWELL,

and a continuous tube extending between the two cells is
organized (Figs. 14,15). When many of the cells of two
parallel filaments become thus united, the appearance is
that of a ladder, with the filaments as the side pieces, and
the connecting tubes as the rounds.

While the connecting tube is being developed the con-
tents of the two cells are organizing, and after the comple-
tion of the tube the contents of one cell pass through and
enter the other cell, fuse with its contents, and a sexual

THE GREAT GROUPS OF ALGE 31

spore is organized. As the gametes
look alike, the process is conjuga-
tion, and the sex spore is a zygote,
which, with its heavy wall, is rec-
ognized to be a resting spore. At
the beginning of each growing
season, the well-protected zygotes
which have endured the winter
germinate directly into new Spi-
rogyra filaments.

On account of this peculiar
style of sexual reproduction, in
which gametes are not discharged,
but reach each other through spe-
cial tubes, Spiroyyra and its allies
are called Conjugate forms—that
is, forms whose bodies are ‘ yoked
together” during the fusion of the
gametes.

In some of the Conjugate forms
the zygote is formed in the connect-
ing tube (Fig. 16, .1), and some-
times zygotes are formed without
conjugation (Fig. 16, B). Among
the Conjugate forms the Desmids
are of great interest and beauty,
being one-celled, the cells being
organized into two distinct halves
(Fig. 17).

27. Conclusions. — The Green
Alge, as indicated by the illustra-
tions given above, include simple
one-celled forms which reproduce
by fission, but they are chiefly fila-

Fic.16 Two Conjugate forms :
al (Vongeotia), showing for-
mation of zygote in conjuga-
ting tnbe; B, ( (Gonatone-
ma), showing formation of
zygote without conjugation.
—After WITTROCK.

mentous forms, simple or branching. These filamentous
bodies either have the cclls separated from one another

39 PLANT STRUCTURES

by walls, or they are ccenocytic, as in the Siphon forms.
The characteristic asexual spores are zoospores, but these
may be wanting, as in the Conjugate forms. In addition
to asexual reproduction, both isogamy and heterogamy are
developed, and both zygotes and oospores are resting spores.

Fia. 17. A group of Desmids, one-celled Conjugate forms, showing various pat-
terns, and the cells organized into distinct halves.—After KERNER.

The Green Algex are of special interest in connection
with the evolution of higher plants, which are supposed to
have been derived from them.

3. PHmopnycn.s (Brown -{lge)

28. General characters—The Blue-green Algw and the
Green Alge are characteristic of fresh water, but the Brown
Alge, or “kelps,” are almost all marine, being very charac-

THE GREAT GROUPS OF ALG 383

teristic coast forms. All of them are anchored by holdfasts,
which are sometimes highly developed root-like structures;
and the yellow, brown, or olive-green floating

bodies are buoyed in the water usually by the
aid of floats or air-bladders, which are often
very conspicuous. The kelps are most highly
developed in the colder waters, and form much
of the “wrack,” “tangle,” etc., of the coasts.

The group is well adapted to
live exposed to waves and cur-
rents with its strong holdfasts,
air-bladders, and tough leathery
bodies. It is what is known as
a specialized group—that is, one
which has become highly organ-
ized for certain special condi-

tions. It is not our
purpose to consider
such a specialized
group in any detail,
as it does not usual-
ly help to explain the
structures of higher
groups.

29. The plant
body.—There is very
great diversity in the
structure of the
plant body. Some
of them, as Fctocar-
pus (Fig. 18), are fil-
amentous forms, like
the Confervas among
the Green Alge, but

Fig. 18. A brown alga (£etocarpus), showing a

body consisting of a simple filament which puts
out branches (A), some sporangia (B) contain-
ing zoospores, and gametangia ((') containing
gametes.—CALDWELL.

others are very much more complex. The thallus of Lam-
inarta is like a huge floating leaf, frequently nine to ten

Fic. 18a. A group of brown seaweeds (Laminarias). Note the various habits of
the plant body with its leaf-like thallus and root-like holdfasts. —Aftcr KERNER,

THE GREAT GROUPS OF ALGE 35

feet long, whose stalk develops root-like holdfasts (Fig. 18a).
The largest body is developed by an Antarctic Laminaria
form, which rises to the surface from a sloping bottom with
a floating thallus six hundred to nine hundred feet long.
Other forms rise from the sea bottom like trees, with
thick trunks, numerous branches, and leaf-like appendages.

The common Fucus,
or “rock weed,” is rib-
bon-form and constantly
branches by forking at
the tip (Fig. 19). This
method of branching is
called dichotomous, as dis-
tinct from that in which
branches are put out
from the sides of the axis
(monopodial). The swol-
len air-bladders distrib-
uted throughout the body
are very conspicuous.

The most differenti-
ated thallus is that of
Sargassum (Fig. 20), or
“oulf weed,” in which
there are slender branch-
ing stem-like axes bearing
lateral members of various
kinds, some of them like re. 19. Fragment of a common brown

rdinar foliage leaves: alga (Fucus), showing the body with
. J 8 Ate dichotomous branching and bladder-like
others are floats or air- air-bladders.—After LUERSSEN.

bladders, which sometimes

resemble clusters of berries; and other branches bear the
sex organs. All of these structures are but different regions
of a branching thallus. Sargassum forms are often torn
from their anchorage by the waves and carried away from
the coast by currents, collecting in the great sea eddies

36 PLANT STRUCTURES

produced by oceanic currents and forming the so-called
“Sargasso seas,” as that of the North Atlantic.

Fie. 20. A portion of a brown alga (Sargassum), showing the thallus differentiated
into stem-like and leaf-like portions, and also the bladder-like floats.—After BEN-
NETT and Murray. ,

30. Reproduction The two main groups of Brown Alge
differ from each other in their reproduction. One, repre-
sented by the Laminarias and a majority of the forms, pro-
duces zoospores and is isogamous (Fig. 18). The zoospores
and gametes are peculiar in having the two cilia attached
at one side rather than at an end; and they resemble each
other very closely, except that the gametes fuse in pairs and
form zygotes.

Fie. 21. Sexual reproduction of Fwevs, showing the eight eggs (six in sight) dis-
charged from the oogonium and surrounded by a membrane (A), eggs liberated
from the membrane (£), antheridium containing sperms ((’), the discharged lat-
erally biciliate sperms (@), and eggs surrounded by swarming sperms (7, H).—
After SINGER.

21

88 PLANT STRUCTURES

The other group, represented by Fucus (Fig. 21), pro-
duces no asexual spores, but is heterogamous. A single
cogonium usually forms eight eggs (Fig. 21, 1), which are
discharged and float freely in the water (Fig. 21, #). The
antheridia (Fig. 21, C’) produce numerous minute laterally
biciliate sperms, which are discharged (Fig. 21, @), swim in
great numbers about the large eggs (Fig. 21, &, H), and
finally one fuses with an egg, and an oospore is formed.
As the sperms swarm very actively about the egg and
impinge against it they often set it rotating. Both an-
theridia and oogonia are formed in cavities of the thallus.

4. Ruopopnyce.e (Red .1lg@)

31. General characters—On account of their red colora-
tion these forms are often called Mloridew. They are mostly
marine forms, and are
anchored by holdfasts
of various kinds. They
belong to the deepest
waters in which Alge
grow, and it is probable
that the red coloring
matter which character-
izes them is associated
with the depth at which
they live. The Red
Alge are also a high-
ly specialized line, and
will be mentioned very
briefly.

32. The plant body.

Bie, 22. A ted alga (Gigartina), showing —The Red Alge, in
branching habit, and ‘fruit bodies.”— ;
After SCHENCK. general, are more deli-

cate than the Brown
Alge, or kelps, their graceful forms, delicate texture, and
brightly tinted bodies (shades of red, violet, dark purple,

A-red alga (Cadlophyllis), with a greatly branched body composed of thin plates of cells.

a3

Fra,

Iie, 24. A red alga (Dasyu), showing a finely divided thallus body.
CALDWELL.

Fie. 25. A red alga (Raddonia), showing holdfasts and branching thallus body.
CALDWELL.

Vie. 26. A red alga (Ptilota). whose branching body resembles moss.—
CALDWELL.

THE GREAT GROUPS OF ALGH 43

and reddish-brown) making them very attractive. They
show the greatest variety of forms, branching filaments,
ribbons, and filmy plates prevailing, sometimes branching
very profusely and delicately, and resembling mosses of
fine texture (Figs. 22, 23, 24, 25, 26). The differentiation
of the thallus into root and stem and leaf-like structures
is also common, as in the Brown Alge.

33. Reproduction.— Red Alge are very peculiar in both
their asexual and sexual reproduction. A sporangium pro-
duces just four asexual spores, but they have no cilia and
no power of motion. They
can not be called zoospores,
therefore, and as each spo-

pia
Fie. 27. A red alga(Cullithamnion), show- Fic. 28. A red alga (Nemalion); A,
ing sporangium (4), and the tetraspores sexual branches, showing antheri-
discharged (B),.—After THURET. dia (a), oogonium (0) with its trich-
ogyne (ft), to which are attached two
spermatia (s): B, beginning of a

rangium always produces just cystocarp (0), the trichogyne (¢) still
four, they have been called showing; C, an almost mature cys-
RNG. 1 tocarp (0), with the disorganizing
tetraspores (Fig. 27). frichiaganie tne sid arene:
Red Alge are also heterog-
amous, but the sexual process has been so much and so
variously modified that it is very poorly understood. The
antheridia (Fig. 28, 4,@) develop sperms which, like the
tetraspores, have no cilia and no power of motion. To dis-

44 PLANT STRUCTURES

tinguish them from the ciliated sperms, or spermatozoids,
which have the power of locomotion, these motionless male
gametes of the Red Alge are usually called spermatia
(singular, spermatium) (Fig. 28, A, s).

Fie. 29. A branch of Polysiphonia,
one of the red alge, showing the
rows of cells composing the body
(A), small branches or hairs (B),
and a cystocarp (C’) with escaping
spores (2) which have no cilia (car-
pospores).—CALDWELL.

The oogonium is very pe-
culiar, being differentiated
into two regions, a bulbous
base and a hair-like process
(trichogyne), the whole struc-
ture resembling a flask with a
long, narrow neck, excepting
that it is closed (Fig. 28, 4,
o, t). Within the bulbous part
the egg, or its equivalent, is
organized; a spermatium at-
taches itself to the trichogyne
(Fig. 28, .1, s); at the point of
contact the two walls become
perforated, and the contents
of the spermatium thus enter
the trichogyne, and so reach
the bulbous base of the oogo-
nium. The above account rep-
resents the very simplest con-
ditions of the process of fer-
tilization in this group, and
gives no idea of the great and
puzzling complexity exhibited
by the majority of forms.

After fertilization the trich-
ogyne wilts, and the bulbous
base in one way or another
develops a conspicuous struc-

ture called the rystocarp (Figs. 28, 29), which is a case con-
taining asexual spores; in other words, a spore case, or kind
of sporangium. In the life history of a red alga, there-

THE GREAT GROUPS OF ALG.E 45

fore, two sorts of asexual spores are produced: (1) the
tetraspores, developed in ordinary sporangia; and (2) the
caurpospores, developed in the cystocarp, which has been
produced as the result of fertilization.

OTHER CHLOROPHYLL-CONTAINING THALLOPHYTES

34. Diatoms—These are peculiar one-celled forms, which
occur in very great abundance in fresh and salt waters.

Fie. 30. A group of Diatoms : cand d, top and side views of the same form; e, colony
of stalked forms attached to an alga; f and g, top and side views of the form shown
ate; h, acolony; i, a colony, the top and side view shown at x.—After KERNER.

They are either free-swimming or attached by gelatinous
stalks; solitary, or connected in bands or chains, or im-
bedded in gelatinous tubes or masses. In form they are
rod-shaped, boat-shaped, elliptical, wedge-shaped, straight
or curved (Fig. 30).

46 PLANT STRUCTURES

The chief peculiarity is that the wall is composed of two
valves, one of which fits into the other like the two parts of
a pill box. This wall is so impregnated with silica that it
is practically indestructible, and siliceous skeletons of dia-
toms are preserved abundantly in certain rock deposits.
They multiply by cell division in a peculiar way, and some

of them have been observed to con-

ts jugate.

(Ys They occur in such numbers in the
hth Uy} | ocean that they form a large part of
a Wh the free-swimming forms on the sur-

a face of the sea, and doubtless showers

of the siliceous skeletons are constant-
ly falling on the sea bottom. There
are certain deposits known as “si-
liceous earths,” which are simply
masses of fossil diatoms.

Diatoms have been variously placed
in schemes of classification. Some
have put them among the Brown
Algew because they contain a brown
coloring matter; others have placed
them in the Conjugate forms among
the Green Alge on account of the
occasional conjugation that has been
observed. They are so different from
other forms, however, that’ it seems
best to keep them separate from all
other Algz.

35. Characeee.—These are common-
ly called “stoneworts,” and are often
Fig. 31. A common Chara, included as a group of Green Alga,

showing tip of main axis. ‘
—After Srraspurarr, a8 they seem to be Thallophytes, and
have no other coloring matter than
chlorophyll. However, they are so peculiar that they are
better kept by themselves among the Alge. They are such

THE GREAT GROUPS OF ALG 44

specialized forms, and are so much more highly organized
than all other Alga, that they will be passed over here with
a bare mention. They grow in fresh or brackish waters,
fixed to the bottom, and forming great masses. The cylin-
drical stems are jointed, the joints sending out circles of
branches, which repeat the jointed and branching habit
(Fig. 31).

The walls become incrusted with a deposit of lime,
which makes the plants harsh and brittle, and has sug-
gested the name “stoneworts.” In addition to the highly
organized nutritive body, the antheridia and oogonia are
peculiarly complex, being entirely unlike the simple sex
organs of the other Alge.

CHAPTER V

THALLOPHYTES: FUNGI

36. General characters.—In general, Fungi include Thal-
lophytes which do not contain chlorophyll. From this fact
it follows that they can not manufacture food entirely out
of inorganic material, but are dependent for it upon other
plants or animals. This food is obtained in two general
ways, either (1) directly from the living bodies of plants or
animals, or (2) from dead bodies or the products of living
bodies. In the first case, in which living bodies are at-
tacked, the attacking fungus is called a parasite, and the
plant or animal attacked is called the host. In the second
case, in which living bodies are not attacked, the fungus is
called a saprophyte. Some Fungi can live only as parasites,
or as saprophytes, but some can live in either way.

Fungi form a very large assemblage of plants, much
more numerous than the Alge. As many of the parasites
attack and injure useful plants and animals, producing
many of the so-called ‘“ diseases,” they are forms of great
interest. (Governments and Experiment Stations have ex-
pended a great deal of money in studying the injurious
parasitic Fungi, and in trying to discover some method of
destroying them or of preventing their attacks. Many of
the parasitic forms, however, are harmless; while many of
the saprophytic forms are decidedly beneficial.

It is generally supposed that the Fungi are derived from
the Alge, having lost their chlorophyll and power of inde-
pendent living. Some of them resemble certain Alge so
closely that the connection seems very plain; but others

48

THALLOPHYTES: FUNGI 49

have been so modified by their parasitic and saprophytic
habits that they have lost all likeness to the Alge, and
their connection with them is very obscure.

3%. The plant body.—Discarding certain problematical
forms, to be mentioned later, the bodies of all true Fungi
are organized upon a uniform general plan, to which they
can. all be referred (Fig. 32). A set of colorless branching

Fig. 32 A diagrammatic representation of cor. showing the profusely branching
mycelium. and three vertical hyphe (sporophores), sporangia forming on } and c.
—After Zopr. :

filaments, either isolated or interwoven, forms the main
working body, and is called the mycelium. The interweay-
ing may be very loose, the mycelium looking like a delicate
cobweb; or it may be close and compact, forming a felt-like
mass, as may often be seen in connection with preserved
fruits. The individual threads are called hyphe (singular,
hypha) or hyphal threads. The mycelium is in contact with
its source of food supply, which is called the sudstratum.

50) PLANT STRUCTURES

From the hyphal threads composing the mycelium verti-
cal ascending branches arise, which are set apart to produce
the asexual spores, which are scattered and produce new
mycelia. These branches are called ascending hyphe or
sporophores, meaning “ spore bearers.”

Sometimes, especially in the case of parasites, special
descending branches are formed, which penetrate the sub-
stratum or host and absorb the food material. These spe-
cial absorbing branches are called haustoria, meaning “ ab-
sorbers.”

Such a mycelial body, with its sporophores, and perhaps
haustoria, lies either upon or within a dead substratum in
the case of saprophytes, or upon or within a living plant or
animal in the case of parasites.

38. The subdivisions—The classification of Fungi is in
confusion on account of lack of knowledge. They are so
much modified by their peculiar life habits that they have
lost or disguised the structures which prove most helpful in
classification among the Alge. Four groups will be pre-
sented, often made to include all the Fungi, but doubtless
they are insufficient and more or less unnatural.

The constant termination of the group names is mycetes,
a Greek word meaning “fungi.” The prefix in each case is
intended to indicate some important character of the group.
The names of the four groups to be presented are as follows:
(1) Phycomycetes (“ Alga-Fungi’”), referring to the fact
that the forms plainly resemble the Alge ; (2) Ascomycetes
(“ Ascus-Fungi”); (3) @#eidiomycetes (“Aicidium-Fungi ”) ;
(4) Basidiomycetes (“ Basidium-Fungi”). Just what the
prefixes ascus, ecidium, and basidiwm mean will be ex-
plained in connection with the groups. The last three
groups are often associated together under the name My-
comycetes, meaning “ Fungus-Fungi,” to distinguish them
from the Phycomycetes, or “ Alga-Fungi,” referring to the
fact that they do not resemble the Algw, and are only like
themselves.

THALTOPHY TES? FUNGL 1

ar

One of the ordinary life processes which seems to be
seriously interfered with by the saprophytic and parasitic
habit is the sexual process. At least, while sex organs
and sexual spures are about as cyident in Phycomycetes
as in Alew, they are either obscure or wanting in the
Mycomycete groups.

1. Puycomycetes (Alga-Fung!)

39. Saprolegnia.—This is a group of “ water-moulds,”
with aquatic habit like the Alge. They live upon the dead
bodies of water plants and animals (Fig. 33), and some-
times attack living fish, one kind being very destructive
to young fish in hatcheries. The hyphe composing the
mycelium are c:enocytes, as in the Siphon forms.

Sporangia are organized at the ends of branches by
forming a partition wall separating the cavity of the tip
from the general cavity (Fig. 33, B). The tip becomes
more or less swollen, and within it are formed numerous
biciliate zoospores, which are discharged into the water
(Fig. 33, ('), swim ubout for a short time, and rapidly form
new mycelia. The provess is very suggestive of Claduphora
and Taucheria. Oogonia and antheridia are also formed
at the ends of the branches (Fig. 33, 4"), much as in Vaw-
cheria. The oogonia are spherical, and form one and some-
times many eggs (Fig. 33, D, £). The antheridia are
formed on branches near the oogonia. An antheridium
comes in contact with an oogonium, and sends out a deli-
cate tube which pierces the oogonium wall (Fig. 33, F’).
Through this tube the contents of the antheridium pass,
fuse with the ecg, and a heavy-walled oospore or resting
spore is the result.

It is an interesting fact that sometimes the contents of
an antheridium do not enter an oogonium, or antheridia
may not even be formed, and still the egg, without fertiliza-
tion, forms an oospore which can germinate. This peculiar

59 PLANT STRUCTURES

habit is called parthenogenesis, which means reproduction
by an egg without fertilization.

Fig. 33. A common water mould (Saprolegnia): A, a fly from which mycelial fila-
ments of the parasite are growing; B, tip of a branch organized as a sporangium,
C, sporangium discharging biciliate zoospores; F, oogonium with antheridium in
contact, the tube having penetrated to the egg; D and #, oogonia with several
eggs.— 4-Cafter Tourgt, D-F after DeBary.

40. Mucor.—One of the most common of the Mucors, or
“black moulds,” forms white furry growths on damp bread,
preserved fruits, manure heaps, ete. It is therefore a
saprophyte, the ccenocytic mycelium branching extensively
through the substratum (Fig. 34).

THALLOPHYTES: FUNGI 58

Erect sporophores arise from it in abundance, and at
the top of each sporophore a globular sporangium is formed,
within which are numerous small asexual spores (Figs. 35,

Fig. 34. Diagram showing mycelium and sporophores of a common Mucor.—

CALDWELL.

36). The sporangium wall bursts (Fig. 37), the light spores
are scattered by the wind, and, falling upon a suitable sub-

stratum, germinate and
form new mycelia. It is
evident that these asex-
ual spores are not z00-
spores, for there is no
water medium and swim-
ming is impossible. This
method of transfer being
impossible, the spores are
scattered by currents of
air, and must be corre-
spondingly light and pow-
dery. They are usually
spoken of simply as
“spores,” without any
prefix.
22

Fie. 35. Forming sporangia of ucor, show-
ing the swollen tip of the sporophore (A),
and a later stage (B), in which a wall is
formed separating the sporangium from
the rest of the body.—CaLDWELL.

54 PLANT STRUCTURES

While the ordinary method of reproduction through the
growing season is by means of these rapidly germinating
spores, in certain conditions a sexual process is observed,
by which a heavy-walled sexual spore is formed as a resting
spore, able to outlive unfavorable conditions. Branches
arise from the hyphe of the mycelium just as in the forma-

Fig. 36. Mature sporangium of Mucor, showing Fic. 37. Bursted sporangium of

the wall (A), the numerous spores ((), and Mucor, the ruptured wall not
the columella (8)—that is, the partition wall being shown, and the loose
pushed up into the cavity of the sporangium. spores adhering to the colu-
—CALDWELL. mella.—CALDWELL,

tion of sporophores (Fig. 38). Two contiguous branches
come in contact by their tips (Fig. 38, .1), the tips are cut
off from the main ccenocytic body by partition walls (Fig.
38, 2), the walls in contact disorganize, the contents of
the two tip cells fuse, and a heavy-walled sexual spore is
the result (Fig. 38, ('). It is evident that the process is
conjugation, suggesting the Conjugate forms among the

THALLOPHYTES: FUNGI 55

Alge ; that the sexual spore is a zygote; and that the two
pairing tip cells cut off from the main body by partition
walls are gametangia. J/ueor, therefore, is isogamous.

Fic. 38. Sexual reproduction of J/vcor, showing tips of sex branches meeting (A),
the two gametangia cut off by partition walls (2), and the heavy-walled zygote
(C).—CALDWELL.

41. Peronospora.—These are the “downy mildews,” very
common parasites on seed plants as hosts, one of the most
common kind attacking grape leaves. The mycelium is cceeno-
eytic and entirely internal, ramifying among the tissues
within the leaf, and piercing the living cells with haustoria
which rapidly absorb their contents (Fig. 39). The pres-
ence of the parasite is made known by discolored and

56 PLANT STRUCTURES

finally deadened spots on the leaves, where the tissues have
been killed.

From this internal mycelium numerous sporophores
arise, coming to the surface of the host and securing the
scattering of their
spores, which fall
upon other leaves
and germinate, the
new mycelia pene-
trating among the
tissues and begin-

ning their ravages.
The sporophores af- Fie. 39. A branch of Peronospora in contact with
J

oo two cells of a host plant, and sending into them
ter rising above the its large haustoria.—After DEBary.

surface of the leaf,

branch freely; and many of them rising near together,
they form little velvety patches on the surface, suggesting
the name “ downy mildew.”

Fie. 40. Peronospora, one of the Phycomycetes, showing at @ an oogonium (0) con-
taining an egg, and an antheridium (7) in contact; at b the antheridial tube pene-
trating the oogonium and discharging the contents of the antheridium into the
egg; at ¢ the oogonium containing the oospore or resting spore.—After DEBary.

In certain conditions special branches arise from the
mycelium, which organize antheridia and oogonia, and
remain within the host (Fig. 40). The oogonium is of the
usual spherical form, organizing a single egg. The an-

THALLOPHYTES: FUNGI 57

theridium comes in contact with the oogonium, puts out a
tube which pierces the oogonium wall and enters the egg,
into which the contents of the antheridium are discharged,
and fertilization is effected. The result is a heavy-walled
oospore. .\s the oospores are not for immediate germina-
tion, they are not brought to the surface of the host and
scattered, as are the asexual spores. When they are ready
to germinate, the leaves bearing them have perished and
the oospores are liberated.

42. Conclusions—The ccenocytic bodies of the whole group
are very suggestive of the Siphon forms among Green Alge,
as is also the method of forming oogonia and antheridia.

The water-moulds, Suprolegnia and its allies, have re-
tained the aquatic habit of the Alge, and their asexual
spores are zoospores. Such forms as Jdwcor and Perono-
spora, however, have adapted themselves to terrestrial con-
ditions, zoospores are abandoned, and light spores are de-
veloped which can be carried about by currents of air.

In most of them motile gametes are abandoned. Even
in the heterogamons forms sperms are not organized within
the antheridium, but the contents of the antheridium are
discharged through a tube developed by the wall and pene-
trating the oogonium. It should be said, however, that a
few forms in this group develop sperms, which make them
all the more alga-like.

They are both isogamous and heterogamous, both zygotes
and oospores being resting spores. Taking the characters
all together, it seems reasonably clear that the Phycomycetes
are an assemblage of forms derived from Green Algz (Chlo-
rophycez) of various kinds.

2. ASCOMYCETES (Lscus- or Suc-Fungi)

43, Mildews.—These are very common parasites, growing
especially upon leaves of seed plants, the mycelium spread-
ing over the surface like a cobweb. A very common mil-

58 PLANT STRUCTURES

dew, Microsphera, grows on lilac leaves, which nearly
always show the whitish covering after maturity (Fig. 41).
The branching hyphe show numerous partition walls, and
are not ceenocytic as in the Phycomycetes. Small disk-like
haustoria penetrate into the superficial cells of the host,
anchoring the mycelium and absorbing the cell contents.

Sporophores arise, which form asexual spores in a pe
culiar way. The end of the sporophore rounds off, almost
separating itself from the part below, and becomes a spore
or spore-like body. Below this another organizes in the
same way, then another, until
a chain of spores is developed,
easily broken apart and scat-
tered by the wind. Falling
upon other suitable leaves,
they germinate and form new
mycelia, enabling the fungus
to spread rapidly. This meth-
od of cutting a branch into
sections to form spores is
called adstriction, and the
spores formed in this way
are called conidia, or conidi-
ospores (Fig. 43, B).

At certain times the myce-
lium develops special branches
which develop sex organs, but
they are seldom seen and may
Fra. 41. Lilac leaf covered with mi Ot always occur. An 00go0-

dew (Microsphwra), the shaded ree pium and an antheridium, of

and the back dots theaceoearpe the usual forms, but probably

CALDWELL. without organizing gametes,

come into contact, and as a
result an elaborate structure is developed—the ascocarp,
sometimes called the “spore fruit.” These ascocarps ap-
pear on the lilac leaves as minute dark dots, each one being

THALLOPHYTES: FUNGI 59

a little sphere, which suggested the name Microsphera
(Fig. 41). The heavy wall of the ascocarp bears beauti-
ful branching hair-like appendages (Fig. 42).

Bursting the wall of this spore fruit several very delicate,
bladder-like sacs are extruded, and through the transparent
wall of each sac there may be
seen several spores (Fig. 42).
The ascocarp, therefore, is
a spore case, just as is the
cystocarp of the Red Alge
(§$ 33). The delicate sacs
within are the asci, a word
meaning “sacs,” and each
ascus is evidently a mother
cell within which asexual
spores are formed. These
spores are distinguished

from other asexual spores
by the name ascospore.

It is these peculiar moth-
er cells, or asci, which give

Fic. 42. Ascocarp of the lilac mildew,
showing branching appeudages and
two asci protruding from the rup-
tured wall and containing ascospores.
—CALDWELL.

name to the group, and an

Ascomycete, Ascus-fungus, or Sac-fungus, is one which pro-
duces spores in asci; and an ascocarp is a spore case which
contains asci.

In the mildews, therefore, there are two kinds of asexual
spores: (1) conidia, formed from a hyphal branch by abstric-
tion, by which the mycelium may spread rapidly; and (2)
ascospores, formed in a mother cell and protected by a heavy
case, so that they may bridge over unfavorable conditions,
and may germinate when liberated and form new mycelia.
The resting stage is not a zygote or an oospore, as in the
Alge and Phycomycetes, no sexual spore probably being
formed, but a heavy-walled ascocarp.

44. Other forms.—The mildews have been selected as a
simple illustration of Ascomycetes, but the group is a very

60 PLANT STRUCTURES

large one, and contains a great variety of forms. All of
them, however, produce spores in asci, but the asci are not
always inclosed by an ascocarp. Here belong the common
blue mould (Penicillium), found on bread, fruit, etc., in
which stage the branching chains of conidia are very con-
spicuous (Fig. 43); the truffle-fungi, upon whose subter-

Fie. 43. Penicillium, a common mould: 4, mycelium with numerous branching
sporophores bearing conidia; B, apex of a sporophore enlarged, showing branch-
ing and chains of conidia.—After BREFELD.

ranean mycelia ascocarps develop which are known as
“truffles”; the black fungi, which form the diseases known
as “ black knot ” of the plum and cherry, the “ergot ” of
rye (Fig. 44), and many black wart-like growths upon the
bark of trees; other forms causing * witches’-brooms ” (ab-
‘normal growths on various trees), “ peach curl,” etc., the
cup-fungi (Figs. 45, 46), and the edible morels (Fig. £7).

THALLOPHYTES: FUNGI 61

Fie. 45. Two species of cup-fungus
(Peziza).—After LinDav.

Fie. 44. Head of rye attacked by “‘er- Fic. 46. A cup-fungus (Pitya) grow-
got” (a), peculiar grain-like masses ing on a spruce (Picea).— After
replacing the grains of rye; also a REM.
mass of ‘‘ergot’’ germinating to
form spores (%).—After TULASNE.

In some of these forms the ascocarp is completely closed,
as in the lilac mildew; in others it is flask-shaped; in
others, as in the cup-fungi, it is like a cup or disk; but in
all the spores are inclosed by a delicate sac, the ascus.

62 PLANT STRUCTURES

Here must probably be included the yeast-fungi (Fig.
48), so commonly used to excite alcoholic fermentation.

Fie. 47. The common edible morel (Morchella Fic. 48. Yeast cells, reprodu-
esculenta). The structure shown and used cing by budding, and form-
represents the ascocarp, the depressions of ing chains.—CALDWELL.

whose surface are lined with asci contain-
ing ascospores.—After Gipson.

The “ yeast cells ” seem to be conidia having a peculiar bud-
ding method of multiplication, and the remarkable power
of exciting alcoholic fermentation in sugary solutions.

3. AZECIDIOMYCETES (.2eidium-Fung?)

45. General characters.—This is a large group of very
destructive parasites known as “rusts” and “ smuts.” The
rusts attack particularly the leaves of higher plants, pro-
ducing rusty spots, the wheat rust probably being the best
known. The smuts especially attack the grasses, and are
very injurious to cereals, producing in the heads of oats,
barley, wheat, corn, etc., the disease called smut.

THALLOPHYTES: FUNGI 63

No indication of a sexual process has been obtained, and
the life histories are so complicated and obscure that the
position of the group is very uncertain. The forms should
probably be included with the Basidiomycetes, but they are
so unlike the ordinary forms of that group that they are
here kept distinct.

Most of the forms are very polymorphic—that is, a plant
assumes several dissimilar appearances in the course of its
life history. These phases are often so dissimilar that they
have been described as different plants. This polymorphism
is often further complicated by the appearance of different
phases upon entirely different hosts. For example, the
wheat-rust fungus in one stage lives on wheat, and in an-
other on barberry.

46. Wheat rust.—This is one of the few rusts whose life
histories have been traced, and it may be taken as an illus-
tration of the group.

The mycelium of the fungus is found ramifying among
the leaf and stem tissues of the wheat. While the wheat is
growing this mycelium sends to the surface numerous spo-

Fie. 49. Wheat rust, showing sporophores breaking through the tissues of the host
and bearing summer spores (uredospores).—After H. MansHALL WaRD.

rophores, each bearing at its apex a reddish spore (Fig. 49).
As the spores occur in great numbers they form the rusty-
looking lines and spots which give name to the disease.
The spores are scattered by currents of air, and falling upon
other plants, germinate very promptly, thus spreading the

64 PLANT STRUCTURES

disease with great rapidity (Fig. 50). Once it was thought
that this completed the life cycle, and the fungus received
the name (redo. When it was known that this is but one

Fic. 50 —Wheat rust, showing a young hypha forcing its way from the surface of a
leaf down among the nutritive cells.—After H. MarsuaLL Warp.

stage in a polymorphic life history it was called the Uredo-
stage, and the spores wredospores, sometimes “summer

spores.”

Fie. 51. Wheat rust, showing the winter spores (telentospores).—After
H. MarsHaui WARD.

Toward the end of the summer the same mycelium
develops sporophores which bear an entirely different kind
of spore (Fig. 51). It is two-celled, with a very heavy black

THALLOPHYTES: FUNGI 65

wall, and forms what is called the “black rust,” which ap-
pears late in the summer on wheat stubble. These spores
are the resting spores, which last through the winter and
germinate in the following spring. They are called felewto-
spores, meaning the “last spores” of the growing season.
They are also called “ winter spores,” to distinguish them
from the uredospores or ‘summer spores.” At first this
teleutospore-bearing mycelium was not recognized to be
identical with the uredospore-bearing mycelium, and it was
called Puccinia. This name is now
retained for the whole polymorphous
plant, and wheat rust is Puccinia
graminis. This mycelium on the
wheat, with its summer spores and
winter spores, is but one stage in
the life history of wheat rust.

In the spring the teleutospore
germinates, each cell developing a
small few-celled filament (Fig. 52).
From each cell of the filament a
little branch arises which develops
at its tip a small spore, called a spo-
ridium, which means “ spore-like.”
This little filament, which is not a
parasite, and which bears sporidia, ee en Bes
is a second phase of the wheat rust, ino'a teleatosporewermins:

really the first phase of the growing _tingand forming a short fil-
ament, from four of whose

season. cells a spore branch arises,
The sporidia are scattered, fall the lowest one bearing at
5 its tip a sporidium.—After
upon barberry leaves, germinate,and yy yfansnarz Wanp.
develop a mycelium which spreads
through the leaf. This mycelium produces sporophores
which emerge on the under surface of the leaf in the
form of chains of reddish-yellow conidia (Fig. 53). These
chains of conidia are closely packed in cup-like receptacles,

and these reddish-yellow cup-like masses are often called

66 PLANT

STRUCTURES

“cluster-cups.” This mycelium on the barberry, bearing
cluster-cups, was thought

to be a distinct plant, and was

Above is a flask-shaped mass discharging

af, with two ecidia below, one of them having broken through

nidia (zecidiospores)

very minute bodies, which are probably still other spores of the parasite.—After H. MarsnaLi Warp.

Fie. 53. Wheat rust, showing section of barberry
the epidermis and exposed it» chains of

called &cidium. The
name now is applied to
the cluster-cups, which
are called eridia, and
the conidia-like spores
which they produce are
known as cecidiospores.

It is the wcidia which
give name to the group,
and Aicidiomycetes are
those Fungi in whose
life history ecidia or
cluster-cups appear.

The wxcidiospores are
scattered by the wind,
fall upon the spring
wheat, germinate, and
develop again the myce-
lium which produces the
rust on the wheat, and
so the life cycle ix com-
pleted. There are thus
at least three distinct
stages in the life history
of wheat rust. Begin-
ning with the vrowing
season they are as fol-
lows: (1) The phase bear-
ing the sporidia, which
is not parasitic; (2) the
ecidium phase, pirasitic

on the barberry; (3) the uredo-teleutospore phase, para-

sitic on the wheat.

In this life cycle at least four kinds of asexual spores

THALLOPHYTES: FUNGI 67

appear: (1) sporidia, which develop the stage on the barber-
ry; (2) ecidiospores, which develop the stage on the wheat ;
(3) wredospores, which repeat the mycelium on the wheat ; (4)
teleutospores, which last through the winter, and in the spring
produce the stage bearing sporidia. It should be said that
there are other spores of this plant produced on the barberry
(Fig. 53), but they are too uncertain to be included here.

The barberry is not absolutely necessary to this life cycle.
In many cases there is no available barberry to act as host,
and the sporidia germinate directly upon the young wheat,
forming the rust-producing mycelium, and the cluster-cup
stage is omitted.

Fic. 54. Two species of ‘cedar apple” (Gymnosporangium), both on the common
juniper (Juniperus Virginiana).—A after Fartow, B after ENGLER and PRANTL.

47. Other rusts—Many rusts have life histories similar
to that of the wheat rust,in others one or more of the
stages are omitted. In very few have the stages been con-

68 PLANT STRUCTURES

nected together, so that a mycelium bearing uredospores is
called a Uredo, one bearing teleutospores a Puccinia, and
one bearing ecidia an .Leidiwm ; but what forms of Uredo,
Puccinia, and .£cidiwn belong together in the same life
cycle is very difficult to discover.

Another life cycle which has been discovered is in con-
nection with the “cedar apples” which appear on red
cedar (Fig. 54). In the spring these diseased growths be-
come conspicuous, especially after a rain, when the jelly-
like masses containing the orange-colored spores swell.
This corresponds to the phase which produces rust in
wheat. On the leaves of apple trees, wild crab, hawthorn,
ete., the ecidium stage of the same parasite develops.

4. BasIDIOMYCETES (Basidiwmn-Fungt).

48. General characters——This group includes the mush-
rooms, toadstools, and puffballs. They are not destructive
parasites, as are many
forms in the preceding
groups, but mostly harm-
less and often useful sap-
rophytes. They must
also be regarded as the
most highly organized of
the Fungi. The popular
distinction between toad-
stools and mushrooms is
not borne out by botan-
ical characters, toadstool
and mushroom being the
same thing botanically,
and forming one group,
puffballs forming an-
other.

Ss] wastrel
Fr. 55. The common edible mushroom, Asin Ec idiomycetes,
Agaricus canupestris.—Afler GrBsoNn. no sexual process has

THALLOPHYTES: FUNGI 69

been discovered. The life history seems simple, but this
apparent simplicity may represent a very complicated his-
tory. The structure of the common mushroom (.lyari-
cus) will serve as an illustration of the group (Fig. 55).
49. A common
mushroom, — The
mycelium, of white
branching threads,
spreads extensively
through the decay-
ing substratum,
and in cultivated
forms is spoken of
as the “spawn.”
Upon this myce-
lium little knob-
like protuberances
begin to arise, grow-
ing larger and
larger, until they
are organized into
the so-called
‘‘mushrooms.”’
The real body of
the plant is the
white thread -lke
mycelium, while
the “mushroom ”
part seems to rep-

resent a great num-
f sporophores Fis. 56. A common Agaricus : A, section through one
hen . : P side of pileus, showing sections of the pendent gills;
organized together B, section of a gill more enlarged, showing the cen-
i i he ba-
m ing] tral tissue, and the broad border formed by th
a aa is sidia: (, still more enlarged section of one side of
com pl ex spore- a gill, showing the club-shaped basidia standing at
ir 5 re. tight angles to the surface, and sending out a pair
Dearing SEeHavIn of small branches, each of which bears a single ba-
The mushroom sidiospore.—After Sacus.

23

“NOSAIY IdJJY—'alqipa | (s2ppwoo snur
-dog) snsuny ,, ouvur ASSvys,, aL 69 “81

“ITAMATYO— STIS pus ‘snoid
‘ads Surmoys “(pseipuepy [ooys
-pvo} snouosiod wouttl0d WY "8g "PL

"NOSED Id1py—‘olqrpa $ (sapnaso
snwuspapyy) susung , Sula Aiey,, Yo "LG ‘DIT

THALLOPHYTES: FUNGI 71

has a stalk-like portion, the stipe, at the base of which the
slendér mycelial threads look like white rootlets; and an
expanded, umbrella-like top called the pilews. From the
under surface of the pileus there hang thin radiating plates,
or gills (Fig. 55). Each gill is a mass of interwoven fila-
ments (hyphe), whose tips turn toward the surface and
form a compact layer of end cells (Fig. 56). These end

Fic. 60. A bracket fungus (Polyporus) growing on the trunk of a red oak.—
CALDWELL.

cells, forming the surface of the gill, are club-shaped, and
are called dasidia. From the broad end of each basidium
two or four delicate branches arise, each bearing a minute
spore, very much as the sporidia appear in the wheat rust.

"9 PLANT STRUCTURES

These spores, called basidiospores, shower down from the
gills when ripe, germinate, and produce new mycelia. The
peculiar cell called the basidium gives name to the group
Basidiomycetes.

50. Other forms—Mushrooms display a great variety of
form and coloration, many of them being very attractive

Fra. 61. A toadstool of the bracket form which has grown about blades of grass
without interfering with their activity CALDWELL,

(Figs. 57, 58, 59). The “ pore-fungi” have pore-like depres-
sions for their spores, instead of gills, as in the very com-
mon “bracket-fungus” (Polyporus), which forms hard
shell-like outgrowths on tree-trunks and stumps (Figs. 60,

Fic. 62. The common edible Boletus (B. edu- Fig. 68. Another edible Boletus (B. stro-
dis), in which the gills are replaced by bilaceus).— After Gipson.
pores,—After GIBSON.

Fie. 64. The common edible ‘coral fun- Fie. 65. Hydrum repandum, in which gills
gus’’ (Clavaria).—After Gipson. are replaced by spinous processes; edi-
ble.—After Gipson.

q4 PLANT STRUCTURES

61), and the mushroom-like Bolett (Figs. 62, 63). The
“ear-fungi” form gelatinous, dark-brown, shell-shaped
masses, and the “coral fungi” resemble branching corals
(Fig. 64). The Hydnum forms have spinous processes
instead of gills (Fig.
fo 65). The puffballs or-
: ganize globular bodies
(Fig. 66), within which
the spores develop, and
are not liberated until
ripe; and with them
belong also the “ bird’s
nest fungus,” the “earth
star,” the ill-smelling
“stink-horn,” etc.

OTHER THALLOPHYTES
WITHOUT CHLOROPHYLL

51. Slime - moulds. —
These perplexing forms,
named Aywrumiyretes, do
Fie. 66, Puffballs, in which the basidia ana Ot seem to be related

spores are inclosed ; edible.—After Gmson. to any group of plants,

and it is a question
whether they are to be regarded as plants or animals. The
working body is a mass of naked protoplasm called a plius-
modium, suggesting the term “slime,” and slips along like
a gigantic ameeba. They are common in forests, upon
black soil, fallen leaves, and decaying logs, the slimy yel-
low or orange masses ranging from the size of a pmhead
to as large as a man’s hand. They are saprophytic, and
are said to engulf food as do the amuwhbas. So suggestive
of certain low animals is this hody and food habit that
slime-moulds have also been called A/ycedozod or fungus-
animals.”

THALLOPHYTES: FUNGI 45

In certain conditions, however, these slimy bodies come
to rest and organize most elaborate and often very beau-
tiful sporangia, full of spores (Fig. 67). These varied
and easily preserved sporangia are used to classify the

Fie. 67. Three common slime moulds (Myxomycetes) on decaying wood: to the
left above, groups of the sessile sporangia of Trichia ; to the right above, a group
of the stalked sporangia of Stemonitis, with remnant of old plasmodium at base;
below, groups of sporangia of Hemiarcyria, with a plasmodium mass at upper
left hand.—CALDWELL,

forms. Slime-moulds, or “ slime-fungi,” therefore, seem
to have animal-like bodies which produce plant-like spo-
rangia.

52. Bacteria.—These are the “ Fission-Fungi,” or Schizo-
mycetes, and are popularly known as “ bacteria,” “ baci.li,”
“ microbes,” “germs,” etc. They are so important and pe-
culiar in their life habits that their study has developed a
special branch of botany, known as “ Bacteriology.” In
many ways they resemble the Cyanophycewx, or “ Fission-
Algez,” so closely that they are often associated with them
in classification (see § 21).

Fie 68. A group of Bacteria, the bodies being black, and bearing motile cilia in

various ways. .L, the two to the left the common hay Pacil/us (B. subtilis), the
one to the right a Spiriflam ; By a Cocens form (Planocaccus); C.D. E. species of
Pseudomonas ; 7, @, species of Bacillus, # being that of typhoid fever; ZZ, Jfiero-
spira; J, WK, L, M, species of Spirtdium.—After ENGLER and PRANTL.

THALLOPHYTES: FUNGI 44

They are the smallest known living organisms, the one-
celled form which develops on cooked potatoes, bread, milk,
meat, etc., forming a blood-red stain, having a diameter of
but 0.0005 mm. (g5)57 in.). They are of various forms
(Fig. 68), as Coccus forms, single spherical cells; Bacterium
forms, short rod-shaped cells; Bacillus forms, longer rod-
shaped cells; Leptothrix forms, simple filaments; Spirillum
forms, spiral filaments, etc.

They multiply by cell division with wonderful rapidity,
and also form resting spores for preservation and distri-
bution. They occur everywhere—in the air, in the water,
in the soil, in the bodies of plants and animals; many of
them harmless, many of them useful, many of them dan-
gerous.

They are intimately concerned with fermentation and
decay, inducing such changes as the souring of fruit juices,
milk, etc., and the development of pus in wounds. What
is called antiseptic surgery is the use of various means to
exclude bacteria and so prevent inflammation and decay.

The pathogenic forms—that is, those which induce dis-
eases of plants and animals—are of great importance, and
means of making them harmless or destroying them are
being searched for constantly. They are the causes of such
diseases as pear-blight and peach-yellows among plants, and
such human diseases as tuberculosis, cholera, diphtheria,
typhoid fever, etc.

LICHENS

53. General character.— Lichens are abundant every-
where, forming various colored splotches on tree-trunks,
rocks, old boards, etc., and growing also upon the ground
(Figs. 69, 70, 71). They have a general greenish-gray color,
but brighter colors may also be observed.

The great interest connected with Lichens is that they are
not single plants, but each Lichen is formed of a fungus and
an alga, living together so intimately as to appear like a single

“WIEMGTIVO— [IL ‘YlVd Joe IwoN “(osafiq¢ng sqiaydopshg) susay Jo WMOoIs
do} Uo puv ‘suayaI[ Jo [Mord asuep v Aq padaacd JYSIA oy} 07 oJ oY] Furmoys ‘poor Jo espa, WV 69 “OL

THALLOPHYTES: FUNGI 79

plant. In other words, a Lichen is not an individual, but a
firm of two individuals very unlike each other. This habit

Fie. 70. A common lichen (Physcia) growing on bark, showing the spreading thallus
and the numerons dark disks (apothecia) bearing the asci— CALDWELL.

of living together has been called symbiosis, and the indi-
viduals entering into this relation are called symbiouts.

Fig. 71. A common foliose lichen (Parmelia) growing upon a board, and showing
apothecia.—CaLDWELL.

Missing Page

Missing Page

82 PLANT STRUCTURES

bles an incrustation upon its substratum of rock, soil, ete. ;
(2) Foliose Lichens, with flattened, leaf-like, lobed bodies, at-

Fie. 74. Much enlarged section of a portion of the apothecium of Anaptychia, show-
ing the fungus mycelium (7m), which is massed above (y), just beneath the layer of
asci (1, 2,3, 4), im which spores in various stages of development are shown.—
After Sacus.

tached only at the middle or irregularly to the substratum ;
(8) Fruticose Lichens, with filamentous bodies branching
like shrubs, either erect, pendulous, or prostrate.

CHAPTER VI

THE FOOD OF PLANTS

54. Introductory.— All plants use the same kind of food,
but the Alge and Fungi suggest that they may have very
different wavs of obtaining it. The Algez can manufacture
food from raw material, while the Fungi must obtain it
already manufactured. Between these two extreme condi-
tions there are plants which can manufacture food, and at
the same time have formed the habit of supplementing this
by obtaining elsewhere more or less manufactured food.
Besides this, there are plants which have learned to work
together in the matter of food supply, entering into a con-
dition of symbiosis, as described under the Lichens. These
various habits will be presented here briefly.

55. Green plants—The presence of chlorophyll enables
plants to utilize carbon dioxide (CO,), a gas present in the
atmosphere and dissolved in waters, and one of the waste
products given off in the respiration of all living organisms.
This gas is absorbed by green plants, its constituent ele-
ments, carbon and oxygen, are dissociated, and with the ele-
ments obtained from absorbed water (H,O) are recombined to
form a carbohydrate (sugar, starch, etc.), which is an organ-
ized food. With this as a basis other foods are formed,
and so the plant can live without help from any other
organism.

This process of utilizing carbon dioxide in the formation
of food is not only a wonderful one, but also very important.
It is wonderful, because carbon dioxide and water, both of

them very refractory substances, are broken up at ordinary
83

84 PLANT STRUCTURES

temperatures and without any special display of energy. It
is important, because the food of all plants and animals de-
pends upon it, as it is the only known process by which inor-
ganic material can be organized.

The process is called photosynthesis, or photosyntir,
words indicating that the presence of light is necessary.
The mechanism on the part of the plant is the chloroplast,
which when exposed to light is able to do this work. The
process is often called * carbon assimilation,” ‘ chlorophyll
assimilation,” “ fixation of carbon,” etc. It should be noted
that it is not the chlorophyll which does the work, but the
protoplasmic plastid stained green by the chlorophyll. The
chlorophyll manipulates the light in some way so that the
plastid may obtain from it the energy needed for the work.
Further details concerning it may be obtained by reading
§$ 112 of Plant Relations.

It is evident that green plants must expose their chloro-
phyll to the light. For this reason the Alge can not live
in deep waters or in dark places. In the case of the large
marine kelps, although they may be anchored in considera-
ble depth of water, their working bodies are floated up
toward the light by air-bladders. In the case of higher
plants, specially organized chlorophyll-bearing organs, the
foliage leaves, are developed.

56. Saprophytes—Only cells containing chloroplasts can
live independently. In the higher plants, where bodies be-
come large, many living cells are shut away from the hght,
and must depend upon the more superficial green cells for
their food supply. The habit of cells depending upon one
another for food, therefore, is a very common one.

When none of the cells of the plant body contain chloro-
phyll, the whole plant becomes dependent, and must live as
a saprophyte or a parasite. In the case of saprophytes dead
bodics or body products are attacked, and sooner or later all
organic matter is attacked and decomposed by them. The
decomposition is a result of the nutritive processes of plants

THE FOOD OF PLANTS 85

without chlorophyll, and were it not for them “the whole
surface of the earth would be covered with a thick deposit
of the animal and plant remains of the past thousands of
years.”

The green plants, therefore, are the manufacturers of
organic material, producing far more than they can use,
while the plants without chlorophyll are the destroyers of
organic material. The chief destroyers are the Bacteria
and ordinary Fungi, but some of the higher plants have
also adopted this method of obtaining food. Many ordinary
green plants have the saprophytic habit of absorbing organic
material from rich humus soil; and many orchids and heaths
are parasitic, attaching their subterranean parts to those of
other plants, becoming what are called “root parasites.”
The cultivated plants, also, may be regarded as partially
saprophytic, in so far as they use the organic material sup-
plied to them in fertilizers.

57. Parasites—Certain plants Hthonk chlorophyll are
not content to obtain organic material from dead bodies,
but attack living ones. As in the case of saprophytes, the
vast majority of plants which have formed this habit are
Bacteria and ordinary Fungi. Parasites are not only modi-
fied in structure in consequence of the absence of chloro-
phyll, but they have developed means of penetrating their
hosts. Many of them have also cultivated a very selective
habit, restricting themselves to certain plants or animals, or
even to certain organs.

The parasitic habit has also been developed by some of
the higher plants, sometimes completely, sometimes par-
tially. Dodder, for example, is completely parasitic at
maturity (Fig. 75), while mistletoe is only partially so,
doing chlorophyll work and also absorbing from the tree
into which it has sent its haustoria.

That saprophytism and parasitism are both habits grad-
ually acquired is inferred from the number of green plants

which have developed them more or less, as a supplement to
pea

86 PLANT STRUCTURES

the food which they manufacture. The less chlorophyll is
used the less is it developed, and a green plant which is
obtaining the larger amount of its food in a saprophytic
or parasitic way is
on the way to losing
all of its chlorophyll
and becoming a com-
plete saprophyte or
parasite.

Certain of the low-
er Alge are in the
habit of living in the
body cavities of high-
er plants, finding in
such situations the
moisture and protec-
tion which they need.
They may thus have
brought within their
reach some of the
organic products of
the higher plant. If
they can use some of
these, as is very like-
ly, a partially para-
sitic habit is begun,
which may lead to
loss of chlorophyll
and complete para-

Fie. 75. A dodder plant purasitic on a willow twig. sitism.

The leafless dodder twines a bout the willow, and 58. Symbionts. ae
sends out sucking processes which penctrate and
absorb.—After STRASBURGER. The phenomenon of

symbiosis has already
been referred to in connection with Lichens ($ 53). In
its broadest sense the word includes any sort of depend-
ence between living organisms, from the vine and the tree

THE FOOD OF PLANTS 87

upon which it climbs, to the alga and fungus so intimately
associated in a Lichen as to seem a single plant. In a nar-
rower sense it includes only cases in which there is an inti-
mate organic relation between the symbionts. This would
include parasitism, the parasite and host being the sym-
bionts, and the organic relation certainly being intimate.
In a still narrower sense symbiosis includes only those cases
in which the symbionts are mutually helpful. This fact,
however, is very difficult to determine, and opinions vary
widely as to the mutual advantage of the relation. How-
ever large a set of phenomena may be included under the
term symbiosis, we use it here in this narrowest sense, which
is often distinguished as mutualism.

(1) Lichens.—The main facts of symbiosis in connection
with Lichens were presented in § 53. That the fungus-
symbiont can not live without the alga has been demon-
strated, but whether the alga-symbiont derives any benefit
from this association is a question in dispute. The latter
can live independently of the former, but enmeshed by the
fungus the alga seems to thrive and to live in situations
which would be impossible to it without the protection and
moisture supplied by the fungus-thallus. Those who lay
stress on the first fact regard the Lichen merely as a pecul-
iar case of parasitism, which has been called helotism, or a
condition of slavery, indicating that the alga is enslaved
and even cared for by the fungus for its own use. Those
who see an advantage to the alga in this association regard
a Lichen as an example of mutualism.

It may be of interest to know that artificial Lichens have
been formed, not only by cultivating together spores of a
Lichen-fungus and some Lichen-alga, but also by using
“wild ” Alga—that is, Alge which are in the habit of living
independently.

(2) Mycorrhiza.—The name means “root-fungus,” and
refers to an association which exists between certain Fungi
of the soil and roots of higher plants, such as orchids, heaths,

Fic. 76. Mycorrhiza: to the left is the tip of a rootlet of beech enmeshed by the
fungus; A, diagram of longitudinal section of an orchid root, showing the cells
of the cortex (7) filled with hyphe; ZB, part of longitudinal section of orchid root
much enlarged, showing epidermis (e), outermost cells of the cortex (p) filled with
hyphal threads, which are sending branches into the adjacent cortical cells (@, i).
—After Frank.

Fig. 77. Mycorrhiza: A, rootlets of white poplar forming mycorrhiza; B, enlarged
section of single rootlets, showing the hyphe penetrating the cells.—After
KERNER.

THE FOOD OF PLANTS 89

oaks and their allies, etc. (Figs. 76, 77). The delicate
branching filaments (hyphz) of the fungus spread through
the soil, wrap the rootlets with a mesh of hyphe, and pene-
trate into the cells. It seems clear that the fungus obtains
food from the rootlet as a parasite; but it is also thought
that the hyphal threads, spreading widely through the soil,
are of great service to the host plant
in aiding the rootlets in absorbing.
If this be true, there is mutual ad-
vantage in the association, for the
small amount of nourishment taken
by the fungus is more than compen-
sated by its assistance in absorption.

(3) Root-tubercles.—On the roots
of many legume plants, as clovers,
peas, beans, etc., little wart-like
outgrowths are frequently found,
known as “root-tubercles” (Fig.
78). It is found that these tuber-
cles are caused by certain Bacteria,
which penetrate the roots and in-
duce these excrescent growths. The
tubercles are found to swarm with
Bacteria, which are doubtless ob-
taining food from the roots of the
host. At the same time, these Bac-
teria have the peculiar power of
laying hold of the free nitrogen of
the air circulating in the soil, and
of supplying it to the host plant

7 ' : Fie. 78. Root-tubercles on
in some usable form. Ordinarily Vicia Faba.—after Nout.

plants can not use free nitrogen,
although it occurs in the air in such abundance, and this
power of these soil Bacteria is peculiarly interesting.

This habit of clover and its allies explains why they are
useful in what is called “restoring the soil.” After ordi-

90 PLANT STRUCTURES

nary crops have exhausted the soil of its nitrogen-contain-
ing salts, and it has become comparatively sterile, clover is
able to grow by obtaining nitrogen from the air through the
root-tubercles. If the crop of clover be “plowed under,”
nitrogen-containing materials which the clover has organ-
ized will be contributed to the soil, which is thus restored
to a condition which will support the ordinary crops again.
This indicates the significance of a very ordinary “rotation
of crops.”

(4) Ant-plants, etc—In symbiosis one of the symbionts
may he an animal. Certain fresh-water polyps and sponges
become green on account of Alge which they harbor with-
in their bodies (Fig. 79). Like
the Lichen-fungus, these ani-
mals use the food manufactured
by the Alge, which in turn find
a congenial situation for living.
By some this would also be re-
garded as a case of helotism,
the animal enslaving the alga.

Very definite arrangements
are made by certain plants for
harboring ants, which in turn
Fic. 79. A fresh-water polyp (y- guard them against the attack

dra) attached toa twig and feed- Of leaf-cutting insects and oth-
ing upon alge (C), which may — er foes. These plants are called
be seen through the transparent
body wall (#).—-CALDWELL. Myrmecophytes, which means
“ant-plants,” or myrmecophtlous
plants, which means “ plants loving ants.” These plants
are mainly in the tropics, and in stem cavities, in hollow
thorns, or elsewhere, they provide dwelling places for tribes
of warlike ants (Fig. 80). In addition to these dwelling
places they provide special kinds of food for the ants.

(5) Flowers and insects.—A very interesting and impor-
tant case of symbiosis is that existing between flowers and
insects. The flowers furnish food to the insects, and the

THE FOOD OF PLANTS 91

latter are used by the flowers as agents of pollination. An
account of this relationship is deferred until seed-plants are

Fig. 80. An ant plant (Hydnophytvm) from South Java, in which an excrescent
growth provides a habitation for ants.—After SCHIMPER.

considered, or it may be found, with illustrations, in Plant
Relations, Chapter VII.

99 PLANT STRUCTURES

59. Carnivorous plants—Certain green plants, growing
in situations poor in nitrogen-containing salts, have learned
to supplement the proteids which they manufacture by cap-
turing and digesting insects. The various devices employed
for securing insects have excited great interest, since they
do not seem to be associated with the ordinary idea of plant
activities. Prominent among these forms are the bladder-
worts, pitcher-plants, sundews, Venus’s fly-trap, etc. For
further account and illustrations of these plants see Plant
Relations, § 119..

CHAPTER VII

BRYOPHYTES (MOSS PLANTS)

60. Summary from Thallophytes.—Before considering the
second great division of plants it is well to recall the most
important facts connected with the Thallophytes, those
things which may be regarded as the contribution of the
Thallophytes to the evolution of the plant kingdom, and
which are in the background when one enters the region of
the Bryophytes.

(1) Inereasing complexity of the body.—Beginning with
single isolated cells, the plant body attains considerable
complexity, in the form of simple or branching filaments,
cell-plates, and cell-masses.

(2) Appearance of spores.—The setting apart of repro-
ductive cells, known as spores, as distinct from nutritive
cells, and of reproductive organs to organize these spores,
represents the first important differentiation of the plant
body into nutritive and reproductive regions.

(3) Differentiation of spores.—After the introduction of
spores they become different in their mode of origin, but
not in their power. The asexual spore, ordinarily formed
by cell division, is followed by the appearance of the sexual
spore, formed by cell union, the act of cell union being
known as the sexual process.

(4) Differentiation of gametes.—At the first appearance
of sex the sexual cells or gametes are alike, but after-
ward they become different in size and activity, the large

passive one being called the egg, the small active one the
93

94 PLANT STRUCTURES

sperm, the organs producing the two being known as oogo-
nium and antheridium respectively.

(5) Alge the main line-—The Alge, aquatic in habit,
appear to be the Thallophytes which lead to the Bryophytes
and higher groups, the Fungi being regarded as their de-
generate descendants; and among the Alge the Chloro-
phycex seem to be most probable ancestors of higher forms.
It should be remembered that among these Green Alge the
ciliated swimming spore (zoospore) is the characteristic
asexual spore, and the sexual spore (zygote or oospore) is
the resting stage of the plant, to carry it over from one
growing season to the next.

61. General characters of Bryophytes——The name given
to the group means “‘ moss plants,” and the Mosses may be
regarded as the most representative forms. Associated
with them in the group, however, are the Liverworts, and
these two groups are plainly distinguished from the Thallo-
phytes below, and from the Pteridophytes above. Starting
with the structures that the Alge have worked out. the
Bryophytes modify them still further, and make their own
contributions to the evolution of the plant kingdom, so
that Bryophytes become much more complex than Thallo-
phytes.

62, Alternation of generations— Probably the most im-
portant fact connected with the Bryophytes is the distinct
alternation of generations which they exhibit. So impor-
tant is this fact in connection with the development of the
plant kingdom that its general nature must be clearly under-
stood. Probably the clearest definition may be obtained by
tracing in bare outline the life history of an ordinary moss.

Beginning with the asexual spore, which is not ciliated,
as there is no water in which it can swim, we may imagine
that it has been carried by the wind to some spot suitable
for its germination. It develops a branching filamentous
growth which resembles some of the Conferva forms among
the (rreen Alge (Fig. 81). It is prostrate, and is a regu-

BRYOPHYTES 95

lar thallus body, not at all resembling the ‘‘moss plant”
of ordinary observation, and is not noticed by those una-
ware of its existence.

Presently one or more buds appear on the sides of this
alga-like body (Fig. 81, 4). A bud develops into an erect

Fic, 81. Protonema of moss: A, very young protonema, showing spore (8) which
has germinated it; B, older protonema, showing branching habit, remains of
spore (s), rhizoids (7), and buds (2) of leafy branches (gametophores).—After
MULLER and THURGAU.

stalk upon which are numerous small leaves (Figs. 82, 102).
This leafy stalk is the ‘“‘moss plant” of ordinary observa-
tion, and it will be noticed that it is simply an erect leafy
branch from the prostrate alga-like body.

At the top of this leafy branch sex-organs appear, cor-
responding to the antheridia and oogonia of the Alge, and
within them there are sperms and eggs. A sperm and egg
fuse and an oospore is formed at the summit of the leafy
branch.

The oospore is not a resting spore, but germinates im-
mediately, forming a structure entirely unlike the moss

96 PLANT STRUCTURES

plant from which it came. This
new leafy body consists of a slender
stalk bearing at its summit an urn-
like case in which are developed nu-
merous asexual spores (Figs. 82, 107).
This whole structure is often called
the ‘‘spore fruit,” and its stalk is
imbedded at base in the summit of
the leafy branch, thus obtaining firm
anchorage and absorbing what nour-
ishment it needs, but no more a part
of the leafy branch than is a para-
site a part of the host.

When the asexual spores, pro-
duced by the ‘‘ spore fruit,” germi-
nate, they reproduce the alga-like
body with which we began, and the
life cycle is completed.

In examining this life history, it
is apparent that each spore produces
a different structure. The asexual
spore produces the alga-like body
with its erect leafy branch, while
the oospore produces the ‘‘ spore
fruit” with its leafless stalk and
spore case. These two structures,
one produced by the asexual spore,
the other by the oospore, appear in
alternating succession, and this is
ee ae what is meant by alfernalion of yen-

(Polytrichum commune), erattons.

showing the leafy gameto- These two “ generations » differ
phore with rhizoids (rh), 2 :

and twosporophytes (sporo. strikingly from one another in the
gonia), with seta (s), calyp- spores which they produce. The
tra (c), and operculum (@), m1 i
the calyptra having been re. generation composed of alga-like
moved.—After Scuenck. hody and erect leafy branch pro-

BRYOPHYTES 97

duces only sexual spores (oospores), and therefore pro-
duces sex organs and gametes. It is known, therefore,
as the gametophyte—that is, ‘‘the gamete plant.”

The generation which consists of the ‘‘spore fruit ”—
that is, leafless stalk and spore case—produces only asexual
spores, and is called the sporophyte—that is, ‘‘the spore
plant.”

Alternation of generations, therefore, means the alter-
nation of a gametophyte and a sporophyte in completing a
life history. Instead of having the same body produce both
asexual and sexual spores, as in most of the Algz, the two
kinds of spores are separated upon different structures,
known as “ generations.” It is evident that the gameto-
phyte is the sexual generation, and the sporophyte the
asexual one; and it should be kept clearly in mind that
the asexual spore always produces the gametophyte, and
the sexual spore the sporophyte. In other words, each
spore produces not its own generation, but the other one.

The relation between the two alternating generations
may be indicated clearly by the following formula, in
which G and § are used for gametophyte and sporophyte
respectively :

G—§>0—S—o—G= > 0—S—o—G, ete.

The formula indicates that the gametophyte produces
two gametes (sperm and egg), which fuse to form an oospore,
which produces the sporophyte, which produces an asexual
spore, which produces a gametophyte, ete.

That alternation of generations is of great advantage is
evidenced by the fact that it appears in all higher plants.
It must not be supposed that it appears first in the Bryo-
phytes, for its beginnings may be seen among the Thallo-
phytes. The Bryophytes, however, first display it fully
organized and without exception. Just what this alterna-
tion does for plants may not be fully known, but one
advantage seems prominent. By means of it many gameto-
phytes may result from a single oospore ; in other words,

98 PLANT STRUCTURES

it multiplies the product of the sexual spore. A glance at
the formula given above shows that if there were no sporo-
phyte (S) the oospore would produce but one gametophyte
(G). By introducing the sporophyte, however, as many
gametophytes may result from a single oospore as there are
asexual spores produced by the sporophyte, which usually
produces a very great number.

In reference to the sporophytes and gametophytes of
Bryophytes two peculiarities may be mentioned at this
point: (1) the sporophyte is dependent upon the gameto-
phyte for its nourishment, and remains attached to it;
(2) the gametophyte is the special chlorophyll-generation,
and hence is the more conspicuous. It follows that, in a
general way, the sporophyte of the Bryophytes only pro-
duces spores, while the gametophyte both produces gametes
and does chlorophyll work.

It is important also to note that the protected resting
stage in the life history is not the sexual spore, as in the
Alge, but is the asexual spore in connection with the
sporophyte. These spores have a protecting wall, are
scattered, and may remain for some time without germi-
nation.

If the ordinary terms in reference to Mosses be fitted
to the facts given above, it is evident that the ‘moss
plant” is the leafy branch of the gametophyte; that
the “‘moss fruit” is the sporophyte ; and that the alga-
like part of the gametophyte has escaped attention and
a name.

The names now given to the different structures which
appear in this life history are as follows: The alga-like part
of the gametophyte is the protonema, the leafy branch is
the gametophore (‘‘ gamete-bearer ”) ; the whole sporophyte
is the sporogonium (a name given to this peculiar leafless
sporophyte of Bryophytes), the stalk-like portion is the
seta, the part of it imbedded in the gametophore is the
foot, and the urn-like spore-case is the capsule,

BRYOPHYTES 99

63. The antheridium.—The male organ of the Bryophytes
is called an antheridium, just as among Thallophytes, but
it has a very different structure. In general among the

Fig. 83. Sex organs of a common moss (Funaria): the group to the right represents
an antheridium (1) discharging from its apex a mass of sperm mother cells (a), a
single mother cell with its sperm (J), and a single sperm (¢). showing body and
two cilia; the group to the left represents an archcgonial cluster at summit of
stem (4), showing archezonia (@), and paraphyses and leaf sections (0), and also a
single archegonium (ZB), with venter (0) containing egg and ventral canal cell, and
neck (f) containing the disorganizing axial row (neck canal cells).—After Sacus.

Thallophytes it is a single cell (mother cell), and may be
called a simple antheridium, but in the Bryophytes it is a
many-celled organ, and may be regarded as a compound
antheridium. Itis usually a stalked, club-shaped, or oval to

100 PLANT STRUCTURES

globular body (Figs. 83, 84, 103). A section through this
body shows it to consist of a single layer of cells, which
forms the wall of the antheridium, and within this a com-
pact mass of small cubical (square in section) cells, within
each one of which there is formed a single sperm (Fig. 84).
These cubical cells are evidently moth-
er cells, and to distinguish them from
others they are called sperm mother cells.
An antheridium, therefore, aside from
its stalk, is a mass of sperm mother
cells surrounded by a wall consisting
of one layer of cells.

The sperm is a very small cell with
two long cilia (Fig. 83). The two
parts are spoken of as ‘‘ body” and
cilia, and the body may be straight or
somewhat curved. These small bicili-
Fie. 84, Antheridium of @¢€ sperms are one of the distinguish-

aliverwort in section, ing marks of the Bryophytes. The
showy single layer existence of male gametes in the form
ing the mass of moth- _ of ciliated sperms indicates that fertil-
er cells.—After STRAS- : : :
Bee ization can take place only in the pres-
ence of water, so that while the plant
has become terrestrial, and its asexual spores have respond-
ed to the new conditions and are no longer ciliated, its
sexual process is conducted as among the Green Alge. It
must not be supposed, however, that any great amount of
water is necessary to enable sperms to swim, even a film
of dew often answering the purpose.

When the mature antheridia are wet they are ruptured
at the apex and discharge the mother cells in a mass (Figs.
83, 105, #), the walls of the mother cells become mucilagi-
nous, and the sperms escaping swim actively about and are
attracted to the organ containing the egg.

64. The archegonium.—This name is given to the female
sex organ, and it is very different from the oogonium of

BRYOPHYTES 101

Thallophytes. Instead of being a single mother cell, it is
a many-cellcd structure, shaped like a flask (Figs. 83, 98).
The neck of the flask is more or less elongated, and within
the bulbous base (venter) the single egg is organized. The
archegonium, made up of neck and venter, consists mostly
of a single layer of cells. This hollow flask is solid at first,
there being a central vertical row of cells surrounded by
the single layer just referred to. All of the cells of this
axial row, except the lowest one, disorganize and leave a
passageway down through the neck. The lowest one of
the row, which lies in the venter of the archegonium, or-
ganizes the egg. In this way there is formed in the arche-
gonium an open passageway through the neck to the egg
lying in the venter.

To this neck the swimming sperms are attracted, enter
and pass down it, one of them fuses with the egg, and this
act of fertilization results in an oospore.

It is supposed that archegonia have been derived in some
way from oogonia, but no intermediate stages suggest the
steps. In any event, the presence of the archegonia is one
strong and unvarying distinction between Thallophytes
and Bryophytes. Pteridophytes also have archegonia, and
so characteristic an organ is it that Bryophytes and Pteri-
dophytes are spoken of together as Archegoniates.

65. Germination of the oospore.—The oospore in Bryo-
phytes is not a resting spore, but germinates immediately
by cell division, forming the sporophyte embryo, which
presently develops into the mature sporophyte (Fig. 85, 4).
The lower part of the embryo develops downward into the
gametophore, forming the foot, which penetrates and ob-
tains a firm anchorage in the gametophore (Fig. 85, B, C).
The upper part of the embryo develops upward, organizing
the seta and capsule. In true Mosses, when the embryo
becomes too large for the venter of the archegonium in
which it is developing, the archegonium is broken near the

base of the venter and is carried upward perched on the top
25

102 PLANT STRUCTURES

of the capsule like a loose cap or hood, known as the calyp-
tra (Figs. 82, c, 107), which sooner or later falls off. As

Fie. 85. Sporogonium of Fuvaria: A, an em-
bryo sporogonium (7, 7”), developing within
the venter (0, b) of an archegonium ; B, C,
tips of leufy shoots bearing young sporo-
gonia, pushing up calyptra (¢) and archego-
nium neck (7), and sending the foot down
into the apex of the gametophore.—After
GOEBEL.

stated before, the ma-
ture structure devel-
oped from the oospore
is called a sporogoni-
um, a form of sporo-
phyte peculiar to the
Bryophytes.

66. The sporogonium.
—In its fullest devel-
opment the sporogoni-
um is differentiated
into the three regions,
foot, seta, and capsule
(Figs. 82, 107); but in
some forms the seta
may be lacking, and
in others the foot also,
the sporogonium in this
last case being only the
capsule or spore case,
which, after all, is the
essential part of any
sporogonium.

At first the capsule
is solid, and its cells
are all alike. Later a
group of cells within
begins to differ in ap-
pearance from those
about them, being set
apart for the produc-
tion of spores. This

initial group of spore-producing cells is called the arche-
sportwm, « word meaning ‘‘the beginning of spores.” It

BRYOPUYTES 103

does not follow that the archesporial cells themselves pro-
duce spores, but that the spores are to appear sooner or
later in their progeny. Usually the archesporial cells
divide and form a larger mass of spore-producing cells.
Such cells are known as sporogenous (‘ spore-producing ””)
cells, or the group is spoken of as sporogenous tissue. Spo-
rogenous cells may divide more or less, and the cells of the
last division are mother cells, those which directly produce
the spores. The usual sequence, therefore, is archesporial
cells (archesporium), sporogenous cells, and mother cells ;
but it must be remembered that they all may be referred
to as sporogenous cells.

Each mother cell organizes within itself four spores,
the group being known as a tetrad. In Bryophytes and
the higher groups asexual spores are always produced in
tetrads. After the spores are formed the walls of the
mother cells disorganize, and the spores are left lying loose
in a cavity which was formerly occupied by the sporoge-
nous tissue. All mother cells do not always organize spores.
In some cases some of them are used up in supplying nour-
ishment to those which form spores. Such mother cells are
said to function as nutritive cells. In other cases, certain
mother cells become much modified in form, being organ-
ized into elongated, spirally-banded cells called elaters (Figs.
97, 101), meaning “‘ drivers” or “‘hurlers.” These elaters
lie among the loose ripe spores, are discharged with them,
and by their jerking movements assist in scattering them.

The cells of the sporogonium which do not enter into
the formation of the archesporium, and are not sporoge-
nous, are said to be sterzle, and are often spoken of as
sterile tissue. Hvery sporogonium, therefore, is made up
of sporogenous tissue and sterile tissue, and the differences
found among the sporogonia of Bryophytes depend upon
the relative display of these two tissues.

The sporogonium is a very important structure from
the standpoint of evolution, for it represents the conspicu-

Lot PLANT STRUCTURES

ous part of the higher plants. The “fern plant,” and
the herbs, shrubs, and trees among ‘flowering plants”
correspond to the sporogonium of Bryophytes, and not to
the leafy branch (gametophore) or ‘‘moss plant.” Conse-
quently the evolution of the sporogonium through the
Bryophytes is traced with a great deal of interest. It may
be outlined as follows:

In a liverwort called Riccia the simplest sporogonium
is found. It is a globular capsule, without seta or foot

Fie. 86. Diagrammatic sections of sporogonia of liverworts: A, Riccia, the whole
capsule being archesporium except the sterile wall layer; B, Marchantia, one
half the capsule being sterile, the archesporium restricted to the other half; D,
ulnthoceros, archesporium still more restricted, being dome-shaped and capping a
central sterile tissue, the columella (col).—After GoEBEL.

(Fig. 86, 1). The only sterile tissue is the single layer of
cells forming the wall, all the cells within the wall be-
longing to the archesporium. The ripe sporogonium,
therefore, is nothing but a thin-walled spore case. It is
well to note that the sporophyte thus begins as a spore
case, and that any additional structures that it may de-
velop later are secondary.

In another liverwort (Marchantia) the entire lower half
of the sporogoniun is sterile, while in the upper half there

BRYOPHYTES 105

is a single layer of sterile cells as a wall about the arche-
sporium, which is composed of all the remaining cells of the
upper half (Fig. 86, 8). It will be noted that the sterile
tissue in this sporogonium has encroached upon the arche-
sporium, which is restricted to one half of the body. In
this case the archesporium has the form of a hemisphere.
In another liverwort (Jungermannia) the archesporium
is still more restricted (Fig. 87). The sterile tissue is organ-

Fie. 87. Diagrammatic section of spo- Fie. 88. Section through sporogonium of

rogonium of a Jungermannia form, Sphagnum, showing capsule (k) with
showing differentiation into foot, old archegoninm neck (ah), calyptra (ca),
seta, and capsule, the archesporium dome-shaped mass of sporogenons tissue
restricted to upper part of sporogo- (spo), and columella (co), also the bulb-
nium.—After GoEBEL. ous foot (spf) imbedded in the pseudo-

podium (ps) —After SCHIMPER.

ized into a foot and a seta, and the archesporium is a com-
paratively small mass of cells in the upper part of the
sporogonium.

In another liverwort (Anthoceros) the sterile tissue or-
ganizes foot and seta, and the archesporium is still more
restricted (Fig. 86, D). Instead of a solid hemispherical

106

PLANT STRUCTURES

mass, it is a dome-shaped mass, the inner cells of the hemi-
sphere having become sterile. This central group of sterile

Fre. 89. Young sporogoni-
um of a true moss, show-
ing foot, scta, and young
capsule, in which the ar-
chesporium (darker por-
tion) is harrel-shaped, and
through it the columella is
continuous with the lid.—
After CAMPBELL.

cells which is surrounded by the ar-
chesporium is called the columella,
which means ‘‘a small column.”

In a moss called Sphagnum there
is the same dome-shaped archespori-
wn with the columella, as in -Ln-
thoceros, but it is relatively smaller
on account of the more abundant
sterile tissue (Fig. 88).

In the highest Mosses the arche-
sporium becomes very small as com-
pared with the sterile tissue (Fig.
89). A foot, a long seta, and an
elaborate capsule are organized from
the sterile tissue, while the arche-
sporium is shaped like the walls of
a barrel, as though the dome-shaped
archesporium of Sphagnum or An-
thoceros had become sterile at the
apex. In this way the columella is
continued through the capsule, and
is not capped by the archesporium.

This series indicates that after
the sporogonium begins as a simple
spore case (irei/a), its tendency is
to increase sterile tissue and to re-
strict sporogenous tissue, using the
sterile tissue in the formation of the
organs of the sporogonium body, as
foot, seta, capsule walls, ete.

Among the Green Algw there is
a form known as Coleorhete, whose
body resembles those of the sim-
plest Liverworts (Fig. 90). When

BRYOPHYTES 107

its oospores germinate there is formed a globular mass of
cells, every one of which is a spore mother cell (Fig. 90, C).
If an outer layer of mother cells should become sterile and
form a wall about the others, such a spore case as that of

Fie. 90..—Coleochete, one of the green alge: A, a portion of the thallus, showing
oogonia with trichogynes (og), antheridia (a1), and two enlarged biciliate sperms
(z); B, a fertilized oogonium containing oospore and invested by a tissue (7)
which has developed after fertilization; C, an oospore which has germinated
and formed a mass of cells (probably a sporophyte), each one of which organizes
a biciliate zoospore (D).—After PrinasHEIm.

Riecia would be the result (Fig. 86, 4). For such reasons
many believe that the Liverworts have been derived from
such forms as Coleochete.

67. The gametophyte—Having considered the sporo-
phyte body as represented by the sporogonium, we must
consider the gametophyte body as represented by proto-
nema and leafy branch (gametophore). The gametophyte
results from the germination of an asexual spore, and in
the Mosses it is differentiated into protonema and leafy
gametophore (Figs. 81, 82, 102). Like the sporophyte,

108 PLANT STRUCTURES

however, it shows an interesting evolution from its sim-
plest condition in the Liverworts to its most complex con-
dition in the true Mosses.

In the Liverworts the spore develops a flat thallus body,
one plate of cells or more in thickness, which generally
branches dichotomously (see § 29) and forms a more or less
extensive body (Fig. 92). This thallus is the gametophyte,
there being no differentiation into protonema and. leafy
branch.

In the simpler Liverworts the sex organs (antheridia
and archegonia) are scattered over the back of this thallus
(Fig. 92). In other forms they become collected in certain
definite regions of the thallus. In other forms these defi-
nite sexual regions become differentiated from the rest of
the thallus as disks. In other forms these disks, bearing
the sex organs, become short-stalked, and in others long-
stalked, until a regular branch arises from the thallus
body (Figs. 96, 97). This erect branch, bearing the sex or-
gans, is, of course, a gametophore, but it is leafless, the
thallus body doing the chlorophyll work.

In the Sphagnum Mosses the spore develops the same
kind of flat thallus (Fig. 104), but the gametophore be-
comes leafy, sharing the chlorophyll work with the thallus.
In the true Mosses most of the chlorophyll work is done by
the leafy, gametophore, and the flat thallus is reduced to
branching filaments (the protonema) (Fig. 102).

The protonema of the true Mosses, therefore, corre-
sponds to the flat thallus of the Liverworts and Sphagnum,
while the leafy branch corresponds to the leafless gameto-
phore found in some Liverworts. It also seems evident
that the gametophore was originally set apart to bear sex
organs, and that the leaves which appear upon it in the
Mosses are subsequent structures.

CIIAPTER VII

THE GREAT GROUPS OF BRYOPHYTES
Heratice (Liverworts)

68. General character—Liverworts live in a variety of
conditions, some floating on the water, many in damp
places, and many on the bark of trees. In general they are
moisture-loving plants (hydrophytes), though some can en-
dure great dryness. The gametophyte body is prostrate,
though there may be erect and leafless gametophores.

This prostrate habit develops a dorsiventral body—that
is, one whose two surfaces (dorsal and ventral) are expused
to different conditions and become unlike in structure. In
Liverworts the ventral surface is against the substratum,
and puts out numerous hair-like processes (rhizoids) for ab-
sorption and anchorage. The dorsal region is exposed to
the light and its cells develop chlorophyll. If the thallus
is thin, chlorophyll is developed in all the cells; if it be so
thick that the light is cut off from the ventral cells, the
thallus is differentiated into a green dorsal region doing the
chlorophyll work, and a colorless ventral region producing
absorbing rhizoids. This latter represents a simple differ-
entiation of the nutritive body into working regions, the
ventral region absorbing material and conducting it to the
green dorsal cells which use it in making food.

There seems to have been at least three main lines of
development among Liverworts, each beginning in forms
with a very simple thallus, and developing in different di-

rections. They are briefly indicated as follows:
109

110

PLANT STRUCTURES

69. Marchantia forms.—In this line the simple thallus

gradually becomes changed into a very complex one.

Fie. 91. A very small species of Riccia,
one of the Marchantia forms: A, a
group of thallus bodies slightly en-
larged ; B, section of a thallus, show-
ing rhizoids and two sporogonia im-
bedded and communicating with the
outside by tubular passages in the
thallus.—After STRASBURGER.

ventral regions (Fig. 94).

The
thallus retains its simple
outlines, but becomes thick
and differentiated in tissues
(groups of similar cells).
The line may be distin-
guished, therefore, as one
in which the differentia-
tion of the tissues of the
gametophyte is emphasized
(Figs. 91-93). In Mar-
chantia proper the thallus
becomes very complex, and
it may be taken as an illus-
tration.

The thallus is so thick
that there are very distinct
green dorsal and colorless

The latter puts out numerous

rhizoids and scales from the single layer of epidermal cells.
Above the ventral epidermis are several layers of colorless

Fia. 92.

Rieciocarpus, 2 Marchantia form, showing numerous rhizoids from ventral

surface, the dichotomous branching, und the position of the sporogonia on the
dorsal surface along the ‘‘ midribs.’— CALDWELL.

Fie. 98. Two common liverworts: to the left is Conocephalus, a Marchantia form,
showing rhizoids, dichotomous branching, and the conspicuous rhombic areas
(areola) on the dorsal surface; to the right is Anthoceros, with its simple thallus
and pod-like sporogonia.—C'ALDWELL,

Fra. 94. Cross-sections of thallus of J/archantia: A, section from thicker part of
thallus, where supporting tissue (y) is abundant, and showing lower epidermis
giving rise to rhizoids (%) and plates (0), also chlorophyll tissue (¢//) organized
into chambers by partitions (0); B, section near margin of thallus more magnified,
showing lower epidermis. two layers of supporting tissue (gy) with reticulate walls,
a single chlorophyll chamber with its bounding walls (s) and containing short,
often branching filaments whose cells contain chloroplasts (¢//), overarching
upper epidermis (0) pierced by a large chimney-like air-pore (sp).—After GoEBEL.

Fig. 95. Section through eupule of Warchantia, showing wall in which are chloro-
phyll-bearing air-chambers with air-pores, and gemmu (a) in various stages of
development,—After Knr.

Fra. 96. Murehantia polymorpha: the lower figure represents a gametophyte bear-
ing a mature antheridial branch (@), some young antheridial branches, and also
some cupules with toothed margins, in which the gemma may be seen; the
upper figure represents a partial section through the antheridial disk, and shows
antheridia within the antheridial cavities (a, 0, ¢, a, e, f).—After Kny,

THE GREAT GROUPS OF BRYOPHYTES 113

cells more or less modified for conduction. Above these
the dorsal region is organized into a series of large air cham-
bers, into which project chlorophyll-containing cells in the

Fie. 97. Marchantia polymorpha, a common liverwort: 1, thallus, with rhizoids,
bearing a mature archegonial branch (f) and several younger ones (a, 0, ¢, @, €);
2 and 3, dorsal and ventral views of archegonial disk; 4 and 5, young sporophyte
(sporogonium) embryos; 6, more mature sporogonium still within enlarged venter
of archegonium; 7, mature sporogonium discharging spores; 5, three spores and
an elater —After Kwy.

form of short branching filaments. Overarching the air
chambers is the dorsal epidermis, and piercing through it
into each air chamber is a conspicuous air pore (Fig. 94, B).

114 PLANT STRUCTURES

The air chambers are outlined on the surface as small
rhombic areas (aveole), each containing a single air pore.

Peculiar reproductive bodies are also developed upon
the dorsal surface of Murchantia for vegetative multiplica-

Fig. 98. Marchantia potymorpha: 1, partial section through archegonial disk, show-
ing archegonia with long necks, and venters containing eges; 9, young archego-
nium showing axial row; 10, superficial view at luter stage; 12, mature archego-
nium, with axial row disorganized and leaving an open passage to the large egg;
12, cross-section of venter; 13, cross-section of neck.—After Kyy.

tion. Little cups (cvpiles) appear, and in them are numer-
ous short-stalked bodies (gemm), which are round and
flat (biscuit-shaped) and many-celled (Figs. 95, 96). The

THE GREAT GROUPS OF BRYOPHYTES 115

gemme fall off and develop new thallus bodies, making
rapid multiplication possible.

Marchantia also possess remarkably prominent gameto-
phores, or ‘*sexual branches” as they are often called.
In this case the gametophores are differentiated, one bear-
ing only antheridia (Fig. 96), and known as the ‘anthe-
ridial branch,” the other bearing only archegonia (Figs. 97,
98), and known as the ‘‘archegonial branch.” The scal-
loped antheridial disk and the star-shaped archegonial disk,
each borne up by the stalk-like gametophore, are seen in the
illustrations. Not only are the gametophores sexually dif-
ferentiated, but as only one appears on each thallus, the thal-
lus bodies are sexually differentiated. When the two sex
organs appear upon different individuals, the plant is said to
be diecious, meaning ‘‘two households”; when they both
appear upon the same individual, the plant is wonwcious,
meaning “one household.” Some of the Bryophytes are mo-
neecious, and some of them are dicecious (as Aurchantia).

Another distinguishing mark of the line of Marchantia
forms is that the capsule-like sporogonium opens irregu-
larly to discharge its spores (Fig. 97, 7).

70. Jungermannia forms.—This is the greatest line of
the Liverworts, the forms being much more numerous
than in the other lines. They grow in damp places; or in
drier situations on rocks, ground, or tree-trunks ; or in the
tropics also on the leaves of forest plants. They are gen-
erally delicate plants, and resemble small Mosses, many of
them doubtless being commonly mistaken for Mosses.

This resemblance to Mosses suggests one of the chief
features of the line. Beginning with a simple thallus, as
in the Marchantia line, the structure of the thallus re-
mains simple, there being no such differentiation of tissues
as in the Marchantia line; but the form of the thallus
becomes much modified (Figs. 99,100). Instead of a flat
thallus with even outline, the body is organized into a cen-
tral stem-like axis bearing two rows of small, often crowded

116 PLANT STRUCTURES

leaves. There are really three rows of leaves, but the third
is on the ventral side against the substratum, and is often
so much modified as not to look like the other leaves. In
consequence of this the Jungermannia forms are usually
called ‘leafy liverworts,” to distinguish them from the

af

Fic. 99. Two liverworts, both Jungermannia forms: to the left is Blasia, which re-
tains the thallus form but has lobed margins; to the right is Scupunia, with dis-
tinct leaves and sporogonia (A).—CALDWELL.

other Liverworts, which are ‘‘thallose.” They are also
often called ‘‘ scale mosses,” on account of their moss-like
appearance and their small scale-like leaves.

The line may be distinguished, therefore, as one in
which the differentiation of the form of the gametophyte
is emphasized. Another distinguishing mark is that the
sporogonium has a prominent seta, and the capsule splits
down into four pieces (elves) when opening to discharge
the spores (Fig. 100, ().

71. Anthoceros forms.—This line contains comparatively
few forms, but they are of great interest, as they are sup-
posed to represent forms which have given rise to the

THE GREAT GROUPS OF BRYOPHYTES a ta bv

Fie. 100. Species of Lepidozia, a genus of leafy liverworts, showing different leaf
forms, and in .4 and (‘the dehiscence of the sporogonium by four valves. In @
rhizoids are evident; and in B, D, and # the three rows of leaves are seen, the
leaves of the ventral row being comparatively small.—After ENGLER and PRANTL.

Mosses, and possibly to the Pteridophytes also. The

thallus is very simple, being differentiated neither in

structure nor form, as in the two other lines; but the
26

118 PLANT STRUCTURES

special development has been in connection with the

sporogonium (Figs. 93, 101).

This complex sporogonium (sporophyte) has a large
bulbous foot imbedded in the simple thallus, while
above there arises a long pod-like capsule. The com-

Fie. 101. Anthoceros gracilis: A, several
gametophytes, on which sporogonia have
developed ; B, an enlarged sporogonium,
showing its elongated character and de-
hiscence by two valves leaving exposed
the slender columella on the surface of
which are the spores; (, D, H, F, cla-
ters of various forms; G, spores.—After
SCHIFFNER.

plex walls of this cap-
sule contain chlorophyll
and air pores, so that
the sporogonium is or-
ganized for chlorophyll
work. If the foot could
send absorbing processes
into the soil, this sporo-
phyte could live inde-
pendent of the gameto-
phyte. In opening to
discharge spores the pod-
like capsule splits down
into two valves.

Another peculiarity
of the .Lnthocervs forms
is in connection with
the antheridia and arch-
egonia. These organs,
instead of growing out
free from the body of the
thallus, as in other Liv-
erworts, are imbedded in
it. The significance of
this peculiarity lies in
the fact that it is a char-
acter which belongs to
the Pteridophytes.

The chief direction of development of the three liv-
erwort lines may be summed up briefly as follows: The
Murchantia line has differentiated the structure of the

THE GREAT GROUPS OF BRYOPIYTES 119

gametophyte; the Junxgermannia line has differentiated
the form of the gametophyte; the -lnthoceros line has
differentiated the structure of the sporophyte. It should
be remembered that other characters also serve to distin-
guish the lines from one another.

Muscr (Josses)

72. General character.—Mosses are highly specialized
plants, probably derived from Liverworts, the numerous
forms being adapted to all conditions, from submerged to
very dry, being most abundantly displayed in temperate
and arctic regions. Many of them may be dried out com-
pletely and then revived in the presence of moisture, as is
true of many Lichens and Liverworts, with which forms
Mosses are very commonly associated.

They also have great power of vegetative multiplica-
tion, new leafy shoots putting out from old ones and from
the protonema indefinitely, thus forming thick carpets and
masses. Bog mosses often completely fill up bogs or small
ponds and lakes with a dense growth, which dies below
and continues to grow above as long as the conditions are
favorable. These quaking bogs or “‘ mosses,” as they are
sometimes called, furnish very treacherous footing unless
rendered firmer by other plants. In these moss-filled bogs
the water and silt shut off the lower strata of moss from
complete disorganization, and they become modified into a
coaly substance called peat. which may accumulate to con-
siderable thicknéss by the continued upward growth of the
mass of moss.

The gametophyte body is differentiated into two very
distinct regions: (1) the prostrate dorsiventral thallus,
which is called protonema in this group, and which may be
either a broad flat thallus (Fig. 104) or a set of branching
filaments (Figs. 81, 102); (2) the erect leafy branch or
gametophore (Fig. 82). This erect branch is said to be

120 PLANT STRUCTURES

radial, in contrast with the dorsiventral thallus, referring
to the fact that it is exposed to similar conditions all
around, and its organs are arranged about a central axis

like the parts of a radiate animal.

Fig. 102. A moss (Bryum), showing base of a
leafy branch (gametophore) attached to the
protonema, and having sent out rhizoids. On
the protoncmal filament to the right and be-
low is the young bud of another leafy branch.
—MULLER.

This position is much
more favorable for the
chlorophyll work than
the dorsiventral posi-
tion, as the special
chlorophyll organs
(leaves) can be spread
out to the light freely
in all directions.

It should be re-
marked that the gam-
etophyte im all groups
of plants is a thallus,
doing its chlorophyll
work, when it does
any, in a dorsiventral
position ; the only ex-
ception being the ra-
dial leafy branch that
arises from the thal-
lus of Mosses. From
Mosses onward the
gametophyte becomes
less conspicuous, so
that the prominent
leafy plants of the
higher groups hold no

relation to the little erect leafy branch of the Mosses,
which is put out by the gamctophyte, and which is the
best the gametophyte ever does toward getting into a bet-

ter position for chlorophyll work.

The leafy branch of the Mosses usually becomes inde-
pendent of the thallus by putting out rhizoids at its base

THE GREAT GROUPS OF BRYOPIYTES 191

(Fig. 102), the thallus part dying. Sometimes, however,
the filamentous protonema is very persistent, and gives rise
to a perennial succession of leafy branches.

ie)
ie)
ie)
°

og
[oxe)

Fie. 103. Tip of leafy branch of a moss (Fwvaria), bearing a cluster of sex organs,
showing an old antheridium (A), a younger one (B), some of the curious associated
hairs (p), and leaf sections (2).—After CAMPBELL.

At the summit of the leafy gametophore, either upon
the main axis or upon a lateral branch, the antheridia and
archegonia are borne (Figs. 83, 103). Often the leaves at
the summit become modified in form and arranged to form

129 PLANT STRUCTURES

a rosette, in the center of which are the sex organs. This
rosette is often called the ‘* moss flower,” but it holds no
relation to the flower of Seed-plants, and the phrase should
not be used. <A rosette may contain but one kind of sex
organ (Figs. 83, 103), or it may contain both kinds, for
Mosses are both dicecious and monecious. The two prin-
cipal groups are as follows:

73. Sphagnum forms.—These are large and pallid bog
mosses, found abundantly in marshy ground, especially of
temperate and arctic regions, and are conspicuous peat-
formers (Fig. 105, 1). The leaves and gametophore axis
are of peculiar struc-
ture to enable them
to suck up and hold
a large amount of wa-
ter. This abundant
water -storage tissue
and the comparative-
ly poor display of
chlorophyll - contain-
ing cells gives the
peculiar pallid ap-
pearance.

They resemble the
Liverworts in the
broad thallus body
of the gametophyte,
Fie. 104, Thallus body of gametophyte of Sphag- from which the large

num, giving rise to rhizoids (7) and bnds (h)

which develop into the large leafy branches leafy gametophore

(gametophores).—After CAMPBELL. arises (Fig. 104).

They also resemble
«lnthoceros forms in the sporogonium, the archesporium
being a dome-shaped mass (Fig. 105, (’). On the other
hand, they resemble the true Mosses, not only in the leafy
gametophore, but also in the fact that the capsule opens
at the apex by a circular lid, called the operculum (Fig.

THE GREAT GROUPS OF BRYOPHYTES 123

105, D), which means a “cover” or “lid.” This may
serve to illustrate what is called an “intermediate” or
“transition” type, Sphagnum showing characters which
ally it to Anthoceros forms on the one side, and to true
Mosses on the other.

A peculiar feature of the sporogonium is that it has no
long stalk-like seta, as have the true Mosses, although it
appears to have one. This false appearance arises from the

alin
aa
B C

Fie. 105. Sphagnum; A, a leafy branch (gametophore) bearing four mature sporo-
gonia; B, archegonium in whose venter a young embryo sporophyte (em) is de-
veloping; (, section of a young sporogonium (sporophyte), showing the bulbous
foot (spf) imbedded in the apex of the pseudopodium (ps), the capsule (x), the
columella (co) capped by the dome-shaped archesporium (so). a portion of the
calyptra (ca), and the old archegonium neck (ah); D, branch bearing mature
sporogonium and showing pseudopodium (ps), capsule (4), and operculum (@); 2,
antberidium discharging sperms; F, a single sperm, showing coiled body and two
cilia.—After SCHIMPER.

fact that the axis of the gametophore is prolonged above
its leafy portion, the prolongation resembling the seta of
an ordinary moss (Fig. 105, D). This prolongation is

124 PLANT STRUCTURES

called a pseudopodium, or ‘false stalk,” and in the top of
it is imbedded the foot of the sporogonium carrying the
globular capsule (Fig. 105, C’).

74, True Mosses—This immense and most highly organ-
ized Bryophyte group contains the great majority of the
Mosses, which are sometimes called the Brywm forms, to
distinguish them from the Sphagnum forms. They are

Fic. 106. Different stages in the development of the leafy gametophore from the pro-
tonema of acommon moss (Fvnaria): A, the first few cells and a rhizoid (7); B,
C, later stages, showing apical cell (7) and young leaves (2); D, later stage much
less magnified, showing protonemal filaments and the young gametophore (gam)
—After CAMPBELL.

the representative Bryophytes, the only group vying with
them being the leafy Liverworts, or Jiiagermaniic forms.
They grow in all conditions of moisture, from actual sub-
mergence in water to dry rocks, and they also form exten-
sive peat deposits in bogs.

The thallus body of the gametophyte is made up of
branching filaments (Figs. 81, 102), those exposed to the

THE GREAT GROUPS OF BRYOPHYTES 195

light containing chlorophyll, and those in the substratum
being colorless and acting as rhizoids. The leafy gameto-
phores are often highly organized (Figs. 102, 106), the
leaves and stems showing a certain amount of differentia-
tion of tissues.

It is the sporophyte, however, which shows the great-
est amount of specialization (Fig. 107). The sporogonium

Fie. 107. A common moss (Faria): in the center is the leafy shoot (gametophore),
with rhizoids, several leaves, and a sporogonium (sporophyte), with a long seta,
capsule, and at its tip the calyptra (cal); to the right a capsule with calyptra re-
moved, showing the operculum (0); to the left a young sporogonium pushing up
the calyptra from the leafy shoot.—After CAMPBELL.

has a foot and a long slender seta, but the capsule is espe-
cially complex. The archesporium is reduced to a small
hollow cylinder (Fig. 88), the capsule wall is most elabo-
rately constructed, and the columella runs through the

Fie. 108, Longitudinal section of moss capsule
(Funaria), showing its complex character:
d, operculum; p, peristome: c, c’, columel-
la; s, sporogenous tissne; outside of s the
complex wall consisting of layers of cells
and large open spaces (/) traversed by
strands of tissue.—After GOEBEL.

Fig. 110. Sporogonia of Grimmia, from all of
which the operculum has fallen, displaying
the peristome teeth : 4, position of the teeth
when dry; /, position when moist.—After
KERNER.

eoofac

ae

2

Fie. 109. Partial longitudinal
section through a moss cap-
sule: A, younger capsule,
showing wall cells (@), cells
of columella (é), and sporag-
enous cells (sw); B, some-
what older capsule, @ and ¢
same as before, and sm the
spore mother cells, — After
GOEBEL.

THE GREAT GROUPS OF BRYOPHYTES 127

center of the capsule to the lid-like operculum (Figs. 108,
109). When the operculum falls off the capsule is left
like an urn full of spores, and at the mouth of the urn
there is usually displayed a set of slender, often very beau-
tiful teeth (Fig. 110), radiating from the circumference to
the center, and called the per/stome, meaning ‘* about the
mouth.” These teeth are hygroscopic, and by bending
inward and outward help to discharge the spores.

CHAPTER IX
PTERIDOPHYTES (FERN PLANTS)

75. Summary from Bryophytes—In introducing the Bryo-
phytes a summary from the Thallophytes was given (see §
60), indicating certain important things which that group
has contributed to the evolution of the plant kingdom.
In introducing the Pteridophytes it is well to notice certain
important additions made by the Bryophytes.

(1) -llternation of gencrations—The great fact of alter-
nating sexual (gametophyte) and sexless (sporophyte) gen-
erations 1s first clearly expressed by the Bryophytes, although
its beginnings are to be found among the Thallophytes.
Each generation produces one kind of spore, from which is
developed the other generation.

(2) Gametophyte the chlorophyll generation.—On account
of this fact the food is chiefly manufactured by the gameto-
phyte, which is therefore the more conspicuous generation.
When a moss or a liverwort is spoken of, therefore, the
gametophyte is usually referred to.

(3) Gametophyte and sporophyte not independent.—The
sporophyte is mainly dependent upon the gametophyte for
its nutrition, and remains attached to it, being commonly
called the sporogonium, and its only function is to produce
spores.

(4) Differentiation af thallus into stem and leaves,—
This appears incompletely in the leafy Liverworts (./iuger-
maunia forms) and much more clearly in the erect and
radial leafy branch (gametophore) of the Mosses.

128

PTERIDOPHY TES 129

(5) Many-celled sex organs —The antheridia and the
flask-shaped archegonia are very characteristic of Bryo-
phytes as contrasted with Thallophytes.

76. General characters of Pteridophytes.— The name means
‘fern plants,” and the Ferns are the most numerous and the
most representative forms of the group. Associated with
them, however, are the Horsetails (Scouring rushes) and
the Club-mosses. By many the Pteridophytes are thought
to have been derived from such Liverworts as the .lntho-
ceros forms, while some think that they may possibly have
been derived directly from the Green Algw. Whatever
their origin, they are very distinct from Bryophytes.

One of the very important facts is the appearance of
the vascular system, which means a ‘‘system of vessels,”
organized for conducting material through the plant body.
The appearance of this system marks some such epoch in
the evolution of plants as is marked in animals by the
appearance of the ‘* backbone.” As animals are often
grouped as “‘ vertebrates ” and “invertebrates,” plants are
often grouped as ‘‘ vascular plants” and ‘‘non-vascular
plants,” the former being the Pteridophytes and Spermato-
phytes, the latter being the Thallophytes and Bryophytes.
Pteridophytes are of great interest, therefore, as being the
first vascular plants.

“7. Alternation of generations—This alternation con-
tinues in the Pteridophytes, but is even more distinct than
in the Bryophytes, the gametophyte and sporophyte be-
coming independent of one another. An outline of the life
history of an ordinary fern will illustrate this fact, and will
serve also to point out the prominent structures. Upon the
lower surface of the leaves of an ordinary fern dark spots
or lines are often seen. These are found to yield spores,
with which the life history may be begun.

When such a spore germinates it gives rise to a small,
green, heart-shaped thallus, resembling a delicate and sim-
ple liverwort (Fig. 111, -1). Upon this thallus antheridia

130 PLANT STRUCTURES

and archegonia appear, so that it is evidently a gameto-
phyte. This gametophyte escapes ordinary attention, as it
is usually very small, and lies prostrate upon the substra-
tum. It has received the name prothalliwm or prothallus,
so that when the term prothallium is used the gametophyte
of Pteridophytes is generally referred to ; just as when the
term sporogonium is used the sporophyte of the Bryophytes
isreferred to. Within an archegonium borne upon this little
prothallium an oospore is formed. When the oospore ger-

Fig. 111. Prothallium of a common fern (Aspidivm): A, ventral surface, showing
rhizoids (72), antheridia (@7), and archegonia (ar); B, ventral surface of an older
gametophyte, showing rhizoids (7) and young sporophyte with root (zw) and leaf
(b).—After SCHENCK.

minates it develops the large leafy plant ordinarily spoken
of as ‘“‘the fern,” with its subterranean stem, from which
roots descend, and from which large branching leaves rise
above the surface of the ground (Fig. 111, 2). It is in
this complex body that the vascular system appears. No
sex organs are developed upon it, but the leaves bear numer-
ous sporangia full of asexual spores. This complex vascular
plant, therefore, is a sporophyte, and corresponds in this
life history to the sporogonium of the Bryophytes. This

PTERIDOPHY TES 131

completes the life cycle, as the asexual spores develop the
prothallium again.

In contrasting this life history with that of Bryophytes
several important differences are discovered. The most
striking one is that the sporophyte has become a large,
leafy, vuscular, and independent structure, not at all re-
sembling its representative (the sporogonium) among the
Bryophytes.

Also the gametophyte has become much reduced, as
compared with the gametophytes of the larger Liverworts
and Mosses. It seems to have resumed the simplest liver-
wort form, even the gametophore being suppressed, and
represented, if at all, by a rudiment. The conspicuous
leafy branch of the Mosses, commonly called ‘* the moss
plant,” corresponds to nothing in the Pteridophytes, there-
fore, except possibly the rudiment referred to, the prothal-
lium representing only the protonema part of the gameto-
phyte of the true Mosses.

This reduction of the gametophyte seems to be associ-
ated with the fact that the chlorophyll work has been trans-
ferred to the sporophyte, which hereafter remains the
conspicuous generation. The ‘‘fern plant” of ordinary
observation, therefore, is the sporophyte ; while the ‘* moss
plant” is a leafy branch of the gametophyte.

Another important contrast indicated is that in Bryo-
phytes the sporophyte is dependent upon the gametophyte
for its nutrition, remaining attached to it; while in the
Pteridophytes both generations are independent green
plants, the leafy sporophyte remaining attached to the
small gametophyte only while beginning its growth (Fig.
iy By,

Among the Ferns some interesting exceptions to this
method of alternation have been observed. Under certain
conditions a leafy sporophyte may sprout directly from the
prothallium (gametophyte) instead of from an oospore.
This is called apogamy, meaning ‘‘ without the sexual act.”

132 PLANT STRUCTURES

Under certain other conditions prothallia are observed to
sprout directly from the leafy sporophyte instead of from
a spore. This is called apospory, meaning “without a
spore.”

78. The gametophyte—The prothallium, like a simple
liverwort, is a dorsiventral body, and puts out numerous

Fig. 112. Stag-horn fern (Platycertum grande), an epiphytic tropical form, showing
the two forms of leaves: a and 2, young sterile leaves ; c, leaves bearing spo-
rangia ; d, an old sterile leaf.—CaLDWELL.

rhizoids from its ventral surface (Fig. 111). It is so thin
that all the cells contain chlorophyll, and it is usually short-
lived. In rare cases it becomes quite large and permanent,

Fig, 113. Archegonium of Pteris at the time of fertilization, showing tissue of gam-
etophyte (1), the cells forming the neck (2B), the passaceway formed by the dis-
organization of the canal cells (C'), and the egg (D) lying exposed in the venter.
—CALDWELL.

Fie. 114. Antheridium of Peris (B), showing wall cells (a), opening for escape of
sperm mother cells (e), escaped mother cells (¢), sperms free from mother cells (0),
showing spiral and multiciliate character.—CALDWELL.

27

134 PLANT

STRUCTURES

being a conspicuous object in connection with the sporo-

phyte.

At the bottom of the conspicuous notch in the prothal-

lium is the growing point,
representing the apex of the
plant. This notch is always
a conspicuous feature.

The antheridia and arch-
egonia are usually developed
on the under surface of the
prothallium (Fig. 111, .1),
and differ from those of all
Bryophytes, except the .fv-
thocerox forms, in being sunk
in the tissue of the prothal-
lium and opening on the sur-

ae

Fie. 115. Development of gamctophyte
of Plerix; the figure to the left shows
the old spore (B), the rhizoid (4, and
the thallus (4); that to the right is
older, showing the same parts, and
also the apical cell (D).—CaLDWELL,

Fig, 116.

Young gametophyte of P/r7is,
showing old spore wall (2B), rhizoids
((), apical cell (7), a young anther.
idium (/’), and an older one in which
sperms have organized (#').—Ca.p-
WELL.

PTERIDOPHYTES 135

face, more or less of the neck of the archegonium projecting
(Fig. 113). The eggs are not different from those formed
within the archegonia of Bryophytes, but the sperms are
very different. The Bryophyte sperm has a small body and
two long cilia, while the Pteridophyte sperm has a long
spirally coiled body, blunt behind and tapering to a point in
front, where numerous cilia are developed (Fig. 114). It
is, therefore, a large, spirally-coiled, multiciliate sperm, and
is quite characteristic of all Pteridophytes excepting the
Club-mosses. It is evident that a certain amount of water
is necessary for fertilization—in fact, it is needed not only

Fig. 117. Sections of portions of the gametophyte of Pteris, showing development
of archegonium: A, young stage, showing cells which develop the neck (a), and
the cell from which the egg cell and canal cells develop (4); B, an older stage,
showing neck cells (a), neck canal cell (2). and cell from which is derived the egg
cell, and the ventral canal cell (c); Ca still older stage, showing increased num-
ber of neck cells (a), two neck canal cells (4), the ventral canal cell (c), and the
cell in which the egg is organized (¢@).—CALDWELL.

by the swimming sperm, but also to cause the opening of
the antheridium and of the archegonium neck. There
seems to be a relation between the necessity of water for
fertilization and a prostrate, easily moistened gametophyte.

Prothallia are either moncecious or dicecious (see § 69).
When the prothallia are developing (Fig. 115) the anther-

SEAMHOHR

Fic. 118. A fern (lspidium), showing three large branching leaves coming from a
horizontal subterranean stem (rvotstock); young leaves are also shown, which
show circinate vernation. The stem, young leaves, and petioles of the large
Icaves are thickly covered with protecting hairs, The stem gives rise to numerous
small roots from its lower surface. The figure marked 3 represents the under sur-
face of a portion of the leaf, showing seven sori with shield-like indusia; at 4 is
represented a section through a sorus. showing the sporangia attached and pro-
tected by the indusium; while at 6 is represented a single sporangium opening
and discharging its spores, the heavy annulus extending along the back and over
the top.—After Woss1DLo.

PTERIDOPHYTES 137

idia begin to appear very early (Fig. 116), and later the
archegonia (Fig. 117). If the prothallium is poorly nour-
ished, only antheridia appear; it needs to be well developed
and nourished to develop archegonia. There seems to be
a very definite relation, therefore, between nutrition and
the development of the two sex organs, a fact which must
be remembered in connection with certain later develop-
ments.

79. The sporophyte.—This complex body is differentiated
into root, stem, and leaf, and is more highly organized
than any plant body heretofore mentioned (Fig. 118). The
development of this body and its three great working regions
must be considered separately.

(1) Development of embryo.—The oospore, from which
the sporophyte develops, rests in the venter of the arche-
gonium, which at this stage resembles a depression in the

Fig. 119. Embryos of a common fern (Pferis): A, young embryo, showing direction
of basal wall (7), and of second walls (77), which organize quadrants, each of
which subsequently develops into foot (f), root (w), leaf (6), and stem (s); B, an
older embryo, in which the four regions (lettered as in A) have developed further,
also showing venter of archegonium (a7), and some tissue of the prothallium (pr).
—A after Krenirz-Geriorr; B after HoFMEISTER.

lower surface of the prothallium (Fig. 119, B). It germi-
nates at once, as in Bryophytes, not being a resting spore
asin Green Alge. The resting stage, as in the Bryophytes,

138 PLANT STRUCTURES

is in connection with the asexual spores, which may be
kept for a long time and then germinated.

The first step in germination is for the oospore to di-
vide into two cells, forming a two-celled embryo. In the
ordinary Ferns this first dividing wall is at right angles to
the surface of the prothallium, and is called the dasal wall
(Fig. 119, A). One of the two cells, therefore, is anterior
(toward the notch of the prothallium), and the other is
posterior.

The two cells next divide by forming walls at right
angles to the basal wall, and a four-celled embryo is the
result. This is called the ‘‘ quadrant stage” of the em-
bryo, as each one of the four cells is like the quadrant of a
sphere.

With the appearance of the quadrant, four body regions
are organized, each cell by its subsequent divisions giving
rise to a distinct working region (Fig. 119, 4). Two of the
cells are inner (away from the substratum) ; also one of the
inner and one of the outer (toward the substratum) cells
are anterior ; while the two other inner and outer cells are
posterior. The anterior outer cell develops the first leaf of
the embryo, generally called the cotyledon (Fig. 119, &) ; the
anterior inner cell develops the stem (Fig. 119, s) ; the pos-
terior outer cell develops the first (primary) root (Fig.
119, w); the posterior inner cell develops a special organ
for the use of the embryo, called the foot (Fig. 119, f).
The foot remains in close contact with the prothallinm and
absorbs nourishment from it for the young embryo. When
the young sporophyte has developed enough to become in-
dependent the foot disappears. It is therefore spoken of
as a temporary organ of the embryo. It is necessary for the
leaf to emerge from beneath the prothallium, and it may
be seen usually curving upward through the notch. The
other parts remain subterranean.

(2) The root.—The primary root organized by one of
the quadrants of the embryo is a temporary affair (Figs.

PTERIDOPHY TES 139

111, 119), as it is in an unfavorable position in reference to
the dorsiventral stem, which puts out a series of more favor-
ably placed secondary roots into the soil (Fig. 118). The
mature leafy sporophyte, therefore, has neither foot nor
primary root, the product of two of the quadrants of the
embryo having disappeared.

The secondary roots put out by the stem are small, and
do not organize an extensive system, but they are interest-
ing as representing the first appearance of true roots, which
therefore come in with the vascular system. In the lower
groups the root function of absorption is conducted by sim-
ple hair-like processes called rhizoids; but true roots are
complex in structure and contain vessels.

(3) Zhe stem.—In most of the Ferns the stem is sub-
terranean and dorsiventral (Fig. 118), but in the “tree
ferns” of the tropics it forms an erect, aérial shaft bearing
a crown of leaves (Fig. 120). In the other groups of Pteri-
dophytes there are also aérial stems. both erect and pros-
trate. The stem is complex in structure, the cells being
organized into different “‘ tissue systems,” prominent among
which is the vascular system. These tissue systems of vas-
cular plants are described in Chapter AV.

The appearance of the vascular system in connection
with the leafy sporophyte is worthy of note. The leaves
are special organs for chlorophyll work, and must receive
the raw material from air and soil or water. The leaves
of the moss gametophyte are very small and simple affairs,
and can be supplied with material by using very little ap-
paratus. In the leafy sporophyte, however, the leaves are
very prominent structures. capable of doing a great deal
of work. To such working structures material must be
brought rapidly in quantity, and manufactured food ma-
terial must be carried away, and therefore a special con-
ducting apparatus is needed. This is supplied by the vas-
cular system. These vessels extend continuously from root-
tips, through the stem, and out into the leaves, where they

Fig. 120. A group of tropical plants. To the left of the center is a tree fern, with its
slender columnar stem and crown of large leaves. The laree-leayed plants to the
right are bananas (Monocotyledons).—From “ Plant Relations,”

PTERIDOPHYTES 141

are spoken of as ‘leaf veins.” Large working leaves and
a vascular system, therefore, belong together and appear
together; and the vascular plants are also the plants with
leafy sporophytes.

(4) The leaf.—lLeaves are devices for spreading out
green tissue to the light, and in the Ferns they are usually
large. There is a stalk-like portion (petiole) which rises
from the subterranean stem, and a broad expanded portion
(Slade) exposed to the light and air (Fig. 118). In Ferns
the blade is usually much branched, being cut up into
segments of various sizes and forms.

The essential structure consists of an expansion of
green tissue (mesophyll), through which strands of the
vascular system (veins) branch, forming a supporting
framework, and over all a compact layer of protecting
cells (epidermis). A surface
view of the epidermis shows ca )
that it is pierced by numer- +5 gs i
ous peculiar pores, called : ae, * Y 1s
stomata, meaning “mouths.” § ‘ ls i aly U
The surface view of a stoma + a y_ ¢ f
shows two crescentic cells *
(guard cells) in contact at
the ends and leaving be-
tween them a lens-shaped
opening (Fig. 121).

A cross-section through
a leaf gives a good view of
the three regions (Fig. 122). Fic. 121. Some epidermal cells from leaf

Above and below is the col- of Pleris, showing the interlocking

s : . walls and three stomata, the guard
orless epidermis, pierced cells containing chloroplasts.—CaLp-
here and there by stomata ; WELL,

between the epidermal lay-

ers the cells of the mesophyll are packed; and among
the mesophyll cells there may be seen here and there the
cut ends of the veins. The leaf is usually a dorsiventral

149 PLANT STRUCTURES

organ, its two surfaces being differently related to light.
To this different relation the mesophyll cells respond in
their arrangement. Those in contact with the upper epi-
dermis become elongated and set endwise close together,
forming the palisade tissue ; those below are loosely ar-

Soot)

BE
Go
Sose2.80

@\OS,
ag

5 SEX

Fig. 122. Cross-section through a portion of the leaf of Preris, showing the heavy-
walled epidermis above and below, two stomata in the lower epidermis (one on
each side of the centcr) opening into intercellular passages, the mesophyll cells
containing chloroplasts, the upper row arranged in palisade fushion, the other
cells loosely arranged (spongy mesophyll) and leaving large intercellular passages,
and in the center a scetion of a veinlet (vascular bundle), the xylem being repre-
sented by the central group of heavy-walled cells. —CALDWELL.

ranged, leaving numerous intercellular spaces, forming
the spongy tissue, These spaces form a system of inter-
cellular passageways among the working mesophyll cells,
putting them into communication with the outer air
through the stomata. The freedom of this communication

P'TERIDUPHYTES 143

is regulated by the guard cells of the stomata, which come
together or shrink apart as occasion requires, thus dimin-
ishing or enlarging the opening between them. ‘The sto-
mata have well been called ‘‘ automatic gateways” to the
system of intercellular passageways.

One of the peculiarities of ordinary fern leaves is
that the vein system branches dichotomously, the forking
veins being very conspicuous (Figs. 123-126). Another
fern habit is that the leaves in expanding seem to unroll
from the base, as though they had been rolled from the
apex downward, the apex being in the center of the roll
(Fig. 118). This habit is spoken of as circinate, from a
word meaning ‘‘circle” or ‘‘ coil,” and circinate leaves
when unrolling have a crozier-like tip. The arrangement
of leaves in bud is called vernation (‘‘ spring condition”),
and therefore the Ferns are said to have circinate verna-
tion. The combination of dichotomous venation and cir-
cinate vernation is very characteristic of Ferns.

80. Sporangia— Among Thallophytes sporangia are usu-
ally simple, mostly consisting of a single mother cell ; among
Bryophytes simple sporangia do not exist, and in connec-
tion with the usually complex capsule of the sporogonium
the name is dropped; but among Pteridophytes distinct
sporangia again appear. They are not simple mother cells,
but many-celled bodies. Their structure varies in different
groups of Pteridophytes, but those of ordinary Ferns may
be taken as an illustration.

The sporangia are borne by the leaves, generally upon
the under surface, and are usually closely associated with
the veins and organized into groups of definite form, known
as sort. A sorus may be round or elongated, and is usually
covered by a delicate flap (¢ndusiwm) which arises from the
epidermis (Figs. 118, 123, 124). Occasionally the sori are
extended along the under surface of the margin of the leaf,
as in maidenhair fern (4d/antum), and the common brake
(Pteris), in which case they are protected by the inrolled

Fig. 123. Fragrant shield fern (Aspid-
ium fragrans), showing gencral
habit, and to the left (a) the under
surface of a leaflet bearing sori
covered by shield-like indusia.—
After MARION SATTERLEE.

Fig, 124. The bladder fern ( Cystopteris bulh-
ifera), showing general habit, and to the
right (a) the under surface of a leaflet,
showing the dichotomons venation, and
five sori protected by pouch-like indusia,
—After MARION SATTERLEE.

P'TERIDOPILYTES 145

margin (Figs. 125, 126), which may be called a ‘false in-
dusium.”

It is evident that such leaves are doing two distinct
kinds of work—chlorophyll work and spore formation.
This is true of most of the ordinary Ferns, but some of
them show a tendency to di-
vide the work. Certain leaves,
or certain leaf-branches, pro-
duce spores and do no chloro-
phyll work, while others do
chlorophyll work and produce
no spores. This differentia-
tion in the leaves or leaf-re-
gions is indicated by appro-
priate names. Those leaves
which produce only spores are
called sporophylls, meaning
“spore leaves,” while the leaf
branches thus set apart are
called sporophyll branches.

Fic. 125. Leaflets of two common

Those leaves which only do ferns: 1, the common brake
: (Pteris); B, maidenhair (Adian-
chlorophyll work are called So- tm), both showing sori borne
liage leaves ; and such branch- at the margin and protected by
es are foliage branches. As the infolded margin, which thus
2 forms a false indusium.—CaLp-

sporophylls are not called upon weit

for chlorophyll work they often

become much modified, being much more compact, and not
at all resembling the foliage leaves. Such a differentiation
may be seen in the ostrich fern and sensitive fern ( Onoclea)
(Figs. 127, 128), the climbing fern (Zygodium), the royal
fern (Osmunda), the moonwort (Botrychium) (Fig. 129),
and the adder’s tongue (Ophioglossum) (Fig. 130).

An ordinary fern sporangium consists of a slender stalk
and a bulbous top which is the spore case (Fig. 118, 6).
This case has a delicate wall formed of a single layer of
cells, and extending around it from the stalk and nearly to

146 PLANT STRUCTURES

the stalk again, like a meridian line about a globe, is a row
of peculiar cells with thick walls, forming a heavy ring,
called the annulus. The annulus is hke a bent spring,
and when the delicate wall becomes yielding the spring
straightens violently, the wall is torn, and the spores are
discharged with considerable force (Fig. 131). This dis-

Fig. 126.—The purple cliff brake (Pred atropurpurea), showing general habit, and
at @a single leaflet showing the dichotomous venation and the infolded margin
covering the sori.— After MARION SATTERLEE.

charge of fern spores may be seen by placing some sporangia
upon a moist slide, and under a low power watching them
as they dry and burst.

Within this sporangium the archesporium (sce § 66)
consists of a single cell, which by division finally produces

PTERIDOPHYTES 147

numerous mother cells, in each of which a tetrad of spores
is formed. The disorganization of the walls of the mother

POPES OI

DWMUHELLLLL Ey LLM AAI VA SH
_esseerg OTN
ae Lede WAS

pre SEPERENO NTS TPS EA 4 y

Metin

DOP DEON

C
{
=

| c

Fig. 127. The ostrich fern (Onoclea struthiopteris), showing differentiation of foliage
leaf (a) and sporophyll (4).—After Marion SATTERLEE.

cells sets the spores free in the cavity of the sporangium,
and ready for discharge.

Fie. 128. The sensitive fern (Onoclea sensibilis), showing differentiation of foliage
leayes and sporophylls.—From ‘“ Field, Forest, and Wayside Flowers.”

PTERIDOPHYTES 149

Among the Bryophytes the sporogenous tissue appears
very early in the development of the sporogonium, the pro-
duction of spores being its only function ; also there is a

Fie. 129. A moonwort (Botrychi-
um), showing the leaf differen-
tiated into foliage and sporophyll
branches.—After STRASBURGER.

28

Fie. 130, The adder’s tongue (Ophioglossum
vulgatum), showing two leaves, each
with a foliage branch anda much longer
sporophyll branch.—After Marion Sat-
TERLEE,

150 PLANT STRUCTURES

tendency to restrict the sporogenous tissue and increase the
sterile tissue. It will be observed that with the introduc-
tion of the leafy sporophyte among the Pteridophytes the
sporangia appear much later in its development, sometimes
not appearing for several years, as though they are of

Fic. 131. A series showing the dchiscence of a fern sporangium, the rupture of the
wall, the straightening and bending back of the annulus, and the recoil.—After
ATKINSON,

secondary importance as compared with chlorophyll work ;
and that the sporogenous tissue is far more restricted, the
sporangia forming a very small part of the bulk of the
sporophyte body.

PTERIDOPHYTES 151

81. Heterospory.—This phenomenon appears first among
Pteridophytes, but it is not characteristic of them, being en-
tirely absent from the true Ferns, which far outnumber all
other Pteridophytes. Its chief interest lies in the fact that
it is universal among the Spermatophytes, and that it rep-
resents the change which leads to the appearance of that
high group. It is impossible to understand the greatest
group of plants, therefore, without knowing something
about heterospory. As it begins in simple fashion among
Pteridophytes, and is probably the greatest contribution
they have made to the evolution of the plant kingdom,
unless it be the leafy sporophyte, it is best explained here.

In the ordinary Ferns all the spores in the sporangia
are alike, and when they germinate each spore produces a
prothallium upon which both antheridia and archegonia
appear. It has been remarked, however, that some pro-
thallia are dicecious—that is, some bear only antheridia
and others bear only archegonia. In this case it is evident
that the spores in the sporangium, although they may ap-
pear alike, produce different kinds of prothallia, which
may be called male and female, as each is distinguished by
the sex organ which it produces. As archegonia are only
produced by well-nourished prothallia, it seems fair to sup-
pose that the larger spores will produce female prothallia,
and the smaller ones male prothallia.

This condition of things seems to have developed finally
into a permanent and decided difference in the size of the
spores, some being quite small and others relatively large,
the small ones producing male gametophytes (prothallia,
with antheridia), and the large ones female gametophytes
(prothallia with archegonia). When asexual spores differ
thus permanently in size, and give rise to gametophytes of
different sexes, we have the condition called heterospory
(‘‘spores different’), and such plants are called heterospo-
rous (Fig.139). In contrast with heterosporous plants, those
in which the asexual spores appear alike are called homos-

152 PLANT STRUCTURES

porous, or sometimes tsosporous, both terms meaning
‘spores similar.” The corresponding noun form is homos-
pory or isospory. Bryophytes and most Pteridophytes are
homosporous, while some Pteridophytes and all Spermato-
phytes are heterosporous.

It is convenient to distinguish by suitable names the
two kinds of asexual spores produced by the sporangia of
heterosporous plants (Fig. 139). The large ones are called
megaspores, or by some writers macrospores, both terms
meaning “large spores”; the small ones are called micro-
spores, or **small spores.” It should be remembered that
megaspores always produce female gametophytes, and mi-
crospores male gametophytes.

This differentiation does not end with the spores, but
soon involves the sporangia (Fig. 139). Some sporangia
produce only megaspores, and are called megasporangiu ;
others produce only microspores, and are called microspo-
rangia. It is important to note that while microsporangia
usually produce numerous microspores, the megasporangia
produce much fewer megaspores, the tendency being to
diminish the number and increase the size, until finally
there are megasporangia which produce but a single large
megaspore.

The differentiation goes still further. If the sporangia
are born upon sporophylls, the sporophylls themselves may
differentiate, some bearing only megasporangia, and others
only microsporangia, the former being called megasporo-
phylls, the latter microsporophylls. In such a case the
sequence is as follows: megasporophylls produce megaspo-
rangia, which produce megaspores, which in germination
produce the female gametophytes (prothallia with archego-
nia); while the microsporophylls produce microsporangia,
which produce microspores, which in germination produce
male gametophytes (prothallia with antheridia).

A formula may indicate the life history of a heteros-
porous plant. The formula of homosporous plants with

PTERIDOPHYTES 153

alternation of generations (Bryophytes and most Pterido-
phytes) was given as follows (§ 62) :
Gx > 0—S—o—G==8 > o—S—o— G23 > 0—n, ete.

In the case of heterosporous plants (some Pteridophytes
and all Spermatophytes) it would be modified as follows :

G_-0 > 0S §—8 > 0- AGT i=3 > 04, ete.

In this case two gametophytes are involved, one pro-
ducing a sperm, the other an egg, which fuse and form the
oospore, which in germination produces the sporophyte,
which produces two kinds of asexual spores (megaspores
and microspores), which in germination produce the two
gametophytes again.

One additional fact connected with heterospory should
be mentioned, and that is the great reduction of the gam-
etophyte. In the homosporous ferns the spore develops
a small but free and independent prothallium which pro-
duces both sex organs. When in heterosporous plants this
work of producing sex organs is divided between two gam-
etophytes they become very much reduced in size and lose
their freedom and independence. They are so small that
they do not escape entirely, if at all, from the embrace of
the spores which produce them, and are mainly dependent
for their nourishment upon the food stored up in the spores
(Figs. 140, 141). As the spore is produced by the sporo-
phyte, heterospory brings about a condition in which the
gametophyte is dependent upon the sporophyte, an exact
reversal of the condition in Bryophytes.

The relative importance of the gametophyte and the
sporophyte throughout the plant kingdom may be roughly
indicated by the accompanying diagram, in which the

c Ss

shaded part of the parallelogram represents the gameto-
phyte and the unshaded part the sporophyte. Among the

154 PLANT STRUCTURES

lowest plants the gametophyte is represented by the whole
plant structure. When the sporophyte first appears it is
dependent upon the gametophyte (some Thallophytes and
the Bryophytes), and is relatively inconspicuous. Later
the sporophyte becomes independent (most Pteridophytes),
the gametophyte being relatively inconspicuous. Finally
(heterosporous Pteridophytes) the gametophyte becomes
dependent upon the sporophyte, and in Spermatophytes is
so inconspicuous and concealed that it is only observed by
means of laboratory appliances, while the sporophyte is the
whole plant of ordinary observation.

CHAPTER X

THE GREAT GROUPS OF PTERIDOPHYTES

82. The great groups—At least three independent lines
of Pteridophytes are recognized: (1) filicales (Ferns),
(2) Equisetales (Scouring rushes, Horsetails), and (3) Ly-
copodiales (Club-mosses). The Ferns are much the most
abundant, the Club-mosses are represented by a few hun-
dred forms, while the Horsetails include only about twenty-
five species. These three great groups are so unlike that
they hardly seem to belong together in the same division
of the plant kingdom.

FrnicaLes (/erns)

83. General characters—The Ferns were used in the
preceding chapter as types of Pteridophytes, so that little
need be added. They well deserve to stand as types, as
they contain about four thousand of the four thousand five
hundred species belonging to Pteridophytes. Although
found in considerable numbers in temperate regions, their
chief display is in the tropics, where they form a striking
and characteristic feature of the vegetation. In the trop-
ics not only are great masses of the low forms to be seen,
from those with delicate and filmy moss like leaves to those
with huge leaves, but also tree forms with cylindrical
trunks encased by the rough remnants of fallen leaves and
sometimes rising to a height of thirty-five to forty-five
feet, with a great crown of leaves fifteen to twenty feet
long (Fig. 120).

155

‘TITMAIVO
—"(punru
2Uojhv)/) DpunuseE) surdj Jo
yueq vy"
EE OL

THE GREAT GROUPS OF PTERIDOPHYTES 157

There are also epiphytic forms (air plants)—that is,
those which perch “upon other plants” but derive no
nourishment from them (Fig. 112). This habit belongs
chiefly to the warm and moist tropics, where the plants
can absorb sufficient moisture from the air without send-
ing roots into the soil. In this way many of the tropical
ferns are found growing upon living and dead trees and
other plants. In the temperate regions the chief epi-
phytes are Lichens, Liverworts, and Mosses, the Ferns be-
ing chiefly found in moist woods and ravines (Fig. 132),
although a number grow in comparatively dry and exposed
situations, sometimes covering extensive areas, as the com-
mon brake (Péeris) (Fig. 125).

The Filicales differ from the other groups of Pterido-
phytes chiefly in having few large leaves, which do chloro-
phyll work and bear sporangia. In a few of them there isa
differentiation of functions in foliage branches and sporo-
phyll branches (Figs. 127-180), but even this is excep-
tional. Another distinction is that the stems are un-
branched.

84. Origin of sporangia—An important feature in the
Ferns is the origin of the sporangia. In some of them a
sporangium is developed from a single epidermal cell of
the leaf, and is an entirely superficial and generally stalked
affair (Fig. 118, 5) ; in others the sporangium in its devel-
opment involves several epidermal and deeper cells of the
leaf, and is more or less of an imbedded affair. In the first
case the ferns are said to be leptosporangiate ; in the sec-
ond case they are eusporangiate.

The leptosporangiate Ferns are overwhelmingly abun-
dant as compared with the Eusporangiates. Back in the
Coal-measures, however, there was an abundant fern vege-
tation which was probably all eusporangiate. The Lep-
tosporangiates seem to be the modern Ferns, the once
abundant Eusporangiates being represented now in the
temperate regions only by such forms as moonwort (Bo-

158 PLANT STRUCTURES

trychium) (Fig. 129) and adder’s tongue (Ophioglossum)
(Fig. 130). It is important to note, however, that the
Horsetails and Club-mosses are Eusporangiates, as well as
all the Seed-plants.

Another small but interesting group of Ferns includes
the ‘‘ Water-ferns,” floating forms or sometimes on muddy
flats. The common Jursilia may be taken as a type (Fig.
133). The slender creeping stem
sends down numerous roots into
the mucky soil, and at intervals
gives rise to a comparatively large
leaf. This leaf has a long erect
petiole and a blade of four spread-

Fig. 133.—A water-fern (Marsilia), Fie. 184, One of the floating water-ferns (Sa?-

showing horizontal stem, with vinia), showing side view (4) and view from
descending roots, and ascend- above (B). The dangling root-like processes
ing leaves; a, a young leaf are the modified submerged leaves. In A,
showing circinate vernation ; near the top of the cluster of submerged
8,8, 8porophyl]l branches (‘‘spo- leaves, some sporophyll branches (‘ sporo-
rocarps”"’).—After BIscHorr. carps’’) may be seen.—After BiscHorF.

ing wedge-shaped leaflets like a “ four-leaved clover."’ The
dichotomous venation and circinate vernation at once sug-
gest the fern alliance. From near the base of the petiole

THE GREAT GROUPS OF PTERIDOPHYTES 159

another leaf branch arises, in which the blade is modified
as a sporophyll. In this case the sporophyll incloses the
sporangia and becomes hard and nut-like. Another com-
mon form is the floating Salvinia (Fig. 134). The chief
interest lies in the fact that the water-ferns are heteros-
porous. As they are leptosporangiate they are thought
to have been derived from the ordinary leptosporangiate
Ferns, which are homosporous.

Three fern groups are thus outlined: (1) homosporous-
eusporangiate forms, now almost extinct ; (2) homosporous-
leptosporangiate forms, the great overwhelming modern
group, not only of Filicales but also of Pteridophytes, well
called true Ferns, and thought to be derived from the pre-
ceding group; and (3) heterosporous-leptosporangiate
forms, the water-ferns, thought to be derived from the pre-
ceding group.

EQuiseraues (Horsetatls or Scouring rushes)

85. General characters—The twenty-five forms now rep-
resenting this great group belong to a single genus (Aquwise-
tum, meaning ‘‘horsetail”), but they are but the linger-
ing remnants of an abundant flora which lived in the time
of the Coal-measures, and helped to form the forest vegeta-
tion. The living forms are small and inconspicuous, but
very characteristic in appearance. They grow in moist or
dry places, sometimes in great abundance (Fig. 135).

The stem is slender and conspicuously jointed, the joints
separating easily; it is also green and fluted with small
longitudinal ridges ; and there is such an abundant deposit
of silica in the epidermis that the plants feel rough. This
last property suggested its former use in scouring, and its
name ‘‘scouring rush.” At each joint is a sheath of minute
leaves, more or less coalesced, the individual leaves some-
times being indicated only by minute teeth. This arrange-
ment of leaves in a circle about the joint is called the cyclic

Fie. 135. Equisetum arvense, a common horsetail: 1, three fertile shoots rising from
the dorsiventral stem, showing the cycles of coalesced scale-leaves at the joints
and the terminal strobili with numerous sporophylls, that at a@ being mature; 2,
a sterile shoot from the same stem, showing branching; 3, a single peltate sporo-
phyll bearing sporangia; 4, view of sporophyll from beneath, show ing dehiscence
of sporangia; 5, 6, 7, spores, showing the unwinding of the outer coat, which aids
in dispersal.—After WossIDLo,

THE GREAT GROUPS OF PTERIDOPIHYTES 161

arrangement, or sometimes the whorled arrangement, each
such set of leaves being called a cycle or a whorl. These
leaves contain no chlorophyll and have evidently abandoned
chlorophyll work, which is carried on by the green stem.
Such leaves are known as scales, to distinguish them from
foliage leaves. The stem is either simple or profusely
branched (Fig. 135).

st. The strobilus—One of the distinguishing characters
of the group is that chlorophyll-work and spore-formation
are completely differentiated. Although the foliage leaves

Fie. 136. Dicecious gametophytes of guisetum: A. the female gametophyte, show-
ing branching, rhizoids. and an archegonium (ar); B, the male gametophyte,
showing several antheridia ( 2 ).—After CAMPBELL.

are reduced to scales, and the chlorophyll-work is done by
the stem, there are well-organized sporophylls. The sporo-
phylls are grouped close together at the end of the stem in
a compact conical cluster which is called a strodilus, the
Latin name for “pine cone,” which this cluster of sporo-
phylls resembles (Fig. 135).

Each sporophyll consists of a stalk-like portion and a
shield-like (peltate) top. Beneath the shield hang the

162 PLANT STRUCTURES

sporangia, which produce spores of but one kind, hence
these plants are homosporous ; and as the sporangia origi-
nate in eusporangiate fashion, Lyuisetum has the homospo-
rous-eusporangiate combination shown by one of the Fern
groups. It is interesting to know, however, that some of
the ancient, more highly organized members of this group
were heterosporous, and that the present forms have
dicecious gametophytes (Fig. 136).

LycopopiaLeEs (('Jub-mosses)

87. General characters—This group is now represented
by about five hundred species, most of which belong to
the two genera Lycopodium and Selaginella, the latter
being much the larger genus. The plants have slender,
branching, prostrate, or erect stems completely clothed
with small foliage leaves, having a general moss-like
appearance (Fig. 137). Often the erect branches are
terminated by conspicuous conical or cylindrical strobili,
which are the ‘‘ clubs” that enter into the name ‘ Club-
mosses.” There is also a certain kind of resemblance
to miniature pines, so that the name ‘‘ Ground-pines” is
sometimes used.

Lycopodiales were once much more abundant than now,
and more highly organized, forming a conspicuous part of
the forest vegetation of the Coal-measures.

One of the distinguishing marks of the group is that the
sperm does not resemble that of the other Pteridophytes,
but is of the Bryophyte type (Fig. 140, 7’). That is, it
consists of a small body with two cilia, instead of a large
spirally coiled body with many cilia. Another distinguish-
ing character is that there is but a single sporangium pro-
duced by each sporophyll (Fig. 137). This is in marked
contrast with the Filicales, whose leaves bear very numer-
ous sporangia, and with the Equisetales, whose sporophylls
bear several sporangia.

THE GREAT GROUPS OF PTERIDOPHYTES 163

Fic. 187. A common club-moss (Lycopodium clavatum): 1, the whole plant, showing
horizontal stem giving rise to roots and to erect branches bearing strobili; 2, a
single sporophyll with its sporanginm; 3, spores, much magnified.—After Wos-
SIDLO.

88. Lycopodium.—This genus contains fewer forms than
the other, but they are larger and coarser and more charac-
teristic of the temperate regions, being the ordinary Club-
mosses (Fig. 137). They also more commonly display
conspicuous and distinct strobili, although there is every

164 PLANT STRUCTURES

gradation between ordinary foliage leaves and distinct
sporophylls.

The sporangia are borne either by distinct sporophyils
or by the ordinary foliage leaves near the summit of the
stem. At the base of each of these leaves, or sporophylls,
on the upper side, is a single sporangium (Fig. 137). The
sporangia are eusporangiate in origin, and as the spores are
all alike, Lycopodium has the same homosporous-eusporan-
giate combination noted in Equisetales and in one of the
groups of Filicales.

89. Selaginella—This large genus contains the smaller,
more delicate Club-mosses, often being called the “ little
Club-mosses.” They are especially displayed in the trop-

Fie. 188, Selaginelia, showing general spray-like habit, and dangling leafless stems
which strike root (rhizophores).—From “ Plant Relations.”

ics, and are common in greenhouses as delicate, mossy,
decorative plants (Fig. 138). In general the sporophylls
are not different from the ordinary leaves (Fig. 139), but
sometimes they are modified, though not so distinct as in
certain species of Lycopodium.

THE GREAT GROUPS OF PTERIDOPHYTES 165

The solitary sporangium appears in the ails (upper
angles formed by the leaves with the stem) of the leaves
and sporophylls, but arise from the stem instead of the

Fic. 189. Selaginella Martensii; A, branch bearing strobili; B, a microsporophy]]
with a microsporangium, showing microspores through a rupture in the wall; C,
a megasporophyll with a megasporangium; J, megaspores; Z, microspores.—
CALDWELL.

29

166 PLANT STRUCTURES

leaf (Fig. 139). This is important as showing that sporan-
gia may be produced by stems as well as by leaves, those
being produced by leaves being called foliar, and those by
stem cauline.

The most important fact in connection with Selaginella,
however, is that it is heterosporous. Megasporangia, each
usually containing but four megaspores, are found in the
axils of a few of the lower leaves of the strobilus, and more
numerous microsporangia occur in the upper axils, con-
taining very many microspores (Fig. 139). The character
of the gametophytes of heterosporous Pteridophytes may
be well illustrated by those of Selaginella.

The microspore germinates and forms a male gameto-
phyte so small that it is entirely included within the spore

Fig. 140 Male gametophyte of Selaginella; in each case p is the prothallial cell, w
the wall cells of the antheridium, s the sperm tissue: /, the bicilfate sperms.—
After BELAJEFF.

wall (Fig. 140). A single small cell is all that represents
the ordinary cells of the prothallium, while all the rest is
an antheridium, consisting of a wall of a few cells sur-
rounding numerous sperm mother cells. In the presence

THE GREAT GROUPS OF PTERIDOPHYTES 167

of water the antheridium wall breaks down, as also do the
walls of the mother cells, and the small biciliate sperms
are set free.

The much larger megaspores germinate and become
filled with a mass of numerous nutritive cells, representing
the ordinary cells of a prothallium (Fig. 141). The spore
wall is broken by this growing prothallium, a part of which
thus protrudes and becomes exposed, although the main
part of it is still invested by the old megaspore wall. In
this exposed portion
of the female gameto-
phyte the archegonia
appear, and thus be-
come accessible to the
sperms. In the case
of Isoetes (see § 90)
the reduction of the
female gametophyte is
even greater, as it does
not project from the
megaspore wall at all,
and the archegonia
are made accessible
through cracks in the
wall immediately over

Fie. 141. Female gametophyte of a Selaginella:
spm, wall of megaspore ; pr, gametophyte;

them. ar, an archegonium; emd, and eh, em-
The embryo of Se- bryo sporophytes ; «f, suspensors ; the gam-
5 a a etophyte bas developed a few rhizoids,—
laginella is also impor- ‘After PrnkeR:

tant to consider. Be-

ginning its development in the venter of the archegonium,
it first hes upon the exposed margin of the prothallium,
while the mass of nutritive cells lie deep within the mega-
spore (Fig. 141, emd,, emb,). It first develops an elongated
cell, or row of cells, which thrusts the embryo cell deeper
among the nutritive cells. This cell or row of cells, formed
by the embryo to place the real embryo cell in better rela-

168 PLANT STRUCTURES

tion to its food supply, is called the suspensor, and is a
temporary organ of the embryo (Figs. 141, 142, et). At
the end of the suspensor the real embryo develops, and
when its regions become organized it shows the following
parts: (1) a large foot buried among the nutritive cells of
the prothallium and absorbing nourishment; (2) a root
stretching out toward the substratum ; (3) a stem extend-

C3 eae,
Siisttingr nme eee
OT LL

oe, a ee r

Fig. 142. Embryo of Selaginella removed from the gametophyte, showing suspensor
(et), root-tip (w), foot (f), cotyledons (0/), stem-tip (s¢), and ligules (/ég).—After
PFEFFER.

ing in the other direction, and bearing just behind its tip
(4) a pair of opposite leaves (cotyledons) (Fig. 142).

As the sporangia of Selayinella are eusporangiate, this
genus has the heterosporous-eusporangiate combination—a
combination not mentioned heretofore, and being of special
interest as it is the combination which belongs to all the
Spermatophytes. For this and other reasons, Selaginella
is one of the Pteridophyte forms which has attracted
special attention, as possibly representing one of the an-
cestral forms of the Seed-plants.

THE GREAT GRUUPS OF PTERIDOPHYTES 169

90. Isoetes—This little group of aquatic plants, known
as “‘quillworts,” is very puzzling as to its relationships
among Pteridophytes. By some it is put with the Ferns,
forming a distinct division of Filicales ; by others it is put

\

!

TA
cr i i
e '

AS

I
fe RAYA
Fig. 143. A common quillwort (Isoetes lacus- Fie. 144. Sperm of Isoetes, show-
tris), showing cluster of roots dichoto- ing spiral body and seven long
mously branching, and cluster of leaves cilia arising from the beak.—
each enlarged at base and inclosing a sin- After BELAJEFF.

gle sporangium.—After ScHENCK.

with the Club-mosses, and is associated with Selayinella.
It resembles a bunch of fine grass growing in shoal water
or in mud, but the leaves enlarge at the base and overlap
one another and the very short tuberous stem (Fig. 143).
Within each enlarged leaf base a single sporangium is
formed, and the cluster contains both megasporangia and
microsporangia. The sporangia are eusporangiate, and
therefore Jscetes shares with Selaginella the distinction of

170 PLANT STRUCTURES

having the heterosporous-eusporangiate combination, which
is a feature of the Seed-plants.

The embryo is also peculiar, and is so suggestive of the
embryo of the Monocotyledons (see § 114) among Seed-
plants that some regard it as possibly representing the
ancestral forms of that group of Spermatophytes. The
peculiarity lies in the fact that at one end of the axis of the
embryo is a root, and at the other the first leaf (cotyledon),
while the stem tip rises as a lateral outgrowth. This is
exactly the distinctive feature of the embryo of Monocoty-
ledons.

The greatest obstacle in the way of associating these
quillworts with the Club-mosses is the fact that their sperms
are of the large and spirally coiled multiciliate type which
belongs to Filicales and Equisetales (Fig. 144), and not at
all the small bicihate type which characterizes the Club-
mosses (Fig. 140). To sum up, the short unbranched stem
with comparatively few large leaves, and the coiled multi-
ciliate sperm, suggest Filicales; while the solitary spo-
rangia and the heterosporous-eusporangiate character sug-
gest Selaginella.

CHAPTER XI
SPERMATOPHYTES: GYMNOSPERMS

91. Summary from Pteridophytes.—In considering the
important contributions of Pteridophytes to the evolution
of the plant kingdom the following seem worthy of note :

(1) Prominence of sporophyte and development of vuscu-
lar system.—This prominence is associated with the display
of leaves for chlorophyll work, and the leaves necessitate
the work of conduction, which is arranged for by the vas-
cular system. This fact is true of the whole group.

(2) Differentiation of sporuphylls.—The appearance of
sporophylls as distinct from foliage leaves, and their or-
ganization into the cluster known as the strobilus, are facts
of prime importance. This differentiation appears more or
less in all the great groups, but the strobilus is distinct only
in Horsetails and Club-mosses.

(3) Introduction of heterospory and reduction of gameto-
phytes.—Heterospory appears independently in all of the
three great groups—in the water-ferns among the Fili-
cales, in the ancient horsetails among the Equisetales, and
in Seluginella and Jsoetes among Lycopodiales. All the
other Pteridophytes, and therefore the great majority of
them, are homosporous. The importance of the appear-
ance of heterospory lies in the fact that it leads to the
development of Spermatophytes, and associated with it is
a great reduction of the gametophytes, which project little,
if at all, from the spores which produce them.

92. Summary of the four groups—It may be well in this

connection to give certain prominent characters which will
171

172 PLANT STRUCTURES

serve to distinguish the four great groups of plants. It
must not be supposed that these are the only characters,
or even the most important ones in every case, but they
are convenient for our purpose. Two characters are given
for each of the first three groups—one a positive character
which belongs to it, the other a negative character which
distinguishes it from the group above, and becomes the
positive character of that group.

(1) Thallophytes.—Thallus body, but no archegonia.

(2) Bryophytes.—Archegonia, but no vascular system.

(3) Pteridephytes.—Vascular system, but no seeds.

(+) Spermatophytes.—Seeds.

93. General characters of Spermatophytes.—This is the
greatest group of plants in rank and in display. So con-
spicuous are they, and so much do they enter into our
experience. that they have often been studied as ‘‘ botany,”
to the exclusion of the other groups. The lower groups
are not meiely necessary to fill out any general view of the
plant kingdom, but they are absolutely essential to an
understanding of the structures of the highest group.

This great dominant group has received a variety of
names. Sometimes they are called .{xthophytes, meaning
“Flowering plants,” with the idea that they are distin-
guished by the production of “flowers.” A flower is diffi-
cult to define, but in the popular sense all Spermatophytes
do not produce flowers, while in another sense the strobilus
of Pteridophytes is a flower. Hence the flower does not
accurately limit the group, and the name Anthophytes is
not in general use. Much more commonly the group is
called Phanerogams (sometimes corrupted into Phenogams
or even Phenogams), meaning “evident sexual reproduc-
tion.” At the time this name was proposed all the other
groups were called Crypfogams, meaning “hidden sexual
reproduction.” It is a curious fact that the names ought
to have been reversed, for sexual reproduction is much more
evident in Cryptogams than in Phanerogams, the mistake

SPERMATOPHYTES: GYMNOSPERMS 1%3

arising from the fact that what were supposed to be sexual
organs in Phanerogams have proved not to be such. The
name Phanerogam, therefore, is being generally abandoned ;
but the name Cryptogam is a useful one when the lower
groups are to be referred to; and the Pteridophytes are
still very frequently called the Vascular Cryptogams. The
most distinguishing mark of the group seems to be the
production of seeds, and hence the name Spermatophytes,
or ** Seed-plants,” is coming into general use.

The seed can be better defined after its development
has been described, but it results from the fact that in this
group the single megaspore is never discharged from its
megasporangium, but germinates just where it is devel-
oped. The great fact connected with the group, therefore,
is the retention of the megaspore, which results in a seed.
The full meaning of this will appear later.

There are two very independent lines of Seed-plants,
the Gymnosperms and the Angiosperms. The first name
means ‘‘ naked seeds,” referring to the fact that the seeds
are always exposed; the second means ‘‘inclosed seeds,”
as the seeds are inclosed in a seed vessel.

GYMNOSPERMS

94. General characters——The most familiar Gymnosperms
in temperate regions are the pines, spruces, hemlocks,
cedars, etc., the group so commonly called ‘‘ evergreens.”
It is an ancient tree group, for its representatives were
associated with the giant club-mosses and horsetails in
the forest vegetation of the Coal-measures. Only about
four hundred species exist to-day as a remnant of its for-
mer display, although the pines still form extensive forests.
The group is so diversified in its structure that all forms
can not be included in a single description. The common
pine (Pinus), therefore, will be taken as a type, to show
the general Gymnosperm character.

174 PLANT STRUCTURES

95, The plant body.—The great body of the plant, often
forming a large tree, is the sporophyte; in fact, the
gametophytes are not visible to ordinary observation. It
should be remembered that the sporophyte is distinctly a
sexless generation, and that it develops no sex organs.
This great sporophyte body is elaborately organized for
nutritive work, with its roots, stems, and leaves. These
organs are very complex in structure, being made up of
various tissue systems that are organized for special kinds
of work. The leaves are the most variable organs, being
differentiated into three distinct kinds—(1) foliage leaves,
(2) scales, and (3) sporophylls.

96. Sporophylls—The sporophylls are leaves set apart to
produce sporangia, and in the pine they are arranged in
a strobilus, as in the Horsetails and Club-mosses. As
the group is heterosporous, however, there are two kinds
of sporophylls and two kinds of strobili. One kind of
strobilus is made up of megasporophylls bearing mega-
sporangia ; the other is made up of microsporophylls bear-
ing microsporangia. These strobili are often spoken of as
the “‘ flowers” of the pine, but if these are flowers, so are
the strobili of Horsetails and Club-mosses.

97. Microsporophylls—In the pines the strobilus com-
posed of microsporophylls is comparatively small (Figs.
145, /, 164). Each sporophyll is like a scale leaf, is nar-
rowed at the base, and upon the lower surface are borne
two prominent sporangia, which of course are microspo-
rangia, and contain microspores (Fig. 146).

These structures of Need-plants all received names
before they were identified with the corresponding struc-
tures of the lower groups. The microsporophyll was called a
stumen, the microsporangia pollen-saes, and the microspores
pollen grains, or simply pollen, These names are still very
convenient to use in connection with the Spermatophytes,
but it should be remembered that they are simply other
names for structures found in the lower groups.

Fie. 145.

Pinus Laricio, showing tip of branch bearing needle-leaves, scale-leaves,
and cones (strobili): @, very young carpellate cones. at time of pollination, borne
at tip of the young shoot upon which new leaves are appearing; 5, carpellate cones
one year old; ¢, carpellate cones two years old, the scales spreading and shedding
the seeds; d, young shoot bearing a cluster of staminate cones.—CaLDWELL.

176 PLANT STRUCTURES

The strobilus composed of microsporophylls may be
called the staminate strobilus—that is, one composed of
stamens; it is often called the staminate cone, “cone”
being the English translation of the word “strobilus.”
Frequently the staminate cone is spoken of as the ‘‘ male
cone,” as it was once supposed that the stamen is the

Fic. 146. Staminate cone (strobilus) of pine (Pinus): A, section of cone, showing
microsporophylls (stamens) bearing microsporangia; B, longitudinal section of a
single stamen, showing the large sporangium beneath ; (C, cross-section of a sta-
men, showing the two sporangia; D, a single microspore (pollen grain) much en-
larged, showing the two wings, and a male gametophyte of two cells, the lower
and larger (wall cell) developing the pollen tube, the upper and smaller (genera-
tive cell) giving rise to the sperms.—After SciimMPER.

male organ. This name should, of course, be abandoned,
as the stamen is now known to be a microsporophyll, which
is an organ produced by the sporophyte, which never pro-
duces sex organs. It should be borne distinctly in mind
that the stamen is not a sex organ, for the literature of
botany is full of this old assumption, and the beginner is in

SPERMATOPHYTES: GYMNOSPERMS 7%

danger of becoming confused and of forgetting that pollen
grains are asexual spores.

98. Megasporophylls—The strobili composed of mega-
sporophylls become much larger than the others, forming

Fig. 147. Pinus sylvestris, showing mature cone partly sectioned, and showing car-
pels (sg, sg}, sg?) with seeds in their axils (g), in which the embryos (e771) may be
distinguished; 1, a young carpel with two megaspcrangia; B, an old carpel with
mature seeds (ch), the micropyle being below (J/).—After BEssEY.

the well-known cones so characteristic of pines and their
allies (Figs. 145, a, 6, c, 163). Each sporophyll is some-
what leaf-like, and at its base upon the upper side are two
megasporangia (Fig. 147). It is these sporangia which are
peculiar in each producing and retaining a solitary large
megaspore. This megaspore resembles a sac-like cavity in

178 PLANT STRUCTURES

the body of the sporangium (Fig. 148, 7), and was at first
not recognized as being a spore.

These structures had also received names before they
were identified with the corresponding structures of the
lower groups. The megasporophyll was called a carpel,
the megasporangia ovules, and the megaspore an embryo-
sac, because the young embryo was observed to develop
within it (Fig. 147, em).

The strobilus of megasporophylls, therefore, may be
ealled the carpellate strobilus or curpellate cone. As the
carpel enters into the organization of a structure known as
the pistil, to be described later, the cone is often called
the pistillate cone, As the staminate cone is sometimes
wrongly called a ‘*male cone,” so the carpellate cone is
wrongly called a ‘‘female cone.” the
old idea being that the carpel with
its ovules represented the female scx
organ.

The structure of the megaspo-
rangium, or ovule, must be known.
The main body is the nucellus (Figs.
148, ¢, 149, nc); this sends out from
near its base an outer membrane
(ufegument) which is distinct above
(Figs. 148 6, 149 7), covering the main
part of the nucellus and projecting
seetie: Beae arate beyond its apex as a prominent neck,

carpel structures of pine, the passage through which to the apex
showin the heavy seale of the nucellus is called the micropyle
(A) which Dears the a = A
ovule CB). inwhich ame (Little. gate) (Mie. 44s; @). Oeus
seen the micropyle «@, {rally placed within the body of the
integument (/), nncellus Fi :
(©), embryo sue or megn. TUCellus is the conspicuous cavity
spore ().—CarpwetL. called the embryo-sac (Fig. 148, «/),
in reality the retained megaspore.
The relations between integument, micropyle, nucellus,
and embryo-sac should be kept clearly in mind. In the

SPERMATOPHYTES: GYMNOSPERMS 179

pine the micropyle is directed downward, toward the base
of the sporophyll (Figs. 147, 148).

99. Female gametophyte—The female gametophyte is
always produced by the germination of a megaspore, and

therefore it should be
produced by the sc-
called embryo-sae with-
in the ovule. This im-
bedded megaspore ger-
minates, just as does
the megaspore of v-
laginella or Isoetes, by
cell division becoming
filled with a compact
mass of nutritive tissue
representing the ordi-
nary cells of the female
prothallium (Fig. 149,
e). This prothallium
naturally does not
protrude beyond the
boundary of the mega-
spore wall, beg com-
pletely surrounded by
the tissues of the
sporangium. It must
be evident that this
gametophyte is abso-
lutely dependent upon
the sporophyte for its
nutrition, and remains
not merely attached to
it, but is actually im-
bedded within its tis-

Fie. 149. Diagrammatic section through ovule
(megasporangium) of spruce (Picea), showing
integument (i), nucellus (7c), endosperm or
female gametophyte (e) which fills the large
megaspore imbedded in the nucellus, two
archegonia (@) with short neck (¢) and. venter
containing the egg (0), and position of ger-
minating pollen grains or microspores (p)
whose tubes (f) penetrate the nucellus tissue
and reach the archegonia,—Aftet “i HIIPER.

sues like an internal parasite. So conspicuous a tissue
within the ovule, as well as in the seed into which the

180 PLANT STRUCTURES

ovule develops, did not escape early attention, and it was
called endosperm, meaning ‘‘ within the seed.” The endo-
sperm of Gymnosperms, therefore, is the female gameto-
phyte.

At the margin of the endosperm nearest the micropyle
regular flask-shaped archegonia are developed (Fig. 149, a),
making it sure that the endosperm is a female gameto-
phyte. It is evident that the necks of these archegonia
(Fig. 149, c) are shut away from the approach of sperms by
swimming, and that some new method of approach must be
developed.

100. Male gametophyte.—The microspores are developed
in the sporangium in the usual tetrad fashion, and are pro-
duced and scattered in very great abundance. It will be
remembered that the male gametophyte developed by the
microspore of Selaginella is contained entirely within the
spore, and consists of a single ordinary prothallial cell
and one antheridium (see § 89). In the pine it is no bet-
ter developed. One or two small cells appear, which may
be regarded as representing prothallial cells, while the rest
of the gametophyte seems to be a single antheridium (Fig.
146, D). At first this antheridium seems to consist of a
large cell called the wal? cell, and a small one called the
generative cell. Sooner or later the generative cell divides
and forms two small cells, one of which divides again and
forms two cells called mule cells. which seem to represent
the sperm mother cells of lower plants. The three active
cells of the completed antheridium, therefore, are the wall
cell, with a prominent nucleus, and two small male cells
which are free in the large wall cell.

These sperm mother cells (male cells) do not form
sperms within them, as there is no water connection be-
tween them and the archegonia, and a new method of
transfer is provided. This is done by the wall cell, which
develops a tube, known as the podlen-fube. Into this tube
the male cells enter, and as it penetrates among the cells

SPERMATOPHYTES: GYMNOSPERMS 181

which shut off the archegonia it carries the male cells
along, and so they are brought to the archegonia (Fig. 150).

Fic. 150. Tip of pollen tube of pine, Fic. 151. Pollen tube passing through the

showing the two male cells (4, B), neck of an archegonium of spruce (Picea),
two nuclei ((’) which accompany and containing near its tip the two male
them, and the numerous food nuclei, which are to be discharged into the
granules (D): the tip of the tube egg whose cytoplasm the tube is just en-
is just about to enter the neck of tering.—After STRASBURGER.

the archegonium,—CaLDWELL.

101. Fertilization.—Before fertilization can take place
the pollen-grains (microspores) must be brought as near as
possible to the female gametophyte with its archegonia.
The spores are formed in very great abundance, are dry
and powdery, and are scattered far and wide by the wind.
In the pines and their allies the pollen-grains are winged
(Fig. 146, D), so that they are well organized for wind dis-
tribution. This transfer of pollen is called pollination, and
those plants that use the wind as an agent of transfer are
said to be anemophilous, or ‘* wind-loving.”

The pollen must reach the ovule, and to insure this it
must fall like rain. To aid in catching the falling pollen
the scale-like carpels of the cone spread apart, the pollen

grains slide down their sloping surfaces and collect in a
30

182 PLANT STRUCTURES

little drift at the bottom of each carpel, where the ovules
are found (Fig. 147, A, B). The flaring lips of the micro-
pyle roll inward and outward as they are dry or moist, and
by this motion some of the pollen-grains are caught and
pressed down upon the apex of the nucellus.

In this position the pollen-tube develops, crowds its
way among the cells of the nucellus, reaches the wall of
the embryo-sac, and penetrating that, reaches the necks
of the archegonia (Fig. 149, p, ¢); crowding into them
(Fig. 151), the tip of the tube opens, the male cells are

Fie. 152. Fertilization in spruce (Picea): B is an egg, in the tip of which a pollen
tube (p) has entered and has discharged into the cytoplasm a male nucleus (sz),
which is to unite with the egg (female) nucleus (on); C, a later stage in which the
two nuclei are uniting.—After ScHIMPER.

discharged, one male cell fuses with the egg (Fig. 152),
and fertilization is accomplished, an oospore being formed
in the venter of the archegonium.

It will be noticed that the cell which acts as a male
gamete is really the sperm mother cell, which does not
organize a sperm in the absence of a water connection.
This peculiar method of transferring the male cells by
means of a special tube developed by the antheridium is

SPERMATOPHYTES: GYMNOSPERMS 183

called siphonogamy, which means “sexual reproduction by
means of a tube.” So important is this character among
Spermatophytes that some have proposed to call the group
Siphonogams.

102. Development of the embryo—The oospore when
formed lies at the surface of the endosperm (female gameto-
phyte) nearest to the micropyle. As the endosperm is to
supply nourishment to the em-
bryo, this position is not the
most favorable. Therefore, as
in Selaginella, the oospore first
develops a suspensor, which in
pine and its allies becomes very
long and often tortuous (Fig.
153, d,s), At the tip of the
suspensor the cell or cells (em-
bryo cells) which are to develop
the embryo are carried (Fig. 153,
dA, ka), and thus become deeply
buried, about centrally placed,
in the endosperm.

Fie. 153. Embryos of pine: A,

Several suspensors may start very young embryos (ka) at the

from as many archegonia in the tips of long and contorted sus-

pensors (s); B, older embryo,

same ovule, and several embryos showing attachment to snspen-

may begin to develop, but as a sor (x), the extensive root sheath

I A d th (wh), root tip (ws), stem tip

rule only one survives, an e Go) anil eoigledons qi Aten
solitary completed embryo (Fig. STRASBURGER.

153, B) les centrally imbedded

in the endosperm (Fig. 153). The development of more
than one embryo in a megasporangium (ovule)is called
polyembryony, a phenomenon natural to Gymnosperms with
their several archegonia upon a single gametophyte.

103. The seed.—While the embryo is developing some
important changes are taking place in the ovule outside of
the endosperm. The most noteworthy is the change which
transforms the integument into a hard bony covering,

184 PLANT STRUCTURES

known as the seed coat, or testa (Fig. 153a). The devel-
opment of this testa hermetically seals the structures with-
in, further development and activity
are checked, and the living cells pass
into the resting condition. This pro-
Fie. 158. Pine seca, tected structure with its dormant cells
is the seed.

In a certain sense the seed is a transformed ovule (mega-

sporangium), but this is true only as to its outer configura-

Fra. 154. Pine seedlings, showing the long hypocotyl and the numerous cotyledons,
with the old seed case still attached.—After ATKINSON,

SPERMATOPHYTES: GYMNOSPERMS 185

tion. If the internal structures be considered it is much
more. It is made up of structures belonging to three gen-
erations, as follows: (1) The old sporophyte is represented
by seed coat and nucellus, (2) the endosperm is a gameto-
phyte, while (3) the embryo is a young sporophyte. It can
hardly be said that the seed is simple in structure, or that
any real conception of it can be obtained without approach-
ing it by way of the lower groups.

The organization of the seed checks the growth of the
embryo, and this development within the seed is known as

Fie. 155. A cycad, showing the palm-like habit. with much branched leaves and
scaly stem.—From “ Plant Relations.”

the intra-seminal development. In this condition the em-
bryo may continue for a very long time, and it is.a ques-
tion whether it is death or suspended animation. Is a seed
alive ? is not an easy question to answer, for it may be kept
in a dried-out condition for years, and then when placed
in suitable conditions awaken and put forth a living plant.

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SPERMATOPHYTES: GYMNOSPERMS 187

This ‘‘ awakening ” of the seed is spoken of as its ‘‘ ger-
mination,” but this must not be confused with the germi-
nation of a spore, which is real germination. In the case
of the seed an oospore has germinated and formed an embryo,
which stops growing for a time, and then resumes it. This
resumption of growth is not germination, but is what

Fie. 157. Tip of pollen tube of Cycas revoluta, containing the two spiral, multiciliate
sperms.—After IKENO.

happens when a seed is said to ‘‘ germinate.” This second
period of development is known as the exfra-seminal, for it
is inaugurated by the escape of the sporophyte from the
seed (Fig. 154).

104. The great groups of Gymnosperms.—There are at
least four living groups of Gymnosperms, and two or three

Fig. 158. A pine (Pinus) showing the central shaft and also the bunching of the
needle leaves toward the tips of the branches.—From “ Plant Relations.”

SPERMATOPHYTES: GYMNOSPERMS 189

extinct ones. The groups differ so widely from one an-
other in habit as to show that Gymnosperms can be very
much diversified. They are all woody forms, but they may
be trailing or straggling
shrubs, gigantic trees, or
high-climbing vines ; and
their leaves may be nee-
dle-like, broad, or ‘‘ fern-
like.” For our purpose it
will be only necessary to
define the two most prom-
inent groups.

105. Cycads, — Cycads
are tropical, fern - like
forms, with large branched
(compound) leaves. The
stem is either a columnar
shaft crowned with a ro-
sette of great branching
leaves, with the general
habit of tree-ferns and
palms (Figs. 155, 156);
or they are like great tu-
bers, crowned in the same
way. In ancient times
(the Mesozoic) they were
very abundant, forming
a conspicuous feature of
the vegetation, but now
they are represented only
by about eighty forms
scattered through both
the oriental and occiden-
tal tropics. Fie. 159. The giant redwood (Seguoia gi-

They are very fern- gantea) of California: the relative size

: J is indicated by the figure of a man stand-
like in structure as well ing at the right.—After WILL1amson.

190 PLANT STRUCTURES

as in appearance, but they produce seeds and must be
associated with Spermatophytes, and as the seed is ex-
posed they are Gymnosperms. A discovery has been made

Fie. 160. An araucarian pine (Araucaria),
showing the central shaft, and the regular
cycles of branches spreading in every direc-
tion and bearing numerous small leaves.—
From “ Plant Relations.”

recently that strikingly
emphasizes their fern-
like structure. In fer-
tilization a pollen-tube
develops, as described
for pine and its allies,
but the male cells
(sperm mother - cells)
which it contains or-
ganize sperms, and
these sperms are of
the coiled multiciliate
type (Fig. 157) charac-
teristic of all the Pter-
idophytes except Club-
mosses. This associa-
tion of the old ciliated
sperm habit with the
new pollen-tube habit
is a very interesting in-
termediate or transition
condition. It should be
said that these sperms
havebeen actually found
in but two species of
the Cycads, but there
are reasons for suppos-
ing that they may be
found in all. Another
one of the Gymnosperm
groups, represented to-
day only by the com-
monly cultivated maid-

SPERMATOPHYTES: GYMNOSPERMS 191

enhair tree (Gingko), with broad dichotomously veined
leaves, also develops multiciliate sperms.

The testa of the seed, instead of being entirely hard as
described for pine and its allies, develops in two layers, the
inner hard and bony, and the outer pulpy, making the ripe
fruit resemble a plum.

106. Conifers—This is the great modern Gymnosperm
group, and is characteristic of the temperate regions, where
it forms great forests. Some of the forms are widely dis-
tributed, as the great genus of pines (Pinus) (Fig. 158),
while some are now very much restricted, although for-
merly very widely distributed, as the gigantic redwoods
(Sequoia) of the Pacific slope (Fig. 159). The habit of
the body is quite charac-
teristic, a central shaft
extending continuously to
the very top, while the
lateral branches spread
horizontally, with dimin-
ishing length to the top,
forming a conical outline
(Figs. 160, 162). This
habit of firs, pines, etc.,

Fie. 161.—Cross-section of a needle-leaf of

gives them an appearance
very distinct from that of
other trees.

Another peculiar fea-
ture is furnished by the
characteristic ‘“‘needle-

pine, showing epidermis (¢) in which
there are sunken stomata (sp), heavy-
walled hypodermal tissue (es) which
gives rigidity, the mesophyll region (7)
in which a few resin-ducts (2) are seen,
and the central region (s¢ede) in which
two vascular bundles.are developed.—
After Sacus.

leaves,” which seem to be

poorly adapted for foliage. These leaves have small spread
of surface and very heavy protecting walls, and show
adaptation for enduring hard conditions (Fig. 161). As
they have no regular period of falling, the trees are always
clothed with them, and have been called ‘‘ evergreens.”
There are some notable exceptions to this, however, as in

tate . ieee
PEN Wola a

Hie. 162. A larch (Zaria), showing the continuous central shatt and horizontal
branches, the general outline being distinctly conical. The larch is peculiar
among Conifers in periodically shedding its leaves.—From *t Plant Relations,”

, Ce
Tal hax

SPERMATOPHYTES: GYMNOSPERMS 193

the case of the common larch or tamarack, which sheds
its leaves every season (Fig. 162). There are Conifers,
also, which do not produce needle-leaves, as in the com-
mon arbor-vite#, whose leaves consist of small closely-over-
lapping scale-like bodies
(Fig. 163).

The two types of leaf
arrangement may also be
noted. In most Conifers
the leaves are arranged
along the stem in spiral
fashion, no two leaves
being at the same level.
This is known as the spi-
ral or alternate arrange-
ment. In other forms, as
the cypresses, the leaves
are in cycles, as was men-
tioned in connection with
the Horsetails, the ar-
rangement being known
as the cyclic or whorled.

The character which
gives name to the group
is the ‘‘cone”—that is,
the prominent carpellate
cone which becomes so
conspicuous in connec- Fie. 163. Arbor-vite (Thuja), showing a

tion with the ripening of branch with scaly overlapping leaves,
and some carpellate cones (strobili).—
the seeds. These cones After EICHLER.

generally ripen dry and
hard (Figs. 145, 147, 163), but sometimes, as in junipers,
they become pulpy (Fig. 164), the whole cone forming the
so-called ‘ berry.”

There are two great groups of Conifers. One, repre-
sented by the pines, has true cones which conceal the

194 PLANT STRUCTURES

ovules, and the seeds ripen dry. The other, represented
by the yews, has exposed ovules, and the seed either ripens
fleshy or has a fleshy investment.

Fia. 164. The common juniper (.Jivniperus communis), the branch to the left bearing
staminate strobili; that to the right bearing staminate strobili above and earpel-
late strobili below, which latter have matured into the fleshy, berry-like fruit.
—After Bere and Scumiprt.

CHAPTER XII
SPERMATOPHYTES: ANGIOSPERMS

107. Summary of Gymnosperms.—Before beginning An-
giosperms it is well to state clearly the characters of Gym-
nosperms which have set them apart as a distinct group of
Spermatophytes, and which serve to contrast them with
Angiosperms.

(1) The microspore (pollen-grain) by wind-pollination
is brought into contact with the megasporangium (oyule),
and there develops the pollen-tube, which penetrates the
nucellus. This contact between pollen and ovule implies
an exposed or naked ovule and hence seed, and therefore
the name “‘ Gymnosperm.”

(2) The female gametophyte (endosperm) is well organ-
ized before fertilization.

(3) The female gametophyte produces archegonia.

108. General characters of Angiosperms,— This is the great-
est group of plants, both in numbers and importance, being
estimated to contain about 100,000 species, and forming
the most conspicuous part of the vegetation of the earth.
It is essentially a modern group, replacing the Gymnosperms
which were formerly the dominant Seed-plants, and in the
variety of their display exceeding all other groups. The
name of the group is suggested by the fact that the seeds
are inclosed in a seed case, in contrast with the exposed
seeds of the Gymnosperms.

These are also the true flowering plants, and the ap-

pearance of true flowers means the development of an
195

196 PLANT STRUCTURES

elaborate symbiotic relation between flowers and insects,
through which pollination is secured. In Angiosperms,
therefore, the wind is abandoned as an agent of pollen
transfer and insects are used; and in passing from Gym-
nosperms to Angiosperms one passes from anemophilous to
entomophilous (‘‘insect-loving”) plants. This does not
mean that all Angiosperms are entomophilous, for some are
still wind-pollinated, but that the group is prevailingly ento-
mophilous. This fact, more than anything else, has re-
sulted in a vast variety in the structure of flowers, so char-
acteristic of the group.

109. The plant body.—This of course is a sporophyte,
the gametophytes being minute and concealed, as in Gym-
nosperms. Thesporophyte represents the greatest possible
variety in habit, size, and duration, from minute floating
forms to gigantic trees; herbs, shrubs, trees; erect, pros-
trate, climbing ; aquatic, terrestrial, epiphytic ; from a few
days to centuries in duration.

Roots, stems, and leaves are more elaborate and vari-
ously organized for work than in other groups, and the
whole structure represents the high-
est organization the plant body has
attained. As in the Gymnosperms,
the leat is the most variously used
organ, showing at least four distinct
modifications: (1) foliage leaves, (2)
scales, (3) sporophylls, and (4) floral
leaves. The first three are present
in Gymnosperms, and even in Pteri-
dophytes, but floral leaves are pecul-
Fie. 105. Stamens of hen. iar to Angiosperms, making the true

bane (Zyoseyamus): A, flower, and being associated with en-
ce view, pune. Hla: tomophily.

ment (7) and anther (p);

B, Wack view, showing 110. Microsporophylls—The micro-
the connective () be snorophyll of Angiosperms is more

tween the pollen-sacs. ~
—After ScumreEn. definitely known asa ‘‘ stamen ” than

SPERMATOPHYTES: ANGIOSPERMS 197

that of Gymnosperms, and has lost any semblance to a leaf.
It consists of a stalk-like portion, the filament; and a
sporangia -bearing portion, the anther (Figs. 165, 167a).

Fig. 166. Cross-section of anther of thorn apple (Datura), showing the four imbedded
sporangia (@, p) containing microspores; the pair on each side will merge and
dehisce along the depression between them for the discharge of pollen.—After
FRANK.

The filament may be long or short, slender or broad, or
variously modified, or even wanting. The anther is simply
the region of the sporophyll which bears sporangia, and is

Fie. 167. Diagrammatic cross-sections of anthers: A, younger stage, showing the
four imbedded sporangia, the contents of two removed, but the other two con-
taining pollen mother cells (pm) surrounded by the tapetum (¢); B, an older stage,
in which the microspores (pollen grains) are mature, and the pair of sporangia on
each side are merging together to form a single pollen-sac with longitudinal
dehiscence.—After BaiLLon and LUERSSEN.

therefore a composite of sporophyll and sporangia and is
often of uncertain limitation. Such a term is convenient,

but is not exact or scientific.
al

198 PLANT STRUCTURES

.If a young anther be sectioned transversely four sporan-
gia will be found imbedded beneath the epidermis, a pair
on each side of the axis (Figs. 166, 167). When they reach
maturity, the paired sporangia on each side usually merge to-
gether, forming two spore-containing cavities (Fig. 167, B).
These are generally called ‘‘ pollen-sacs,” and each anther is
said to consist of two pollen-sacs, although each sac is made
up of two merged sporangia, and is not the equivalent of the
pollen-sac in Gymnosperms, which is a single sporangium.

Fig. 1674. Various forms of stamens: A, from Solanum, showing dehiscence by
terminal pores; B, from Ardufus, showing anthers with terminal pores and
“horns”; C, from Berberas; D, from Atherosperma, showing dehiscence by
uplifted valves; £, from Aqvilegia, showing longitudinal dehiscence ; #, from
Popowia, showing pollen-sacs near the middle of the stamen,—After ENGLER
and PRANTL.

SPERMATOPHYTES: ANGIOSPERMS 199

The opening of the pollen-sac to discharge its pollen-
grains (microspores) is called dehiscence, which means “‘a

splitting open,” and the methods of
dehiscence are various (Fig. 167a).
By far the most common method
is for the wall of each sac to split
lengthwise (Fig. 168), which is
called longitudinal dehiscence ; an-
other is for each sac to open by a
terminal pore (Fig. 167a), in which
case it may be prolonged above into
a tube.

111. Megasporophylls, — These
are the so-called *‘ carpels” of Seed-
plants, and in Angiosperms they
are organized in various ways, but
always so as to inclose the mega-
sporangia (ovules). In the simplest
cases each carpel is independent (Fig.

Fig. 168. Cross-section of

anther of a lily (Butomus),
showing the separating walls
between the members of each
pair of sporangia broken
down at z, forming a con-
tinuous cavity (pollen sac)
which opens by a longitudi-
nal slit.—After Sacus.

169, 4), and is dif-

ferentiated into three regions: (1) a hollow bulbous base,

Fie. 169. Types of pistils: .4, three simple pistils
(apocarpous), each showing ovary and style tipped
with stigma; 2B, a compound pistil (syncarpous),
showing ovary (f), separate styles (g), and stigmas
(n); OC, a compound pistil (syncarpous), showing
ovary (f), single style (g), and stigma ().—After
Bere and ScHmiptT.

which contains the
ovules and is the
real seed case,
known as the
ovary; (2) sur-
mounting this is a
slender more or less
elongated process,
the style; and (3)
usually at or near
the apex of thestyle
a special receptive
surface for the pol-
len, the stigma.

In other cases
several carpels to-

2000 PLANT STRUCTURES

gether form a common ovary, while the styles may also
combine to form one style (Fig. 169, (’), or they may remain
more or less distinct (Fig. 169, 2). Such an ovary may
contain a single chamber, as if the carpels had united edge
to edge (Fig. 170, 4); or it may contain as many chambers
as there are constituent carpels (Fig. 170, 4), as though
each carpel had formed its own ovary before coalescence.
In ordinary phrase an ovary is either ‘‘one-celled” or
** several-celled,” but as the word “cell” has a very differ-
ent application, the ovary chamber had better be called a
loculus, meaning “‘a compartment.” Ovaries,

A B C

Fic. 170. Diagrammatic sections of ovaries: 1, cross-section of an ovary with one
loculus and three carpels, the three scts of ovules said to be attached to the wall
(parietal); B, cross-section of an ovary with three loculi and three carpels, the
ovules being in the center (central); C, longitudinal section of B.—After Scuim-
PER.

therefore, may have one loculus or several loculi. Where
there are several loculi each one usually represents a con-
stituent carpel (Fig. 170, B); where there is one loculus
the ovary may comprise one carpel (Fig. 169, 1), or several
(Fig. 170, 4).

There is a very convenient but not a scientific word,
which stands for any organization of the ovary and the
accompanying parts, and that is p/sti7. A pistil may be
one carpel (Fig. 169, .!), or it may be several carpels or-
ganized together (Fig. 169, B, ('), the former case being a
stmple pistil, the latter a compound pistil. Tn other words,

SPERMATOPHY TES:

any organization of carpels which ap-
pears as a single organ with one ovary
is a pistil.

The ovules (megasporangia) are
developed within the ovary (Fig. 170)
either from the carpel wall, when they
are foliar, or from the stem axis which
ends within the ovary, when they are
cauline (see § 89). They are similar
in structure to those of Gymnosperms,
with integument and micropyle, nu-
cellus, and embryo-sac (megaspore),
except that there are often two integu-
ments, an outer and an inner (Fig.
171).

ANGIOSVERMS

Fic. 171. A diagrammatic
section of an ovule of
Angiosperms, showing
outer integument (ai),
inner integument (ii),
micropyle (m), nucellus
(k), and embryo sac or
megaspore (em).—After
Sacus.

112, The male gametophyte.— When the pollen-grain
(microspore) germinates there is formed within it the sim-

plest known gametophyte (Fig. 172).

No trace of the

Fie. 172. Germination of microspore (pollen grain) in duckweed (Zemna): A, mature

spore with its nucleus; B, nucleus of spore dividing;

(. twe nuclei resulting from

the division; D, a large and small cell following the nuclear division, forming the
two-celled male gametophyte; #, division of smaller cell (generative) to form the
two male cells; F, the two male cells completed and lying near the large tube

nucleus. —CALDWELL.

902 PLANT STRUCTURES

ordinary nutritive cells of the gametophyte remains, and
the whole structure seems to represent a single antherid-
ium. At first it consists of two cells, the large wall cell
and the small free generative cell (Fig. 172, 2). Later

g
9.
i Te
ti ‘ Ey i b
ai ae Ba )
\ 5 2 Mi 2
‘> : se i k

Fig. 173. Diagram of a longitudinal section through
a carpel, to illustrate fertilization with all parts
in place: s, stigma; g, style; 0, ovary ; ai, ii,
outer and inner integuments; 7, base of nucel-
lus ; f, funiculus ; 4, antipodal cells; ¢, endo-
sperm nucleus; 4, egg and one synergid; p, pol-
len-tube, having grown from stigma and passed
through the micropyle (m) to the egy.—After
LUERSSEN.

the generative cell di-
vides (Fig. 172, £),
either while in the
pollen-grain or after
entrance into the pol-
len-tube, and two male
cells (sperm mother-
cells) are formed (Fig.
172, #), which do not
organize sperms, but
which function direct-
ly as gametes.

When _ pollination
occurs, and the pollen
has been transferred
from the pollen-sacs
to the stigma, it is de-
tained by the minute
papille of the stig-
matic surface, which
also excretes a sweet-
ish sticky fluid. This
fluid is a nutrient so-
lution for the micro-
spores, which begin to
put out their tubes.
A pollen-tube pene-
trates through the
stigmatic surface, en-
ters among the tissues

of the style, which is sometimes very long, slowly or rap-
idly traverses the length of the style supplied with food by

SPERMATOPHYTES: ANGIOSPERMS 903

its cells but not penetrating them, enters the cavity of the
ovary, passes through the micropyle of an ovule, penetrates
the tissues of the nucellus (if any), and finally reaches and
pierces the wall of the embryo-sac, within which is the egg
awaiting fertilization (Fig. 173).

This remarkable ability of the pollen-tube to make its
way through so much tissue, directly to the micropyle of
an inclosed ovule, can only be explained by supposing that
it is under the guidance of some strong attraction.

113. The female gametophyte—The megaspore (embryo-
sac) occupies the same position in the ovule as in Gymno-
sperms, but its germination is remarkably modified. The
development of the female gametophyte shows two distinct

Fic. 174. Lilium Philadelphicum; to the left a young megasporangium (ovule),
showing integuments (C’), nucellus (A), and megaspore (B) containing a large nu-
cleus. To the right a megaspore whose nucleus is undergoing the first division
in the formation of the gametophyte.—CALDWELL.

periods, separated from one another by the act of fertiliza-
tion. If fertilization is not accomplished the second stage
of the gametophyte is usually not developed.

First period.—The megaspore nucleus divides (Fig.
174), and one nucleus passes to each end of the embryo-

204 PLANT STRUCTURES

sac (Fig. 175, at left). Each of these nuclei divide (Fig.
175, at right), and two nuclei appear at each end of the
sac (Fig. 175, at middle). Each of the four nuclei divide

Fie. 175. Liliwimn Philadelphicum; to the left is an embryo-sac with a gametophyte
nucleus in each end; to the right these two nuclei are dividing to form the two
nuclei shown in each end of the sac in the middle figure. —CaLDWELL.

(Fig. 176, at left), and four nuclei appear at each end (Fig.
176, at middle). When eight nuclei have appeared, nuclear
division stops. Then a remarkable phenomenon occurs.
One nucleus from each end, the two being called ‘> polar
nuclei,” moves toward the center of the sac, the two meet
and fuse (Fig. 176, at right, C’), and a single large nucleus
is the result.

The three nuclei at the end of the sac nearest the micro-
pyle are organized into cells, each being definitely sur-
rounded by cytoplasm, but there is no wall and the cells
remain naked but distinct. These three cells constitute
the egg-apparatus (Fig. 176, at right, .!), the central one,
which usually hangs lower in the sac than the others, being
the egg, the two others being the sywergids, or ** helpers.”
Here, therefore, is an egg without an archegonium, a dis-
tinguishing feature of Angiosperms.

SPERMATOPILYTES: ANGIOSPERMS 905

The three nuclei at the other end of the sac are also or-
ganized into cells, and usually have walls. These cells are
known as antipodal cells (Fig. 176, at right,
B). The large nucleus near the center of
the sac, formed by the fusion of the two

Fie. 176. Lilium Philadelphicum, showing last stages of germination of megaspore
before fertilization: the embryo sac to the left contains the pair of nuclei in each
end in a state of division preparatory to the stage represented by the middle figure,
in which there are four nuclei at each end; the figure to the right shows an embryo-
sac containing a gametophyte about ready for fertilization, with the egg apparatus
(A) composed of the two synergids and egg (central and lower), the three antipo-
dal cells (B), and the two polar nuclei fusing ((’) to form the primary endosperm
nucleus.—CALDWELL.

polar nuclei, is known as the primary endosperm nucleus
or the definitive nucleus.

206 PLANT STRUCTURES

Fic. 177. Fertilization in the cotton plant,
a Dicotyledon, showing the pollen tube (P)
passing throngh the micropyle and con-
taining a single sperm (male cell), and hay-
ing entered the embryo-sac is in contact
with one of the synergids (.S) on its way to
the egg (#).—After Duaaar.

This completes the first
period of gametophyte de-
velopment, and it is ready
for fertilization.

Fertilization. — The
pollen-tube, carrying the
two male cells, has passed
down the style and en-
tered the micropyle (Fig.
173). It then reaches the
wall of the embryo-sac,
pierces it, and is in con-
tact with the egg-appa-
ratus. Usually it passes
along the side of one of
the synergids (Fig. 177),
feeding upon and disor-
ganizing it. When it
comes near the conspicu-
ous nucleus of the egg,
the tip of the tube breaks
and one male cell is dis-
charged into the cyto-
plasm of the egg (Fig.
178). The egg and the
male cell now fuse, and
an oospore, which invests
itself with a wall, is the
result.

Second period.—After
fertilization the gameto-
phyte begins its second
period of development.
The primary endosperm
nucleus begins a series of
divisions, and as a result

SPERMATOPHYTES: ANGIOSPERMS DT

the sac becomes more or less filled
with nutritive cells, which are
often organized into a compact
tissue (Fig. 179). These nutri-
tive cells correspond to the endo-
sperm of Gymnosperms, and re-
ceive the same name. In Gymno-
sperms, therefore, the endosperm
(the nutritive body of the female
gametophyte) is mainly formed
before fertilization, while in An-
glosperms it is mainly formed
after fertilization. This means
that in Angiosperms eggs are
formed and fertilization takes

lace in a very youn ameto- Fie. 178. End of embryo-sac of
P ey 8 8 lily (Lilium Philadelphicum):

phyte, while in Gymnosperms and a pollen tube has entered the

heterosporous Pteridophytes the sac and has discharged a male

cell, whose nucleus is seen

egss appear much later. uniting with the nucleus of

The antipodal cells also proba- the egg; near the tip of the

. wat lls of th tube is the disorganizing nu-

bly represent nutritive cells o e cleus of one of the synergids.
gametophyte. Sometimes they dis- —CALDWELL.

Fig. 179. One end of the embryo-sac in wake-robin (77rillium). showing endosperm
(shaded cells) in which a young embryo is imbedded.—After ATKINSON.

208 PLANT STRUCTURES

appear very soon after they are formed; but sometimes
they become very active and even divide and form a con-
siderable amount of tissue, aiding the endosperm in nour-
ishing the young embryo.

114. Development of embryo.—While the endosperm is
forming, the oospore has germinated and the sporophyte
embryo is developing (Fig. 180). Usually a suspensor, more
or less distinct, but never so prominent as in Gymnosperms,
is formed; at the end of it the
embryo is developed (Fig. 181),
which, when completed, is more
or less surrounded by nourish-
ing endosperm (Fig. 183).

The two groups of Angio-
sperms differ widely in the struc-
ture of the embryo. In Mono-
cotyledons the axis of the em-
bryo develops the root-tip at one
end and the ‘seed-leaf ” (coty-
ledon) at the other, the stem-tip
arising from the side of the axis
as a lateral member (Fig. 182).
rem coed ames, ot This relation of orgs Teva

ing in the upper right enda the embryo of Jsoetes (see § 90).
young embryo, in the other Naturally there can be but one
end the antipodal cells cut off s

by a partition, and seatterea COtyledon under such cireum-
through the sac a few free en- stances, and the group has been
Se eeene nn aaptiatee Monocotyledons.

In Dicotyledons the axis of
the embryo develops the root-tip at one end and the stem-
tip at the other, the cotyledons (usually two) appearing as
a pair of opposite lateral members on either side of the
stem-tip (Fig. 181). This recalls the relation of parts in
the embryo of Se/uyinella (see § 89). As the cotyledons
are lateral members their number may vary. In Gymno-
sperms, whose embryos are of this type, there are often

SPERMATOPHYTES: ANGIOSPERMS 209

several cotyledons in a cycle (Fig. 154); and in Dicotyle-
dons there may be one or three cotyledons; but as a pair
of opposite cotyledons is almost without exception in the
group, it is named Dicotyledons.

The axis of the embryo between the root-tip and the
cotyledons is called the hypocotyl (Figs. 154, 193,194), which

Fie. 181. Development of embryo of shepherd's purse (Capsella), a Dicotyledon:
beginning with J, the youngest stage, and following the sequence to VJ, the old-
est stage, v represents the suspensor, ¢ the cotyledons, s the stem-tip, w the root,
h the root-cap. Note the root-tip at one end of the axis and the stem-tip at the
other between the cotyledons.—After HANSTEIN.

means ‘‘ under the cotyledon,” a region which shows pecul-
iar activity in connection with the escape of the embryo
from the seed. Formerly it was called either cawlicle or
radicle. In Dicotyledons the stem-tip between the coty-

910 PLANT STRUCTURES

ledons often organizes the rudiments of subsequent leaves,
forming a little bud which is called the plumule.

Embryos differ much as to com-
pleteness of their development within
the seed. In some plants, especially
those which are parasitic or sapro-
phytic, the embryo is merely a small
mass of cells, without any organiza-
tion of root, stem, or leaf. In many
cases the embryo becomes highly de-
veloped, the endosperm being used
up and the cotyledons stuffed with
food material, the plumule contain-
ing several well-organized young
leaves, and the embryo completely
filling the seed cavity. The com-
mon bean is a good illustration of
this last case, the whole seed within
Fie. 188. Young embryo of | the integument consisting of the two

Water plantain (Alisma@),€ Jaroe, fleshy cotyledons, between

Monocotyledon, the root a c

being organized at one Which le the hypocotyl and a plu-

end (next the suspensor), mule of several leaves.

atthe other and thestem, 115. The seed,— As in Gymno-

tip arising from a lateral sperms, while the processes above

notch (#).— After HAN” deseribed are taking place within

the ovule, the integument or integu-

ments are becoming transformed into the testa (Fig. 183).
When this hard coat is fully developed, the activities
within cease, and the whole structure passes into that con-
dition of suspended animation which is so little under-
stood, and which may continue for a long time.

The testa is variously developed in seeds, sometimes
being smooth and glistening, sometimes pitted, sometimes
rough with warts or ridges. Sometimes prominent append-
ages are produced which assist in seed-dispersal, as the
wings in Catulpa or Bignonia (Fig. 184), or the tufts of

SPERMATOPHYTES; ANGIOSPERMS O11

Fig. 183. The two figures to the left are seeds of violet, one showing the black, hard
testa, the other being sectioned and showing testa, endosperm, and imbedded
embryo; the figure to the right is a section of a pepper fruit (Piper), showing
modified ovary wall (pe), seed testa (sc), nucellus tissue (py), endosperm (en), and
embryo (em).—After ATKINSON.

hair on the seeds of milkweed, cotton, or fireweed (Fig.
185). For a fuller account of the methods of seed-dispersal
see Plant Relations, Chapter VI.

Fie. 184. A winged seed of Bignonia.—After STRASBURGER.

116. The fruit—The effect of fertilization is felt beyond
the boundaries of the ovule, which forms the seed. The
ovary is also involved, and becomes more or less modified.
It enlarges more or less, sometimes becoming remarkably
enlarged. It also changes in structure, often becoming
hard or parchment-like. In case it contains several or
numerous seeds, it is organized to open in some way and
discharge them, as in the ordinary pods and capsules (Fig.
185). In case there is but one seed, the modified ovary

212

¥ Ze
"Yj =

Fig. 185. A pod of fireweed
(Epilobium) opening and
exposing its plumed seeds
which are transported by
the wind.-—After Brat.

PLANT STRUCTURES

wall may invest it as closely as another
integument, and a seed-like fruit is
the result—a fruit which never opens
and is practically a seed. Such a
fruit is known as an akene, and is
very characteristic of the greatest
Angiosperm family, the Composite,
to which sunflowers, asters, golden-
rods, daisies, thistles, dandelions,
ete., belong. Dry fruits which do
not open to discharge the seed often
bear appendages to aid in dispersal
by wind (Figs. 186, 187), or by animals
(Fig. 188).

Capsules, pods, and akenes are said
to be dry fruits, but in many cases
fruits ripen fleshy. In the peach,
plum, cherry, and all ordinary ‘‘ stone
fruits,” the modified ovary wall or-
ganizes two layers, the inner being
very hard, forming the ‘‘stone,” the
outer being pulpy (Fig. 189), or vari-

ously modified (Fig. 190). In the true berries, as the
grape, currant, tomato, etc., the whole ovary becomes a
thin-skinned pulpy mass in which the seeds are imbedded.

In some cases
the effect of ferti-
lization in chang-
ing structure is
felt beyond the

ovary. Intheap- /

ple, pear, quince,
and such fruits,
the pulpy part is
the modified
calyx (one of the

Fie. 186. Winged fruit of maple.—After KERNER,

SPERM

ATOPHYTES: ANGIOSPERMS 913

floral leaves), the ovary and its contained seeds being repre-
sented by the “core.” In other cases, the end of the stem
bearing the ovaries (receptacle) becomes enlarged and
pulpy, as in the strawberry (Fig. 191). This effect some-

times involves even
more than the
parts of a single
flower, a whole
flower-cluster,
with its axis and
bracts, becoming
an enlarged pulpy
mass, as in the
pineapple (Fig.
192).

The term
“fruit,” therefore,

Fig. 188. An akene of beg-
gar ticks, showing the two
barbed appendages which
lay hold of animals.—Af-
ter BEAL.

32

Fig. 187. A ripe dandelion head, showing the mass of
plumes, a few seed-like fruits (akenes) with their
plumes still attached to the receptacle, and two
fallen off.—After KERNER.

Fie. 189. To the left a section of a peach (fruit),
showing pulp and stone formed from ovary wall,
and the contained seed (kernel); to the right
the fruit of almond, which ripens dry.—After
Gray.

214

PLANT STRUCTURES

is a very indefinite one, so far as the structures it includes
are concerned. It is simply an effect which follows fer-
tilization, and involves more or less of the structures adja-

Fie. 190. Fruit of nutmeg (I/yristica): A, section of fruit, showing seed within the
heavy wall; B, section of seed, showing peculiar convoluted and hard endosperm
(m) in which an embryo (7) is imbedded.—After BERG and ScumiptT.

cent to the seeds.

As has been seen, this effect may extend

only to the ovary wall, or it may include the calyx, or it

Fie, 191. Fruit of straw-
berry, showing the per-
sistent calyx, and the en-
larged pulpy receptacle
in which numerous sim-
ple and dry fruits (a-
kenes) are imbedded.—
After BaILEy.

lodgment. If the

may be specially directed toward the
receptacle, or it may embrace a whole
flower-cluster. It is what is called a
physiological effect rather than a defi-
nite morphological structure.

117. Germination of the seed.—lIt
has been pointed out (§ 103) that the
so-called “ germination of the seed”
is not true germination like that of
spores. It is the awakening and es-
cape of the young sporophyte, which
has long before passed through its
germination stage.

By various devices seeds are sepa-
rated from the parent plant, are dis-
persed more or less widely, and find

lodgment is suitable, there are many

devices for burial, such as twisting stalks and awns, bur-

SPERMATOPHYTES: ANGIOSPERMS 215

rowing animals, etc. The period of rest may be long or
short, but sooner or later, under the influence of moisture,
suitable temperature, and oxygen the quiescent seed begins
to show signs of life.

The sporophyte within begins to grow, and the seed
coat is broken or penetrated through some thin spot or

Fig. 192, Pineapple: A, the cluster of fruits forming the so-called ‘fruit’; B, single
flower, showing small calyx and more prominent corolla; (, section of flower,
showing the floral organs arising above the ovary (epigynous).—4, B after Koc;
C after LE Maovt and DECAISNE.

opening. The root-tip emerges first, is protruded still
farther by the rapid elongation of the hypocotyl, soon
curves toward the earth, penetrates the soil, and sending
out rootlets, becomes anchored. After anchorage in the

216 PLANT STRUCTURES

soil, the hypocotyl again rapidly elongates and develops a
strong arch, one of whose limbs is anchored, and the other
is pulling upon the cotyledons (Fig. 193). This pull finally
frees the cotyledons, the hypocotyl straightens, the cotyle-

Fie. 193. Germination of the garden bean, showing the arch of the hypocotyl] above
ground, its pull on the seed to extricate the cotyledons and plumule, and the final
straightening of the stem and expansion of the young leaves.—After ATKINSON.

dons are spread out to the air and light, and the young
sporophyte has become independent (Fig. 194).

In the grain of corn and other cereals, so often used in
the laboratory as typical Monocotyledons, but really excep-
tional ones, the embryo escapes easily, as it is placed on
one side of the seed near the surface. The hypocotyl and
stem split the thin covering, and the much-modified cotyle-
don is left within the grain to absorb nourishment.

In some cases the cotyledons do not escape from the
seed, either being distorted with food storage (oak, buck-
eye, etc.), or being retained to absorb nourishment from
the endosperm (palms, grasses, etc.). In such cases the
stem-tip is liberated by the elongation of the petioles of the

SPERMATOPHYTES: ANGIOSPERMS O17

cotyledons, and the seed coat containing the cotyledons
remains like a lateral appendage upon the straightened axis.

It is also to be observed in
many cases that the young root
system, after gripping the soil,
contracts, drawing the young
plant deeper into the ground.

118. Summary from Angio-
sperms.—At the beginning of this
chapter (§ 107) the characters of
the Gymnosperms were summar-
ized which distinguished them
from Angiosperms, whose con-
trasting characters may be stated
as follows:

(1) The microspore (pollen-
grain), chiefly by insect pollina-
tion, is brought into contact with
the stigma, which is a receptive
region on the surface of the car-
pel, and there develops the pollen-
tube, which penetrates the style
to reach the ovary cavity which
contains the ovules (megasporan-
gia). The impossibility of con-
tact between pollen and ovule im-
plies inclosed ovules and hence
seeds, and therefore the name
“« Angiosperm.”

(2) The female gametophyte
is but slightly developed before
fertilization, the egg appearing
very early.

Fic. 194. Seedling of hazel ( Car-
pinus), showing primary root
(iw) bearing rootlets (sw)
upon which are numerous
root hairs (r), hypocotyl (%),
cotyledons (¢), young stem
(e), and first (/) and second
(/’) true leaves.—After Scumm-
PER.

(3) The female gametophyte produces no archegonia,

but a single naked egg.

CHAPTER AIII
THE FLOWER

119. General characters——In general the flower may be
regarded as a modified branch of the sporophyte stem bear-
ing sporophylls and usually floral leaves. Its representa-
tive among the Pteridophytes and Gymnosperms is the stro-
bilus, which has sporophylls but not floral leaves. Among
Angiosperms it begins in a simple and somewhat indefinite
way, gradually becomes more complex and modified, until
it appears as.an elaborate structure very efficient for its
purpose.

This evolution of the flower has proceeded along many
lines, and has resulted in endless diversity of structure.
These diversities are largely used in the classification of
Angiosperms, as it is supposed that near relatives are indi-
cated by similar floral structures, as well as by other fea-
tures. The significance of these diversities is supposed to
be connected with securing proper pollination, chiefly by
insects, and favorable seed distribution.

Although the evolution of flowers has proceeded along
several lines simultaneously, now one feature and now
another being emphasized, it will be clearer to trace some
of the important lines separately.

120. Floral leaves.—In the simplest flowers floral leaves
do not appear, and the flower is represented only by the
sporophylls. Both kinds of sporophylls may be associated,
in which case the flower is said to be perfect (Fig. 195); or
they may not both occur in the same flower, in which case

one flower is staminate and the other pistillute (Fig. 196).
218

THE FLOWER 919

When the floral leaves first appear in connection with
the sporophylls they are inconspicuous, scale-like bodies.
In higher forms they become more prominent and inclose

Fie. 196. Naked flowers of dif-
ferent willows (Salix), each
from the axil of a bract:
a, 6, ¢c, staminate flowers ;
d, e, f, pistillate flowers, the
pistil composed of two car-
pels (syncarpous). — After
WARMING.

Fic. 195. Lizard’s tail(Saururus): A, tipofbranch Pye, 197, Flower of calamus

bearing leaves and elongated cluster of flowers; (Acorus), showing simple
B, a single naked flower from A, showing sta- perianth, stamens, and syn-
mens and four spreading and stigmatic styles; carpous pistil: a hypogynous
C, flower from another species, showing sub- flower without differentiation
tending bract, absence of floral leaves, seven of calyx and corolla.—After
stamens, and a syncarpous pistil; the flowers . Byer.

naked and perfect.—After ENGLER.

Fie. 199. Common flax (Linum):
1. entire flower, showing calyx
and corolla; B, floral leaves re-
moved, showing stamens and
syncarpous p‘stil; @, a mature

Fie. 198. Flowers of elm (Ulmus): A, branch capsule splitting open. —After
hearing clusters of flowers and scaly buds ; ScHIMPER.

B, single flower, showing simple perianth
and stamens, being a stamirate flower; (',
flower showing perianth, stamens. and the two divergent styles stigmatic on inner
surface, being a perfect flower; DJ, section through perfect flower, showing peri-
anth, stamens, and pistil with two loculi each with a single ovule —After ENGLER.

Fie. 200. A flower of peony, showing the four sects of floral organs: k, the sepals, to-
gether called the calyx; vc, the petals, together called the corolla; a, the numerous
stamens; g, the two carpels, which contain the ovules.—After STRASBURGER.

THE FLOWER 991

the young sporophylls, but they are all alike, forming what
is called the pertanth (Figs. 197, 198).

In still higher forms the perianth differentiates, the
inner floral leaves become more delicate in texture, larger
and generally brightly colored (Fig. 199, 1). The outer
set may remain scale-like, or become like small foliage
leaves. When the dif-
ferentiation of the peri-
anth is distinct, the
outer set of floral leaves
is called the calyz, each
leaf being a seval; the
inner set is the corolla,
each leaf being a petal
(Fig. 200). Sometimes,
as in the lily, all the
floral leaves become
uniformly large and
brightly colored, in
which case the term
perianth is retained
(Fig. 201). In other
cases, the calyx may be
the large and colored
set, but whenever there
is a clear distinction
between sets, the outer
is the calyx, the inner
the corolla.

Both floral sets may
not appear, and it has
become the custom to
regard the missing set Fie. 201.—An easter-lily. a Monocotyledon,
as the corolla, such showing perianth (a), stamens (4), stigma (c),

e c flower bud (d), and a carpel after the peri-
o
flowers being called anth has fallen (7), with its knob-like stigma,

ape talou 8, meaning long style, and slender ovary.—CALDWELL.

229, PLANT STRUCTURES

“without petals.” It is not always possible to tell whether
a flower is apetalous—that is, whether it has lost a floral
set which it once had—or is simply one whose perianth has
not yet differentiated, in which case it would be a ‘ primi-
tive type.”

The line of evolution, therefore, extends from flowers
without floral leaves, or naked flowers, to those with a dis-
tinctly differentiated calyx and corolla.

121. Spiral to cyclic flowers——In the simplest flowers the
sporophylls and floral leaves (if any) are distributed about
an elongated axis in a spiral, like a succession of leaves.
That part of the axis which bears the floral organs is for
convenience called the receptacle (Fig. 202). As the recep-

Fie. 202. A buttercup (Ranwneulus): a, complete flower, showing sepals, petals, sta-
mens, and head of numerous carpels on a large receptacle; 6, section showing
relation of parts; a hypogynous, polypetalous, apocarpous, actinomorphic flower.
—After Barton.

tacle is elongated and capable of continued growth, an in-
definite number of each floral organ may appear, especially
of the sporophylls. With the spiral arrangement, there-
fore, there is no definiteness in the number of floral organs ;
there may be one or very many floral leaves, or stamens, or
carpels. The spiral arrangement and indefinite numbers
are features of the ordinary strobilus, and therefore such
flowers are regarded as more primitive than the others.

In higher forms the receptacle becomes shorter, the
spiral more closely coiled, until finally the sets of organs

THE FLOWER 993

appear to be thrown into rosettes or cycles. This change
does not necessarily affect all the parts simultaneously.
For example, in the common buttercup the sepals and
petals are nearly in cycles, while the carpels are spirally
arranged and indefinitely numerous on the head-lke recep-
tacle (Fig. 202). On the other hand, in the common water-

I

Fie. 203. Flower of water-lily (Vymphea), showing numerous petals and stamens.—
After Caspary.

lily the petals and stamens are spiral, and indefinitely re-
peated, while the sepals and carpels are approximately
cyclic (Fig. 203).

Finally, in the highest forms, all the floral organs are
in definite cycles, and there is no indefinite repetition of
any part. All through this evolution from the spiral to the
cyclic arrangement there is constantly appearing a tend-
ency to ‘‘settle down” to certain definite numbers. When
the complete cyclic arrangement is finally established these
numbers are established, and they are characteristic of
great groups. In cyclic Monocotyledons there are nearly
always just three organs in each cycle, forming what is
called a ¢rimerous flower (Fig. 204) ; while in cyclic Dicot-

994 PLANT STRUCTURES

4

yledons the number five prevails, but often four appears,
forming pentumerous or tetramerous flowers (Fig. 199).
This does not mean that there are necessarily just three,
four, or five of each organ in the flower, for there may be
two or more cycles of some one organ. For example, in the
common lily there are six floral leaves in two sets, six sta-

mens in two sets, and three carpels (Fig. 204).
In the cyclic flowers it is also to be noted that each set
alternates with the next set outside (Fig. 204). The petals
are not directly opposite the se-

fillies pals, but are opposite the spaces

Tams between sepals; the stamens in

OS turn alternate with the petals; if

(o =) there is a second set of stamens,

iy 2 it alternates with the outer set,

% and so on. If two adjacent sets

are found opposing one another,

it is usually due to the fact that

Fic. 204. Diagram of such a @ Set between has disappeared.

flower as the lily, showing re- Foy example, if a set of stamens
lation of parts: uppermost . : .

oraan is the bract intheaxil 18 opposite the set of petals, either

of which the flower occurs; an outer stamen set or an inner

black dot below indicates po- .
sition of stem ; floral parts in petal set has disappeared.

threes and in five alternating This line of evolution, there-
cyeles (two stamen sets), being — fore, extends from flowers whose
a trimerous, pentacyclic flow- 2 .

cr.—After SCHIMPER. parts are spirally arranged upon

an elongated receptacle and in-
definite in number, to those whose parts are in cycles and
definite in number.

122. Hypogynous to epigynous flowers—In the simpler
flowers the sepals, petals, and stamens arise from beneath
the ovary (Figs. 197, 202, 205, 7). As in such cases the
ovary or ovaries may be seen distinctly above the origin
(insertion) of the other parts, such a flower is often said to
have a ‘‘ superior ovary.” The more usual term, however,
is hypogynous, meaning in effect “‘ under the ovary,” refer-

THE FLOWER

lo

25

ring to the fact that the insertion of the other parts is
under the ovary.

Hypogyny is very largely displaved among flowers, but
there is to be observed a tendency in some to carry the
insertion of the outer parts higher up. When the outer
parts arise from the rim of an urn-like outgrowth from the

Fiz, 205. Flowers of Rose family: 1, a hypogynous
flower of Pofentilia, sepals. petals, and stamens
arising from beneath the head of carpels; 2, a
perigynous flower of Alchemilia. sepals. petals,
and stamens arising from rim of urn-like pro-
longation of the receptacle. which surrounds the
carpel; 3. an epizynons flower of the common
apple, in which all the parts seem to arise from
the top of the ovary, two of whose loculi are
seen.—After FocKE.

receptacle, which surrounds the pistil or pistils, the flower
is said to be perigynous (Figs. 205, 2, 206), meaning * around
the pistil.” Finally, the insertion is carried above the ovary.
and sepals. petals. and stamens seem to urise from the top
of the ovary (Fig. 205, 2), such a flower being epigynozs.
the outer parts appearing “‘upon the ovary.” In such a
case the ovary does not appear within the flower. but below
it (Figs. 205, 252, 261), and the flower is often said to have
an ‘* inferior ovary.”

123. Apocarpous to syncarpous flowers——In the simpler
flowers the carpels are entirely distinct, each carpel organ-

926 PLANT STRUCTURES

izing a simple pistil, a single flower containing as many
pistils as there are carpels, as in the buttercups (Figs.
200, 202). Such a flower is said to be apocarpous, meaning
“carpels separate.” There is a very strong tendency,

Fie. 206. Sweet-scented shrub (Calycanthus): A, tip of branch bearing flowers; B,
section through flower, showing numerous floral leaves, stamens, and carpels, and
also the development of the receptacle about the carpels, making a perigynous
flower.—After THIEBAULT.

however, for the carpels of a flower to organize together
and form a single compound pistil. In such a flower there
may be several carpels, but they all appear as one organ
(Figs. 195, C, 197, 198, D, 199, B), and the flower is said
to be syncarpous, meaning ‘‘ carpels together.”

124. Polypetalous to sympetalous flowers—The tendency
for parts of the same set to coalesce is not confined to the
carpels. Sepals often coalesce (Fig. 208), and sometimes
stamens, but the coalescence of petals seems to be more
important. Among the lower forms the petals are entirely
separated (Figs. 109, .f, 202, 203, 207), a condition which

THE FLOWER

has received a variety of names, but
probably the most common is poly-
petalous, meaning “petals many,”
although elewtheropetalous, meaning
‘petals free,” is much more to the
point.

In the highest Angiosperms, how-
ever, the petals are coalesced, form-
ing a more or less tubular organ
(Figs. 208-210). Such flowers are
said to be sympetalous, meaning
“petals united.” The words gamo-
petalous and monopetalous are also

Fic, 207. Flower of straw-
berry, showing sepals, pet-
als, numerous stamens,
and head of carpels; the
flower is actinomorphic,
hypogynous, and with no
coalescence of parts.—Af-
ter BaILEY.

much used, but all three words refer to the same condition
of the flower. Often the sympetalous corolla is differenti-

Fie. 208. A flower of the tobacco plant: a, a complete flower, showing the calyx with
its sepals blended below, the funnelform corolla made up of united petals, and the
stamens just showing at the month of the corolla tube; 5. a corolla tube split open
and showing the five stamens attached to it near the base; c, a syncarpous pistil
made up of two carpels, showing ovary, style, and stigma.—After STRASBURGER.

298 PLANT STRUCTURES

ated into two regions (Fig. 210, 6), a more or less tubular
portion, the ¢wbe, anda more or less flaring portion, the limb.

125. Actinomorphic
to zygomorphic flow-
ers.—In the simpler
flowers all the mem-
bers of any one cycle
are alike; the petals
are all alike, the
stamens are all alike,
etc. Looking at the
center of the flower,
all the parts are re-
peated about it like
the parts of a radi-
ate animal. Such a

flower is actinomor-
Fie 209. Flower of morning-glory (Ipomea), with phic, meaning ra.
sympetalous corolla split open, showing the five 3 ” ie
attached stamens, and the superior ovary with diate, and 1S often
prominent style and stigma; the flower is hy- called ai ‘“* regular

pogynons, sympetalous, and actinomorphic.— »
After MuIssNER. flower. Although

the term actinomor-
phic strictly applies to all the floral organs, it is especially
noteworthy in connection with the corolla, whose changes
will be noted.

Fie. 210. A group of sympetalous flower forms: @, a flower of harebell, showing a
bell-shaped corolla; }, a lower of phlox, showing a tube and spreading limb; ¢, a
flower of dead-nettle, showing a zygomorphic two-lipped corolla; @, a flower of
toad-flax, showing a two-lipped corolla, and also a spur formed by the base of the
corolla; é, a flower of the snapdragon, showiug the two lips of the corolla closed.
—After Gray.

THE FLOWER 929

In many cases the petals are not all alike, and the radi-
ate character, with its similar parts repeated about a cen-

ter, is lost. In the
common violet, for
example, one of the
petals develops a spur
(Fig. 211); in the
sweet pea the petals
are remarkably un-
like, one being broad
and erect, two small-
er and drooping
downward, and the
other two much modi-
fied to form together
a boat-like structure
which incloses the

Fie. 211. The pansy (Violu tricolor): A, section
showing sepals (/,/’), petals (¢) one of which
produces a spur (cs). the flower being zygomor-
phic; B, mature fruit (a cap-ule) and persistent
calyx (k%); C, the three boat-shaped valves of
the fruit open, most of the seeds (s) having
been discharged.— After Sacus.

sporophylls. Such flowers are called zygomorphir, meaning
‘“ yoke-form,” and they are often called ‘irregular flowers.”

When zygomorphic flowers are also sympetalous the
corolla is often curiously shaped. A very common form

Fig. 212. Flower of a mint (Jfwtha aquaticai: A, the entire flower. showing calyx
of united sepals, unequal petals. stamens, and style with two stigma lobes; B, a
corolla split open, showing petals united and the four stamens attached to the
tube; the flower is sympetalous and zygomorphic.—After WERMING.

33

230

PLANT STRUCTURES

is the dilabiate, or ** two-lipped,” in which two of the petals
usually organize to form one lip, and the other three form

Fic. 213. Flower of a Labiate (Teucrium),

showing the calyx of coalesced sepals,
the sympetalous and two-lipped (bilabi-
ate) corolla with three petals (middle one
largest) in the lower lip and two small
ones in the upper, and the stamens and
style emerging through a slit on the up-
per side of the tube; a sympctalous and
zygomorphic flower.—After Brique.

the other lip (Figs. 210,
¢, d, é, 212, 213). The two
lips may be nearly equal,
the upper may stand high
or overarch the lower, the
lower may project more or
less conspicuously, etc.
126. Inflorescence—
Very often flowers are soli-
tary, either on the end of
a stem or branch (Figs.
231, 236), or in the axil
of a leaf (Fig. 258). But

such cases grade insensibly into others where a definite
region of the plant is set aside to produce flowers (Figs.
253, 260). Such a region forms what is called the znflo-
rescence. The various ways in which flowers are arranged
in an inflorescence have received technical names, but they
do not enter into our purpose here. They are simply dif-
ferent ways in which plants seek to display their flowers
so as to favor pollination and seed distribution.

There are several tendencies, however, which may be
noted. Some groups incline to loose clusters, either elon-
gated (Fig. 260) or flat-topped (Fig. 253); others prefer
large and often solitary flowers (Fig. 258) to a cluster of
smaller ones; but in the highest groups there is a distinct
tendency to reduce the size of the flowers, increase their
number, and mass them into a compact cluster. This ten-
dency reaches its highest expression in the greatest family
of the Angiosperms, the Composite, of which the sunflower
or dandelion can be taken as an illustration (Figs. 261, 262),
in which numerous small flowers are closely packed together
in a compact cluster which resembles a single large flower.
It does not follow that all very compact inflorescences in-

THE FLOWER 231

dicate plants of high rank, for the cat-tail flag (Fig. 221)
and many grasses have very compact inflorescences, and
they are supposed to be plants of low rank. It is to be
noted, however, that the very highest groups have settled
upon this as the best type of inflorescence.

127, Summary.—In tracing the evolution of flowers,
therefore, the following tendencies become evident: (1)
from naked flowers to those with distinct calyx and corolla ;
(2) from spiral arrangement and indefinite numbers to cyclic
arrangement and definite numbers; (3) from hypogynous
to epigynous flowers; (+) from apocarpous to syncarpous
pistils ; (5) from polypetalous to sympetalous corollas ; (6)
from actinomorphic or regular to zygomorphic or irregular
flowers ; (7) from loose to compact inflorescences.

These various lines appear in all stages of advancement
in different flowers, so that it would be impossible to deter-
mine the relative rank in all cases. However, if a flower
is naked, spiral, with indefinite numbers, hypogynous, and
apocarpous, it would certainly rank very low. On the con-
trary, the flowers of the Composite have calyx and corolla,
are cyclic, epigynous, syncarpous, sympetalous, often zygo-
morphic, and are in a remarkably compact inflorescence,
indicating the highest possible combination of characters.

128. Flowers and insects.— The adaptations between
flowers and insects, by which the former secure pollination
and the latter food, are endless. Many Angiosperm flowers,
especially those of the lower groups, are still anemophilous,
as are the Gymnosperms, but most of them, by the presence
of color, odor, and nectar, indicate an adaptation to the
visits of insects. This wonderful chapter in the history of
plants will be found discussed, with illustrations, in Plant
Relations, Chapter VII.

CHAPTER XIV
MONOCOTYLEDONS AND DICOTYLEDONS

129. Contrasting characters—The two great groups of
Angiosperms are quite distinct, and there is usually no dif-
ficulty in recognizing them. The monocotyledons are
usually regarded as the older and the simpler forms, and
are represented by about twenty thousand species. The
Dicotyledons are much more abundant and diversified, con-
taining about eighty thousand species, and form the domi-
nant vegetation almost everywhere.
The chief contrasting characters
may be stated as follows:

Monocotyledons. — (1) Embryo
with terminal cotyledon and lat-
eral stem-tip. This character is
practically without exception.

(2) Vascular bundles of stem
scattered (Hig. 214). This means
that there is no annual increase in

re the diameter of the woody stems,

Fig. 214. Section of stem of : :
corn, showing the scatterea @Nd no extensive branching, but
bundles, indicated by black to this there are some exceptions.

dots in cross-section, and by : :

lines in Jongitudinal section, (3) Leat veins forming a closed
—From ‘Plant Relations.” system (Fig. 215, figure to left).
As a rule there is an evident set
of veins which run approximately parallel, and intricately
branching between them is a system of minute veinlets not

readily seen. ‘The vein system does not end freely in the
282

MONOCOTYLEDONS AND DICOTYLEDONS 933

margin of the leaf, but forms a ‘‘ closed venation,” so that
the leaves usually have an even (ev/ire) margin. There
are some notable exceptions
to this character.

(4) Cyclic flowers trim-
erous. The “ three-parted ”

i
s

CN

A

Fig. 215. Two types of leaf venation: the figure to the left is from Solomon’s seal,
a Monocotyledon, and shows the principal veins parallel, the very minute cross
veinlets being invisible to the naked eye; that to the right is from a willow, a
Dicotyledon, and shows netted veins, the main central vein (midrib) sending out
a series of parallel branches, which are connected with one another by a network
of veinlets.—After ETTINGSHAUSEN.

flowers of cyclic Monocotyledons are quite characteristic,
but there are some trimerous Dicotyledons.
Dicatyleduns.—(1) Embryo with lateral cotyledons and
terminal stem-tip.
(2) Vascular bundles of stem forming a hollow cylinder
(Fig. 216, wv). This means an annual increase in the diam-

234 PLANT STRUCTURES

Fig. 216. Section across a young twig of
box elder, showing the four stem regions:
é, epidermis, represented by the heavy
bounding line; ¢, cortex; w, vascular cyl-
inder; p, pith. From ‘‘ Plant Relations.”

eter of woody stems (Fig.
217, w), and a possible
increase of the branch
system and foliage dis-
play each year.

(3) Leaf veins form-
ing an open system (Fig.
215, figure to right).
The network of smaller
veinlets between the
larger veins is usually
very evident, especially
on the under surface of
the leaf, suggesting the
name ‘‘net-veined”

leaves, in contrast to the “‘ parallel-veined ” leaves of Mono-

cotyledons.

this, although the leaf
may remain entire, it
very commonly be-
comes toothed, lobed,
and divided in various
ways. Two main types
of venation may be
noted, which influence
the form of leaves. In
one case a single very
prominent vein (77d)
runs through the mid-
dle of the blade. and
is called the midrib.
From this all the mi-
nor veins arise as
branches (Figs. 218,
219), and such a leaf

The vein system ends freely in the margin of
the leaf, forming an ‘* open venation.”

In consequence of

Fra. 217. Section across 1 twig of box elder

three years old, showing three annual rings,
or growth rings, in the vascular cylinder, the
radiating lines (m) which cross the vascular
region (w) represent the pith rays, the princi-
pal ones extending from the pith to the cor-
tex (c).—From ‘ Plant Relations.”

MONOCOTYLEDONS AND DICOTYLEDONS 93°

Or

is said to be pinnate or pinnately veined, and inclines to
elongated forms. In the other case several ribs of equal
prominence enter the blade and diverge through it (Fig.
218). Such a leaf is palmate or palinately veined, and in-
clines to broad forms.

(4) Cyclic flowers pentamerous or tetramerous. The
flowers ‘‘in fives” are greatly in the majority, but some

Fic. 218. Leaves showing pinnate and palmate branching; the one to the left is from
sumach, that to the right from buckeye.—CALDWELL.

very prominent families have flowers “‘in fours.” There
are also dicotyledonous families with flowers ‘‘in threes,”
and some with flowers ‘in twos.”

It should be remembered that no one of the above char-
acters, unless it be the character of the embryo, should be
depended upon absolutely to distinguish these two groups.

a) PLANT STRUCTURES

It is the combination of characters which determines a
group.
MonocoTyLEDONS

130. Introductory.—This great group gives evidence of
several distinct lines of development, distinguished by what
may be called the working out of different ideas. In this
way numerous families have resulted—that is, groups of

Fie. 219, A leaf of honey locust, to show twice pinnate branching (bipinnate leaf).—
CALDWELL.

forms which seem to belong together on account of similar
structures. This similarity of structure is taken to mean
relationship. A family, therefore, is made up of a group
of nearly related forms. Opinions may differ as to what
forms are so nearly related that they deserve to consti-
tute a distinct family. <A single family of some botanists
may be ‘‘split up” into two or more families by others.
Despite this diversity of opinion, most of the families are
fairly well recognized.

MONOCOTYLEDONS AND DICOTYLEDONS 237

Within a family there are smaller groups, indicating
closer relationships, known as genera (singular, genus).
For example, in the great family to which the asters belong,
the different asters resemble one another more than they do
any other members of the family, and hence are grouped
together in a genus .{stev. In the same family the golden-
rods are grouped together in the genus Solidago. The
different kinds of Aster or of Solidago are called species
(singular also species). A group of related species, there-
fore, forms a genus ; and a group of related genera forms a
family.

The technical name of a plant is the combination of its
generic and specific names, the former always being written
first. For example, Quercus alba is the name of the com-
mon white oak, Quercus being the name of the genus to
which all oaks belong, and a/ba the specific name which
distinguishes this oak from other oaks. No other names
are necessary, as no two genera of plants can bear the same
name.

In the Monocotyledons about forty families are recog-
nized, containing numerous genera, and among these
genera the twenty thousand species are distributed. It is
evident that it will be impossible to consider such a vast
array of forms, even the families being too numerous to
mention. A few important families will be mentioned,
which will serve to illustrate the group.

131. Pondweeds,—These are submerged aquatics, found
in most fresh waters (some are marine), and are regarded
as among the simplest Monocotyledons. They are slender,
branching herbs, growing under water, but often having
floating leaves, and sending the simple flowers or flower
clusters above the surface for pollination and seed-distri-
bution. The common pondweed (Potamogeton) contains
numerous species (Fig. 220), while .Va‘as (naiads) and
Zannichellia (horned pondweed) are common genera in.
ponds and slow waters.

938 PLANT STRUCTURES

The simple character of these forms is indicated by their
aquatic habit and also by their flowers, which are mostly
naked and with few sporophylls. A flower may consist of
a single stamen, or a single carpel; or there may be several
stamens and carpels associated, but without any coalescence
(Fig. 220, B).

In the same general line with the pondweeds, but with
more complex flowers, are the genera Sagittaria (arrow-

Fia. 220. Pondweed (Potamogeton): A, branch with cluster (spike) of simple flowers,
showing also the broad floating leaves and the narrow submerged ones; B, a sin-
gle flower, showing the inconspicuous perianth lobes (¢), the short stamens (a),
and the two short styles with conspicuous stigmatic surfaces.—A after REIOHEN-
BacH; B after Le Maour and Drcatsne.

Fic. 221. Cat-tails (Typha), showing the dense spikes of very simple flowers, each
showing two regions, the lower the pistillate flowers, the upper the staminate.—
From “ Field, Forest, and Wayside Flowers.”

240 PLANT STRUCTURES

leaf) and disma (water-plantain), in which there is a dis-
tinct calyx and corolla. The genus Typha (cat-tail) is also
an aquatic or marsh form of very simple type, the flow-

Fie, 222. A common meadow grass (Fi s/vea): A,
portion of flower cluster (spikelet), showing the
bracts, in the axils of two of which flowers are
exposed ; B, a single flower with its envelop-
ing bract, showing three stamens, and a_pistil
whose ovary bears two style branches with much
branched stigmas.—After STRASBURGFR.

ers being in dense
cylindrical clusters
(spikes), the upper
flowers consisting of
stamens, the lower of
carpels, thus forming
two very distinct re-
gions of the spike
(Fig. 221).

132. Grasses,—
This is one of the
largest and probably
one of the most use-
ful groups of plants,
as well as one of the
most peculiar. It is
world-wide in its dis-
tribution, and is re-
markable in its dis-
play of individuals,
often growing so
densely over large
areas as to form a
close turf. If the
grass-like sedges be
associated with them
there are about six
thousand species,
representing nearly
one third of the Mon-
ocotyledons. Here
belong the various
cereals, sugar canes,

MONOCOTYLEDONS AND DICOTYLEDONS O41

4

bamboos, and pasture grasses, all of them immensely use-
ful plants.

The flowers are very simple, having no evident perianth
(Fig. 222). Most commonly a flower consists of three sta-
mens, surrounding a single carpel, whose ovary ripens into
the grain, the characteristic seed-like fruit of the group.
The stamens, however, may be of any number from one to
six. The flowers, therefore, are naked, with indefinite num-
bers, and hypogynous, indicating a comparatively simple
type. It is also noteworthy that the group is anemophilous.

One of the noteworthy features of the group is the
prominent development of peculiar leaves (4racts) in con-
nection with the flowers. Each flower is completely pro-
tected or even inclosed by one of these bracts, and as the
bracts usually overlap one another the flowers are invisible
until the bracts spread apart and permit the long dangling
stamens to show themselves. These bracts form the so-
called *‘ chaff” of wheat and other cereals, where they
persist and more or less envelop the grain (ripened ovary).
As they are usually called glumes, the grasses and sedges
are said to be glumaceous plants.

Grasses are not always lowly plants, for in the tropics
the bamboos and canes form growths that may well be
called forests. The grasses constitute the family Gramineae,
and the sedges the family Cyperacee.

133. Palms.—More than one thousand species of palms
are grouped in the family Palmucew. These are the tree
Monocotyledons, and are very characteristic of the tropics,
only the palmetto getting as far north as our Gulf States.
The habit of body is like that of tree-ferns and C'yeads, a
tall unbranched columnar trunk bearing at its summit a
crown of huge leaves which are pinnate or palmate in char-
acter, and often splitting so as to appear lobed or compound
(Figs. 223, 224).

The flower clusters are usually very large (Fig. 223),
and each cluster at first is inclosed in a huge bract, which

Fig, 223. A date palm, showing the unbranched columnar trunk covered with old leaf
bases, and with a cluster of huge pinnate leaves at the top, only the lowest por-
tions of which are shown; two of the very heavy fruit clusters are also shown.—
From ‘“ Plant Relations.”

MONOCOTYLEDONS AND DICOTYLEDONS IAB

is often hard. Usually a perianth is present, but with no
differentiation of calyx and corolla, and the flower parts are
quite definitely in “‘ threes,” so that the cyclic arrangement
with the characteristic Monocotyledon number appears.

split so as to appear palmately branched.—From * Plant Relations.”

134. Aroids—This is a group of nearly one thousand
species, most of them belonging to the family 4racee. In
our flora the Indian turnip or Jack-in-the-pulpit (4risema)
(Fig. 225), sweetflag (Acorws), and skunk-cabbage (Symplo-
carpus), may be taken as representatives ; while the culti-
vated Calla-lily is perhaps even better known. The great
display of aroids, however, is in the tropics, where they are
endlessly modified in form and structure, and are erect, or
climbing, or epiphytic.

944 PLANT STRUCTURES

The flowers are usually very simple, often being naked,
with two to nine stamens, and one to four carpels (Fig.

i b) f
2 '

case a side view shows the naked tip of the projecting spadix.—After ATKINSON. ~

197). They are inconspicuous and closely set upon the
lower part of a fleshy axis, which is naked above and often

MONOCOTYLEDONS AND DICOTYLEDONS O45

modified in a remarkable way into a club-shaped or tail-like
often brightly colored affair. This singular flower-cluster
with its fleshy axis is called a spudir. The flowers often
include but one sort of sporophyll, and staminate and
pistillate flowers hold different positions upon the spadix
(Fig. 226).

The spadix is enveloped by a great bract, which sur-
rounds and overarches like a large loose hood, and is called
the spathe. The spathe is exceedingly
variable in form, and is often conspic-
uously colored, forming in the Calla-
lily the conspicuous white part, within
which the spadix may be seen, near the
base of which the flowers are found.
In Jack-in-the-pulpit (Fig. 225) it is
the overarching spathe which suggests
the *‘ pulpit.” The spadix and spathe
are the characteristic features of the
group, and the spathe is variously
modified in form, structure, and color

for insect pollination, as is the peri- “yim with spathe ro-
anth of other entomophilous groups. moved, showing cluster
« cee of naked pistillate flow-
Aroids are further peculiar in hav- Gard tatey Wek dot
ing broad net-veined leaves of the Di- a cluster of staminate
flowers, and the club-
cotyledon type. Altogether they form shaned tip’ 08 the ph:
a remarkably distinct group of Mon- — aix.—atter Wosstpio.
ocotyledons.

135. Lilies—The lily and its allies are usually regarded
as the typical Monocotyledon forms. The perianth is
fully developed, and is very conspicuous, either undifferen-
tiated or with distinct calyx and corolla, and the flower is
well organized for insect pollination. The flowers are either
solitary or few in a cluster and correspondingly large, or in
more compact clusters and smaller. In any event, the
perianth is the conspicuous thing, rather than spathes or
glumes.

246 PLANT STRUCTURES

In the general lily alliance, composed of eight or nine
families, there are more than four thousand species, repre-
senting about one fifth of all the Monocotyledons, and they
are distributed everywhere. They are almost all terrestrial
herbs, and are prominently geophilous (** earth-lovers “)—
that is, they develop
bulbs, rootstocks, etc.,
which enable them to
disappear from above
the surface during un-
favorable conditions
(cold or drought), and
then to reappear rap-
idly upon the return
of favorable conditions
(Figs. 227, 225, 231,
233).

In the regular lly
family (Lilivcew) the
flowers are hypogy-
nous and actinomor-
phic (Fig. 231), the
six perianth parts are
mostly alike and some-
times sympetalous (as
in the lily-of-the-val-

Fie. 227. Wake-robin (Zrillimn), showing root- ley, hyacinth, easter
stock, from which two branches arise, each bear- 7 ‘3 Ia: 290
ing a cycle (whorl) of three leayes and a single lily) (Figs. 201, x 20),
trimerons flower.—After ATKINSON. the stamens are usu-

ally six (two sets),
and the three carpels are syncarpous (Figs. 204, 230).
This is a higher combination of floral characters than
any of the preceding groups presents. Hypogyny and
actinomorphy are low, but a conspicuous perianth, syn-
carpy, and occasional sympetaly indicate considerable ad-
vancement,

MONOCOTYLEDONS AND DICOTYLEDONS 944

In the amaryllis family (4maryllidacee), a higher fam-
ily of the same general line, represented by species of .Var-
rissus (jonquils, daffodils, etc.), gave, etc., the flowers
are distinctly epigynous.

Fig. 228. Star-of-Bethlehem (Ornithogalum): a, entire plant with tuberous base and
trimerous flowers; 0, a single flower; c, portion of flower showing relation of
parts, perianth lobes and stamens arising from beneath the prominent ovary (hy-
pogynous); d, mature fruit; ¢, section of the syncarpous ovary, showing the three
carpels and loculi.—After SCHIMPER.

In the iris family (Jridacee), the most highly specialized
family of the lily line, and represented by the various spe-

Fie. 229. The Japan lily, showing a tubular perianth, the parts of the perianth
distinct above —From “ Field, Forest, and Wayside Flowers.”’

MONOCOTYLEDONS AND DICOTYLEDONS 9AQ

cies of Iris (flags) (Fig. 232), Crocus, Gladiolus (Figs. 233,
234), etc., the flowers are not only epigynous, but some of
them are zygomorphic.
When a plant has
reached both epigyny
and zygomorphy in its
flowers, it may be re-
garded as of high rank.

136. Orehids—In
number of species this
(Orehidacee) is the
greatest family among
the Monocotyledons,
the species being yvari-
ously estimated from Fic. 230. Diagrammatic cross-section of ovary

s tl sand. 46:4 of Lilium Philadedphicum, showing the three
S1x Lousan 0 en loculi, in each of which are two ovules (mega-

thousand, representing sporangia); -, ovule; B, integuments; (, nu-
: cellus; D, embryo-sac (megaspore),—C'aLp-
between one third and die

one half of all known

Monocotyledons. In display of individuals, however, the
orchids are not to be compared with the grasses, or even
with lilies, for the various species are what are called ‘rare
plants ’—that is, not extensively distributed, and often
very much restricted. Although there are some beautiful
orchids in temperate regions, as species of Hubenariu (rein-
orchis) (Fig. 255). Poyonta, Calapagon, Calypso, Cypripe-
dium (lady-slipper, or moccasin flower) (Fig. 236), ete.,
by far the greatest display and diversity zre in the tropics,
where many of them are brilliantly flowered epiphytes
(Fig. 237).

Orchids are the most highly specialized of Monocoty-
ledons, and their brilliant coloration and bizarre forms are
associated with marvelous adaptation for insect visitation
(see Plant Relations, pp. 134, 135). The flowers are epigy-
nous and strongly zygomorphic. One of the petals is re-
markably modified, forming a conspicuous ly which is

\—

Fie. 231. The common dog-tooth violet, showing the large mottled leaves and con-
spicuous flowers which are sent rapidly above the surface from the subterranean
bulb (see cut in the left lower corner), also some petals and stamens and the pistil
dissected out.—From “‘ Plant Relatious,”

MONOCOTYLEDONS AND DICUTYLEDONS 951

modified in a great variety of
ways, and a prominent, often
very long, sywr, in the bottom of
which nectar is secreted, which
must be reached by the proboscis
of an insect (Fig. 235). The
stamens are reduced to one or
two, and welded with the style

Fic. 232. Flower of flag (Z7is),
showing some of the sepals
and petals, one of the three
stamens, and the distinctly in-
ferior ovary, being an epigy-
nons flower.—After Gray.

Fic. 233 Gladiolus, showing tuberons subter-

Fie. 234. Flower cluster of Gla- ranean stem from which roots descend, grass-
diolus, showing somewhat zrgo- like leaves, and somewhat zygomorphic flow-
morphic flowers.—CaLDWELL, ers.—After REICHENBACH,

252 PLANT STRUCTURES

and stigmatic surface into an indistinguishable mass in
the center of the flowers. The pollen-grains in each sac
are sticky and cohere in a club-shaped mass (pollinium),
which is pulled out and carried to another flower by the

Fic. 235. A flower of an orchid (Habena-
via): at 1 the complete flower is shown,
with three sepals behind and three pet-
als in front, the lowest one of which has
developed a long strap-shaped portion
(ip) and a still longer spur portion, the
opening to which is seen at. the base of
the strap, and behind the spur the long
inferior ovary (epigynous character) ;
the two pollen sacs of the single stamen
are sccn in the center of the flower, di-
verging downward, and between them
stretches the stigma surface; the rela-
tion between pollen sacs and stigma sur-
face is shown in 2; within each pollen
sac is a mass of sticky pollen (pollini-
um), ending lhclow in a sticky disk,

which may be seen in 7 and 2; in 3 a pollen mass (a) is shown sticking to each

cye of a moth.—After Gray.

visiting insect. The whole structure indicates a very
highly specialized type, elaborately organized for insect
pollination.

Another interesting epigynous and zygomorphic trop-
ical group, but not so elaborate as the orchids, is repre-
sented by the cannas and bananas (Fig. 120). common in
cultivation as foliage plants, and the aromatic gingers.

From the simple pondweeds to the complex orchids the
evolution of the Monocotyledons has proceeded, and be-
tween them many prominent and successful families have
been worked out.

LS ee rs

Fig. 236. A clump of lady-slippers (Cypripedium), showing the habit of the plant
and the general] strncture of the zygomorphic flower.—After GiBson,

254 PLANT STRUCTURES

Fie. 237. A group of orchids (Cattleya), showing the very zygomorphic flowers, the
lip being well shown in the flower to the left (lowest petal).—-CALDWELL.

DiIcoTYLEDONS

137. Introductory.— Dicotyledons form the greatest group
of plants in rank and in numbers, being the most highly
organized, and containing about eighty thousand species.
They represent the dominant and successful vegetation in
all regions, and are especially in the preponderance in tem-
perate regions. They are herbs, shrubs, and trees, of every
variety of size and habit, and the rich display of leaf forms
is notably conspicuous.

Two great groups of Dicotyledons are recognized, the
Archichlamydew and the Sympetale. In the former there
is either no perianth or its parts are separate (polypeta-
lous) ; in the latter the corolla is sympetalous. The Archi-
chlamydez are the simpler forms, beginning in as simple a
fashion as do the Monocotyledons ; while the Sympetale

MONOCOTYLEDONS AND DICOTYLEDONS 955

are evidently derived from them and become the most
highly organized of all plants. The two groups each con-
tain about forty thousand species, but the Archichlamydex
contain about one hundred and sixty families, and the
Sympetale about fifty.

To present over two hundred families, containing about
eighty thousand species. is clearly impossible, and a very
few of the prominent ones will be selected for illustrations.

Archichlamydee

138. Poplars and their allies—This great alliance repre-
sents nearly five thousand species, and seems to form an
isolated group. It is a notable tree assemblage, and appar-
ently the most primitive and ancient group of Dicotyledons,
containing the most important deciduous forest forms of

fe

Fie. 238. An oak in winter condition.—From ‘Plant Relations,”

256 PLANT STRUCTURES

temperate regions, for here belong the oak (Fig. 238), hick-
ory, walnut, chestnut, beech, poplar, birch, elm (Figs. 198,
239), willow (Fig. 240), etc. The primitive character is in-
dicated not merely by the floral structures, but also by the
general anemophilous habit.

In the poplar (Populus) and its allied form, the willow
(Salix), the flowers are naked and hypogynous (Fig. 16),

Fie. 239. An elm in foliage.—From ‘‘ Plant Relations,”

MONOCOTYLEDONS AND DICOTYLEDONS 257

the stamens are indefinite in number (two to thirty), and
the pistil is syncarpous (two carpels). The stamens and

Fiu. 240. Flower clusters of willow (aments); that to the left is pistillate, the other
staminate.—After WaRMING.

pistils are not only separated in different flowers, but upon
different plants, some plants being staminate and others
pistillate (Fig. 240). The flowers are clustered upon a long
axis, and each one is
protected by a promi-
nent bract. It is these
scaly bracts which
give character to the
cluster, which is called
an ament or cathin,
and the plants which
produce such clusters
are said to be wmenta-
ceous. These aments
of poplars, ‘“‘pussy
willows,” and the Fie. 241. Aments of alder (Alnvs): a, branch

alders and birches are with staminate aments (n), pistillate aments

very familiar obj ects (m), and a young bud (x); 0, pistillate ament. at
‘ time of discharging seeds, showing the promi-
(Figs. wt), 241). nent bracts.—After WaRMINa.

958 PLANT STRUCTURES

The only advanced character in the flowers as described
above is the syncarpous pistil, but in the great allied pepper
family (Piperacee) of the tropics, with its one thousand
species, and most nearly represented in our flora by the

Fie. 242. Ovule of hornbeam (Carpinvs), showing chalazogamy: m, the micropyle;
pt, the pollen tube, which may be traced to its entrance into the embryo-sac at its
antipodal end, and thence upward through the sac toward the egg.—Aftcr Mary
Ewart.

lizard-tail (Saururvs) of the swamps (Fig. 195), the flowers
are not merely naked, but also apocarpous, and the whole
structure is much like that of the simplest Monocotyle-

MONOCOTYLEDONS AND DICOTYLEDONS 959

dons. The peppers seem to represent the simplest of the
Dicotyledons, and this great line may have begun with
some such forms.

A very interesting fact in connection with the fertiliza-
tion of certain amentaceous plants has been discovered.
In birch, alder, walnut, hornbeam, and some others, the
pollen-tube does not enter the ovule by way of the micro-
pyle, but pierces through in the region of the base of the
ovule and so penetrates to the embryo-sac (Fig. 242). As
the region of the ovule where integument and nucellus are
not distinguishable is called the chalaza, this phenomenon
is known as chalazogamy, meaning “fertilization through
the chalaza.”

139. Buttercups and their allies—This is a great assem-
blage of terrestrial herbs, including nearly five thousand
species, and is thought by many to be the great stock from
which most of the higher Dicotyledons have been derived.
The alliance includes the water-lilies, buttercups, and pop-
pies, the specialized mustards, and certain notable tree
forms, as magnolias, custard-apples. and the tropical laurels
with one thousand species represented in our flora only
by the sassafras. Here also is the strange group of *: car-
nivorous” plants (Sarracenia, Drosera, Dionea, ete.). The
group is distinctly entomophilous, in striking contrast with
the preceding one.

Taking the buttercup (Ranunculus) as a type (Fig. 202),
the flower is hypogynous, the calyx and the corolla are dis-
tinctly differentiated and actinomorphic, and adapted for
insect-pollination, but the spiral arrangement and indefinite
numbers are very apparent, notably in connection with the
apocarpous pistils, which are very numerous upon a promi-
nent receptacle, but involving more or less all the parts.
The stamens are also very numerous (Figs. 200, 243, 24+).
In the water-lilies the petals and stamens are indefinitely
numerous (Fig. 203), and in the poppies there is no definite
number. In many of the forms. however, in connection

Fre. 243. Marsh marigold ((a/thi), a member of the Buttercup family, also showing
floral diagram, in which the floral leaves are five, but the stamens and apocarpous
pistils are indefinitely numerous —After ATKINSON.

Fig 244. Zygomorphie flower of larkspur Fie, 245. Diagram of the zygomorphic

(Delphinium), with sepals removed, show- flower of larkspur (De/phinium), show-
ing two petals with prominent spurs, and ing the spur developed by a sepal and
numerous stamens.—After BATLLON. inclosing the two petal spurs.—After

BAtrLion.

MONOCOTYLEDONS AND DICOTYLEDONS 961

with one or more of the parts, the Dicotyl number (five)
appears (Figs. 243, 245), but with no special constancy.

In certain genera of the buttercup family (Renuncula-
cew) zygomorphy appears, as in the larkspur (Delphiniun)
with its spurred petals and sepals (Figs. 244, 245), and the
monkshood (Aconitum) with its hooded sepal; and in the

Fic. 246. The common cabbage (Brassica), a member of the mustard family: 1,
flower cluster, showing buds at tip, open flowers below with four spreading petals,
and forming pods below; B, mature pod, with the persistent style; (. pod opening
by two valves, and showing seeds attached to the false partition.—After WaRMING.

water-lily family (Vympheacee) and poppy family (Papa-
veracee) syncarpy appears. In this alliance, also, belong
the sweet-scented shrubs (Calycanthus), with their perigy-
nous flowers containing numerous parts (Fig. 206).

35

252 PLANT STRUCTURES

The most specialized large group in this alliance is
the mustard family (Crucifere), with twelve hundred
species, to which belong the mustards, cresses, shep-
herd’s purse, peppergrass, radish, cabbage (Fig. 246), etc.

The sepals are four in two sets, the

petals four in one set, the stamens

ao six with two short ones in an outer

fe, = \ set and four long ones in an inner

¢ @) 9 set, and one carpel whose ovary be-

Ks 8 comes divided into two loculi by

pS what is called a ‘false partition ”

(Figs. 246, C, 247), and usually be-

oe gpm: temas comes an elongated pod (Fig. 246,

of parts; four sepals, four A, B). This specialized structure

— abs stamens, and one of the flower distinctly marks the

pel with a false partition.

--After Waraine. family, whose name is suggested

by the fact that the four spreading

petals often form a Maltese cross (Fig. 246, 4). The pecul-

iar stamen character, four long and two short stamens, is
called fefradynamous (‘four strong”).

140. Roses—This family (Rosacer) of one thousand
species is one of the best known and most useful groups of
the temperate regions. In it are such forms as NSpired,
five-finger (Poten-
tilla), strawberry
(Fragaria) (Figs.
191, 207), raspberry
(Fig. 248), and
blackberry (Ru-
bus), rose (usa),
hawthorn § ('rute-

gus), apple, and = .

Ria < 1a, 248. The common raspberry: the figure to the
pear (Pir us) (Fig. left showing flower-stalk, calyx, old stamens
249), plum, cherry, ({s), and prominent receptacle, from which the

“fruit” (a cluster of small stone fruits, each
almond, and peach representing a carpel) has been removed.— After

(Pranus). Baier,

MONOCOTYLEDONS AND DICOTYLEDONS 963

Many of the true roses have a strong resemblance (Fig.
207) to the buttercups (Ranunenlvs), with their hypogy-
nous regular flowers, and indefinite number of stamens and
carpels, but the sepals and petals are much more frequently
five, the Dicotyl number being better established. The

Fie. 249, The common.pear (Pirus communis), showing branch with flowers (1). sec-
tion of a flower (?) showing its epigynous character, section of fruit (3) showing
the thickened calyx outside of the ovary or ‘‘core”’ (indicated by dotted outline),
and flower diagram (4) showing all the organs in fives except the stamens. —After
WossIDLo.

whole family remains actinomorphic, but perigyny and
epigyny appear in certain forms (Fig. 205), giving rise to
the peculiar fruit (pome) of apples and pears (Fig. 249), in
which the calyx and ovary ripen together. Another spe-
cialized group of roses is that which develops the stone-

264 PLANT STRUCTURES

fruits (drupes), as apricots, peaches (Fig. 189), plums,
cherries.

141. Legumes,—This is far the greatest family (Legumi-
nose) of the Archichlamydew, containing about seven thou-
sand species, distributed everywhere and of every habit. It
is the great zygomorphic group of the Archichlamydee,
being elaborately adapted to insect pollination. The more

Fig. 250. A legume plant (Lofus), showing flowering branch (1), a single flower (2)
showing zygomorphic corolla, the cluster of ten stamens (3) which with the carpel
is included in the keel, the solitary carpel (4) which develops into the pod or le-
gume (5), the petals (6) dissected apart and showing standard (qa), wings (0), and
the two lower petals (¢) which fold together to form the keel, and the floral dia-
gram (7).—After WossIDLo.

primitive forms of the Leguminose, the mimosas, acacias
(Fig. 251), etc., very much resemble true roses and the but-
tercups, with their hypogynous regular flowers and nu-
merous stamens, but the vast majority are Payilio forms
with very irregular (zygomorphic) flowers and few stamens

MONOCOTYLEDONS AND DICOTYLEDONS 265

(Fig. 250). The petals are very dissimilar, the upper one
(standard) being the largest, and erect or spreading, the two
lateral ones (7ings) oblique and descending, the two lower
ones coherent by their edges to form a projecting boat-shaped
body (Keel), which
incloses the sta-
mens and pistil.
From a fancied re-
semblance to a but-
terfly such flowers
are said to be papil-
tonaceous.

The whole fam-
ily is further char-
acterized by the sin-
gle carpel, which
after fertilization
develops a pod
(Fig. 250, 5), which

compared with the
carpel. It is this
peculiar pod (/e-
gume) which has
given to the family
its technical name Fie. 251. A sensitive-plant (Acacia), showing the
Leguminose and flowers with inconspicuous petals and very nu-

merous stamens, and the pinnately branched sen-
the common name sitive leaves.—After Meyer and ScHuMANN.
“Legumes.”

Well-known members of the family are lupine (Lupi-
nus), Clover (Trifolium), locust (Robinia), Wistaria, pea
(Pisum), bean (Phaseolus), tragacanth (1s¢ragalus), vetch
(Vicia), redbud ((ere/s), senna (Cassia), honey-locust
(Gleditschia), indigo (Indigofera), sensitive-plants (Acacia,
Mimosa, etc.) (Fig. 251), ete.

266 PLANT STRUCTURES

142. Umbellifers—This is the most highly organized
family (Umbellifere) of the Archichlamydex, which may
be said to extend from Peppers to Umbellifers. The Le-
gumes adopt zygomorphy, but remain hypogynous ; and in
some of the Roses epigyny appears; but the Umbellifers
with their fifteen hundred species are all distinctly epigy-

Fig. 252. The common carrot (Daucus Carota): 4. branch bearing the compound
umbels; B, u single epigynous flower, showing inferior ovary, five spreading
petals, five stamens alternating with the petals, and the two styles of the bicarpel-
lary pistil; ( section of flower, showing relation of parts, and also the minute
sepals near the top of the ovary and just beneath the other parts, —After WARMING.

nous (Fig. 252, B, (), being one of the very few epigy-
nous families among the Archichlamydee. In addition
to epigyny, the cyclic arrangement and definite Dicotyl
number is established, there being five sepals, five petals.
five stamens, and two carpels, the highest known floral

MONOCOTYLEDONS AND DICOTYLEDONS 267

formula, and one that appears among the highest Sym-

petale.

The name of the family is suggested by the character-
istic inflorescence, which is also of advanced type. The

flowers are reduced in
size and massed in flat-

topped clusters called He

umbels (Figs. 252, 4, 253).
The branches of the clus-
ter arise in cycles from
the axis like the braces
of an umbrella. As a re-
sult of the close approxi-
mation of the flowers the
sepals are much reduced
in size and often obsolete
(Fig. 252, C).

The Umbellifers are
mainly perennial herbs of
the north temperate re-
gions, forming a very dis-
tinct family, and contain-
ing the following familiar
forms: carrot (Daucus)
(Fig. 252), parsnip (Pasti-
naca), hemlock (Conium)
(Fig. 253), pepper-and-
salt (Erigenia), caraway
(Carum), fennel (Fente-
ulum), coriander (Cori-
andrum), celery (Apt-
um), parsley (Petroseli-
num), etc. Allied to the
Umbellifers are the Ara-
lias (Araliacee), and the
Dogwoods (Cornacee).

Fie. 253. Hemlock (Conium), an Umbellifer,
showing the umbels, with the principal
rays rising from a cycle of bracts (invo-
lucre), and each bearing at its summit a
secondary umbel with its cycle of second-
ary bracts (énvolucel).—After SCHIMPER.

268 PLANT STRUCTURES

Sympetale

143. Introductory.—These are the highest and the most
recent Dicotyledons. While they contain numerous shrubs
and trees in the tropics, they are by no means such a shrub
and tree group in the temperate regions as are the Archi-
chlamydee. The flowers are constantly cyclic, the num-
ber five or four is established, and the corolla is sympeta-
lous, the stamens usually being borne upon its tube (Figs.
208, 209, 212).

There are two well-defined groups of Sympetale, distin-
guished from one another by the number of cycles and the
number of carpels in the flower. The group containing
the lower forms is pexfacyclic, meaning ‘ cycles five,” there
being two sets of stamens. In it also there are five carpels,
the floral formula being, Sepals 5, Petals 5, Stamens 5 + 5,
Carpels 5. As the carpels are the same in number as the
other parts, the flowers are called dsocarpic, meaning * car-
pels same.” The group is named either Pentacyrl or [sv-
carpe, and contains about ten families and 4,000 species.

The higher groups, containing about forty families and
36,000 species, is fetracyclic, meaning ** cycles four,” and
anisocarpic, meaning *‘carpels not the same,” the floral
formula being, Sepals 5, Petals 5, Stamens 5, Carpels 2.
The group name, therefore, is Tefrarycle or Anisocurpe.

144. Heaths.—The Heath family (ricacer) and its allies
represent about two thousand species. They are mostly
shrubs, sometimes trailing, and are displayed chiefly in
temperate and arctic or alpine regions, in cold and damp
or dry places, often being prominent vegetation in bogs
and heaths, to which latter they give name (Fig. 254). The
flowers are pentacyclic and isocarpic, as well as mostly hyp-
ogynous and actinomorphic. It is interesting to note that
some forms are not sympetalous, the petals being distinct,
showing a close relationship to the Archichlamydex. One
of the marked characteristics of the group is the dehiscence

MONOCOTYLEDONS AND DICOTYLEDONS 969

of the pollen-sacs by terminal pores, which are often pro-
longed into tubes (Fig. 255).

Fie. 254. Characteristic heath plants: 4, B. (. Lyonia, showing sympetalous flowers
and single style from the lobed syncarpous ovary; D, two forms of Cassiope,
showing trailing habit, small overlapping leaves, and sympetalous flowers, but in
the smaller form the petals are almost distinct.—After DRUDE.

Common representatives of the family are as follows:
huckleberry ((@aylussacia), cranberry and blueberry ( Vuc-
cinium), bearberry (i retostaphylos), trailing arbutus (£p/-

270 PLANT STRUCTURES

gea), wintergreen (Gaultheria), heather (Calluna), moun-
tain laurel (Aalmia), Azalea, Rhododendron (Fig. 256),
Indian pipe (Monotropa), etc.

Fig, 255. Flowers of heath plants (#rica), showing complete flowers (4), the sta-
mens with ‘‘ two-horned”’ anthers which discharge pollen throngh terminal pores,
and the lobed syncarpous ovary with single style and prominent terminal stigma
(B, C, D).—After DruveE.

145. Convolvulus forms.—The well-known morning-glory
(Jpomea) (Fig. 209) may be taken as a type of the Convol-

MOSOCOTYLEDONS AND DICOTYLEDORKS 971

vulus family (Convolvulacew). Allied with it are Polemo-
nium and Phlow (Fig. 210, b) (Polemoniacee), the gentians
(Gentianacew), and the dog-banes (lpocynacee) (Fig. 257).
It is here that the regular sympetalous flower reaches its
highest expression in the form of conspicuous tubes, fun-

Fie. 256. A cluster of Rhododendron flowers.—After HooKER.

nels (Fig. 258), trumpets, etc. The flowers are tetracyclic
and anisocarpic, besides being hypogynous and actinomor-
phic. These regular tubular forms represent about five
thousand species, and contain many of the best-known
flowers.

979 PLANT STRUCTURES

146. Labiates—This great family (Zadiate) and its alli-
ances represent more than ten thousand species. The con-
spicuous feature is the
zygomorphic flower, dif-
fering in this regard from

the Convolvulus forms,
which they resemble in
being tetracyclic and ani-
socarpic, as well as hypogy-
nous. The irregularity
consists in organizing the
mouth of the sympetalous
corolla into two ‘‘ lips,”
resulting in the /adiate or

Fie. 257. A common dogbane (.fpocynum).—From “ Field, Forest, and Wayside
Flowers.”

Fig. 258. The hedge bindweed ( Conro/eudus), showing the twining habit and the con-
spicuous funnelform corollas.—From “ Field. Forest, and Wayside Flowers.”

O74 PLANT STRUCTURES

bilabiate structure (Fig. 210, ¢, d, ¢), and suggesting the
name of the dominant family. The upper lip usually con-
tains two petals, and the lower three ; the two lips are some-
times widely separated, and sometimes in close contact, and
differ widely in relative prominence.

Associated with zygomorphy in this group is a frequent
reduction in the number of stamens, which are often four
(Fig. 212) or two. The whole structure is highly special-
ized for the visits of insects, and this great zygomorphic
alliance holds the same
relative position among
Sympetale as is held
by the zygomorphic Le-
gumes among Archi-
chlamydee.

In the mint family,
as the Labiates are often
called, there are about
two thousand seven hun-
dred species, including
mint (Mentha) (Fig.
212), dittany (Cunila),
hyssop (Hyssopus), mayr-
joram (Origanum),

Fie. 259. Flowers of dead nettle (Za- Fre. 260. A labiate plant (Zeucrium), show-
mium): A, entire bilabiate flower ; ing branch with flower clusters (4), and
B, section of flower, showing rela- side view of a few flowers (B), showing
tion of parts.—After Warmina, their bilabiate character.—After Briquet,

MONOCOTYLEDONS AND DICOTYLEDONS 975

thyme (Thymus), balm (Jelissa), sage (Salvia), catnip
(-Vepeta), skullcap (Scutelluria), horehound (Murrubium),
lavender (Lavandula), rosemary (Rosmarinus), dead nettle
(Lamium) (Fig. 259), Teuerium (Figs. 2138, 260), ete., a
remarkable series of aromatic forms.

Allied is the Nightshade family (Solanacew), with fif-
teen hundred species, containing such common forms as
the nightshades and potato (So/anwm), tomato (Lycoper-
sicum), tobacco (.Vicotiana) (Fig. 208), etc., in which the
corolla is actinomorphic or nearly so; also the great Fig-
wort family (Scrophulariacee), with two thousand species,
represented by mullein ( Verbascum), snapdragon (.intir-
rhinum) (Fig. 210, ¢), toad-flax (Linarta) (Fig. 210, d),
Pentstemon, speedwell (Veronica), Gerardia, painted cup
(Castilleta), etc.; also the Verbena family (Verbenacee),
with over seven hundred species; and the two hundred
plantains (Pluntaginucee), etc.

147. Composites—This greatest and ranking family
(Composite) of Angiosperms is estimated to contain at least
twelve thousand species, containing more than one seventh
of all known Dicotyledons and more than one tenth of all
Seed-plants. Not only is it the greatest family, but it is
the youngest. Composites are distributed everywhere, but
are most numerous in temperate regions, and are mostly
herbs.

The name of the family suggests the most conspicuous
feature—namely, the remarkably complete organization of
the numerous small flowers into a compact head which
resembles a single flower, formerly called a ‘‘ compound
flower.” Taking the head of an Arnica as a type (Fig.
261), the outermost set of organs consists of more or less
leaf-like bracts or scales (‘nvolucre), which resemble sepals ;
within these is a circle of flowers with conspicuous yellow
corollas (rays), which are zygomorphic, being split above
the tubular base and flattened into a strap-shaped body,
and much resembling petals (Fig. 261, 1, 2); within the

Fie. 261. Flowers of Arnica? .1, lower part of stem, and upper part bearing a
head, in which are seen the conspicuous rays and the disk; D, single ray flower,
showing the corolla, tubular at base and strap-shaped above, the two-parted style,
the tuft of pappus hairs, and the inferior ovary which develops into a seed-like
fruit (akene); Z#. single disk flower, showing tubular corolla with spreading limb,
the two-parted style emerging from the top of the stamen tube, the prominent
pappus, and the inferior ovary or akene; (', a single stamen,—Aftcr IlorFMAN.

276

MONOCOTYLEDONS AND DICOTYLEDONS OWT

ray-flowers is the broad expanse supplied by a very much
broadened axis, and known as the dish (Fig. 261, 4), which
is closely packed with very numerous small and regular
tubular flowers, known as disk-flowers (Fig. 261, e).

Fic. 262. The common dandelion ( Tararacuvm): 1, two flower stalks; in one the head
is closed, showing the double involucre, the inner erect, the outer reflexed, in the
other the head open, showing that all the flowers are strap-shaped; 2, a single
flower showing inferior ovary, pappus, corolla, stamen tube, and two-parted style;
3, a mature akene; 4, a head from which all but one of the akenes have been re-
moved, showing the pitted receptacle and the prominent pappus beak.—After
STRASBURUER.

The division of !abor among the flowers of a single head
is plainly marked, and sometimes it becomes quite com-
plex. The closely packed flowers have resulted in modity-
ing the sepals extremely. Sometimes they disappear en-

36

278 PLANT STRUCTURES

tirely ; sometimes they become a tuft of delicate hairs, as
in Arnica (Fig. 261, D, #), thistle (Caicus), and dandelion
(Taravacum) (Fig. 263), surmounting the seed-like akene
and aiding in its transportation through the air ; sometimes
they are converted into two or more tooth-like and often

Fie. 263. Flowers of dandelion, showing action of style in removing pollen from the
stamen tube: 7, style having elongated through the tube and carrying pollen; 2,
style branches beginning to recurve; 3, style branches completely recurved.—
From ‘ Field, Forest, and Wayside Flowers.”

barbed processes arising from the akene, as in tickseed
(Coreopsis) and beggar-ticks (Fig. 188) or Spanish needles
(Bidens), to lay hold of passing animals ; sometimes they
become beautifully plumose bristles, as in the blazing star
(Liatris) ; sometimes they simply form a more or less con-
spicuous cup or set of scales crowning the akene. In all
of these modifications the calyx is called pappus.

The stamens within the corolla are organized into a
tube by their coalescent anthers (Fig. 263), and discharge
their pollen within, which is carried to the surface of the

MONOCOTYLEDONS AND DICOTYLEDONS 979

head and exposed by the swab-like rising of the style (Fig.
263). The head is thus smeared with pollen, and visiting
insects can not fail to distribute it over the head or carry
it to some other head.

In the dandelion and its allies the flowers of the disk
are like the ray-flowers, the corolla being zygomorphic and
strap-shaped (Figs. 262, 263).

The combination of characters is sympetalous, tetracyc-
lic, and anisocarpic flowers, which are epigynous and often
zygomorphic, with stamens organized into a tube and calyx
modified into a pappus, and numerous flowers organized
into a compact involucrate head in which there is more or
less division of labor. There is no group of plants that
shows such high organization, and the Composite seem to
deserve the distinction of the highest family of the plant
kingdom.

The well-known forms are too numerous to mention,
but among them, in addition to those already mentioned,
there are iron-weed (Vernonia), Aster, daisy (ellis),
goldenrod (Solidago), rosin-weed and compass-plant (Si/ph-
tum), sunflower (Helianthus), Chrysanthemum, ragweed
(Ambrosia), cocklebur (.Yanthiwm), ox-eye daisy (Leucan-
themum), tansy (ZLanacetum), wormwood and sage-brush
(Artemisia), lettuce (Lactuca), etc.

CHAPTER XV
DIFFERENTIATION OF TISSUES

148. Introductory— Among the simplest Thallophytes
the cells forming the body are practically all alike, both as
to form and work. What one cell does all do, and there
is very little dependence of cells upon one another. As
plant bodies become larger this condition of things can not
continue, as all of the cells can not be put into the same
relations. In such a body certain cells can be related to
the external food supply only through other cells, and the
body becomes differentiated. In fact, the relating of cells
to one another and to the external food-supply makes large
bodies possible.

The first differentiation of the plant body is that which
separates nutritive cells from reproductive cells, and this is
accomplished quite completely among the Thallophytes.
The differentiation of the tissues of the nutritive body,
however, is that which specially concerns us in this chapter.

A tissue is an aggregation of similar cells doing similar
work. Among the Thallophytes the nutritive body is prac-
tically one tissue, although in some of the larger Thallo-
phytes the outer and the inner cells differ somewhat. This
primitive tissue is composed of cells with thin walls and
active protoplasm, and is called parenchyma, meaning
“parent tissue.”

Among the Bryophytes, in the leafy gametophore and
in the sporogonium, there is often developed considerable
dissimilarity among the cells forming the nutritive body,
but the cells may all still be regarded as parenchyma. It

280

DIFFERENTIATION OF TISSUES O81

isin the sporophyte of the Pteridophytes and Spermato-
phytes that this differentiation of tissues becomes extreme,
and tissues are organized which differ decidedly from
parenchyma. This differentiation means division of labor,
and the more highly organized the body the more tissues
there are.

All the other tissues are derived from parenchyma, and
as the work of nutrition and of reproduction is always
retained by the parenchyma cells, the derived tissues are
for mechanical rather —
than for vital purposes. )

There is a long list of <

these derived and me-
chanical tissues, some of
them being of general’
occurrence, and others
more restricted, and

there is every gradation NA A
between them and the gre. 264. Parenchyma and sclerenchyma from
parenchyma from which the pa of Pteris, in cross-section.—CHAmM-
they have come. We ~

shall note only a few which are distinctly differentiated
and which are common to all vascular plants.

149. Parenchyma,—The parenchyma of the vascular plants
is typically made up of cells which have thin walls and whose
three dimensions are approximately equal (Figs. 264, 265).
though sometimes they are elongated. Until abandoned,
such cells contain very active protoplasm, and it is in them
that nutritive work and cell division are carried on. So
long as these cells retain the power of cell division the
tissue is called meristem, or it is said to be meristematic,
from a Greek word meaning ‘to divide.” When the cells
stop dividing, the tissue is said to be permanent. The
growing points of organs, as stems, roots, and leaves, are
composed of parenchyma which is meristematic (Figs. 266,
274), and meristem occurs wherever growth is going on.

982 PLANT STRUCTURES

150. Mestome and stereome—When the plant body be-
comes complex a conductive system is necessary, so that
the different regions of the body may be put into communi-
cation. The material absorbed
by the roots must be carried to
the leaves, and the food manu-
factured in the leaves must
be carried to regions of growth
and storage. This business of
transportation is provided for
by the specially organized ves-
sels referred to in preceding
chapters, and all conducting tis-
sue, of whatever kind. is spoken
of collectively as mestome.

If a complex body is to main-
tain its form, and especially if
it is to stand upright and be-
come large, it must develop
structures rigid enough to fur-
nish mechanical support. All
the tissues which serve this pur-
pose are collectively known as

Fie. 265. Same tissues as in pre- stereome.
ceding figure, in longitudinal sec- The sporophyte body of

mele —CHametius. Pteridophytes and Spermato-

phytes, therefore, is mostly

made up of living and working parenchyma, which is
traversed by mechanical mestome and stereome.

151. Dicotyl and Conifer stems.—The stems of these two
groups are so nearly alike in general plan that they may
be considered together. In fact, the resemblances were
once thought to be so important that these two groups
were put together and kept distinct from Monocotyledons ;
but this was before the gametophyte structures were
known to bear very different testimony.

DIFFERENTIATION OF TISSUES 283

At the apex of the growing stem there is a group of
active meristem cells, from which all the tissues are de-
rived (Fig. 266). This group is known as the apical group.
Below the apical group the tissues and regions of the stem
begin to appear, and still farther down they become dis-
tinctly differentiated, passing into permanent tissue, the
apical group by its
divisions continually
adding to them and
increasing the stem
in length.

Just behind the
apical group, the
cells begin to give the
appearance of being
organized into three
great embryonic re-

gions, the cells still

remaining meristem- Fic. 266. Section through growing point of stem of
3 : Hippuris : below the growing point, composed

atic (Fig. 266). At of a uniform meristem tissue, the three embry-

the surface there is a onic regions are outlined, showing the dermato-
“ gen (ad, d), the central plerome (,/, p), and be-
single layer of cells tween them the periblem.—After DE Bary.

distinct from those
within, known as the dermatagen, or “ skin-producer,” as
farther down, where it becomes permanent tissue, it is the
epidermis. In the center of the embryonic region there
is organized a solid cylinder of cells, distinct from those
around it, and called the plerome, meaning “that which
fills up.” Farther down, where the plerome passes into
permanent tissue, it is called the central cylinder or stele
(‘‘column”). Between the plerome and dermatogen is
a tissue region called the periblem, meaning “that which
is put around,” and when it becomes permanent tissue it
is called the cor/ex, meaning “ bark” or “rind.”

Putting these facts together, the general statement is
that at the apex there is the apical group of meristem cells ;

”

284 PLANT STRUCTURES

below them are the three embryonic regions, dermatogen,
periblem, and plerome; and farther below these three
regions pass into permanent tissue, organizing the epider-
mis, cortex, and stele. The three embryonic regions are
usually not so distinct in the Conifer stem as in the Dico-
tyl stem, but both stems have epidermis, cortex, and stele.
Epidermis.—The epidermis is a protective layer, whose
cells do not become so much modified but that they may
be regarded as parenchyma. It gives rise also to super-
ficial parts, as hairs, etc. In the case of trees, the epidermis
does not usually keep up with the increasing diameter, and
disappears. This puts the work of protection upon the
cortex, which organizes a superficial tissue called cork, a
prominent part of the structure known as bark.
Cortee.—The cortex is characterized by containing
much active parenchyma, or primitive tissue, being the
chief seat of the life activities of the stem. Its superficial
cells, at least, contain chlorophyll and do chlorophyll work,
while its deeper cells are usually temporary storage places
for food. The cortex is also char-
acterized by the development of
stereome, or rigid tissues for me-
chanical support. The stereome
may brace the epidermis, forming
the hypodermis ; or it may form
bands and strands within the cor-
tex; in fact, its amount and ar-
rangement differ widely in differ-
ent plants.
The two principal stereome tis-
Fr ee mn em sues are collenchyma and seleren-
mon dock (umes), showing ehyma, meaning *‘ sheath-tissue ”
aie ee me and “hard-tissue” respectively.
In collenchyma the cells are thick-
ened at the angles and have very elastic walls (Fig. 26%),
making the tissue well adapted for parts which are growing

DIFFERENTIATION OF TISSUES 985

in length. The chief mechanical tissue for parts which
have stopped growing in length is sclerenchyma (Figs. 264,
265). The cells are thick-walled, and usually elongated
and with tapering ends, including the so-called “ fibers.”

Via
ZN Fs
SE san SZ) )

A, cross-section; B, longitudinal section; the letters in both referring to the same
structures; J/, pith; XY, xylem, containing spiral (s, s’) and pitted (¢, ¢’) vessels;
¢, cambium; P, phloem, containing sieve vessels (sb); 6, a mass of bast fibers or
sclerenchyma; ic, pith rays between the bundles; e, the bundle sheath; 7, cor-
tex.—After VINES.

Stele.—The characteristic feature of the stele or central
cylinder is the development of the mestome or vascular

286 PLANT STRUCTURES

tissues, of which there are two prominent kinds. The
tracheary vessels are for water conduction, and are cells
with heavy walls and usually large diameter (Fig. 268).
The thickening of the walls is not uniform, giving them a
very characteristic appearance, the thickening taking the
form of spiral bands, rings, or reticulations (Fig. 268, B).
Often the reticulation has such close meshes that the cell
wall has the appearance of being covered with thin spots,
and such cells are called ‘ pitted vessels.” The vessels with
spirals and rings are usually much smaller in diameter than
the pitted ones. The true tracheary cells are more or less
elongated and without tapering ends, fitting end to end
and forming a continuous longitudinal series, suggesting a
trachea, and hence the name. In the Conifers there are
no true tracheary ceils, as in
the Dicotyledons, except a few
small spiral vessels which are
formed at first in the young
stele, but the tracheary tissue
is made up of ¢racherds, mean-
ing “trachea-like,” differing
from truchee or true tracheary
vessels in having tapering ends
and in not forming a continu-
ous series (Fig. 269). The walls
of these tracheids are ** pitted”
in a way which is characteristic
of Gymnosperms, the ‘pits ”
appearing as two concentric
rings, called “ bordered pits.”
Fra. 269. ‘Tracheids from wood of The other prominent mes-
pine, sng teri ovis tome tissue developed inthe
stele is the steve vessels, for the
conduction of organized food, chiefly proteids (Fig. 208).
Sieve cells are so named because in their walls special areas
are organized which are perforated like the lid of a pepper-

DIFFERENTIATION OF TISSUES IST

box or a “sieve.” These perforated areas are the szeve-
plates, and through them the vessels communicate with
one another and with the adjacent tissue.

The tracheary and sieve vessels occur in separate
strands, the tracheary strand being called .rylem (“ wood”),
the sieve strand phloem (“bark”). A xylem and a phloem
strand are usually organized together to form a vascular
bundle, and it is these fiber-like bundles which are found
traversing the stems of all vascular plants and appearing
conspicuously as the veins of leaves. Among the Dicotyls
and Conifers the vascular bundles appear in the stele in
such a way as to outline a hollow cylinder (Fig. 216), the
xylem of each bundle being toward the center, the phloem
toward the circumference of the stem. The undifferenti-
ated parenchyma of the stele which the vascular cylinder
incloses is called the pith. In older parts of the stem the
pith is often abandoned by the activities of the plant, and
either remains as a dead spongy tissue, or disappears en-
tirely, leaving a hollow stem. Between the bundles form-
ing the evsrulur cylinder there is also undifferentiated
parenchyma, and as it seems to extend from the pith out
between the bundles like ‘‘rays from the sun,” the rays
are called pith rays.

Such vascular bundles as described above, in which the
xylem and phloem strands are ‘‘ side-by-side ” upon the same
radius, are called collatvral (Fig. 270). One of the pecul-
iarities of the collateral bundles of Dicotyls and Conifers,
however. is that when the two strands of each bundle are
organized some meristem is left between them. This means
that between the strands the work of forming new cells can
goon. Such bundles are said to be open; and the apen
collateral bundle is characteristic of the stems of the Dico-
tyls and Conifers.

The meristem between the xylem and phloem of the
open bundle is called cambium (Figs. 268, 270). The cam-
bium also extends across the pith rays between the bundles,

288 PLANT STRUCTURES
connecting the cambium in the bundles, and thus forming

acambium cylinder, which separates the xylem and phloem
of the vascular cylinder. This cambium continues the for-

PE

Fig. 270. Cross-section of open collateral vascular bundle from stem of castor-oil
plant (Ricinus), showing pith cells (a), xylem containing spiral (2) and pitted (q)
vessels, cambium of bundle (c) and of pith rays (cb), phloem containing sieve ves-
sels (y), three bundles of bast fibers or sclerenchyma (), the bundle sheath con-
taining starch grains, und outside of it parenchyma of the cortex (r),—After Sacits.

mation of xylem tissue on the one side and phloem tissue
on the other in the bundles, und new parenchyma between
the bundles, and so the stem increases in diameter. If the
stem lives from year to year the addition made by the cam-
bium each season is marked off from that of the previous
season, giving rise to the so-called growth rings or annual
rings, 80 conspicuous a feature of the cross-section of tree

DIFFERENTIATION OF TISSUES 989

trunks (Fig. 217). This continuous addition to the vessels
increases the capacity of the stem for conduction, and per-
mits the further extension of branches and a larger display
of leaves.

The annual additions to the xylem are added to the in-
creasing mass of wood. The older portions of the xylem
mass are gradually abandoned by the ascending water
(<‘sap”), often change in color, and form the heart-wood.
The younger portion, through which the sap is moving, is
the sup-wood. It is evident, however, that the annual ad-
ditions to the phloem are not in a position for permanency.
The new phloem is deposited inside of the old, and this, to-
gether with the new xylem, presses upon the old phloem,
which becomes ruptured in various ways, and rapidly or
very gradually peels off, being constantly renewed from
within. It is the protecting layers of cork (see this section
under Cortez), the old phloem, and the new phloem down
to the cambium, which constitute the so-called bark of
trees, a structure exceedingly complex and extremely vari-
able in different trees.

The stele also frequently develops stereome tissue in the
form of sclerenchyma. These thick-walled fibers are often
closely associated with one or both of the vascular strands
of the bundles (Fig. 270), and lead to the old name jidro-
vascular bundles.

To sum up, the stems of Dicotyledons and Conifers are
characterized by the development of a vascular cylinder, in
which the bundles are collateral and open, permitting
increase in diameter, extension of the branch system, and
a continuous increase in leaf display.

152. Monocotyl stems—In the stems of Monocotyledons
there is the same apical development and differentiation
(Fig. 266). The characteristic difference from the Dicotyl
and Conifer type, just described, is in connection with the
development of the vascular bundles in the stele. Instead
of outlining a hollow cylinder, the bundles are scattered

290 PLANT STRUCTURES

through the stele (Fig. 214). This lack of regularity would
interfere with the organization of a cambium cylinder, and
we find the bundles collateral but closed—that is, with no
meristem left between the xylem and phloem (Fig. 271).

Rs

evar: }

Fig. 271. Cross-section of a closed collateral bundle from the stem of corn, showing
the xylem with annular (7), spiral (s), and pitted (g) vessels: the phloem contain-
ing sieve vessels (v), and separated from the xylem by no intervening cambium;
both xylem and phloem surrounded by 2 mass of sclerenchyma (fibers); and in-
vesting vessels and fibers the parenchyma (p) of the pith-like tissue through
which the bundles are distributed.—After Sacus.

This lack of cambium means that stems living for sey-
eral years do not increase in diameter, but become columnar

DIFFERENTIATION OF TISSUES 291

shafts, as in the palm, rather than much elongated cones.
It also means lack of ability to develop an extending branch
system or to display more numerous leaves each year. The
palm may be taken as a typical result of such a structure,
with its columnar and unbranched trunk, and its foliage
crown containing about the same number of leaves each year.

The lack of regular arrangement of the bundles also
prevents the outlining of a pith region or the organization
of definite pith rays. The failure to increase in diameter
also precludes the necessity of bark, with its protective cork
constantly renewed, and its sloughing-off phloem.

To sum up, the stems of the Monocotyledons are
characterized by the vascular bundles not developing a
cylinder or any regular arrangement, and by collateral and
closed bundles, which do not permit increase in diameter,
or a branch system, or increase in leaf display.

153. Pteridophyte stems.—The stems of Pteridophytes
are quite different from those of Spermatophytes. While
the large Club-mosses (Lyco-
podium) and Jscetes usually
have an apical group of meris-
tem cells, as among the Seed-
plants, the smaller Club-mosses
(Selaginella), Ferns, and Horse-
tails usually have a single api-
cal cell, whose divisions give
rise to all the cells of the stem.

Fig. 272. Diagram of tissnes in cross-
section of stem of a fern (Pferis),

Generally also a dermatogen is showing two masses of scleren-
Site * . chyma (sf), between and about
not organized, and in such which are vascular bundles. —

cases there isno true epidermis, — Cuamperrary.

the cortex developing the ex-

ternal protective tissue. In the cortex there is usually an
extensive development of stereome. in the form of scleren-
chyma (Fig. 272), the stele furnishing little or none, and
the vascular bundles not adding much to the rigidity, as
they do in the Seed-plants.

299 PLANT STRUCTURES

In ELquasetum and Isocetes the vascular bundles may be
said to be collateral, as in the Seed-plants, but the charac-
teristic Pteridophyte type is very different. In fact, the
vascular masses can hardly be compared with the bundles
of the Seed-plants, although they are called bundles for
convenience. In the stele one or more of these bundles
are organized (Fig. 272), the tracheary vessels (xylem) being
in the center and completely invested by the sieve vessels

Fic. 278. Cross-section of concentric vascular bundle of a fern (Pteris): the single
row of shaded cells investing the others is the bundle sheath; the large and heavy-
walled cells within constitute the xylem; and between the xylem and the bundle
sheath is the phloem.—CHAMBERLAIN.

(phloem). This is called the concentric bundle (Fig. 273),
as distinguished from the collateral bundles of Seed-plants,
and is characteristic of Pteridophyte stems.

DIFFERENTIATION OF TISSUES 993

154. Roots—True roots appear only in connection with
the vascular plants (Pteridophytes and Spermatophytes) ;
and in all of them the structure is essentially the same,
and quite different from stem structure. A single ap-
ical cell (in most Pteridophytes) (Fig. 274) or an apical
group (in Spermatophytes) usually gives rise to the three
embryonic regions—dermatogen, periblem, and plerome
(Fig. 275).

A fourth region, how-
ever, peculiar to root, is
usually added. The apical

Fie. 274. Section through root-tip of Fig. 275. A longitudinal section through
Pteris; the cell with a nucleus is the the root-tip of shepherd’s purse,

single apical cell, which in front has showing the plerome (p/), surround-
cut off cells which organize the root- ed by the periblem (p), outside of
cap.—CHAMBERLAIN. periblem the epidermis (e) which
disappears in the older parts of the

cell or group cuts off a tis- root, and the prominent root-cap (¢).

—From ‘Plant Relations.”

sue in front of itself (Fig.
274), known as the calyptrogen, or “cap producer,” for it
organizes the root-cap, which protects the delicate meri-
stem of the growing point.

Another striking feature is that in the stele there is
organized a single solid vascular cylinder, forming a tough
central axis (Fig. 277), from which the usually well-devel-
oped cortex can be peeled off as a thick rind. In this vas-
cular axis, which is called ‘‘a bundle ” for convenience but
does not represent the bundle of Seed-plant stems, the ar-
rangement of the xylem and phloem is entirely unlike that

37

294 PLANT STRUCTURES

Fie. 276. Cross-section of the vascular axis of a root, showing radiate type of bundle
the xylem (j) and phloem (pf) alternating. —After Sacus.

found in stems. The xylem is in the center and sends out
a few radiating arms, between which are strands of phloem,

Fie, 277. Endogenous origin of root branch-
es, showing them (7) arising from the cen-
tral axis (7) and breaking through the
cortex (7).—After VINEs.

forming the so-called
radiate bundle (Fig. 276).
This arrangement brings
the tracheary vessels
(xylem) to the surface of
the bundle region, which
is not true of either the
concentric or collateral
bundle. This seems to
be associated with the
fact that the xylem is to
receive and conduct the
water absorbed from the
soil. It should be said
that this characteristic

DIFFERENTIATION OF TISSUES 295

bundle structure of the root appears only in young and
active roots. In older ones certain secondary changes take
place which obscure the structure and result in a resem-
blance to the stem.

The origin of branches in roots is also peculiar. In
stems branches originate at the surface, involving epi-
dermis, cortex, and vascular bundles, such an origin being
called exogenous (** produced outside“); but in roots
branches originate on the vascular cylinder, burrow through
the cortex, and emerge at the surface (Fig. 277). If the
cortex be stripped off from a root with branches, the
branches are left attached to the woody axis, and the cor-
tex is found pierced with holes made by the burrowing
branches. Such an origin is called endogenous, meaning
+ produced within.”

To sum up the peculiarities of the root, it may be said
to develop a root-eap. to have a solid vascular cylinder in
which the xylem and phloem are arranged to form a bundle
of the radiate type, and to branch endogenously.

Z ra
sh St
Fig. 278. A section through the leaf of lily, showing upper epidermis (we), lower epi-
dermis (/e) with its stomata (sf), mesophyll (dotted cells) composed of the palisade
region (p) and the spongy region (sp) with air spaces among the cells. and two
veins (v) cut across.—From * Plant Relations.”

296 PLANT STRUCTURES

155. Leaves—Leaves usually develop from an apical
region in the same general way as do stems and roots,
modified by their common dorsiventral character. Com-
paring the leaf of an ordinary seed-plant with its stem, it
will. be noted that the three regions are represented (Fig.
278): (1) the epidermis ; (2) the cortex, represented by
the mesophyll ; (3) the stele, represented by the veins.

In the case of collateral bundles, where in the stem the
xylem is always toward the center and the phloem is toward
the circumference, in the leaves the xylem is toward the
upper and the phloem toward the lower surface.

CHAPTER XVI
PLANT PHYSIOLOGY

156. Introductory.—Plants may be studied from several
points of view, each of which has resulted in a distinct
division of Botany. The study of the forms of plants and
their structure is MoRPHOLOGY, and it is this phase of Bot-
any which has been chiefly considered in the previous chap-
ters. The study of plants at work is PaysioLoGy, and as
structure is simply preparation for work, the preceding
chapters have contained some Physiology, chiefly in refer-
ence to nutrition and reproduction. The study of the clas-
sification of plants is Taxonomy, and in the preceding
pages the larger groups have been outlined. The study of
plants as to their external relations is EcoLoey, a subject
which will be presented in the following chapter, and which
is the chief subject of Plant Relations. The study of the
diseases of plants and their remedies is ParnoLoey ; their
study in relation to the interests of man is Economic
Borany.

Besides these general subjects, which apply to all plants,
the different groups form the subjects of special study. The
study of the Morphology, Physiology, or Taxonomy of the
Bacteria is Bacteriology; of the Alge, Algology; of the
Fungi, Mycology; of the Bryophytes, Bryology ; of the
fossil plants, Paleobotany or Paleophytology, etc.

In the present chapter it is the purpose to give a very
brief outline of the great subject of Plant Physiology, not
with the expectation of presenting its facts adequately, but
with the hope that the important field thus presented may

297

298 PLANT STRUCTURES

attract to further study. It is merely the opening of a door
to catch a fleeting glimpse.

A common division of the subject presents it under five
heads: (1) Stability of form, (2) Nutrition, (3) Respira-
tion, (4) Movement, (5) Reproduction.

STABILITY OF FORM

157. Turgidity.—It is a remarkable fact that plants and
parts of plants composed entirely of cells with very thin and
delicate walls are rigid enough to maintain their form.
It has already been noted (see § 20) that such active cells
exert an internal pressure upon their walls. This seems to
be due to the active absorption of liquid, which causes the
very elastic walls to stretch, as in the ‘‘ blowing up ” of a
bladder. In this way each gorged and distended cell be-
comes comparatively rigid, and the mass of cells retains its
form. It seems evident that the active protoplasm greedily
pulls liquid through the wall and does not let it escape so
easily. If for any reason the protoplasm of a gorged cell
loses its hold upon the contained liquid the cell collapses.

158. Tension of tissues—The rigidity which comes to
active parenchyma cells through their turgidity is increased
by the tensions developed by adjacent tissues. For exam-
ple, the internal and external tissues of a stem are apt to
increase in volume at different rates; the faster will pull
upon the slower, and the slower will resist, and thus be-
tween the two a tension is developed which helps to keep
them rigid. This is strikingly shown by splitting a dande-
lion stem, when the inner tissue, relieved somewhat from
the resistance of the outer, elongates and causes the strip
to become strongly curved outward or cven coiled. Experi-
ments with strips from active twigs, including the pith,
will usually demonstrate the same curve outward. Tension
of tissues is chiefly developed, of course, where elongation
is taking place.

PLANT PHYSIOLOGY 299

159. Stereome—When growth is completed, cell walls
lose their elasticity. turgidity becomes less, and therefore
tensions diminish, and rigidity is supplied by special ster-
eome tissues, chief among which is sclerenchyma. An-
other stereome tissue is collenchyma, which on account of
its elastic walls can be used to supplement turgidity and
tension where elongation is still going on. For a fuller
account of stereome tissues see § 150.

NUTRITION

160. Food—Plant food must contain carbon (C), hydro-
gen (H), oxygen (Q), and nitrogen (\). and also more
or less of other elements, notably sulphur, phosphorus,
potassium, calcium, magnesium, and iron. In the case
of green plants these elements are obtained from inor-
ganic compounds and food is manufactured ; while plants
without chlorophyll obtain their food already organized.
The sources of these elements for green plants are as
follows: Carbon from carbon dioxide (CQ,) of the air;
hydrogen and oxygen from water (H,0):; and nitrogen
and the other elements from their various salts which
occur in the soil and are dissolved in the water which
enters the plant.

All of these substances must present themselves to
plants in the form of a gas or a liquid, as they must pass
through cell walls: and the processes of absorption have
to do with the taking in of the gas carbon dioxide and of
water in which the necessary salts are dissolved.

161. Absorption—Green plants alone will be considered,
as the unusual methods of securing food have been men-
tioned in Chapter VII. For convenience also, only terres-
trial green plants will be referred to, as it is simple to
modify the processes to the aquatic habit, where the sur-
rounding water supplies what is obtained by land plants
from both air and soil.

300 PLANT STRUCTURES

In such plants the carbon dioxide is absorbed directly
from the air by the foliage leaves, whose expanse of surface
is as important for this purpose as for exposing chlorophyll
to light. When the work of foliage leaves is mentioned it
must always be understood that it applies as well to any
green tissue displayed by the plant.

The water, with its dissolved salts, is absorbed from the
soil by the roots. Only the youngest parts of the root-
system can absorb, and the absorbing capacity of these
parts is usually vastly increased by the development of
numerous root hairs just behind the growing tip (Fig. 194).
These root hairs are ephemeral, new ones being continu-
ally put out as the tip advances, and the older ones disap-
pearing. They come in very close contact with the soil
particles, and ‘suck in” the water which invests each
particle as a film.

162. Transfer of water.—The water and its dissolved salts
absorbed by the root-system must be transferred to the foli-
age leaves, where they are to be used, along with the carbon
dioxide, in the manufacture of food.

Having entered the epidermis of the absorbing rootlets
the water passes on to the cortex, and traversing it enters
the xylem system of the central axis. In some way this
transfer is accompanied by pressure, known as root pres-
sure, which becomes very evident when an active stem is
cut off near the ground. The stump is said to “bleed,”
and sends out water (‘‘sap”) as if there were a force
pump in the root-system. This root pressure doubtless
helps to lift the water through the xylem of the root into
the stem, and in low plants may possibly be able to send it
to the leaves, but for most plants this is not possible.

When the water enters the xylem of the root it is ina
continuous system of vessels which extends through the
stem and out into the leaves. The movement of the ab-
sorbed water through the xylem is called the transpiration
current, or very commonly the ‘‘ascent of sap.” An ex-

PLANT PHYSIOLOGY 301

periment demonstrating this ascent of sap and its route
through the xylem will be found described in Plant [ela-
tions, p. 151. How it is that the transpiration current
moves through the xylem is not certainly known.

163. Transpiration— When the water carrying dissolved
salts reaches the mesophyll cells, some of the water and all
of the salts are retained for food manufacture. However,
much more water enters the leaves than is needed for food,
this excess having been used for carrying soil salts. When
the soil salts have reached their destination the excess of
water is evaporated from the leaf surface, the process being
called transpiration. For an experiment demonstrating
transpiration see Plant Relations, § 26.

This transpiration is regulated according to the needs
of the plant. If the water is abundant, transpiration is
encouraged ; if the water supply is low, transpiration is
checked. One of the chief ways of regulating is by means
of the very small but exceedingly numerous stomata (see §
79 [4]), whose guard cells become turgid or collapse and so
determine the size of the opening between them. It has
been estimated that a leaf of an ordinary sunflower contains
about thirteen million stomata, but the number varies widely
in different plants. In ordinary dorsiventral leaves the sto-
mata are much more abundant upon the lower surface than
upon the upper, from which they may be lacking entirely.
In erect leaves they are distributed equally upon both sur-
faces ; in floating leaves they occur only upon the upper
surface ; in submerged leaves they are lacking entirely.

The amount of water thus evaporated from active
leaves is very great. It is estimated that the leaves of a
sunflower as high as a man evaporate about one quart of
water in a warm day; and that an average oak tree in its
five active months evaporates about twenty-eight thousand
gallons. If these figures be applied to a meadow or a
forest the result may indicate the large importance of this
process.

802 PLANT STRUCTURES

164. Photosynthesis—This is the process by which car-
bon dioxide and water are “broken up,” their elements
recombined to form a carbohydrate, and some oxygen given
off as a waste product, the mechanism being the chloroplasts
and light. It has been sufficiently described in § 55, and
also in Plant Relations, pp. 28 and 150.

165. Formation of proteids—The carbohydrates formed
by photosynthesis, such as starch, sugar, etc., contain car-
bon, hydrogen, and oxygen. Ont of them the living cells
must organize proteids, and in the reconstruction nitrogen
and sulphur, and sometimes phosphorus, are added. This
work goes on both in green cells and other living cells, as
it does not seem to be entirely dependent upon chloroplasts
and light.

166. Transfer of carbohydrates and proteids——These two
forms of food having been manufactured, they must be
carried to the regions of growth or storage. In order to be
transported they must be in soluble form, and if not already
soluble they must be digested, insoluble starch being con-
verted into soluble sugar, etc. In these digested forms
they are transported to regions where work is going on,
and there they are assimilated—that ‘is, transformed into
the enormously complex working substance protoplasm ;
or they are transported to regions of storage and there they
are reconverted into insoluble storage forms, as starch, etc.

These foods pass through both the cortex and phloem
in every direction, but the long-distance transfer of pro-
teids, as from leaves to roots, seems to be mainly through
the sieve vessels.

RESPIRATION

167. Respiration.—This is an essential process in plants
as well as in animals, and is really the phenomenon of
“breathing.” The external indication of the process is
the absorption of oxygen and the giving out of carbon di-
oxide ; and it goes on in all organs, day and night. When

PLANT PHYSIOLOGY 303

it ceases death ensues sooner or later. By this process
energy, stored up by the processes of nutrition, is liberated,
and with this liberated energy the plant works. It may be
said that oxygen seems to have the power of arousing pro-
toplasm to activity.

It is not sufficient for the air containing oxygen to come
in contact merely with the outer surface of a complex plant,
as its absorption and transfer would be too slow. There
must be an ‘internal atmosphere” in contact with the
living cells. This is provided for by the intercellular
spaces, which form a labyrinthine system of passageways,
opening at the surface through stomata and lenticels (pores
through bark). In this internal atmosphere the exchange
of oxygen and carbon dioxide is effected, the oxygen being
renewed by diffusion from the outside, and the carbon
dioxide finally escaping by diffusion to the outside.

MOVEMENT

168. Introductory.—In addition to movements of mate-
rial, as described above, plants execute movements depend-
ent upon the activity of protoplasm, which result in change
of position. Naked masses of protoplasm, as the plas-
modium of slime-moulds (see § 51), advance with a sliding,
snail-like movement upon surfaces ; zoospores and ciliated
sperms swim freely about by means of motile cilia; while
many low plants, as Bacteria (§ 52), Diatoms (§ 34), Oseil-
laria (§ 20), ete., have the power of locomotion.

When the protoplasm is confined within rigid walls and
tissues, as in most plants, the power of locomotion usually
disappears, and the plants are fixed ; but within active cells
the protoplasm continues to move, streaming back and
forth and about within the confines of the cell.

In the case of complex plants, however, another kind
of movement is apparent, by which parts are moved and
variously directed, sometimes slowly, sometimes with great

304 PLANT STRUCTURES

rapidity. In these cases the part concerned develops a
curvature, and by various curvatures it attains its ultimate
position. These curvatures are not necessarily permanent,
for a perfectly straight stem results from a series of cur-
vatures near its apex. Curvatures may be developed by
unequal growth on the two sides of an organ, or by unequal
turgidity of the cells of the two sides, or by the unequal
power of the cell walls to absorb water.

169. Hygroscopic movements.—These movements are only
exhibited by dry tissues, and hence are not the direct result
of the activity of protoplasm. The dry walls absorb mois-
ture and swell up, and if this absorption of moisture and
its evaporation is unequal on two sides of an organ a curva-
ture will result. In this way many seed vessels are rup-
tured, the sporangia of ferns are opened, the operculum of
mosses is lifted off by the peristome, the hair-like pappus
of certain Composites is spread or collapsed, certain seeds
are dispersed and buried, etc. One of the peculiarities of
this hygroscopic power of certain cells is that the result
may be obtained through the absorption of the moisture of
the air, and the hygroscopic awns of certain fruits have
been used in the manufacture of rough hygrometers
(‘‘ measures of moisture ”).

170. Growth movements.—Growth itself is a great physi-
ological subject, but certain movements which accompany
it are referred to here. Two kinds of growth movements
are apparent.

One may be called nutation, by which is meant that the
growing tip of an organ does not advance in a straight
line, but bends now toward one side, now toward the other.
In this way the tip describes a curve, which may be a
circle, or an ellipse of varying breadth; but as the tip is
advancing all the time, the real curve described is a spiral
with circular or elliptical cross-section. The sweep of a
young hop-vine in search of support, or of various tendrils,
may be taken as extreme illustrations, but in most cases

PLANT PHYSIOLOGY 305

the nutation of growing tips only becomes apparent through
prolonged experiment.

The other prominent growth movement is that which
places organs in proper relations for their work, sending
roots into the soil and stems into the air, and directing
leaf planes in various ways. For example, in the germina-
tion of an ordinary seed, in whatever direction the parts
emerge the root curves toward the soil, the stem turns
upward, and the cotyledons spread out horizontally.

The movement of nutation seems to be due largely to
internal causes, while the movements which direct organs
are due largely to external causes known as stimuli, Some
of the prominent stimuli concerned in directing organs are
as follows:

Heliotropism.—tIn this case the stimulus is light, and
under its influence acrial parts are largely directed. Plants
growing in a window furnish plain illustration of helio-
tropism. In general the stems and petioles curve toward
the light, showing positive heliutropism (Fig. 279); the
leaf blades are directed at right angles to the rays of light,
showing transverse heliotropism ; while if there are hold-
fasts or aérial roots they are directed away from the light,
showing negative heliotropism. The thallus bodies of ferns,
liverworts, etc., are transversely heliotropic, as ordinary
leaves. a position best related to chlorophyll work. If the
light is too intense, leaves may assume an edgewise or pro-
file position, a condition well illustrated by the so-called
“compass plants.” (See Plant Relations, p. 10.)

Geotropism.—In this case the stimulus is gravity, and
its influence in directing the parts of plants is very great.
All upward growing plants, as ordinary stems. some leaves,
etc.. are negatively geotropic, growing away from the center
of gravity. Tap-roots are notable illustrations of positive
geotropism, growing toward the source of gravity with con-
siderable force. Lateral branches from a main or tap-root,
however. are usually transversely geotropic.

Fig, 279. Sunflower stems with the upper part of the stem sharply bent toward the
light, giving the leaves better exposure, the stem showing positive heliotropism,—
After SCHAFPNER.

PLANT PITYSIOLOGY 307

That these influences in directing are very real is testi-
fied to by the fact that when the organs are turned aside
from their proper direction they will curve toward it and
overcome a good deal of resistance to regain it. Although
these curvatures are mainly developed in growing parts,
even mature parts which have been displaced may be
brought back into position. For example, when the stems
of certain plants, notably the grasses, have been prostrated
by wind, etc., they often can resume the erect position under
the influence of negative geotropism, a very strong and even
angular curvature being developed at certain joints.

Hydrotropism.—The influence of moisture is very strong
in directing certain organs, notably absorbing systems.
Roots often wander widely and in every direction under
the guidance of hydrotropism, even against the geotropic
influence. Ordinarily geotropism and hydrotropism act in
the same direction, but it is interesting to dissociate them
so that they may “‘pull” against one another. For such
an experiment see Plant Relutionsx, p. 91.

Other stimuli.—Other outside stimuli which have a
directive influence upon organs are chemical substances
(chemotropism), such as direct sperms to the proper female
organ ; heat (¢hermofrapism) ; water currents (rheotrapism) 5
mechanical contact, etc. The most noteworthy illus-
trations of the effect of contact are furnished by tendril-
climbers. When a nutating tendril comes in contact with
a support a sharp curvature is developed which grasps it.
In many cases the irritable response goes further. the ten-
dril between the plant axis and the support developing a
spiral coil.

171. Irritable movements.—The great majority of plants
can execute movements only in connection with growth, as
described in the preceding section, and when mature their
parts are fixed and incapable of further adjustment. Cer-
tain plants, however, have developed the power of moving
mature parts, the motile part always being a leaf, such as

308 PLANT STRUCTURES

foliage leaf, stamen, etc. It is interesting to note that these
movements have been cultivated by but few families, nota-
ble among them being the Legumes (§ 141).

These movements of mature organs, some of which are
very rapid, are due to changes in the turgidity of cells. As
already mentioned (§ 157), turgid cells are inflated and
rigid, and when turgidity ceases the cells collapse and the
tissue becomes flaccid. A special organ for varying tur-
gidity, known as the pulvinus, is usually associated with
the motile leaves and leaflets. The pulvinus is practically
a mass of parenchyma cells, whose turgidity is made to vary
by various causes, and leaf-movement is the result.

The causes which induce some movements are unknown,
as in the case of Desmodium gyrans (see Plant Relations,
p. 49), whose small lateral leaflets uninterruptedly de-
scribe circles, completing a cycle in one to three minutes.

In other cases the inciting cause is the change from light
to dark, the leaves assuming at night a very dif-
ferent position from that during the day. Dur-
ing the day the leaflets are spread out freely,

Fig. 280. A leaf of a sensitive plant in two conditions: in the figure to the left the leaf
is fully expanded, with its four main divisions and numcrous leaflets well spread;
in the figure to the right is shown the same leaf after it has been ‘‘ shocked” by
a sudden touch, or by sudden heat, or in some other way; the leaflets have been
thrown together forward and upward, the four main divisions have been moved
together, and the main leaf-stalk has been directed sharply downward,—After
DucuaRtTRE.

PLANT PHYSIOLOGY 309

while at night they droop and usually fold together (see
Plant Relutions, pp. 9, 10). These are the so-called nycti-
tropic movements or *‘ night movements,” which may be ob-
served in many of the Legumes, as clover, locust, bean, etc.

In still other cases, mechanical irritation induces move-
ment, as sudden contact, heat, injury, etc. Some of the
“carnivorous plants” are notable illustrations of this, es-
pecially Dionea, which snaps its leaves shut like a steel
trap when touched (see Plunt Relutivns, p. 161). Among
the most irritable of plants are the so-called *‘ sensitive
plants,” species of Mimosa, Acacia, etc., all of them Le-
gumes. The most commonly cultivated sensitive plant is
Uinosa pudica (Fig. 280), whose sensitiveness to contact
and rapidity of response are remarkable (see Plant Rela-
tions, p. 48).

REPRODUCTION

172. Reproduction.—The important function of repro-
duction has been considered in connection with the various
plant groups. Among the lowest plants the only method
of reproduction is cell division, which in the complex
forms results in growth. In the more complex plants va-
rious outgrowths or portions of the body, as gemme, buds,
bulbs, tubers, various branch modifications, etc., furnish
means of propagation. All of these methods are included
under the head of vegetative multiplication. as the plants
are propagated by ordinary vegetative tissues.

When a special cell is organized for reproduction, dis-
tinct from the vegetative cells. it is called a spore, and re-
production by spores is introduced. The first spores devel-
oped seem to have been those produced by the division of
the contents of a mother cell. and are called axerval spores.
These spores are scattered in various ways—by swimming
(zoospores), by floating, by the wind, by insects.

Another type of spore is the serval spore. formed by
the union of two sexual cells called gametes. The gametes

38

310 PLANT STRUCTURES

seem to have been derived from asexual spores. At first
the pairing gametes are alike, but later they become differ-
entiated into syerms or male cells, and eggs or female cells.

With the establishment of alternation of generations,
the asexual spores are restricted to the sporophyte, and the
gametes to the gumetophyte. With the further introduction
of heterospory, the male and the female gametes are sepa-
rated upon different gametophytes, which become much
reduced.

With the reduction of the megaspores to one in a spo-
rangium (ovule), and its retention, the seed is organized,
and the elaborate scheme of insect-pollination is developed.

CHAPTER XVII
PLANT ECOLOGY

173. Introductory.— Ecology has to do with the external
relations of plants, and forms the principal subject of the
volume entitled Plant Relations, which should be consulted
for fuller descriptions and illustrations. It treats of the
adjustment of plants and their organs to their physical
surroundings, and also their relations with one another
and with animals, and has sometimes been called ‘plant
sociology.”

LIFE RELATIONS

174. Foliage leaves.—The life relation essential to foliage
leaves is the relation to light. This is shown by their
positions and forms, as well as by their behavior when
deprived of light. This light relation suggests the answer
to very many questions concerning leaves. It is not very
important to know the names of different forms and differ-
ent arrangements of leaves, but it is important to observe
that these forms and arrangements are in response to the
light relation.

In general a leaf adjusts its own position and its relation
to its fellows so as to receive the greatest amount of light.
Upon erect stems the leaves occur in vertical rows which
are uniformly spaced about the circumference. If these
rows are numerous the leaves are narrow; if they are few
the leaves are usually broad. If broad leaves were associ-

ated with numerous rows there would be excessive shading ;
311

312 PLANT STRUCTURES

if narrow leaves were associated with few rows there would
be waste of space.

It is very common to observe the lower leaves of a stem
long-petioled, those above short-petioled, and so on until
the uppermost have sessile blades, thus thrusting the blades
of lower leaves beyond the shadow of the upper leaves.
There may also be a gradual change in the size and direc-
tion of the leaves, the lower ones being relatively large and
horizontal, and the upper ones gradually smaller and more
directed upward. In the case of branched (compound)
leaves the reduction in the size of the upper leaves is not
so necessary, as the light strikes between the upper leaflets
and reaches those below.

On stems exposed to light only or chiefly on one side,
the leaf blades are thrown to the lighted side in a variety
of ways. Inivies, many prostrate stems, horizontal branches
of trees, etc., the leaves brought to the lighted side are
observed to form regular mosaics, each leaf interfering
with its neighbor as little as possible.

There is often need of protection against too intense
light, against chill, against rain, etc., which is provided
for in a great variety of ways. Coverings of hairs or scales,
the profile position, the temporary shifting of position,
rolling up or folding, reduction in size, etc., are some of
the common methods of protection.

175. Shoots—The stem is an organ which is mostly
related to the leaves it bears, the stem with its leaves being
the shoot. In the foliage-bearing stems the leaves must be
displayed to the light and air. Such stems may be sub-
terranean, prostrate, floating, climbing, or erect, and all of
these positions have their advantages and disadvantages,
the erect type being the most favorable for foliage display.

In stems which bear scale leaves no light relation is
necessary, so that such shoots may be and often are sub-
terranean, and the leaves may overlap, as in scaly buds
and bulbs. The subterranean position is very favorable

PLANT ECOLOGY 313

for food storage, and such shoots often become modified as
food depositories, as in bulbs, tubers, rootstocks, ete. In
the scaly buds the structure is used for protection rather
than storage.

The stem bearing floral leaves is the shoot ordinarily
called ‘the flower,” whose structure and work have been
sufficiently described. Its adjustments have in view polli-
nation and seed dispersal, two very great ecological sub-
jects full of interesting details.

176. Roots.—Roots are absorbent organs or holdfasts or
both, and ‘they enter into a variety of relations. Most
common is the soil relation, and the energetic way in
which such roots penetrate the soil, and search in every
direction for water and absorb it, proves them to be highly
organized members. Then there are roots related to free
water, and others to air, each with its appropriate struc-
ture. More mechanical are the clinging roots (ivies, etc.),
and prop roots (screw pines, banyans, etc.), but their adap-
tation to the peculiar service they render is none the less
interesting.

The above statements concerning leaves, shoots, and
roots should be applied with necessary modifications to the
lower plants which do not produce such organs. The
light relation and its demands are no less real among the
Alge than among Spermatophytes, as well as relations to
air, soil, water, mechanical support, etc.

PLANT SOCIETIES

177. Introductory—Plants are not scattered at hap-
hazard over the surface of the earth, but are organized
into definite communities. These communities are deter-
mined by the conditions of living—conditions which admit
some plants and forbid others. Such an association of
plants living together in similar conditions is a plant so-
ciety. Closely related plants do not usually live together

314 PLANT STRUCTURES

in the same society, as their rivalry is too intense; but
each society is usually made up of unrelated plants which
can make use of the same conditions.

There are numerous factors which combine to deter-
mine societies, and it is known as yet only in a vague way
how they operate.

178. Ecological factors— Water.—This is a very impor-
tant factor in the organization of secieties, which are usu-
ally local associations. Taking plants altogether, the
amount of water to which they are exposed varies from
complete submergence to perpetual drought, but within
this range plants vary widely as to the amount of water
necessary for living.

Heat.—In considering the general distribution of plants
over the surface of the earth, great zones of plants are out-
lined by zones of temperature ; but in the organization of
local societies in any given area the temperature condi-
tions are nearly uniform. Usually plants work only at
temperatures between 32° and 122° Fahr., but for each
plant there is its own range of temperature, sometimes
extensive, sometimes restricted. Even in plant societies,
however, the effect of the heat factor may be noted in the
succession of plants through the working season, spring
plants being very different from summer and autumn
plants.

Soil.—The great importance of this factor is evident,
even in water plants, for the soil of the drainage area deter-
mines the materials carried by the water. Soil is to be
considered both as to its chemical composition and its
physical properties, the latter chiefly in reference to its
disposition toward water. Soils vary greatly in the power
of receiving and retaining water, sand having a high recep-
tive and low retentive power, and clay just the reverse,
and these factors have large effect upon vegetation.

Light.—All green plants can not receive the same amount
of light. Hence some of them have learned to live with a

PLANT ECOLOGY 315

less amount than others, and are ‘‘shade plants” as dis-
tinct from “light plants.” In forests and thickets many
of these shade plants are to be seen, which would find an
exposed situation hard to endure. In almost every society,
therefore, plants are arranged in strata, dependent upon
the amount of light they receive, and the number of these
strata and the plants characterizing each stratum are im-
portant factors to note.

Wind.—This is an important factor in regions where
there are strong prevailing winds. Wind has a drying
effect and increases the transpiration of plants, tending to
impoverish them in water. In such conditions only those
plants can live which are well adapted to regulate tran-
spiration.

The above five factors are among the most important,
but no single factor determines a society. As each factor
has a large possible range, the combinations of factors may
be very numerous, and it is these combinations which de-
termine societies. For convenience, however, societies are
usually grouped on the basis of the water factor, at least
three great groups being recognized.

179. Hydrophyte societies—These are societies of water
plants, the water factor being so conspicuous that the
plants are either submerged or standing in water. A plant
completely exposed to water, submerged, or floating, may
be taken to illustrate the usual adaptations. The epi-
dermal walls are thin, so that water may be absorbed
through the whole surface; hence the root system is very
commonly reduced or even wanting ; and hence the water-
conducting tissues (xylem) are feebly developed. The tis-
sues for mechanical support (stereome) are feebly devel-
oped, the plant being sustained by the buoyant power of
water. Such a plant, although maintaining its form in
water, collapses upon removal. Very common also is the
development of conspicuous air passages for internal aéra-
tion and for increasing buoyancy ; and sometimes a special

316 PLANT STRUCTURES

buoyancy is provided for by the development of bladder-
like floats.

Conspicuous among hydrophyte societies may be men-
tioned the following: (1) Free-swimming societies, in which
the plants are entirely sustained by water, and are free to
move either by locomotion or by water currents. Here
belong the “plankton societies,” consisting of minute
plants and animals invisible to the naked eye, conspicuous
among the plants being the diatoms ; also the ‘‘ pond so-
cieties,” composed of alge, duckweeds, etc., which float in
stagnant or slow-moving waters.

(2) Pondweed societies, in which the plants are an-
chored, but their bodies are submerged or floating. Here
belong the ‘‘rock societies,” consisting of plants anchored
to some firm support under water, the most conspicuous
forms being the numerous fresh-water and marine alge,
among which there are often elaborate systems of holdfasts
and floats. The ‘loose-soil societies” are distinguished
by imbedding their roots or root-like processes in the mucky
soil of the bottom (Figs. 281, 282). The water lilies with
their broad floating leaves, the pondweeds or pickerel weeds
with their narrow submerged leaves, are conspicuous illus-
trations, associated with which are alge, mosses, water
ferns, etc.

(3) Swamp societies, in which the plants are rooted in
water, or in soil rich in water, but the leaf-bearing stems
rise above the surface. The conspicuous swamp societies
are ‘reed swamps,” characterized by bulrushes, cat-tails
and reed-grasses (Figs. 283, 28+), tall wand-like Monocoty-
ledons, usually forming a fringe about the shallow margins
of small lakes and ponds; ‘‘swamp-moors,” the ordinary
swamps, marshes, bogs, etc., and dominated by coarse
sedges and grasses (Fig. 282); ‘‘swamp-thickets,” consist-
ing of willows, alders, birches, etc. ; ‘* sphagnum-moors,” in
which sphagnummoss predominates, and is accompanied by
numerous peculiar orchids, heaths, carnivorous plants, etc. ;

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PLANT ECOLOGY 319

““swamp-forests,” which are largely coniferous, tamarack
(larch), pine, hemlock, etc., prevailing.

showing the reed swamp growth of rushes and sedyes.—Cow Les.

Shore of Calionet Lake, OL,

283.

Kia.

180. Kerophyte societies—These societies are exposed to
the other extreme of the water factor, and are composed
of plants adapted to dry air and soil. To meet these

320 PLANT STRUCTURES

drought conditions numerous adaptations have been de-
veloped and are very characteristic of xerophytic plants.
Some of the conspicuous adaptations are as follows: peri-

water, eventually leading to filimg up.—Cow es.

Fig. 284, The border of Lake Calumet, Ill., showing the advance of sedges and rushes into the deeper

odic reduction of surface, annuals bridging over a period
of drought in the form of seeds, geophilous plants also dis-
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3824 PLANT STRUCTURES

parts, deciduous trees and shrubs dropping their leaves,
etc. ; temporary reduction of surface, the leaves rolling up
or folding together in various ways; profile position, the
leaves standing edgewise and not exposing their flat sur-
faces to the most intense light; motile leaves which can
shift their position to suit their needs ; small leaves, a very
characteristic feature of xerophytic plants; coverings of
hair; dwarf growth; anatomical adaptations, such as
cuticle, palisade tissue, etc. Probably the most conspicu-
ous adaptation, however, is the organization of ‘‘ water-
reservoirs,” which collect and retain the scanty water sup-
ply, doling it out as the plant needs it.

Some of the prominent societies are as follows: ‘‘rock-
societies ” composed of plants living upon exposed rock sur-
faces, walls, fences, etc., notably lichens and mosses ;
“sand societies,” including beaches, dunes, and sandy
fields ; ‘‘shrubby heaths,” characterized by heath plants ;
“plains,” the great areas of dry air and wind developed in
the interiors of continents; “‘ cactus deserts,” still more
arid areas of the Mexican region, where the cactus, agave,
yucca, etc., have learned to live by means of the most ex-
treme xerophytic modifications ; ‘‘ tropical deserts,” where
xerophytic conditions reach their extreme in the combina-
tion of maximum heat and minimum water ; ‘‘ xerophyte
thickets,” the most impenetrable of all thicket-growths,
represented by the “chaparral” of the Southwest, and the
“bush” and “scrub” of Africa and Australia; ‘‘ xero-
phyte forests,” also notably coniferous. (See Figs. 285,
286, 287.)

181. Mesophyte societies—Mesophytes make up the com-
mon vegetation, the conditions of moisture being medium,
and the soil fertile. This is the normal plant condition,
and is the arable condition—that is, best adapted for the
plants which man seeks to cultivate. If a hydrophytic
area is to be cultivated, it is drained and made mesophytic ;
if a xerophytic area is to be cultivated, it is irrigated and

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PLANT ECOLOGY 327

made mesophytic. As contrasted with hydrophyte and xero-
phyte societies. the mesophyte societies are far richer in
leaf forms and in general luxuriance. The artificial soci-
eties which have been formed under the influence of man,
through the introduction of weeds and culture plants. are
all mesophytic.

Among the mesophyte grass and herb societies are the
‘arctic and alpine carpets.” so characteristic of high lati-
tudes and altitudes where the conditions forbid trees. shrubs,
or even tall herbs : ‘‘ meadows,” areas dominated by grasses,
the prairies being the greatest meadows, where crasses and
flowering herbs are richly displaved ; ‘* pastures.” drier and
more open than meadows.

Among the woody mesophyte societies are the ‘ thick-
ets.” composed of willow. alder. birch, hazel, etc., either
pure or forming a jungle of mixed shrubs. brambles, and
tall herbs: ‘ deciduous forests.” the glory of the temperate
regions, rich in forms and foliage display. with annual fall
of leaves. and exhibiting the remarkable and conspicuous
phenomenon of autumnal coloration : ‘rainy tropical for-
ests.” in the region of trade winds, heavy rainfalls, and
great heat, where the world’s vegetation reaches its climax,
and where in a saturated atmosphere gigantic jungles are
developed, composed of trees of various heights, shrubs of
all sizes. tall and low herbs, all bound together in an inex-
tricable tangle by great vines or lianas, and covered by a
luxuriant growth of numerous epiphytes. (See Figs. 233,
289.)

GLOS 5A RY

(The definitions of a glossary are often unsatisfactory. It is much better to con-
sult the fuller explanations of the text by means of the index. The following glos-
sary includes only frequently recurring technical terms. Those which are found only
in reasonably close association with their explanation are omitted. The number fol-
lowing each definition refers to the page where the term will be found most fully
defined. }

ACTINOMORPHIC: applied to a flower in which the parts in each set are
similar; regular. 228.

AKENE: a one-seeded fruit which ripens dry and seed-like. 212.

ALTERNATION OF GENERATIONS: the alternation of gametophyte and
sporophyte in a life history. 94,

ANEMOPHILOUS: applied to flowers or plants which use the wind as agent
of pollination, 181.

ANISOCARPIC: applied to a flower whose carpels are fewer than the other
floral organs. 268.

ANTHER: the sporangium-bearing part of astamen. 197.

ANTHERIDIUM: the male organ, producing sperms. 16.

ANTIPODAL CELLS: in Angiosperms the cells of the female gametophyte
at the opposite end of the embryo-sac from the egg-apparatus.
205.

APETALOUS : applied to a flower with no petals. 221.

APocARPOUS: applied to a flower whose carpels are free from one an-
other. 226.

ARCHEGONIUM: the female, egg-producing organ of Brrophytes, Pteri-
dophrtes, and Gymnosperms. 100.

ARCHESPORIUM : the first cell or group of cells in the spore-producing
series. 102.

AscocaRP: a special case containing asci. 58.

AASCOSPORE : a spore formed within an ascus. 59.

Ascus: a delicate sac (mother-cell) within which ascospores develop.
59.

ASEXUAL SPORE: one produced usually by cell-division, at least not by
cell-union. 9.

829

330 GLOSSARY

CaLyx : the outer set of floral leaves. 221.

CapsuLE: in Bryophytes the spore-vessel ; in Angiosperms a dry fruit
which opens to discharge its seeds. 98, 211.

Carpe: the megasporophyll of Spermatophytes. 178.

CHLOROPHYLL: the green coloring matter of plants. 5.

CuLoropiast: the protoplasmic body within the cell which is stained
green by chlorophyll. 7.

CoLUMELLA: in Bryophytes the sterile tissue of the sporogonium which
is surrounded by the sporogenous tissue. 106.

Conrpium : an asexual spore formed by cutting off the tip of the sporo-
phore, or by the division of hyphe. 58.

ConsuGation : the union of similar gametes. 15.

Corot: the inner set of floral leaves. 221.

CoryLEpon : the first leaf developed by an embryo sporophyte. 188.

Cyciic: applied to an arrangement of leaves or floral parts in which
two or more appear upon the axis at the same level, forming a cycle,
or whorl, or verticil. 159.

DeuiscENcE: the opening of an organ to discharge its contents, as in
sporangia, pollen-sacs, capsules, ete. 199.

Dicuotomous: applied to a style of branching in which the tip of the
axis forks. 35.

Diaecious : applied to plants in which the two sex-organs are upon dif-
ferent individuals. 115.

DorsiventRaL: applied to a body whose two surfaces are differently
exposed, as an ordinary thallus or leaf. 109.

Eee: the female gamete. 16.

Eac-apparatus : in Angiosperms the group of three cells in the embryo-
sac composed of the egg and the two synergids. 204.

Exater: in Liverworts a spore-mother-cell peculiarly modified to aid
in scattering the spores. 103.

Enpryo: a plant in the earliest stages of its development from the
spore. 187.

Empryo-sac: the megaspore of Spermatophytes, which later contains
the embryo. 178.

EyposprrM : the nourishing tissue developed within the embryo-sac, and
thought to represent the female gametophyte. 180.

ENposPerM NUCLEUS: the nucleus of the embryo-sac which gives rise to
the endosperm. 205.

EntomopiiLous : applied to flowers or plants which use insects as agents
of pollination. 196.

GLOSSARY 331

Epieynovs: applied to a flower whose outer parts appear to arise from
the top of the ovary, 225.

Evsporanerate: applied to those Pteridophytes and Spermatophytes
whose sporangia develop from a group of epidermal and deeper
cells, 157.

Famity: a group of related plants, usually comprising several genera.
236.

Fertinizatioy : the union of sperm and egg. 16.

FILAMENT: the stalk-like part of a stamen. 197.

Fission: cell- division which includes the wall of the old cell.
10.

Foot: in Bryophytes the part of the sporogonium imbedded in the
gametophore; in Pteridophytes an organ of the sporophyte embryo
to absorb from the gametophyte. 98, 188,

GAMETANGIUM: the organ within which gametes are produced. 11.

GaAMETE: a sexual cell, which by union with another produces a sexual
spore. 10.

GAMETOPHORE: a special branch which bears sex organs. 98,

GAMETOPHYTE: in alternation of generations, the generation which bears
the sex organs. 97.

GENERATIVE CELL: in Spermatophytes the cell of the male gameto-
phyte (within the pollen grain) which gives rise to the male
cells. 180.

GeEnvs: a group of very closely related plants, usually comprising sev-
eral species. 237.

Havstoricm: a special organ of # parasite (usually a fungus) for ab-
sorption. 90.

Herrerogamovs: applied to plants whose pairing gametes are un-
like. 15.

Hererosporots : applied to those higher plants whose sporophyte pro-
duces two forms of asexual spores. 151.

Ilomosporous: applied to those plants whose sporophyte produces simi-
lar asexual spores. 151.

Host: a plant or animal attacked by a parasite. 48.

Hypua: an individual filament of a mycelium. 49.

Hypocoryn: the axis of the embryo sporophyte between the root-tip and
the cotyledons. 209.

Hyrpoernovs: applied to a flower whose outer parts arise from beneath
the ovary. 224.

832 GLOSSARY

Inpusium : in Ferns a flap-like membrane protecting a sorus. 148.

INFLORESCENCE: a flowet-cluster. 280.

Insertion: the point of origin of an organ, 224,

InteGuMENT: in Spermatophytes a membrane investing the nucellus.
178.

InvoLucre: a cycle or rosette of bracts beneath a flower-cluster, as in
Umbellifers and Composites. 275.

Isocarpic: applied to a flower whose carpels equal in number the other
floral organs. 268.

Isocamous: applied to plants whose pairing gametes are similar. 15.

LEPTOSPORANGIATE: applied to those Ferns whose sporangia develop
from a single epidermal cell. 157.

MALE cELL.: in Spermatophytes the fertilizing cell conducted by the
pollen-tube to the egg. 180.

MrGasporaNGium: asporangium which produces only megaspores. 152.

Mecaspore: in heterosporous plants the large spore which produces a
female gametophyte. 152.

MeGasporopHyLL: a sporophyll which produces only megasporangia.
152.

MesopnyLi: the tissue of a leaf between the two epidermal layers which
usually contains chloroplasts, 141.

MicRosPORANGIUM: a sporangium which produces only microspores.
152.

Microspore: in heterosporous plants the small spore which produces a
male gametophyte. 152.

MicRosPoROPHYLL : a sporophyll which produces only microsporangia.
152.

MicRopyLe: the passageway to the nucellus left by the integument.
178.

Monacrous: applied to plants in which the two sex organs are upon
the same individual. 115.

MoyopopiaL: applied to a style of branching in which the branches
arise from the side of the axis. 35.

Moruer ceLn: usually a cell which produces new cells by internal divi-
sion. 9.

Mycetium: the mat of filaments which composes the working body of
a fungus. 49.

NAKED FLOWER: one with no floral leaves. 222.
Nucenuus: the main body of the ovule. 178.

GLOSSARY 333

Ooco1um : the female, egg-producing organ of Thallophytes. 16.

OospHERE: the female gamete, or egg. 16.

OosporeE: the sexual spore resulting from fertilization. 16.

Ovary: in Angiosperms the bulbous part of the pistil, which contains
the ovules, 199.

OvuLE: the megasporangium of Spermatophytes. 178.

Pappus : the modified calyx of the Composites. 278.

PaRasiTE: a plant which obtains food by attacking living plants or ani-
mals. 48.

PENTACYCLIC : applied to a flower whose four floral organs are in five
cycles, the stamens being in two cycles. 268.

Prrianru: the set of floral leaves when not differentiated into calyx
and corolla. 221.

Prricynous: applied to a flower whose outer parts arise from a cup
surrounding the ovary. 225.

Peta: one of the floral leaves which make up the corolla. 221.

PnorosynrueEsis: the process by which chloroplasts, aided by light,
manufacture carbohydrates from carbon dioxide and water. 84.

Pisin: the central organ of the flower, composed of one or more car-
pels. 200.

PIsTILLATE : applied to flowers with carpels but no stamens. 218.

PoLLen : the microspores of Spermatophytes. 174.
PoLLEN-TUBE: the tube developed from the wall of the pollen grain
which penetrates to the egg and conducts the male cells. 180.
PoLLination: the transfer of pollen from anther to ovule (in Gymno-
sperms) or stigma (in Angiosperms). 181.

PoLyPETaLous: applied to flowers whose petals are free from one an-
other. 227.

ProtHaLLium : the gametophyte of Ferns. 130.

Protoxema: the thallus portion of the gametophyte of Mosses. 98.

Raprau; applied to a body with uniform exposure of surface, and pro-
ducing similar organs about a common center. 120.

RecepracLe: in Angiosperms that part of the stem which is more or
less modified to support the parts of the flower. 222.

Rauizorw : a hair-like process developed by the lower plants and by inde-
pendent gametophytes to act as a holdfast or absorbing organ, or
both. 109.

SaPROPHYTE: a plant which obtains food from the dead bodies or body
products of plants or animals. 48.

334 GLOSSARY

ScaLeE: a leaf without chlorophyll, and usually reduced in size,
161,

SEpaL: one of the floral leaves which make up the calyx. 221.

Sera: in Bryophytes the stalk-like portion of the sporogonium. 98.

SEXUAL SPORE: one produced by the union of gametes. 10.

Species : plants so nearly alike that they all might have come from a
single parent. 287.

Sperm: the male gamete. 16.

SPIRAL: applied to an arrangement of leaves or floral parts in which
no two appear upon the axis at the same level; often called alter-
nate. 193.

SporanGium: the organ within which asexual spores are produced (ex-
cept in Bryophytes). 10.

Spore: a cell set apart for reproduction. 9.

Sporocontum : the leafless sporophyte of Bryophytes. 98.

SPoROPHORE : a special branch bearing asexual spores. 49.

SpoROPHYLL: a leaf set apart to produce sporangia. 145.

Sporopuyte: in alternation of generations, the generation which pro-
duces the asexual spores. 97.

Sramen: the microsporophyll of Spermatophytes. 174.

STAMINATE: applied to a flower with stamens but no carpels. 218.

Sriema: in Angiosperms that portion of the carpel (usually of the style)
prepared to receive pollen. 199.

Stroma (pl. Sromava): an epidermal organ for regulating the communi-
cation between green tissue and the air. 141.

Srropiius: a cone-like cluster of sporophylls. 161.

SryLe: the stalk-like prolongation from the ovary which bears the
stigma, 199.

Suspensor : in heterosporous plants an organ of the sporophyte embryo
which places it in a more favorable position in reference to food

supply. 168.
SymBionT: an organism which enters into the condition of symbio-
sis. 79.

Symprosts: usually applied to the condition in which two different
organisms live together in intimate and mutually helpful rela-
tions, 7.

Symprratous: applied to a flower whose petals have coalesced.
227,

Syycarpous: applied to a flower whose carpels have coalesced.
226.

Synerer: in Angiosperms one of the pair of cells associated with the
egg to form the egg-apparatus. 204.

GLOSSARY 335

Testa: the hard coat of the seed. 184.

TETRACYCLIc: applied to a flower whose four floral organs are in four
cycles. 268.

TETRAD: a group of four spores produced by a mother-cell. 103.

ZoosPoRE : a motile asexual spore. 10.

Zycomorpuic: applied to a fluwer in which the parts in one or more
sets are not similar; irregular, 229.

ZyGore: the sexual spore resulting from conjugation. 15.

INDEX TO PLANT STRUCTURES

[The italicized numbers indicate that the subject is illustrated upon the page cited.
In such case the subject may be referred to only in the illustration, or it may be

referred to also in the text.]

A

Absorption, 299.

Acacia, 265.

Aconitum, 261.

Acorus, 219, 248.

Actinomorphy, 228.

Adder's tongue : see Ophioglossuin.

Adiantum, 148, 145.

ZEcidiomycetes, 50, 62.

AKicidiospore, 66.

ZEcidium, 66.

Agaricus, 68, 69.

Agave, 247.

Air pore: see Stoma.

Akene, 212, 213, 214, 276, 277.

Alchemilla, 225.

Alder: see Alnus,

Algw, 4, 5, 17.

Alisma, 210, 240.

Almond: see Prunus.

Alnus, 257.

Alternation of generations, 94, 129.

Amanita, 70.

Amaryllidacex, 247,

Amaryllis family: see Amarylli-
dace.

Ambrosia, 279.

Ament, 257.

Anaptychia, 87, 82,

Anemophilous, 181.
Angiosperms, 178, 195, 217.
Anisocarpx, 268.
Annulus, 136, 146, 150.
Anther, 196, 197, 199.
Antheridium, 16, 99, 100, 112, 121,

133, 134, 161, 166.
Antherozoid, 16.
Anthoceros, 104, 105, 111, 116, 118.
Anthophytes, 172.
Antipodal cells, 202, 205, 208.
Antirrhinum, 228, 275,
Ant-plants, 90, 92.
Apical cell, 234.
Apical group, 283.
Apium, 267.
Apocarpy, 199, 222, 225.
Apocynacee, 271,
Apocynum, 272,
Apogamy, 181,
Apospory, 182.
Apothecium, 79, 81, 82.
Apple: see Pirus.
Aquilegia, 198.
Aracer, 243,
Araliacez, 267.
Araucaria, 190.
Arbor vite: see Thuja.
Arbutus, 198: see Epigea,
Archegoniates, 101.

337

338

Archegonium, 99, 100, 713, 114, 133,
185, 161, 167, 179.

Archesporium, 102, 104, 105, 146.

Archichlamydew, 255.

Arctostaphylos, 269.

Areolie, 111, 114.

Ariswma, 248, 244,

Arnica, 275, 276, 278.

Aroids, 248.

Artemisia, 279.

Arum, 245.

Ascocarp, 58, 59.

Ascomycetes, 50, 57.

Ascospore, 59.

Ascus, 59.

Asexual spore, 9.

Aspidium, 180, 1/6, 144.

Assimilation, 802.

Aster, 279.

Astragalus, 265.

Atherosperma, 198.

Azalea, 270.

B

Bacillus, 76.

Bacteria, 21, 75. 76.
Balm: see Melissa.
Banana, 140.

Bark, 284, 289.
Basidiomycetes, 50, 68
Basidiospore, 6.9, 72.
Basidium, 69, 71.

Bean: see Phaseolus.
Bearberry : see Arctostaphylos.
Beech, 256.

Bellis, 279.

Berberis, 198.

Bidens, 278.
Beggar-ticks, 213.
Bignonia, 211.

Birch, 256.

Blackberry: see Rubus.

INDEX

Black knot, 60.

Black mould, 52.

Blasia, 116.

Blueberry: see Vaccinium.

Blue-green alge, 6, 17.

Blue mould, 60.

Boletus, 73, 74.

Botrychium, 145, 749.

Botrydium, 28.

Box elder, 234,

Bracket fungus, 72.

Brake: see Pteris.

Brassica, 261.

Bryophytes, 2, 98, 172.

Brown alge, 6, 32.

Bryum, 720, 124.

Buckeye, 235.

Butomus, 199.

Buttercup: see Ranunculus.

Buttercup family: see Ranuncu-
lacea.

C

Cabbage: see Brassica.
Calamus: see Acorus.
Calla-lily, 248.
Callithamnion, 43.
Callophyllis, 39.
Calluna, 270.
Calopogon, 249.

Caltha, 260.
Calycanthus, 226, 261,
Calypso, 24.

Calyptra, 102, 125.
Calyptrogen, 293.
Calis, 22 oT.
Cambium, 285, 287, 288.
Capsella, 209, 29:3.
Capsule, 98, 123, 125, 126, 211, 212.
Caraway: sce Carum,
Carbohydrate, 3802.
Carbon dioxide, 83.

Carnivorous plants, 92.

Carpel, 177, 178, 199, 219, 220.

Carpinus, 217, 258.
Carpospore, 44, 45.
Carrot: see Daucus,
Carum, 267.

Cassia, 265,
Cassiope, U9.
Castilleia, 275,
Catkin, 257.
Catnip: see Nepeta.
Cat-tail: see Typha.
Cattleya, 254.
Caulicle, 209,
Cauline, 166.

Cedar apple, 67, 68.
Celery: see Apium.
Cell, 6, 7.

Cellulose, 7.

Cercis, 265.
Chalazogamy, 258, 259,
Characew, 46.
Chemotropism, 307.
Cherry: see Prunus,
Chestnut, 256,
Chlorophycee, 6, 21.
Chlorophyll, 5, 88.
Chloroplast, 7, 8.
Chrysanthemum, 279.
Cilia, 10.

Circinate, 736, 143.
Cladophora, 25.
Clavaria, 72.

Climbing fern: see Lygodium.

Closed bundle, 290.
Clover: see Trifolium.
Club mosses, 162.

Cnicus, 278.

Cocklebur: see Xanthium.
Cenocyte, 27.
Coleochete, 106, 707.
Collateral bundle, 287,

INDEX 339

Collenchyma, 284.

Columella, 104, 105, 106, 126

Compass plant: see Silphium,

Composite, 275.

Composites, 275, 276, 277, 278.

Concentric bundle, 292.

Conferva forms, 22.

Conidia, 58, 60.

Conifers, 191, 282.

Conium, 267,

Conjugate forms, 31.

Conjugation, 15.

Connective, 196.

Conocephalus, 122.

Convolvulaces, 271.

Conyolvulus forms, 270.

Convolvulus, 272,

Coprinus, 7”.

Coral fungus, 73, 74.

Coreopsis, 278.

Coriandrum, 267.

Cork, 284.

Corn, 216, 28.2, 290.

Cornacee, 267.

Corolla, 22u, 221.

Cortex, 285, 284, 288.

Cotton, 206.

Cotyledon, 737, 188, 168, 184, 209,
BLO dls OL

Cranberry: see Vaccinium.

Crategus, 262.

Crocus, 249,

Crucifer, 262.

Crucifere, 262.

Cryptogams, 172.

Cunila, 274.

Cup fungus, 60, 62.

Cupule, 722, 114.

Cyanophycee, 6, 17.

Cycads, 185, 186, 187, 189.

Cyclic, 159, 193.

Cyperacee, 241.

840

Cypripedium, 249, 253.
Cystocarp, 43, 44.0
Cystopteris, 78, 144.
Cytoplasm, 7.

D

Daisy: see Bellis.

Dandelion: see Taraxacum.

Dasya, 40.

Datura, 197.

Daucus, 266, 267.

Dead-nettle, 228.

Definitive nucleus: see Endosperm
nucleus.

Dehiscence, 198, 199.

Delphinium, 260, 261.

Dermatogen, 283.

Desmids, 81, 32.

Desmodium, 308.

Diatoms, 45.

Dichotomous, 35.

Dicotyledons, 208, 288, 254, 282.

Differentiation, 3, 280.

Dogbane: see Apocynum.

Dog-tooth violet: see Erythronium.

Dogwood family: see Cornace.

Dorsiventral, 109.

Downy mildew, 55.

Drupe, 264.

Digestion, 302.

Dicecious, 115,

Disk, 276, 277.

Dodder, 86.

E

Ear-fungus, 74.

Easter lily, 2:27.

Ecology, 297, 311.
Economic botany, 297.
Ectocarpus, 33.
Edogonium, 22, 23.

Egg, 16, 202, 204, 205, 206.

INDEX

Egg-apparatus, 204, 205, 206.

Elater, 103, 113, 118.

Elm: see Ulmus.

Embryo, 137, 167, 168, 170, 183, 207,
208, 209, 210, 211.

Embryo-sac, 178, 179, 201, 205, 208.

Endosperm, 179, 180, 207, 208, 211.

Endosperm nucleus, 202, 205.

Entomophilous, 196.

Epidermis, 141, 142, 191, 288, 284,
295.

Epigea, 269.

Epigyny, 224, 228.

Kpilobium, 212.

Epiphyte, 157.

Equisetales, 159.

Equisetum, 159, 260, 261.

Ergot, 60, 62.

Erica, 270.

Ericacer, 268.

Erigenia, 267.

Krythronium, 250.

Eusporangiate, 157.

Evolution, 3.

F

Fennel: see Foeniculum.

Ferns, 155, 156.

Fertilization, 16, 181, 206, 207.

Festuca, 240.

Figwort family: see Scrophula-
riacer.

Filament, 8, 796, 197.

Filicales, 155.

Fireweed: see Epilobium.

Fission, 10.

Flax: see Linum.

Floral leaves, 218,

Floridex, 38.

Flower, 218.

Flowering plants, 172.

Feeniculum, 267.

INDEX

Foliar, 166.

Food, 83, 299.

Foot, 98, 102, 137, 138, 168.
Fragaria, 214, 2.77, 262.

Fruit, 211, 222, 213, 214, 215
Fucus, 03, 37.

Funaria, 99, 102, 121, 124, 125, 126.
Fungi, 4, 48.

G

Gametangium, 11.
Gamete, 10, 12.
Gametophore, 9%, 1172, 120, 124.

Gametophyte, 97, 107, 182, 134, 162.
166, 167, 176, 179, 180, 201, v8,

204, 205.
Gaultheria, 270.
Gaylussacia, 260.
Gemma, 712, 114.
Generative cell, 180, 201.
Gentianacex, 271.
Geophilous, 246.
Geotropism, 305.
Gerardia, 275.
Germination, 187, 214.
Gigartina, 38.
Gills, 71.
Ginkgo, 191.
Gladiolus, 249, 257.
Gleditschia, 236, 265.
Gleocapsa, 17, 18.
Glume, 241.
Goldenrod: see Solidago.
Gonatonema, 31.
Graminee, 241.
Green alge, 6. 21.
Green plants, 88.
Green slimes, 20.
Grimmia, 176.
Growth movement, 304,
Growth ring, 234,
Grain, 241.

40

Grasses, 240.

Grass family: see Graminee.
Gymnosperms, 171, 178, 195.
Gymnosporangium, 7.

H
Habenaria, 249, 252.
Harebell, 7/8.
Haustoria, 50.
Hazel: see oo
Heart-wood, 28
Heat, 314.

: Heath family: see Ericacez.

Heaths, 268, 269, 27
Helianthus, 279, 283, 306.
Heliotropism, 305.
Hemiarcyria, 75.

Hemlock: see Conium.
Henbane: see Hyoscyamus.
Hepatic, 109.

Heterocyst, 18.

Heterogamy, 15.
Heterospory, 151,

Hickory, 256,

Hippuris, 283,

Homospory, 151.

Honey locust: see Gleditschia.
Horehound: see Marrubium.
Hornbeam : see Carpinus.
Horsetail, 159.

Host, 48.

Huckleberry: see Gaylussacia.
Hydnum, 73, 74

Hydra, 90.

Hydrophytes. 6, 315.
Hydrophytum, 91.
Hydrotropism, 307.
Hygroscopie movement, 304.
Hyosceyamus, 156.

Hypha, 49.

Hypocotyl, 184, 209, 216, 217.

342

Hypodermis, 284.
Hypogyny, 224, 225.
Hyssopus, 274.

ii

Indigo: see Indigofera.
Indigofera, 265.
Indusium, 136, 148, 144.
Inflorescence, 230.
Insects and flowers, 90.
Integument, 178, 179, 201, 202, 208.
Involucre, 267, 275, 277.
Ipomoea, 228, 270,
Tridacev, 247.

Tris, 248, 251.

Iris family: see Iridacee.
Irritable mavement, 307.
Isocarpa, 268.

Isoetes, 169.

Isogamy, 15.

Japan lily, 248.
Jungermannia, 105, 115, 226, 117.
Juniper, 194.

k
Kalmia, 270.

Labiate, 272.

Lahiates, 272.

Lactuca, 279.

Laminaria, 838, 34.
Lamium, 274, 275.

Larch: see Larix.

Larix, 192.

Larkspur: see Delphinium.
Laurel: see Kalmia.
Lavandula, 275.

Leaf, 141, 142, 295, 296, 811.
Legumes, 250, 251, 264.

INDEX

Leguminose, 264.

Lemna, U1.

Lepidozia, 127.

Leptosporangiate, 157,

Lettuce: see Lactuca.

Leucanthemum, 279.

Liatris, 278.

Lichens, 77, 78, 79, 87.

Life relations, 311.

Light, 314.

Ligule, 168,

Liliacew, 246.

Lilies, 245.

Lilium, 208, 204, 205, 207, 224, 249,
2a5.

Lily: see Lilium.

Lily family: see Liliacez.

Linaria, 228, 275.

Linum, 220.

Liverworts, 109.

Loculus, 200.

Locust: see Robinia.

Lotus, 204.

Lupinus, 265,

Lycopersicum, 275.

Lycopodiales, 162.

Lycopodium, 162, 763.

Lygodium, 145,

Lyonia, 269.

M

Macrospore, 152.

Maidenhair fern: see Adiantum.

Male cell, 180, 187, 201, 206, 207.

Maple, 272.

Marasmius, 7.

Marchantia, 704, 110, 271, 112, 113,
11h.

Marguerite: see Leucanthemum.

Marjoram : see Origanum.

Marrubium, 275.

Marsh marigold: see Caltha,

INDEX.

Marsilia, 158.
Megasporangium, 152, 177, 170.

Megaspore, 152, 165, 167, 179, 201.

BUS

Megasporophyll, 152, 165, 177, 109.

Melissa, 275.

Mentha, 229, 274.

Meristem, 281.

Mesophyll, 141, 142, 191, 295.
Mesophytes, 324.

Mestome, 282.

Micropyle, 178, 201, 20.2, 200.
Microspira, 76.

Microsphera, 58.
Microsporangium, 152, 176, 197.

Microspore, 152. 105, 166, 779, 197.

201.

Microsporophyll, 152, 163, 174, 196,

198.
Midrib, 234.
Mildews, 57.
Mimosa, 265, 308, 309.
Mint: see Mentha.
Mint family: see Labiate.

Monocotyledons, 208, 252, 286, 280.

Moneecious, 115.
Monopodial, 35.

Monotropa, 270.

Moonwort: see Botrychium.
Morels, 60, 6?
Morning-glory: see Ipomeea.
Morphology, 297.

Mosses, 98, 119, 124.

Mother cell, 9.

Mougeotia, 31.

Movement, 303.

Mucor, 49, 52, 53, 54, 58.
Mullein: see Verbascum.
Musci, 119.
Mushrooms, 68.
Mustard family:
Mycelium, 49.

see Crucifere.

343

Mycomycetes, 50.
Mycorrhiza, 87, 83.
Muyristica, 214.
Myrmecophytes. 90, 91.
Myxomycetes, 74, 75.

N
Naias, 237.
Narcissus, 247,
Nemalion, 42.
Nepeta, 275.
Nicotiana, 227, 275.
Nightshade family : see Solanacee,
Nostoe, 18.
Nueellus, 178, 179, 2v1,
Nucleus, 7

202, 203.

' Nutation, 304.

Nutmeg, 214.

Nutrition, 3, 299.
Nyctitropic movement, 309.
Nympheacee, 261.

O
Oak, 255, 256.
(Edogonium : see Edogonium,
Onoclea, 145, 147, 148.
Oogonium, 16.
Oosphere, 16.
Oospore, 16, 101.
Open bundle, 287.
Operculum, 122, 125.
Ophioglossum, 145, 249.
Orchidaceew, 249.
Orchids; 249; 252. 25.2. 254.
Orchid family: see Orchidacez.
Origanum, 274.
Ornithogalum, 247.
Oscillaria, 29.
Osmunda, 145. 156.
Ostrich fern: see Onoclea,
Ona 299, 200: 202:
Ovule, 178, 179, 201, 203.

344

P

Palisade tissue, 742, 295.
Palmacer, 241.

Palm family: see Palmacew.
Palms, 241, 242, 243.
Papaveraceex, 261.

Pappus, 270, 277, 278.
Parasites, 48, 85.

Parenchyma, 280, 281, 282, 288.
Parmelia, 70.

Parsley: see Petroselinum.
Parsley family: see Umbelliferw.
Parsnip: see Pastinaca.
Parthenogenesis, 52.
Pastinaca, 267.

Pathology, 297.

Pea: see Pisum.

Peach: see Prunus.

Peach curl, 60.

Pea family: see Leguminose,
Pear: see Pirus.

Peat, 119.

Pellewa, 146.

Penicillium, 60.

Pentacycle, 268.

Pentstemon, 275.

Peony, 20.

Pepper, /17, 258.

Pepper family: see Piperacex.
Perianth, 219, 22, 221.
Periblem, 283.

Perigyny, 225, 220.

Peristome, 16, 127.
Peronospora, 55, 56.

Petal, 220, 221.

Petiole. 141.

Petroselinum, 267.
Phophycew, 6, 32.
Phanerogams, 172.

Phaseolus, 216, 265.

Phloem, 286, 287, 288, 290, 20.2, 204

INDEX

Phlox, 228, 271.
Photosyntax, 84.
Photosynthesis, 84, 302.
Phycomycetes, 50, 51.
Physcia, 79.
Physiology, 297.
Picea, 179, 181, 18.
Pileus, 71.
Pine: see Pinus.
Pineapple, 215.
Pinus, 173, 175, 176, 177, 178, 181,
183, IN4, ISS, 101, 280.
Piperace, 258.
Pirus, 225, 262, 263.
Pistil, 299, 200, 219, 220.
Pisum, 265.
Pith, 285, 287, 288.
Planococeus, 74.
Plantaginacee, 275.
Plant body, 6.
Plant societies, 313.
Plasmodium, 74, 7.
Plastid, 7, 8.
Platycerium, 132.
Plerome, 283.
Pleurococeus, 21.
Plum : see Prunus.
Plumule, 210.
Pod, 211, 212.
Pogonia, 249.
Polemoniacee, 271.
Polemonium, 271.
Pollen, 174, 176, 197, 201.
Pollen-tube, 179, 180, 181, 187, 202,
206, 207.
Pollination, 181.
Polyembryony, 183.
Polymorphism, 63.
Polypetaly, 226.
Polyporus, 71, 7.2.
Polysiphonia, 44.
Polytrichum, 96,

INDEX

Pome, 268.

Pondweeds, 237.

Poplars, 255.

Popowia, 108.

Poppy, 261.

Poppy family: see Papaveracee.

Populus, 256.

Pore-fungus, 72.

Potamogeton, 237, 238.

Potato: see Solanum.

Potentilla, 2/5, 262.

Proteid, 302.

Prothallium, 130, 132, 1/4.

Protococcus forms, 22.

Protonema, 95, 98.

Protoplasm, 7.

Prunus, 71, 262.

Pseudomonas, 76.

Pseudopodium, 105, 123, 124.

Pteridophytes, 2, 128, 172, 201.

Pteris, 133, 134, 135, 137, 141, 132,
148, 145, 281, 291, 292, 298.

Ptilota, 42.

Puccinia, 63, 64, 65, 66.

Puff-balls, 68, 74.

Pulvinus, 308.

Q

Quillwort: see Isoetes.

R
Rabdonia, 41.
Radiate bundle, 294.
Radicle, 209.
Radish, 120.
Ragweed: see Ambrosia.
Ranunculaceex, 261.
Ranunculus, 222, 259.
Raspberry: see Rubus.
Rays, 275, 276.
Receptacle, 222.
Red alge, 6, 38.

Redbud : see Cercis.
Redwood: see Sequoia.
Reproduction, 3. 8. 309,
Respiration, 302.
Rheotropism, 307,
Rhizoid, 109, 170, 134.
Rhizophores, 164.
Rhododendron, 270. 271.
Rhodophycee, 6, 3%.
Riccia, 104, 110.
Ricciocarpus, 110.
Ricinus. 288,

Robinia, 265.

Root, 138. 217, 293, 294, 818.
Root-cap, 29.2.
Root-fungus, $7. 88.
Root-hairs, 217, 300.
Root-pressure, 300.
Root-tubereles, $9.
Rosacea, 262.

Rose family: see Rosacew.
Rosin-weed : see Silphium.
Rosmarinus, 275.

Royal fern: see Osmunda.
Rubus, 202.

Rumex, 284.

Rust, 62, 63, 64. 65, 66.

8
Sac-fungi, 57.
Sage: see Salvia.
Sage-brush: see Artemisia.
Sagittaria, 208, 388.
Salix, 219, 233, 256, 257.
Salvia, 275.
Salvinia, 158.
Saprolegnia, 51. 52.
Saprophyte, 48, 84.
Sap-wood, 289.
Sargassum, 35, 36.
Saururus, 219, 258.
Seales, 161.

346

Seapania, 116.

Schizomycetes, 21.

Schizophytes, 21.

Sclerenchyma, 281, 282, 284, 255,
288, 290, 201.

Scouring rush, 159.

one

Scrophulariacee, 279.

Scutellaria, 275,

Sedge family: see Cyperacee.

Seed, 183, 284, 210, 211, 212, 214.

Selaginella, 162, 264, 105, 100, 168.

Sensitive fern: see Onoclea.

Sensitive-plant: see Acacia.

sepal, 220, 221.

Sequoia, 789.

Seta, 98, 125.

Sex, 12.

Sexual spore, 10.

Shepherd’s purse: see Capsella.

Shield fern: see Aspidium.

Shoot, 812.

Sieve vessels, 285, 286.

Silphium, 279.

Siphon forms, 27.

Siphonogams, 183.

Siphonogamy, 183.

Slime moulds, 74, 75.

mt, 62:

Snapdragon: see Antirrhinum.

Soil, 314.

Solanacew, 275.

Solanum, 798, 275.

Solidago, 279.

Solomon’s seal, 2.3.3.

Sorus, 196, 143, 144.

Spadix, 244, 245.

Spathe, 244, 245.

Sperm, 16, 100, 7.33,
169, 187, 190.

Spermatia, 43, 44.

Spermatophytes, 2, 171, 172.

Spermatozoid, 16.

35, 162, 166,

INDEX

Sperm mother cell, 100.

Sphagnum, 105, 106, 122, 123.

Spike, 240.

Spirea, 262.

Spiral, 193.

Spirillum, 76.

Spirogyra, 28, 29, 30.

Spongy tissue, 142.

Sporangium, 10, 236, 148, 145, 150,
157, 163, 179.

Spore, 9.

Sporidium, 65.

Sporogenous tissue, 103.

Sporogonium, 98, 102, 104, 105, 106,
£5, dou.

Sporophore, 49, 50.

Sporophyll, 145, 247, 148, 149, 174,
176.

Sporophyte, 97, 102, 137.

Spruce: see Picea.

Stability of form, 298.

Stamen, 174, 176, 196, 198, 219,
220.

Stele, 191, 288, 285.

Stem, 189, 282, 289, 291, 312.

Stemonitis, 75.

Stereome, 282, 299.

Sterile tissue, 103.

Sticta, 80.

Stigma, 199, 202.

Stomata, 141, 142, 191, 295, 301.

Strawberry: see Fragaria.

Strobilus, 160, 161, 163, 165, 174,
175, 106, 198, 14,

Style, 199, 202.

Substratum, 49.

Sumach, 225,

Sunflower: see Helianthus.

Suspensor, 107, 168, 183,
210.

Symbiont, 79, 86.

Symbiosis, 79, 86.

209,

Sympetale, 268.
Sympetaly, 226, 227.
Symplocarpus, 243.
Synearpy, 199, 219, 225,

Synergid, 2u2, 204, 205, 2uc.

E,

Tanacetum, 279.

Tansy: see Tanacetum.
Taraxacum, 210, 277, 278.
Taxonomy, 207.
Teleutospore, 64, 65.
Tension of tissues, 298.
Testa, 184, 211.
Tetracyclie, 268,

Tetrad, 103.

Tetraspore, 43.
Teucrium, 230, 274, 275.
Thallophytes, 2, 4, 172.
Thermotropism, 307.
Thistle: see Cnicus.
Thorn apple: see Datura.
Thuja, 192.

Thymus, 274.

Tickseed: see Coreopsis.
Tissues, 280.

Toad-flax: see Linaria.
Toadstools, 68.
Tobacco: see Nicotiana,

Tomato: see Lycopersicum.

Trachew, 285, 286.
Tracheids, 286.
Transfer of water, 300.
Transpiration, 301.
Tree fern, 140.
Trichia, 74.
Trichogyne, 43, 44.
Trillium, 207, 246, 265.
Truffles, 60.

Turgidity, 298.

Typha, 239, 240.

INDEX

347

U

Umbel, 266, 267.
Umbelliferee, 266,
Umbellifers, 266.
Ulmus, 710, 256.
Ulothrix, 12, 13, 22.
Uredo, 64.
Uredospore, 63, 64,

Vv

Vaccinium, 269,

Vascular bundle, 22.2, 23.4, 287, 291.
Vascuiar cylinder, 234, 287.
Vascular system, 129, 139.
Vaucheria, 26, 27, 28.
Vegetative multiplication, 9.
Veins, 141, 142.

Venation, 233.

Verbascum, 275.
Verbenacer, 275.
Vernation, 148.

Vernonia, 279.

Veronica, 275,

Vicia, 265.

Violet, 211, 229.

WwW

Wall cell, 180.

Walnut, 256.

Water, 83, 314.

Water ferns, 158.

Water-lily, 223, 261.

Water-lily family: see Nymphea-
cer.

Water moulds, 51.

Wheat rust, 63, 64, 65, 66.

Willow: see Salix.

Wind, 315.

Wintergreen: see Gaultheria.

348 INDEX

Wistaria, 265. Y
Witches’-broom, 60. Yeast, 62.
Wormwood: see Artemisia. y

Zannichellia, 237.

Xx
Zoospore, 10.
Xanthium, 279. Zygomorphy, 228, 229.
Xerophytes, 319. Zygospore, 15,

Xylem, 285, 287, 288, 290, 292, 294. | Zygote, 15.

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