''W 1 5 1924
!
ELEMENTARY BOTANY -
BY
GEORGE FRANCIS ATKINSON, Pn.B.
Professor of Botany in Cornell University
THIRD EDITION, REVISED
f
NEW YORK I
HENRY HOLT AND COMPANY
1908
Copyright, 1898, 1905
BY
HENRY HOLT AND COMPANY
ROBERT DRCMMOND COMPANY, PRINTERS, NEW YORK
PREFACE.
THE present book is the result of a revision and elaboration
of the author's "Elementary Botany," New York, 1898. The
general plan of the parts on physiology and general morphology
remains unchanged. A number of the chapters in the physio-
logical part are practically untouched, while others are thoroughly
revised and considerable new matter is added, especially on the
subjects of nutrition and digestion. The principal chapters
on general morphology are unchanged or only slightly modified,
the greatest change being in a revision of the subject of the
morphology of fertilization in the gymnbsperms and angiosperms
in order to bring this subject abreast of the discoveries of the
past few years. One of the greatest modifications has been in
the addition of chapters on the classification of the algae and
fungi with studies of additional examples for the benefit of those
schools where the time allowed for the first year's course makes
desirable the examination of a broader range of representative
plants. The classification is also carried out with greater definite-
ness, so that the regular sequence of classes, orders, and families
is given at the close of each of the subkingdoms. Thus all the
classes, all the orders (except a few in the algas), and many of
the families, are given for the algae, fungi, mosses, liverworts,
pteridophytes, gymnosperms, and angiosperms.
But by far the greatest improvement has been in the complete
reorganization, rewriting, and elaboration of the part dealing
with ecology, which has been made possible by studies of the
past few years, so that the subject can be presented in a more
logical and coherent form. As a result the subject-matter of
iii
iv PREFACE.
the book falls naturally into three parts, which may be passed
in review as follows:
Part I. Physiology. This deals with the life processes of plants,
as absorption, transpiration, conduction, photosynthesis, nutrition,
assimilation, digestion, respiration, growth, and irritability.
Since protoplasm is fundamental to all the life work of the
plant, this subject is dealt with first, and the student is led
through the study of, and experimentation with, the simpler as
well as some of the higher plants, to a general understanding
of protoplasm and the special way in which it enables the plant
to carry on its work and to adjust itself to the conditions of its
existence. This study also serves the purpose of familiarizing
the pupil with some of the lower and unfamiliar plants.
Some teachers will prefer to begin the study with general
morphology and classification, thus studying first the represen-
tatives of the great groups of plants, and others will prefer to
dwell first on the ecological aspects of vegetation. This can
be done in the use of this book by beginning with Part II or
with Part III.
But the author believes that morphology can best be com-
prehended after a general study of life processes and functions
of the different parts of plants, including in this study some of
the lower forms of plant life where some of these processes can
more readily be observed. The pupil is then prepared for a
more intelligent consideration of general and comparative
morphology and relationships. Even more important is a first
study of physiology before taking up the subject of ecology.
The great value to be derived from a study of plants in their
relation to environment lies in the ability to interpret the dif-
ferent states, conditions, behavior, and associations of the plant,
and for this physiology is indispensable. It is true that a con-
siderable measure of success can be obtained by a good teacher
in beginning with either subject, but the writer believes that
measure of success would be greater if the subjects were taken
up in the order presented here.
Part II. Morphology and lije history of representative plants.
PREFA CE. V
This includes a rather careful study of representative examples
among the algae, fungi, liverworts, mosses, ferns and their
allies, gymnosperms and angiosperms, with especial emphasis
on the form of plant parts, and a comparison of them in the
different groups, with a comparative study of development,
reproduction, and fertilization, rounding out the work with a
study of life histories and noting progression and retrogression
of certain organs and phases in proceeding from the lower to the
higher plants. Thus, in the algae a first critical study is made
of four examples which illustrate in a marked way progressive
stages of the plant body, sexual organs, and reproduction. Addi-
tional examples are then studied for the purpose of acquiring a
knowledge of variations from these types and to give a broader
basis for the brief consideration of general relationships and
classification.
A similar plan is followed in the other great groups. The
processes of fertilization and reproduction can be most easily
observed in the lower plants like the algae and fungi, and this
is an additional argument in favor of giving emphasis to these
forms of plant life as well as the advantage of proceeding logic-
ally from simpler to' more complex forms. Having also learned
some of these plants in our study of physiology, we are following
another recognized rule of pedagogy, i.e., proceeding from
known objects to unknown structures and processes. Through
the study of the organs of reproduction of the lower plants and
by general comparative morphology we have come to an under-
standing of the morphology of the parts of the flower, and of
the true sexual organs of the seed plants, and no student can
hope to properly interpret the significance of the flower, or the
sexual organs of the seed plants who neglects a careful study
of the general morphology of the lower plants.
Part III. Plant members in relation to environment. This part
deals with the organization of the plant body as a whole in its
relation to environment, the organization of plant tissues with
a discussion of the principal tissues and a descriptive synopsis of
the same. This is followed by a complete study from a biological
VI PREFACE.
standpoint of the different members of the plant, their special
function and their special relations to environment. The stem,
root, leaf, flower, etc., are carefully examined and their ecological
relations pointed out. This together with the study of physiology
and representatives in the groups of plants forms a thorough
basis for pure plant ecology, or the special study of vegetation
in its relation to environment.
There is a study of the factors of environment or ecological
factors, which in general are grouped under the physical, climatic,
and biotic factors. This is followed by an analysis of vegeta-
tion forms and structures, plant formations and societies. Then
in order are treated briefly forest societies, prairie societies,
desert societies, arctic and alpine societies, aquatic societies, and
the special societies of sandy, rocky, and marshy places.
Acknowledgments. The author wishes to express his grate-
fulness to all those who have given aid in the preparation of this
work, or of the earlier editions of Elementary Botany; to his
associates, Dr. E. J. Durand, Dr. K. M. Wiegand, and Professor
W. W. Rowlee, of the botanical department, and to Professor
B. M. Duggar of the University of Missouri, Professor J, C.
Arthur of Purdue University, and Professor W. F. Ganong of
Smith College, for reading one or more portions of the text;
as well as to all those who have contributed illustrations.
Illustrations. The large majority of the illustrations are new
(or are the same as those used in earlier editions of the author's
Elementary Botany) and were made with special reference to
the method of treatment followed in the text. Many of the
photographs were made by the author. Others were contributed
by Professor Rowlee of Cornell University; Mr. John Gifford
of New Jersey; Professor B. M. Duggar, University of Missouri;
Professor C. E. Bessey, University of Nebraska; Dr. M. B. Howe,
New York Botanical Garden; Mr. Gifford Pinchot, Chief of
the Bureau of Forestry; Mr. B. T. Galloway, Chief of the
Bureau of Plant Industry; Professor Tuomey of Yale University;
and Mr. E. H. Harriman, who through DC. C. H. Merriam
of the National Museum allowed the use of several of his copy-
PREFA CE . Vli
righted photographs from Alaska. To those who have con-
tributed drawings the author is indebted as follows: to Professor
Margaret C. Ferguson, Wellesley College; Professor Bertha
Stoneman of Huguenot College, South Africa; Mr. H. Hassel-
bring of Chicago; Dr. K. Miyake, formerly of Cornell University
and now of Doshisha College, Japan; and Professors Ikeno
and Hirase of the Tokio Imperial University. The author
is also indebted to Ginn & Co., Boston, for the privilege to
use from his "First Studies of Plant Life" the following figures:
28, 29, 46, 48, 49, 56, 62, 66, 67, 87, 102, 103, 422-426, 429,
430, 438-44o, 443, 444, 448, 449> 452> 472~475- A few others
are acknowledged in the text.
CORNELL UNIVERSITY, April, 1905.
/y
PART I. PHYSIOLOGY.
CHAPTER I.
PAGE
PROTOPLASM i
CHAPTER II.
ABSORPTION, DIFFUSION, OSMOSE 13
CHAPTER III.
How PLANTS OBTAIN WATER 22
CHAPTER IV.
TRANSPIRATION, OR THE Loss OF WATER BY PLANTS 35
CHAPTER V.
PATH OF MOVEMENT OF WATER IN PLANTS 48
CHAPTER VI.
MECHANICAL USES OF WATER 56
CHAPTER VII.
STARCH AND SUGAR FORMATION 60
1 . The Gases Concerned 60
2. Where Starch is Formed 64
3. Chlorophyll and the Formation of Starch 67
CHAPTER VIII.
STARCH AND SUGAR CONCLUDED; ANALYSIS OF PLANT SUBSTANCE 73
1. Translocation of Starch 73
2. Sugar, and Digestion of Starch 75
3. Rough Analysis of Plant Substance 79
h
X TABLE OF CONTENTS.
CHAPTER IX.
PAGE
How PLANTS OBTAIN THEIR FOOD, 1 81
1. Sources of Plant Food 81
2. Parasites and Saprophytes 83
3. How Fungi Obtain their Food 86
4. Mycorhiza. 91
5. Nitrogen-gatherers 92
6. Lichens 93
CHAPTER X.
How PLANTS OBTAIN THEIR FOOD, II 97
Seedlings, 97. Digestion, 107. Assimilation 109
CHAPTER XI.
RESPIRATION. . . no
CHAPTER XII.
GROWTH 118
CHAPTER XIII.
IRRITABILITY 125
PART II. MORPHOLOGY AND LIFE HISTORY
OF REPRESENTATIVE PLANTS.
CHAPTER XIV.
SPIROGYRA. 136
CHAPTER XV.
VAUCHERIA. > 142
CHAPTER XVI.
CEDOGONIUM. 147
CHAPTER XVH.
COLEOCH^TE. 153
CHAPTER XVIII.
CLASSIFICATION AND ADDITIONAL STUDIES OF THE ALG^E. 158
CHAPTER XIX.
FUNGI: MuoOR AND SAPROLEGNIA i?7
TABLE OF CONTENTS. xl
CHAPTER XX.
PAGE
FUNGI CONTINUED (" Rusts " Uredineae) 187
CHAPTER XXI.
THE HIGHER FUNGI 195
CHAPTER XXII.
CLASSIFICATION OF THE FUNGI 213
CHAPTER XXIII.
LIVERWORTS (Hepaticae) 222
Riccia, 222. Marchantia 226
CHAPTER XXIV.
LIVERWORTS CONTINUED. 231
Sporogonium of Marchantia 231
Leafy-stemmed Livenvorts 236
The Horned Liverworts 240
Classification of the Liverworts 242
CHAPTER XXV.
MOSSES (Musci) 243
Classification of Mosses 248
CHAPTER XXVI.
FERNS 251
CHAPTER XXVII.
FERNS CONTINUED 262
Gametophyte of Ferns 262
Sporophyte 268
CHAPTER XXVIII.
DIMORPHISM OF FERNS 273
CHAPTER XXIX.
HORSETAILS 280
CHAPTER XXX.
CLUB-MOSSES. 284
CHAPTER XXXI.
QUILL WORTS (Isoetes) 289
xii TABLE OF CONTENTS.
CHAPTER XXXII.
PAGE
COMPARISON OF FERNS AND THEIR RELATIVES 292
Classification of the Pteridophytes 295
CHAPTER XXXIII.
GYNMOSPERMS 297
CHAPTER XXXIV.
FURTHER STUDIES ON GYMNOSPERMS 311
CHAPTER XXXV.
MORPHOLOGY OF THE ANGIOSPERMS: TRILLIUM; DENTARIA 318
CHAPTER XXXVI.
GAMETOPHYTE AND SPOROPHYTE OF ANGIOSPERMS ' 325
CHAPTER XXXVII.
MORPHOLOGY OF THE NUCLEUS AND SIGNIFICANCE OF GAMETOPHYTE
AND SPOROPHYTE 340
PART III. PLANT MEMBERS IN RELATION
TO ENVIRONMENT.
CHAPTER XXXVIII.
THE ORGANIZATION OF THE PLANT 349
I. Organization of Plant Members 349 '
II. Organization of Plant Tissues 356
CHAPTER XXXIX.
THE DIFFERENT TYPES OF STEMS 365
I. Erect Stems 365
II. Creeping, Climbing, and Floating Stems 369
III. Specialized Shoots and Shoots for Storage of Food 372
IV. Annual Growth and Winter Protection of Shoots and Buds. . . 374
CHAPTER XL.
FOLIAGE LEAVES 383
I. General Form and Arrangement of Leaves 383
II. Protective Modifications of Leaves 392
III. Protective Positions 395
IV. Relation of Leaves to Light ' 397
V. Leaf Patterns 4°4
TABLE OF CONTENTS. Xlll
CHAPTER XLI.
PAGE
THE ROOT 410
I. Function of Roots 410
II. Kinds of Roots 415
CHAPTER XLII.
THE FLORAL SHOOT 419
I. The Parts of the Flower 419
II. Kinds of Flowers 421
III. Arrangement of Flowers, or Mode of Inflorescence 426
CHAPTER XLIII.
POLLINATION 433
CHAPTER XLIV.
THE FRUIT 450
I. Parts of the Fruit 450
II. Indehiscent Fruits 451
III. Dehiscent Fruits 452
TV. Fleshy and Juicy Fruits 454
V. Reinforced, or Accessory, Fruits 455
VI. Fruits of Gymnosperms 456
VII. " Fruit" of Ferns, Mosses, etc 457
CHAPTER XLV.
SEED DISPERSAL 458
CHAPTER XLVL
VEGETATION IN RELATION TO ENVIRONMENT 464
CHAPTER XLVII.
CLASSIFICATION OF ANGIOSPERMS 487
INDEX 503
PART I.
PHYSIOLOGY.
CHAPTER I.
PROTOPLASM.*
1. In the study of plant life and growth, it will be found
convenient first to inquire into the nature of the substance
which we call the living material of plants. For plant growth,
as well as some of the other processes of plant life, are at bottom
dependent on this living matter. This living matter is called in
general protoplasm.
2. In most cases protoplasm cannot be seen without the
help of a microscope, and it will be necessary for us here to em-
ploy one if we wish to see protoplasm, and to satisfy ourselves
by examination that the substance we are dealing with is
protoplasm.
3. We shall find it convenient first to examine protoplasm in
some of the simpler plants ; plants which from their minute size
and simple structure are so transparent that when examined with
the microscope the interior can be seen.
For our first study let us take a plant known as spirogyra,
though there are a number of others which would serve the pur-
pose quite as well, and may quite as easily be obtained for
study.
PHYSIOLOGY.
Protoplasm in spirogyra.
4. The plant spirogyra. — This plant is found in the water
of pools, ditches, ponds, or in streams of slow-running water.
It is green in color, and occurs in loose mats, usually floating
near the surface. The name "pond-scum" is sometimes given
to this plant, along with others which are more or less closely
related. It is an alga, and belongs to a group of plants known
as algce. If we lift a portion of it from the water, we see that
the mat is made up of a great tangle of green silky threads.
Each one of these threads is a plant, so that the number con-
tained in one of these floating mats is very great.
Let us place a bit of this thread tangle on a glass slip, and
examine with the microscope and we will see certain things about
the plant which are peculiar to it, and which enable us to 'dis-
tinguish it from other minute green water plants. We shall
also wish to learn what these peculiar parts of the plant are, in
order to demonstrate the protoplasm in the plant.*
5. Chlorophyll bands in spirogyra. — We first observe the
presence of bands ; green in color, the edges of which are
usually very irregularly notched. These bands course along in
a spiral manner near the surface of the thread. There may be
one or several of these spirals, according to the species which
we happen to select for study. This green coloring matter of
the band is chlorophyll, and this substance, which also occurs in
the higher green plants, will be considered in a later chapter.
At quite regular intervals in the chlorophyll band are small
starch grains, grouped in a rounded mass enclosing a minute
body, the pyrenoid, which is peculiar to many algae.
6. The spirogyra thread consists of cylindrical cells end to
end. — Another thing which attracts our attention, as we examine
a thread of spirogyra under the microscope, is that the thread is
* If spirogyra is forming fruit some of the threads will be lying parallel in
pairs, and connected with short tubes. In some of the cells there will be
found rounded or oval bodies known as zygospores. These may be seen in
fig. 86, and will be described in another part of the book.
PROTOPLASM.
made up of cylindrical segments or compartments placed end to
end. We can see a distinct separating line be-
tween the ends. Each one of these segments or
compartments of the thread is a cell, and the
boundary wall is in the -form of a cylinder with
closed ends.
7. Protoplasm. — Having distinguished these
parts of the plant we can look for the protoplasm.
It occurs within the cells. It is colorless (i.e.,
hyaline) and consequently requires close observa-
tion. Near the center of the cell can be seen a
rather dense granular body of an elliptical or
irregular form, with its long diameter transverse
to the axis of the cell in some species ; or trian-
gular, or quadrate in others. This is the nucleus.
Around the nucleus is a granular layer from which
delicate threads of a shiny granular substance
radiate in a starlike manner, and terminate in the
chlorophyll band at one of the pyrenoids. A
granular layer of the same substance lines the
inside of the cell wall, and can be seen through
the microscope if it is properly focussed. This
granular substance in the cell is protoplasm.
8. Cell-sap in spirogyra. — The greater part of
the interior space of the cell, that between the
radiating strands of protoplasm, is occupied by
a watery fluid, the " cell-sap."
9. Reaction of protoplasm to certain reagents.
—We can employ certain tests to demonstrate
that this granular substance which we have seen
is protoplasm, for it has been found, by repeated
. . . . , ... Thread of spiro-
expenments with a great many kinds of plants, gyra, showing lone
.1 . i . , r .^ ... cells, chlorophyll
that protoplasm gives a definite reaction in re- band, nucleus,
sponse to treatment with certain substances called plasm,8 andpr°he
granular wall layer
reagents. Let us mount a few threads of the of protoplasm,
spirogyra in a drop of a solution of iodine, and observe the
PHYSIOLOGY.
results with the aid of the microscope. The iodine gives a
yellowish-brown color to the protoplasm, and it can be more
distinctly seen. The nucleus is also much more prominent
since it colors deeply, and we can perceive within the nucleus
one small rounded body, sometimes more, the nudeolus. The
iodine here kills and stains the protoplasm. The proto-
plasm, however, in a living condition will resist for a time some
other reagents,
as we shall see
if we attempt
to stain it with
a one per cent
aqueous solu-
tion of a dye
known as eosin.
Let us mount a
few living
threads in such
a solution of
eosin, and after
Fig. ». Fig. 3. a time wash off
Cell of spirogyra before treat- Cell of spirogyra after treatment «.i,- Ot0i-n TV>a
ment with iodine. with alcohol and iodine. HWH.
protoplasm remains uncolored. Now let us place these threads
for a short time, two or three minutes, in strong alcohol, which
kills the protoplasm. Then mount them in the eosin solution.
The protoplasm now takes the eosin stain. After the proto-
plasm has been killed we note that the nucleus is no longer
elliptical or angular in outline, but is rounded. The strands of
protoplasm are no longer in tension as they were when alive.
10. Let us now take some fresh living threads and mount
them in water. Place a small drop of dilute glycerine on the
slip at one side of the cover glass, and with a bit of filter paper
at the other side draw out the water. The glycerine will flow
under the cover glass and come in contact with the spirogyra
threads. Glycerine absorbs water promptly. Being in contact
with the threads it draws water out of the cell cavity, thus caus-
PROTOPLASM.
ing the layer of protoplasm which lines the inside of the cell
wall to collapse, and separate from the wall, drawing the
chlorophyll band
inward toward the
center also. The
wall layer of proto-
plasm can now be
more distinctly
seen and its gran-
ular character ob-
served.
We have thus
employed three
tests to demon-
strate that this sub-
stance with which
we are dealing
shows the reac-
tions which we
know by experi-
' Cell of spirogyra before Cells of spirogyra after treatment
tO be given treatment with glycerine. with glycerine.
Fig. 4-
by protoplasm. We therefore conclude that this colorless and
partly granular, slimy substance in the spirogyra cell is proto-
plasm, and that when we have performed these experiments,
and noted carefully the results, we have seen protoplasm.
11. Earlier use of the term protoplasm. — Early students of the living
matter in the cell considered it to be alike in substance, but differing in
density; so the term protoplasm was applied to all of this living matter. The
nucleus was looked upon as simply a denser portion of the protoplasm, and
the nucleolus as a still denser portion. Now it is believed that the nucleus is
a distinct substance, and a permanent organ of the cell. The remaining por-
tion of the protoplasm is now usually spoken of as the cytoplasm.
In spirogyra then the cytoplasm in each cell consists of a layer which lines
the inside of the cell wall, a nuclear layer, which surrounds the nucleus, and
radiating strands which connect the nucleus and wall layers, thus suspending
the nucleus near the center of the cell. But it seems best in this elementary
study to use the term protoplasm in its general sense.
PHYSIOLOGY.
Protoplasm in mucor.
12. Let us now examine in a similar way another of the
simple plants with the special object in view of demonstrating
the protoplasm. For this purpose we may take one of the plants
belonging to the group of fungi. These plants possess no
chlorophyll. One of several species of mucor, a common
mould, is readily obtainable, and very suitable for this study.*
13. Mycelium of mucor. — A few days after sowing in some
gelatinous culture medium we find slender, hyaline threads, which
are very much branched, and, radiating from a central point, form
circular colonies, if the plant has not been too thickly sown, as
shown in fig. 6. These threads of the fungus form the myce-
lium. From these characters of the plant, which we can readily
see without the aid of a microscope, we note how different it is
from spirogyra.
To examine for protoplasm let us lift carefully a thin block of
gelatine containing the mucor threads, and mount it in water on
a glass slip. Under the microscope we see only a small portion
of the branched threads. In addition to the absence of chlo-
rophyll, which we have already noted, we see that the myce-
lium is not divided at short intervals into cells, but appears
like a delicate tube with branches, which become successively
smaller toward the ends.
14. Appearance of the protoplasm. — Within the tube-like
thread now note the protoplasm. It has the same general ap-
pearance as that which we noted in spirogyra. It is slimy, or
semi-fluid, partly hyaline, and partly granular, the granules con-
sisting of minute particles, (the microsomes) . While in mucor the
protoplasm has the same general appearance as in spirogyra, its
arrangement is very different. In the first place it is plainly
* The most suitable preparations of mucor for study are made by growing
the plant in a nutrient substance which largely consists of gelatine, or, better,
agar-agar, a gelatinous preparation of certain seaweeds. This, after the
plant is sown in it, should be poured into sterilized shallow glass plates,
called Fetrie dishes.
PROTOPLASM.
continuous throughout the tube. We do not see the prominent
radiations of strands around a large nucleus, but still the proto-
Colonies of mucor.
plasm does not fill the interior of the threads. Here and there
are rounded clear spaces termed vacuoles, which are filled with
the watery fluid, cell-sap. The nuclei in mucor are very mi-
nute, and cannot be seen except after careful treatment with
special reagents.
15 Movement of the protoplasm in mucor. — While exam-
ining the protoplasm in mucor we are likely to note streaming
movements. Often a current is seen flowing slowly down one
side of the thread, and another flowing back on the other side,
or it may all stream along in the same direction.
16. Test for protoplasm. — Now let us treat the threads with
a solution of iodine. The yellowish-brown color appears which
is characteristic of protoplasm when subject to this reagent.
8 PHYSIO LOG Y.
If we attempt to stain the living protoplasm with a one per
cent aqueous solution of eosin it resists it for a time, but if we
first kill the protoplasm with strong alcohol, it reacts quickly to
the application of the eosin. If we treat the living threads
with glycerine the protoplasm is contracted away from the wall,
as we found to be the case with spirogyra. While the color,
Fig. 7.
Thread of mucor, showing protoplasm and vacuoles.
form and structure of the plant mucor is different from spiro-
gyra, and the arrangement of the protoplasm within the plant
is also quite different, the reactions when treated by certain re-
agents are the same. We are justified then in concluding that
the two plants possess in common a substance which we call
protoplasm.
Protoplasm in nitella.
17. One of the most interesting plants for the study of one remarkable
peculiarity of protoplasm is Nitella. This plant belongs to a small group
known as stoneworts. They possess chlorophyll, and, while they are still
quite simple as compared with the higher plants, they are much higher in the
scale than spirogyra or mucor.
18. Form of nitella. — A common species of nitella is Nitella flexilis.
It grows in quiet pools of water. The plant consists of a main axis, in the
form of a cylinder. At quite regular intervals are whorls of several smaller
thread-like outgrowths, which, because of their position, are termed " leaves,"
though they are not true leaves. These are branched in a characteristic fash-
ion at the tip. The main axis also branches, these branches arising in the axil
of a whorl, usually singly. The portions of the axis where the whorls arise
are the nodes. Each node is made up of a number of small cells definitely
arranged. The portion of the axis between two adjacent whorls is an inter-
PROTOPLASM.
node. These internodes are peculiar. They consist of but a single " cell,"
and are cylindrical, with closed ends. They are sometimes 5-10 cm. long.
19. Internode of nitella. — For the study of an internode of nitella, a
small one, near the end, or the ends of one of the " leaves" is best suited,
since it is more transparent. A small
portion of the plant should be placed
on the glass slip in water with the
cover glass over a tuft of the branches
near the growing end. Examined with
the microscope the green chlorophyll bodies, which
form oval or oblong discs, are seen to be very numer-
ous. They lie quite closely side by side and form in
perfect rows along the inner surface of the wall. One
peculiar feature of the arrangement of the chlorophyll
bodies is that there are two lines, extending from one
end of the internode to the other on opposite sides,
where the chlorophyll bodies are wanting. These are
known as neutral lines. They run parallel with the
axis of the internode, or in a more or less spiral
manner as shown in fig. 9.
20. Cyclosii in nitella. — The chlorophyll bodies
are stationary on the inner surface of the wall, but
if the microscope be properly focussed just beneath
this layer we notice a rotary motion of particles in
the protoplasm. There are small granules and quite
large masses of granular matter which glide slowly
along in one direction on a given side of the neutral
line. If now we examine the protoplasm on the other
side of the neutral line, we see that the movement is
in the opposite direction. If we examine this move-
ment at the end of an internode the particles are seen
to glide around the end from one side of the neutral line to the other. So
that when conditions are favorable, such as temperature, healthy state of the
plant, etc., this gliding of the particles or apparent streaming of the proto-
plasm down one side of the " cell," and back upon the other, continues in
an uninterrupted rotation, or cyclosis. There are many nuclei in an internode
of nitella, and they move also.
21. Test for protoplasm. — If we treat the plant with a solution of iodine
we get the same reaction as in the case of spirogyra and mucor. The proto-
plasm becomes yellowish brown.
22. Protoplasm in one of the higher plants. — We now wish
to examine, and test for, protoplasm in one of the higher plants.
Fig. 8.
Portion of plant nitella.
IO PHYSIOLOG y.
Young or growing parts of any one of various plants — the petioles
of young leaves, or young stems of growing plants — are suitable
for study. Tissue from the pith of corn (Zea mays) in young
shoots just back of the
growing point or quite
near the joints of older but
growing corn stalks fur-
Fig. 9. nishes excellent material.
Cyclosis in nitella. If we should place part
of the stem of this plant under the microscope we should find
it too opaque for observation of the interior of the cells. This
is one striking difference which we note as we pass from the low
and simple plants to the higher and more complex ones ; not
only in general is there an increase of size, but also in general
an increase in thickness of the parts. The cells, instead of lying
end to end or side by side, lire massed together so that the parts
are quite opaque. In order to study the interior of the plant
we have selected it must be cut into such thin layers that the
light will pass readily through them.
For this purpose we section the tissue selected by making with
a razor, or other very sharp knife, very thin slices of it. These
are mounted in water in the usual way for microscopic study. In
this section we notice that the cells are polygonal in form.
This is brought about by mutual pressure of all the cells. The
granular protoplasm is seen to form a layer just inside the wall,
which is connected with the nuclear layer by radiating strands
of the same substance. The nucleus does not always lie at the
middle of the cell, but often is near one side. If we now apply
an alcohol solution of iodine the characteristic yellowish-brown
color appears. So we conclude here also that this substance is
identical with the living matter in the other very different plants
which we have studied.
23. Movement of protoplasm in the higher plants. — Cer-
tain parts of the higher plants are suitable objects for the study
of the so-called streaming movement of protoplasm, especially
the delicate hairs, or thread-like outgrowths, such as the silk of
PROTOPLASM.
II
corn, or the delicate staminal hairs of some plants, like those of
the common spiderwort, tradescantia, or of the tradescantias
grown for ornament in greenhouses and plant conservatories.
Sometimes even in the living cells of the corn plant which we
have just studied, slow streaming or gliding movements of the
granules are seen along the strands of protoplasm where they
radiate from the nucleus. See note at close of this chapter.
24. Movement of protoplasm in cells of the staminal hair of
" spiderwort." — A cell of one of these hairs from a stamen of a
tradescantia grown in glass houses is shown in fig. 10. The
Fig. 10. *
Cell from stamen hair of tradescantia showing movement of the protoplasm.
nucleus is quite prominent, and its location in the cell varies con-
siderably in different cells and at different times. There is a
layer of protoplasm all around the nucleus, and from this the
strands of protoplasm extend outward to the wall layer. The
large spaces between the strands are, as we have found in other
cases, filled with the cell-sap.
An entire stamen, or a portion of the stamen, having seveial hairs attached,
should be carefully mounted in water. Care should be taken that the room be
not cold, and if the weather is cold the water in which the preparation is
mounted should be warm. With these precautions there should be little diffi-
culty in observing the streaming movement.
The movement is detected by observing the gliding of the
granules. These move down one of the strands from the nucleus
along the wall layer, and in towards the nucleus in another
strand. After a little the direction of the movement in any one
portion may be reversed.
25. Cold retards the movement. — While the protoplasm is
moving, if we rest the glass slip on a block of ice, the move-
ment will become slower, or will cease altogether. Then if we
12 PHYSIOLOGY.
warm the slip gently, the movement becomes normal again. We
may now apply here the usual tests for protoplasm. The result
is the same as in the former cases.
26. Protoplasm occurs in the living parts of all plants. —
In these plants representing such widely different groups, we find
a substance which is essentially alike in all. Though its arrange-
ment in the cell or plant body may differ in the different plants
or in different parts of the same plant, its general appearance
is the same. Though in the different plants it presents, while
alive, varying phenomena, as regards mobility, yet when killed
and subjected to well known reagents the reaction is in general
identical. Knowing by the experience of various investigators
that protoplasm exhibits these reactions under given conditions,
we have demonstrated to our satisfaction that we have seen proto
plasm in the simple alga, spirogyra, in the common mould,
mucor, in the more complex stonewort, nitella, and in the cells
of tissues of the highest plants.
27. By this simple process of induction of these facts concerning
this substance in these different plants, we have learned an im-
portant method in science study. Though these facts and deduc-
tions are well known, the repetition of the methods by which they
are obtained on the part of each student helps to form habits of
scientific carefulness and patience, and trains the mind to logical
processes in the search for knowledge.
28. While we have by no means exhausted the study of protoplasm, we can,
from this study, draw certain conclusions as to its occurrence and appearance
in plants. Protoplasm is found in the living and growing parts of all plants.
It is a semi-fluid, or slimy, granular, substance ; in some plants, or parts of
plants, the protoplasm exhibits a streaming or gliding movement of the gran-
ules. It is irritable. In the living condition it resists more or less for some
ume the absorption of certain coloring substances. The water may be with-
d> wn by glycerine. The protoplasm may be killed by alcohol. When
i =*ted with iodine it becomes a yellowish-brown color.
Note. In some plants, like elodea for example, it has been found that
the streaming of the protoplasm is often induced by some injury or stimu-
lus, while in the normal condition the protoplasm does not move.
CHAPTER II.
ABSORPTION, DIFFUSION, OSMOSE.
29. We may next endeavor to learn how plants absorb
water or nutrient substances in solution. There are several
very instructive experiments, which can be easily performed,
and here again some of the lower plants will be found useful.
30. Osmose in spirogyra. — Let us mount a few threads of
this plant in water for microscopic examination, and then draw
under the cover glass a five per cent solution of ordinary table
salt (NaCl) with the aid of filter paper. We shall soon see
that the result is similar to that which was obtained when glycer-
ine was used to extract the water from the cell-sap, and to con-
tract the protoplasmic membrane from the cell wall. But the
process goes on evenly and the plant is not injured. The proto-
plasmic layer contracts slowly from the cell wall, and the move-
ment of the membrane can be watched by looking through the
microscope. The membrane contracts in such a way that all
the contents of the cell are finally collected into a rounded or
oval mass which occupies the center of the cell.
If we now add fresh water and draw off the salt solution,
we can see the protoplasmic membrane expand again, or move
out in all directions, and occupy its former position against the
inner surface of the cell wall. This would indicate that there is
j*
some pressure from within while this process of absorption is
going on, which causes the membrane to move out against »j^
cell wall.
The salt solution draws water from the cell-sap. There
is thus a tendency to form a vacuum in the cell, and the
pressure on the outside of the protoplasmic membrane causes it
13
PHYSIOLOGY.
to move toward the center of the cell. When the salt solution
is removed and the thread of spirogyra is again bathed with
water, the movement of the water is inward in
the cell. This would suggest that there is some
substance dissolved in the cell-sap which does not
readily filter out through the membrane, but draws
on the water outside. It; is this which produces
the pressure from within and crowds the mem-
brane out against the cell wall again.
Fig. ii.
Spirogyra before
placing in salt solu-
tion.
Fig. 13-
Spirogyra from sal.
solution into water.
Fig. 12.
Spirogyra in 5? salt solution.
31. Turgescence. — Were it not for the resistance which tht
cell wall offers to the pressure from within, the delicate pro to
ABSORPTION, DIFFUSION, OSMOSE.
plasmic membrane would stretch to such an extent that it would
be ruptured, and the protoplasm therefore would be killed. If
we examine the cells at the ends of the
threads of spirogyra we shall see in most
cases that the cell wall at the free end is
arched outward.
This is brought
about by the press-
Fig. 16.
From salt solution placed in water.
Figs. 14-16. — Osmosis in threads of mucor.
Fig. 14.
Before treatment with salt
solution.
ure from within
upon the proto- After J^J^
plasmic mem- salt soluti°°-
brane which itself presses against
the cell wall, and causes it to
arch outward. This is beauti-
fully shown in the case of threads
which are recently broken. The cell wall is therefore elastic;
it yields to a certain extent to the pressure from within, but a
point is soon reached beyond which it will not stretch, and an
equilibrium then exists between the pressure from within on the
protoplasmic membrane, and the pressure from without by the
elastic cell wall. This state of equilibrium in a cell is forges
cence, or such a cell is said to be turgescent, or turgid.
32. Experiment with beet in salt and sugar solutions. —
We may now test the effect of a five per cent salt solution on a
portion of the tissues of a beet or carrot. Let us cut several
slices of equal size and about ^mm in thickness. Immerse a
few slices in water, a few in a five per cent salt solution and a
few in a strong sugar solution. It should be first noted that all
the slices are quite rigid when an attempt is made to bend them
between the fingers. In the course of one or two hours or less,
i6
PHYSIOLOGY.
if we examine the slices we shall find that those in water remain,
as at first, quite rigid, while those in the salt and sugar solutions
are more or less flaccid or limp, and readily bend by pres-
Fig. 17. Fig. 18. Fig. 19.
Before treatment with salt After treatment with salt From salt solution into water
solution. solution. again.
Figs. 17-19. — Osmosis in cells of Indian corn.
sure between the fingers, the specimens in the salt solution,
perhaps, being more flaccid than those in the sugar solution.
The salt solution, we judge after our experiment with spirogyra,
Fig. 20.
lit ion of
section.
Fig. 21.
Fig. 22.
Kigid condition of fresh beet Limp condition after lying in Rigid again after lying again
section. salt solution. in water.
Figs. 20-22. — Turgor and osmosis in slices of beet.
withdraws some of the water from the cell-sap, the cells thus
losing their turgidity and the tissues becoming limp Or flaccid
from the loss of water.
ABSORPTION, DIFFUSION, OSMOSE.
33. Let us now remove some of the slices of the beet from
the sugar and salt solutions, wash them with water and then
immerse them in fresh water. In the course of thirty minutes
to one hour, if we examine them again, we find that they have
regained, partly or completely, their rigidity. Here again we
infer from the former experiment with spirogyra that the sub-
stances in the cell-sap now draw water inward ; that is, the
diffusion current is inward through the cell walls and the proto-
plasmic membrane, and the tissue becomes turgid again.
34. Osmose in the cells of the beet. — We should now make a section of the
fresh tissue of a red colored beet for examination with the microscope, and
treat this section with the salt solution. Here we can see that the effect of the
salt solution is to draw water out of the cell, so that the protoplasmic mem-
L
Fig. 23
Before treatment with salt
solution.
Fig. 25.
Later stage of the same.
Fig. 24.
After treatment with salt
solution.
Figs. 23-25. — Cells from beet treated with salt solution to show osmosis and movement of
the protoplasmic membrane.
brane can be seen to move inward from the cell wall just as was observed in
the case of spirogyra.* Now treating the section with water and removing
the salt solution, the diffusion current is in the opposite direction, that is in-
* We should note that the coloring matter of the beet resides in the cell-
sap. It is in these colored cells that we can best see the movement take
place, since the red color serves to differentiate well the moving mass from the
cell wah. The protoplasmic membrane at several points usually clings tena-
ciously so that at several places the membrane is arched strongly away from
the cell wall as shown in fig. 24. While water is removed from the cell-sap,
we note that the coloring matter does not escape through the protoplasmic
membrane.
IS PHYSIOLOGY.
ward through the protoplasmic membrane, so that the latter is pressed outward
until it comes in contact with the cell wall again, which by its elasticity soon
resists the pressure and the cells again become turgid.
35. The coloring matter in the cell sap does not readily escape from the
living protoplasm of the heet. — The red coloring matter, as seen in the sec-
tion under the microscope, does not escape from the cell-sap through the pro-
toplasmic membrane . When the slices are placed in water, the water is not
colored thereby. The same is true when the slices are placed in the salt or
sugar solutions. Although water is withdrawn from the cell-sap, this coloring
substance does not escape, or if it does it escapes slowly and after a consider-
able time.
36. The coloring matter escapes from dead protoplasm. — If, however, we
heat the water containing a slice of beet up to a point which is sufficient to
kill the protoplasm, the red coloring matter in the cell-sap filters out through
the protoplasmic membrane and colors the water. If we heat a preparation
made for study under the microscope up to the thermal death point we can
see here that the red coloring matter escapes through the membrane into the
water outside. This teaches that certain substances cannot readily filter
through the living membrane of protoplasm, but that they can filter through
when the protoplasm is dead. A very important condition, then, for the suc-
cessful operation of some of the physical processes connected with absorption
in plants is that the protoplasm should be in a living condition.
37. Osmose experiments with leaves. — We may next take the leaves of
certain plants like the geranium, coleus or other plant, and place them in
shallow vessels containing water, salt, and sugar solutions respectively. The
leaves should be immersed, but the petioles should project out of the water or
solutions. Seedlings of corn or beans, especially the latter, may also be
placed in these solutions, so that the leafy ends are immersed. After one or
two hours an examination shows that the specimens in the water are still
turgid. But if we lift a leaf or a bean plant from the salt or sugar solution,
we find that it is flaccid and limp. The blade, or lamina, of the leaf
droops as if wilted, though it is still wet. The bean seedling also is flaccid,
the succulent stem bending nearly double as the lower part of the stem is held
upright. This loss of turgidity is brought about by the loss of water from the
tissues, and judging from the experiments on spirogyra and the beet, we con-
clude that the loss of turgidity is caused by the withdrawal of some of the
. water from the cell-sap by the strong salt solution.
38. Now if we wash carefully these leaves and seedlings, which have been
in the salt and sugar solutions, with water, and then immerse them in fresh
water for a few hours, they will regain their turgidity. Here again we are led
to infer that the diffusion current is now inward through the protoplasmic
membranes of all the living cells of the leaf, and that the resulting turgidity
of the individual cells causes the turgidity of the leaf or stem.
ABSORPTION, DIFFUSION, OSMOSE.
Fig. 27.
Ml
39. Absorption by root hairs. — If we examine seedlings,
which have been grown in a germinator or in the folds of paper
or cloths so that the roots will be free from particles of soil, we
see near the growing point of the roots that the surface is
covered with numerous slender, delicate, thread-
like bodies, the root hairs. Let us place a por-
tion of a small root containing some of these
root hairs in water on a glass slip, and prepare it
for examination with the microscope. We see
that each thread, or root hair, is a continuous
tube, or in other words it is a single cell which
has become very much elongated. The proto-
plasmic membrane lines the wall, and strands of
protoplasm extend across at irregular intervals, the
interspaces being occupied by the cell-sap.
We should now draw under the cover glass
some of the five per cent salt solution. The
protoplasmic membrane moves away from the cell
wall at certain points, showing that plasmolysis is
taking place, that is, the diffusion current is out-
ward so that the cell-sap loses some of its water,
and the pressure from the outside moves the
membrane inward. We should not allow the salt
solution to work on the root hairs long. It should
be very soon removed by drawing in fresh water
before the protoplasmic membrane has been
broken at intervals, as is
apt to be the case by the
strong diffusion current
and the consequent
strong pressure from
Without. The membrane Seedling of n&h, .showing root treatment^ with
of protoplasm now moves
outward as the diffusion current is inward, and soon regains its
former position next the inner side of the cell wall. The
root hairs then, like other parts of the plant which we have
f
20
PHYSIOLOGY.
investigated, have the power of taking up water under press-
ure.
40. Cell-sap a solution of certain substances. — From these experiments we
are led to believe that certain substances reside in the cell-sap of plants, which
behave very much like the salt solution when separated from water by the
protoplasmic membrane. Let us attempt to interpret these phenomena by
recourse to diffusion experiments, where an animal membrane separates two
liquids of different concentration.
41. An artificial cell to illustrate turgor. — Fill a small wide-mouthed
vial with a very strong sugar solution. Over the mouth tie firmly a piece
of bladder membrane. Be certain that as the membrane is tied over the
open end of the vial, the sugar solution fills it in order to keep out air-
FIG. 28. Puncturing
a make-believe cell
after it has been
lying in water.
FIG. 29. Same as Fig. 28
after needle is removed.
bubbles. Sink the vial in a vessel of fresh water a.nd leave it there for twenty-
four hours. Remove the vial and note that the membrane is arched out-
ward. Thrust a sharp needle through the membrane when it is arched
outward, and quickly pull it out. The liquid spurts out because of the
inside pressure.
42. Diffusion through an animal membrane. — For this experiment we
may use a thistle tube, across the larger end of which should be stretched and
tied tightly a piece of a bladder membrane. A strong sugar solution (three
parts sugar to one part water) is now placed in the tube so that the bulb is
ABSORPTION, DIFFUSION, OSMOSE. . 21
filled and the liquid extends part way in the neck of the tube. This is im-
mersed in water within a wide-mouth bottle, the neck of the tube being sup-
ported in a perforated cork in such a way that the sugar solution in the tube is
on a level with the water in the bottle or jar. In a short while the liquid
begins to rise in the thistle tube, in the course of several hours having risen
several centimeters. The diffusion current is thus stronger through the mem-
brane in the direction of the sugar solution, so that this gains more water than
it loses.
We have here two liquids separated by an animal membrane, water on
the one hand which diffuses readily through the membrane, while on the other
is a solution of sugar which diffuses through the animal membrane with diffi-
culty; The water, therefore, not containing any solvent, according to a
general law which has been found to obtain in such cases, diffuses more
readily through the membrane into the sugar solution, which thus increases in
volume, and also becomes more dilute. The bladder membrane is what is
sometimes called a diffusion membrane, since the diffusion currents travel
through it.
43. In this experiment then the bulk of the sugar solution is increased, and
the liquid rises in the tube by this pressure above the level of the water in the
jar outside of the thistle tube. The diffusion of liquids through a membrane
is osmosis.
44. Importance of these physical processes in plants. — Now if we recur
to our experiment with spirogyra we find that exactly the same processes take
place. The protoplasmic membrane is the diffusion membrane, through which
the diffusion takes place. The salt solution which is first used to bathe the
threads of the plant is a stronger solution than that of the cell -sap within the
cell. Water therefore is drawn out of the cell-sap, but the substances in
solution in the cell-sap do not readily move out. As the bulk of the cell-sap
diminishes the pressure from the outside pushes the protoplasmic membrane
away from the wall. Now when we remove the salt solution and bathe
the thread with water again, the cell-sap, being a solution of certain sub-
stances, diffuses with more difficulty than the water, and the diffusion current
is inward, while the protoplasmic membrane moves out against the cell wall,
and turgidity again results. Also in the experiments with salt and sugar solu-
tions on the leaves of geranium, on the leaves and stems of the seedlings, on
the tissues and cells of the beet and carrot, and on the root hairs of the seed-
lings, the same processes take place.
These experiments not only teach us that in the protoplasmic membrane, the
cell wall, and the cell-sap of plants do we have structures which are capable of
performing these physical processes, but they also show that these processes are
of the utmost importance to the plant ; not only in giving the plant the power
lo take up solutions of nutriment from the soil, but they serve also other pur-
poses, as we shall see later.
CHAPTER III.
HOW PLANTS OBTAIN WATER.
In connection with the study of the means of absorption from the soil
or water by plants, it will be found convenient to observe carefully the
various forms of the plant. Without going into detail here, the suggestion
is made that simple thread forms like spirogyra, cedogonium, and vau-
cheria; expanded masses of cells as are found in the thalloid liverworts,
the duckweed, etc., be compared with those liverworts, and with the mosses,
where leaf-like expansions of a central axis have been differentiated. We
should then note how this differentiation, from the physiological stand-
point, has been carried farther in the higher land plants.
45. Absorption by Algae and Fungi. — In the simpler forms of plant life,
as in spirogyra and many of the algae and fungi, the plant body is not dif-
ferentiated into parts.* In many other cases the only differentiation is
between the growing part and the fruiting part. In the algae and fungi
there is no differentiation into stem and leaf, though there is an approach
to it in some of the higher forms. Where this simple plant body is flat-
tened, as in the sea-wrack, or ulva, it is a frond. The Latin word for
frond is thallus, and this name is applied to the plant body of all the lower
plants, the algas and fungi. The algae and fungi together are sometimes
called the thallophytes, or thattus plants. The word thallus is also some-
times applied to the flattened body of the liverworts. In the foliose liver-
worts and mosses there is an axis with leaf-like expansions. These are
believed by some to represent true stems and leaves, by others to represent
a flattened thallus in which the margins are deeply and regularly divided, or
in which the expansion has only taken place at regular intervals.
In nearly all of the algae the plant body is submerged in water. In these
* See Chapter 38 for organization of members of the plant body.
22
HOW PLANTS OBTAIN WATER.
cases absorption takes place through all portions of the surface in contact
with the water, as in spirogyra, vaucheria, and all of the larger seaweeds.
Comparatively few of the algae grow on the surfaces of rocks or trees. It
these examples it is likely that at times only portions of the plant body
serve in the process of absorption of water from the substratum. A few of
the algae are parasitic, living in the tissues of higher plants, where they are
surrounded by the water or liquids within the host. Absorption takes
place in the same way in many of the fungi. The aquatic fungi are im-
mersed in water. In other forms, like mucor, a portion of the mycelium
is within the substratum, and being bathed by the water or watery solu-
tions absorbs the same, while the fruiting portion and the aerial mycelium
obtain their water and food solutions from the mycelium in the substratum.
In higher fungi, like the mushrooms, the mycelium within the ground or
decaying wood absorbs the water necessary for the fruiting portion; while
in the case of the parasitic fungi the mycelium lies in the water or liquid
within the host.
46. Absorption by liverworts. — In many of the plants termed liverworts
the vegetative part of the plant is a thin, flattened, more or less elongated
green body know as a thallus.
Riccia. — One of these, belonging to the genus riccia, is shown in fig. 30.
Its shape is somewhat like that
of a minute ribbon which is
forked at intervals in a dichot-
omous manner, the character-
istic kind of branching found in
these thalloid liverworts. This
riccia (known as R. lutescens)
occurs on damp soil; long,
slender, hair-like processes grow
out from the under surface of
the thallus which resemble root
hairs and serve the same pur-
pose in the processes of absorp-
tion. Another species of riccia
(R. crystallina) is shown in fig.
252. This plant is quite circular in outline and occurs on muddy flats.
Some species float on the water.
Fig. 30.
Thallus of Riccia lutescens.
47. Marchantia. — One of the larger and coarser liverworts is
figured at 31. This is a very common liverwort, growing in
very damp and muddy places and also along the margins of
streams, on the mud or upon the surfaces of rocks which are
24 PHYSIOLOGY.
bathed with the water. This is known as Marchantia poly-
morpha. If we examine the under surface of the marchantia
we see numerous hair-like processes which attach the plant to
the soil. Under the microscope we see that some of these are
similar to the root hairs of the seedlings which we have .been
studying, and they serve the purpose of absorption. Since, how-
ever, there are no roots on the marchantia plant, these hair-like
Fig. 31.
Marchantia plant with cupules and gemmae; rhizoids below.
outgrowths are usually termed here rhizoids. In marchantia they
are of two kinds, one kind the simple ones with smooth walls,
and the other kind in which the inner surfaces of the walls are
roughened by processes which extend inward in the form of irreg-
ular tooth-like points. Besides the hairs on the under side of
the thallus we note especially near the growing end that there are
two rows of leaf-like scales, those at the end of the thallus curv-
ing up over the growing end, thus serving to protect the delicate
tissues at the growing point.
HOW PLANTS OBTAIN WATER.
48. Frullania. — In fig. 32 is shown another liverwort, which
differs greatly in form from the ones we have
just been studying in that there is a well-defined
axis with lateral leaf-like outgrowths. Such liver-
worts are called foliose liverworts. Besides these
two quite prominent rows of leaves there is a
third row of poorly developed leaves on the under
surface. Also
from th e
under surface
of the axis
we see here
and there
slender out-
Fig. 34- growths, the
Under side,
showing forked rhlZOldS,
under row of
leaves and lobes t h T O U g h
of lateral leaves. .
which much
Fig. 32- Fig. 33.
Portion of plant of Portion of same
Frullania, a foliose more highly magni-
fied, showing over-
lapping leaves.
liverwort.
of the water is absorbed.
49. Absorption by the mosses. — Among the mosses, which are
usually common in moist and shaded
situations, examples are abundant
which are suitable for the study of
the organs of absorption. If we take
for example a plant of mnium
(M. affine), which is illustrated in fig.
36, we note that it consists of a slender
Fig. 35-
Foliose liverwort (bazzania) showing dichotomous branching and overlapping leaves.
axis with thin flat, green, leaf-like expansions. Examining with
26
PffYSlOLOG Y.
the microscope the lower end of the axis, which is attached to
the substratum, there are seen numerous brown-colored threads
more or less branched.
50. Absorption by the higher aquatic plants. — Examples of
the water plants which are entirely submerged in water are the
water-crowfoots, some of the pond-
weeds, elodea or water-weeds, the tape-
grass, vallisneria, etc. In these plants
all parts of the body being submerged,
they absorb water with which they are
in contact. In other aquatic plants, like
the water-lilies, some of the pond-
weeds, the duck-meats, etc., are only
partially submerged in the water; the
upper surface of the leaf or of the leaf-
like expansion being exposed to the air,
while the under surface lies in close
contact with the water, and the stems
and the petioles of the leaves are also
immersed in water. In these plants
absorption takes place through those
parts in contact with the water.
51. Absorption by the duck-meats.
— These plants are very curious ex-
amples of the higher plants.
Lemna. — One of these is illustrated in fig.
37. This is the common duckweed, Lemna
trisulca. It is very peculiar in form and in
its mode of growth. Each one of the lateral
leaf-like expansions extends outwards by the
elongation of the basal part, which becomes
^ng ^d slender. Next, two new lateral ex-
rhizoids below and the tuft of pansions are formed on these by prolification
leaves above, which protect the r r
archegonia. from near the base, and thus the plant con-
tinues to extend. The plant occurs in ponds and ditches and is sometimes
very common and abundant. It floats on the surface of the water. While
the flattened part of the plant resembles a leaf, it is really the stem, no
leaves being present. This expanded green body is usually termed a
Fig- 36.
HOW PLANTS OBTAIN WATER. 2J
•frond." A single rootlet grows out from the under side and is destitute
Fig. 37-
Fronds of the duckweed (Lemna trisculca).
of root hairs. Absorption of water therefore takes place through this rootlet
and through the under
side of the "frond."
52. Spirodela poly-
rhiza. — This is a very
curious plant, closely re-
lated to the lemna and
sometimes placed in the
same genus. It occurs
in similar situations, and pjg 3g
is very readily grown in Spirodela polyrhiza.
aquaria. It reminds one of a little insect as
seen in fig. 38. There are several rootlets on
the under side of the frond. Absorption of
water takes place here in the same way as in
lemna.
53. Absorption in wolffia. — Perhaps the most curious of these modified
water plants is the little wolffia, which contains the smallest specimens of
the flowering plants. Two species of this genus are shown in figs. 39-41-
The plant body is reduced to nothing but a rounded or oval green body,
which represents the stem. No leaves or roots are present. The plants
multiply by "prolification," the new fronds growing out from a depression
oft the under side of one end. Absorption takes place through the surface
in contact with the water.
54. Absorption by land plants. — Water cultures. — In connec-
tion with our inquiry as to how land plants obtain their water, it
28
PHYSIOLOGY.
will be convenient to prepare some water cultures to illustrate
this and which can also be used later in our study of nutrition
(Chapter IX).
Fig. 39-
Young frond of wolffia
growing out of older one.
Fig. 40.
Young frond of wolffia
separating trom older one.
Fig. 41-
Another species of
wolffia; the two fronds
still connected.
Chemical analysis shows that certain mineral substances are
common constituents of plants. By growing plants in different
solutions of these various substances it has been possible to deter-
mine what ones are necessary constituents of plant food. While
the proportion of the mineral elements which enter into the com-
position of plant food may vary considerably within certain
limits, the concentration of the solutions should not exceed cer-
tain limits. A very useful solution is one recommended by Sachs,
and is as follows:
55 . Formula for water cultures :
Water. 1000 cc.
Potassium nitrate o . 5 gr.
Sodium chloride o . 5 "
Calcium sulphate o . 5 ' '
Magnesium sulphate o. 5 "
Calcium phosphate ° • 5 "
The calcium phosphate is only partly soluble. The solution which is not in
use should be kept in a dark cool place to prevent the growth of minute algae.
56. Several different plants are useful for experiments in water cultures,
as peas, corn, beans, buckwheat, etc. The seeds of these plants may be
germinated, after soaking them for several hours in warm water, by placing
HOW PLANTS OBTAIN WATER. 2$
them between the folds of wet paper on shallow trays, or in the folds of wet
cloth. The seeds should not be kept immersed in water after they have
imbibed enough to thoroughly soak and swell them. At the same time
that the seeds are placed in damp paper or cloth for germination, one lot of
the soaked seeds should be planted in good soil and kept under the same
temperature conditions, for control. When the plants have germinated
one series should be grown in distilled water, which possesses no plant food;
another in the nutrient solution, and still another in the nutrient solution to
which has been added a few drops of a solution of iron chloride or ferrous
sulphate. There would then be four series of cultures which should be
carried out with the same kind of seed in each series so that the compari-
sons can be made on the same species under the different conditions. The
series should be numbered and recorded as follows:
No. I, soil.
No. 2, distilled water.
No. 3, nutrient solution.
No. 4, nutrient solution with a few drops of iron solution added.
57. Small jars or wide-mouth bottles, or crockery jars, can be used for the
water cultures, and the cultures are set up as follows : A cork which will just
fit in the mouth of the bottle, or which can be supported by pins, is perforated
so that there is room to insert the seedling,
with the root projecting below into the liquid.
The seed can be fastened in position by insert-
ing a pin through one side, if it is a large one,
or in the case of small seeds a cloth of a coarse
mesh can be tied over the mouth of the bottle
instead of using the cork. After properly set-
ting up the experiments the cultures should be
arranged in a suitable place, and observed from
time to time during several weeks. In order to
obtain more satisfactory results several dupli-
cate series should be set up to guard against the
error which might arise from variation in indi-
vidual plants and from accident. Where there
are several students in a dass, a single series
set up by several will act as checks upon one
another. If glass jars are used for the liquid Fig. 42-
cultures they should be wrapped with black Culture cylinder to show position of
com seedling \ Hansen).
paper or cloth to exclude the light from the
liquid, otherwise numerous minute algae are apt to grow and interfere with the
experiment. Or the jars may be sunk in pots of earth to serve the same
purpose. If crockery jars are used they will not need covering.
58. For some time all the plants grow equally well, until the nutriment
stored in the seed is exhausted. The numbers I, 3 and 4, in soil and nutri-
30 PHYSIOLOGY.
ent solutions, should outstrip number 2, the plants in the distilled water.
No. 4 in the nutrient solution with iron, having a perfect food, compares favor-
ably with the plants in the soil.
59. Plants take liquid food from the soil. — From these ex-
periments then we judge that such plants take up the food the)
receive from the soil in the form of a liquid, the elements being
in solution in water.
If we recur now to the experiments which were performed with
the salt solution in producing plasmolysis in the cells of spirogyra,
in the cells of the beet or corn, and in the root hairs of the corn
and bean seedlings, and the way in which these cells become tur-
gid again when the salt solution is removed and they are again
bathed with water, we shall have an explanation of the way in
which plants take up nutrient solutions of food material through
their roots.
60. How food solutions are carried into the plant. — We can
Fig. 43-
Section of corn root, showing root hairs formed from elongated epidermal cells.
see how water and food solutions are carried into the plant,
HOW PLANTS OBTAIN WATER, 31
and we must next turn our attention to the way in which these
solutions are carried farther into the plant. We should make a
section across the root of a seedling in the region of the root
hairs and examine it with the aid of a microscope. We here see
that the root hairs are formed by the elongation of certain of the
surface cells of the root. These cells elongate perpendicularly to
the root, and become $mm to 6mm long. They are flexuous or
irregular in outline and cylindrical, as shown in fig. 43. The
end of the hair next the root fits in between the adjacent superfi-
cial cells of the root and joins closely to the next deeper layer of
cells. In studying the section of the young root we see that the
root is made up of cells which lie closely side by side, each with
its wall, its protoplasm and cell-sap, the protoplasmic membrane
lying on the inside of each cell wall.
61. In the absorption of the watery solutions of plant food by the root
hairs, the cell-sap, being a more concentrated solution, gains some of the
former, since the liquid of less concentration flows through the protoplasmic
membrane into the more concentrated cell-sap, increasing the bulk of the lat-
ter. This makes the root hairs turgid, and at the same time dilutes the cell-
sap so that the concentration is not so great. The cells of the root lying in-
side and close to the base of the root hairs have a cell-sap which is now more
concentrated than the diluted cell-sap of the hairs, and consequently gain
some of the fpod solutions from the latter, which tends to lessen the content
of the root hairs and also to increase the concentration of the cell-sap of the
same. This makes it possible for the root hairs to draw on the soil for more
of the food solutions, and thus, by a variation in the concentration of the sub-
stances in solution in the cell-sap of the different cells, the food solutions are
carried along until they reach the -vascular bundles, through which the solu-
tions are carried to distant parts of the plant. Some believe that there is a
rhythmic action of the elastic cell walls in these cells between the root hairs and
the vascular bundles. This occurs in such a way that, after the cell becomes
turgid, it contracts, thus reducing the size of the cell and forcing some of the
food solutions into the adjacent cells, when by absorption of more food solu-
tions, or water, the cell increases in turgidity again. This rhythmic action of
the cells, if it does take place, would act as a pump to force the solutions
along, and would form one of the causes of root pressure.
62. How the root hairs get the watery solutions from the soil. — If we
examine the root hairs of a number of seedlings which are growing in the soil
under normal conditions, we shall see that a large quantity of soil readily
clings to the roots. We should note also that unless the soil has been recently
watered there is no free water in it ; the soil is only moist. We are curious
PHYSIOLOGY.
to know how plants can obtain water from soil which is not wet. If we at-
tempt to wash off the soil from the roots, being careful not to break away the
Fig. 44-
Root hairs of corn seedling with soil particles adhering closely.
root hairs, we find that small particles cling so tenaciously to
the root hairs that they are not removed. Placing a few such
root hairs under the microscope it appears as if here and there the root hairs
were glued to the minute soil particles.
63. If now we take some of the soil which is only moist, weigh it, and
then permit it to become quite dry on exposure to dry air, and weigh again,
we find that it loses weight in drying. Moisture has been given oft.
This moisture, it has been found, forms an exceedingly thin film on the sur-
face of the minute soil particles. Where these soil particles lie closely to-
gether, as they usually do when massed together in the pot or elsewhere, this
thin film of moisture is continuous from the surface of one particle to that of an-
ther. Thus the soil particles which are so closely attached to the root hairs
connect the surface of the root hairs with this film of moisture. As the cell-
sap of the root hairs draws on the moisture film with which they are in con-
tact, the tension of this film is sufficient to draw moisture from distant parti-
cles. In this way the roots are supplied with water in soil which is only
moist.
64. Plants cannot remove all the moisture from the soil. — If we now take
a potted plant, or a pot containing a number of seedlings, place it in a moder-
ately dry room, and do not add water to the soil we find in a few days that
the plant is wilting. The soil if examined will appear quite dry fo the
sense of touch. Let us weigh some of this soil, then dry it by artificial
HOW PLANTS OBTAIN WATER. 33
heat, and weigh again. It has lost in weight. This has been brought about
by driving off the moisture which still remained in the soil after the plant
began to wilt. This teaches that while plants can obtain water from soil
which is only moist or which is even rather dry, they are not able t(j with-
draw all the moisture from the soil.
65. " Root pressure " or exudation pressure. — It is a very com-
mon thing to note, when certain shrubs or vines are pruned in
the spring, the exudation of a watery fluid from the cut surfaces.
In the case of the grape vine this has been known to continue for
a number of days, and in some cases the amount of liquid, called
"sap," which escapes is considerable. In many cases it is
directly traceable to the activity of the roots, or root hairs, in
the absorption of water from the soil. For this reason the term
root pressure has been used to denote the force exerted in sup-
plying the water from the soil. But there are some who object
to the use of this term "root pressure." The principal objec-
tion is that the pressure which brings about the phenomenon
known as ' ' bleeding ' ' by plants is not present in the roots alone.
This pressure exists under certain conditions in all parts of the
plant. The term exudation pressure has been proposed in lieu
of root pressure. It should be remembered that the movement
of water in the plant is started by the pressure which exists in
the root. If the term "root pressure" is used, it should be
borne clearly in mind that it does not express the phenomenon
exactly in all cases.
Root pressure may be measured. — It is possible to measure
not only the amount of water which the roots will raise in a
given time, but also to measure the force exerted by the roots
during root pressure. It has been found that root pressure in
the case of the nettle is sufficient to hold a column of water about
4.5 meters (15 ft.) high (Vines), while the root pressure of the
vine (Hales, 1721) will hold a column of water about 10 meters
(36.5 ft.) high, and the birch (Betula lutea) (Clark, 1873) has a
root pressure sufficient to hold a column of water about 25 meters
(84.7 ft.) high.
66. Experiment to demonstrate root pressure. — By a very simple method
this lifting of water by root pressure is shown. During the summer season
34
PHYSIOLOGY.
plants in the open may be used if it is preferred, but plants grown In pots
are also very serviceable, and one may use a potted begonia or balsam, the
latter being especially useful. The plants are usually convenient to obtain
from the greenhouses, to illustrate this phenomenon.
The stem is cut off rather close to the soil and a long
glass tube is attached to the cut end of the stem, still
connected with the roots, by the use of rubber tubing,
as shown in figure 45, and a very small quantity of water
may be poured in to moisten the cut end of the stem.
In a few minutes the water begins to rise in the glass
tube. In some cases it rises quite rapidly, so that the
column of water can readily be seen to extend higher
and higher up in the tube when observed at quite
short intervals. (To measure the force of root pressure
is rather difficult for elementary work. To measure it
see Ganong, Plant Physiology, pp. 67, 68, or some other
book for advanced work.")
Pig. 45.
67. In either case where the experiment is
continued for several days it is noticed that the
column of water or of mercury rises and falls at
different times during the same day, that is, the
column stands at varying heights; or in other
words the root presssure varies during the day. With some plants
it has been found that the pressure is greatest at certain times
of the day, or at certain seasons of the year. Such variation
of root pressure exhibits what is termed a periodicity, and in
the case of some plants there is a daily periodicity; while in
others there is in addition an annual periodicity. With the
grape vine the root pressure is greatest in the forenoon, and
decreases from 12-6 P.M., while with the sunflower it is greatest
before 10 A.M., when it begins to decrease. Temperature of
the soil is one of the most important external conditions affect-
ing the activity of root pressure.
CHAPTER IV.
TRANSPIRATION, OR THE LOSS OF WATER BY
PLANTS.
68. We should now inquire if all the water which is taken up
in excess of that which actually suffices for turgidity is used in the
elaboration of new materials of construction. We notice when a
leaf or shoot is, cut away from a plant, unless it is kept in quite
a moist condition, or in a damp, cool place, that it becomes flac-
cid, and droops. It wilts, as we say. The leaves and shoot lose
their turgidity. This fact suggests that there has been a loss of
water from the shoot or leaf. It can be readily seen that this
loss is not in the form of drops of water which issue from the cut
end of the shoot or petiole. What then becomes of the water in
the cut leaf or shoot ?
Fig. 46.
To show loss of water from leaves, the leaves just covered.
69. Loss of water from excised leaves. — Let us take a handful
of fresh, green, rather succulent leaves, which are free from
35
36'
PHYSIOLOGY.
water on the surface, and place them under a glass bell jar, which
is tightly closed below but which contains no water. Now place
this in a brightly lighted window, or in sunlight. In the course
of fifteen to thirty minutes we notice that a thin film of moisture
is accumulating on the inner surface of the glass jar. After an
hour or more the moisture has accumulated so that it appears in
the form of small drops of condensed water. We should set up
at the same time a bell jar in exactly the same way but which
contains no leaves. In this jar there is no condensed moisture
on the inner surface. We thus are justified in concluding that
Fig. 47-
After a few hours drops of water have accumulated on the inside of the jar covering
the leaves.
the moisture in the former jar comes from the leaves. Since
there is no visible water on the surfaces of the leaves, or at the
cut ends, before it may have condensed there, we infer that the
water escapes from the leaves in the form of water vapor, and
that this water vapor, when it comes in contact with the surface
of the cold glass, condenses and forms the moisture film, and
later the drops of water. The leaves of these cut shoots there-
fore lose water in the form of water vapor, and thus a loss of
turgidity results.
70. Loss of water from growing plants. — Suppose we now
take a small and actively growing plant in a pot, and cover the
pot and the soil with a sheet of rubber cloth or flexible oilcloth
TRANSPIKA TION. 37
which fits tightly around the stem of the plant so that the mois-
ture from the soil or from the surface of the pot cannot escape.
Then place a bell jar over the plant, and set in a brightly lighted
place, at a temperature suitable for growth. In the course of a
few minutes on a dry day a moisture film forms on the inner
surface of the glass, just as it did in the case of the glass jar con-
taining the cut shoots and leaves. Later the moisture has con-
densed so that it is in the form of drops. If we have the same
leaf surface here as we had with the cut shoots, we shall prob-
ably find that a larger amount of water accumulates on the
surface of the jar from the plant that is still attached to its
roots.
71. Water escapes from the surfaces of living leaves in the
form of water vapor. — This living plant then has lost water, which
also escapes in the form of water vapor. Since here there are no
cut places on the shoots or leaves, we infer that the loss of water
vapor takes place from the surfaces of the leaves and from the
shoots. It is also to be noted that, while this plant is losing
water from the surfaces of the leaves, it does not wilt or lose its
turgidity. The roots by their activity and pressure supply water
to take the place of that which is given off in the form of water
vapor. This loss of water in the form of water vapor by plants
is transpiration.
72. A test for the escape of water vapor from plants. — Make
a solution of cobalt chloride in water. Saturate several pieces of
filter paper with it. Allow them to dry. The water solution of
cobalt chloride is red. The paper is also red when it is moist,
but when it is thoroughly dry it is blue. It is very sensitive
to moisture and the moisture of the air is often sufficient to
redden it. Before using dry the paper in an oven or over a
flame.
73. Take two bell jars, as shown in fig. 49. Under one place
a potted plant, the pot and earth being covered by oiled paper.
Or cover the plant with a fruit jar. To a stake in the pot pin a
piece of the dried cobalt paper, and at the same time pin to a
3 » PHYSIOLOGY.
stake, in another jar covering no plant, another piece of cobalt
paper. They should both be put under the jars at the same
time. In a few moments the paper in the jar with the plant will
begin to redden. In a short while, ten or fifteen minutes, prob-
ably, it will be entirely red, while the paper under the other jar
will remain blue, or be only slightly reddened. The water vapor
passing off from the living plant comes in contact with the sensi-
Fig. 48. Fig. 49-
Fig. 48. — Water vapor is given off by the leaves when attached to the living plant-
It condenses into drops of water on the cool surface of the glass covering the plant.
Fig. 49. — A good way to show that the water passes off from the leaves in the form
of water vapor.
tive cobalt chloride in the paper and reddens it before there is
sufficient vapor present to condense as a film of moisture on the
surface of the jar.
74. Experiment to compare loss of water in a dry and a
humid atmosphere. — We should now compare the escape of
water from the leaves of a plant covered by a bell jar, as in the
last experiment, with that which takes place when the plant is
TRANSPIRA TION. 39
exposed in a normal way in the air of the room or in the open.
To do this we should select two plants of the same kind growing
in pots, and of approximately the same leaf surface. The potted
plants are placed one each on the arms of a scale. One of the
plants is covered in this position with a bell jar. With weights
placed on the pan of the other arm the two sides are balanced.
In the course of an hour, if the air of the room is dry, moisture
has probably accumulated on the inner surface of the glass jar
which is used to cover one of the plants. This indicates that
there has here been a loss of water. But there is no escape of
water vapor into the surrounding air so that the weight on this
arm is practically the same as at the beginning of the experiment.
We see, however, that the other arm of the balance has risen.
We infer that this is the result of the loss of water vapor from the
plant on that arm. Now let us remove the bell jar from the other
plant, and with a cloth wipe off all the moisture from the inner
surface, and replace the jar over the plant. We note that the
end of the scale which holds this plant is still lower than the
other end.
75. The loss of water is greater in a dry than in a humid
atmosphere. — This teaches us that while water vapor escaped
from the plant under the bell jar, the air in this receiver soon
became saturated with the moisture, and thus the farther escape
of moisture from the leaves was checked. It also teaches us an-
other very important fact, viz. , that plants lose water more rapidly
through their leaves in a dry air than in a humid or moist atmos-
phere. We can now understand why it is that during the very
hot and dry part of certain days plants often wilt, while at night-
fall, when the atmosphere is more humid, they revive. They lose
more water through their leaves during the dry part of the day,
other things being equal, than at other times.
76. How transpiration takes place. — Since the water of
transpiration passes off in the form of water vapor we are led to
inquire if this process is simply evaporation of water through the
surface of the leaves, or whether.it is controlled to any appreci-
able extent by any condition of the living plant. An experiment
40 PHYSIOLOGY.
which is instructive in this respect we shall find in a comparison '
between the transpiration of water from the leaves of a cut shoot,
allowed to lie unprotected in a dry room, and a similar cut shoot
the leaves of which have been killed.
77. Almost any plant will answer for the experiment. For this purpose I
have used the following method. Small branches of the locust (Robinia
pseudacacia), of sweet clover (Melilotus alba), and of a heliopsis were
selected. One set of the shoots was immersed for a moment in hot water near
the boiling point to kill them. The other set was immersed for the same
length of time in cold water, so that the surfaces of the leaves might be well
wetted, and thus the two sets of leaves at the beginning of the experiment
would be similar, so far as the amount of water on their surfaces is con-
cerned. All the shoots were then spread out on a table in a dry room, the
leaves of the killed shoots being separated where they are inclined to cling
together. In a short while all the water has evaporated from the surface of
the living leaves, while the leaves of the dead shoots are still wet on the sur-
face. In six hours the leaves of the dead shoots from which the surface
water had now evaporated were beginning to dry up, while the leaves of the
Jiving plants were only becoming flaccid. In twenty -four hours the leaves
of the dead shoots were crisp and brittle, while those of the living shoots were
only wilted. In twenty-four hours more the leaves of the sweet clover and
of the heliopsis were still soft and flexible, showing that they still contained
more water than the killed shoots which had been crisp for more than a
day.
78. It must be then that during what is termed transpiration the living
plant is capable of holding back the water to some extent, which in a dead
plant would escape more rapidly by evaporation. It is also known that a
body of water with a surface equal to that of z. given leaf surface of a plant
loses more water by evaporation during the same length of time than the
plant loses by transpiration.
79. Structure of a leaf. — We are now led to inquire why it is
that a living leaf loses water less rapidly than dead ones, and
why less water escapes from a given leaf surface than from an
equal surface of water. To understand this it will be necessary
to examine the minute structure of a leaf. For this purpose we
may select the leaf of an ivy, though many other leaves will
answer equally well. From a portion of the leaf we should make
very thin cross sections with a razor or other sharp instrument.
These sections should be perpendicular to the surface of the leaf
TRANSPIRA TION.
and should be then mounted in water for microscopic examina-
tion.*
80. Epidermis of the leaf. — In this section we see that the
green part of theleaTis bordered on what are its upper and
lower surfaces by a row of cells which
possess no green color. The walls of
the cells of each row have nearly par-
allel sides, and the cross walls are per-
pendicular. These cells form a single
layer over both surfaces of the leaf and
are termed the epidermis. Their walls
are quite stout and the outer walls are
cuticularized.
81. Soft tissue of the leaf.— The
cells which contain the green chloro-
phyll bodies are arranged in two dif- .
Section through ivy leaf showing
ferent Ways. Those On the Upper side communication between stomateand
» the large intercellular spaces of the
of the leaf are usually long and pris- leaf' stoma closed,
matic in form and lie closely parallel to each other. Because of
this arrangement of these cells they are termed the palisade cells,
and form what is called the palisade layer. The other green
cells, lying below,
vary greatly in size in
different plants and to
some extent also in the
same plant. Here we
notice that they are
elongated, or oval, or
somewhat irregular in
form. The most striking peculiarity, however, in their arrange-
ment is that they are not usually packed closely together, but each
cell touches the other adjacent cells only at certain points. This
arrangement of these cells forms quite large spaces between them,
the intercellular spaces. If we should examine such a section of
a leaf before it is mounted in water we would see that the inter-
* Demonstrations may be made with prepared sections of leaves.
Fig. 51.
Stoma open.
Figs. 34, 35. — Section through stomata of ivy leaf.
42 PHYSIO LOG Y.
cellular spaces are not filled with water or cell-sap, but are filled
with air or some gas. Within the cells, on the other hand, we
find the cell -sap and the protoplasm.
82. Stomata. — If we examine carefully the row of epidermal
cells on the under surface of the leaf, we find here and there
a peculiar arrangement of cells shown at figs. 51, 52. This
opening
through the
e pi de rmal
layer is a
sloma. The
cells which
immediately
surround the
openings are
the guard
Fig- S3.
Portion of epidermis of ivy, showing irregular epidermal cells, stoma C611S.
and guards. form Qf ^
guard cells can be better seen if we tear a leaf in such a way as
to strip off a short piece of the lower epidermis, and mount this
in water. The guard cells are nearly crescent shaped, and the
stoma is elliptical in outline. The epidermal cells are very
irregular in outline in this view. We should also note that while
the epidermal cells contain no chlorophyll, the guard cells do.
82a. In the ivy leaf the guard cells are quite plain, but in most
plants the form as seen in cross-section is irregular in outline, as
shown in fig. 530, which is from a section of a wintergreen leaf.
This leaf is interesting because it shows the characteristic struc-
ture of leaves of many plants growing in soil where absorption of
water by the roots is difficult owing to the cold water, acids, or
salts in the water or soil, or in dry soil (see Chapters 47, 54? 55)-
The cuticle over the upper epidermis is quite thick. This
lessens the loss of water by the leaf. The compact palisades of
cells are in two to three cell layers, also reducing the loss of water.
83. The living protoplasm retards the evaporation of water from the
leaf. — If we now take into consideration a few facts which we have learned
TRANSPIRA TION.
,'43
in a previous chapter, with reference to the physical properties of the living
cell, we shall be able to give a partial explanation of the comparative slow-
ness with which the water escapes from the leaves. The inner surfaces of
the cell walls are lined with the membrane of protoplasm, and within this
is the cell-sap. These cells have become turgid by the absorption of the
Fig. 533-
* •»• JO^'
Cross-section of leaf of wintergreen. Cu. cuticle; Epid., epidermis; v.d., vascular
duct; Int. c. sp., intercellular space; L. ep., lower epidermis; St., stoma.
water which has passed up to them from the roots. While the protoplas-
mic membrane of the cells does not readily permit the water to filter through,
yet it is saturated with water, and the elastic cell wall with which it is in
contact is also saturated. From the cell wall the water evaporates into the
intercellular spaces. But the water is given up slowly through the proto-
plasmic membrane, so that the water vapor cannot be given off as rapidly
from the cell walls as it could if the protoplasm were dead. The living
protoplasmic membrane then which is only slowly permeable to the water of
the cell-sap is here a very important factor in checking the too rapid loss of
water from the leaves.
44 PHYSIOLOGY.
By an examination of our leaf section we see that the intercellulai spaces
are all connected, and that the stomata, where they occur, open also into
intercellular spaces. There is here an opportunity for the water vapoi
in the intercellular spaces to escape when the stomata are open,
84. Action of the stomata. — The guard cells serve an important func-
tion in regulating transpiration. During normal transpiration the guard
cells are turgid and their peculiar form then causes them to arch away
from each other, allowing the escape of water vapor. When the air becomes
too dry transpiration is in excess of absorption by the roots. The guard
cells lose some of their v/ater, and collapse so that their inner faces meet
in a straight line and close the stoma. Thus the rapid transpiration is
checked. Some evaporation of water vapor, however, takes place through
the epidermal cells, and if the air remains too dry, the leaves eventually
become flaccid and droop. During the day the effect of sunlight is to
increase certain sugars or salts in the guard cells so that they readily be-
come turgid and open the stomates, but at night the cell-sap is less con-
centrated and the stomates are usually closed. Light therefore favors
transpiration, while in darkness transpiration is checked.
85. Compare transpiration from the two surfaces of the leaf. — This can
be done by using the cobalt chloride paper. This paper can be kept from
year to year and used repeatedly. It is thus a very simple matter to make
these experiments. Provide two pieces of glass (discarded glass nega-
tives, cleaned, are excellent), two pieces of cobalt chloride paper, and some
geranium leaves entirely free from surface water. Dry the paper until it is
blue. Place one piece of the paper on a glass plate; place the geranium
leaf with the under side on the paper. On the upper side of the leaf now
place the other cobalt paper, and next the second piece of glass. On the
pile place a light weight to keep the parts well in contact. In fifteen or
twenty minutes open and examine. The paper next the under side of the
geranium leaf is red where it lies under the leaf. The paper on the upper
side is only slightly reddened. The greater loss of water, then, is through
the under side of the geranium leaf. This is true of a great many leaves,
but it is not true of all.
86. Negative pressure. — This is not only indicated by the drooping of
the leaves, but may be determined in another way. If the shoot of such a
plant be cut underneath mercury, or underneath a strong solution of eosin,
it will be found that some of the mercury or eosin, as the case may be, will
be forcibly drawn up into the stem toward the roots. This is seen on
quickly splitting the cut end of the stem. When plants in the open cannot
be obtained in this condition, Oiie may take a plant like a balsam plant
from the greenhouse, or some other potted plant, knock it out of the pot,
free the roots from the soil and allow to partly wilt. The stem may then
be held under the eosin solution and cut.
TRANSPIRA TION.
45
87. Lifting power of transpiration. — Not only does transpiration go on
quite independently of root pressure, as we have discovered from other
experiments, but transpiration is capable of exerting a
lifting power on the water in the plant. This may
be demonstrated in the following way: Place the cut
end of a leafy shoot in one end of a U tube and fit it
water-tight. Partly fill this arm of the U tube with
water, and add mercury to the other arm until it
stands at a level in the two arms as in fig. 54. In a
short time we note that the mercury is rising in the
tube.
88. Boot pressure may exceed transpiration. — If we
cover small actively growing plants, such as the pea,
corn, wheat, bean, etc., with a bell jar, and place them
in the sunlight where the temperature is suitable for
growth, in a few hours, if conditions are favorable,
we shall see that there are drops of water standing out
on the margins of the leaves. These drops of water
Fig. 54.
Experiment to
have exuded through the ordinary stomata, or in show lifting power of
• . ,, , transpiration.
other cases what are called water stomata, through
the influence of root pressure. The plant being covered by the glass jar,
the air soon becomes saturated with moisture and transpiration is checked.
Root pressure still goes on, however, and the result is shown in the exuding
drops. Root pressure is here in excess of transpiration.
This phenomenon is often to be observed during the sum-
mer season in the case of low-growing plants. During the
bright warm day transpiration
"" •"•^"^^"•""!I" "" ' equals, or may be in excess of,
pjg ss> root pressure, and the leaves
Estimation of the amount of are consequently flaccid. As
transpiration. The tubes are • . .c n *u
filled with water, and as the nightfall comes on the air
water transpires from the leaf becomes more moist, and the
surface its movement in the tube
from a to b can be measured, conditions of light are sxich
(After Mangin.)
also that transpiration is les-
sened. Root pressure, however, is still active because the soil is still warm.
In these cases drops of water may be seen exuding from the margins of the
leaves due to the excess of root pressure over transpiration. Were it not
for this provision for the escape of the excess of water raised by root pres-
sure, serious injury by lesions, as a result of the great pressure, might
result. The plant is thus to some extent a self-regulatory piece of
apparatus so far as root pressure and transpiration are concerned.
89. Injuries caused by excessive root pressure. — Some varieties of toma-
toes when grown in poorly lighted and poorly ventilated greenhouses suffer
PHYSIOLOGY.
serious injury through lesions of the tissues. This is brought about by the
cells at certain parts becoming charged so full with water through the
activity of root pressure and lessened transpiration, assisted also probably
by an accumulation of certain acids in the cell-sap which cannot be got
rid of by transpiration. Under these conditions some of the cells here
swell out, forming extensive cushions, and the cell walls become so weak-
ened that they burst. It is possible to imitate the excess of root pressure
in the case of some plants by connecting the stems with a system of
water pressure, when very quickly
the drops of water will begin to
exude from the margins of the
leaves.
90. It should be stated that in
reality there is no difference between
transpiration and evaporation, if we
bear in mind that evaporation takes
place more slowly from living plants
than from dead ones, or from an
equal surface of water.
91. The escape of water vapor is
not the only function of the stomata.
The exchange of gases takes place
through them as we shall later see.
A large number of experiments show
that normally the stomata are open
when the leaves are turgid. But
when plants lose excessive quantities
of water on dry and hot days, so
that the leaves become flaccid, the
guard cells automatically close the
stomata to check the escape of water
Some water escapes through
of many plants,
though the cuticularized mem-
brane of the epidermis largely prevents evaporation. In arid regions
plants are usually provided with an epidermis of several layers of cells to
more securely prevent evaporation there. In such cases the guard cells
are often protected by being sunk deeply in the epidermal layer.
92. Demonstration of stomates and intercellular air spaces.— A good
demonstration of the presence cf stomates in leaves, as well as the presence
and intercommunication of the intercellular spaces, can be made by blow-
ing into the cut end of the petiole of the leaf of a calla lily, the lamina being
Fig. 56.
The roots are lifting more water into vaDor
the plant than can be given off in the form
of water vapor, so it is pressed out in the epidermis
drops. From " First Studies Plant Life."
TRANSPIRATION. 47
immersed in water. The air is forced out through the stomata and rises as
bubbles to the surface of the water. A.t the close of the experiment some
of the air bubbles will still be in contact with the leaf surface at the opening
of the stomata. The pressure of the water gradually forces this back into
the leaf. Other plants will answer for the experiment, but some are more
suitable than others.
92a. Number of stoiuata. — The larger number of stomata are on the
under side of the leaf. (In leaves which float on the surface of the water
all of the stomata are on the upper side of the leaf, as in the water lily.) It
has been estimated by investigation that in general there are 40-300 stomata
to the square millimeter of surface. In some plants this number is exceeded,
as in the olive, where there are 625. In an entire leaf of Brassica rapa
there are about 11,000,000 stomata, and in an entire leaf of the sunflower
there are about 13,000,000 stomata.
92b. Amount of water transpired by plants. — The amount of water
transpired by plants is very great. According to careful estimates a sun-
flower 6 feet high transpires on the average about one quart per day; an
acre of cabbages 2,000,000 quarts in four months; an oak tree with 700,000
leaves transpires about 180 gallons of water per day. According to von Hoh-
nel, a beech tree no years old transpired about 2250 gallons of water in
one summer. A hectare of such trees (about 400 on 2^ acres) would at the
same rate transpire about 900,000 gallons, or about 30,000 barrels in one
summer.
CHAPTER V.
PATH OF MOVEMENT OF WATER IN PLANTS.
93. In our study of root pressure and transpiration we have
seen that large quantities of water or solutions move upward
through the stems of plants. We are now led to inquire
through what part of the stems the liquid passes in this upward
movement, or in other words, what is the path of the "sap" as
it rises in the stem. This we can readily see by the following
trial.
94. Place the cut ends of leafy shoots in a solution of some
of the red dyes. — We may cut off leafy shoots of various plants
and insert the cut ends in a vessel of water to which have been
added a few crystals of the dye known as fuchsin to make a deep
red color (other red dyes may be used, but this one is especially
good). If the study is made during the summer, the "touch-
me-not" (impatiens) will be found a very useful plant, or the
garden-balsam, which may also be had in the winter from con-
servatories. Almost any plant will do, however, but we should
also select one like the corn plant (zea mays) if in the summer,
or the petioles of a plant like caladium, which can be obtained
from the conservatory. If seedlings of the castor-oil bean are at
hand we may cut off some shoots which are 8— 10 inches high,
and place them in the solution also.
95. These solutions color the tracts in the stem and leaves
through which they flow. — After a few hours in the case of the
impatiens, or the more tender plants, we can see through the
stem that certain tracts are colored red by the solution, and
after 12 to 24 hours there may be seen a red coloration of the
48
PATH OF MOVEMENT.
49
leaves of some of the plants used. After the shoots have been
standing in the solution for a few hours, if we cut them at
various places we will note that there are several points in the
section where the tissues are colored red. In the impatiens
perhaps from four to five, in the sunflower a larger number. In
these plants the colored areas on a cross section of the stem are
situated in a concentric ring which separates more or less com-
pletely an outer ring of the stem from the central portion. If
we now split portions of the stem lengthwise we see that these
colored areas continue throughout the length of the stem, in some
cases even up to the leaves and into them.
96. If we cut across the stem of a corn plant which has been
in the solution, we see that instead of the colored areas being in
a concentric ling they are irregularly scattered, and on splitting
Fig 57.
Broken corn stalk, showing libro-vascular bundles.
the stem we see here also that these colored areas extend for long
distances through the stem. If we take a corn stem which is
mature, or an old and dead one, cut around through the outer
hard tissues, and then break the stem at this point, from the
softer tissue" long strings of tissue will pull out as shown in fig.
57. These strings of denser tissue correspond to the areas
which are colored by the dye. They are in the form of minute
bundles, and are called vascular bundles.
50 PHYSIO LOG Y.
97. We thus see that instead of the liquids passing through
the entire stem they are confined to definite courses. Now that
we have discovered the path of the upward movement of water
in the stem, we are curious to see what the structure of these
definite portions of the stem is.
98. Structure of the fibro-vascular bundles. — We should now make quite
thin cross sections, either free hand and mount in water for microscopic
examination, or they may be made with a microtome and mounted in Canada
balsam, and in this condition will answer for future study. To illustrate the
structure of the bundle in one type we may take the stem of the castor-oil
bean. On examining these cross sections we see that there are groups of
cells which are denser than the ground tissue. These groups correspond to
the colored areas in the former experiments, and are the vascular bundles
Fig. 58.
Xylem portion of bundle. Cambium portion of bundle. Bast portion of bundle
Section of vascular bundle of sunflower stein.
cut across. These groups are somewhat oval in outline, with the pointed
end directed toward the center of the stem. If we look at the section
as a whole we see that there is a narrow continuous ring* of small cells
* This ring and the bundles separate the stem into two regions, an outer
one composed of large cells with thin walls, known as the cortical cells, or
collectively the cortex. The inner portion, corresponding to ^hat is called
the pith, is made up of the same kind of cells and is called the medulla, or
pith. When the cells of the cortex, as well as of the pith, remain thin walled
the tissue is called parenchyma. Parenchyma belongs to the group of
tissues called fundamental.
PATH OF MOVEMENT. 5 1
situated at the same distance from the center of the stem as the middle part
of the bundles, and that it divides the bundles into two groups of cells.
99. Woody portion of the bundle. — In that portion of the bundle on the
inside of the ring, i.e., toward the "pith," we note large, circular, or angu-
lar cavities. The walls of these cells are quite thick and woody. They are
therefore called wood cells, and because they are continuous with cells above
and below them in the stem in such a way that long tubes are formed, they
are called woody vessels. Mixed in with these are smaller cells, some of
which also have thick walls and are wood cells. Some of these cells may
have thin walls. This is the case with all when they are young, and they
are then classed with the fundamental tissue or soft tissue (parenchyma).
This part of the bundle, since it contains woody vessels and fibres, is the
•wood portion of the bundle, or technically the xylem.
100. Bast portion of the handle. — If our section is through a part of the
stem which is not too young, the tissues of the outer part of the bundle will
show either one or several groups of cells which have white and shiny walls,
that are thickened as much or more than those of the wood vessels. These
cells are bast cells, and for this reason this part of the bundle is the bast por-
tion, or the phloem. Intermingled with these, cells may often be found which
have thin walls, unless the bundle is very old. Nearer the center of the
bundle and still within the bast portion are cells with thin walls, angular and
irregularly arranged. This is the softer portion of the bast, and some of
these cells are what are called sieve tubes, which can be better seen and
studied in a longitudinal section of the stem.
101. Cambium region of the bundle. — Extending across the center of the
bundle are several rows of small cells, the smallest of the bundle, and we can
see that they are more regularly arranged, usually in quite regular rows,
like bricks piled upon one another. These cells have thinner walls than any
others of the bundle, and they usually take a deeper stain when treated
with a solution of some of the dyes. This is because they are younger, and
are therefore richer in protoplasmic contents. This zone of young cells
across the bundle is the cambium. Its cells grow and divide, and thus increase
the size of the bundle. By this increase in the number of the cells of the
cambium layer, the outermost cells on either side are continually passing
over into the phloem, on the one hand, and into the wood portion of the
bundle, on the other hand.
102. Longitudinal section of the bundle. — If we make thin longisections of
the vascular bundle of the castor-oil seedling (or other dicotyledon) so that we
have thin ones running through a bundle radially, as shown in fig. 59, we
can see the structure of these parts of the bundle in side view. We see here
that the form of the cells is very difierent from what is presented in a cross
section of the same. The walls of the various ducts have peculiar markings
on them. These markings are caused by the walls being thicker in some
PHYSIO LOG Y.
places than in others, and this thickening takes place so regularly in some
instances as to form regular spiral thickenings. Others have the thickenings
II
n
*
B
Fig- 59.
Longitudinal section of vascular bundle of sunflower stem ; spiral, scalariform and pitted
vessels at left ; next are wood fibers with oblique cross walls ; in middle are cambium cells
with straight cross walls, next two sieve tubes, then phloem or bast cells.
in the form of the rounds of a ladder, while still others have pitted walls or the
thickenings are in the form of rings.
103. Vessels or ducts. — One way in which the cells in side view differ
greatly from an end view, in a cross section in the bundle, is that they are
much longer in the direction of the axis of the stem. The cells have become
elongated greatly. If we search for the place where two of these large cells
with spiral, or ladder-like, markings meet end to end, we see that the
wall which formerly separated the cells has nearly or quite disappeared. In
other words the two cells have now an open communication at the ends.
This is so for long distances in the stem, so that long columns of these large
cells form tubes or vessels through which the water rises in the stems of
plants.
104. In the bast portion of the bundle we detect the cells of the bast fibers
by their thick walls. They are very much elongated and the ends taper, out to
thin points so that they overla p. In this way they serve to strengthen the stem-
105. Sieve tubes. — Lying near the bast cells, usually toward the cambium,
are elongated cells standing end to end, with delicate markings on their cross
walls which appear like finely punctured plates or sieves. The protoplasm
in such cells is usually quite distinct, and sometimes contracted away from
the side walls, but attached to the cross walls, and this aids in the detection
of the sieve tubes (fig. 59.) The granular appearance which these plates pre-
sent is caused by minute perforations through the wall so that there is a com-
munication between the cells. The tubes thus formed are therefore called
sieve tubes and they extend for long distances through the tube so that there
PATH OF MOVEMENT.
53
is communication throughout the entire length of the stem. (The function of
the sieve tubes is supposed to be that for the downward transportation of sub-
stances elaborated in the leaves.)
106 If we section in like manner the stem of the sunflower we shall see simi-
lar bundles, but the number is greater than eight. In the garden balsam the
number is from four to six in an ordinar\r stem Ty-^nim diameter. Here we
can see quite well the origin of the vascular bundle. Between the larger
bundles we can see especially in free-hand sections of stems through which
a colored solution has been lifted by transpiration, as in our former experi-
ments, small groups of the minute cells in the cambial ring which are colored.
These groups of cells which form strands running through the stem are pro-
cambium strands. The cells divide and increase just like the cambium cells,
and the older ones thrown off on either side change, those toward the center
of the stem to wood vessels and fibers, and those on the outer side to bast
cells and sieve tubes.
107. Fibrovascular bundles in the Indian corn. — We should now make
a thin transection of a portion of the center of the stem of Indian corn, in
order to compare the structure of the
bundle with that of the plants which we
have just examined. In fig. 60 is repre-
sented a fibrovascular bundle of the stem
of the Indian corn. The large cells are
those of the spiral and reticulated and
annular vessels. This is the woody por-
tion of the bundle or xylem, Opposite
this is the bast portion or phloem, marked
by the lighter colored tissue at i. The
larger of these cells are the sieve tubes,
and intermingled with them are smaller
cells with thin walls. Surrounding the
entire bundle are small cells with thick
walls. These are elongated and the taper-
ing ends overlap. They are thus slender
and long and form fibers. In such a stem . f> ,argg
bundle all of the cambium has passed vessel ; r, annular vessel ; /, air cavity
. formed by breaking apart of the cells ; *,
over into permanent tissue and is said to £0ft bast, a form of sieve tissue ; /, thin-
be closed. walled parenchyma. (Sachs.)
108. Rise of water in the vessels. — During the movement of the water or
nutrient solutions upward in the stem the vessels of the wood portion of the
bundle in certain plants are nearly or quite filled, if root pressure is active
and transpiration is not very rapid. If, however, on dry days transpiration
is in excess of root pressure, as often happens, the vessels are not filled with
the water, but are partly filled with certain gases because the air or other
Fig. 60.
Transection of fibrovascular bundle of
Indian corn, a, toward periphery of
stem ; f, large pitted vessels ; s, spiral
54 PHYSIOLOGY.
gases in the plant become rarefied as a result of the excessive loss of water.
There are then successive rows of air or gas bubbles in the vessels separated
by films of water which also line the walls of the vessels. The condition of
the vessel is much like that of a glass tube through which one might pass the
" froth " which is formed on the surface of soapy water. This forms a chain
of bubbles in the vessels. This chain has been called Jamin's chain because
of the discoverer.
109. Why water or food solutions can be raised by the plant to the height
attained by some trees has never been satisfactorily explained. There are
several theories propounded which cannot be discussed here. It is probably
a very complex process. Root pressure and transpiration both play a part,
or at least can be shown, as we have seen, to be capable of lifting water to a
considerable height. In addition to this, the walls of the vessels absorb water
by diffusion, and in the other elements of the bundle capillarity comes also
into play, as well as osmosis.
See Organization of Tissues, Chapter 38.
110. Flow of tap in the spring. — The cause of the bleeding of trees and
the flow of sap in the spring is little understood. One of the remarkable
cases is the flow of sap in maple trees. It begins in early spring and ceases
as the buds are opening, and seems to be initiated by alternation of high
and low temperatures of day and night. It has been found that the pres-
sures inside of the tree at this time are enormously increased during the
day, when the temperature rises after a. cold night. This has led to the
belief that the pressure is caused by the expansion of the gases in the vas-
cular ducts. The warming up of the twigs and branches of the tree would
take place rapidly during the day, while the interior of the trunk would be
only slightly affected. The pressures then would cause the sap to flow
downward during the day, and at night the branches becoming cool, sap
would flow back again from the roots and trunk
Recent experiments by Jones et al. show that while some of the pressure
is due to the expansion of gas in the tree by the rise of temperature, this
cannot account for the enormous pressures which are often present, for ex-
ample, when after a rise in the temperature of 2° C. there was an increase
of 20 Ibs. pressure.
Then again, after the cessation of the flow in late spring there are often as
great differences between night and day temperatures. It therefore
seems reasonable to conclude that the expansion of gases by a rise in tem-
perature is not the direct cause.
Activities of the cells. — It has been suggested by some that the rise in
temperature exercises an influence on the protoplasts, or living cells, so
that they are stimulated to a special activity resulting in an exudation pres-
sure from the individual cells, which is known to take place. With the fall of
PATH OF MOVEMENTS. 55
emperature at night this activity would cease and there might result a
lessened pressure in the cells. Since the specific activities of cells are
known to vary in different plants, and in the same plant at different
seasons, some support is gained for this theory, though it is generally
believed that the activities of the living cells in the stems are not necessary
for the upward flow of water. It must be admitted, however, that at
present we know very little about this interesting problem.
CHAPTER VI.
MECHANICAL USES OF WATER.
111. Turgidity of plant parts. — As we have seen by the
experiments on the leaves, turgescence of the cells is one of the
conditions which enables the leaves to stand out from the stem,
and the lamina of the leaves to remain in an expanded position,
so that they are better exposed to the light, and to the currents
of air. Were it not for this turgidity the leaves would hang
down close against the stem.
112. Restoration of turgidity in shoots. — If we cut off a
living stem of geranium, coleus, tomato, or " balsam," and allow
the leaves to partly wilt so that the shoot loses its turgidity, it is
possible for this shoot to regain turgidity. The end may be
freshly cut again, placed in a vessel of water, covered with a bell
jar and kept in a room where the temperature
is suitable for the growth of the plant. The
shoot will usually become turgid again from
the water which is absorbed through the cut
end of the stem and is carried into the leaves
where the individual cells become turgid, and
the leaves are again expanded. Such shoots,
and the excised leaves also, may often be made
turgid again by simply immersing them in
water, as one of the experiments with the salt
solution would teach.
Fig. 61.
Restoration of turgidity
(Sachs).
113. Turgidity may be restored more certainly and
quickly in a partially wilted shoot in another way.
The cut end of the shoot may be inserted in a U tube as shown in fig. 61, the
end of the tube around the stem of the plant being made air-tight. The arm
56
TURGESCENCE. 57
of the tube in which the stem is inserted is filled with water and the water is
allowed to partly fill the other arm. Into this other arm is then poured
mercury. The greater weight of the mercury causes such pressure upon the
water that it is pushed into the stem, where it passes up through the vessels
in the stems and leaves, and is brought more quickly and surely to the cells
which contain the protoplasm and cell-sap, so that turgidity is more quickly
and certainly attained.
114. Tissue tensions. — Besides the turgescence of the cells of
the leaves and shoots there are certain tissue tensions without
which certain tender and succulent shoots, etc., would be limp,
and would droop. There are a number of plants usually accessi-
ble, some at one season and some at others, which may be used
to illustrate tissue tension.
115. Longitudinal tissue tension. — For this in early summer
one may use the young and succulent shoots of the elder
(sambucus); or the petioles of rhubarb during the summer and
early autumn ; or the petioles of richardia. Petioles of cala-
dium are excellent for this purpose, and these may be had at
almost any season of the year from the greenhouses, and are
thus especially advantageous for work during late autumn or
winter. The tension is so strong that a portion of such a
petiole T.o—i$cm long is ample to demonstrate it. As we grasp
the lower end of the petiole of a caladium, or rhubarb leaf, we
observe how rigid it is, and how well it supports the heavy
expanded lamina of the leaf.
116. The ends of a portion of such a petiole or other object
which may be used are cut off squarely. With a knife a strip
from 2-ynm in thickness is removed from one side the full
length of the object. This strip we now find is shorter than
the larger part from which it was removed. The outer tissue
then exerts a tension upon the petiole which tends to shorten
it. Let us remove another strip lying next this one, and
another, and so on until the outer tissues remain only upon
one side. The object will now bend toward that side. Now
remove this strip and compare the length of the strips re-
moved with the central portion. We find that they are nmcb
58 PHYSIOLOGY.
shorter now. In other words there is also a tension in the tissue
of the central portion of the petiole, the direction of which is
opposite to that of the superficial tissue. The parts of the petiole
now are not rigid, and they easily bend. These two longitudi-
nal tissue tensions acting in opposition to each other therefore
give rigidity to the succulent shoot. It is only when the indi-
vidual cells of such shoots or petioles are turgid that these tissue
tensions in succulent shoots manifest themselves or are promi-
nent.
117. To demonstrate the efficiency of this tension in giving support, let us
take a long petiole of caladium or of rhubarb. Hold it by one end in a hori-
zontal position. It is firm and rigid, and does not droop, or but little. Re-
move all of the outer portion of the tissues, as described above, leaving only
the central portion. Now attempt to hold it in a horizontal position by one
end. It is flabby and droops downward because the longitudinal tension is
removed.
118. Longitudinal tension in dandelion stems. — Take long
and fresh dandelion stems. Split
them. Note that they coil. The
longitudinal tension is very great.
Place some of these strips in
fresh water. They coil up into
close curls because by the ab*
sorption of water by the cells the
turgescence of the individual cells
is increased, and this increases
the tension in the stem. Now
place them in salt water (a 5 per
cent solution). Why do they
uncoil ?
119. To imitate the coiling
of a tendril. — Cut out a narrow
strip from a long dandelion stem.
Strip from dandeHon stem made to Fasten to a piece of Soft Wood,
imitate a plant tendril. with the gnds dose together> as
shown in fig. 62. Now place it in fresh water and watch it coil.
Part of it coils one way and part another way, just as a ten-
MECHANICAL USES OF WATER. 59
dril does after the free end has caught hold of some place for
support.
120. Transverse tissue tension. — To illustrate this one may
take a willow shoot 3~5cw in diameter and saw off sections about
2cm long. Cut through the bark on one side and peel it off in a
single strip. Now attempt to replace it. The bark will not
quite cover the wood again, since the ends will not meet. It
must then have been held in transverse tension by the woody
part of the shoot.
CHAPTER VII.
STARCH AND SUGAR FORMATION
1 . The Gases Concerned.
191. Gas given off by green plants in the sunlight. — Let
us take some green alga, like spirogyra, which is in a fresh con-
dition, and place one lot in a beaker or tall glass vessel of water
and set this in the direct sunlight or in a well lighted place. At
the same time cover a similar vessel
of spirogyra with black cloth so that
it will be in the dark, or at least in
very weak light.
122. In a short time we note that in
the first vessel small bubbles of gas are
accumulating on the surface of the
threads of the spirogyra, and now and
then some free themselves and rise to
the surface of the water. Where there
is quite a tangle of the threads the gas
is apt to become caught and held back-
in larger bubbles, which on agitation of
the vessel are freed.
If We now examine the Second Vessel Oxygen gas given off by spirogyra
we see that there are no bubbles, or only a very few of them.
We are led to believe then that sunlight has had something to
do with the setting free of this gas from the plant.
123. We may now take another alga like vaucheria and per-
form the experiment in the same way, or to save time the
two may be set up at once. In fact if we take any of the green
60
Kie.
STARCH FORMATION: THE GASES. 6 1
algae and treat them as described above gas will be given off in a
similar manner.
124. We may now take otfe of the higher green plants, an
aquatic plant like elodea, callitriche, etc. Place the plant in
> the water with the cut end of the stem uppermost,
but still immersed, the plant being weighted down
by a glass rod or other suitable object. If we
place the vessel of water containing these leafy
stems in the bright sunlight, in a short time bub-
bles of gas will pass off quite rapidly from the cut
end of the stem. If in the same vessel we
|| place another stem, from which the leaves
have been cut, the number of bubbles of gas
tig. 04. given off will be very few. This indicates that
Bubbles of oxygen gas °
given off from elodea in a large part of the gas is furnished by the
presence of sunlight. J
leaves.
125. Another vessel fitted up in the same way should be placed in the
dark or shaded by covering with a box or black cloth. It will be seen here,
as in the case of spirogyra, that very few or no bubbles of gas will be set
free. Sunlight here also is necessary for the rapid escape of the gas.
126. We may easily compare the rapidity with which light of varying
intensity effects the setting free of this gas. After cutting the end of the stem
let us plunge the cut surface several times in melted paraffine, or spread
over the cut surface a coat of varnish. Then prick with a needle a small
hole through the paraffine or varnish. Immerse the plant in water and
place in sunlight as before. The gas now comes from the puncture through
the coating of the cut end, and the number of bubbles given off during a
given period can be ascertained by counting. If we duplicate this experi-
ment by placing one plant in weak light or diffused sunlight, and another in
the shade, we can easily compare the rapidity of the escape of the gas under
the different conditions, which represent varying intensities of light. We
see then that not only is sunlight necessary for the setting free of this gas, but
that in diffused light or in the shade the activity of the plant in this respect
is less than in direct sunlight.
127. What this gas is. — If we take quite a quantity of the
plants of elodea and place them under an inverted funnel
which is immersed in water, the gas will be given off in quite
large quantities and will rise into the narrow exitot the funnel.
62
PHYSIOLOGY.
The funnel should be one with a short tube, or the vessel one
which is quite deep so that a small test tube which is filled with
water may in this condition be inverted over the
opening of the funnel tube. With this arrange-
ment of the experiment the gas will rise in the
inverted test tube, slowly displace a portion of
the water, and become collected in a sufficient
quantity to afford us a test. When a consider-
able quantity has accumulated in the test tube, we
may close the end of the tube in the water with
the thumb, lift it from the water and invert. Flg' 6s"
Apparatus for col-
The gas will rise against the thumb. A dry Acting quantity of
• oxygen from elodea.
soft pine splinter should be then lighted, and (Detmer.)
after it has burned a short time, extinguish the flame by blowing
upon it, when the still burning end of the splinter should be
brought to the mouth of the tube as the thumb is quickly moved
to one side. The glowing of the splinter shows that the gas is
oxygen.
128. It is better to allow the apparatus to stand several days
in the sunlight in order to
catch a full tube of the gas.
Or on a sunny day carbon
dioxide gas can be led into
the water in the jar from
a generator, such an one
as is used for the evolution of
CO2. The CO2 can be produced
by the action of hydrochloric acid
on bits of marble. The COa
should not be run below the fun-
nel. The test-tube should be
fastened so that the light oxygen
gas will not raise it off the fun-
nel. With the tube full of gas the
ReadytoseFew^t'thegasis. test for oxygen can be made by
lifting the tube with one hand and
STARCH FORMATION — THE GASES. 63
quickly thrusting the glowing end of the splinter in with the
other hand. If properly
handled, the splinter will
flame again. If it is neces-
sary to keep the appa-
ratus standing for more
than one day it is Well The splinter lights again in the presence of
j, , , ., oxygen gas.
to add fresh water in the
place of most of the water in the jar. Do not use leaves of land
plants in this experiment, since the bubbles which rise when these
leaves are placed in water are not evidence that this process is
taking place.
129. Oxygen given off by green land plants also. — If we should extend
our experiments to land plants we should find that oxygen is given off by
them under these conditions of light. Land plants, however, will not do
this when they are immersed in water, hut it is necessary to set up rather
complicated apparatus and to make analyses of the gases at the beginning
and at the close of the experiments. This has been done, however, in a suffi-
ciently large number of cases so that we know that all green plants in the
sunlight, if temperature and other conditions are favorable, give off oxygen.
130. Absorption of carbon dioxide. — We have next to inquire
where the oxygen comes from which is given off by green plants
when exposed to the sunlight, and also to learn something more
of the conditions necessary for the process. We know that
water which has been for some time exposed to the air and soil,
and has been agitated, like running water of streams, or the
water of springs, has mixed with it a considerable quantity of
oxygen and carbon dioxide.
If we boil spring water or hydrant water which comes from
a stream containing oxygen and carbon dioxide, for about 20
minutes, these gases are driven off. We should set this aside
where it will not be agitated, until it has cooled sufficiently to
receive plants without injury. Let us now place some spirogyra
or vaucheria, and elodea, or other green water plant, in this
boiled water and set the vessel in the bright sunlight under the
same conditions which were employed in the experiments for the
evolution of oxygen. No oxygen is given off.
64 PHYSIO LOG Y.
Can it be that this is because the oxygen was driven from
the water in boiling? We shall see. Let us take the vessel
containing the water, or some other boiled water, and agitate it
so that the air will be thoroughly mixed with it. In this way
oxygen is again mixed with the water. Now place the plant
again in the water, set in the sunlight, and in several minutes
observe the result. No oxygen or but little is given off. There
must be then some other requisite for the evolution of the oxygen
132. The gases are interchanged in the plants. — We will now
introduce carbon dioxide again in the water. This can be done
by leading CO2 from a gas generator into the water. Broken
bits of marble are placed in the generator, acted upon by hydro-
chloric acid, and the gas is led over by glass tubing. Now if we
place the plant in the water and set the vessel in the sunlight, in
a few minutes the oxygen is given off rapidly.
133. A chemical change of the gas takes place within the
plant cell. — This leads us to believe then that CO2 is in some
way necessary for the plant in this process. Since oxygen is
given off while carbon dioxide, a different gas, is necessary, it
would seem that a chemical change takes place in the gases
within the plant. Since the process takes place in such simple
plants as spirogyra as well as in the more bulky and higher
plants, it appears that the changes go on within the cell, in fact
within the protoplasm.
134. Gases as well as water can diffuse through the proto-
plasmic membrane. — Carbon dioxide then is absorbed by the
plant while oxygen is given off. We see therefore that gases as
well as water can diffuse through the protoplasmic membrane of
plants under certain conditions.
2. Where Starch is Formed.
We have found by these simple experiments that some
chemical change takes place within the protoplasm of the green
cells of plants during the absorption of carbon dioxide and the
giving off of oxygen. We should examine some of the green
parts of those plants used in the experiments, or if they are not
STARCH: PHOTOSYNTHESIS. 65
at hand we should set up others in order to make this examina-
tion.
135. Starch formed as a result of this process. — We may take
spirogyra which has been standing in water in the bright sun-
light for several hours. A few of the threads should be placed
in alcohol for a short time to kill the protoplasm. From the
alcohol we transfer the threads to a solution of iodine in potas-
sium iodide. We find that at certain points in the chlorophyll
band a bluish tinge, or color, is imparted to the ring or sphere
which surrounds the pyrenoid. In our first study of the spirogyra
cell we noted this sphere as being composed of numerous small
grains of starch which surround the pyrenoid,
136. Iodine used as a test for starch. — This color reaction
which we have obtained in treating the threads with iodine is
the well-known reaction, or test, for starch. We have demon-
strated then that starch is present in spirogyra threads which
have stood in the sunlight with free access to carbon dioxide.
If we examine in the same way some threads which have stood
in the dark for a few days we obtain no reaction for starch, or at
best only a slight reaction. This gives us some evidence that a
chemical change does take place during this process (absorption
of CO2 and giving off of oxygen), and that starch is a product of
that chemical change.
137. Schimper's method of testing for the presence of starch.
— Another convenient and quick method of testing for the pres-
ence of starch is what is known as Schimper's method. A
strong solution of chloral hydrate is made by taking 8 grams of
chloral hydrate for every $cc of water. To this solution is added
a little of an alcoholic tincture of iodine. The threads of spi-
rogyra may be placed directly in this solution, and in a few
moments mounted in water on the glass slip and examined with
the microscope. The reaction is strong and easily seen.
We should also examine the leaves of elodea, or one of
the higher green plants which has been for some time in the
sunlight. We may use here Schimper's method by placing the
leaves directly in the solution of chloral hydrate and iodine.
66
PHYSIOLOG Y.
The leaves are made transparent by the chloral hydrate so that
the starch reaction from the iodine is easily detected.
The following is a convenient and safe method of extract-
ing chlorophyll from leaves. Fill a large pan, preferably a
dishpan, half full of hot water. This may be kept hot by a
small flame. On the water float an evaporating dish partly
filled with alcohol. The leaves should be first immersed in
the hot water for several minutes, then placed in the alcohol,
which will quickly remove the chlorophyll. Now immerse the
leaves in the iodine solution.
138. Green parts of plants form starch when exposed to
light. — Thus we find that in the case of all the green plants we
have examined, starch is present in the green cells of those which
Fig. 68. Fig. 69.
Leaf of coleus showing green and white Similar leaf treated with iodine, the starch
areas, before treatment with iodine. reaction only showing where the leaf
was green.
have been standing for some time in the sunlight where the proc-
ess of the absorption of CO2 and the giving off of oxygen can
go on, and that in the case of plants grown in the dark, or in
STARCH AND SUGAR: CHLOROPHYLL. 67
leaves of plants which have stood for some time in the dark,
starch is absent. We reason from this that starch is the product
of the chemical change which takes place in the green cells
under these conditions. The CO2 which is absorbed by the
plant mixes with the water (H2O) in the cell and immediately
forms carbonic acid. The chlorophyll in the leaf absorbs xadi-
ant energy from the sun which splits up the carbonic acid, and
its elements then are put together into a more complex com-
pound, starch. This process of putting together the elements
of an organic compound is a synthesis, or a synthetic assimila-
tion, since it is done by the living plant. It is therefore a syn-
thetic assimilation of carbon dioxide. Since the sunlight sup-
plies the energy it is also called photosynthesis, or photo synthetic
assimilation. We can also say carbon dioxide assimilation, or
CO2 assimilation (see paragraph on assimilation at close of
Chapter 10).
139. Starch is formed only in the green parts of variegated
leaves. — If we test for starch in variegated leaves like the leaf of
a coleus plant, we shall have an interesting demonstration of the
fact that the green parts of plants only form starch. We may
take a leaf which is partly green and partly white, from a plant
which has been standing for some time in bright light. Fig. 68
is from a photograph of such a leaf. We should first boil at in
alcohol to remove the green color. Now immerse it in the
potassium iodide of iodine solution for a short time The parts
which were formerly green are now dark blue or nearly black,
showing the presence of starch in those portions of the leaf,
while the white part of the leaf is still uncolored. This is well
shown in fig. 69, which is from a photograph of another coleus
leaf treated with the iodine solution.
3. Chlorophyll and the Formation of Starch.
140. In our experiments thus far in treating of the absorption
of carbon dioxide and the evolution of oxygen, with the accom-
panying formation of starch, we have used green plants.
68 PHYSIOLOGY.
141. Fungi cannot form starch. — If we should extend our
experiments to the fungi, which lack the green color so charac-
teristic of the majority of plants, we should find that photosyn-
thesis does not take place even though the plants are exposed
to direct sunlight. These plants cannot then form starch, but
obtain carbohydrates for food from other sources.
142. Photosynthesis cannot take place in etiolated plants. —
Moreover photosynthesis is usually confined to the green plants,
and if by any means one of the ordinary green plants loses its
green color this process cannot take place in that plant, even
when brought into the sunlight, until the green color has ap-
peared under the influence of light.
This may be very easily demonstrated by growing seedlings
of the bean, squash, corn, pea, etc. (pine seedlings are green even
when grown in the dark), in a dark room, or in a dark receiver
of some kind which will shut out the rays of light. The room
or receiver must be quite dark. As the seedlings are " coming
up," and as long as they remain in the dark chamber, they will
present some other color than green; usually they are somewhat
yellowed. Such plants are said to be etiolated. If they are
brought into the sunlight now for a few hours and then tested
for the presence of starch the result will be negative. But if the
plant is left in the light, in a few days the leaves begin to take
on a green color, and then we find that carbon dioxide assimila-
tion begins.
143. Chlorophyll and chloroplasts. — The green substance in
plants is then one of the important factors in this complicated
process of forming starch. This green substance is chlorophyll,
and it usually occurs in definite bodies, the chlorophyll bodies,
or chloroplasts.
The material for new growth of plants grown in the dark is derived from
the seed. Plants grown in the dark consist largely of water and protoplasm,
the walls being very thin.
144. Form of the chlorophyll bodies. — Chlorophyll bodies
vary in form in some different plants, especially in some of the
STARCH AND SUGAR: CHLOROPHYLL. 69
lower plants. This we have already seen in the case of
spirogyra, where the chlorophyll body is in the form of a very
irregular band, which courses around the inner side of the cell
wall in a spiral manner. In zygnema, which is related to
spirogyra, the chlorophyll bodies are star-shaped. In the
desmids the form varies greatly. In oedogonium, another of
the thread-like algae, illustrated in fig. 144, the chlorophyll bodies
Fig. 6ga.
Section of ivy leaf, palisade cells above, loose parenchyma, with large intercellular spaces
in center. Epidermal cells on either edge, with no chlorophyll bodies.
are more or less flattened oval disks. In vaucheria, too, a
branched thread-like alga shown in fig. 138, the chlorophyll
bodies are oval in outline. These two plants, cedogonium and
vaucheria, should be examined here if possible, in order to be-
come familiar with their form, since they will be studied later
under morphology (see chapters on oedogonium and vaucheria,
for the occurrence and form of these plants). The form of the
chlorophyll body found in cedogonium and vaucheria is that
which is common to many of the green alga?, and also occurs in
the mosses, liverworts, ferns, and the higher plants. It is a
more or less rounded, oval, flattened body.
145. Chlorophyll is a pigment which resides in the chloroplast. — That
the chlorophyll is a coloring substance which resides in the chloroplastid,
and does not form the body itself, can bo demonstrated by dissolving out the
chlorophyll when the framework of the chloroplastid is apparent. The
green parts of plants which have been placed for some time in alcohol lose
7° PHYSIOLOG Y.
their green color. The alcohol at the same time becomes tinged with green.
In sectioning such plant tissue we find that the chlorophyll bodies, or chloro-
plastids as they are more properly called, are still intact, though the green
color is absent. From this we know that chlorophyll is a substance distinct
from that of the chloroplastid.
146. Chlorophyll absorbs energy from sunlight for pho*osynthesis. —It
has been found by analysis with the spectroscope that chlorophyll absorbs cer-
tain of the rays of the sunlight. The energy which is thus obtained from
the sun, called kinetic energy, acts on the molecules of CH2O3, separating
them into molecules of C, H, and O. (When the CO2 from the air enters
the plant cell it immediately unites with some of the water, forming carbonic
acid = CH2O3. ) After a series of complicated chemical changes starch is
formed by the union r f carbon, oxygen, and hydrogen. In this process of
the reduction of the CH,O3 and the formation of starch there is a surplus of
oxygen, which accounts for the giving off of oxygen during the process.
147. Eays of light concerned in photosynthesis. — If a solution of
chlorophyll be made, and light be passed through it, and this light be
examined with the spectroscope, there appear what are called absorption bands.
These are dark bands which lie across certain portions of the spectrum.
These bands lie in the red, orange, yellow, green, blue, and violet, but the
bands are stronger in the red, which shows that chlorophyll absorbs more of
the red rays of light than of the other rays. These are the rays of low
refrangibility. The kinetic energy derived by the absorption of these rays
of light is transformed into potential energy. That is, the molecule of
CH,O3 is broken up, and then by a different combination of certain elements
starch is formed.*
148. Starch grains formed in the chloroplasts. — During photosynthesis the
starch formed is deposited generally in small grains within the green chloro-
plast in the leaf. We can see this easily by examining the leaves of some
moss like funaria which has been in the light, or in the chloroplasts of the
prothallia of ferns, etc. Starch grains may also be formed in the chloro-
plasts from starch which was formed in some other part of the plant, but
* In the formation of starch during photosynthesis the separated mole-
cules fvom the carbon dioxide and water unite in such a way that carbon,
hydrogen, and oxygen are united into a molecule of starch. This result is
usually represented by the following equation: CO2+H2O = CH2O + O2.
Then by polymerization 6(CH2O) = C6H12O6 = grape sugar. Then
CBH12O6 — H2O = C6H1%O5 = starch. It is believed, however, that the
process is much more complicated than this, that several different com-
pounds are formed before starch finally appears, and that the formula for
starch is much higher numerically than is represented by C6H,0O&.
STARCH AND SUGAR; CHLOROPHYLL. /I
which has passed in solution. Thus the functions of the chloroplast are
twofold, that of photosynthesis and the formation of starch grains.
149. In the translocation of starch when it becomes stored up in various
parts of the plant, it passes from the state of solution into starch grains in
connection with plastids similar to the chloroplasts, but which are not green.
The green ones are sometimes called chloroplasts, while the colorless ones
are termed leiicoplasts, and those possessing other colors, as red and yellow,
in floral leaves, the root of the carrot, etc., are called chronwplasts.
150. Photosynthesis in other than green plants. — While carbohydrates
are usually only formed by green plants, there are some exceptions. Ap-
parent exceptions are found in the blue-green alga?, like oscillatoria, nostoc,
or in the brown and red sea weeds like fucus, rhabdonia, etc. These plants,
however, possess chlorophyll, but it is disguised by another pigment or
color. There are plants, however, which do not have chlorophyll and yet
form carbohydrates with evolution of oxygen in the presence of light, as
for example a purple bacterium, in which the purple coloring substance
absorbs light, though the rays absorbed most energetically aie not the
red.
151. Influence of light on the movement of chlorophyll bodies. — In fern
prothallia. — If we place fern prothallia in weak light for a few hours, and
then examine them under the microscope, we find that the most of the chloro-
phyll bodies in the cells are arranged along the inner surface of the hori-
zontal wall. If now the same prothallia are placed in a brightly lighted
place for a short time most of the chlorophyll bodies move so that they are
Fig. 70.
Cell exposed to weak diffused light
showing chlorophyll bodies along the
horizontal walls.
Fig. 71.
Same cell exposed to strong light,
showing chlorophyll bodies have
moved to perpendicular walls.
Figs. 70, 71. — Cell of prothallium of fern.
arranged along the surfaces of the perpendicular walls, and instead of hav-
ing the flattened surfaces exposed to the light as in the former case, the
edges of the chlorophyll bodies are now turned toward the light. (See figs.
72 PHYSIOLOG Y.
70, 71.) The same phenomenon has been observed in man}' plants. Light
then has an influence on chlorophyll bodies, to some extent determining
their position. In weak light they are arranged so that the flattened sur-
faces are exposed to the incidence of the rays of light, so that the chloro-
phyll will absorb as great an amount as possible of kinetic energy; but
intense light is stronger than necessary, and the chlorophyll bodies move so
that their edges are exposed to the incidence of the rays. This movement
of the chlorophyll bodies is different from that which takes place in some
water plants like elodea. The chlorophyll bodies in clodea are free in the
protoplasm. The protoplasm in the cells of elodea streams around the
inside of the cell wall much as it does in nitella and the chlorophyll bodies
are carried along in the currents, while in nitella they are stationary.
CHAPTER VIII.
STARCH AND SUGAR CONCLUDED. ANALYSIS OF
PLANT SUBSTANCE.
1 . Translocation of Starch.
152. Translocation of starch. — It has been found that leaves of many
plants grown in the sunlight contain starch when examined after being in
the sunlight for several hours. But when the plants are left in the dark for
a day or two the leaves contain no starch, or a much smaller amount. This
suggests that starch after it has been formed may be transferred from the
leaves, or from those areas of the leaves where it has been formed.
To test this let us perform an experiment which is often made. We
may take a plant such as a
garden tropaeolum or a clover
plant, or other land plant in
which it is easy to test for the
presence of starch. Pin a
piece of circular cork, which
is smaller than the area of
the leaf, on either side of the
leaf, as in fig. 72, but allow
free circulation of air between Fis- ?2- ,
. , , . .. , Leaf of tropaeolum Leaf of tropaeolum treated
the cork and the under side ot with portion covered with iodine after removal of
the leaf Place the nlant with corks to Pre" cork, to show that starch is
Jeal- Plant vent the formation removed from the leaf dur-
where it will be in the sunlight, of starch. (After ing the night.
Detmer.)
On the afternoon of the fol-
lowing day, if the sun has been shining, test the entire leaf for starch. The
part covered by the cork will not give the reaction for starch, as shown by
the absence of the bluish color, while the other parts of the leaf will show it.
The starch which was in that part of the leaf the day before was dissolved
and removed during the night, and then during the following day, the
parts being covered from the light, no starch was formed in them.
73
74 PHYSIOLOG Y.
153. Starch in other parts of plants than the leaves. — We
may use the iodine test to search for starch in other parts of
plants than the leaves. If we cut a potato tuber, scrape some of
the cut surface into a pulp, and apply the iodine test, we obtain
a beautiful and distinct reaction showing the presence of starch.
Now we have learned that starch is only formed in the parts
containing chlorophyll. We have also learned that the starch
which has been formed in the leaves disappears from the leaf or
is transferred from the leaf. We judge therefore that the starch
which we have found in the tuber of the potato was formed first
in the green leaves of the plant, as a result of photosynthesis.
From the leaves it is transferred in solution to the underground
stems, and stored in the tubers. The starch is stored here by
the plant to provide food for the growth of new plants from the
tubers, which are thus much more vigorous than the plants
would be if grown from the seed.
154. Form of starch grains. — Where starch is stored as a reserve material
it occurs in grains which usually have certain characters peculiar to the
species of plant in which they are found. They vary in size in many
Different plants, and to some extent in form also. If we scrape some of
the cut surface of the potato tuber into a pulp and mount a small quantity
in water, or make a thin section for microscopic examination, we find
large starch grains of a beautiful structure. The grains are oval in
form and more or less irregular in outline. But the striking peculiarity is
the presence of what seem to be alternating dark and light lines in the starch
grain. We note that the lines form irregular rings, which are smaller
and smaller until we come to the small central spot termed the "hilum " of
the starch grain. It is supposed that these apparent lines in the starch
grain are caused by the starch substance being deposited in alternating dense
and dilute layers, the dilute layers containing more water than the dense
ones; others think that the successive layers from the hilum outward are
regularly of diminishing density, and that this gives the appearance of alter-
nating lines. The starch formed by plants is one of the organic substances
which are manufactured by plants, and it (or glucose) is the basis for the
formation of other organic substances in the plant. Without such organic
substances green plants cannot make any appreciable increase of plant
substance, though 3. considerable increase in size of the plant may take
place.
NOTE. — The organic compounds resulting from photosynthesis, since
they are formed by the union of carbon, hydrogen, and oxygen in such a
way that the hydrogen and oxygen are usually present in the same proper-
STARCH: TRANSLOCATION. 75
tion as in water, are called carbohydrates. The most common carbo-
hydrates are sugars (cane sugar, C^H^On, for example, in beet roots,
sugar cane, sugar maple, etc.), starch, and cellulose.
155. Vaucheria. — The result of carbon dioxide assimilation in the
threads of Vaucheria is not clearly understood. Starch is absent or diffi-
cult to find in all except a few species, while oil globules are present in
most species. These oil globules are spherical, colorless, globose and
highly refringent. Often small ones are seen lying against chlorophyll
bodies. Oil is a hydrocarbon (containing C, H, and O, but the H and O
are in different proportions from what they are in H2O) and until recently
it was supposed that this oil in Vaucheria was the direct result of photo-
synthesis. But the oil does not disappear when the plant is kept for a
long time in the dark, which seems to show that it is not the direct prod-
uct of carbon dioxide assimilation, and indicates that it comes either from
a temporary starch body or from glucose. Schimper found glucose in sev-
eral species of Vaucheria, and Waltz says that some starch is present in
Vaucheria sericea, while in V. tuberosa starch is abundant and replaces the
oil. To test for oil bodies in Vaucheria treat the threads with weak osnric
acid, or allow them to stand for twenty-four hours in Fleming's solution
(which contains osmic acid). Mount some threads and examine with
microscope. The oil globules are stained black.
2. Sugar, and Digestion of Starch.*
156. The sugar produced as the result of photosynthesis may be stored
as sugar or changed to starch. In general sugar is more common in the
green parts of monocotyledonous plants, while starch is most frequent in
dicotyledons. Plant sugars are of three general kinds : cane sugar or sucrose,
abundant in the sugar cane, sugar beet, sugar maple, etc.; glucose or
fruit sugar, found in the fruit of a majority of plants, and abundant in some,
as in apples, pears, grapes, etc. (in many fruits and other parts of plants
both glucose and cane sugar are present) ; and maltose, as in malted barley.
157a. Test for sugars. — Make a weak solution of pure commercial
grape sugar (glucose) and also one of pure granulated cane sugar. Partly
fill two test tubes with Fehling's solution.! To one add some of the grape-
sugar solution and to the other add some of the cane-sugar solution. After
these tubes have stood in a warm place a few hours, it will be found that
a bright orange-brown or cinnabar-colored precipitate of copper and cuprous
oxide has formed in the tube containing grape sugar, while the other solu-
tion is unchanged. Grape sugar or glucose therefore^ reduces Fehling's
solution, while cane sugar as such has no effect upon it.
1576. Test for cane sugar. — Place a small quantity of pure granulated
cane sugar in a test tube and add about 15 cc. of distilled water. To
* Paragraphs 156-160 were prepared by Dr. E. J. Durand.
* See page 712 for formula for Fehling's solution.
76 PHYSIOLOGY.
this add i to 2 cc. of cobaltous nitrate solution (5 grams cobalt nitrate in 100
cc. distilled water. Keep in a stoppered bottle), then add a small quantity
of a strong sodium hydrate solution (50 grams caustic soda, in sticks, to
100 cc. distilled water. Keep in a bottle). A beautiful violet color appears.
Test glucose or grape sugar in the same way and a blue color appears,
which gradually changes to green.
157c. Cane sugar (sucrose) can be changed to glucose or invert sugar
in the following way: To a weak solution of pure granulated cane sugar
in a small beaker add a few drops of strong hydrochloric acid, rest on gauze
wire, and boil for a minute or two over a flame. This inverts the cane
sugar to glucose (equal parts of dextrose and laevulose). To test for the
invert sugar the acid must be neutralized. Add sodium carbonate until on
adding no effervescence takes place. Now add the Fehling's solution and
boil; the red precipitate appears, showing that it reduces Fehling's solution.
158a. Tests for sugar in plant tissue. — Scrape out a little of the tissue
from the inside of a ripe apple or pear, place it with a little water in a test
tube, and add a few drops of Fehling's solution. After standing half an
hour the characteristic precipitate of copper and cuprous oxide appears,
showing that grape sugar is present in quantity.
Make thin sections of the apple and mount in a drop of Fehling's solution
on a slide. After an hour examine with the microscope. The granules
of cuprous oxide are present in the cells of the tissue in great abundance.
1586. Prepare another tube with some of the pulp in 15 cc. of water;
add 2 cc. of cobaltous nitrate solution, and then some of the strong sodium
hydrate solution, as in paragraph 157^. Cane sugar as well as grape
sugar is present in these fruits.
158c. Cut up several leaves of a vigorous young Indian corn seedling
in a small beaker and add 25 or 30 cc. distilled water. Boil for one or
two minutes. Filter. In another small beaker boil Fehling's solution,
and if it is free from sediment (if not, filter) add a portion of the filtered
corn-leaf solution and boil for two minutes. Hold the beaker toward the
light and look on the bottom for the red precipitate. Filter. The red
precipitate shows the presence of glucose (or invert sugar). Take the
remaining portion of the corn-leaf decoction in a test tube and test for cane
sugar by adding cobaltous nitrate and sodium hydrate as in paragraph
1576. If the violet color does riot appear at once, do not agitate it, but
allow it to stand for a while. The violet color appears at the bottom of the
tube, showing the presence of cane sugar, while the reaction for glucose may
appear in the upper portion of the solution. For comparison take similar
corn leaves, remove the chlorophyll with alcohol, and test with iodine. No
starch reaction appears. The carbohydrate in corn leaves is therefore sugar
and not starch. If now the grain of corn be examined the cells will be
found to be full of starch grains, which give the beautiful blue reaction
SUGAR: DIGESTION OF STARCH. 77
with iodine. This experiment shows that sugar is formed in the leaves of
the Indian corn plant, but is changed to starch when stored in the seed.
158J. Take several leaves of bean seedlings; test for glucose and cane
sugar as in i$8c. Both are present. Test a leaf for starch. It is present.
158e. Select a branch of sugar maple during autumn, winter, or spring,
about i cm. in diameter. From a portion scrape off all the bark so as
to remove all th^ color. Cut off some shavings of the white woody portion
and boil in a small beaker for one or two minutes. Filter and test for the
presence of both glucose and cane sugar as in paragraphs 158^ and 1576.
Both are present (at least in several tests made in Decemb_r, 1906). The bark
is to be removed, since the coloring matter in it also reduces Fehling's solution
158/. Scrape some pulp from the inside of a sugar beet. Mix in dis-
tilled water in two test tubes. Test one for glucose and the other for cane
sugar. Cane sugar is present.
159. How starch is changed to sugar. — We have seen that in many plants
the carbohydrate formed as the result of carbon dioxide assimilation is
stored as starch. This substance being insoluble in water must be changed
to sugar, which is soluble before it can be used as food or transported to
other parts of the plant. This is accomplished through the action of cer-
tain enzymes, principally diastase. This substance has the power of act-
ing upon starch under proper conditions of temperature and moistiire,
causing it to take up the elements of water, and so to become sugar.
This process takes place commonly in the leaves where starch is formed,
but especially in seeds, tubers (during the sprouting, etc.), and other parts
which the plant uses as storehouses for starch food. It is probable that
the same conditions of temperature and moisture which favor germination
or active growth are also favorable to the production of diastase.
160. Experiments to show the action of diastase. — (a) Place a bit of
starch half as large as a pea in a test tube, and cover with a weak solution *
(about ^ per cent) of commercial taka diastase. After it has stood in a
warm place for five or ten minutes test with Fehling's solution. The pre-
cipitate of cuprous oxide appears showing that some of the starch has been
changed to sugar. By using measured quantities, and by testing with
iodine at frequent intervals, it can be determined just how long it takes a
given quantity of diastase to change a known quantity of starch. In this
connection one should first test a portion of the same starch with Fehling's
solution to show that no sugar is present.
(b) Repeat the above experiment using a little tissue from a potato, and
some from a corn seed.
(r) Take 25 germinating barley seeds in which the radicle is just appear-
* This solution of taka diastase should be made up cold. If it is heated
to 60° C. or over it is destroyed.
78 PHYSIOLOGY.
ing. Grind up thoroughly in a mortar with about three parts of water.
After this has stood for ten or fifteen minutes, filter. Fill a test tube one-
third full of water, add a piece of starch half the size of a pea or less, and
boil the mixture to make starch-paste. Add the barley extract. Put in a
warm place and test from time to time with iodine. The first samples so
treated will be blue, later ones violet, brown, and finally colorless, showing
that the starch has all disappeared. This is due to the action of the dias-
tase which was present in the germinating seeds, and which was dissolved
out and added to the starch mixture. The office of this diastase is to
change the starch in the seeds to sugar. Germinating wheat is sweet, and
it is a matter of common observation that bread made from sprouted wheat
is sweet.
(d) Put a little starch-paste in a test tube and cover it with saliva from
the mouth. After ten or fifteen minutes test with Fehling's solution. A
strong reaction appears showing how quickly and effectively saliva acts in
converting starch to sugar. Successive tests with iodine will show the
gradual disappearance of the starch.
161. These experiments have shown us that diastase from three different
sources can act upon starch converting it into sugar. The active principle
in the saliva is an animal diastase (ptyalin), which is necessary as one step
in the digestion of starch food in animals. The taka diastase is derived
from a fungus (Eurotium oryzae) which feeds on the starch in rice grains
converting it into sugar which the fungus absorbs for food. The malt dias-
tase and leaf diastase are formed by the seed plants. That in seeds con-
verts the starch to sugar which is absorbed by the embryo for food. That
in the leaf converts the starch into sugar so that it can be transported to
other parts of the plant to be used in building new tissue, or to be stored
again in the form of starch (example, the potato, in seeds, etc.). The
starch is formed in the leaf during the daylight. The light renders the
leaf diastase inactive. But at night the leaf diastase becomes active and
converts the starch made during the day. Starch is not soluble in water,
while the sugar is, and the sugar in solution is thus easily transported
throughout the plant. In those green plants which do not form starch in
their leaves (sugar beet, corn, and many monocotyledons), grape sugar
and fruit sugar are formed in the green parts as the result of photosynthesis.
In some, like the corn, the grape sugar formed in the leaves is transported
to other parts of the plant, and some of it is stored up in the seed as starch.
In others like the sugar beet the glucose and fruit sugar formed in the
leaves flow to other parts of the plant, and much of it is stored up as cane
sugar in the beet root. The process of photosynthesis probably proceeds
in the same way in all cases up to the formation of the grape sugar and
fruit sugar in the leaves. In the beet, corn, etc., the process stops here,
while in the bean, clover, and most dicotyledons the process is carried one
step farther in the leaf and starch is formed.
ANALYSIS OF PLANT SUBSTANCE. 79
3. Rough Analysis of Plant Substance.
162. Some simple experiments to indicate the nature of plant substance. —
After these building-up processes of the plant, it is instructive to perform
some simple experiments which indicate roughly the nature of the plant
substance, and serve to show how it can be separated into other substances,
some of them being reduced to the form in which they existed when the
plant took them as food. For exact experiments and results it would be
necessary to make chemical analyses.
163. The water in the plant. — Take fresh leaves or leafy shoots or other
fresh plant parts. Weigh. Permit them to remain in a dry room until
they are what we call "dry." Now weigh. The plants have lost weight,
and from what we have learned in studies of transpiration this loss in weight
we know to result from the loss of water from the plant.
164. The dry plant material contains water. — Take air-dry leaves, shav-
ings, or other dry parts of plants. Place them in a test tube. With a
holder rest the tube in a nearly horizontal position, with the bottom of the
tube in the flame of a Bunsen burner. Very soon, before the plant parts
begin to "burn," note that moisture is accumulating on the inner surface
of the test tube. This is water driven off which could not escape by drying
in air, without the addition of artificial heat, and is called "hygroscopic
water."
165. Water formed on burning the dry plant material. — Light a soft-pine
or bass-wood splinter. Hold a thistle tube in one hand with the bulb down-
ward and above the flame of the splinter. Carbon will be deposited over
the inner surface of the bulb. After a time hold the tube toward the win-
dow and look through it above the carbon. Drops of water have accumu-
lated on the inside of the tube. This water is formed by the rearrangement
of some of the hydrogen and oxygen, which is set free by the burning of
the plant material, where they were combined with carbon, as in the cellu-
lose, and with other elements.
166. Formation of charcoal by burning. — Take dried leaves, and shav-
ings from some soft wood. Place in a porcelain crucible, and cover about
3 cm. deep with dry fine earth. Place the crucible in the flame of a Bun-
sen burner and let it remain for about fifteen minutes. Remove and empty
the contents. If the flame was hot the plant material will be reduced to a
good quality of charcoal. The charcoal consists largely of carbon.
167. The ash of the plant. — Place in the porcelain crucible dried leaves
and shavings as before. Do not cover with earth. Place the crucible in
the flame of the Bunsen burner, and for a moment place on the porcelain
cover; then remove the cover, and note the moisture on the under surface
from the escaping water. Permit the plant material to burn; it may even
flame for a time. In the course of fifteen minutes it is reduced to a whitish
8o
PHYSIO LOG y.
powder, much smaller in bulk than the charcoal in the former experiment.
This is the ash of the plant.
168. What has become of the carbon 1 — In this experiment the air was
not excluded from the plant material, so that oxygen combined with carbon
as the water was freed, and formed carbon dioxide, passing off into the air
in this form. This it will be remembered is the form in which the plant
took the carbon-food in through the leaves. Here the carbon dioxide met
the water coming from the soil, and the two united to form, ultimately,
starch, cellulose, and other compounds of carbon; while with the addition
of nitrogen, sulphur, etc., coming also from the soil, still other plant sub-
stances were formed.
169. The carbohydrates are classed among the non-nitrogenous sub-
stances. Other non-nitrogenous plant substances are the organic acids
like oxalic acid (JLjCjOJ, malic acid (H2C4H4O5), etc.; the fats and fixed
oils, which occur in the seeds and fruits of many plants. Of the nitrogenous
substances the proteids have a very complex chemical formula and contain
carbon, hydrogen, oxygen, nitrogen, sulphur, etc. (example, aleuron, or
proteid grains, found in seeds). The proteids are the source of nitrogenous
food for the seedling during germination. Of the amides, asparagin
(C4H8N2O3) is an example of a nitrogenous substance; and of the alkaloids,
nicotin (C;0H14N2) from tobacco.
All living plants contain a large per cent of water. According to Vines
"ripe seeds dried in the air contain 12 to 15 per cent of water, herbaceous
plants 60 to 80 per cent, and many water-plants and fungi as much as 95
per cent of their weight. ' ' When heated to 100° C. the water is driven off.
The dry matter remaining is made up partly of organic compounds, exam-
ples of which are given above, and inorganic compounds. By burning this
dry residue the organic substances are mostly changed into volatile prod-
ucts, principally carbonic acid, water, and nitrogen. The inorganic sub-
stances as a result of combustion remain as a white or gray powder, the ash.
The amount of the ash increases with the age of the plant, though the
percentage of ash may vary at different times in the different members of
the plant. The following table taken from Vines will give an idea of the
amount and composition of the ash in the dry solid of a few plants:
CONTENT OF 1000 PARTS OF DRY SOLID MATTER.
, .
u
o
O ^
•c
o
A
fli P
o"2
.c'D
3-d
C
3
J
«
a.3
•r*'x
§"*<
•aS
o!
'C
^j
•a
|
sfa
n o
0 0
— <3
.y
^
<
o
a.
eg
a
fa
P,'C
3^*
U)
CO
O
Clover, in blossom
68.3
21 .96
I .SO 24.06 7.44
0.72
6.74
2.06
1.62
2.66
Wheat, grain
19.7
6.14
o. .54 0.66 2.36
o. 26
9. 26
0.07, 0.42
0.04
Wheat, straw. . . .
53-7
7-33
0.74 3-°9 1-33
0-33
2.58
1.32 36.25
0.90
Potato tubers. . . .
37-7
22. 76
0.99 0.97
1-77
0-45
6.53
2.45 o . 80
1.17
Apples
14.4
5-14
3.76
0-59
1.26
0.20
1 .96
0.88 0.62
Peas (the seed). . .
27-3
11.41
o. 26
1.36
2.17
o. 16
9-95
o 95
o. 24
0.42
CHAPTER IX.
HOW PLANTS QBTAIN THEIR FOOD. I.-
1 . Sources of Plant Food.
170. The necessary constituents of plant food. — As indicated in Chap-
ter 3, investigation has taught us the principal constituents of plant food.
Some suggestion as to the food substances is derived by a chemical analysis
of various plants. In Chapter 8 it was noted that there are two principal
kinds of compounds in plant substances, the organic compounds and the
inorganic compounds or mineral substances. The principal elements in
the organic compounds are hydrogen, carbon, oxygen and nitrogen. The
elements in the inorganic compounds which have been found indispensable
to plant growth are calcium* potassium, magnesium, phosphorus, sulphur
and iron. (See paragraphs 54-58, and complete observations on water
cultures.) Other elements are found in the ash of plants; and while they
are not absolutely necessary for growth, some f of them are beneficial in
one way or another.
171. The carbohydrates are derived, as we have learned, from the CO2
of the air, and water in the plant tissue drawn from the soil; though in the
case of aquatic plants entirely submerged, all the constituents are absorbed
from the surrounding water.
172. Food substances in the soil. — Land plants derive their mineral food
from the soil, the soil received the mineral substances from dissolving and
disintegrating rocks. Nitrogenous food is chiefly derived from the same
source, but under a variety of conditions which will be discussed in later
paragraphs, but the nitrogen comes primarily from the air. Some of the
mineral substances, those which are soluble as well as some of the nitrog-
enous substances, are found in solution in the soil. These are absorbed
by the plant, as needed, along with water, through the root hairs.
* Calcium is not essential for the growth of the fungi,
t For example, silicon is used by some plants in strengthening supporting
tissues. Buckwheat thrives better when supplied with a chloride.
81
82 PHYSIOLOGY.
173. Absorption of soluble substances. — Since these substances are dis-
solved in the water of the soil, it is not necessary for us to dwell on the
process of absorption. This in general is dwelt upon in Chapter 3^ It
should be noted, however, that food substances in solution, during absorp-
tion, diffuse through the protoplasmic membrane independently of each
other and also independently of the rate of movement of the water from
the soil into the root hairs and cells of the root.
When the cells have absorbed a certain amount of a given substance, no
more is absorbed until the concentration of the cell-sap in that particular
substance is reduced. This, however, does not interfere with the absorp-
tion of water, or of other substances in solution by the same cells. Plants
have therefore a certain selective power in the absorption of food substances.
174. Action of root hairs on insoluble substances. Acidity of
root hairs. — If we take a seedling which has been grown in a
germinator, or in the folds of cloths or paper, so that the roots are
free from the soil, and touch the moist root hairs to blue litmus
paper, the paper becomes red in color where the root hairs have
come in contact. This is the reaction for the presence of an acid
salt, and indicates that the root hairs excrete certain acid sub-
stances. This acid property of the root hairs serves a very im-
portant function in the preparation of certain of the elements of
plant food in the soil. Certain of the chemical compounds of
potash, phosphoric acid, etc., become deposited on the soil par-
ticles, and are not soluble in water. The acid of the root hairs
dissolves some of these compounds where the particles of soil are
in close contact with them, and the solutions can then be taken up
by the roots. Carbonic acid and other acids are also formed in
the soil, and aid in bringing these substances into solution.
175. This corrosive action of the roots can be shown by the well-known
experiment of growing a plant on a marble plate which is covered by soil
In lieu of the marble plate, the peas may be planted -in clam or oyster
shells, which are then buried in the soil of the pot, so that the roots of the
seedlings will come in contact with the smooth surface of the shell. After
a few weeks, if the soil be washed from the marble where the roots have
been in close contact, there will be an outline of this part of the root sys-
tem. Several different acid subsjances are excreted from the roots of
plants which have been found to redden blue litmus paper by contact
Experiments by Czapek show, however, that the carbonic acid excreted by
the roots has the power of directly bringing about these corrosion phenom-
PARASITES AND SAPROPHYTES. 83
ena. The "acid salts are the substances which are most actively concerned
in reddening the blue Litmus paper. They do not directly aid in the corro-
sion phenomena. In the soil, however, where these compounds of potash,
phosphoric acid, etc., are which are not soluble in water, the acid salt
(primary acid potassium phosphate) which is most actively concerned in
reddening the blue litmus paper may act indirectly on these mineral sub-
stances, making them available for plant food. This salt soon unites with
certain Chlorides in the soil, making among" other things small quantities
of hydrochloric acid.
176. NOTE. — It is a general rule that plants cannot take solid food into
their bodies, but obtain^ all food in either a liquid or gaseous state. The
only exception to this is in the case of the plasmodia of certain Myxomy-
cetes (Slime Moulds), and also perhaps some of the Flagellates and other
very low forms, which engulf solid particles of food. It is uncertain, how-
ever, whether these organisms belong to the plant or animal kingdom,
and they probably occupy a more or less intermediate position.
177. Action of nitrite and nitrate bacteria. — Many of the higher green
plants prefer their nitrogenous food in the form of nitrates. (Example,
nitrate of soda, potassium nitrate, saltpetre.) Nitrates are constantly
eing formed in soil by the action of certain bacteria. The nitrite bacteria
(Nitromonas) convert ammonia in the soil to nitrous acid (a nitrite), while
at this point the- nitrate bacteria (Nitrobacter) convert the nitrites into
nitrates. The fact that this nitrification is going on constantly in soil is of
the utmost importance, for while commercial nitrates are often applied
to the soil, the nitrates are easily washed from the soil by heavy rains.
These nitrite and nitrate bacteria require oxygen for their activity, and
they are able to obtain their carbohydrates by decomposing organic matter
in the soil, or directly by assimilating the CO2 in the soil, deriving the energy
for the assimilation of the carbon dioxide from the chemical process of
nitrification. This kind of carbon dioxide assimilation is called chemo-
synthetic assimilation.
2. Parasites and Saprophytes.
178. Parasites among the fungi. — A parasite is an organism which
derives all or a part of its food directly from another living organism (its
host) and at the latter's expense. The larger number of plant parasites
are found among the fungi (rusts, smuts, mildews, etc.). (See Nutrition of
the Fungi, paragraph 185.) Some of these are not capable of develop-
ment unless upon their host, and are called obligate parasites. Others can
grow not only as parasites but at other times can also grow on dead organic
matter, and are called facultative parasites, i.e. they can choose either a
parasitic life or a saprophytic one.
179. Parasites among the seed plants. — Cuscuta. — There are, however,
parasites among the seed plants; for example, the dodder (Cuscuta), para-
84
PHYSIOLOGY.
sitic on clover, and a great variety of other plants. There is food enough
in the seed for the young plant to take root and develop a slender stem until
it takes hold of its host. It then twines around the stem of its host send-
ing wedge-shaped haustoria into the stem to obtain food. The part then
in connection with the ground dies.
The haustoria of the dodder form a complete junction with the vascular
bundles of its host so that through the vessels water and salts are obtained,
while through the junction of sieve tubes the elaborated organic food is
obtained. The union of the dodder with its host is like that between a
graft and the graft stock. The beech drops (Epiphegus) is another exam-
ple of a parasitic seed plant. It is parasitic on the roots of the beech.
180. The mistletoe (Phoradendron), which grows on the branches of
trees, sends its roots into the branches, and only the vessels of the vascular
system are fused according to some. If this is true then it probably ob-
tains only water and salts from its host. But the mistletoe has green leaves
and is thus able to assimilate carbon dioxide and manufacture its own
PARASITES AND SAPROPHYTES. 85
organic substances. It is claimed by some, however, that the host derives
some food from the parasite during the winter when the host has shed its
leaves, and if this is true it would seem that organic food could also be
derived during the summer from the host by the mistletoe.
181. Saprophytes. — A saprophyte is a plant which is enabled to obtain
its food, especially its organic: food, directly from dead animals or plants or
from dead organic substances. Many fungi are saprophytes, as the moulds,
mushrooms, etc. (See Nutrition of the Fungi.)
182. Humus saprophytes. — The action of fungi as described in the pre-
ceding chapter, as well as of certain bacteria, gradually converts the dead
plants or plant parts into the finely powdered brown substance known as
humus. In general the green plants cannot absorb organic food from
humus directly. But plants which are devoid of chlorophyll can live
saprophytically on this humus. They are known as humus saprophytes.
Many of the mushrooms and other fungi, as well as some seed plants which
lack chlorophyll or possess only a small quantity, are able to absorb all
their organic food from humus. It is uncertain whether any seed plants
can obtain all of their organic food directly from humus, though it is be-
lieved that many can so obtain a portion of it. But a number of seed
plants, like the Indian pipe (Monotropa) and certain orchids, obtain organic
food from humus. These plants lack chlorophyll and cannot therefore
manufacture their own carbohydrate food. Not being parasitic on plants
which can, as in the case of the dodder and beech drops mentioned above,
they undoubtedly derive their organic food from the humus. But fungus
mycelium growing in the humus is attached to their roots, and in some
orchids enters the roots and forms a nutritive connection. The fungus
mycelium can absorb organic food from the humus and in some cases at
least can transfer it over to the roots of the higher plant (see Mycorhiza).
183. Antotrophic, heterotrophic, and mizotrophic plants. — An auto-
trophic plant is one which is self-nourishing, i.e. it is provided with an
abundant chlorophyll apparatus for carbon dioxide assimilation and with
absorbing organs for obtaining water and salts. Heterotrophic plants
are not provided with a chlorophyll apparatus sufficient to assimilate all
the carbon dioxide necessary, so they nourish themselves by other means.
Mixotrophic plants are those which are intermediate between the other two,
i.e. they have some chlorophyll but not enough to provide all the organic
food necessary, so they obtain a portion of it by other means. Evidently
there are all gradations of mixotrophic plants between the two other kinds
(example, the mistletoe).
184. Symbiosis. — Symbiosis means a living with or living together, and
is said of those organisms whirh live so closely in connection with each
other as to be influenced for better or worse, especially from a nutrition
standpoint. Conjunctive symbiosis has reference to those cases whert
86
PHYSIOLOGY.
there is a direct interchange of food material between the two organisms
(lichens, mycorhiza, etc.) Disjunctive symbiosis has reference to an inter
life relation without any fixed union between them (example, the relations
between flowers and insects, ants and plants, and even in a broad sense the
relation between saprophytic plants in reducing organic matter to a con-
dition in which it may be used for food by the green plants, and these in
turn provide organic matter for the saprophytes to feed upon, etc.). Antag-
onistic symbiosis is shown in the relation of parasite to its host, reciprocal
symbiosis, or miuualistic symbiosis is shown in those cases where both
symbionts derive food as a result of the union (lichens, mycorhiza, etc.).
3. How Fungi Obtain their Food.
185. Nutrition of moulds. — In our study of mucor, as we have seen, the
growing or vegetative part
of the plant, the mycelium,
lies within the substratum,
which contains the food
materials in solution, and the
slender threads are thus
bathed on all sides by them.
The mycelium absorbs the
watery solutions throughout
the entire system of ramifica-
tions. When the upright
fruiting threads are devel-
oped they derive the materials
for their growth directly from
the mycelium with which
they are in connection. The
moulds which grow on de-
caying fruit or on other
organic matter derive their
nutrient materials in the same
way. The portion of the
mould which we usually see
on the surface of these sub-
stances is in general the fruit-
ing part. The larger part
of the mycelium lies hidden
within the subtratum.
186. Nutrition of para-
Camation rust on leaf and flower stem. From photo- sitic ^ngi.— Certain of the
graph. fungi grow on or within the
higher plants and derive their food materials from them and at their ex-
pense. Such a fungus is called a parasite, and there are a large number
HOW PLANTS OBTAIN FOOD.
of these plants which are known as parasitic fungi. The plant at whose
expense they grow is called the "host."
One of these parasitic fungi, which it is quite easy to obtain in green-
houses or conservatories during the autumn and winter, is the carnation
rust (Uromyces caryophyllinus}, since it breaks out in rusty dark brown
patches on the leaves and stems of the carnation (see fig. 75). If we make
thin cross sections through one of these spots on a leaf, and place them for a
Fig. 76.
Several teleutospores, showing the variations in form.
few minutes in a solution of chloral hydrate, portions of the tissues of the
leaf will be dissolved. After a few minutes we wash the sections in water on
a glass slip, and stain them with a solution of eosin. If the sections were care-
Fig- 77-
Cells from the stem of a rusted carnation, showing the intercellular mycelium and haustoria.
Object magnified 30 times more than the scale.
fully made, and thin, the threads of the mycelium will be seen coursing be-
tween the cells of the leaf as slender threads. Here and there will be seen
short branches of these threads which penetrate the cell wall of tin- host and
project into the interior of the cell in the form of an irregular knob. Such
a branch is a haustorium. By means of this haustorium, which is here
88
PHYSIOLOGY.
only a short branch of the mycelium, nutritive substances are taken by the
fungus from the protoplasm or cell-sap of the carnation. From here it
passes to the threads of the mycelium. These in turn supply food material
for the development of the dark brown gonidia, which we see form the dark-
looking powder on the spots. Many other fungi form haustoria, which take
up nutrient matters in the way described for the carnation rust. In the case
Fig. 78.
Cell from carnation leaf, showing
haustorium of rust mycelium grasping
the nucleus of the host. A, haustori-
um ; n, nucleus of host.
Fig. 79-
Intercellular mycelium with haustoria entering
the cells. A, of Cystopus candidus (white rust);
B, of Peronospora calotheca. (De Bary.)
of other parasitic fungi the threads of the mycelium themselves penetrate
the cells of the host, while in still others the mycelium courses only between
the cells of the host (fungus of peach leaf-curl for example) and derives food
materials from the protoplasm or cell-sap of the host by the process of
osmosis.
187. Nutrition of the larger fungi. — If we select some one
of the larger fungi, the majority of which belong to the mush-
room family and its relatives, which is growing on a decaying log
or in the soil, we shall see on tearing open the log, or on remov-
ing the bark or part of the soil, as the case may be, that the
stem of the plant, if it have one, is connected with whitish
strands. During the spring, summer, or autumn mojiths, exam-
ples of the mushrooms connected with these strands may usually
be found readily in the fields or woods, but during the winter and
HOW PLANTS OBTAIN FOOD.
89
colder parts of the year often they may be seen in forcing houses,
especially those cellars devoted to the propagation of the mush-
room of commerce.
188. These strands are made up of numerous threads of the
mycelium which are closely twisted and interwoven into a cord
or strand, which is called a mycelium strand, or rhizomorph.
These are well shown in fig. 236, which is from a photograph of
the mycelium strands, or "spawn " as the grower of mushrooms
calls it, of Agaricus campestris. The little knobs or enlargements
on the strands are the young fruit bodies, or "buttons."
189. While these threads or strands of the mycelium in the
decaying wood or in the decaying organic matter of the soil are
Fig. 80.
Sterile mycelium on wood props in coal mine, 400 feet below surface. (Photographed by
the author.)
90 PHYSIOLOGY.
not true roots, they function as roots, or root hairs, in the ab-
sorption of food materials. In old cellars and on damp soil in
moist places we sometimes see fine examples of this vegetative
part- of the fungi, the mycelium. But most magnificent examples
are to be seen in abandoned mines where timber has been taken
down into the tunnels far below the surface of the ground to
support the rock roof above the mining operations. I have
visited some of the coal mines at Wilkesbarre, Pa. , and here on
the wood props and doors, several hundred feet below the surface,
and in blackest darkness, in an atmosphere almost completely
saturated at all times, the mycelium of some of the wood-destroy-
ing fungi grows in a profusion and magnificence which is almost
beyond belief. Fig. 80 is from a flash-light photograph of a
beautiful example 400 feet below the surface of the ground.
This was growing over the surface of a wood prop or post, and
the picture is much reduced. On the doors in the mine one can
see the strands of the mycelium which radiate in fan-like figures
at certain places near the margin of growth, and farther back the
delicate tassels of mycelium which hang down in fantastic figures,
all in spotless white and rivalling the most beautiful fabric in the
2xquisiteness of its construction.
190. How fungi derive carbohydrate food. — The fungi being devoid of
chlorophyll cannot assimilate the CO, from the air. They are therefore
dependent on the green plants for their carbohydrate food. Among the
saprophytes, the leaf and wood destroying fungi excrete certain substances
(known as enzymes) which dissolve the carbohydrates and certain other
organic compounds in the woody or leafy substratum in which they grow.
They thus produce a sort of extracellular digestion of carbohydrates, con-
verting them into a soluble form which can be absorbed by the mycelium.
The parasitic fungi also obtain their carbohydrates and other organic food
from the host. The mycelium of certain parasitic, and of wood destroying
fungi, excretes enzymes (cytase) which dissolve minute perforations in the
cell walls of the host and thus aid the hypha during its boring action in
penetrating cell walls.
NOTE. — Certain wood destroying fungi growing in oaks absorb tannin
directly, i.e. in an unchanged form. One of the pine destroying fungi
(Trametes pini) absorbs the xylogen from the wood cells, leaving the pure
cellulose in which the xylogen was nitrated; while Poly par us mollis absorbs
the cellulose, leaving behind only the wood element.
HOW PLANTS OBTAIN FOOD. £1
4. Mycorhiza.
191. While such plants as the Indian pipe (Monotropa), some of the
orchids, etc., are humus saprophytes and some of them are possibly able to
absorb organic food from the humus, many of them have fungus mycelium
in close connection with their roots, and these fungus threads aid in the
absorption of organic food. The roots of plants which have fungus myce-
lium intimately associated in connection with the process of nutrition, are
termed mycorhiza. There is a mutual interchange of food between the
fungus and the host, a reciprocal symbiosis.
192. Mycorhiza are of two kinds as regards the relation of the fungus to
the root; ectolrophic (or epiphytic), where the mycelium is chiefly on the
outside of the root, and endotrophic (or endophytic} where the mycelium is
chiefly within the tissue of the root.
193. Ectotrophic mycorhiza. — Ectotrophic mycorhiza occur on the roots
of the oak, beech, hornbean, etc., in forests where there is a great deal of
humus from decaying leaves and other vegetation. The young growing
roots of these trees become closely covered with a thick felt of the mycelium,
so that no root hairs can develop. The terminal roots also branch pro-
fusely and are considerably thickened. The fungus serves here as the
absorbent organ for the tree. It also acts on the humus, converting some
of it into available plant food and transferring it over to the tree.
194. Endotrophic mycorhiza. — These are found on many of the humus
saprophytes, which are devoid of chlorophyll, as well as on those possess-
ing little or even on some plants possessing an abundance, of chlorophyll.
Examples are found in many orchids (see the coral root orchid, for exam-
ple), some of the ferns (Bolrychium), the pines, leguminous plants, etc.
In endotrophic mycorhiza the mycelium is more abundant within the tissues
of the root, though some of the threads extend to the outside. In the case
of the mycorhiza on the humus saprophytes which have no chlorophyll, or
but little, it is thought by some that the fungus mycelium in the humus
assists in converting organic substances and carbohydrates into a form
available for food by the higher plant and then conducts it into the root,
thus aiding also in the process of absorption, since there are few or no root
hairs on the short and fleshy mycorhiza. The roots, however, of some of
these humus saprophytes have the power of absorbing a portion of their
organic compounds from the humus. It is thought by some, though not
definitely demonstrated, that in the case of the oaks, beeches, hornbeans,
and other chlorophyll-bearing symbionts, the fungus threads do not absorb
any carbohydrates for the higher symbiont, but that they actually derive
their carbohydrates from it.* But it is reasonably certain that the fungus
* Evidence points to the belief that certain cells of the host form substances
which attract, chemitropically, the fungus threads, and that in these cells the
lungus threads are more abundant than in others. Furthermore in the vi-
cinity of the nucleus of the host seems to be the place where these activities
are more marked.
92
PHYSIOLOGY.
threads do assimilate from the humus certain unoxidized, or feebly oxi-
dized, nitrogenous substances (ammonia, for example), and transfer them
over to the host, for the higher plants with difficulty absorb these sub-
stances, while they readily absorb nitrates which are not abundant in
humus. This is especially important in the iorest. It is likely therefore
that the fungus symbiont supplies nitrogen to its host, though it does not
assimilate free nitrogen as is the case in the following examples.
5. Nitrogen gatherers.
195. How clovers, peas, and other legumes gather nitrogen. — It has long
been known that clover plants, peas, beans, and
many other leguminous plants are often able to
thrive in soil where the cereals do but poorly.
Soil poor in nitrogenous plant food becomes richer
in this substance where clovers, peas, etc., are
grown, and they are often planted for the purpose
of enriching the soil. Leguminous plants, espe-
cially in poor soil, are almost certain to have en-
largements, in the form of nodules, or ' ' root
tubercles." A root of the common vetch with
some of these root tubercles is shown in fig. 81.
196. A fungal or bacterial organism in these
root tubercles. — If we cut one of these root tuber-
cles open, and mount a small portion of the in-
terior in water for examination with the micro-
scope, we shall find small rod-shaped bodies,
some of which resemble bacteria, while others are more or less forked into
forms like the letter Y, as shown in fig. 82. These bodies are rich in
nitrogenous substances, or proteids. They are portions of a minute organism,
of a fungus or bacterial nature, which attacks the roots of leguminous plants
Fig. 81.
Root of the common vetch,
showing root tubercles.
Fig. 82. Fig. 83.
Root-tubercle organism from vetch, old con- Root-tubercle organism from Medicago
dition. denticulata.
and causes these nodular outgrowths. The organism (Phytomyxa legumi-
nosarum) exists in the soil and is widely distributed where legumes grow.
HOW PLANTS OBTAIN FOOD. 93
197. How the organism gets into the roots of the legumes. — This minute
organism in the soil makes its way through the wall of a root hair near the
end. It then grows down the interior of the root hair in the form of a
thread. When it reaches the cell walls it makes a minute perforation,
through which it grows to enter the adjacent cell, when it enlarges again.
In this way it passes from the root hair to the cells of the root and down to
near the center of the root. As soon as it begins to enter the cells of the
root it stimulates the cells of that portion to greater activity. So the root
here develops a large lateral nodule, or "root tubercle." As this "root
tubercle" increases in size, the fungus threads branch in all directions,
entering many cells. The threads are very irregular in form, and from cer-
tain enlargements it appears that the rod-like bodies are formed, or the
thread later breaks into myriads of these small " bacteroids. "
198. The root organism assimilates free nitrogen for its host. — This
organism assimilates the free nitrogen from the air in the soil, to make the
proteid substance which is found stored in the bacteroids in large quantities.
Some of the bacteroids, rich in proteids, are dissolved, and the proteid sub-
stance is made use of by the clover or pea, as the case may be. This is why
such plants can thrive in soil with a poor nitrogen content. Later in the
season some of the root tubercles die and decay. In this way some of the
proteid substance is set free in the soil. The soil thus becomes richer in
nitrogenous plant food.
The forms of the bacteroids vary. In some of the clovers 'they are oval,
in vetch they are rod-like or forked, and other forms occur in some of the
other genera.
199. NOTE. — So far as we know the legume tubercle organism does not
assimilate free nitrogen of the air unless it is within the root of the legume.
But there are microorganisms in the soil which are capable of assimilating
free nitrogen independently. Example, a bacterium, Clo.rtridium pasteur-
ianum. Certain bacteria and algae live in contact symbiosis in the soil, the
bacteria fixing free nitrogen, while in return for the combined nitrogen, the
algas furnish the bacteria with carbohydrates. It seems that these bac-
teria cannot fix the free nitrogen of the air unless they are supplied with
carbohydrates, and it is known that Clostridium pasteurianum cannot assim-
ilate free nitrogen unless sugar is present.
6. Lichens.
200. Nutrition of lichens. — Lichens are very curious plants which grow
on rocks, on the trunks and branches of trees, and on the soil. They form
leaf-like expansions more or less green in color, or brownish, or gray, or they
occur in the form of threads, or small tree-like formations. Sometimes the
94
PHYSIOLOGY.
plant fits so closely to the rock on which it grows that it seems merely k.
paint the rock a slightly different color, and in the case of many which occur on
trees there appears to be to the eye only a very slight discoloration of the bark
of the trunk, with here and there the darker colored points where fruit bodies
Fig. 84.
Frond of lichen (peltigera), showing rhizoids.
are formed. The most curious thing about them is, however, that while they
form plant bodies of various form, these bodies are of a "dual nature" as
regards the organisms composing them. The plant bodies, in other words, are
formed of two different organisms which, woven together, exist apparently
as one. A fungus on the one hand grows around and encloses in the
meshes of its mycelium the cells or threads of an alga, as the case may be.
If we take one of the leaf-like forms known as peltigera, which grows on
damp soil or on the surfaces of badly decayed logs, we see that the plant
body is flattened, thin, crumpled, and irregularly lobed. The color is dull
greenish on the upper side, while the under side is white or light gray, and
mottled with brown, especially the older portions. Here and there on the
under surface are quite long slender blackish strands. These are composed
entirely of fungus threads and serve as organs of attachment or holdfasts,
and for the purpose of supplying the plant body with mineral substances
which are in solution in the water of the soil. If we make a thin section of
the leaf-like portion of a lichen as shown in fig. 85, we shall see that it is
composed of a mesh of colorless threads which in certain definite portions
contain entangled green cells. The colorless threads are those of the fungus,
while the green cells are those of the "alga. These green cells of the alga per-
form the function of chlorophyll bodies for the dual organism, while the threads
of the fungus provide the mineral constituents of plant food. The alga,
HOW PLANTS OBTAIN FOOD.
95
while it is not killed in the embrace of the fungus, does not reach the per-
fect state of development which it attains when not in connection with the
fungus. On the other hand the fungus profits more than the alga by this
association. It forms fruit bodies, and perfects spores in the special fruit
bodies, which are so very distinct in the case of so many of the species of
the lichens. These plants have lived for so long a time in this close associa-
tion that the fungi are rarely found separate from the algae in nature, but in
i number of cases they have been induced to grow in artificial cultures sep-
Fig. 85.
Lichen (peltigera), section of thallus ; dark zone of rounded bodies made up largely of the
algal cells. Fungus cells above, and threads beneath and among the algal cells.
irate from the alga. This fact, and also the fact that the algae are often
found to occur separate from the fungus in nature, is regarded by many as an
indication that the plant body of the lichens is composed of two distinct or-
ganisms, and that the fungus is parasitic on the alga.
201. Others regard the lichens as autonomous plants, that is, the two or-
ganisms have by this long-continued community of existence become unified
into an individualized organism, which possesses a habit and mode of life
96
PHYSIOLOGY.
distinct from that of either of the organisms forming the component parts.
This community of existence between two different organisms is called by
some mutualism, or symbiosis. While the alga inclosed within the meshes
of the fungus is not so free to develop, and probably does not attain the full
development which it would alone under favorable conditions, still it is
Section of fruit body or apothecium of lichen (parmelia), showing asci and spores
of the fungus.
very likely that it is often preserved from destruction during very dry
periods, within the tough thallus, on the surface of bare rocks.
CHAPTER X.
HOW PLANTS OBTAIN THEIR FOOD, II.
Seedlings.
202. It is evident from some of the studies which we have made in con-
nection with germination of seeds and nutrition of the plant that there is a
period in the life of the seed plants in which they are able to grow if sup-
plied with moisture, but may entirely lack any supply of food substance
from the outside, though we understand that growth finally comes to a
standstill unless they are supplied with food from the outside. In con-
nection with the study of the nutrition of the plant, therefore, it will be well
to study some of the representative seeds and seedlings to learn more accu-
rately the method of germination and nutrition in seedlings during the ger-
minating period.
203. To prepare seeds for germination. — Soak a handful of seeds (or
more if the class is large) in water for 12 to 24 hours. Take shallow crockery
plates, or ordinary plates, or a germinator with a fluted bottom. Place in
the bottom some sheets of paper, and if sphagnum moss is at hand scatter
some over the paper. If the moss is not at hand, throw the upper layer of
paper into numerous folds. Thoroughly wet the paper and moss, but do
not have an excess of water. Scatter the seeds among the moss or the folds
of the paper. Cover with some more wet paper and keep in a room where
the temperature is about 20° C. to 25° C. The germinator should be looked
after to see that the paper does not become dry. It may be necessary to
cover it with another vessel to prevent the too rapid evaporation of the water.
The germinator should be started about a week before the seedlings are
wanted for study. Some of the soaked seeds should be planted in soil in
pots and kept at the same temperature, for comparison with those grown in
the germinator.
204. Structure of the grain of corn. — Take grains of corn that have been
97
9 PHYSIO LOG Y.
soaked in water for 24 hours and note the form and difference in the two
sides (in all of these studies the form and structure of the seed, as well a;-
the stages in germination, should be illustrated by the student). Make a
longisection of a grain of corn through the middle line, if necessary
making several in order to obtain one which shows the structures well near
the smaller end of the grain. Note the following structures: ist, the hard
^^^ outer ' ' wall' ' (formed of the consoli-
/r~'x\^*^ -i:V»_ f \^^^ dated wall of the ovary with the in-
V^ ^^—^* \^2A^ teguments of the ovules — see Chap-
ters 35 and 36) ; 2d, the greater mass
Section of com seed' 'at upper right of of starch and other Plant food (the
each is the plantlet, next the cotyledon, at endosperm) in the centre: ?d, a some-
left the endosperm. ^
what crescent-shaped body (the
scutellum) lying next the endosperm and near the smaller end of the
grain; 4th, the remaining portion of the young embryo lying between the
scutellum and the seed coat in the depression. When good sections are
made one can make out the radicle at the smaller end of the seed, and a
few successive leaves (the plumule) which lie at the opposite end of the
embryo shown by sharply cuived parallel lines. Observe the attachment
of the scutellum to the caulicle at the point of junction of the plumule and
the radicle. The scutellum is a part of the embryo and represents a coty-
ledon. The endosperm is also called albumen, and such a seed is albumin-
ous.
Dissect out an embryo from another seed, and compare with that seen in
the section.
205. In the germination of the grain of corn the endosperm supplies the
food for the growth of the embryo until the roots are well established in
the soil and the leaves have become expanded and green, in which stage
the plant has become able to obtain its food from the soil and air and live
independently. The starch in the endosperm cannot of course be used for
food by the embryo in the form of starch. It is first converted into a solu-
ble form and then absorbed through the surface of the scutellum or coty-
ledon and carried to all parts of the embryo. An enzyme developed by the
embryo acts upon the starch, converting it into a form of sugar which is in
solution and can thus be absorbed. This enzyme is one of the so-called
diastatic " ferments " which are formed during the germination of all seeds
which contain rood stored in the form of starch. In some seedlings,
this diastase formed is developed in much greater abundance than in
others, for example, in barley. Examine grains of corn still attached
to seedlings several weeks old and note that a large part of their content
has been used up. The action of diastase on starch is described in
Chapter 8.
HOW PLANTS OBTAIN THE IK FOOD. 99
206. Structure of the pumpkin seed. — The pumpkin seed has
a tough papery outer covering for the protection of the embryo
plant within. This covering is made up of the seed coats.
When the seed is opened by slitting off these coats there is seen
within the " meat " of the pumpkin seed. This is nothing
more than the embryo plant. The larger part of this embryo
consists of two flattened bodies which are more prominent than
any other part of the plantlet at this time. These two flattened
bodies are the two first leaves, usually called cotyledons. If we
spread these cotyledons apart we see that they are connected at
one end. Lying between them at this point of attachment is a
small bud. This is the plumule. The plumule consists of the
very young leaves at the end of the stem which will grow as the
seed germinates. At the other end where the cotyledons are
joined is a small projection, the young root, often termed the
radicle.
207. How the embryo gets out of a pumpkin seed. — To see
how the embryo gets out of the pumpkin seed we should
examine seeds germinated in the folds of damp paper or on damp
sphagnum, as well as some which have been germinated in earth.
Seeds should be selected which represent several different stages
of germination.
Fig. 88.
Germinating seed of pumpkin, showing how the heel or " peg " catches on the seed coat
to cast it off.
208. The peg helps to pull the seed coats apart. — The root
pushes its way out from between the stout seed coats at the
smaller end, and then turns downward unless prevented from so
100
PHYSIOLOGY.
doing by a hard surface. After the root is 2-^cm long, and the
two halves of the seed coats have begun to be pried apart, if we
look in this rift at the
junction of the root
and stem, we shall see
that one end of the seed
coat is caught against
heel, or "peg,"
which has grown out
from the stem for this
purpose. Now if we
examine one which is
a little
>more ad-
vanced,
we shall see this heel
more distinctly, and
also that the stem is
arching out away from
the seed coats. As the
stem arches up its back
in this way it pries with
the cotyledons against
the upper seed coat,
but the lower seed coat
is caught against this heel, and the two are pulled gradually
apart. In this way the embryo plant pulls itself out from be-
tween the seed coats. In the case of seeds which are planted
deeply in the soil we do not see this contrivance unless we dig
down into the earth. The stem of the seedling arches through
the soil, pulling the cotyledons up at one end. Then it
straightens up, the green cotyledons part, and open out their
inner faces to the sunlight, as shown in fig. 90. If we dig into
the soil we shall see that this same heel is formed on the stem,
and that the seed coats are cast off into the soil.
Fig. 89.
Escape of the pumpkin seedling from the seed coats.
HOW PLANTS OBTAIN THEIR FOOD.
101
209. Parts of the pumpkin seedling. — During the germination
of the seed all parts of the embryo have enlarged. This in-
crease in size of a plant is one of the peculiarities of growth.
The cotyledons have elongated and expanded somewhat, though
not to such a great extent as the root and the stem. The
cotyledons also have become green on exposure to the light.
Very soon after the main root has emerged from the seed coats,
other lateral roots begin to form, so that the
root soon becomes very much branched.
The main root with its branches makes
up the root system of the seedling. Be-
tween the expanded cotyledons is seen
the plumule. This has enlarged some-
what, but not nearly so much as the root,
or the part of the stem which extends
below the cotyledons. This part of the
stem, i.e., that
part below the
cotyledons and
extending to the
beginning of the
root, is called in
all seedlings the
hypocotyl, which means " below the cotyledon."
210. The common garden bean. — The common garden bean
or the lima bean, may be used for study. The garden bean is
not so flattened or broadened as the lima bean. It is rounded-
compressed, elongate slightly curved, slightly concave on one
side and convex on the other, and the ends are rounded. At
the middle of the concave side note the distinct scar (the hilum)
formed where the bean seed separates from its attachment to
the wall of the pod. Upon one side of this scar is a slight prom-
inence which is continued for a short distance toward the end
of the bean in the form of a slight ridge. This is the raphe, and
represents that part of the stalk of the ovule which is joined to
the side of the ovule when the latter is curved around against it
Fig. 90.
Pumpkin seedling rising from the ground.
102
PHYSIO LOG y.
r, raphe ; c, point
where
lies.
(see Chapter 36), and at the outer end of the raphe is the cha-
laza, the point where the stalk is joined to the end of the ovule,
best understood in a straight ovule. Upon the
opposite side of the scar and close to it can be
seen a minute depression, the micro pyle. Under-
neath the seed coat and lying between this point
and the end of the seed is the embryo, which gives
greater prominence to the bean at this point, but it
is especially more prominent after the bean has been
soaked in water. Soak the beans in water and as
• •
Garden bean, they are swelling note how the seed coats swell
'iiOTscar! faster than the inner portion of the seed, which
chafazl causes them to wrinkle in a curious way, but finally
the inner portion swells and fills the seed coat out
smooth again. Sketch a bean showing all the external features
both in side view and in front. Split one lengthwise and sketch
the half to which the embryo clings, noting the young root,
stem, and the small leaves which were lying
between the cotyledons. There is no endo-
sperm here now, since it was all used up in
the growth of the embryo, and a large part of
its substance was stored up in the cotyledons.
As the seed germinates the young plant gets its
first food from that stored in the cotyledons.
The hypocotyl elongates, becomes strongly
arched, and at last straightens up, h'fting the cotyledons from
the soil. As the cotyledons become exposed to the light they
assume a green color. Some of the stored food in them goes
to nourish the embryo during germination, and they therefore
become smaller, shrivel somewhat, and at last fall off.
211. The castor-oil bean. — This is not a true bean, since it
belongs to a very different family of plants (Euphorbiaceae). In
the germination of this seed a very interesting comparison can
be mad? with that of the garden bean. As the "bean" swells
the very hard outer coat generally breaks open .at the free end
and slips off at the stem end. The next coat within, which is
Fig. 02.
Bean seed split
open to show plant-
let.
HO W PLANTS OBTAIN THEIR FOOD.
-03
also hard and shining black, splits open at the opposite end, that
is at the stem end. It usually splits
open in the form of three ribs.
Next within the inner coat is a
very thin, whitish film (the remains
of the nucellus, and corresponding
to the perisperm) which shrivels up
and loosens from the white mass,
the endosperm, within. In the
castor-oil bean, then, the endosperm
is not all absorbed by the embryo
during the formation of the seed.
As the plant becomes
older we should note that
the fleshy endosperm be-
comes thinner and thin-
ner, and at
last there is
nothing but
Fig. 03.
How the garden bean comes out of the ground. First the looped hypocotyl,
then the cotyledons pulled out, next casting off the seed coat, last the plant erect,
bearing thick cotyledons, the expanding leaves, and the plumule between them.
a thin, whitish film covering the green faces of the cotyledons.
The endosperm has been gradually absorbed by the germinat-
ing plant through its cotyledons and used for food.
Arisaema triphyllum.*
212. Germination of seeds of jack-in-the-pulpit. — The oVaries
of jack-in-the-pulpit form large, bright red berries with a soft
pulp enclosing one to several large seeds. The seeds are oval in
form. Their germination is interesting, and illustrates one type
* In lieu of Arisaema make a practical study of the pea. See paragraph
2160.
IO4
PHYSIOLOGY.
of germination of seeds common among monocotyledonous plants.
If the seeds are covered with sand, and
kept in a moist place, they will germi-
nate readily.
213. How the embryo backs out of
the seed. — The embryo lies within the
mass of the endosperm; the root end,
near the smaller end of the
seed. The club-shaped
cotyledon lies near the
Fig. 94.
Germination of castor-oil bean.
middle of the seed, surrounded firmly on all sides by the endo-
sperm. The stalk, or petiole, of the cotyledon, like the lower
part of the petiole of the leaves, is a hollow cylinder, and
contains the younger leaves, and the growing end of the stem
or bud. When germination begins, the stalk, or petiole, of the
cotyledon elongates. This pushes the root end of the embryo
out at the small end of the seed. The free end of the embryo
now enlarges somewhat, as seen in the figures, and becomes the
bulb, or corm, of the young plant. At first no roots are visible,
but in a short time one, two, or more roots appear on the enlarged
end.
214. Section of an embryo.— If we make a longisection of
the embryo and seed at this time we can see how the club-
shaped cotyledon is closely surrounded by the endosperm.
Through the cotyledon, then, the nourishment from the endo-
sperm is readily passed over to the growing embryo. In the
hollow part of the petiole near the bulb can be seen the first
leaf.
HOW PLANTS OBTAIN THEIR FOOD.
Fig. 95.
Seedlings of castor-oil bean casting the seed coats, and showing papery remnant
of the endosperm.
Fig. 96.
Seedlings of jack-in-the-
pulpit; embryo backing out
pf the seed.
Fig. 97-
Secti9n of germinating embryos
of jack-in-the-pulpit, showing young
leaves inside the petiole of the
cotyledon. At the left cotyledon
shown surrounded by the endo-
sperm in the seed; at right endo-
sperm removed to show the club-
shaped cotyledon.
io6
PHYSIOLOG Y.
215. How the first leaf appears. — As the embryo backs out
of the seed, it turns downward into the soil, unless the seed
is so lying that it pushes straight
downward. On the upper side of
arch thus formed, in the petiole
the cotyledon, a slit appears, and
through thif ~pening the first
arches its way out. The loop of
petiole comes out first, and the
later, as shown in
fig. 98. The petiole
now gradually
the
of
leaf
the
leaf
Fig. 98. Fig. 99. Fig. 100.
Seedlings of jack-in-tlie- Embryos of jack-in-the-pulpit Seedling of jack-in-
pulpit, first leaf arching still attached to the endosperm in the-pulpit; section
out of the petiole of the seed coats, and showing the simple of the endosperm
cotyledon. first leaf. and cotyledon.
straightens up, and as it elongates the leaf expands.
216. The first leaf of the jack-in-the-pulpit is a simple one.
— The first leaf of the embryo jack-in-the-pulpit is very different
in form from the leaves which we are accustomed to see on
mature plants. If we did not know that it came from the seed
HO IV PLANTS OBTAIN THEIR FOOD. 10?
of this plant we would not recognize it. It is simple, that is it
consists of one lamina or blade, and not of three leaflets as in.
the compound leaf of the mature plant. The simple leaf is
ovate and with a broad heart-shaped base. The jack-in-the-
pulpit, then, as trillium, and some other monocotyledonous
plants which have compound leaves on the mature plants, have
simple leaves during embryonic development. The ancestral
monocotyledons are supposed to have had simple leaves. Thus
there is in the embryonic development of the jack-in-the-pulpit,
and others with compound leaves, a sort of recapitulation of the
evolutionary history of the leaf in these forms.
216a. Germination of the pea. — Compare with the bean.
Note especially that the cotyledons are not lifted above the soil
as in the beans. Compare germination of acorns.
Digestion.
2166. To test for food substance in the seedlings studied. — The pumpkin,
squash, and castor-oil bean are examples of what are called oily seeds, though
flaxseed, cotton-seed, and nuts are better. Remove a small portion of the
substance from the cotyledon of the squash and crush it on a glass slip in
a drop or two of osmic acid.* Put on a cover-glass and examine with the
microscope. The black amorphous matter shows the presence of oil in the
protoplasm. The small bodies which are stained yellow are aleurone
grains, a form of protein or albuminous substance. Make sections of the
meat of a Brazil nut or hickory nut and immerse for several hours in os-nic
acid. They become black because of the quantity of oil. Mount in
water and examine under the microscope. The oil is in globules which
are colored black. The oil is converted into an available food form by
the action of an enzyme called lipase, which splits up the fatty oil into
glucose and other substances. Lipase has been found in the endosperm of
the castor bean, cocoanut, and in the cotyledons of the pumpkin, as well
as in other seeds containing oil as a stored product. The aleurone is made
available by an enzyme of the nature of trypsin.
Test the cotyledon of the bean with iodine for the presence of starch. If
the endosperm of corn seed has not been tested do so now with iodine.
The endosperm consists largely of starch. The starch is converted to glu-
* Dissolve a half gram of osmic acid in 50 cc. of water and keep tightlj
corked when not using.
IO8 PHYSIOLOGY.
cose by a diastatic " ferment " formed by the seedling as it germinates.
Make a thin cross-section of a grain of wheat, including the seed coat and a
portion of the interior, treat with iodine and mount for microscopic exam-
ination. Note the abundance of starch in the internal portion of endo-
sperm. Note a layer of cells on the outside of the starch portions filled
with small bodies which stain yellow. These are aleurone grains. The
cellulose in the cell walls of the endosperm is dissolved by another enzyme
called cytase, and some plants store up cellulose for food. For example, in
the endosperm of the date the cell walls are very much thickened and pitted.
The cell walls consist of reserve cellulose and the seedling makes use of it
for food during growth.
216c. Albuminous and exalbuminons seeds. — In seeds where the food is
stored outside of the embryo they are called albuminous; examples, corn,
wheat and other cereals, Indian turnip, etc. In those seeds where the food
is stored up in the embryo they are called exalbuminous; examples, bean,
pea, pumpkin, squash, etc.
217. Digestion has a well-defined meaning in animal physiology and
relates to the conversion of solid food, usually within the stomach, into a
soluble form by the action of certain gastric juices, so that the liquid food
may be absorbed into the circulatory system. The term is not often ap-
plied in plant physiology, since the method of obtaining food is in general
fundamentally different in plants and animals. It is usually applied to
the process of the conversion of starch into some form of sugar in solution,
as glucose, etc. This we have found takes place in the leaf, especially at
night, through the action of a diastatic ferment developed more abundantly
in darkness. As a result, the starch formed during the day in the leaves is
digested at night and converted into sugar, in which form it is transferred
to the growing parts to be employed in the making of new tissues, or it is
stored for future use; in other cases it unites with certain inorganic sub-
stances, absorbed by the roots and raised to the leaf, to form proteids and
other organic substances. In tubers, seeds, parts of stems or leaves where
starch is stored, it must first be "digested" by the action of some enzyme
before it can be used as food by the sprouting tubers or germinating seeds.
For example, starch is converted to a glucose by the action of a diastase.
Cellulose is converted to a glucose by cytase. Albuminoids are converted
into available food by a tryptic ferment. Fatty oils are converted into
glucose and other products by lipase.
Inulin, a carbohydrate closely related to starch, is stored up for food in
solution in many composite plants, as in the artichoke, the root tuber of
dahlia, etc. When used for food by the growing plant it is converted into
glucose by an enzyme, inulase. Make a section of a portion of a dahlia
root and immerse in 95% alcohol for several hours. The inulin is precipi-
tated into sphaero crystals. (See also paragraphs 156-161 and 2166.)
HOW PLANTS OBTAIN THEIR FOOD. 1OQ
218. Then there are certain fungi which feed on starch or other organic
substances whether in the host or not, which excrete certain enzymes to
dissolve the starch, etc., to bring it into a soluble form before they can
absorb it as food. Such a process is a sort of extracellular digestion, i.e.,
the organism excretes the enzyme and digests the solid outside, since it
cannot take the food within its cells in the solid form. To a certain degree
the higher plants perform also extracellular digestion in the action of root-
hair excretion on insoluble substances, and in the case of the humus sapro-
phytes.^ But for them soluble food is largely prepared by the action of
acids, etc., in the soil or water, or by the work of fungi and bacteria as
described in Chapter 9.
219. Assimilation. — In plant physiology the term assimilation has been
chiefly used for the process of carbon-dioxide assimilation (= photosyn-
thesis). Some objections have been raised against the use of assimilation
here as one of the life processes of the plant, since its inception stages are
due to the combined Action of light, an external factor, and chlorophyll in
the plant along with the living chloroplastid. So long, however, as it is
not known that this process can take place without the aid of the living
plant, it does not seem proper to deny that it is altogether not a process of
assimilation. It is not necessary to restrict the term assimilation to the
formation of new living matter in the plant cell ; it can be applied also to
the synthetic processes in the formation of carbohydrates, proteids, etc.,
and called synthetic assimilation. The sun supplies the energy, which is
absorbed by the chlorophyll, for splitting up the carbonic acid, and the
living chloroplast then assimilates by a synthetic process the carbon, hydro-
gen, and oxygen. This process then can be called photo synthetic assimi-
lation. The nitrite and nitrate bacteria derive energy in the process of
nitrification, which enables them to assimilate CO2 from the air, and this is
called chemosynthetic assimilation. The inorganic material in the form
of mineral salts, nitrates, etc., absorbed by the root, and carried up to the
leaves, here meets with the carbohydrates manufactured in the leaf. Under
the influence of the protoplasm synthesis takes place, and proteids and
other organic compounds are built up by the union of the salts, nitrates,
etc., with the carbohydrates. This is also a process of synthetic assimila-
tion. These are afterward stored as food, or assimilated by the proto-
plasm in the making of new living matter, or perhaps without the first
process of synthetic assimilation some of the inorganic salts, nitrates, and
carbohydrates meeting in the protoplasm are assimilated into new living
matter directly.
CHAPTER XI.
RESPIRATION.
220. One of the life processes in plants which is extremely
interesting, and which is exactly the same as one of the life proc-
esses of animals, is easily demonstrated in several ways.
221. Simple experiment to demonstrate the evolution of
C02 during germination. — Where there are a number of stu-
dents and a number of large cylinders are not
at hand, take bottles of a pint capacity and
place in the bottom some peas soaked for 12 to
24 hours. Cover with a glass plate which has
been smeared with vaseline to make a tight
joint with the mouth of the bottle. Set aside
in a warm place for 24 hours. Then slide
the glass plate a little to one side and quickly
pour in a little baryta water so that it will run
down on the inside of the bottle. Cover the
bottle again. Note the precipitate of barium
carbonate which demonstrates the presence of
Fig. 101. t f r
Test for presence of CO2 in the bottle. Lower a lighted taper. It
carbon dioxide in ves- . , , , ... .
sei with germinating is extinguished because of the great quantity
of CO2. If flower buds are accessible, place
a small handful in each of several jars and treat the same as in
the case of the peas. Young growing mushrooms are excellent
also for this experiment, and serve to show that respiration takes
place in the fungi.
no
RESPIRA TION,
III
222. If we now take some of the baryta water and blow our
"breath" upon it the same film will be formed. The carbon
dioxide which we exhale is absorbed by the baryta water, and
forms barium carbonate, just as in the case of the peas. In the
case of animals the process by which oxygen is taken into the
body and carbon dioxide is given off is respiration. The process
in plants which we are now studying is the same, and also is res-
piration. The oxygen in the vessel was partly used up in the
process, and carbon dioxide was given off. (It will be seen that
this process is exactly the opposite of that which takes place in
carbon-dioxide assimilation.)
223. To show that oxygen from the air is used up while
plants respire. — Soak some wheat for 24 hours in water.
Remove it from the water and place
it in the folds of damp cloth or
paper in a moist vessel. Let it
remain until it begins to germinate.
Fill the bulb of a thistle tube with
the germinating wheat. By the aid
of a stand and clamp, support the
tube upright, as shown in fig. 102.
Let the small end of the tube rest
in a strong solution of caustic potash
(one stick caustic potash in two-
thirds tumbler of water) to which
red ink has been added to give a
deep red color. Place a small glass
plate over the rim of the bulb and
seal it air-tight with an abundance
of vaseline. Two tubes can be set
up in one vessel, or a second one
can be set up in strong baryta water
colored in the same way.
224. The result. — It will be seen that the solution of caustic
potash rises slowly in the tube; the baryta water will also, if
that is used. The solution is colored so that it can be plainly
Fig- I02-
" resPiration o£
112
PHYSIOLOGY.
seen at some distance from the table as it rises in the tube. In
the experiment from which the figure was made for the accom-
'_ panying illustration, the solution had risen
in 6 hours to the height shown in fig. 102.
In 24 hours it had risen to the height shown
in fig. 103.
225. Why the solution of caustic
potash rises in the tube. — Since no air can
get into the thistle tube from above or
below, it must be that some part of the
air which is inside of the tube is used up
while the wheat is germinating. From
our study of germinating peas, we know
that a suffocating gas, carbon dioxide, is
given off while respiration takes place.
The caustic potash solution, or the baryta
water, whichever is used, absorbs the car-
bon dioxide. The carbon dioxide is heavier
than air, and so it settles down in the tube
where it can be absorbed.
226. Where does the carbon dioxide
come from? — We know it comes from the
growing seedlings. The symbol for carbon dioxide is CO2. The
carbon comes from the plant, because there is not enough in
the air. Nitrogen could not join with the carbon to make CC>2.
Some oxygen from the air or from the protoplasm of the grow-
ing seedlings (more probably the latter) joins with some of the
carbon of the plant. These break away from their association
with the living substance and unite, making CC>2. The oxygen
absorbed by the plant from the air unites with the living sub-
stance, or perhaps first with food substances, and from these the
plant is replenished with carbon and oxygen. After the demon-
stration has been made, remove the glass plate which seals the
thistle tube above, and pour in a small quantity of baryta water.
The white precipitate formed affords another illustration that
carbon dioxide is released.
Fig. 103.
Apparatus to show
respiration of germinat-
ing wheat.
RESPIRA TION.
\
227. Respiration is necessary for growth. — After performing experiment in
paragraph 221, if the vessel has not been open
too long so that oxygen has entered, we may use
the vessel for another experiment, or set up a
new one to be used in the course of 12 to 24
hours, after some oxygen has been consumed.
Place some folded damp filter paper on the
germinating peas in the jar. Upon this place
one-half dozen peas which have just been
germinated, and in which the roots are about - I04-
20-25 «« long. The vessel should be covered at St left&no oxygen
tightly again and set aside in a warm room. and u"le growth took
place, the one at the right
A second jar with water in the bottom instead m oxygen and growth
of the germinating peas should be set up as a W
check. Damp folded filter paper should be supported above the water,
and on this should be placed one-
half dozen peas with roots of the
same length as those in the jar
containing carbon dioxide.
228. In 24 hours examine and
note how much growth has taken
place. It will be seen that the
roots have elongated but very little
or none in the first jar, while in
the second one we see that the
roots have elongated consider-
ably, if the experiment has been
carried on carefully. Therefore
in an atmosphere devoid of oxygen
very little growth will take place,
which shows that normal respira-
tion with access of oxygen (aerobic
respiration) isnecessary for growth.
229. Another way of perform-
ing the experiment. — If we wish
we may use the following experi-
ment instead of the simple one
indicated above. Soak a handful
of peas in water for 1 2-24 hours,
and germinate so that twelve with
the radicles 20-25 mm long may
be selected. Fill a test tube with
mercury and carefully invert it in a vessel of mercury so that there will
Fig. 105.
Experiment to show that growth takes
place more rapidly in presence of oxygen
than in absence of oxygen. The two tubes
in the vessel represent the condition at the
beginning of the experiment. At the close
of the experiment the roots in the tube at
the left were longer than those in the tube
filled at the start with mercury. The tube
outside of the vessel represents the condi-
tion of things where the peas grew in ab-
sence of oxygen ; the carbon dioxide given
off has displaced a portion of the mercury.
This also shows anaerobic respiration.
114 PHYSIOLOGY.
be no air in the upper end. Now nearly fill another tube and invert in the
same way. In the latter there will be some air. Remove the outer coats
from the peas so that no air will be introduced in the tube filled with the
mercury, and insert them one at a time under the edge of the tube beneath
the mercury, six in each tube, having first measured the length of the radicles
Place in a warm room. In 24 hours measure the roots. Those in the air
will have grown considerably, while those in the other tube will have grown
but little or none.
230. Anaerobic respiration. — The last experiment is also an excelled
one to show anaerobic respiration. In the tube filled with mercury so tha
when inverted there will be no air, it will be seen after 24 hours that a gas
has accumulated in the tube which has crowded out some of the mercury.
With a wash bottle which has an exit tube properly curved, some water
may be introduced in the tube. Then insert underneath a small stick of
caustic potash. This will form a solution of potash, and the gas will be
partly or completely absorbed. This shows that the gas was carbon di-
oxide. This evolution of carbon dioxide by living plants when there is no
access of oxygen is anaerobic respiration (sometimes called intramoleculai
respiration). It occurs to a marked extent in the yeast plant.
231. Energy set free daring respiration. — From what we have learned of
the exchange of gases during respiration we infer that the plant loses carbon
during this process. If the process of respiration is of any benefit to the
plant, there must be some gain in some direction to compensate the plant
for the loss of carbon which takes place.
It can be shown by an experiment that during respiration there is a
slight, elevation of the temperature in the plant tissues. The plant then
gains some heat during respiration. Energy is also manifested by growth.
232. Eespiration in a leafy plant. — We may take a potted plant which
has a well-developed leaf surface and place it under a tightly fitting bell jar.
Under the bell jar there also should be placed
a small vessel containing baryta water. A sim-
ilar apparatus should be set up, but with no
plant, to serve as a check. The experiment must
be set up in a room which is not frequented by
persons, or the carbon dioxide in the room from
respiration will vitiate the experiment. The bell
jar containing the plant should be covered with
a black cloth to prevent carbon assimilation. In
Test for HbeVatkm of car- the course of IO or I2 hours' if even-thing has
bon dioxide from leafy plant worked properly, the baryta water under the jar
during respiration. Baryta ... ,-.,..
water in smaller vessel, with the plant will show the film of barium ca*~-
(Sachs.) bonate, while the other one will show none. Res-
piration, therefore, takes place in a leafy plant as well as in germinating seed*
RESPIRA TION.
233. Eespiration in fungi. — If several large actively growing mushrooms
are accessible, place them in a tall 'glass jar as described for determining
respiration in germinating peas. In the course of 1 2 hours test with the
lighted taper and the baryta water. Respiration takes place in fungi as
well as in green plants.
234. Respiration in plants in general. — Respiration is general in all
plants; though not universal. There are some exceptions in the lower
plants, notably in certain of the bacteria, which can only grow and thrive
in the absence of oxygen.
235. Respiration a breaking-down process. — We have seen that in res-
piration the plant absorbs Oxygen and gives off carbon dioxide. We should
endeavor to note some of the effects of respiration on the plant. Let us
take, say, two dozen dry peas, weigh them, soak for 12-24 hours in water,
and, in the folds of a cloth kept moist by covering with wet paper or sphag-
num, germinate them. When well germinated and before the green color
appears dry well in the sun, or with artificial heat, being careful not to burn
or scorch them. The aim should be to get them about as dry as the seed
were before germination. Now weigh. The
germinated seeds weigh less than the dry peas.
There has then been a loss of plant substance
during respiration.
236. Fermentation of yeast. — Take two fer-
mentation tubes. Fill the closed tubular parts
of each with a weak solution of grape sugar, or
with potato decoction, leaving the open bulb
nearly empty. Into the liquid of one of the
tubes place a piece of compressed yeast as large
as a pea. If the tubes are kept in a warm place
for 24 hours bubbles of gas may be noticed
rising in the one in which the yeast was placed,
while in the second tube no such bubbles appear,
especially if the filled tubes are first sterilized.
The tubes may be kept until the first is entirely
filled. with the gas. Now dissolve in the liquid
a small piece of caustic potash. Soon the
gas will begin to be absorbed, and the liquid
will rise until it again fills the tube. The gas
was carbon dioxide, which was chiefly pro-
duced during the anaerobic respiration of the
rapidly growing yeast cells. In bread making
, this gas is produced in considerable quantities, and rising through the
dough fills it with numerous cavities containing gas, so that the brea>~
"rises." When it is baked the heat causes the gas in the cavities to ex-
Fig. 107.
Fermentation tube with
culture of yeast.
PHYSIOLOGY.
pand greatly. This causes the bread to "rise" more, and baked in
this condition it is "light." There are two special processes accom-
panying the fermentation by yeast: ist, the evolution of carbon dioxide
as shown above; and, 2d, the formation of alcohol. The best illus-
tration of this second process is the brewing of beer, where a form of
the same organism which is employed in "bread rising" is used to "brew
beer."
237. The yeast plant. — Before the caustic potash is placed in the tube
some of the fermented liquid should be taken for study of the yeast plant,
unless separate cultures are made for this pur-
pose. Place a drop of the fermented liquid
on a glass slip, place on this a cover-glass, and
examine with the microscope. Note the min-
ute oval cells with granular protoplasm. These
are the yeast plant. Note in some a small
"bud" at one side of the end. These buds
increase in size and separate from the parent
plant. The yeast plant is ' one celled, and
multiplies by "budding"
or "sprouting." It is z
fungus, and some species
of yeast like the present
one do not form any my-
celium. Under certain
conditions, which are not
very favorable for growth
Fig. io8a.
Yeast. Saccharo- (Cample, when the yeast is
myces cerivisex. a, grown in a weak nutrient
small colony; b, single , . . .
cell budding; c, single substance on a thin layer
i°8- cell forming an ascus f , t p rf } b)
Fermentation tube filled wlth f°,ur spores; d,
with CO2 from action of sPores *?<* fr°m *e several spores are formed
yeast in a sugar solution. «s.) ^ many of ^ yeast ^
After a period of rest these spores, will sprout and produce the yeast plant
again. Because of this peculiar spore formation some place the yeast
among the sac fungi. (See classification of the fungi.)
238. Organized ferments and unorganized ferments. — An organism
like the yeast plant which produces a fermentation of a liquid with evo-
lution of gas and alcohol is sometimes called a ferment, or ferment or-
ganism, or an organized ferment. On the other hand the diastatic fer-
ments or enzymes like diastase, taka diastase, animal diastase (ptyalin in
the saliva), cytase, etc., are unorganized ferments. In the case of these
it is better to say enzyme and leave the word ferment for the ferment
organisms.
RESPIKA 7Y0.V.
239. Importance of green plants in maintaining purity of air. — By respi-
ration, especially of animals, the air tends to become " foul " by the increase
of CO2. Green plants, i.e., plants with chlorophyll, purify the air during
photosynthesis by absorbing CO2 and giving off oxygen. Animals absorb
in respiration large quantities of oxygen and exhale large quantities of CO2
Plants absorb a comparatively small amount of oxygen in respiration and
give off a comparatively small amount of CO2. But they absorb during
photosynthesis large quantities of CO2and give off large quantities of oxygen.
In this way a balance is maintained between the two processes, so that tin-
percentage of CO2 in the air remains approximately the same, viz., about
four- tenths of one per cent, while there are approximately 21 parts oxygen
and 79 parts nitrogen
239a. Comparison of respiration and photosynthesis.
Carbon dioxide is taken in by the plant and oxygen
is liberated.
Starch is formed as a result of the metabolism, or
chemical change.
The process takes place only in green plants, and in
the green parts of plants, that is, in the presence
of the chlorophyll. (Exception in purple bacte-
rium. }
The process only takes place under the influence oi
sunlight.
It is a building-up process, because new plant sub-
stance is formed.
Oxygen is taken in by the plant and carbon dioxide
is liberated.
Carbon dioxide is formed as a result of the meta-
bolism, or chemical change.
The process takes place in all plants whether they
Respiration. \ possess chlorophyll or not (exceptions in anaerobic
bacteria).
The process takes place in the dark as well as in
the sunlight.
It is a breaking-down process, because disintegra-
tion of plant substance occurs.
Starch formation or
Photosynthesis.
CHAPTER XII.
GROWTH.
By growth is usually meant an increase in the bulk of the
plant accompanied generally by an increase in plant sub-
stance. Among the lower plants growth is easily studied in
some of the fungi.
240. Growth in mucor. — Some of the gonidia (often called
spores) may be sown in nutrient gelatine or agar, or even in
prune juice. If the culture has been placed in a warm room, in
the course of 24 hours, or even less, the preparation will be ready
for study.
241. Form of the gonidia. — It will be instructive if we first
examine some of the gonidia which have not been sown in the cul-
ture medium. We should note their rounded or globose form, as
well as their markings if they belong to one of the species with
spiny walls. Particularly should we note the size, and if possible
measure them with the micrometer, though this would not be
absolutely necessary for a comparison, if the comparison can be
made immediately. Now examine some of the gonidia which
were sown in the nutrient medium. If they have not already
germinated we note at once that they are much larger than
those which have not been immersed in a moist medium.
242. The gonidia absorb water and increase in size before
germinating. — From our study of the absorption of water or
watery solutions of nutriment by living cells, we can easily un-
derstand the cause of this enlargement of the gonidium of the
mucor when surrounded by the moist nutrient medium. The
cell-sap in the spore takes up more water than it loses by diffu-
118
GRO WTH.
119
sion, thus drawing water forcibly through the protoplasmic mem-
brane. Since it does not filter out readily, the increase in
Fig. 109.
Spores of mucor, and different stages of germination.
quantity of the water in the cell produces a pressure from within
which stretches the membrane, and the elastic cell wall yields.
Thus the gonidium becomes larger.
243. How the gonidia germinate. — We should find at this
time many of the gonidia extended on one side into a tube-like
process the length of which varies according to time and tempera-
ture. The short process thus begun continues to elongate. This
elongation of the plant is growth, or, more properly speaking, one
of the phenomena of growth.
244. The germ tube branches and forms the mycelium. —
In the course of a day or so branches from the tube will appear.
This branched form of the threads of the fungus is, as we
remember, the mycelium. We can still see the point where
growth started from the gonidium. Perhaps by this time several
tubes have grown from a single one. The threads of the m\ce-
lium near the gonidium, that is, the older portions of them, have
increased in diameter as they have elongated, though this increase
in diameter is by no means so great as the increase in length.
After increasing to a certain extent in diameter, growth in this
direction ceases, while apical growth is practically unlimited,
being limited only by the supply of nutriment.
245. Growth in length takes place only at the end of the
thread. — If there were any branches on the mycelium when the
I2O PHYSIOLOGY.
culture was first examined, we can now see that they remain
practically the same distance from the gonidium as when they
were first formed. That is, the older portions of the mycelium
do not elongate. Growth in length of the mycelium is confined
to the ends of the threads.
246. Protoplasm increases by assimilation of nutrient
substances. — As the plant increases in bulk we note that there
is an increase in the protoplasm, for the protoplasm is very
easily detected in these cultures of mucor. This increase in the
quantity of the protoplasm has come about by the assimilation
of the nutrient substance, which the plant has absorbed. The
increase in the protoplasm, or the formation of additional plant
substance, is another phenomenon of growth quite different from
that of elongation, or increase in bulk.
247. Growth of roots. — For the study of the growth of roots
we may take any one of many different plants. The seedlings of
such plants as peas, beans, corn, squash, pumpkin, etc., serve
excellently for this purpose.
248. Roots of the pumpkin. — The seeds, a handful or so, are
soaked in water for about 1 2 hours, and then placed between
layers of paper or between the folds of clothf which must be kept
quite moist but not very wet, and should be kept in a warm place.
A shallow crockery plate, with the seeds lying on wet filter paper,
and covered with additional filter paper, or with a bell jar, an-
swers the purpose well.
The primary or first root (radicle) of the embryo pushes its way
out between the seed coats at the small end. When the seeds are
well germinated, select several which have the root 4~$cm long.
With a crow-quill pen we may now mark the terminal portion of
the root off into very short sections as in fig. no. The first mark
should be not more than imm from the tip, and the others not
more than imm apart. Now place the seedlings down on damp
filter paper, and cover with a bell jar so that they will re-
main moist, and if the season is cold place them in a warm room.
At intervals of 8 or 10 hours, if convenient, observe them and
note the farther growth of the root.
GRO WTH.
121
249. The region of elongation. — While the root has elon-
gated, the region of elongation is not at the tip of the root. It lies
a little distance back from the tip, beginning at
about 2mm from the tip and extending over
an area represented by from 4-5 of the milli-
meter marks. The
root shown in fui. no
was marked at IOA.M.
on July 5. At 6 P.M.
of the same day, 8
Fig. no.
Root of germinating pumpkin, showing region of
elongation just back of the tip.
hours later, growth had taken place as shown in the middle
figure. At 9 A.M. on the following day, 15 hours later, the
growth is represented in the lower one. Similar experiments
upon a number of seedlings give the same result : the region of
elongation in the growth of the root is situated a little distance
back from the tip. Farther back very little or no elongation
takes place, but growth in diameter continues for some time, as
we should discover if we examined the roots of growing pump-
kins, or other plants, at different periods.
250. Movement of region of greatest elongation. — In the
region of elongation the areas marked off do not all elongate
equally at the same time. The middle spaces elongate most
rapidly and the spaces marked off by the 6, 7, and 8 mm marks
elongate slowly, those farthest from the tip more slowly than the
others, since elongation has nearly ceased here. The spaces
marked off between the 2-^mm marks also elongate slowly, but
soon begin to elongate more rapidly, since that region is becom-
ing the region of greatest elongation. Thus the region of greatest
elongation moves forward as the root grows, and remains ap-
proximately at the same distance behind the tip.
251. Formative region. — If we make a longitudinal section of the tip of a
growing root of the pumpkin or other seedling, and examine it with the mi-
122 PH YSIOL OG Y.
croscope, we see that there is a great difference in the character of the
cells of the tip and those in the region of elongation of the root. First there
is in the section a V-shaped cap of loose cells which are constantly being
sloughed off. Just back of this tip the cells are quite regularly isodiametric,
that is, of equal diameter in all directions. They are also very rich in pro-
toplasm, and have thin walls. This is the region of the root where new cells
are formed by division. It is the formative region. The cells on the outside
of this area are the older, and pass over into the older parts of the root and root
cap. If we examine successively the cells back from this formative region
we find that they become more and more elongated in the direction of the
axis of the root. The elongation of the cells in this older portion of the root
explains then why it is that this region of the root elongates more rapidly
than the tip.
252. Growth of the stem. — We may use a bean seedling
growing in the soil. At the junction of the leaves with the stem
there are enlargements. These are the nodes, and the spaces on
the stem between successive nodes are the internodes. We should
mark off several of these internodes, especially the younger ones,
into sections about $mm long. Now observe these at several
times for two or three days, or more. The region of elongation
is greater than in the case of the roots, and extends back farther
from the end of the stem. In some young garden bean plants
the region of elongation extended over an area of ^omm in one
internode. See also Chapters 38, 39.
253. Force exerted by growth. — One of the marvelous things connected
with the growth of plants is the force which is exerted by various members of
the plant under certain conditions. Observations on seedlings as they are
pushing their way through the soil to the air often show us that considerable
force is required to lift the hard soil and turn it to one side. A very striking
illustration may be had in the case of mushrooms which sometimes make
their way through the hard and packed soil of walks or roads. That succu-
lent and tender plants should be capable of lifting such comparatively heavy
weights seems incredible until we have witnessed it. Very striking illustra-
tions of the force of roots are seen in the case of trees which grow in rocky
situations, where rocks of considerable weight are lifted, or small rifts in
large rocks are widened by the lateral pressure exerted by the growth of a
root, which entered when it was small and wedged its way in.
254. Zone of maximum growth. — Great variation exists in the rapidity of
growth even when not influenced by outside conditions. In our study of the
elongation of the root we found that the cells just back of the formative region
GRO WTH.
123
elongated slowly at first. The rapidity of the elongation of these cells in
creases until it reaches the maximum. Then the rapidity of elongation les-
sens as the cells come to lie farther from the tip. The period of maximum
elongation here is the zone of maximum growth of these cells.
255. Just as the cells exhibit a zone of maximum growth, so the members of
the plant exhioit a similar zone of maximum growth. In the case of leaves,
when they are young the rapidity of growth is comparatively slow, then it
increases, and finally diminishes in rapidity again. So it is with the stem.
When the plant is young the growth is not so rapid ; as it approaches middle
age the rapidity of growth increases; then it declines in rapidity at the close
of the season.
256. Energy of growth. — Closely related to the zone of maximum growth is
what is termed the energy of growth. This is manifested in the compara-
r^j tive size of the members of a given plant.
To take the sunflower for example, the
lower and first leaves are comparatively
small. As the plant grows larger the
leaves are larger, and this increase in
size of the leaves increases up to a maxi-
mum period, when the size decreases
until we reach the small leaves at the top
of the stem. The zone of maximum growth
of the leaves corresponds with the maxi-
mum size of the leaves on the stem. The
rapidity and energy of growth of the stem
is also correlated with that of the leaves,
and the zone of maximum
growth is coincident with
that of the leaves. It would
be instructive to note it
in the case of other plants
and also in the case of
fruits.
257. Nutation. — During the growth of the stem all of the cells of a given
section of the stem do not elongate simultaneously. For example the cells
at a given moment on the south side are elongating more rapidly than the
cells on the other side. This will cause the stem to bend slightly to the
north. In a few moments later the cells on the west side are elongating more
rapidly, and the stem is turned to the east; and so on, groups of cells in suc-
cession around the stem elongate more rapidly than the others. This causes
the stem to describe a circle or ellipse about a central point. Since the re-
gion of greatest elongation of the cells of the stem is gradually moving toward
the apex of the growing stem, this line of elongation of the cells which is
Lever auxanometer (Oels) for measuring elongation of
the stem during growth.
1 24 flf YS1OL OGY,
traveling around the stem does so in a spiral manner. In the same way,
while the end of the stem is moving upward by the elongation of the cells,
and at the same time is slowly moved around, the line which the end of the
stem describes must be a spiral one. This movement of the stem, which is
common to all stems, leaves, and roots, is nutation.
258- The importance oi nutation to twining stems in their search for a
place of support, as well as for the tendrils on leaves or stems, will be seen.
In the case of the root it is of the utmost importance, as the root makes its
way through the soil, since the particles of soil are more easily thrust aside.
The same is also true in the case of many stems before they emerge from the
soil.
CHAPTER XIII.
IRRITABILITY.
259. We should now examine the movements of plant parts
in response to the influence of certain stimuli. By this
time we have probably observed that the direction which the
root and stem take upon germination of the seed is not due to
the position in which the seed happens to lie. Under normal
conditions we have seen that the root grows downward and the
stem upward.
260. Influence of the earth on the direction of growth. —
When the stem and root have been growing in these directions
for a short time let us place the seedling in a horizontal position,
so that the end of the root extends over an object of support in
such a way that it will be free to go in any direction. It should
be pinned to a cork and placed in a moist chamber. In the
course of twelve to twenty-four hours the root which was formerly
horizontal has turned the tip downward again. If we should
mark off millimeter spaces beginning at the tip of the root, we
should find that the motor zone, or region of curvature, lies in
the same region as that of the elongation of the root.
Knight found that the stimulus which influences the root to
turn downward is the force of gravity. The reaction of the root
in response to this stimulus is geotropism, a turning influenced
by the earth. This term is applied to the growth movements of
plants influenced by the earth with regard to direction. While
the motor zone lies back of the root tip, the latter receives the
stimulus and is the perceptive zone. If the root tip is cut off,
the root is no longer geotropic, and will not turn downward
when placed in a horizontal position. Growth toward the earth
"5
126
PHYSIOLOGY.
is progeotropism. The lateral growth of secondary roots is dia~
geotropism.
The stem, on the other hand, which was placed in a horizontal
position has become again erect. This turning of the stem in
Fig. 112. Fig. 113.
Germinating pea placed in a hori- In 24 hours gravity has caused the root to
zontal position. turn downward.
Figs, iia, 113.— Progeotropism of the pea root.
the upward direction takes place in the dark as well as in the
light, as we can see if we start the experiment at nightfall, or
place the plant in the dark. This up-
ward growth of the stem is also influ-
enced by the earth, and therefore is a
case of geotropism. The special desig-
nation in the case of. upright stems. is
negative geotropism, or apogeotropism, or
the stems are said
to be apogeotropic.
Fig. 114.
Pumpkin seedling showing apogeotropism. Seedling at the left placed hori-
zontally, in 24 hours the stem has become erect.
If we place a rapidly growing potted plant in a horizontal
position by laying the pot on its side, the ends of the shoots
will soon turn upward again when placed in a horizontal
position. Young bean plants growing in a pot began within
two hours to turn the ends of the shoots upward.
IRRITABILITY.
127
Horizontal leaves and shoots can be shown to be subject to
the same influence, and are therefore diageotropic.
261. Influence of light. — Not only is light a very important
factor for plants during photosynthesis, it exerts great influ-
ence on plant growth and movement.
262. Growth in the absence of light. — Plants grown in the dark
are subject to a number of changes. The stems are often longer,
more slender and
weaker since they
contain a larger
amount of water
in proportion to
building material
which the plant
obtains from car-
bohydrates manu-
factured in the
light. On many
plants the leaves
are very small
when grown in the
dark.
263. Influence of light on direction of
growth. — While we are growing seedlings,
the pots or boxes of some of them should be
rig. no.
placed SO that the plants will have a One- Radish seedlings grown in
. j , .,, . ,. ,™ . . the light, shorter, stouter,
sided illumination. I his can be done by and green in c9ior. Growth
, • .., . , retarded by light.
placing them near an open window, in a
room with a one-sided illumination, or they may be placed in a
box closed on all sides but one which is facing the window or
light. In 12-24 hours, or even in a much shorter time in some
cases, the stems of the seedlings will be directed toward the
source of light. This influence exerted by the rays of light is
heliotropism, a turning influenced by the sun or sunlight.
264. Diaheliotropism. — Horizontal leaves and shoots are
diaheliotropic as well as diageotropic. The general direction
Fig. ii
Radish seedlings grown
dark, long, slender, not
128
PHYSIOLOGY.
which leaves assume under this influence is that of placing them
with the upper surface perpendicular to the rays of light which
fall upon them. Leaves, then, exposed to
the brightly lighted sky are, in general,
horizontal. This position is taken in direct
response to the
stimulus of light.
The leaves of plants
with a one-sided illu-
mination,
as can be
seen b y
trial, are
turned with
Fl,g< "7> their upper
Seedling of castor-oil bean, before and after
a one-sided illumination. Surfaces tO-
ward the
source of light, or perpendicular to the in-
cidence of the light rays. In this way
light overcomes for the time being the
direction which growth gives to the leaves.
The so-called "sleep" of plants is of
course not sleep, though the leaves " nod,"
or hang downward, in many cases. There
— are many plants in which we can note
this drooping of the leaves at nightfall, and in order to prove
that it is not determined by the time of day we can resort to
a well-known ex-
periment to induce
this condition dur-
ing the day. The
plant which has
been used to illus-
trate this is the sun-
flower. Some of
these plants, which
Fig. 118.
Dark chamber with opening at one side to show heliotropism.
(After Schleichert.)
IRRITABILITY.
I29
were grown in a box, when they were about s$cm high were
covered for nearly two days, so that the light was excluded.
At midday on the second day the box was removed, and the
leaves on the covered plants are well represented by fig. ng, which
was made from one of them. The leaves of the other plants
in the box which were not covered were horizontal, as shown
by fig. 120. Now on leaving these plants, which had exhibited
Sunflower plant removed from
darkness, leaves extending under
influence of light (diaheliotro-
pism.)
induced "sleep" move-
ments, exposed to the light
they gradually assumed
the horizontal position again.
265. Epinasty and hyponasty. — During
the early stages of growth of many leaves,
as in the sunflower plant, the direction of
growth is different from what it is at a later
period. The under surface of the young
leaves grows more rapidly in a longitudinal
direction than the upper side, so that the
leaves are held upward close against the
Fig. 119. bud at the end of the stem. This is termed
diloUnnone\7eSdU^d±CgC«hne ***"»** Or the leaves are Said to te
day in darkness. hyponastic. Later the growth is more rapid
on the upper side and the leaves turn downward or away from the bud.
This is termed epinasty, or the leaves are said to be epinastic. This is shown
by the night position of the leaves, or in the induced "sleep "of the sun-
130 PHYSIOLOGY.
flower plant in the experiment detailed above. Tlie day position of the
leaves on the other hand, which is more or less horizontal, is induced because
of their irritability under the influence of light, the inherent downward or
epinastic growth is overcome for the time. Then at nightfall or in darkness,
the stimulus of light being removed, the leaves assume the position induced
by the direction of growth.
266. In the case of the cotyledons of some plants it would seem that the
growth was hyponastic even after they have opened. The day position of
Fig. i3i. Fig. 122.
Squash seedling. Position of cotyledons in Squash seedling. Position of cotyledons ir.
light. the dark.
the cotyledons of the pumpkin is more or less horizontal, as shown in fig.
121. At night, or if we darken the plant by covering with a tight box, the
leaves assume the position shown in fig. 122.
While the horizontal position is the general one which is assumed by
plants under the influence of light, their position is dependent to a certain
extent on the intensity of the light as well as on the incidence of the light
rays. Some plants are so strongly heliotropic that they change their posi-
tions all during the day.
267. Leaves with a fixed diurnal position. — Leaves of some plants when
they are developed have a fixed diurnal position and are not subject to
IRRITABILITY.
variation. Such leaves tend to arrange themselves in a vertical or para-
heliotropic position, in which the surfaces are not exposed to the incidence
of light of the greatest intensity, but to the incidence of the rays of diffused
light. Interesting cases of the fixed position of leaves are found in the so-
called compass plants (like Silphium laciniatum, Lactuca scariola, etc.). In
these the horizontal leaves arrange themselves with the surfaces vertical, and
also pointing north and south, so that the surfaces face east and west.
268. Importance of these movements. — Not only are the leaves placed in
a position favorable for the absorption of the rays of light which are con-
cerned in making carbon available for food, but they derive other forms of
energy from the light, as heat, which is absorbed during the day. Then
with the nocturnal position, the leaves being drooped down toward the stem,
or with the margin toward the sky, or with the cotyledons as in the pump-
kin, castor-oil bean, etc., clasped upward together, the loss of heat by
radiation is less than it would be if the upper surfaces of the leaves were
exposed to the sky.
269. Influence of light on the structure of the leaf. — In our study of the
structure of a leaf we found that in the ivy leaf the palisade cells were on
the upper surface. This is the case with a
great many leaves, and is the normal arrange-
ment of " dorsiventral " leaves which are dia-
heliotropic. Leaves which are paraheliotropic
tend to have palisade cells on both surfaces.
The palisade layer of cells as we have seen is
made up of cells lying very close together, and
they thus prevent rapid evaporation. They
also check to some extent the. entrance of the
rays of light, at least more so than the loose
spongy parenchyma cells do. Leaves developed
in the shade have looser palisade and paren-
chyma cells. In the case of some plants, if
we turn over a very young leaf, so that the
under side will be uppermost, this side will
develop the palisade layer. This shows that
light has a great influence on the structure of
the leaf.
270. Movement influenced by contact. — In
the case of tendrils, twining leaves, or stems,
the irritability to contact is shown in a move-
ment of the tendril, etc., toward the object in
touch. This causes the tendril or stem to coil
around the object for support. The stimulus is also extended down the part
of the tendril below the point of contact (see fig. 123), and that part coils
Fig. 123.
Coiling tendril of bryony.
132
PHYSIOLOGY.
up like a wire coil spring, thus drawing the leaf or branch from which the
tendril grows closer to the object of support. This coil between the object
of support and the plant is also very important in easing up the plant when
subject to violent gusts of wind which might tear the plant from its support
were it not for the yielding and springing motion of this coil.
271. Sensitive plants. — These plants are remarkable for the
rapid response to stimuli. Mimosa pudica is an excellent plant
to study for this purpose.
272. Movement in response to stimuli. — If we pinch with
the forceps one of the terminal leaflets, or tap it with a pencil,
the two end leaflets fold above the "vein" of the pinna. This
is immediately followed
by the movement of the
next pair, and so on as
shown in fig. 125, until all
the leaflets on this pinna
are closed, then the stimu-
lus travels down the
other pinnae in a simi-
___ _ lar manner, and
Fig. 124.
Sensitive-plant leaf
in normal position.
Fig- 1 25.
Pinnae fold-
ing up after
stimulus.
soon the pinnae approximate each other and
the leaf then drops downward as shown in
Later all the pinnae
fig. 126. The normal position of the leaf is folded and leaf drooped,
shown in fig. 124. If we jar the plant by striking it or by jarring
the pot in which it is grown all the leaves quickly collapse into
the position shown in fig. 126. If we examine the leaf now we
see minute cushions at the base of each leaflet, at the junction of
the pinnae with the petiole, and a larger one at the junction of
the petiole with the stem. We shall also note that the move-
ment resides in these cushions.
IRRITABILITY.
133
273. Transmission of the stimulus. — The transmission of
the stimulus in ihis mimosa from one part of the plant has been
found to be along the cells of the bast.
274, Cause of the movement. — The movement is caused by
a sudden loss of turgidity on the part of the cells in one portion
of the pulvinus, as the cushion is called. In the case of the
large pulvinus at the base of the petiole this loss of turgidity is
in the cells of the lower surface. There is a sudden change in
the condition of the protoplasm of the cells here so that they
lose a large part of their water. This can be seen if with a sharp
knife we cut off the petiole just above the pulvinus before move-
ment takes place. A drop of liquid exudes from the cells of the
lower side.
275. Paraheliotropism of the leaves of the sensitive plant. — If the mimosa
plant is placed in very intense light the leaflets will turn their edges toward
the incidence of the rays of light. This is also true of other plants in
intense light, and is paraheliotropism. Transpiration is thus lessened, and
chlorophyll is protected from too intense light.
We thus see that variations in the intensity of light have an important
.influence in modifying movements. Variations in temperature also exert
a considerable influence, rapid
elevation of temperature causing
certain flowers to open, and
falling temperature causing
them to close.
276. Sensitiveness of insec-
tivorous plants. — The Venus
fly-trap (Dionsea muscipula)and
the sundew (drosera) are in-
teresting examples of sensitive
plants, since the leaves close in
response to the stimulus from
insects.
Fig. 126.
Leaf of Venus fly-
trap (Dionza musci-
pula), showing winged
petiole and toothed
lobes.
Fig. 127.
Leaf of Drosera ro-
tundifolia, some of the
glandular hairs folding
inward as a result of a
stimulus.
277. Hydrotropism. —
Roots are sensitive to mois-
ture. They will turn toward moisture. This is of the greatest
importance for the well-being of the plant, since the roots will seek
those places in the soil where suitable moisture is present. On
1 34 PHYSIOLOG y.
the other hand, if the soil is too wet there is a tendency for the
roots to grow away from the soil which is saturated with water.
In such cases roots are often seen growing upon the surface of
the soil so that they may obtain oxygen, which is important for
the root in the processes of absorption and growth. Plants then
may be injured by an excess of water as well as by a lack of
water in the soil.
278 Temperature. — In the experiments on germination thus far made
it has probably been noted that the temperature has much to do with the
length of time taken for seeds to germinate. It also influences the
rate of growth. The effect of different temperatures on the germination of
seed can be very well noted by attempting to germinate some in rooms at
various temperatures. It will be found, other conditions being equal, that
in a moderately warm room, or even in one quite warm, 25—30 degrees cen-
tigrade, germination and growth goes on more rapidly than in a cool. room,
and here more rapidly than in one which is decidedly cold. In the case of
most plants in temperate climates, growth may go on at a temperature but
little above freezing, but few will thrive at this temperature.
279. If we place dry peas or beans in a temperature of about 70° C. for 15
minutes they will not be killed, but if they have been thoroughly soaked in
water and then placed at this temperature they will be killed, or even at a
somewhat lower temperature. The same seeds in the dry condition will
withstand a temperature of 10° C. below, but if they are first soaked in water
this low temperature will kill them.
280. In order to see the effect of freezing we may thoroughly freeze a sec-
tion of a beet root, and after thawing it out place it in water. The water is
colored by the cell-sap which escapes from the cells, just as we have seen it
does as a result of a high temperature, while a section of an unfrozen beet
placed in water will not color it if it was previously washed.
If the slice of the beet is placed at about — 6° C. in a shallow glass vessel,,
and covered, ice will be formed over the surface. If we examine it with the
microscope ice crystals will be seen formed on the outside, and these will
not be colored. The water for the formation of the crystals came from the
cell-sap, but the concentrated solutions in the sap were not withdrawn by
the freezing over the surface.
281. If too much water is not withdrawn from the cells of many plants in
freezing, and they are thawed out slowly, the water which was withdrawn
from the cells will be absorbed again and the plant will not be killed. But
if the plant is thawed out quickly the water will not be absorbed, but will
remain on the surface and evaporate. Some will also remain in the inter-
cellular spaces, and the plant will die. Some plants, however, no matter how
IRRITABILITY. 135
slowly they are thawed out, are killed after freezing, as the leaves of the
pumpkin, dahlia, or the tubers of the potato.
282. It has been found that as a general rule when plants, or plant parts,
contain little moisture they will withstand quite high degrees of tempera-
ture, as well as quite low degrees, but when the parts are filled with sap or
water they are much more easily killed. For this reason dry seeds and the
winter buds of trees, and other plants, because they contain but little water,
are better able to resist the cold of winters. But when growth begins in the
spring, and the tissues of these same parts become turgid and filled with
water, they are quite easily killed by frosts. It should be borne in mind,
however, that there is great individual variation in plants in this respect,
some being more susceptible to cold than others. There is also great varia-
tion in plants as to their resistance to the cold of winters, and of arctic
climates, the plants of the latter regions being able to resist very low tem-
peratures. We have examples also in the arctic plants, and those which
grow in arctic climates on high mountains, of plants which are able to carry
on all the life functions at temperatures but little above freezing.
For further discussion as to relation of plants to temperature, see Chap-
ters 46, 48, 49, and 53.
PART II.
MORPHOLOGY AND LIFE HISTORY OF REPRE-
SENTATIVE PLANTS.
CHAPTER XIV.
SPIROGYRA.
283. In our study of protoplasm and some of the processes of
plant life we became acquainted with the general appearance of
the plant spirogyra. It is now a familiar object to us. And in
taking up the study of representative plants of the different
groups, we shall find that in knowing some of these lower plants
the difficulties of understanding methods of reproduction and
relationship are not so great as they would be if we were entire-
ly ignorant of any members of the lower groups.
284. Form of spirogyra. — We have found that the plant
spirogyra consists of simple threads, with cylindrical cells
attached end to end. We have also noted that each cell of the
thread is exactly alike, with the exception of certain ' ' hold-
fasts " on some of the species. If we should examine threads in
different stages of growth we should find that each cell is capable
of growth and division, just as it is capable of performing all the (
functions of nutrition and assimilation. The cells of spirogyra
then multiply by division. Not simply the cells at the ends of
the threads but any and all of the cells divide as they grow, and
in this way the threads increase in length.
285. Multiplication of the threads.— In studying living material of this
plant we have probably noted that the threads often become broken by two of
the adjacent cells of a thread b«coming separated. This may be and is accom-
136
SPIROGYRA.
plishcd in many cases without any injury to the cells. In this manner the
threads or plants of spirogyra, if we choose to call a thread a
plant, multiply, or increase. In this breaking of a thread the
cell wall which separates any two cells splits. If we should
examine several species of spirogyra we would probably find
threads which present two types as regards the character of
the walls at the ends of the cells. In fig. 128 we see that the
ends are plain, that is, the cross walls are all straight. But
in some other species the inner wall of the cells presents a
peculiar appearance. This inner wall at the end of the
cell is at first straight across. But it soon becomes folded
back into the interior of its cell, just as the end of an
empty glovf finger may be pushed in. Then the infolded
end is pushed partly out again, so that a peculiar figure is
the result.
286. How some of the threads break.— In the separation
of the cells of a thread this peculiarity is often of advan-
tage to the plant. The cell-sap within the protoplasmic
membrane absorbs water and the pressure pushes on the
ends of the infolded cell walls. The inner wall being so
much longer than the outer wall, a pull is exerted on the
latter at the junction of the cells. Being weaker at this
point the outer wall is ruptured. The turgidity of the two
cells causes these infolded inner walls to push out suddenly
as the outer wall is ruptured, and the thread is snapped
apart as quickly as a pipe-stem may be broken.
287. Conjugation of spirogyra. — Under cer-
tain conditions, when vegetative growth and
multiplication cease, a process of reproduction
takes place which is of a kind termed sexual repro-
duction. If we select mats of spirogyra which
have lost their deep green color, we are likely to
find different stages of this sexual process, which
in the case of spirogyra and related plants is called
conjugation. A few threads of such a mat we
should examine with the microscope. If the
material is in the right condition we see in certain
of the cells an oval or elliptical body. If we
note carefully the cells in which these oval bodies
are situated, there will be seen a tube at one side which con-
Fig. 128.
Thread of spiro"
gyra, showing long
cells, chlorophyll
band, nucleus,
strands of proto-
plasm, and the
granular wall layer
of protoplasm.
138
MORPHOLOGY.
nects with an empty cell of a thread which lies near as shown in
fig. 129. If we search through the material we may see other threads
connected in this ladder fashion, in which
the contents of the cells are in various stages
of collnpse from what we have seen in the
growing cell. In some the protoplasm and
chlorophyll band have moved but little from
the wall ; in others it forms a mass near the
center of the cell, and again in others we
will see that the contents of the cell of one
of the threads has moved partly through the
tube into the cell of the thread with which it
is connected.
289. This suggests to us that the
oval bodies found in the cells of one
thread of the ladder, while the cells
of the other thread were empty, are
formed by the union of the contents
of the two cells. In fact that is what
does take place. This kind of union
of the contents of two similar or nearly
similar cells is conjugation. The oval
bodies which are the result of this
conjugation are zygotes, or zygospores.
When we are examining living ma-
terial of spirogyra in this stage it is ^ '
possible to watch this process of con-
jugation. Fig. 130 represents the differ-
ent stages of conjugation of spirogyra.
290. How the threads conjugate, or join. — The cells of two
threads lying parallel put out short processes. The tubes from'
two opposite cells meet and join. The walls separating the con-
tents of the two. tubes dissolve so that there is an open communi-
cation between the two cells. . The content of each one of these
cells which take part in the conjugation is a gamete. The one
which passes through the tube to the receiving cell is the supply-
Fig. 1 29.
Zygospores of spirogyra.
SPIROG YRA.
139
ing gamete, while that of the receiving cell is the receiving
gamete.
291. How the protoplasm moves from one cell to another. — Before any
movement of the protoplasm of the supplying cell takes place we can see
Fig. 130.
Conjugation in spirogyra ; from left to right beginning in the upper row is shown the
gradual passage of the protoplasm from the supplying gamete to the receiving gamete.
that there is great activity in its protoplasm. Rounded vacuoles appear
which increase in size, are filled with a watery fluid, and swell up like a
vesicle, and then suddenly contract and disappear. As the vacuole disap-
pears it causes a sudden movement or contraction of the protoplasm around
it to take its place. Simultaneously with the disappearance of the vacuole
the membrane of the protoplasm is separated from a .part of the wall. This
is probably brought about by a sudden loss of some of the water in the cell-
sap. These activities go on, and the protoplasmic membrane continues to
slip away from the wall. Every now and then there is a movement by
which the protoplasm is moved a short distance. It is moved toward the
tube and finally a portion of it with one end of the chlorophyll band begins
to move into the tube. About this time the vacuoles can be seen in an
active condition in the receptive cell. At short intervals movement con-
140
MORPHOLOG Y.
tinues until the content of the supplying cell has passed over into that of the
receptive cell. The protoplasm of this one is now slipping away from the
cell wall, until finally the two masses round up into the one zygospore.
292. The zygospore. — This zygospore now acquires a thick wall which
eventually becomes brown in color. The chlorophyll color fades out, and a
large part of the protoplasm passes into an oily substance which makes it
more resistant to conditions which would be fatal to the vegetative threads.
The zygospores are capable therefore of enduring extremes of cold and dry-
ness which would destroy the threads. They pass through a "resting"
period, in which the water in the pond may be frozen, or dried, and with the
oncoming of favorable conditions for growth in the spring or in the autumn
they germinate and produce the green thread again.
293. Life cycle.— The growth of the spirogyra thread, the conjugation oi
the gametes and formation of the zygospore, and the growth of the thread
from the zygospore again, makes what is called a complete life cycle.
294. Fertilization.- — While conjugation results in the fusion of the two
masses of protoplasm, fertilization is accomplished when the nuclei of the
two cells come together in the zygospore and fuse into a single nucleus. The
Fig. 131.
Fertilization in spirogyra ; shows different stages of fusion of the two nuclei, with mature
xygospore at right. (After Overton.)
different stages in the fusion of the two nuclei of a recently formed zygospore
are shown in figure 131.
In the conjugation of the two cells, the chlorophyll band of the supplying
cell is said to degenerate, so that in the new plant the number of chlorophyll
bands in a cell is not increased by the union of the two cells.
295. Simplicity of the process. — In spirogyra any cell of the thread
may form a gamete (excepting the holdfasts of some species). Since all of
the cells of a thread are practically alike, there is no structural difference
between a vegetative cell and a cell about to conjugate. The difference is a
physiological one. All the cells are capable of conjugation if the physiolog-
ical conditions are present. All the cells therefore are potential gametes.
(Strictly speaking the wall of the cell is the gametangiutn, while the content
forms the gamete.)
While there is sometimes a slight difference in size between the conjugal-
SPJKOG YRA.
141
ing cells, and the supplying cell may be the smaller, this is not general. We
say, therefore, that there is no differentiation among the1 gametes, so that
usually before the protoplasm begins to move one cannot say which is to be
the supplying and which the receiving gamete.
296. Position of the plant spirogyra. — From our study then we see that
there is practically no differentiation among the vegetative cells, except
where holdfasts grow out from some of the cells for support. They are all
alike in form, in capacity for growth, division, or multiplication of the
threads. Each cell is practically an independent plant. There is no differ-
entiation between vegetative cell and conjugating cell. All the cells are
potential gametes. Finally there is no structural differentiation between the
gametes. This indicates then a simple condition of things, a low grade of
organization.
297. The alga spirogyra is one of the representatives of the lower algae
belonging to the group called Conjugate, Zygnema with star-shaped chloro- \J
plasts, mougeotia with straight or sometimes twisted chlorophyll bands, be-
long to the same group.' In the latter genus only_jjjortior^of thejirptoplasm
of each cell unites to form the zygospore, which is located in the tube between
the cells.
Fig. 133-
Micrasterias
Fig. 134-
Xanthidium.
Fig- 137.
Cosmarium.
298. The desmids also belong to the same group. The desmids usually live
as separate cells. Many of them are beautiful in form. They grow entangled
among other algae, or on the surface of aquatic plants, or on wet soil. Sev-
eral genera are illustrated in figures 132-137.
CHAPTER XV.
VAUCHERIA.
299. The plant vaucheria we remember from our study in
an earlier chapter. It usually occurs in dense mats floating
on the water or lying on damp soil. The texture and feeling of
these mats remind one of "felt,"
and the species are sometimes called
the " green felts." The branched
threads are continuous, that is there
are no cross walls in the vegetative
threads. This plant multiplies it-
self in several ways which would
be too tedious to detail here. But
when fresh bright green mats can be
obtained they should be placed in
a large vessel of water and set in
a cool place. Only a small amount
of the alga should be placed in a
vessel, since decay
will set in more
rapidly with a large
quantity. For
H ' . Fig. 138.
Portion of branched thread of vaucheria.
should look for
small green bodies which may be floating at the side of the vessel
next the lighted window.
300. Zoogonidia of vaucheria. — If these minute floating green bodies are
found, a small drop of water containing them should be mounted for exami-
142
VAUCHERIA. 143
nation. If they are rounded, with sVmler hair-like appendages over the
surface, which vibrate and cause motion, they very likely are one of the
kinds of reproductive bodies of vaucheria. The hair-like appendages are
cilia, and they occur in pairs, several of them distributed over the surface.
These rounded bodies are gonidia, and because they are motile they are
called zoogonidia.
By examining some of the threads in the vessel where they occurred we
may have perhaps an opportunity to see how they are produced. Short
branches are formed on the threads, and the contents are separated from
those of the main thread by a septum. The protoplasm and other contents of
this branch separate from the wall, round up into a mass, and escape through
an opening which is formed in the end. Here they swim around in the
water for a time, then come to rest, and germinate by growing out into a
tube which forms another vaucheria plant. It will be observed that this
kind of reproduction is not the result of the union of two different parts of
the plant. It thus differs from that which is termed sexual reproduction. A
small part of the plant simply becomes separated from it as a special body,
and then grows into a new plant, a sort of multiplication. This kind of re-
production has been termed asexual reproduction,
301. Sexual reproduction in vaucheria. — The organs which are concerned
in sexual reproduction in vaucheria are very readily obtained for study if
one collects the material at the right season. They are found quite readily
during the spring and autumn, and may be preserved in formalin for study
at any season, if the material cannot be collected fresh at the time it is
desired for study. Fine material for study often occurs on the soil of pots in
greenhouses during the winter.
While the zoogonidia are more
apt to be found in material
which is quite green and fresh-
ly growing, the sexual organs
are usually more abundant
when the threads appear some-
what yellowish, or yellow
green.
jgs 302. Vaucheria sessi-
Klg-139- lis; the sessile vauche-
Young antheridium and oogonium of Vaucheria ses- . T , . . ,
silis, before separation from contents of thread by a Ha. in tniS plant 1X16
septum. . -i
sexual organs are sessile,
that is they are not borne on a stalk as in some other species.
The sexual organs usually occur several in a group. Fig. 139
represents a portion of a fruiting plant.
144
MORPHOLOGY.
303. Sexual organs of vaucheria. Antheridium. — The
antheridia are short, slender, curved branches from a main
thread. A septum is formed which separates an end portion
from the stalk. This end cell is the antheridium. Frequently it
is collapsed or empty as shown in fig. 140. The protoplasm in
Fig. 140.
Vaucheria sessilis, one antheridium between two oogonia.
the antheridium forms numerous small oval bodies each with two
slender lashes, the cilia. When these are formed the antherid-
ium opens at the end and they escape. It is after the escape
of these spermatozoids that the antheridium is collapsed. Each
spermatozoid is a male gamete.
304. Oogonium. — The oogonia are short branches also, but
they become large and , *
somewhat oval. The / *
septum which separates the
protoplasm from that of
the main thread is as we
see near the junction of
the branch with the main
thread. The oogonium,
as shown in the figure, is
usually turned somewhat
to one side. When mature the pointed end opens and a bit of the
protoplasm escapes. The remaining protoplasm forms the large
rounded egg cell which fills the wall of the oogonium. In some
of the oogonia which we examine this egg is surrounded by a
thick brown wall, with starchy and oily contents. This is the
Fig. 141.
Vaucheria sessilis ; oogonium opening and emit-
ting a bit of protoplasm ; spermatozoids ; sperma-
tozoids entering oogonium. (After Pringsheim and
Goebel.)
VA UCHERIA.
fertilized egg (sometimes called here the oospore) . It is freed
from the oogonium by the disintegration of the latter, sinks into
Fig. 142.
Fertilization in vaucheria. mn, male nucleus ; fn, female nucleus. Male nucleus entering
the egg and approaching the female nucleus. (After Oltmans.)
the mud, and remains here until the following autumn or spring,
when it grows directly into a new plant.
305. Fertilization. — Fertilization is accomplished by the
spermatozoids swimming in at the open end of the oogonium.
%mim& wpm&s^ '
?,"/? ^^yWfcn $•'$:*%'£':> ':'•?*?•{;•':''•' v
Fig. 143.
Fertilization of vaucheria. fn, female nucleus; mn, male nucleus. The different figures
show various stages in the fusion of the nuclei.
when one of them makes its way down into the egg and fuses
with the nucleus of the egg.
366. The twin vaucheria (V. geminata). — Another species of vaucheria
is the twin vaucheria. This is also a common one, and may be used for
study instead of the sessile vaucheria if the latter cannot be obtained. The
sexual organs are borne at the end of a club-shaped branch. There are
usually two oogonia, and one antheridium between them which terminates
the branch. In a closely related species, instead of the two oogonia there is
a whorl of them with the antheridium in the center.
307. Vaucheria compared with spirogyra. — In vaucheria we have a plant
•hich is very interesting to compare with spirogyra in several respects.
146
MUKPHOLOG Y.
Growth takes place, not in all parts of the thread, but is localized at the ends
of the thread and its branches. This represents a distinct advance on such
a plant as spirogyra. Again, only specialized parts of the plant in vaucheria
form the sexual organs. These are short branches. Farther there is a great
difference in the size of the two organs, and especially in the size of the
gametes, the supplying gametes (spermatozoids) being very minute,
while the receptive gamete is large and contains all the nutriment for the
fertilized egg. In spirogyra, on the other hand, there is usually no differ-
ence in size of the gametes, as we have seen, and each contributes equally in
the matter of nutriment for the fertilized egg. Vaucheria, therefore, rep-
resents a distinct advance, not only in the vegetative condition of the plant,
but in the specialization of the sexual organs. Vaucheria, with other related
algae, belongs to a group known as the Siphonece, so called because the plants
are tube-like or siphon-\i\ae.
308. Botrydium granulatum, — An example of one of the simpler
members of the Siphoneae is
Botrydium granulatum. It is
found sometimes in abundance
on wet ground which is colored
green or red by its presence,
according to the stage of de-
velopment. The plant body is
long pear-shaped, the smaller
end attached to the ground by
slender branched rhizoids (Fig.
143). The protoplasm contains
many nuclei and lines the inside
of the wall. When multiplication
takes place large numbers of
small zoospores with one cilium
each are formed in the proto-
plasm, and escape at free end.
Reproduction takes place by
two-ciliated gametes, which fuse
in pairs to form zygospores. In
dry seasons the protoplasm in
the pear-shaped plant passes
down into the rhizoids and
forms small rounded planospores.
All the stages of 4 development are too complicated to describe here.
Fig. 143.1.
Botrydium granulatum. A, the whole
plant; B, swarm spore; C, planogametes ; a,
a single gamete; b-e, two gametes in process
of fusion; }, zygote.
CHAPTER XVI.
CEDOGONIUM.
309. CEdogonium is also an alga. The plant is sometimes
associated with spirogyra, and occurs in similar situations. Our
attention was called to it in the study of chlorophyll bodies.
These we recollect are, in this plant, small oval disks, and thus
differ from those in spirogyra.
310. Form of cedogonium. — Like spirogyra, cedogonium
forms simple threads which are made up of cylindrical cells
placed end to end. But the plant is very different from any
member of the group to which spirogyra belongs. In the first
place each cell is not the equivalent of an individual plant as in
spirogyra. Growth is localized or confined to certain cells of
the thread which divide at one end in such a way as to leave a
peculiar overlapping of the cell walls in the form of a series of
shallow caps or vessels (fig. 144), and this is one of the character-
istics of this genus. Other differences we find in the manner of
reproduction.
311. Fruiting stage of cedogonium. — Material in the fruiting
stage is quite easily obtainable, and may be preserved for study
in formalin if there is any doubt about obtaining it at the time
we need it for study. This condition of the plant is easily de-
tected because of the swollen condition of some of the cells, or
by the presence of brown bodies with a thick wall in some of the
cells.
312. Sexual organs of oedogonium. Oogonium and egg.—
The enlarged cell is the oogonium, the wall of the cell being the
walloftheoogonium. (See fig. 145.) The protoplasm inside, before
'47
148
MORPHOLOG Y.
fertilization, is the egg cell. In those cases where the brown body
with a thick wall is present fertilization has taken place, and this
body is the fertilized egg, oroospore. It contains
large quantities of an oily substance, and, like
Fig. 144-
Portion o f
thread of oedo-
gonium, show-
ing chlorophyll
grains, and pe-
culiar cap cell
walls.
tig. I4S-
CEdogoniuin undulatum, with oogonia and dwarf males;
the upper oogonium at the right has a mature oospore.
the fertilized egg of spirogyra and vaucheria, is able to with-
stand greater changes in temperature than the vegetative stage,
and can endure drying and freezing for some time without
injury.
In the oogonium wall there can frequently be seen a rift near
the middle of one side, or near the upper end. This is the
(EDOGONIUM.
149
opening through which the spermatozoid entered to fecundate
the egg.
313. Dwarf male plants. — In some species there will also be
seen peculiar club-shaped dwarf plants attached to the side of the
oogonium, or near it, and in many cases the end of this dwarf
plant has an open lid on the end.
314. Antheridium. — The end cell of the dwarf male in such
species is the anther idium. In other species the spermatozoids
are developed in different cells (antheridia) of the same thread
which bears the oogonium, or on a different thread.
315. Zoospore stage of oedogonium. — The egg after a period of rest starts
into active life again. In doing so it does not develop the thread-like plant
directly as in the case of vaucheria and spirogyra. It first divides into four
zoospores which are exactly like the zoogonidia in form. (See fig. 152.)
These germinate and develop the thread form again. This is a quite re-
markable peculiarity of cedogonium when compared with either vaucheria
or spirogyra. It is the introduction of an intermediate stage between the
fertilized egg and that form of the plant which bears the sexual organs, and
should be kept well in mind.
316. Asexual reproduction. — Material for the study of this stage of oedo-
gonium is not readily obtainable just when we wish it for study. But fresh
plants brought in and placed in a
quantity of fresh water may yield
suitable material, and it should be
examined at intervals for several
days. This kind of reproduction
takes place by the formation of
zoogonidia. The entire contents
of a cell round off into an oval
body, the wall of the cell breaks,
and the zoogonidium escapes. It
has a clear space at the small
end, and around this clear space
Fig. 146.
Zoogonidia of oedogonium escaping.
At the right one is germinating and
forming the holdfasts, by means of which
these algs attach themselves to objects
for support. (After Pringsheim.)
is a row or crown of cilia as shown in fig. 146. By the vibration of these cilia
the zoogonidium swims around for a time, then settles down on some object of
support, and several slender holdfasts grow out in the form of short rhizoids
which attach the young plant.
317. Sexual reproduction. Antheridia. — The antheridia are short cells
which are formed by one of the ordinary cells dividing into a number of
disk-shaped ones as shown in fig. 147. The protoplasm in each antheridium
MORPHOLOGY.
forms two spermatozoids (sometimes only one) which are of the same form as
the zoogonidia but smaller, and yellowish instead of green. In some species
a motile body intermedi-
ate in size and color be-
tween the spermatozoids
and zoogonidia is first
formed, which after
swimming around comes
to rest on the oogonium,
or near it, and develops
what is called a "dwarf
male pl?nt " from which
the real spermatozoid is
produced.
Fig. 148. «1Q n • rp,
Portion of thread of oedo-
gonium showing upper half oogonia are formed di-
of egg open, and a sperma- , , f , .,
tozoid ready to enter. (After rectly trom one of the
Klebahn). vegetative cells. Inmost
species this cell first enlarges in diameter, so that it is easily detected. The
protoplasm inside is the egg cell. The oogonium wall opens, a bit of the
protoplasm is emitted, and the spermatozoid then enters and fertilizes it
(fig 148). Now a hard brown wall is formed around it, and, just as in spirogyra
Fig. 147.
Portion of thread
o f cedogonium
showing antheridia
Fig. 149-
Male nucleus just entering
egg at left side.
Fig. 150. Fig. 151.
Male nucleus fusing with The two nuclei fused, and
fertilization complete.
female nucleus.
Figs. 149-151. — Fertilization in oedogonium. (After Klebahn).
and vaucheria, it passes through a resting period. At the time of germinatior
it does not produce the thread-like plant again directly, but first forms foui
zoospores exactly like the zoogonidia (fig. 152). These zoospores ther
germinate and form the plant.
319. (Edogonium compared with spirogyra. — Now if we compare cedo-
gonium with spirogyra, as we did in the case of vaucheria, we find here also
that there is an advance upon the simple condition which exists in spiro-
gyra. Growth and division of the thread is limited to certain portions. The
sexual organs are differentiated. They usually differ in form and size from
the vegetative cells, though the oogonium is simply a changed vegetative
(EDOGONIUM. 151
cell. The sexual organs are differentiated among themselves, the antheridium
is small, and the oogonium large. The gametes are also differentiated in
size, and the male gamete is motile, and carries in its body the nucleus
which fuses with the nucleus of the egg cell.
But a more striking advance is the fact that the fertilized egg does not
Fig. 152.
' Fertilized egg of cedogonium after a period of rest escaping from the wall of the oogonium,
and dividing into the four zoospores. (After Juranyi.)
produce the vegetative thread of cedogonium directly, but first forms four
zoospores, each of which is then capable of developing into the thread. On
the other hand we found
that in spirogyra the zygp-
spore develops directly
into the thread form of the
plant.
320. Position of cedo-
gonium. — GEdogonium is
one of the true thread-like
algae, green in color, and
the threads are divided
into distinct cells. It,
along with many relatives,
was once placed in the old
genus conferva. These are all now placed in the group
Confervoidea, that is, the conferva-like alga. v ,„
321. Kelatives of cedogonium. — Many other genera Portion of chsetophora
are related to oedogonium. Some consist of simple showing branchmg.
threads, and others of branched threads. An example of the branched
forms is found in chastophora, represented in figures 153, 154. This plant
grows in quiet pools or in slow-running water. It is attached to sticks, rocks,
or to larger aquatic plants. Many threads spring from the same point of
attachment and radiate in all directions. This, together with the branching
of the threads, makes a small, corrpact, greenish, rounded mass, which is
Fig. i S3-
Tuft of chzto-
phora, natural
size.
152 MORPHOLOGY.
held firmly together by a gelatinous substance. The masses in this species
are about the size of a small pea, or smaller. Growth takes place in chae-
tophora at the ends of the threads and branches. That is, growth is api-
cal. This, together with the branched threads and the tendency to form
cell masses, is a great advance of the vegetative condition of the plant upon
that which we find in the simple threads of oedogonium.
I
CHAPTER XVII.
COLEOCH^TE.
322. Among the green algae coleochaete is one of the most
interesting. Several species are known in this country. One
of these at least should be examined if it is possible to obtain it.
It occurs in the water of fresh lakes and ponds, attached to
aquatic plants.
323. The shield-shaped coleochaete. — This plant (C. scutata)
Fig. iSS.
Stem o f
aquatic plant
showing co-
leo c hae t e,
natural size.
Fig. 156.
Thallus of Coleochane scutata.
is in the form of a flattened, circular, green plate, as shown in
fig. 156. It is attached near the center on one side to rushes
154
MORPHOLOGY.
and other plants, and has been found quite abundantly for sev-
eral years in the waters of Cayuga Lake at its southern extremity.
As will be seen it consists of a single layer of green cells which
radiate from the center in branched rows to the outside, the cells
lying so close together as to form a continuous plate. The plant
started its growth from a single cell at the central point, and grew
at the margin in all directions. Sometimes they are quite irregu-
lar in outline, when they lie quite closely side by side and inter-
fere with one another by pressure. If the surface is examined
carefully there will be found long hairs, the base of which is en-
closed in a narrow sheath. It is from this character that the
genus takes its name of coleochaete (sheathed hair).
324. Fruiting stage of coleochsete. — It is possible at some
seasons of the year to find rounded masses of cells situated near
the margin of this green disk. These have developed from a
fertilized egg which remained attached to the plant, and prob-
ably by this time the parent plant has lost its color.
325. Zoospore stage. — This mass of tissue does not develop
directly into the circular green disk, but each of the cells forms
a zoospore. Here then, as
in oedogonium, we have an-
other stage of the plant in-
terpolated between the fer-
tilized egg and that stage
of the plant which bears the
gametes. But in coleochaete
we have a distinct advance in
this stage upon what is pres- Fig. 157.
ent in oedogonium. for in. Portion of thallus of Co-
leochaete scutata, showing
coleochsete the fertilized emP4y cells from which
zoogomdia have escaped,
egg develops first into a °"e. from e,ach ,c?n i z°°g°- gle spermatozoid at
mdia at the left. (After the right. (After
Several-Celled maSS Of tissue Pnngsheim.) Pringsheim.)
before the zoospores are formed, while in oedogonium only four
zoospores are formed directly from the egg.
326. Asexual reproduction. — In asexual reproduction any of the green
cells on the plant may form zoogonida. The contents of a cell round off and
Fig 158.
Portion ot thallus
of Coleochaste
scutata, showing
four antheridia
formed from one
thallus cell ; a sin-
COLEOCH&TE.
155
form a single zoogonidium which has two cilia at the smaller end of the oval
body, fig. 157. After swimming around for a time they come to rest, ger-
minate, and produce another plant.
327. Sexual reproduction. — Oogonium. — The oogonium is formed by the
enlargement of a cell at the end of one of the threads, and then the end of the
Oog--
Fig. ISO-
Coleochaste soluta; at left branch bearing oogonium (oog); antheridia (tint); egg in
oogonium and surrounded by enveloping threads ; at center three antheridia open, and one
spermatozoid ; at right sporocarp, mature egg inside sporocarp wall.
cell elongates into a slender tube which opens at the end to form a channel
through which the spermatozoid may pass down to the egg. The egg is
formed of the contents of the cell (fig. 159). Several oogonia are formed on
one plant, and in such a
plant as C. scutata they are
formed in a ring near the
margin of the disk.
328. Antheridia.— In C.
scutata certain of the cells
of the plant divide into four
smaller cells, and each one
of these becomes an antheri-
Fig.i6o. Fig. 161. .. T „ . .
Two sporocarps still Spororarp ruptured bv dmm' I" C. soluta the an-
surrounded by thallus. growth of egg to form cell theridia grow out from the
Thallus finally decays and mass. Cells of this sporo- ... .
sets sporocarp free. phyte forming zoospores. end of terminal Cells 111 the
Figs.i6o. 161. C. scutata. form of short flasks, some-
times four in number or less (fig. 159). A single spermatozoid is formed
from the contents. It is oval and possesses two long cilia. After swim-
^^£
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1 56 MORPffOLOG Y.
ming around it passes down the tube of the oogonium and fertilizes the
egg-
329. Sporocarp. — After the egg is fertilized the cells of the threads near
the egg grow up around it and form a firm covering one cell in thickness.
This envelope becomes brown and hard, and serves to protect the egg. This
is the "fruit" of the coleochsete, and is sometimes called a sporocarp
(spore fruit). The development of the cell mass and the zoospores from the
egg has been described above.
Some of the species of coleochsete consist of branched threads, while others
form circular cushions several layers in thickness. These forms together
with the form of our plant C. scutata make an interesting series of transi-
tional forms from filamentous structures to an expanded plant body formed
of a mass of cells.
COMPARISON OF ALG^E.
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CHAPTER XVHI.
CLASSIFICATION AND ADDITIONAL STUDIES OF
THE ALGyE.
In order to show the general relationship of the algae studied, the princi-
pal classes are here enumerated as well as some of the families. In some
of the groups not represented by the examples studied above, a few species
are described which may serve as the basis of additional studies if desired.
The principal classes * of algae are as follows:
Class Chlorophyceae.
331. These are the green algae, so called because the chlorophyll green
is usually not masked by other pigments, though in some forms it is. There
are three subclasses.
332. Subclass PBOTOCOCCOIDE.E. — In the Protococcoideae are found the
simplest green plants. Many of them consist of single cells which live an
independent life. Others form "colonies," loose aggregations of individ-
uals not yet having attained the permanency of even a simple plant body,
for the cells often separate readily and are able to form new colonies. The
colonies are often held together by a gelatinous membrane, or matrix.
Some are motile, while others are non-motile. A few of the families are
here enumerated.
333. Family Volvocaceae. — These are all motile, during the vegetative
stage. The individuals are single or form more or less globose colonies.
334. The "red snow" plant (Sphaerella nivalis). — This is often found in
arctic and alpine regions forming a red covering over more or less large
areas of snow or ice. For this reason it is called the "red snow plant."
335. Sphaerella lacustris, a closely related species, is very widely dis-
tributed in temperate regions along streams or on the borders of lakes and
* In Engler & Prantl's Pflanzenfamilien, Wille uses the term class for
these principal subdivisions of the algae. Systomatists are not yet agreed
upon a uniform use of the terms.
158
ALG& CONTINUED: CLASSIFICATION.
'59
ponds, ofcere in dry weather it is often found closely adhering to the dry
rock surface, and giving it a reddish color as if the rock were painted. T his
is especially the case in the shallow basins formed over the uneven surface
of the rock near the water's edge. These places during heavy rains or in
high water are provided with sufficient water to fill the basins. During
such times the red snow plant grows and multiplies, loses its red color and
c
Fig. 163.
Sphaerella lacustris (Girod.) Wittrock. A, mature free-swimming individual
with central! red spot. B, division of mother individual to form two. C, divi-
sion of a red one to form four. D, division into eight. E, a. typical resting cell,
red. F, same beginning to divide. G, one of four daughter zoospores after
swimming around for a time losing its red color and becoming green. (After
Hazen.)
becomes green, and, being motile, is free swimming. It is a single-celled
plant, oval in form, surrounded by a gelatinous sheath and with two cilia
or flagella at the smaller end, by the vibration of which it moves (fig. 162).
The single cell multiplies by dividing into two cells. When the water dries
out of the basin, the motile plant comes to rest, and many of the cells assume
the red color. To obtain the plant for study, scrape some of the red cov-
ering from these rock basins and place it in fresh spring water, and in a da]
or so the swarmers are likely to be found. Under certain conditions small
microzoids are formed.
336. Chlamydomonas is a very interesting genus of motile one-celled
green alg«, because the species are closely related to the Flagellates among
the lower animals. The plant is oval, with a single chloroplast and sur-
rounded by a gelatinous envelope through which the two cilia or flagella
extend. One-celled organisms of this kind are sometimes called monads,
i.e., a one-celled being. This one has a gelatinous cloak and is, therefore,
a cloaked monad (Chlamydomonas). The species often are found as a very
thin green film on fresh water. C. pulvisculus is shown in fig. 163. When
it multiplies the single cell divides into two, as shown in B. Sometimes a
non-motile palmella stage is formed, as shown in C and D. Reproduction
i6o
MORPHOLOGY.
takes place by gametes which are of unequal size, the smaller one repre-
senting the sperm and the larger one the egg, as in E and F. These con-
e a
Fig. 163.
Chlamydomonas pulvisculus (Mull.) Ehrb. A, an old motile individual; n,
nucleus; p, pyrenoid; s, red eye spot; v, contractile vacuole; B, motile indi-
vidual has drawn in its cilia and divided into two; C, mother plant has drawn
in its cilia and divided into four non-motile cells; D, pamella stage; E, female
gamete — egg; F, male gamete — sperm ; G, early stage of conjugation; H, zygo-
spore with conjugating tube and empty male cell attached. (After Wille.)
jugate as in G and H , the protoplasm of the smaller one passing over into
the larger one, and a zygospore is thus formed.
337. Of those which form colonies, Pandorina morum is widely dis-
tributed and not rare. It consists of a sphere formed of sixteen individuals
enclosed in a thin gelatinous mem-
brane. Each cell possesses two cilia
(or flagella), which extend from the
broader end out through the envelop-
ing membrane. By the movement
of these flagella the colony goes roll-
ing around in the water. When the
plant multiplies each individual cell
divides into sixteen small cells, whkh
then grow and form new colonies.
Reproduction takes place when the
individual cells of the young colonies
separate, and usually a small indi-
vidual unites with a larger one and
a zygospore is formed (see fig. 164).
Eudorina elegans is somewhat similar,
I, but when the gametes are formed cer-
tain mother cells divide into sixteen
small motile males or sperms, and
certain other mother cells divide into
sixteen large motile females or eggs.
These separate from the colonies, and
the sperms pair with the eggs and fuse to form zygospores. This plant as
well as Chlamydomonas pulvisculus foreshadows the early differentiation of
sex in plants.
Fig. 164.
Pandorina morum (Mlill.) Bory.
motile colony; II, colony divided into
1 6 daughter colonies; III, sexual colony,
gametes escaping; IV, V, conjugating
gametes; VI, VII, young and old zygo-
spore; VIII. zygospore forming a large
young colony.
.
ter Pnngsheim.)
CONTINUED: CLASSIFICATION.
161
338. Family Tetrasporacese. — This family is well represented by Tetra-
spora lubrica forming slimy green net-like sheets attached to objects in
slow-running water. It is really a single-celled plant. The rounded cells
divide by cross walls into four cells, and these again, and so on, large num-
bers being held in loose sheets by the slime in which they are imbedded.
339. Family Pleurococoaceae. — The members of this family are all non-
motile in the vegetative stage. They consist of single individuals, or of
colonies. Pleurococcus vulgaris (Protococcus vulgaris)
is a single-celled alga, usually obtained with little difficulty.
It is often found on the shaded, and cool, or moist side of
trees, rocks, walls, etc., in damp places. This plant is
not motile. It multiplies by fission (fig. 165) into two,
then four, etc. These cells remain united for a time, then
separate. Sometimes the cells are found growing out into
filaments, and it is thought by some that P. vulgaris may
be only a simple stage of a higher alga. Eremosphaera
viridis is another single-celled alga found in fresh water
among filamentous forms. The cells are large and globose.
340. Family Hydrodictyaceae. — These plants form colonies of cells.
Hydrodictyon reticulatum, the water net, is made up of large numbers of
cylindrical cells so joined at their ends as to form a large open mesh or net.
Pediastrum forms circular flat colonies, as shown in fig. 1 66. Both of these
Fig. 165.
Pleurococcus
(protococcus)
vulgaris.
Fig. 1 66.
Pediastrum boryanum. A, mature colony, most of the young colonies have
escaped from their mother cells; at g, a young colony is escaping; sp, empty
mother cells; B, young colony; C, same colony with spores arranged in order.
(After Braun.)
plants are rather common in fresh-water pools, the latter one intermingled
with filamentous alga, while the former forms large sheets or nets. Mul-
tiplication in Hydrodictyon takes place by the pro'.cplasm in one of the cells
1 62
MORPHOLOG y.
dividing into thousands of minute cells, which gradually arrange themselves
in the form of a net, escape together from the mother cell, and grow into a
large net. In Pediastrum multiplication takes place in a similar way, but
the protoplasm in each cell usually divides into sixteen small cells, and
escaping together from the mother cell arrange themselves and grow to full
size (fig. 1 66).
341. The Conjugateae include several families of green algae, which prob-
ably should be included among the Chlorophycese. They have probably
had their origin from some of the more simple members of the Protococ-
coideae. They are represented by Spirogyra, Zygnema, and the desmids,
studied in Chapter 14.
342. Subclass CONFERVOIDEJE.— These are mostly filamentous algae, the
filaments being composed of cells firmly united, and, with the exception of
the simplest forms, there is a definite growing point. A few of the families
are as follows:
343. Family Ulvaceae. — These contain the sea wracks, or sea lettuce,
like Ulva, forming expanded
green, ribbon-like growths in the
sea.
344. Family Ulotrichaceas,
represented by Ulothrix z,onata,
not uncommon in slow-running
water or in ponds of fresh water
attached to rocks or wood. It
consists of simple threads of
short cells. Multiplication takes
place by zoospores. Repro-
duction takes place by motile
sexual cells (gametes) which
fuse to form a zygospore (fig.
345. Family Chaetophoraceae.
£
Fig. 167.
Ulothrix zonata. A, base of thread. B,
cells with zoospores, C, one cell with zoospores
escaping another cell with small biciliate
gametes escaping and some fusing to form , , _,
zygospores, £, zoospores germinating and represented by Lnaetophora (in
forming threads F £ zygospore growing and chapter 15) and Drapernaudia
forming zoospores. (Alter Caldwell and Dodel-
Port.) in fresh water.
346. Family (Elogoniacese, represented by CEdogonium (Chapter 16).
347. Family Coleochaetaceae, represented by Coleochaete (Chapter 17).
348. Subclass SIPHONEJE. — There are several families.
349. Family Botrydiaceae. — This is represented by Botrydium granu-
latum (Chapter 15, p. 146).
350. Family Vaucheriaceae, represented by Vaucheria (Chapter 15), with
quite a large number of species, is widely distributed.
ALGM CONTINUED: CLASSIFICATION.
Class Schizophyceae ( = Cyanophyceae).
351. The Blue Green Algae, or Cyanophycese form slimy looking thin
mats on damp wood or the ground, or floating mats or scum on the water.
The color is usually bluish green, but in some species it is purple, red or
brown. All have chlorophyll, but it is not in distinct chloroplasts and is
more or less completely guised by the presence of other pigments. Two
orders and eight families are recognized. The following include some of
our common forms:
352. ORDER COCCOGONALES (COCCOGONE2E).— Single-celled plants,
occurring singly or in colonies, in some forms
forming short threads. One of the two fami-
lies is mentioned.
353. Family Chroococcaceae. — The plants
multiply only through cell division. Chroococ-
cus, forms rounded, blue-green cells enclosed
in a thick gelatinous coat, in fresh water and
in damp places; certain species form "lichen-
gonidia" in some genera of lichens. Glceo-
capsa is similar co Chroococcus, but the col-
onies are surrounded by an additional common
gelatinous envelope (fig. 168); on damp rocks,
etc.
354. ORDER HORMOGONALES (HORMOGONEJE).— Plants filamentous,
simple celled or with false
or true branching, usually
several celled (Spirulina is
single celled). Multiplica-
tion takes place through
hormogones, short sections
of the threads becoming
free; also through resting
cells. Two of the six fami-
lies are mentioned.
355. Family Oscillatorl-
aceae. — This family is rep-
resented by the genus Oscil-
latoria, and by several other
genera common and widely
Fig. 1 68.
Gloeocapsa.
Fig. 169.
A, Oscillatoria princeps, a terminal cell; b,
portions from the middle of a filament. In c,
dead cell is shown between the living cells; B,
Oscillatoria froelichii, b, with granules along the contains
partition walls.
They are
distributed. Oscillatoria
many species,
found on the
damp ground or wood, or floating in mats in the water. They often form on
164
MORPHOLOG Y.
the soil at the bottom of the pool, and as gas becomes entangled in the mat
of threads, it is lifted from the bottom and floated to the surface of the water.
The plant is thread-like, and divided up into many short cells. The
threads often show an oscillating movement, whence the name Oscillatoria.
356. Family Nostocacese. — This family is represented by Nostoc, which
forms rounded, slimy, blue-green masses on
wet rocks. The individual plants in the
slimy ball resemble strings of beads, each
cell being rounded, and several of these ar-
ranged in chains as shown in fig. 1 70. Here
and there are often found larger cells (hetero-
cysts) in the chain. Nostoc punctiforme
lives in the intercellular spaces of the roots
of cycads (often found in greenhouses), and
in the stems of Gunnera. N. sphaericum
lives in the spaces between the cells in many
species of liverworts (in the genera Antho-
ceros, Blasia, Pellia, Aneura, Riccia, etc.),
and in the perforated cells of Sphagnum
acutifolium. Anabaena is another common
and widely distributed genus. The species
occur in fresh or salt water, singly or in slimy
Fig. 170.
Nostoc linckii. A, filament
with two heterocysts (h), and a masses. Anabaena azollae lives endophyti-
germinate ;
developed from
Bornet.)
'oore SSXng*to cally in the leaves of the water fern, Azolla.
C, young filament
Class Schizomycetes.
spore. (After
B
857. Bacteriales. — The bacteria are sometimes classified with the Cyano-
phyceae, under the name Schizophyta, and represent the subdivision Schiz-
omycetes, or fission fungi, because
many of them multiply by a divis-
ion of the cells justas the blue-green
algae do. For example, Bacillus
forms rods which increase in length
and divide into two rods, or it may
grow into a long thread of many
short rods. Micrococcus consists Fi8- ll*-
... j j 11 C4. Bacteria. A, Bacillus subtilis. Spores
of single rounded cells. Strepto- in threadSi unstained rods, and stained rods
coccus forms chains of rounded showing cilia; fi Bacillus tetani, the teta-
nus or lockjaw bacillus, found in garden
cells, Sarcina forms irregular cubes soil and on old rusty nails. Spores in club-
, . j ii v-i tu 1-1 shaped ends. C, Micrococcxis ; D., Sarcina;
of rounded cells, while others like E Streptococcus; F, Spirillum. (After
Spirillum are spiral in form. Migula.)
Bacillus subtilis may be obtained by making an infusion from hay and
I
ALG& CONTINUED: CLASSIFICATION. 165
allowing it to stand for several days. Bacillus tetani occurs in the soil, on
old rusty nails, etc. It is called the tetanus bacillus because it causes a
permanent spasm of certain muscles, as in "lockjaw." This bacillus
grows and produces this result on the muscles when it occurs in deep and
closed wounds such as are caused by stepping on an old nail or other object
which pierces the flesh deeply. In such a deep wound oxygen is deficient,
and in this condition the bacillus is virulent. Opening the wounds to
admit oxygen and washing them out with a solution of bichloride of mer-
cury prevents the tetanus. Many bacteria are of great importance in bring-
mg about the decay of dead animal and plant matter, returning it to a con-
dition for plant food. (See also nitrate and nitrite bacteria, Chapter IX.)
While roost bacteria are harmless there are many which cause very serious
diseases of rfian and animals, as typhoid fever, diphtheria, tuberculosis, etc.,
while some others produce disease in plants. Others aid in certain fer-
mentations or liquids and are employed for making certain kinds of wines
or other beverages. Some work in symbiosis with yeasts, as in the kephir
yeast, used in fenrnfndng certain crude beverages by natives of some coun-
tries.
357a. Myxobacterial«« (Hyxobacteriaceae Thaxter *). — These plants con-
sist of colonies of bacterla-hke organisms, motile rods, which multiply by
cross-division and secrete a gelatinous substance or matrix which surrounds
the colonies. They form plasmodium-like masses which superficially
resemble the slime moulds. In the fruiting stage some species become
elevated from the substratum into cylindrical, clavate, or branched forms,
which bear cysts of various shapes containing the rods in a resting stage,
or the rods are converted into spore-like masses. Ex., Chondromyces
crocatus on decaying plant parts, Myxobacter aureus on wet wood and
bark, Myxococcus rubescens on dung, decaying lichens, paper, etc.
Class Flagellata.
358. The flagellates are organisms of very low organization resembling
animals as much as they do plants. They are single celled and possess two
cilia or flagella, by the vibration of which they move. Some are without a
cell wall, while others have a well-defined membrane, but it rarely consists
of cellulose. Some have chromatophores and are able to manufacture
carbohydrates like ordinary green plants. These are green in Euglena,
and brown in Hydrurus. Some possess a mouth-like opening and are able
to in jest solid particles of food (more like animals), while others have no
such opening and absorb food substances dissolved in water (more like
plants). The Euglena viridis is not uncommon in stagnant water, often
forming a greenish film on the water.
* See Bot. Gaz., 17, 389, 1892.
1 66
MORPHOLOG Y.
Class Peridineae.
358a. These are peculiar one-celled organisms provided with two flagella
and show some relationship to the Flagellates. They usually are provided
with a cellulose membrane, which in some forms consists of curiously
sculptured plates. In the higher forms this cellulose membrane consists of
two valves fitting together in such a way as to resemble some of the diatoms.
Like the Flagellates, some have green chromatophores, which in some are
obscured by a yellow or brown pigment (resembling the diatoms), while
still others have no chlorophyll. The Peridinese are abundant in the sea,
while some are found in fresh water.
Class Diatomaphyceae (Bacillariales, Diatomaceee).
358&. The diatoms are minute and peculiar organisms believed to be
algae. They live in fresh, brackish, and salt water. They are often found
covering the surface of rocks, sticks, or the soil in thin sheets. They occur
singly and free, or several individuals may be joined into long threads, or
other species may be attached to objects by slender gelatinous stalks. Each
abed i /,
rra
Fig. 1710.
A group of Diatoms: c and d, top and side views of the same form; e, colony
of stalked forms attached to an alga; j and g, top and side views of the form shown
at e: h, a colony; i, a colony, the top and side view shown at k and n, forming auxo-
spores. (After Kerner.)
protoplast is enclosed in a silicified skeleton in the form of a box with two
halves, often shaped like an old-fashioned pill box, one-half fitting over the
other like the lid of a box. It is evident that in this condition the plant
cannot increase much in size.
They multiply by fission. This takes place longitudinally, i.e., in the
direction of the two halves or valves of the box. Each new plant then has a
valve only on one side. A new valve is now formed over the naked half,
and fits inside the old valve. At each division the individuals thus become
smaller and smaller until they reach a certain point, when the valves are
cast off and the cell forms an auxospore, i.e,, it grows alone, or after conju-
gation with another, to the full size again, and eventually provides itself
ALGM CONTINUED: CLASSIFICATION.
I67
*dth new valves. The valves are often marked with numerous and fine
lines, often making beautiful figures, and some are used for test objects for
microscopes.
The free forms are capable of movement. The movement takes place in
the longitudinal direction of the valves. They glide for some time in one
direction, and then stop and move back again. It is not a difficult thing to
mount them in fresh water and observe this movement.
The diatoms have small chlorophyll plates, but the green color is dis-
guised by a brownish pigment called diatomin. The relationships of the
diatoms are uncertain, but some, because of the color, think they are re-
lated to the Phaeophyceae.
Class Phaeophyceae.
869. The brown algae. (Phaeophyceae). — The members of this class pos-
sess chlorophyll, but it is obscured by a brown pig-
ment. The plants are accessible at the seashore,
and for inland laboratories may be preserved in
formalin (2^ per cent). (See also Chapter LVI.)
360. Ectocarpus. — The genus Ectocarpus repre-
sents well some of the simpler forms of the brown
algae (fig. 172). They are slender, filamentous
branched algae growing in tufts, either epiphytic on
other marine algae (often on Fucaceae), or on stones.
The slender threads are o:.ly divided crosswise,
and thus consist of long series of short cells. The
sporangia are usually plurilocular (sometimes uni-
Fig. 172-
A Ectocarpus siliculosus; B, branch with a young and a ripe
plurilocular sporangium; E, gametes fusing to form zygospore.
(B, after Thuret; E, after Berthold.)
1 68
MORPHOLOG Y.
Fig. 173-
Sphacelaria, portion
locular), and usually occur in the place of lateral branches. The zoospores.
escape from the apex of the sporangium and are biciliate, and they fuse to
form zygospores.
361. Sphacelaria. — The species of this genus repre-
sent an advance in the development of the thallus.
While they are filamentous and branched, division
takes place longitudinally as well as crosswise (fig.
173).
362. Leathesia difformis represents an interesting
type because the plant body is small, globose, later
irregular and hollow, and consists of short radiately
arranged branches, the surface ones in the form of
short, crowded, but free, trichome-like green branches.
This trichothallic body recalls the similar form of
Sphacelana, portion „,. ..... .,„, -,.
of plant slwwing longi- Chaetophora pisiformis (Chapter 16) among the
tudinal division of cells, rhlnrnnVwrpsp
and brood bud; (pluri- UHorophyceae.
locular sporangium). 363. The Giant Kelps. — Among the brown algae
are found the largest specimens, some of the laminarias or giant
kelps, rivaling in size the largest land plants,
and some of them have highly developed tissues.
Postelsia palma/ormis has a long, stout stem, from
the free end of which extend numerous large and
long blades, while the stem is attached to the rocks
by numerous "root" like outgrowths, the holdfasts.
It occurs along the northern Pacific coast, and
appears to flourish where it receives the shock of
the surf beating on the shore. Several species of
Laminaria occur on our north Atlantic coast. In
L. digitata, the stem expands at the end into a
broad blade, which becomes split into several
smaller blades (fig. 174). Macrocystis pyri/era
inhabits the ocean in the southern hemisphere, and
sometimes is found along the north American
coast. It is said to reach a length of 200-300
meters.
364. Fucus, or Rockweed. — This plant is a more
or less branched and flattened thallus or "frond."
One of them, illustrated in fig. 119, measures
I5~3OCOT (6-12 inches) in length. It Is attached to
rocks and stones which are more or less exposed at low tide. From the base
of the plant are developed several short and more or less branched expansions
called "holdfasts," which, as their name implies, are organs of attachment.
Some species (F. vesiculosus) have vesicular swellings in the thallus.
Fig. 174.
Laminaria digitata,
forma cloustoni, North
Sea. (Reduced, i
A G& CONTINUED: CLASSIFICA TION.
169
The fruiting portions are somewhat thickened as shown in the figure.
Within these portions are numerous oval cavities opening by a circular pore,
which gives a punctate appearance to these fruiting cushions. Tufts of hairs
frequently project through them.
365. Structure of the conceptacles. — On making sections of the fruiting
portions one finds the walls of the cavities covered with outgrowths. Some
of these are short branches which bear a large rounded terminal sac, the
Fig. 177-
Oogonium of Fucus
with ripe eggs.
Fig. 175-
Portion of plant of Fucus show-
ing conceptacles in enlarged ends;
and below the vesicles (Fucus
vesiculosus).
Fig. 176.
Section of conceptacle of Fucus, showing
oogonia, and tufts of an.heridia.
oogonium, at maturity containing eight egg cells. More slender and much-
branched threads bear narrowly oval antheridia. In these are developed
several two-ciliated spermatozoids.
366. Fertilization. — At maturity the spermatozoids and egg cells float out-
side of the oval cavities, where fertilization takes place. The spermatozoid
I/O
MORPHOLOGY.
sinks into the protoplasm of the egg cell, makes its way to the nucleus of
the egg, and fuses with it as shown in fig. 181. The fertilized egg then
grows into a new plant. Nearly all the brown algae are maririe.
Fig. 178.
Antheridia of Fucus, on
branched threads.
Fig. 179.
Antheridia of Fucus with
escaping spermatozoids.
Fig. 1 80.
Eggs of Fucus surround-
ed by spermatozoids.
Fig. 181.
Fertilization in Fucus; in, female nucleus; mn, male nucleus; «, nucleolus. In
the left figure the male nucleus is shown moving down through the cytoplasm of the
egg; in the remaining figures the cytoplasm of th_ egg is omitted. (After Stras-
burger. )
367. The Gulf weed (Sargassum bacciferum) in the warmer Atlantic
ocean unites in great masses which float on the water, whence comes the
name "Sargassum Sea." The Sargassum grows on the coast where it is
attached to the rocks, but the beating of the waves breaks many specimens
loose and these float out into the more quiet waters, where they continue
to grow and multiply vegetatively.
368. Uses. — Laminaria japonica and L. angustata are used as food by
the Chinese and Japanese. Some species of the Laminariaceae are used as
food for cattle and are also used for fertilizers, while L digitata is some-
times employed in surgery.
CONTINUED: CLASSIFICATION.
171
Classification. — Kjellman divides the Phaeophyceae into two orders.
369. Order Phaeosporales (Phaeosporeae) including 18 families. One of
the most conspicuous families is the Laminariaceae, including among others
the Giant Kelps mentioned above (Laminaria, Postelsia, Macrocystis, etc.).
370. Order Cyclosporales (Cyclosporese). — This includes one family, the
Fucacea with Ectocarpus, Sphacelaria, Laeathesia, Fucus, Sargassum, etc.
Class Rhodophycese.
371. The red algae (Rhodophyceae). — The larger number of the so-called
red algae occur in salt water, though a few genera occur in fresh water.
The plants possess chlorophyll, but it is usually obscured by a reddish or
purple pigment.
372. Nemalion. — This is one of the lower marine forms, though its thal-
lus is not one of the simplest in struc-
ture. The plant body consists of a
slender cylindrical branched shoot, some-
times very profusely branched. The
central strand is rather firm, while the
cortex is composed of rather loose fila- a
ments.
373. Batrachospermum. — This genus
occurs in fresh water, and the species
are found in slow-running water of
shallow streams or ditches. There is a
central slender strand which is more or
less branched, and on these branches
are whorls of densely crowded slender
branches occurring at regular intervals.
The plants are usually very slippery.
Gonidia are formed on the ends of some
of these branches in globose, sporangia,
called monosporangia, since but a single
.,. • j i j • i A red alga (Nemalion). A, sexual
spore or gomdium is developed in each, branches, showing antheridia (a);
Other branches often terminate in long carpogonium or procarp (o) with its
° tnchogyne (i), to which are attached
slender hyaline setae. two spermatia (5); B, beginning of
O-A T.« Tn.- a cystocarp (o), the trichogyne (t)
374. Lemanea.— This genus also occurs still showing; C, an almost mature
fresh
n res water. The species develop
only during the cold winter months in
rapids of streams or where the water from falls strikes the rocks and is
thoroughly aerated. They form tufts of greenish threads, cylindrical or
vvhiplike, which in the summer are usually much broken down. The
threads are hollow and have a firm cortex. These are the sexual shoots,
172
MORPHOLOGY.
and they arise as branches from a sterile filamentous-branched, Chantransia-
like form.
375. Fertilization in the lower red algae. — The sexual organs in the red
algae consist of antheridia and carpogonia. The antheridia are usually
borne in crowded clusters, or surfaces, and bear terminally the small non-
motile sperm cells. The carpogonium is a branch of one or several cells,
the terminal cell (procarp) extending into a long slender process, the tri.
chogyne. The sperm cell comes in contact with the trichogyne, and in the
case of Nemalion and some others the nucleus has been found to pass down
the inside and fuse with the nucleus of the procarp.
From this point in the lower red algae like Nemalion, Batrachospermum
E
Fig. 183.
A, part of a shoot showing whorls of branches with clusters of carpospones.
B. carpogonic branch or procarp c, procarp cell; tr, trichogyne. C same with
sperm (sp) uniting with trichogyne. D, same with carpospores developing from
procarf* cell. E, male branch with one-celled antheridia. F, same with some of
anthendia empty. (After Schmitz. )
and Lemanea the formation of the spores is very simple. The procarp is
stimulated to growth, and buds in different directions, producing branched
chains of spores (carpospores). The caipospores form a rather compact
CONTINUED: CLASSIFICATION.
173
cluster called the sporocarp, which means spore-fruit or spore-fruit body.
In Batrachospermum it is seen as a compact tuft in the loose branching, in
Nemalion it lies in the surface of the cortex, while in Lemanea the sporo-
carps lie at different positions in the hollow tube of the sexual shoot.
376. Gonidia in the red algae. — The common type of gonidium in the red
algae is found in the tetraspores. A single mother cell divides into four cells
arranged usually in the form of tetrads within the tetrasporangium. In
Callithamnion the tetrasporangium is exposed. In Polysiphonia, Rhab-
Fig. 184.
A red alga (Callithamnion), showing spor-
angium A, and the tetraspores discharged
B. (After Thuret.)
tig. 185.
Gracilaria, portion of frond,
showing position of cystocarps.
Fig. 186.
Gracilaria, section of cysto-
carp showing spores.
donia, Gracilaria, etc., it is imbedded in the cortex. In Batrachospermum
there are monosporangia, each monosporangium containing a single goni-
dium, while in Lemanea, and according to some also in Nemalion, gonidia
are wanting.
174
MORPHOLOGY.
377. Gracilaria. — Gracilaria is one of the marine forms, and one species
is illustrated in fig. 185. It measures i$-2ocm or more long, and is pro-
fusely branched in a palmate manner. The parts of the thallus are more
or less flattened. The fruit is a cystocarp, which is characteristic of the
Rhodophyceae (Florideae). In Gracilaria these fruit bodies occur scat-
tered over the thallus. They are somewhat flask-shaped, are partly sunk
in the thallus, and the Conical end projects strongly above the surface. The
carpospores are grouped in radiating threads within the oval cavity of the
cystocarp. These cystocarps are developed as a result of fertilization.
Other plants bear gonidia in groups of four, the so-called tetraspores.
378. Bhabdonia. — This plant is about the same size as the gracilaria,
though it possesses more filiform branches. The cystocarps form prom-
inent elevations, while the carpospores lie in separated groups around the
Fig. 187.
Rhabdonia, branched
portion of frond show-
ing cystocarps.
Fig. it
Section of cystocarp of rhabdonia, showing
spores.
periphery of a sterile tissue within the cavity. (See figs. 187, 188.) Goni-
dia in the form of tetraspores are also developed in Rhabdonia.
379. Fertilization of the higher red algae. — The process of fertilization in
most of the red algae is very complicated, chiefly because the fertilized egg
cell (procarp) does not develop the spores directly, as in Nemalion, Le-
ALG& CONTINUED: CLASSIFICATION.
'75
let
manea, etc., but fuses directly, or by a short cell or long filament with one
or more auxiliary cells before the sporocarp is finally formed. Examples
are Rhabdonia, Polysiphonia,
Callithamnion, Dudresnaya,
etc. (fig. 189). The auxiliary
cell then develops the sporo-
carp. See fig. 189 for conju-
gation of a filament from the
fertilized procarp with an aux-
iliary cell.
380. Uses of the red algae. —
Many species produce a great
amount of gelatinous sub-
stance in their tissues, and
several of these are used for
food, for the manufacture of "
gelatines and agar-agar. Some
of these are Gracilaria lich-
enoides and wrightii, the for-
mer species occurring along
the coast of India and China.
The plant is easily converted
into gelatinous substance
(agar-agar). Chondrus cris-
pus, widely distributed in the
northern Atlantic is known as
"Irish" moss and is used for food and for certain medicinal purposes.
Gigartina mamillosa in the Atlantic and Arctic oceans is similarly em-
ployed. The following orders are recognized in the red algae:
381. Order Bangiales. — Example, Bangia atropurpurea (= Conferva
atropurpurea) in springs and brooks in North America and Europe. Por-
phyra contains a number of species forming broad, thin, leaf-like purple
sheets in the sea.
382. Order Nemalionales. — Including Lemanea, Batrachospermum,
Nemalion, described above, and many others.
383. Order Oigartinales. — In this order occurs the common Iceland
moss (Chondrus crispus) in the sea, and Rhabdonia and Gigartina men-
tioned above.
384. Order Rhodomeniales. — In this order occurs Gracilaria and Poly-
siphonia mentioned above, also the beautiful marine forms like Ceramium.
385. Order Cryptonemiales. — Examples are Dudresnaya, Melobesia,
Corallina, etc., the last two genera include many species with a wide dis-
tribution.
Fig.
Dudresnaya purpurifera. tr, trichogyne, with
sperm cells attached; ct, connecting-tube
which grows out from below the base of the
trichogyne, and comes in contact with the fertile
branches f , f: ct', young connecting-tube. (After
Thuret and Bornet.)
MOKPHOLOG Y.
Class Charophycese, Order Charales.
386. The Charales are by some thought to represent a distinct class of
algae standing near the mosses, perhaps, because of the biciliate character of
the spermatozoids. There is one family, the Characeae. The plants occur
in fresh and brackish water. Aside from the peculiarity of the reproductive
organs they are remarkable for the large size of the cells of the internodes
and of the "leaves," and the protoplasm exhibits to a remarkable degree
the phenomenon of "cyclosis"
(see paragraphs 17-20). Three
of the genera are found in North
America (Chara, Nitella (Fig. 8)
and Tolypella).
386a. The complicated struc-
ture of the sexual organs shows a
higher state of organization than
any of the other living algae
known. While the internodes in
Nitella are composed of a single,
stout cell, some times a foot or
more in length, the nodes in all are
composed of a group of smaller
cells. From the lateral cells of
this group lateral axes (sometimes
called leaves) arise in whorls.
In Nitella the internodes are
naked, but in most species of
Chara they are corticated, i.e., they
are covered by a layer of numer-
ous elongated cells which grow
downward from the nodes at the
base of the whorl of lateral shoots.
386b. The sexual organs are
situated at the nodes of the
Fig. 1 7 20.
Reproductive organs of Chara fragilis. A ,
a central portion of a leaf, b, with an anther-
idium, a, and a carpogonium, 5, surrounded
by the spirally twisted enveloping cells; c,
crown of five cells at apex; 0, sterile lateral
leaflets; /9', large lateral leaflet near the fruit ;
ft", bracteoles springing from the basal node
of the reproductive organs. B, a young
antheridium, a, and a young carpogonium,
sk; iv, nodal cell of leaf; «, intermediate
cell between if and the basal -node cell of
the antheridium; /, cavity of the internode
of the leaf; br, cortical cells of the leaf.
AX about 33; 5X240. (After Sachs.)
whorled lateral shoots, and consist of antheridia and carpogonia. Most of
the plants are monoecious, and both antheridia and carpogonia are often
attached to the same node, the antheridium projecting downward while the
carpogonium is more or less ascending. The sexual organs are visible
to the unaided eye. The antheridium is a globose red body of an exceed-
ingly complicated structure. The sperms are borne in several very long
coiled slender threads which are divided transversely into numerous cells.
The carpogonium is oval or elliptical in outline, the wall of which is com-
posed of several closely coiled spiral threads enclosing the large egg.
CHAPTER XIX.
FUNGI : MUCOR AND SAPROLEGNIA.
Mucor.
387. In the chapter on growth, and in our study of proto-
plasm, we have become familiar with the vegetative condition of
mucor. We now wish to learn how the plant multiplies and re-
produces itself. For this study we may take one of the mucors.
Any one of several species will answer. This plant may be grown
by placing partially decayed fruits, lemons, or oranges, from which
the greater part of the juice has been removed, in a moist cham-
ber ; or often it occurs on animal excrement when placed under
similar conditions. In growing the mucor in this way we are
likely to obtain Mucor mucedo, or another plant sometimes
known as Mucor stolonifer, or Rhizopus nigricans, which is illus-
trated in fig. 191. This latter one is sometimes very injurious to
stored fruits or vegetables, especially sweet potatoes or rutaba-
gas. Fig. 190 is from a photograph of this fungus on a banana.
388. Asexual reproduction. — On the decaying surface of the
vegetable matter where the mucor is growing there will be seen
numerous small rounded bodies borne on very slender stalks.
These heads contain the gonidia, and if we sow some of them in
nutrient gelatine or agar in a Petrie dish the material can be
taken out very readily for examination under the microscope.
Or we may place glass slips close to the growing fungus in the
moist chamber, so that the fungus will develop on them, though
cultures in a nutrient medium are much better. Or we may take
iH- material directly from the substance on which it is growing.
MORPHOLOG Y.
After mounting a small quantity of the mycelium bearing these
heads, if we have been careful to take it where the heads appear
quite young, it may be possible to study the early stages of their
Fig TOO
Portion of banana with a mould (Rhizopus nigricans) growing on one end.
development. We shall probably note at once that the stalks or
upright threads which support the heads are stouter than the
threads of the mycelium.
These upright threads soon have formed near the end a cross
wall which separates the protoplasm in the end from the remain-
der. This end cell now enlarges into a vesicle of considerable
size, the head as it appears, but to which is applied the name of
sporangium (sometimes called gonidangium), because it encloses
the gonidia.
At the same time that this end cell is enlarging the cross wall
is arching up into the interior. This forms the columella. All
the protoplasm in the sporangium now divides into gonidia.
These are small rounded or oval bodies. The wall of the spo-
FUNGI: MUCOR,
179
rangium becomes dissolved, except a small collar around the
stalk which remains attached below the columella (fig. 192).
Fig. 191.
Group of sporangia of a mucor (Rhizopus nigricans) showing rhizoids and the stolon extend-
ing from an older group.
By this means the gonidia are freed. These gonidia germinate
and produce the mycelium again.
389. Sexual stage. — This stage is not so frequently found, but may some-
times be obtained by growing the fungus on bread.
Conjugation takes place in this way. Two threads of the mycelium which
lie near each other put out each a short branch which is clavate in form.
The ends of these branches meet, and in each a septum is formed which cuts
off a portion of the protoplasm in the end from that of the rest of the my-
celium. The meeting walls of the branches now dissolve and the protoplasm
of each gamete fuses into one mass. A thick wall is now formed around this
mass, and the outer layer becomes rough and brown. This is the zygote or
zygospore. The mycelium dies and it becomes free often with the suspensors,
as the stalks of these sexual branches are called, still attached. This zygo-
spore passes through a period of rest, when with the entrance of favorable
conditions of growth it germinates, and usually produces directly a sporan-
gium with gonidia. This completes the normal life cycle of the plant.
390. Gemmae. — Gcmmas, as they are sometimes called, are often formed on
the mycelium. A short cell with a stout wall is formed on the side of a
i8o
MORPHOLOG Y.
thread of the mycelium. In other cases large portions of the threads of the
mycelium may separate into chains of cells. Both these kinds of cells are
Fig. 194.
A mucor (Rhizopus nigricans) ; at left nearly mature sporangium with columella showing
within; in the middle is ruptured sporangium with some of the gonidia clinging to the colu-
mella ; at right two ruptured sporangia with everted columella.
capable of growing and forming the mycelium again. They are sometimes
called chlamydospores.
890<z. The Mucorinese according to their manner of zygospore formation
are of two kinds: ist, the Iwmothalftc (monoecious), in which all of the colo-
nies or thalli developed from different spores are the same, and both gametes
may be developed from the mycelium from a single spore, as in Sporodinia
grandis, a mould common on old mushrooms; 2d, the heterothallic (dioe-
cious), in which certain plants are of a male nature and small in compari-
son with those of perhaps a female nature which are larger or more vigor-
ous. When grown separately each of these two kinds of thalli, or colonies
of mycelium, produce their own kind but only sporangia. If the two kinds
are brought together, however, branches from one conjugate with branches
from the other and zygospores are produced, as in Rhizopus nigricans, the
common bread or fruit mould. This is one reason why we rarely find this
fungus forming zygospores. (See Blakeslee, Sexual Reproduction in the
Mucorineae, Proc. Am. Acad. Arts and Sci., 40, 205-319, pi. 1-4, 1904.)
FUNGI: SAPKOLEGNIA.
181
Water Moulds (Saprolegnia).
391. The water moulds are very interesting plants to stud}
because they are so easy to obtain, and it is so easy to observe a
type of gonidium here to which we have referred in our studies
ofthealgae, the motile gonidium, or zoogonidium. (See appen-
dix for directions for cultivating this mould.)
392. Appearance of the saprolegnia. — In the course of a
few days we are quite certain to see in some of the cultures deli-
cate whitish threads, radiating outward from the body of the fly
in the water. A few threads should be examined from day to
day to determine the stage of the fungus.
393. Sporangia of saprolegnia. — The sporangia of saprolegnia
can be easily detected because they are much stouter than the
ordinary threads of the myceRum. Some of the threads should
be mounted in fresh water. Search for some of those which
Fig. 195.
porangia of saprolegnia, one showing the escape of the zoogo-
nidia.
show that the protoplasm is divided up into a
great number of small areas, as shown in fig. 195.
With the low power we should watch some of the older ap-
pearing ones, and if after a few minutes they do not open, other
preparations should be made.
1 82 MORPHOLOGY.
394. Zoogonidia of saprolegnia. — The sporangium opens at
Fig. 196.
Branch of saprolegnia showing oogonia with oospores, eggs matured parthenogcnetically.
the end, and the zoogonidia swirl out and swim around for a
short time, when they come to rest. With a good magnifying
Fig. 197.
Downy mildew of grape (Plasmopora viti-
ofg
Fig. 198.
Phytophthora infestans showing pe-
culiar branches ; gonidia below.
cola), showing tuft ofgonidiophpres bearing
gonidia, also intercellular mycelium. (After
Millardet.)
power the two cilia on the end may be seen, or we may make
FUNGI: SAPROLEGNIA.
133
Fig. 199.
Fertilization in saprolegnia, tube of antheridium carrying in the nucleus of the sperm cell
to the egg. In the right-hand figure a smaller sperm nucleus is about to fuse with the
nucleus of the egg. (After Humphrey and Trow.)
Fig. 200.
Branching hypha of Peronospora alsinearum.
Fig. 201.
Branched hypha of downy mildew
of grape showing peculiar branching
(Plasmopara viticola).
1 84
MORPHOLOG Y.
them more distinct by treatment with Schultz's solution, draw-
ing some under the cover glass. The zoogonidium is oval and
the cilia are at the pointed end. After they have been at rest
for some time they often slip out of the thin wall, and swim
again, this time with the two cilia on the side, and then the
zoogonidium is this time more or less bean-shaped or reniform.
395. Sexual reproduction of saprolegnia. — When such cultures are older
we often see large rounded bodies either at the end of a thread, or of a
branch, which contain several smaller rounded bodies as shown in fig. 196.
These are the oogonia (unless the plant is attacked by a parasite), and the
*round bodies inside are the egg cells, if before fertilization, or the eggs, if
after this process has taken place. Sometimes the slender antheridium can
be seen coiled partly around the oogonium, and one end entering to come in
contact with the egg cell. But in some species the antheridium is not
present, and that is the case with the species figured at 196. In this case
B
Fig. 202. Fig. 203.
Gonidiophores and gonidia of potato blight (Phytophthora in- Gonidia of potato
festans). i, an older stage showing how the branch enlarges where bjight forming zoogo-
it grows beyond the older gonidium. (After de Bary.) nidia. (.After de Bary.)
the eggs mature without fertilization. This maturity of the egg without
fertilization is called parthenogenesis, which occurs in other plants also, but
is a rather rare phenomenon.
396. In fig. 199 is shown the oogonium and an antheridium, and the
antheridium is carrying in the male nucleus to the egg cell. Spermatozoids
are not developed here, but a nucleus in the antheridium reaches the egg
cell. It sinks in the protoplasm of the egg, comes in contact wi'h the nu-
cleus of the egg, and fuses with it. Thus, fertilization is accomplished.
FUNGI: DOWNY MILDEWS.
I85
Downy Mildews.^1
397. The downy mildews make up a group of plants which are closely
related to the water moulds, but they are parasitic on land plants, and some
species produce very serious diseases. The mycelium grows between the
Fig. 204.
Fertilization in Peronospora alsinearum; tube from an theridium carrying in the
sperm nucleus in figure at the left, female nucleus near; fusion of the two nuclei
shown in the two other figures. (After Berlese.)
cells of the leaves, stems, etc., of their hosts, and sends haustoria into the
cells to take up nutriment. Gonidia are formed on threads which grow
through the stomates to the out-
side and branch as shown in figs.
198-201. The gonidia are borne
on the tips of the branches. The
kind of branching bears some re-
lation to the different genera.
Fig. 200 is from Peronospora
alsinearum on leaves of ceras-
tium; figs. 197 and 199 arePlas-
mopara viticola, the grape mil-
dew, while figs. 198 and 202 are
from Phytophthora infestans
which causes a disease known as
potato blight. The gonidia of
peronospora germinate by a germ
Fig. 205.
Ripe oospore of Peronospora alsinearum.
tube, those of plasmopara first
form zoogonidia, while in phy-
tophthora the gonidium may either germinate forming a thread, or each
gonidium may first form several zoogonidia, as shown in fig. 20^.
398. In sexual reproduction oogonia and antheridia are developed on the
mycelium within the tissues. Fig. 204 represents the antheridium enter-
1 86 MORPHOL OGY.
ing the oogonium, and the male nucleus fusing with the female nucleus
in fertilization. The sexual organs of Phytophthora infestans are not
sufficiently known.
399. Mucor, saprolegnia, peronospora, and their relatives have few or
no septa in the mycelium. In this respect they resemble certain of the algae
like vaucheria, but they lack chlorophyll. They are sometimes called the
alga-like fungi and belong to a large group called Phycomycetes.
CHAPTER XX.
FUNGI CONTINUED.
"Rusts" (Uredineae).
400. The fungi known as "rusts" are very important ones
to study, since all the species are parasitic, and many produce
serious injuries to crops.
401. Wheat rust (Puccinia graminis). — The wheat rust is
one of the best known of these fungi, since a great deal of study
has been given to it. One form of the plant occurs in long
Fig. 206.
Wheat leaf with red
rust, natural size.
Fig. 208.
Natural size.
Fig. 209.
Enlarged.
Fig. 210.
Single
sorus.
Fig. 207.
Portion of 'eaf
enlarged to show
son.
Figs. 206, 207. — Puccinia framinis, red-rust stage (uredo stage).
Figs. 208-210. — Black rust of wheat, showing sori of teleutospores.
reddish-brown or reddish pustules, and is known as the "red
rust" (figs. 206, 207). Another form occurs in elongated black
pustules, and this form is the ~ne known as the "black rust''
187
188
MOKPHOLOG Y.
(figs. 208-211). These two forms occur on the stems, blades,
etc., of the wheat, also on oats, rye, and some of the grasses.
402. Teleutospores of the black-rust form.— If we scrape off
some portion of one of the black pustules (sori), tease it out
Fig. 212.
Teleutospores oi wheat rust,
showing two cells and the pedicel.
Fig. 211.
Head of wheat showing black rust spots
on the chaff and awns.
Fig. 213.
Uredospores of wheat rust, one
showing remnants of the pedicel.
in water on a slide, and examine with a microscope, we see
numerous gonidia, composed of two cells, and having thick,
brownish walls as shown in fig. 212. Usually there is a slender
brownish stalk on one end. These gonidia are called leleuto-
spores. They are somewhat oblong or elliptical, a little con-
stricted where the septum separates the two cells, and the end
cell varies from ovate to rounded. The mycelium of the fungus
FUNGI: AC/STS.
189
courses between the cells, just as is found in the case of the
carnation rust, which belongs to the same family (see Parag. 186).
403. Uredospores of the red-rust form. — If we make a simi-
lar preparation from the pustules of the red-rust form we see
that instead of two-celled gonidia they are one-celled. The
walls are thinner and not so dark in color, and they are covered
with minute spines. They have also short stalks, but these fall
away very easily. These one-celled gonidia of the red-rust form
are called ' ' uredospores. " The uredospores and teleutospores
are sometimes found in the same pustule.
It was once supposed that these two kinds of gonidia belonged
to different p'ants, but now it is known that the one-celled
form, the uredospores, is a form developed
earlier in the season than the teleutospores.
404. Cluster-cup form on the barberry.
— On the barberry is found still another
form of the wheat rust, the "cluster cup1'
stage. The pustules on the under side of
the barberry leaf are cup-shaped, the cups
being partly sunk in the tissue of the leaf,
while the rim is more or less curved back-
ward against
the leaf, and
split at several
places. These
cups occur in
clusters on the
affected spots
of the barberry
leaf as shown
Fig. 214.
Fig. 215.
Fig. 3 1 6.
Barberry leat witn two
diseased spots, natural
size.
Single spot
showing cluster
enlarged.
fior
Two cluster
cups more en-
larged, showing Within
split margin.
215.
cups enlarged. larged, showing \Vithin the
split margin.
Figs. 2 1 4-2 1 6. — Cluster-cup stage of wheat rust. CUpS numbers
of one-celled gonidia (orange in color, called aecidiospores) are
borne in chains from short branches of the mycelium, which
fill the base of the cup. In fact the wall of the cup (peridium)
190
MORPHOLOG Y.
is formed of similar rows of cells, which, instead of separating
into gonidia, remain united to form a wall. These cups are
usually borne on the under side of the leaf.
405. Spermagonia.— Upon the upper side of the leaves in the same spot
occur small, orange-colored pustules which are flask-shaped. They bear
inside, minute, rod-like bodies on the ends of slender threads, which ooze
Fig. 317.
Section of an aecidium (cluster cup) from barberry leaf. (After Marshall-Ward.)
out on the surface of the leaf. These •flask-shaped pustules are called
spermagonia, and the minute bodies within them sfermatia, since they were
once supposed to be the male element of the fungus. Their function is not
known. They appear in the spots at an earlier time than the cluster cups.
406. How the cluster-cap stage was found to be a part of the wheat rust.
— The cluster-cup stage of the wheat rust was once supposed also to be a dif-
ferent plant, and the genus was called ezcidium. The occurrence of wheat
rust in great abundance on the leeward side of affected barberry bushes in
England suggested to the farmers that wheat rust was caused by barberry
rust. It was later found that the aecidiospores of the barberry, when sown
on wheat, germinate and the thread of mycelium enters the tissues of the
wheat, forming mycelhim between the cells. This mycelium then bears
the uredospores, and later the teleutospores.
FUNGI: RUSTS.
407. Uredospores can produce successive crops of uredospores. — The uredo-
spures are carried by the wind to other wheat or grass plants, germinate
Fig. 218.
Section through leaf of barberry at point affected with the cluster-cup stage of the wheal
rust; spermagoma above, ajcidia below. (After Marshall-Ward.)
form mycelium in the tissues, and later the pustules with a second crop of
uredospores. Several successive crops of uredospores may be developed in
B
Fig. 219.
A, section through sorus of black rust of wheat, showing teleutospores. R, mycelium
bearing both teleutospores and uredospores. (After de Bary.)
one season, so this is the form in which the fungus is greatly multiplied and
widely distributed.
192
MORPHOLOG Y.
407a. Teleutospores the last stage of the fungus in the season.— The teleu-
tospores are developed late in the season, or late in the development of the
host plant (in this case the
wheat is the host). They
then rest during the winter.
In the spring under favor-
able conditions each cell of
the teleutospore germi-
nates, producing a short
mycelium called a promy-
celium, as shown in figs.
222, 223. This promy-
celium is usually divided
into four cells. From each
cell a short, pointed pro-
cess is formed called a
" sterigma. " Through this
the protoplasm moves and
forms a small gonidium on
the end, sometimes called
a sporidium.
408. How the fungus gets from the wheat back to the barberry — If these
sporidia from the teleutospores are carried by the wind so that they lodge on
Fig. 220. Fig. 221.
Germinating uredospore of Germ tube entering the
wheat rust. (After Marshall- leaf through a stoma.
Ward.)
Fig. 222. Fig. 223. Fig. 224.
Teleutospore g e r m i - Promycelium of ger- Germinating sporidia entering leal
nating, forming promy- minating teleutospore.- of barberry by mycelium,
celium. forming sporidia
Figs. 222-224. — Puccinia graminis when' ni t\ ( A "ter Marshall- Ward.)
FUNGI: RUSTS. 1 93
the leaves of the barberry, they germinate and produce the cluster cup again.
The plant has thus a very complex life history. Because of the presence of
several different forms in the life cyle, it is called a polymorphic fungus.
The presence of the barberry does not seem necessary in all cases for the
development of the fungus from one year to another.
409. Synopsis of life history of wheat rust.
Cluster -cup stage on leaf of barberry.
Mycelium between cells of leaf in affected spots.
Spermagonia (sing, spermagonium), small flask-shaped bodies
sunk in upper side of leaf; contain " spermatia."
^Ecidia (sing, aecidium), cup-shaped bodies in under side of
leaf.
Wall or peridium, made up of outer layer of fungus threads
which are divided into short cells but remain united.
At maturity bursts through epidermis of leaf; margin of
cup curves outward and downward toward surface of leaf.
Central threads of the bundle are closely packed, but free.
Threads divide into short angular cells which separate
and become secidiospores, with orange-colored content.
vEcidiospores carried by the wind to wheat, oats, grasses,
etc. Here they germinate, mycelium enters at stomate,
and forms mycelium between cells of the host.
Uredo stage (red rusf) on wheat, oats, grasses, etc.
Mycelium between cells of host.
Bears uredospores (i-celled) in masses under epidermis, which
is later ruptured and uredospores set free.
Uredospores carried by wind to other individual hosts, and
new crops of uredospores formed.
Teleutospore stage (black rust), also on wheat, etc.
Mycelium between cells of host.
Bears teleutospores (2 -celled) in masses (sori) under epidermis,
which is later ruptured.
Teleutospores rest during winter. In spring each cell germi-
nates and produces a promyceli um, a short thread, divided
into four cells.
194 MORPHOLOGY.
Promycelium bears four sterigmata and four gonidia (or spo-
ridia), which in favorable conditions pass back to the bar-
berry, germinate, the tube enters between cells into the
intercellular spaces of the host to produce the cluster cup
again, and thus the life cycle is completed.
410. Other examples of the rusts. — Some of the rusts do great injury to
fruit trees and also to forest trees. The "cedar apples'1 are abnormal
growths on the leaves and twigs of the cedar stimulated by the presence of
the mycelium of a rust known as Gymnosporangium macropus. The
teleutospores are two celled and are formed in the tissue of the "cedar
apple ' ' or gall. The teleutosori are situated at quite regular intervals over
the surface of the gall at small circular depressions, and can be easily seen
in late autumn and during the winter. A quantity of gelatine is developed
along with the teleutospores. In early spring with the warm spring rains
the gelatinous substance accompanying the teleutospores swells greatly, and
causes the teleutospores to ooze out in long, dull, orange-colored strings,
which taper gradually to a slender point and bristle all over the "cedar
apple." Here the teleutospores germinate and produce the sporidia. The
sporidia are carried to apple trees where they infect leaves and even the
fruit, producing here the cluster cups. There are no uredospores.
G. globosum is another species forming cedar apples, but the gelatinous
strings of teleutospores are short and clavate, and the cluster cups are
formed on hawthorns. G. nidusavis forms "witches brooms" or "birds
nests" in the branches of the cedar. The mycelium in the branches stimu-
lates them to profuse branching so that numerous small branches are devel-
oped close together. The teleutosori form small pustules scattered over the
branches. G. clavipes affects the branches of cedar only slightly deform-
ing them or not at all, and the cluster cups are formed on fruits, twigs, and
leaves of the hawthorns or quinces, the cluster cups being long, tubular,
and orange in color.
CHAPTER XXI.
THE HIGHER FUNGI.
411. The series of the higher fungi. — Of these there are two
large series. One of these is represented by the sac fungi, and
the other by the mushrooms, a good example of which is the
common mushroom (Agaricus campestris).
Sac Fungi (Ascomycetes).
412. The sac fungi may be represented by the "powdery mil-
dews"; examples, uncinula, microsphaera, podosphasra, etc.
Fig. 225 is from a photograph of two willow leaves affected by
one of these mildews. The leaves are first partly covered with a
whitish growth of mycelium, and numerous chains of colorless
gonidia are borne on short erect threads. The masses of gonidia
give the leaf a powdery appearance. The mycelium lives on the
outer surface of the leaf, but sends short haustoria into the epi-
dermal cells.
413. Fruit bodies of the willow mildew. — On this same myce-
lium there appear later numerous black specks scattered over
the affected places of the leaf. These are the fruit bodies (per-
ithecia). If we scrape some of these from the leaf, and mount
them in water for microscopic examination, we shall be able to
see their structure. Examining these first with a low power of
the microscope, each one is seen to be a rounded body, from
which radiate numerous filaments, the appendages. Each one
of these appendages is coiled at the end into the form of a little
hook. Because of these hooked appendages this genus is called
uncinula. This rounded body is the perithecium.
196
MORPHOLOGY.
414. Asci and ascospores. — While we are looking at a few of
these through the microsrope with the low power, we should
Fig. 225.
Leaves of willow showing willow mildew. The black dots are the fruit bodies (perithecia)
seated on the white mycelium.
press on the cover glass with a needle until we see a few of the
perithecia rupture. If this is done carefully we see several
small ovate sacs issue, each containing a number of spores, a:-
shown in fig. 227. Such a sac is an ascus, and the spores are
ascospores.
FUNGI: SAC FUNGI.
I97
415. Number of spores in an ascus. — The ascus is the most important
character showing the general relationship of the members of the sac fungi.
Fig. 226. Fig. 227. Fig. 228.
Willow mildew, Fruit of willow mildew, showing hooked Fruit body of an-
bit of mycelium appendages. Genus uncinula. other mildew with
T->- r> -ii • / -ii dichotomous ap-
Figs. 227 228.— Penthecia (penthe- pendages. Q^^
cmm) of two powdery mildews, showing mirrosDhsera
escape of asci containing the spores from r
the crushed fruit bodies.
with erect conidio-
phores, bearing
chain of gonidia;
gonidium at left
germinating.
While many of the powdery mildews have a variable number of spores in
Fig. 229.
Contact o f
an theridium
and carpogo-
nium (carpogo-
nium the larger
cell) ; begin-
ning of fertili-
zation.
Fig. 230.
Disappear-
ance of contact
walls of anthe-
ridium and
Fig. 231.
Fertilized egg surrounded
by the enveloping threads
which grow up around it.
Figs. 229-231. — Fertilization in sphaerothcca; one of the powdery mildews. (After
Harper.)
in an
carpogonium,
and fusion of
the two nuclei.
an ascus, a large majority of the ascomycetes have just 8 spores
198
MORPHOLOGY.
ascus, while some have 4. others 16, and some an indefinite number.
The asci in a perithecium are more variable. In some ascomycetes there
is no perithecium.
416. The black fungi. — These are very cwnmon on dead logs, branches,
Fig. 2310.
Edible Morel. Morchella esculenta. The asci, forming hymenium, cover the
pitted surface.
leaves, etc., and may be collected in the •'vbods at almost any season. The
perithecia are often numerous, scattered or densely crowded as in Rosel-
FUNGI: MUSHROOMS. 1 99
linia. Sometimes they are united to form a crust which is partly formed
from sterile elements as in Hypoxylon, or they form black clavate or
branched bodies as in Xylaria. The black knot of the plum and cherry is
also an example.
The lichens are mostly ascomycetes like the black fungi "or cup fungi,
while a few are basidiomycetes.
417. The morels (Morchella). — There are several species of morels
which are common in early spring on damp ground. Either one of the
species is suitable for use if it is desired to include this in the study. Fig.
2310 illustrates the Morchella esculenta. The stem is cylindrical and
stout. The fruiting portion forms the "head," and it is deeply pitted.
The entire pitted surface is covered by the asci, which are cylindrical and
•eight spored. A thin section may be made of a portion for study, or a
small piece may be crushed under the cover glass.
418. The cup fungi. — These fungi are common on damp ground or on
rotting logs in the summer. They may be preserved in 70 per cent alcohol
for study. Many of them are shaped like broad open cups or saucers.
The inner surface of the cup is the fruiting surface, and is covered with the
cylindrical asci, which stand side by side. A bit of the cup may be sec-
tioned or crushed under a cover glass for study.
Mushrooms (Basidiomycetes).
419. The large group of fungi to which the mushroom belongs is called
the basidiomycetes because in all of them a structure resembling a club,
or basidium, is present, and bears a limited number of spores, usually four,
though in some genera the number is variable. Some place the rusts
(Uredinea?) in the same series (basidium series), because of the short pro-
mycelium and four sporidia deve|pped from each cell of the teleutospore.
420. The gill-bearing fungi (Agaricaceae). — A good example
for this study is the common mushroom (Agaricus campestris).
This occurs from July to November in lawns and grassy fields.
The plant is somewhat umbrella-shaped, as shown in fig. 232,
and possesses a cylindrical stem attached to the under side of the
convex cap or pileus. On the under side of the pileus are thin
radiating plates, shaped somewhat like a knife blade. These are
the gills, or lamellae, and toward the stem they are rounded on
the lower angle and are not attached to the stem. The longer
ones extend from near the stem to the margin of the pileus, and
the V-shaped spaces between them are occupied by successively
200
MORPHOLOGY.
Fig. 232.
Agaricus campestris. View of under side showing stem, annulus, gills, and margin of pileus.
Fig. 233-
Agaricus campestris. Longitudinal section through stem and pileus. a, pileus; b, portion
of veil ou margin of pileus ; c, gill ; f, fragment of annulus ; e, stipe.
FUNGI: MUSHROOMS.
201
shorter ones. Around the stem a little below the gills is a collar,
termed the ring or annulus.
421. Fruiting surface of the mushroom. — The surface of
these gills is the fruiting surface of the mushroom, and bears the
gonidia of the mushroom, which are dark purplish brown when
mature, and thus the gills when old are dark in color. If we- make
a thin section across a few of the gills, we see that each side of
the gill is covered with closely crowded club-shaped bodies, each
one of which is a basidium. In fig. 234 a few of these are en-
larged, so that the
structure of the gill
can be seen. Each
basidium of the com-
mon mushroom has
Fig. 234. Fig 235.
Portion of section of lamella of Agaricus campestris. Portion of hymenium of Co-
tr, trama; sk, subhymemum ; b, basidium; st, sterigma prinus micaceus, showing large
(//. sterigmata) ; g, basidiospore. cystidium in the hymenium.
two spinous processes at the free end. Each one is a sterig'ma
(plural sterig'maia), and bears a gonidium. In a majority of the
members of the mushroom family each basidium bears four
spores. When mature these spores easily fall away, and a mass
of them gives a purplish-black color to objects on which they fall,
so that a print of the under surface of the cap showing the
arrangement of the gills can be obtained by cutting off the stem,
and placing the pileus on white paper for a time.
422. How the mushroom is formed. — The mycelium of the
202
MORPHOLOGY.
FUNGI: MUSHROOMS
203
mushroom lives in the ground, f.nd grows here for several months
or even years, and at the proper seasons develops the mature
mushroom plant. The mycelium lives on decaying organic mat-
ter, and a large number of the threads grow closely together form-
ing strands, or cords, of mycelium, which are quite prominent
if they are uncovered by removing the soil, as shown in fig. 236.
423. From these strands the buttons arise by numerous threads
growing side by side in a vertical direction, each thread growing
independently at the end, but all lying very closely side by
Fig. 237.
Agaricus campestris ; sections of " buttons " of different sizes, showing iormation of gills
and veil covering them.
side. When the buttons are quite small the gills begin to
form on the inside of the under margin of the knob. They
are formed from an interior ring of tissue near the end of the
young fruit body which appears before the end broadens into
a knob. From this ring of tissue threads grow downward in
radiating ridges, just as many ridges being started as there
are to be gills formed. The lateral tissue outside of this in-
terior ring of gills becomes the veil, and sections ot young but-
tons will disclose the gills in the minute cavity thus formed
(fig. 237). This curtain of mycelium which is thus stretched
across the gill cavity is the veil. As the cap expands more
and more this is stretched into a thin and delicate texture as
204
MORPHOLOGY.
shown in fig. 238. Finally, as shown in fig. 239, this veil is
ruptured by the expansion of the pileus, and it either clings
Fig. 238.
Agaricus campestris ; nearly mature plants, showing veil still stretched across the gill
cavity.
Fig. 239-
Agaricus campestris ; under view of two plants just after rupture of veil, fragments of the
latter clinging both to margin of pileus and to stem.
FUNGI: MUSHROOMS.
2O5
Fig. 240.
Agaricus campestris ; plant in natural position just after rupture of veil, showing tendency
to double annulus on the stem. Portions of the veil also dripping from margin of pileus.
Fig. 341.
Agaricus campeauis . spore print.
206
MORPHOLOGY.
FUNGI: MUSHROOMS. 2O7
to the stem as a collar, or a portion of it remains clinging to
the margin of the cap. When the buttons are very young
the gills are white, but they soon become pink in color, and
Fig. 243.
Amanita phalloides ; white form, showing pileus, stipe, annulus, and volva.
very soon after the veil breaks the spores mature, and then
the gills are dark brown.
424. Beware of the poisonous mushroom. — The number of
species of mushrooms, or toadstools as they are often called, is
very great. Besides the common mushroom (Agaricus campes-
208
MORPHOLOG Y.
tris) there are a large number of other edible species. But
one should be very familiar with any species which is gathered
for food, unless collected by one who certainly knows what the
plant is, since carelessness in this respect sometimes results fatally
from eating poisonous ones.
425. A plant very similar in structure to the Agaricus campes-
tris is the Lepiota naucina, but the spores are white, and thus the
gills are white, except that in age they become a dirty pink.
This plant occurs in grassy fields and lawns often along with the
Fig. 244.
Amanita phalloides ; plant turned to one side, after having been placed in a horizontal
position, by the directive force of gravity.
common mushroom. Great care should be exercised in collect-
ing and noting the characters of these plants, for a very deadly
poisonous species, the deadly amanita (Amanita phalloides) is
perfectly white, has white spores, a ring, and grows usually in
wooded places, but also sometimes occurs in the margins of lawns.
In this plant the base of the stem is seated in a cup -shaped struc-
ture, the volva, shown in fig. 243. One should dig up the stem>
carefully so as not to tear off this volva if it is present, for with
the absence of this structure the plant might easily be mistaken
for the lepiota, and serious consequences would result. >.-.•
FUNGI: MUSHROOMS. 2CK)
426. Tube-bearing fungi (Polyporacese). — In the tube-bearing fungi, the
fruiting surface, instead of lying over the surface of gills, lines the surface
of tubes or pores on the under side of the cap. The fruit-bearing portion
therefore is "honey -combed." The sulphur polyporus (Polyporus sulphu-
reus) illustrates one form. The tube-bearing fungi are sometimes called
"bracket" fungi, or "shelf" fungi, because the pileus is attached to the
Fig. 245.
Edible Boletus. Boletus edulis. Fruiting surface honey-combed on undei
side of cap.
tree or stump like a shelf or bracket. One very common form in the woods
is the plant so much sought by "artists," and often called Polyporus ap-
plahatus. It is hard and woody, reddish brown, brown or grayish on the
upper side, according to age, and is marked by prominent and large concentric
ridges. (This form is probably P. leucophaeus.) The under side is white
and honey-combed by numerous very minute pores. This plant is peren-
nial, that is, it lives from year to year. Each year a new layer is added to
the under side, and several new rings usually to the margin. If a plant
two or three years old is cut in two, there will be seen several distinct tube
layers or strata, each one representing a year's growth.
In some of these bracket fungi, each ring on the upper surface marks a
2IO MORPHOLOGY.
year's growth as in the pine polyporus (P. pinicola). In the birch poly-
porus (P. fomentarius) the tubes are quite large. It also occurs on other
trees. The beech polyporus (P. igniarius, also on other trees) often be-
Fig. 246.
Coral fungus. Hydnum coralloides, spines hanging down from branches.
comes very old. I have seen one specimen over eighty years old. Not all
the tube-bearing fungi are bracket form. Some have a stem and cap
(see fig. 245). Some are spread on the surface of logs.
427. Hedgehog fungi (Hydnaceae). — These plants are bracket in form or
have a stem and cap, or are spread on the surface of wood; but the finest
specimens resemble coral masses of fungus tissue (example, Hydnum, fig.
246). In most of them there are slender processes resembling teeth, spines
or awls, which depend from the under surface (fig. 247). The fruiting
surface covers these spines.
428. Coral fungi or fairy clubs (Clavariaceae). — These plants stand
upright from the wood, leaves, or soil, on which they grow (example,
Clavaria). The "coral" ones are branched, while the "fairy clubs" are
simple. The fruiting surface covers the entire exposed surface of the plants
(fig. 248).
FUNGI: MUSHROOMS.
211
Fig. 247.
Hydnum repandum, spines hanging down from under side of cap.
212
MOKPHOLOG Y.
-
Fig. 248.
Clavaria botrytes.
CHAPTER XXII.
CLASSIFICATION OF THE FUNGI.
429. Classification of the fungi.— Those who believe that the fungi repre-
sent a natural group of plants arrange them in three large series related to
each other somewhat as follows-.
The Basidium Type or Series.
The number of gonidia on a ba-
sidium is limited and definite,
and the basidium is a characteris-
tic structure; examples: uredineae
(rusts), mushrooms, etc.
The Ascus Type or Series. The
number of spores in an ascus is
limited and definite, and the ascus is
a characteristic structure; examples:
leaf curl of peach (exoascus), pow-
dery mildews, black knot of plum,
black rot of grapes, etc.
430. Others believe that the fungi do not represent a natural group, but
that they have developed off from different groups of the alga? by becoming
parasitic. As parasites they no longer needed chlorophyll, and conse-
quently lost it.
According to this view the lower fungi have developed off from the lower
algae (saprolegnias, mucors, peronosporas, etc., being developed off from
siphonaceous algae like vaucheria), and the higher fungi being developed
off from the higher algae (the ascomycetes perhaps from the Rhodophyceae).
431. A very general outline of classification,* according to the former of
The Gonidium Type or Series.
The number of gonidia in the spo-
rangium is indefinite and variable.
It may be very large or very small,
or even only one in a sporangium.
To this series belong the lower
fungi; examples: mucor, saprolegnia,
peronospora, etc.
* Class Myxomycetes, or Mycetozoa. — To this class belong the "slime
molds," low organisms consisting of masses of naked protoplasm which
flows among decaying leaves and in decaying wood, coming to the surface
to fruit. The fruit in many cases resembles miniature puff-balls, and these
plants were formerly classed with the puff-balls. The spores germinate by
213
214
MORPHOLOG V.
these views, might be presented here to show the general relationships of
the fungi studied, with the addition of a few more in orders not represented
above. It should be borne in mind that the author in presenting this view
of classification does not necessarily commit himself to it. It is based
on that presented in Engler & Prantl's Pflanzenfamilien. There are three
classes.
I. Class Phycomycetes (Alga-like Fungi).
1. SUBCLASS OOMYCETES.
432. These are the egg-spore fungi. They include the water mold
(Saprolegnia), the downy mildew of the grape (Plasmopara), the potato
\d
Fig. 249.
Chytrids. A, Harpochyttium hedenii, parasitic on spirogyra threads; a, sickle-
form plant; b, the sporangium part with escaping zoospores; c, old plant pro-
liferating by forming new sporangium in the old empty one; d, zoospore; e, two
young plants just beginning to grow. B, Rhizophidium globosum parasitic on
spirogyra. Globose sporangium with delicate threads inside of the host, zoospores
escaping from one. C, Olpidium pendulum, parasitic in spirogyra cell. Ellip-
tical sporangium with slender exit tube through which zoospores are escaping.
D, Lagenidium rabenhorstii parasitic in spirogyra cell. Two slender sporangia
with exit tubes through which protoplasm escapes forming a rounded mass at the
end of tube, this protoplasm forming biciliate zoospores.
forming swarm spores which unite to form a small plasmodium, which in
turn grows to form a large plasmodium or protoplasmic mass. It is doubt-
ful if they are any more plant than animal organisms. Examples: Trichia,
Arcyria, Stemonitis, Physarum, Ceratiomyxa, etc., on rotten wood; Plas-
modiophora brassier is a parasite causing club foot of cabbage, radishes,
etc. It lives within the roots, causing large knots and swellings on the same.
FUNGI CONTINUED: CLASSIFICATION.
215
ant
OOff
blight (Phytophthora), the white rust of cruciferous plants (Cystopus=
Albugo), the damping-off fungus (Pythium), and many parasites of the
dlgae known as chytrids, as Olpidium, Rhizophidium, Lagenidium, Chytri-
dium, etc.
The two following orders are sometimes placed in a separate subclass,
Archimycetes.
433. Order Chytridiales (Chytridinese). — These include the lowest fungi.
Many of them are parasitic on alga? and lack mycelium, the swarm spore
either with or without minute rhizoids, developing into a globose sporan-
gium (Rhizophidium, Chytridium, Olpidium, etc., fig. 249), or the swarm
spore attached to the wall of the host develops into a long sword-shaped
body with a sterile base, which proliferates
and forms a new sporangium in the old one
(Harpochytrium), or with slight develop-
ment of mycelium in aquatic plants (Cla-
dochytrium). Some are parasitic in leaves
and stems of land plants. Synchytrium
decipiens is very common on the trailing
legume, Amphicarpaea monoica.
434. Order Ancylistales (Ancylistinese).
— The members of this order have a slight
development of mycelium and many are
parasitic in algae (Lagenidium, fig. 249).
435. Order Saprolegniales (Saproleg-
niineae). — These include the water molds
(Saprolegnia). See Chapter XIX.
436. Order Monoblepharidales (Mono-
blepharidineae). — These are peculiar water
molds, related to the Saprolegniales, but
motile sperm cells are formed (Monoble-
pharis, etc., fig. 250). Fig. 250.
437. Order Peronosporales (Peronospori- . Monoblepharis insignis Thax-
ter. End of hypha bearing oogo-
neae). — These include the downy mildews nium (oog) and antheridium (ant)
/TI ,,, „, Sperms escaping from antheridium
(Peronospora, Plasmopara, Phytopthora, and creeping up on the oogonium.
etc.), and the white rust of crucifers and (After Thaxter.)
other plants (Cystopus= Albugo), Chapter XIX.
2. SUBCLASS ZYGOMYCETES.
438. These are the conjugating fungi.
439. Order Mucorales (Mucorineae).— This includes the black mold and
its many relatives (Mucor, Rhizopus, etc.). Chapter XIX.
440. Order Entomophthorales (Entomophthorineae). — This order in-
cludes the "fly fungus" (Empusa) and its many relatives parasitic on insects.
216
MORPHOLOGY.
In the autumn and winter dead flies are often found stuck to window-panes,
with a white ring of the conidia around each fly.
II. Class Ascomycetes. (The ascus series.)
1. SUBCLASS HEMIASCOMYCETES.
441. Order Hemiascales (Hemiascineae). — Fungi with a well developed,
septate mycelium, but
with a sporangium-like
ascus, i.e., a large and
indefinite number of
spores in the ascus. Ex-
a m p 1 e s : Protomyces
macrosporus in stems of
Umbelliferae, or P. poly-
sporus in Ambrosia tri-
fida. These two are by
some placed in the Usti-
lagineae. Dipodascus
albidus grows in the
exuding sap of Bromeli-
aceae in Brazil and the
sap of the beech in
Sweden. The ascus is
developed as the result
of the fertilization of an
ascogonium with an an-
. theridium (see fig. 2<i).
maseog
2. SUBCLASS
PBOTOASCOMYCETES.
442. The a sci are well
Fig. 251. defined and usually with
Dipodascus albidus. A, thread with sexual organs, a limited and definite
ascogonium and antheridiuni; B, fertilized ascogonium. , , ,
developing ascus; C, ascus with spores; D, conidia. number ot spores (usu-,
(After Lagerheim.) ally 8> sometimes i, 2,
4, 1 6, or more). Mycelium often well developed and septate. Asci scat-
tered on the mycelium, not associated in definite fields or groups.
443. Order Protoascales (Protoascineae) . — The asci are separate cells,
or are scattered irregularly in loose wefts of mycelium. No fruit body.
(The yeast, Saccharomyces, see paragraph 237; and certain mold-like
fungi, some of which are parasitic , on mushrooms, as Endomyces, are
examples.)
FUNGI CONTINUED: CLASSIFICATION. 217
3. SUBCLASS EUASCOMYCETES.
Asci associated in surfaces forming a hymenium, or in groups or inter-
mingled in the elements of a fruit body. Fruit body usually present.
The following four or five orders comprise the Discomycetes, according
to the usual classification.
444. Order Protodiscales (Protodiscineae). — The asci are exposed and
form large and indefinite groups, but there is no definite fruit body. Ex-
amples: leaf curl of peach, plum pocket, etc. (Exoascus).
445. Order Helvellales (Helvellineae). — The asci form large fields over
the upper portion of the fruit body. This order includes the morels (fig.
2310), helvellas, earth tongues (Geoglossum), etc.
446. Order Pezizales (Pezizineae). — The asci form a definite field or
fruiting surface surrounded on the sides and below by a wall of fungus tis-
sue, forming a fruit body in the shape of a cup. These are known as the
cup fungi (Peziza, Lachnea, etc.).
447. Ordir Phacidiales (Phacidiineae). — Fungi mostly saprophytic, and
fruit body similar to the cup fungi. Examples: Propolis in rotting wood,
Rhytisma forming black crusts on leaves (maple for example), Urnula
craterium, a large black beaker-shaped fungus on the ground.
448. Order Hysteriales (Hysteriinese). — Fungi with a more or less elon-
gated fruit body with an enclosing wall opening by a long slit. In some
forms the fruit body has the appearance of a two-lipped body; in others
it is shaped like a cl&m shell, the asci being inside. Example, Hystero-
graphium common on dry, dead, decorticated sticks.
449. Order Tuberales (Tuberineae). — The more or less rounded fruit
bodies are usually subterranean. The most importantf fungi in this order
are the truffles (Tuber). The mycelium of many species assists in the
formation of mycorhiza on the roots of oaks, etc., and several species are
partly cultivated, or protected, and collected for food. This is especially
the case with Tuber brumale and its forms; more than a million francs
worth of truffles are sold in France and Italy yearly. Dogs and pigs are
employed in the collection of truffles from the ground.
450. Order Plectascales (Plectascineae). — The fruit body of these plants
is more or less globose, and contains the asci distributed irregularly through
the mycelium of the interior. Some are subterranean (Elaphomyces),
while others grow in decaying plants, or certain food substances (Euro-
tium, Sterigmatocystis, Penicillium). Penicillium in its conidial stage
forms blue mold on fruit, bread, etc.
The following four orders comprise the Pyrenomycetes, according to the
usual classification.
451. Order Perisporiales. — The powdery mildews are good examples of
this order (Uncinula, Microsphsera, etc., Chapter XXI).
2l8 MORPHOLOGY.
452. Order Hypocreales.* — The fruit bodies are colorless, or bright
colored and entirely enclose the asci, sometimes opening by an apical pore.
Nectria cinnabarina has clusters of minute orange oval fruit bodies, and is
common on dead twigs. Cordyceps with a number of species is parasitic
on insects, and on certain subterranean Ascomycetes, especially Elapho-
myces (of the order Plectascales=Plectascinea:).
453. Order Dothidiales.* — Fungi with black stroma formed of mycelium
in which are cavities containing the asci. The cavities are usually shaped
like a perithecium, but there is no wall distinct from the tissue of the stroma
(Dothidea, Phyllachora, on grasses).
454. Order Sphaeriales.*— These contain the so-called black fungi, with
separate or clustered, oval, fiuf* ladies, black in color. The black wall
encloses the asci, and usually opens by an apical pore. Examples ar-
found in the black knot of plum and cherry, black rot of grapes, and in
Rosellinia, Hypoxylon, Xylaria, etc., on dead wood.
455. Order Laboulbeniales (Laboulbineae). — These are peculiar fungi
attached to the legs and bodies of insects by a short stalk, and provided
with a sac-like fruit body which contains the asci. Example, Laboulbenia.
III. Class Basidiomycetes. (The basidium series.)
1. SUBCLASS HEMIBASIDIOMYCETES.
456. Order TTstilaginales (Ustilagineae). — This order includes the well-
known smuts on corn, wheat, oats, etc. (Ustilago, Tilletia, etc.).
2. SUBCLASS JECIDIOMYCETES.
457. Order Uredinales f (Uredineae). — This order includes the parasitic
fungi known as rusts. Examples: wheat rust (Chapter XX), the cedar
apple, etc.
The true Basidiomycetes include the following orders:
3. SUBCLASS PBOTOBASIDIOMYCETES.
458. Order Auriculariales.f — This order includes trembling fungi in
which the basidium is long and divided transversely into usually four cells
(example, Auricularia), and similar forms. Pilacre petersii on dead wood
represents an angiocarpous form.
459. Order Tremellales (Tremellinese), trembling or gelatinous fungi
with the globose basidium divided longitudinally into four cells (Tremella) .
* As suborder in Engler and Prantl.
f The Uredinales and Auriculariales in Engler and Prantl are placed in
one order, Auriculariineae.
FUNGI CONTINUED: CLASSIFICATION. 219
4. SUBCLASS EUBASIDIOMYCETES.
460. Order Dacryomycetales (Dacryomycetineae). — This order includes
certain fungi of a gelatinous or waxy consistency, usually of bright colors.
They resemble the Tremellales, but the basidia are slender and fork into
two long sterigmata. (Example, Dacryomyces.) Gyrocephalus rufus is
quite a large plant, 10-15 cm- high, growing on the ground in woods.
461. Order Exobasidiales (Exobasidiineae). — The fungus causing azalea
apples is an example (Exobasidium).
462. Order Hymeniales (Hymenomycetineae). — In this order the basidia
are usually club-shaped and undivided, and bear usually four spores on
the end (sometimes two or six). There are several families.
463. Family Thelephoraceae. — The fruit bodies are more or less mem-
branous and spread over wood or the ground, or somewhat leaflike, grow-
ing on wood or the ground. The fruiting surface is nearly or quite even,
and occupies the under side of the leaflike bodies (Stereum, Thelephora)
or the outside of the forms spread out on wood (Corticium, Coniophora).
464. Family Clavariaceae. — This order includes the fairy clubs, and some
of the coral fungi. The larger number of species are in one genus (Clava-
ria, fig. 248).
465. Family Hydnaceae. — The fungi of this order are known as "hedge-
hog" fungi, because of the numerous awl-like teeth or spines over which
the fruiting surface is spread, as in Hydnum (figs. 246, 247).
466. Family Polyporaceae. — The tube-bearing fungi (Polyporus, Bole-
tus, etc., fig. 245).
467. Family Agaricaceae. — The gill-bearing fungi (Agaricus, Amanita,
etc., see Chapter XXI).
The above five orders, according to the earlier classification (still used at
the present time by some), made up the order Hymenomycetes, while the
following five orders made up the Gasteromycetes. The Hymenomycetes,
according to this system, included those plants in which the fruiting portion
(hymenium) is either exposed from the first, or if covered by a veil or volva
(as in Agaricus, Amanita, etc.) this ruptures and exposes the fruiting sur-
face before,, or at the time of, the ripening of the spores, while the Gaster-
omycetes included those in which the fruit body is closed until after the
maturity of the spores.
468. Order Phallales (Phallineae). — The "stink-horn" fungi, or ".buz-
zard's nose." Usually foul-smelling fungi, the fruiting portion borne aloft
on a stout stalk, and dissolving (Dictyophora, Ithyphallus, etc.).
469. Order Hymenogastrales (Hymenogastrineae). — The basidia form a
distinct hymenium on walls of chambers, which do or do not break down
at maturity, but there are no sterile threads forming a capillitium. Some
of the plants resemble Boletus or Agaricus in the way the fruit bodies open
(Secotiumj etc.), while others open irregularly on the surface (Rhizopogon) or
22O MORPHOLOGY.
like an earth star (Sclerogaster), or portions of the surface become gelatin-
ized (Phallogaster). The last-named one grows on very rotten wood, while
most of the others grow on the ground.
470. Order Lycoperdales (Lycoperdineae). — These include the "puff-
balls," or "devil's snuff-box" (Lycoperdon), and the earth stars (Geaster).
The basidia form a distinct hymenium, but at maturity the entire inner por-
tion of the plant (except certain peculiar threads, the capillitium) disinte-
grates and with the spores forms a powdery mass.
471. Order Nidulariales (Nidulariineae). — These are known as bird-nest
fungi. The fruit body when mature is cup-shaped, or goblet-shaped, and
contains minute flattened circular bodies (peridiola) containing the spores.
The intermediate portions of the fruit body disintegrate and set the peri-
diola free, which then lie in the cup-shaped base like eggs in a nest.
472. Order Plectobasidiales (Plectobasidiineae). — The basidia do not
form a definite hymenium, but are interwoven with the threads inside, or
are collected into knot-like groups. (Examples: Calostoma, Tulostoma,
Astraeus, Sphaerobolus, etc.)
472a. Lichens. — The plant body of the lichens (see paragraphs 200,
201) consists of two component parts, the one a fungus, the other an alga.
The fructification is that of the fungus. The fruit body shows the lichens
to be related some to the Ascomycetes, others to. the Hymenomycetes, and
Gasteromycetes. They are usually classified as a distinct class or order
from the fungi, but a natural arrangement would distribute them in sev-
eral of the orders above. Their special relationship with these orders has
not been satisfactorily worked out. For the present they are arranged as
follows:
Ascolichenes.
Pyrenocarpous lichens (those with a fruit body like the Pyrenomycetes).
Gymnocarpous lichens (those with a fruit body like the Discomycetes).
Hymenolichen.es (those with a fruit body like the Hymenomycetes).
Gasterolichenes (those with a fruit body like the Gasteromycetes).
From a vegetative standpoint there are two types according to the dis-
tribution of the elements.
i st. Where the fungal and algal elements are evenly distributed in the
plant body the lichen is said to be homoiomerous. There are two types of
these:
a. Filamentous lichens, example, Ephebe pubescens.
b. Gelatinous lichens, example, Collema (with the alga nostoc), Physma
(with the Chroococcaceae).
2d. Where the elements are stratified, as in Parmelia, etc., the lichen is
said to be heteromerous. In these there are three types:
a. Crustaceous lichens, the plant body is in the form of a thin incrusta
tion on rocks, etc.
FUNGI CONTINUED: CLASSIFICATION.
221
b. Foliaceous lichens, the plant body is leaflike and lobed and more or less
loosely attached by rhizoids: Parmelia, Peltigera-- etc.
Fig. 2510.
Rock lichen (Parmelia contigua).
c. Fruticose lichens, the plant body is filamentous or band-like and
branched, as in Usnea, Cladonia, etc.
CHAPTER XXIII.
LIVERWORTS (HEPATIC^).
473. We come now to the study of representatives of another
group of plants, a few of which we examined in studying the organs
of assimilation and nutrition. I refer to what are called the liver-
worts. Two of these liverworts belonging to the genus riccia
are illustrated in figs. 30, 252.
Riccia.
474. Form of the floating riccia (R. fluitans). — The gen-
eral form of floating riccia is that of a narrow, irregular, flattened,
ribbon-like object, which forks repeatedly, in a dichotomous
manner, so that there are several lobes to a single plant. It
receives its name from the fact that at certain seasons of the year
it may be found floating on the water of pools or lakes. When
the water lowers it comes to rest on the damp soil, and rhizoids
are developed from the under side. Now the sexual organs, and
later the fruit capsule, are developed.
475. Form of the circular riccia (R. crystallina). — The
circular riccia is shown in fig. 252. The form of this one is quite
different from the floating one, but the manner of growth is much
the same. The branching is more compact and even, so that a cir-
cular plant is the result. This riccia inhabits muddy banks,
lying flat on the wet surface, and deriving its soluble food by
means of the little rootlets (rhizoids) which grow out from the
under surface.
Here and there on the margin are narrow slits, which extend
222
LIVERWORTS: RICCIA.
223
Fig. 252.
Thallus of Riccia crystallina.
nearly to the central point. They are not real slits, however, for
they were formed there as the plant grew. Each one of these
V-shaped portions of the thal-
lus is a lobe, and they were
formed in the young condition
of the plant by a branching
in a forked manner. Since
growth took place in all direc-
tions radially the plant be-
came circular in form. These
large lobes we can see are
forked once or twice again,
as shown by the seeming
shorter slits in the margin.
476. Sexual organs. — In
order to study the sexual organs we must make thin sections
through one of these lobes lengthwise and perpendicular to the
thallus surface. These sections are mounted for examination
with the microscope.
477. Archegonia. — We are apt to find the organs in various stages of de-
velopment, but we will select one of the flask-shaped structures shown in fig.
253 for study. This flask-shaped body we see is entirely sunk in the tissue
of the thallus. This structure is the female organ, and is what we term in
these plants the archegonium. It is more complicated in structure than the
oogonium. The lower portion is enlarged and bellied out, and is the venter
of the archegonium, while the narrow portion is the neck. We here see it in
section. The wall is one cell layer in thickness. In the neck is a canal,
and in the base of the venter we see a large rounded cell with a distinct
and large nucleus. This cell is the egg cell.
478. Antheridia. — The antheridia are also borne in cavities sunk in the
tissue of the thallus. There is here no illustration of the antheridium of this
riccia, but fig. 259 represents an antheridium of another liverwort, and there
is not a great difference between the two kinds. Each one of those little rect-
angular sperm mother cells in the antheridium changes into a swiftly moving
body like a little club with two long lashes attached to the smaller end By
the violent lashing of these organs the sperrnatozoid is moved through the water,
or moisture which is on the surface of the thallus. It moves through the canal
of the archegonium neck and into the egg, where it fuses with the nucleus of
the egg, and thus fertilization is effected.
224
MORPHOLOG Y.
479. Embryo. — In the plants which we have selected thus far for study,
the egg, immediately after fecundation, we recollect, passed into a resting
state, and was enclosed by a thick protecting wall. But in riccia, and in the
other plants of the group which we are now studying, this is not the case.
Fig. 253.
Archegonium of riccia, showing neck,
venter, and the egg; archegonium is partly
surrounded by the tissue of the thallus.
(Riccia crystallina.)
Fig. 254.
Young embryo (sporogoni-
um) of riccia, within the venter
of the archegonium ; the latter
has now two layers of cells.
(Riccia crystallina.)
The egg, on the other hand, after acquiring a thin wall, swells up and fills
the cavity of the venter. Then it divides by a cross wall into two cells.
These two grow, and divide again, and so on until there is formed a quite
large mass of cells rounded in form and still contained in the venter of the
archegonium, which itself increases in size by the growth of the cells of the
wall.
480. Sporogonium of riccia. — The fruit of riccia, which is
developed from the fertilized egg in the archegonium, forms a
rounded capsule still enclosed in the venter of the archegonium,
which grows also to provide space for it. Therefore a section
through the plant at this time, as described for the study
of the archegonium, should show this capsule. The capsule
then is a rounded mass of cells developed from the egg. A sin-
gle outer layer of cells forms the wall, and therefore is sterile.
LIVERWORTS: RICCIA.
225
All the inner cells, which are richer in protoplasm, divide into
four cells each. Each of these cells becomes a spore with a thick
wall, and is shaped like a triangular pyramid whose sides are of
the same extent as the base (tetrahedral). These cells formed in
B
Fig. 255-
Nearly mature sporogonium of Riccia crystallina ;
mature spore at the right.
Fig. 256.
Riccia glauca ; archegonium
containing nearly mature spo-
rogonium. sg, spore-producing
cells surrounded by single layer
of sterile cells, the wall of the
sporogonium.
fours are the spores. At this time the wall of the spore-case dis-
solves, the spores separate from each other and fill the now en-
larged venter of the archegonium. When the thallus dies they
are liberated, or escape between the loosely arranged cells of
the upper surface.
481. A new phase in plant life. — Thus we have here in the
sporogonium of riccia a very interesting phase of plant life, in
which the egg, after fertilization, instead of developing directly
into the same phase of the plant on which it was formed,
grows into a quite new phase, the sole function of which is the
development of spores. Since the form of the plant on which the
sexual organs are developed is called the gametophyte, this new
phase in which the spores are developed is termed the sporo-
phyte.
Now the spores, when they germinate, develop the gameto-
phyte, or thallus, again. So we have this very interesting condi-
226 MORPHOLOG Y.
tion of things, the thallus (gametophyte) bears the sexual organs
and the unfertilized egg. The fertilized egg, starting as it does
from a single-celled stage, develops the sporogonium (sporo-
phyte). Here the single-cell stage is again reached in the spore,
which now develops the thallus.
482. Biccia compared with coleochsete, cedogonium, etc. — We have said
that in the sporogonium of riccia we have formed a new phase in plant life.
If we recur to our study of coleochsete we may see that there is here possibly
a state of things which presages, as we say, this new phase which is so well
formed in riccia. We recollect that after the fertilized egg passed the period
of rest it formed a small rounded mass of cells, each of which now forms a
zoospore. The zoospore in turn develops the normal thallus (gametophyte)
of the coleochsete again. In coleochsete then we have two phases of the
Jplant, each having its origin in a one-celled stage. Then if we go back
to oedogonium, we remember that the fertilized egg, before it developed
into the oedogonium plant again (which is the gametophyte), at first divides
into four cells which become zoospores. These then develop the oedogonium
plant.
Note. Too much importance should not be attached to this seeming ho-
mology of the sporophyte of oadogonium, coleochsete, and riccia, for the nu-
clear phenomena in the formation of the zoospores of oedogonium and coleo-
chsete are not known. They form, however, a very suggestive series.
Marchantia.
483. The marchantia (M. polymorpha) has been chosen for
study because it is such a common and easily obtained plant, and
also for the reason that with comparative ease all stages of
development can be obtained. It illustrates also very well cer-
tain features of the structure of the liverworts.
The plants are of two kinds, male and female. The two dif-
ferent organs, then, are developed on different plants. In
appearance, however, before the beginning of the structures
which bear the sexual organs they are practically the same. The
thallus is flattened like nearly all of the thalloid forms, and
branches in a forked manner. The color is dark green, and
through the middle line of the thallus the texture is different
from that of the margins, so that it possesses what we term a
LIVER WOR TS : MA R CHA N TIA .
227
midrib, as shown in figs. 257, 261. The growing point of the
thallus is situated in the little depression at the free end. If we
examine the upper surface with a hand
lens we see diamond-shaped areas, and
at the center of each of these areas are
the openings known as the stomates.
484. Antheridial plants. — One of
the male plants is figured at 257. It
bears curious structures,
each held aloft by a short
stalk. These are the an-
theridial recep-
tacles (or male
gametophores).
Each one is cir-
cular, thick, and
Fig. 257-
Male plant of marchantia bearing antheridiophores.
shaped some-
what like a bi-
convex lens. The upper surface is marked by radiating fur-
rows, and the margin is crenate. Then we note, on careful
examination of the upper surface, that there are numerous minute
openings. If we make a thin section of this structure perpen-
I/
Fig. 258.
Section of antheridial receptacle from male plant of Marchantia polymorpha, showing
cavities where the antheridia are borne.
dicular to its surface we shall be able to unravel the mystery of
its interior. Here we see, as shown in fig. 258, that each one
of these little openings on the surface is an entrance to quite
228
MORPHOLOG Y.
a large cavity. Within each cavity there is an oval or ellip
tical body, supported from the base of the cavity on a short
stalk. This is an antheridium, and one of them is shown still
more enlarged in fig. 259. This shows the structure of the
antheridium, and that there are within several angular areas,
which are divided by numerous straight cross-lines into countless
tiny cuboidal cells, the sperm mother cells. Each of these, as
stated in the former chapter, changes into a swiftly moving body
resembling a serpent with two long lashes attached to its tail.
485. The way in which one of these sperm mother cells changes into this
spermatozoid is very curious. We first note that a coiled spiral body is appear-
Fig. 259.
Section of antheridium of mar-
chantia, showing the groups of
sperm mother cells.
Fijj. 260.
Spermatozoids of marchantia,
uncoiling and one extended, show-
ing the two cilia.
ing within the thin wall of the cell, one end of the coil larger than the other.
The other end terminates in a slender hair-like outgrowth with a delicate vesi-
cle attached to its free end. This vesicle becomes more and more extended
until it finally breaks and forms two long lashes which are clubbed at their
free ends as shown in fig. 260.
486. Archegonial plants. — In fig. 261 we see one of the
female plants of marchantia. Upon this there are also very
curious structures, which remind one of miniature umbrellas.
The general plan of the archegonial receptacle (or female
LIVERWORTS: MARCHANTIA.
229
gametophore), for this is what these structures are, is similar to
that of the antheridial receptacle, but the rays are more pro-
nounced, and the details of structure are quite different, as we
shall see. Underneath the arms there hang down delicate
fringed curtains. If we make sections of this in the same direc-
Fig. 361.
Marchantia polymorpha, female plants bearing archegoniophores.
tion as we did of the antheridial receptacle, we shall be able to
find what is secreted behind these curtains. Such a section is
figured at 266. Here we find the archegonia, but instead of
being sunk in cavities their bases are attached to the under
230
MORPHOLOG Y.
surface, while the delicate, pendulous fringes afford them pro-
tection from drying. An archegonium we see is not essentially
different in marchantia from what it is in riccia, and it will be
interesting to learn whether the sporogonium is essentially dif-
ferent from what we find in riccia.
487. Homology of the gametophore of marchantia. — To see the relation
of the gametophore to the thallus of
marchantia take portions of the
thallus bearing the female recepta-
cle. On the under side note that
the prominent midrib continues be-
yond the thin lateral expansions and
arches upward in the sinus or notch
at the end, or at the side where the
branch of the thallus has continued
to grow beyond. The stalk of the
gametophore is then a continuation
of the midrib of the thallus. On
the apex of this are organized sev-
eral radial growing points which
develop the digitate or ray-like
receptacle. The gametophore is
thus a specialized branch' of the
thallus. When young, or in many
cases when nearly or quite mature,
the gametophore, as one looks at
the upper surface of the thallus,
appears to arise from the upper
surface, as in fig. 261. This is
p. 26z because the thin lateral expansions
Marchantia polymorpha, showing origin of the thallus project forward and
of gametophore. overlap in advance of the stalk. It
is sometimes necessary to tear these overlapping edges apart to see the
real origin of the gametophore. But in quite old plants these expanded
portions are farther apart and show clearly that the stalk arises from the
midrib below and arches upward in the sinus, as in fig. 262.
CHAPTER XXIV.
LIVERWORTS CONTINUED.
488. Sporogonium of marchantia. — If we examine the plant
shown in fig. 181 we shall see oval bodies which stand out be-
Fig. 263.
Archegonial receptacles of marchantia bearing ripe sporogonia The
capsule of the sporogonium projects outside, while the stalk is attached to
the receptacle underneath the curtain. In the left figure two of the
capsules have burst and the elaters and spores are escaping.
tween the rays of the female receptacle, supported
on short stalks. These are the sporogonia, or
spore-cases. We judge at once that they are quite
different from those which we have studied in
riccia, since those were not stalked. We can see
that some of the spore-cases have opened, the wall
splitting down from the apex in several lines. This
is caused by the drying of the wall. These tooth-
like divisions of the wall now curl backward, and
we can see the yellowish mass of the spores in slow motion,
231
232
MORPHOLOG V.
falling here and there. It appears also as if there were twisting
threads which aided the spores in becoming freed from the
capsule.
Fig. 264.
Section of archegpnial receptacle of March antia polymorpha; ripe
sporogonia. One is open, scattering spores and elaters; two are
stiU enclosed in the wall of the archegonium. The junction of the
stalk of the sporogonium with the receptacle is the point of attach-
ment of the sporophyte of marchantia with the gametophyte.
489. Spores and elaters. — If we take a bit
of this mass of spores and mount it in water
for examination with the microscope, we shall
see that, besides the spores, there are very
peculiar thread-like bodies,
the markings of which remind
one of a twisted rope. These
are very long cells from the
inner part of the spore-case,
and their walls
are marked by spi -
ral thickenings.
This causes them
in drying,and also
when they absorb
Fig. 265.
moisture, tO twist Elater and spore of marchantia. j/, spore; me, mother-cell of
. , ,, spores, showing partly formed spores.
and curl in all
sorts of ways. They thus aid in pushing the spores out of the
capsule as it is drying.
490. Sporophyte of marchantia compared with riccia. —
We must recollect that the sporogonium in marchantia is larger
than in riccia, and that it is also not lying in the tissue of the
thallus, but is only attached to it at one side by a slender stalk.
LIVER WOR TS : MA R CHANTIA .
233
This shows us an increase in the size and complex structure of
this new phase of the plant, the sporophyte. This is one of the
very interesting things which we have to note as we go on in the
study of the higher plants.
Fig. 266.
Marchantia pplymorpha, archeeonium at the left with egg 5 archegonium at the right with
young sporogonium ; /, curtain which hangs down around the archegonia ; e, egg ; v, venter
of archegonium ; n, neck of archegonium ; sp, young sporogonium.
491. Sporophyte dependent on the gametophyte for its nutri-
ment.— We thus see that at no time during the development of the
sporogonium is it independent from the gametophyte* This new
phase of plants then, the sporophyte, has not yet become an in-
dependent plant, but must rely on the earlier phase for sustenance.
492. Development of the sporogonium. — It will be interesting to note
briefly how the development of the marchantia sporogonium differs from that
of riccia. The first division of the fertilized egg is the same as in riccia, that
is a wall which runs crosswise of the axis of the archegonium divides it
. into two cells. In marchantia the cell at the base develops the stalk, so
that here there is a radical difference. The outer cell forms the capsule.
But here after the wall is formed the inner tissue does not all go to m;ike
spores, as is the case with riccia. But some of it forms the elaters. While
in riccia only the outside layer of cells of the sporogonium remained sterile,
in marchantia the basal half of the egg remains completely sterile and
234
MORPHOLOG Y.
develops the stalk, ana in the outer half the part which is formed from some
of the inner tissue is also sterile.
Fig. 267.
Section of developing sporogonia of marchantia ; nt, nutritive tissue of gametophyte ; si,
sterile tissue of sporophyte ; sp, fertile part of sporophyte ; va, enlarged venter of arche-
gonium.
493. Embryo. — In the development of the embryo we can see all the way
through this division line between the basal half, which is completely sterile,
and the outer half, which is the fertile part. In fig. 267 we see a young
embryo, and it is nearly circular in section although it is composed of
numerous cells. The basal half is attached to the base of the inner surface
of the archegonium, and at this time the archegonium still surrounds it. The
archegonium continues to grow then as the embryo grows, and we can see
the remains of the shrivelled neck. The portion of the embryo attached to
the base of the archegonium is the sterile part and is called the "-foot," and
later develops the stalk. The sporogonium during all the stages of its
development derives its nourishment from the gametophyte at this point of
LIVERWORTS: MARCHANTIA. 235
attachment at the base of the archegonium. Soon, as shown in fig. 267 at
the right, the outer portion of the sporogonium begins to differentiate into
the cells which form the elaters and those which form spores. These lie in
radiating lines side by side, and form what is termed the archesporinm. Each
fertile cell forms four spores just as in riccia. They are thus called the
mother cells of the spores, or spore mother cells.
494. How marchantia multiplies. — New plants of marchantia are formed
by the germination of the spores, and growth of the same to the thallus.
The plants may also be multiplied by parts of the old ones breaking away
by the action of strong currents of water, and when they lodge in suitable
places grow into well-formed plants. As the thallus lives from year to year
and continues to grow and branch the older portions die off, and thus sepa-
rate plants may be formed from a former single one.
495. Buds, or gemmae, of marchantia.- — But there is another way in which
marchantia multiplies itself. If we examine the upper surface of such a
Fig. 268.
Marchantia plant with cupules and gemmae ; rhizoids below.
plant as that shown in fig. 268. we shall see that there are minute cup-
' shaped or saucer-shaped vessels, and within them minute green bodies.
If we examine a few of these minute bodies with the microscope we see that
they are flattened, biconvex, and at two opposite points on the margin there
is an indentation similar to that which appears at the growing end of
the old marchantia thallus. These are the growing points of these little
buds. When they free themselves from the cups they come to lie on one
236
MORPHOLOG Y.
side. It does not matter on what side they lie, for whichever side it is, that
will develop into the lower side of the thallus, and forms rhizoids, while the
upper surface will develop the stomates.
Leafy-stemmed liverworts.
496. We should now examine more carefully than we have
done formerly a few of the leafy-stemmed liverworts (called
foliose liverworts).
497. Frullania (Fig. 32). — This plant grows on the bark of
logs, as well as on the bark of standing trees. It lives in quite
dry situations.
If we examine
the leaves we
will see how it is
able to do this.
We note that
there are two
rows of lateral
leaves, which
are very close
together, so
close in fact that
they overlap
like the shingles
on a roof.
Fig. 260. Then, as the
Section of thallus of marchantia. A , through the middle portion ;
B, through the marginal portion ; /, colorless layer ; chl, chlorophyll Creeping Stems
layer; sp, stomate; A, rhizoids; b, leaf-like outgrowths on under
side (Goebel).
lie very close to
the bark of the tree, these overlapping leaves, which also
hug close to the stem and bark, serve to retain moisture
which trickles down the bark during rains. If we examine
these leaves from the under side as shown in fig. 34, we see
that the lower or basal part of each one is produced into a
peculiar lobe which is more or less cup-shaped. This catches
water and holds it during dry weather, and it also holds moisture
which the plant absorbs during the night and in damp days.
FOLIO SE LIVERWORTS.
237
There is so much moisture in these little pockets of the under
side of the leaf that minute animals have found them good places
to live in, and one frequently discovers them in this retreat.
There is here also a third row of poorly developed leaves on the
under side of the stem.
498. Porella. Growing in similar situations is the plant known as
porella. Sometimes there are a few plants
in a group, and at other times large mats
occur on the bark of a trunk. This plant,
porella, also has closely overlapping leaves
in rows on opposite sides of the stem, and
the lower margin of each leaf is curved
under somewhat as
in frullania, though
the pocket is not so
well formed.
The larger plants
are female, that is
they bear archego-
nia, while the male
plants, those which
bear anUieridia, are
smaller and the an-
theridia are borne
on small lateral
branches. The an-
theridia are borne
in the axils of the
leaves. Others of
the leafy-stemmed
liverworts live in
damp situations.
Some of these, as
Cephalozia, grow on damp rotten logs. Cephalozia is much more delicate,
and the leaves are farther apart. It could not live in such dry situations
where the frullania is sometimes found. If possible the two plants should be
compared in order to see the adaptation in the structure and form to their
environment.
499. Sporogonium of a foliose liverwort. — The sporogonium
of the leafy-stemmed liverworts is well represented by that of
several genera. We may take for this study the one illustrated
I'ig. 270.
Thallus of a thalloid liverwort (blasia) showing lobed
margin of the frond, intermediate between thalloid and
foliose plant.
238
MORPHOLOG Y.
in fig. 274, but another will serve the purpose just as well. We
note here that it consists of a rounded capsule borne aloft on a
long stalk, the stalk being much longer proportionately than in
marchantia. At maturity the capsule splits down into four
Fig. 272.
Antheridium of a foliose liverwort (jun-
germannia).
Fig. 271.
Foliose liverwort, male plant showing anthe-
ridia in axils of the leaves (,a jungermannia).
Fig. 273.
Foliose liverwort, female plant with
rhizoids.
quadrants, the wall forming four valves, which spread apart from
the unequal drying of the cells, so that the spores are set free, as
shown in fig. 276. Some of the cells inside of the capsule de-
velop elaters here also as well as spores. These are illustrated
in fig. 278.
500. In this plant we see that the sporophyte remains attached
FOLIO SE LIVERWORTS.
239
to the gametophyte, and thus is dependent on it for sustenance.
This is true of all the plants of this
group. The sporophyte never becomes
capable of an independent existence,
and yet we see that it is becoming
larger and more highly differentiated
than in the simple riccia.
Fig. 275.
Opening capsule
showing escape of
spores and elaters.
Fig. 276.
Capsule parted down
to the stalk.
Fig. 274.
Fruiting plant of a foliose liver-
rort (jungermannia). Leafy part
is the gametophyte ; stalk and cap-
Fig. 277.
Fig. 278.
0 .._,._, f Four spores from Elaters, at left showing the two
sule is the sporophyte (sporogonium mother cell held in spiral marks, at right a branched
in the bryophytes). a group. elater.
Figs. 275-278. — Sporogonium of liverwort (jungermannia) opening by splitting into four
parts, showing details of elaters and spores.
240
MORPHOLOG Y.
The Horned Liverworts.*
501. The horned liverworts take their name from the shape of the spo-
rogonium. This is long, slender, cylindrical, pointed, and very slightly
curved, suggesting the shape of a minute horn. Anthoceros is one of the
most common and widely distributed species. The plant grows on damp
soil or on mud.
Anthoceros.
502. The gametophyte. — The gametophyte is thalloid. It is thin, flat-
tened, green, irregularly ribbon-shaped and branched. It lies on the soil
and is more or less crisped or
wavy, or curled, the edges nearly
plane, or somewhat irregular,
and with minute lobes, or
notches, especially near the
growing end. The general form
and branching can be seen in
fig. 279. Where the plants are
much crowded the thallus is more
irregular, and often possesses nu-
merous small lateral branches in
addition to the main lobes.
Upon the under side are the
slender rhizoids, which attach
to the soil. With a hand lens
there can be seen also upon the
under side small dark, rounded
and thickened spots, where an
alga (nostoc) is located.
Sexual Organs of
AnthoceroSn
2? ^& & 502. The sexual organs of an-
Fig. 279. thoceros differ considerably from
Anthoceros gracilis. A, several gameto- those of the other liverworts
phytes, on which sporangia have developed, _
B, an enlarged sporogonium, showing its studied. In the first place they
va^ves^leaving^xposed1 the blender0 columella are immersed in the true tissue
on the surface of which are the spores, C, D, Qf the thallus, i.e., they do not
E, F, elaters of vanous forms, G-, spores.
(After Schiffner.) project above the surface.
503. Antheridia. — The antheridium arises from an internal cell of the
thallus, a cell just below the upper surface. This cell develops usually a
* May be used as an alternate study for marchantia.
HORNED LIVERWORTS'. 241
group of antheridia which lie in a cavity formed around this cell as the
thallus continues to grow. They are situated along the middle line of the
thallus, and can be seen by making a section in this direction. The anthe-
ridia are oval or rounded, have a wall of one layer of cells which contains
the sperm cells, and each antheridium has a slender stalk. The sperms
are like those of the true liverworts.
504. Archegonia. — The archegonia are also borne along the middle line
of the thallus. Each one arises at an early stage in the development of
the tissue of the thallus from a superficial cell, but the archegonium does
not project above the surface. The venter therefore which contains the
egg is deep down in the thallus, the wall of the neck is formed from cells
indistinguishable from the adjoining cells of the thallus and opens at the
surface.
Sporophyte of Anthoceros.
505. The Sporogonium. — The sporogonium is developed from the fer-
tilized egg, fertilization resulting of course from the fusion of one of the
sperms with the nucleus of the egg. From the lower part of the embryo
certain cells elongate and push out like rhizoids into the thallus (gameto-
phyte), but never reach the outside so that the sporogonium derives its
nutriment from the gametophyte in a parasitic manner like the true liver-
worts. It is surrounded at the base by a sheath, an outgrowth of the
gametophyte.
506. Growing point of the sporogonium. — A remarkable thing about
the sporogonium of anthoceros, and its relatives, is that the growing point
instead of being situated at the free end is located near the base, just above
the nourishing foot. Thus the upper part of the sporogonium is older. In
the old sporogonia there may be ripe spores near the free end, young ones
near the middle, and undifferentiated growing tissue near the base. A
longitudinal section of a sporogonium just as the spores are ripening will
show this.
507. Structure of the sporogonium. — A longitudinal section of the spo-
rogonium shows that the spore-bearing tissue occupies a comparatively
small portion of the sporogonium. In the section there is a narrow layer
(two cells thick) on either side and joined at the top. In the entire spo-
rogonium this fertile tissue is in the shape of an inverted test-tube situated
inside of the sporogonium. The wall of the sporogonium is about four
cells thick. The sterile tissue inside of the spore-bearing tube is the colu-
mella. The cells of the wall contain chlorophyll, and there are true stomata
with guard cells in the epidermal layer.
508. Spores and elaters. — In the spore-bearing tissue there are two layers
of cells (the archesporium) . Each cell is a potential mother-cell. The
cells, however, of alternate tiers do not form spores. They elongate some •
242 MORPHOLOG Y.
what and are somewhat irregular and sometimes divide or branch. They
are supposed to represent rudimentary elaters. The cells in the other tiers
are actual mother-cells, and each one forms four spores.
509. The sporophyte of anthoceros represents the highest type found in
the liverworts. The spongy green parenchyma forming the wall, with the
stomata in the epidermal layer, fits this tissue for the process of photosyn-
thesis, so that this part of the sporophyte functions as the green leaf of the
seed plants. It has been suggested by some that if the rhizoids on the
nourishing foot could only extend outside and anchor in the soil, the sporo-
phyte of anthoceros could live an independent existence. But we see that
it stops short of that.
Classification of the Liverworts.
CLASS HEPATICJE.
510. Order Marchantiales.* — There are two families represented in
the United States.
Family Ricciaceae, including Riccia and Ricciocarpus.
Family Marchantiaceae, including Marchantia, Fegatella (=Cono-
cephalus), Fimbriaria, Targionia, etc.
511. Order Jungermanniales.* — There are two subdivisions of this order.
The Anacrogyna include chiefly thalloid forms with continued apical
growth, the archegonia back of the apical cell. Examples: Blasia, Aneura,
Pellia, etc.
The Acrogyna include chiefly foliose forms, the archegonia arising from
the apical cell and in such cases interrupting apical growth. Examples:
Cephalozia, Frullania, Bazzania, Jungermannia, Ptilidium, Porella, etc.
CLASS ANTHOCEROTES.
512. The Anthocerotes have formerly been placed with the Hepaticae
as an order. But because of their wide divergence from the other liver-
worts in the development of the sexual organs, and especially in the struc-
ture of the sporophyte, they are now by some separated as a distinct class.
There is one order.
Order Anthocerotales.* — This includes one family (Anthocerotaceae)
with Anthoceros and Notothylas in Europe and North America, and Den-
droceros in the tropics. The latter is epiphytic.
* As subclass in Engler and Prantl.
CHAPTER XXV.
MOSSES (MUSCI).
513. We are now ready to take up the more careful study of
the moss plant. There are a great many kinds of mosses, and
they differ greatly from each other in the finer details of struc-
ture. Yet there are certain general resemblances which make it
convenient to take for study almost any one of the common
species in a neighborhood, which forms abundant fruit. Some,
however, are more suited to a first study than others. (Polytri-
chum and funaria are good mosses to study.)
514. Mnium. — We will select here the plant shown in fig. 280.
This is known as a mnium (M. affine), and one or another of the
species of mnium can be obtained without much difficulty.
The mosses, as we have already learned, possess an axis
(stem) and leaf-like expansions, so that they are leafy-stemmed
plants also. Certain of the branches of the mnium stand upright,
or nearly so, and the leaves are all of the same size at any given
point on the stem, as seen in the figure. There are three rows
of these leaves, and this is true of most of the mosses.
515. The mnium plants usually form quite extensive and pretty
mats of green in shady moist woods or ravines. Here and there
among the erect stems are prostrate ones, with two rows of promi-
nent leaves so arranged that it reminds one of some of the leafy-
stemmed liverworts. If we examine some of the leaves of the
mnium we see that the greater part of the leaf consists of a
single layer of green cells, just as is the case in the leafy -stemmed
liverworts. But along the middle line is a thicker layer, so that
it forme a distinct midrib. This is characteristic of the leaves
244
MORPHOLOGY.
of mosses, and is one way in which they are separated from the
leafy-stemmed liverworts, the latter never having a midrib.
516. The fruiting moss plant. — In fig. 280 is a moss plant " in
fruit, " as we say. Above the leafy stem a slender stalk bears
the capsule, and in this capsule are borne
the spores. The capsule then belongs to
the sporophyte phase of the moss plant, and
we should inquire whether the entire plant
as we see it here is the sporophyte, or
whether part of it is gametophyte. If
a part of it is gametophyte and a part
sporophyte, then where does the one end
and the other begin ? If we strip off the
leaves at the end of the leafy stem, and
make a longisection in the middle line, we
should find that the stalk which bears the
capsule is simply stuck into the end of the
Fig. 280.
Portion of moss plant of Mnium affine, showing two
sporogonia from one branch. Capsule at left has just shed
the cap or operculum ; capsule at right is shedding spores,
and the teeth are bristling at the mouth. Next to the right
is a young capsule with calyptra still attached ; next are
two spores enlarged.
leafy stem, and is not organically connected with it. This is
the dividing line, then, between the gametophyte and the sporo-
phyte. We shall find that here the archegonium containing
MOSSES.
245
the egg is borne, which is a surer way of determining the limits
of the two phases of the plant.
517. The male and female moss plants. — The two plants of mnium shown in
figs. 281, 282 are quite different, as one can easily see, and yet they belong
to the same species. One is a female plant, while the other is a male plant.
The sexual organs then in mnium, as
in many others of the mosses, are borne
on separate plants. The archegonia
are borne at the end of the stem, and are
protected by somewhat narrower leaves
which closely overlap and are wrapped
together. They are similar to the
archegonia of the liverworts.
Female plant (gametopiiyte) of a muss
(mnium), showing rhizoids below, and the
tuft of leaves above which protect the arche-
gonia.
Fig. 28 2
Male plant (gametophyle) of a moss
(mnium) showing rhizoids below and the
antheridia at the center above surrounded by
the rosette of leaves.
The male plants of mnium are easily selected, since the leaves at the end
of the stem form a broad rosette with the antheridia, and some sterile threads
packed closely together in the center. The ends of the mass of antheridia
can be seen with the naked eye, as shown in fig. 282. When the antheridia
246
MORPHOLOG Y.
are ripe, if we make a section through a cluster, or if we merely tease out
some from the end with a needle in a drop of water on the slide, then prepare
for examination with the microscope, we can see the form of the antheridia.
They are somewhat clavate or elliptical in outline, as seen in fig. 284. Be-
tween them there stand short threads composed of several cells containing
chlorophyll grains. These are sterile threads (paraphyses).
518. Sporogonium. — In fig. 280 we see illustrated a sporogonium of mnium,
which is of course developed from the fertilized egg cell of the archegonium.
There is a nearly cylindrical capsule, bent downward, and supported on a long
Fig. 283-
Fig. 284.
Antheridium of mnium
with jointed paraphysis
at the left ; spermato-
zoids at the right.
slender stalk. Upon the capsule is a peculiar cap,* shaped like a ladle or
spatula. This is the remnant of the old archegonium, which, for a time sur-
rounded and protected the young embryo of the sporogonium, just as takes
place in the liverworts. In most of the mosses this old remnant of the arche-
gonium is borne aloft on the capsule as a cap, while in the liverworts it is
thrown to one side as the sporogonium elongates.
519. Structure of the moss capsule. — At the free end on the moss capsule
* Called the calyptra.
MOSSES.
247
as shown in the case of mnium in fig. 280, after the remnant of the arche-
gonium falls away, there is seen a conical lid which fits closely over the end.
When the capsule is ripe this lid easily falls away, and can be brushed off
so that it is necessary to handle the* plants with care if it is
desired to preserve this for study.
520. When the lid is brushed away as the capsule dries
more we see that the end of the capsule covered by the lid
appears "frazzled." If we examine this end with the micro-
scope we see that the tissue of the capsule here is torn
with great regularity, so that there are two rows of narrow,
sharp teeth which project outward in a ring around the
opening. If we blow our "breath" upon these teeth they
will be seen to move, and as the
moisture disappears and reappears
in the teeth, they close and open
the mouth of the capsule, so sensi-
tive are they to the changes in the
humidity of the air. In this way
all of the spores are prevented to
some extent from escaping from
the capsule at one time.
521. Note. If we make a sec-
tion longitudinal of the capsule of
mnium, or some other moss, we find
that the tissue which develops the
spores is much more restricted
than in the capsule of the liver-
worts which we have studied. The
spore-bearing tissue is confined to
a single layer which extends around
the capsule some distance from the
outside of the wall, so that a central
Two different stages of young sporogonium of cylinder is left of sterile tissue.
a moss, still within the archegonium and wedg- TMs is the columella, and is pres-
ing their way into the tissue of the end of the stem. r
/«j neck of archegonium ; /, young sporogonium. ent in nearly all the mosses. Each
This shows well the connection of the sporophyte r ,. „ /•../- . -i i
with the gametophyte. of the cells of the fertile layer
divides into four spores.
522. Development ol the sporogonium. — The egg cell after fertilization
divides by a wall crosswise to the axis of the archegonium. Each of these
cells continues to divide for a time, so that a cylinder pointed at both ends is
formed. The lower end of this cylinder of tissue wedges its way down
through the base of the archegonium into the tissue of the end of the moss
stem as shown in fig. 285. This forms the foot through which the nutrient
Fig. 285.
248 MORPHOLOG Y.
materials are passed from the gametophyte to the sporogonium. The upper
part continues to grow, and finally the upper end differentiates into the mature
capsule.
523. Protonema of the moss. — When the spores of a moss germinate they
form a thread-like body, with chlorophyll. This thread becomes branched,
and sometimes quite extended tangles of these threads are formed. This is
called the protonema, that is first thread. The older threads become finally
brown, while the later ones are green. From this protonema at certain
points buds appear which divide by close oblique walls. From these buds
the leafy stem of the moss plant grows. Threads similar to these protonemal
threads now grow out from the leafy stem, to form the rhizoids. These
supply the moss plant with nutriment, and now the protonema usually dies,
though in some few species it persists for long periods.
Classification of the Mosses.
CLASS MTJSCINEJE (MUSCI).
524. Order Sphagnales.* — This order includes the peat mosses. There
is but one family (Sphagnaceae) and but a single genus (Sphagnum). The
peat mosses are widely distributed over the globe, chiefly occurring in
moors, or "bogs," usually low ground around the shores of lakes, ponds, or
along streams, but they often occur on wet dripping rocks in cool shady
places. Small ponds are sometimes filled in by their growth. As the
sphagnum growing in such an abundance of water only partially decays,
"ground" is built up rather rapidly, and the sphagnum remains are known
as "peat." This "ground "-building peculiarity of sphagnum sometimes
enables the plant (often in conjunction with others) to fill in ponds com-
pletely. (See Atoll Moor, Chapter LV.)
The gametophyte of sphagnum, like that of all the mosses, is dimorphic,
but the first part (or protonema) which develops from the spores is thalloid,
and therefore more like the thallose liverworts. The leafy axis (or gameto-
phore) which develops from the thalloid form is very characteristic (see
Chapter LV).
The archegonia are borne on the free end of the main axis, while the
antheridia are borne on short branches which are brightly colored, red,
yellow, etc. The sporophyte (sporogonium) is globose and possesses a
broad foot anchored in the end of a naked prolongation of the end of the
leafy gametophore. This naked prolongation of the gametophore looks
like the stalk of the sporogonium, but a study of its connection with the
sporogonium shows that it is part of the gametophyte, which is only devel-
oped after the fertilization of the egg in the archegonium. In the sporogo-
nium there is a short columella, and the archesporium is in the form 01 an
inverted cup.
* As subclass in Engler and Prantl.
MOSSES. 249
525. Order Andreseales.* — This order includes the single genus An-
dreaea. The plants are small but form extensive mats, growing on rocks
in arctic or alpine regions usually. They are sometimes found in great
abundance on bare, rather dry rocks on mountains. The protonema is
somewhat thalloid. The sporogonium opens by splitting longitudinally into
four valves. An elongated columella is present so that the archesporium
is shaped like an inverted test-tube.
526. Order Archidiales.* — This order contains the single genus Archi-
dium, and by some is piaced as an aberrant genus in the Bryales. There
is no columella in the simple sporogonium. The archesporium occupies
all the internal part of the sporogonium, some cells being fertile and others
sterile.
527. Order Bryales.* — These include the higher mosses, and a very large
number of genera and species. The protonema is filamentous and branched
except in a few forms where it is partly thalloid as in Tetraphis (= Georgia).
(Tetraphis pellucida is a common moss on very rotten logs. The
capsule has four prominent teeth.) In a few of the lower genera (Phas-
cum, Pleuridium, etc.) the capsule opens irregularly, but in the larger num-
ber the capsule opens by a lid (operculum). A cylindrical columella is
present, and the archesporium is in the form of a tube open at both ends.
(Examples: Polytrichum, Bryum, Mnium, Hypnum, etc.)
* As subclass in Engler and PrantL
250
MORPHOLOG Y.
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CHAPTER XXVI.
FERNS.
529. In taking up the study of the ferns we find plants which
are very beautiful objects of nature and thus have always attracted
the interest of those who love the beauties of nature. But they
are also very interesting to the student, because of certain re-
markable peculiarities of the structure of the fruit bodies, and
especially because of the intermediate position which they occupy
within the plant kingdom, representing in the two phases of
their development the primitive type of plant life on the one
hand, and on the other the modern type. We will begin our
study of the ferns by taking that form which is the more promi-
nent, the fern plant itself.
530. The Christinas fern. — One of the ferns which is very
common in the Northern States, and occurs in rocky banks and
woods, is the well-known Christmas fern (Aspidium acrostichoides)
shown in fig. 286. The leaves are the most prominent part of the
plant, as is the case with most if not all our native ferns. The
stem is very short and for the most part under the surface of the
ground, while the leaves arise very close together, and thus form
a* rosette as they rise and gracefully bend outward. The leaf is
elongate and reminds one somewhat of a plume with the pinnae
extending in two rows on opposite sides of the midrib. These
pinnae alternate with one another, and at the base of each pinna
is a little spur which projects upward from the upper edge.
Such a leaf is said to be pinnate. While all the leaves have the
same general outline, we notice that certain ones, especially those
toward the center of the rosette, are much narrower from the
252
MORPHOLOG }'.
middle portion toward the end. This is because of the shorter
pinnae here.
531. Fruit "dots" (sorus, indusium). — If we examine the
under side of such short pinnae of the Christmas fern \ve see that
there are two rows of small circular dots, one row on either side of
(the pinna. These are called the "fruit
dots," or sori (a single one is a sorus). If
we examine it with a low power of the mi-
croscope,
or with a
p o c k e t
lens, we
see that
there is a
circular
disk which
c o v e r s
more or
less com-
pletelyvery
minute objects, usual-
ly the ends of the
latter projecting just be-
yond the edge if they are
mature. This circular disk
is what is called the indti-
sium, and it is a special
outgrowth of the epidermis
of the leaf here for the
protection of the spore-
cases. These minute ob-
jects underneath are the
fruit bodies, which in the
case of the ferns and their allies are called sporangia. This
indusium in the case of the Christmas fern, and also in some
Others, is attached to the leaf by means of a short slender stalk
Fig. 286.
Christmas fern (Aspidium acrostichoides).
FEKWS.
253
which is fastened to the middle of the under side of this shield,
as seen in cross section in fig. 292.
532. Sporangia. —If we section through the leaf at one of the
fruit dots, or if we tease off some of the sporangia so that the
stalks are still attached, and
examine them with the mi-
croscope, we can see the
form and structure of these
peculiar bodies. Different
views of a sporangium are
shown in fig. 293. The
slender portion is the stalk,
and the larger part is the
spore-case proper. We
should examine the structure
of this spore-case quite care-
fully, since it will help us to
understand better than we
otherwise could the remark-
able operations which it
performs in scattering the
spores.
533. Structure of a spo-
rangium.— If we examine
one of the sporangia in side
view as shown in fig. 293,
Fig 287. we note a prominent row of
Rhizome with bases of leaves, and roots of the cells which extend around
Christmas fern.
the margin of the dorsal
edge from near the attachment of the stalk to the upper front
angle. The cells are prominent because of the thick inner
walls, and the thick radial walls which are perpendicular to the
inner walls. The walls on the back of this row and on its
sides are very thin and membranous. We should make this
out carefully, for the structure of these cells is especially adapt-
ed to a special function which they perform. This row of cells
2 $4 MORPHOLOGY.
is termed the annulus, which means a little ring. While this
is not a complete ring, in some other ferns the ring is nearly
complete.
534. In the front of the sporangium is another peculiar group
Fig. 288.
Rhizome of sensitive fern (Onoclea sensibilis).
of cells. Two of the longer ones resemble the lips of some crea-
ture, and since the sporangium opens between them they are
sometimes termed the lip cells. These lip cells are connected with
the upper end of the annulus on one
side and with the upper end of the stalk
on the other side by thin-walled cells,
which may be termed connective cells,
since they hold each lip cell to its part
of the opening sporangium. The cells
on the side of the sporangium are also
thin-walled. If we now examine a
sporangium from the back, or dorsal
Fig. 289.
Under side of pinna of Aspidium edge as we say, it will appear as in the
spinulosum showing fruit dots . , . . -
(son). left-hand figure. Here we can see
how very prominent the annulus is. It projects beyond the
surface of the other cells of the sporangium. The spores are
contained inside this case.
FEKNS.
255
535. Opening of the sporangium and dispersion of the
spores. — If we take some fresh fruiting leaves of the Christmas
fern, or of any one of many of the species of the true ferns just
at the ripening of the spores, and place a portion of it on apiece
of white paper in a dry room, in a very short time we shall see
that the paper is being dusted with .minute brown objects which
fly out from the leaf. Now if we take a portion of the same
leaf and place it under the low power of the microscope, so that
the full rounded sporangia can be seen, in a short time we note
that the sporangium opens, the upper half curls backward as
Fig. 290.
Four pinnas of adiantum, showing recurved margins which cover the sporangia.
shown in fig. 294, and soon it snaps quickly, to near its former
position, and the spores are at the same time thrown for a consid-
erable distance. This movement can sometimes be seen with the
aid of a good hand lens.
536. How does this opening and snapping of the sporan-
gium take place ? — We are now more curious than ever to see
just how this opening and snapping of the sporangium takes place.
We should now mount some of the fresh sporangia in water and
cover with a cover glass for microscopic examination. A drop
of glycerine should be placed at one side of the cover glass on the
slip so that the edge of the glycerine will come in touch with the
water. Now as one looks through the microscope to watch the
256
MORPHOLOG Y.
sporangia, the water should be drawn from under the cover glass
with the aid of some bibulous paper, like filter paper, placed at the
edge of the cover glass on
the opposite side from the
glycerine. As the glycer-
ine takes the place of the
water around the sporangia
it draws the water out of
the cells of the annulus,
just as it took the water
out of the cells of the
spirogyra as we learned
some time ago. As the
water is drawn out of these
cells there is produced a
pressure from without, the
atmospheric pressure upon
the glycerine. This causes
the walls of these cells of
the annulus to bend in-
ward, because, as we have
Fig. 291. already learned, the glycer-
Section through sorus of Polypodium vulgare jne (JoCS not DaSS through
showing different stages of sporangium, and one
muiticefiuiar capitate hair. the walls nearly so fast
as the water comes out.
537. Now the structure of the cells of this annulus, as we
have seen, is such that the inner walls and the perpendicular
Fig. 292.
Section through sorus and shield-shaped indusium of aspidium.
walls are stout, and consequently they do not bend or collapse
when this pressure is brought to bear on the outside of the cells.
FEKNS.
The thin membranous walls on the back (dorsal walls) and on
the sides of the annul us, however, yield readily to the pressure
and bend inward. This, as we can readily see, pulls on the ends
of each of the perpendicular walls drawing them closer together.
This shortens the outer surface of the annulus and causes it to
first assume a nearly straight position, then curve backward until
it quite or nearly becomes doubled on itself. The sporangium
Fig. 293.
Rear, side, and front views of fern sporangium, d, e, annulus; a, lip cells.
opens between the lip cells on the front and the lateral walls of
the sporangium are torn directly across. The greater mass of
spores are thus held in the upper end of the open sporangium,
and when the annulus has nearly doubled on itself it suddenly
snaps back again in position. While treating with the glycerine
we can see all this movement take place. Each cell of the
annulus acts independently, but often they all act in concert.
When they do not all act in concert, some of them snap sooner
than others, and this causes the annulus to snap in segments.
538. The movements of the sporangium can take place in
old and dried material. — If we have no fresh material to study
258
MORPHOLOGY.
the sporangium with, we can use dried material, for the move-
ments of the sporangia can be well seen in dried material, pro-
vided it was collected at about the time the sporangia are mature,
that is at maturity, or soon afterward. We take some of the
dry sporangia (or we may wash the glycerine off those which we
have just studied) and mount them in water, and quickly examine
Fig. 294.
Dispersion of spores from sporangium of Aspidium acrostichoides, showing different
.stages in the opening and snapping of the annulus.
them with a microscope. We notice that in each cell of the
annulus there is a small sphere of some gas. The water which
bathes the walls of the annulus is absorbed by some substance
inside these cells. This we can see because of the fact that this
sphere of gas becomes smaller and smaller until it is only a mere
FEKNS. 259
dot, when it disappears in a twinkling. The water has been taken
in under such pressure that it has absorbed all the gas, and the
farther pressure in most cases closes the partly opened sporangium
more completely.
539. Now we should add glycerine again and draw out the
water, watching the sporangia at the same time. We see that
the sporangia which have opened and snapped once will do it
again. And so they may be made to go through this operation
several times in succession. We should now note carefully the
annulus, that is after the sporangia have opened by the use of
glycerine. So soon as they have snapped in the glycerine we can
see those minute spheres of gas again, and since there was no air
on the outside of the sporangia, but only glycerine, this gas must,
it is reasoned, have been given up by the water before it was all
drawn out of the cells.
540. The common polypody. — We may now take up a few other ferns for
study. Another common fern is the polypody, one or more species of which
have a very wide distribution. The stem of this fern is also not usually seen,
but is covered with the leaves, except in the case of those species which grow
on the surface of rocks. The stem is slender and prostrate, and is covered
with numerous brown scales. The leaves are pinnate in this fern also, but we
find no difference between the fertile and sterile leaves (except in some rare
cases). The fruit-dots occupy much the same positions on the under side of the
leaf that they do in the Christmas fern, but we cannot find any indusium. In
the place of an indusium are club-shaped hairs as shown in fig. 291. The en-
larged ends of these clubs reaching beyond the sporangia give some protection
to them when they are young.
541. Other ferns. — We might examine a series of ferns to see how different
they are in respect to the position which the fruit dots occupy on the leaf. The
common brake, which sometimes covers extensive areas and becomes a trouble-
some weed, has a stout and smooth underground stem (rhizome) which is often
1 2 to 20 cm beneath the surface of the soil. There is a long leaf stalk, which
bears the lamina, the latter being several times pinnate. The margins of the
fertile pinnae are inrolled, and the sporangia are found protected underneath
in this long sorus along the margin of the pinna. The beautiful maidenhair fern
and its relatives have obovate pinnae, and the sori are situated in the same posi-
tions as in the brake. In other ferns, as the walking fern, the sori are borne
along by the side of the veins of the leaf.
542. Opening of the leaves of ferns. — The leaves of ferns open in a peculiar
manner. The tip of the leaf is the last portion developed, and the growing
260
MORPHOLOG Y.
leaf appears as if it was rolled up as in fig. 287 of the Christmas fern. As the
leaf elongates this portion unrolls.
543. Longevity of ferns. — Most ferns live from year to year, by growth
adding to the advance of the stem, while by decay of the older parts the stem
shortens up behind. The leaves are short-lived, usually dying down each
year, and a new set arising from the growing end of the stem. Often one can
see just back or below the new leaves the old dead ones of the past season,
and farther back the remains of the petioles of still older leaves.
544. Budding of ferns. — A few
ferns produce what are called bulbils
or bulblets on the leaves. One of
these, which is found throughout the
greater part of the eastern United
States, is the bladder fern (Cystop-
teris bulbifera), which grows in shady
rocky places. The long graceful
delicate leaves form in the axils of
the pinnae, especially near the end of
the leaf, small oval bulbs as shown
in fig. 295. If we examine one of
these bladder-like bulbs we see that
the bulk of it is made up of short
thick fleshy leaves, smaller ones ap-
pearing between the outer ones at the
smaller end of the bulb. This bulb
contains a stem, young root, and
several pairs of these fleshy leaves.
They easily fall to the ground or
rocks, where, with the abundant
moisture usually present in localities
where the fern is found, the bulb
Fig. 295-
Cystopteris bulbifera, young plant growing grows until the roots attach the plant
from bulb. At right is young bulb in axil of to the soji or in the crevices of the
pinna 01 leaf.
rocks. A young plant growing from
one of these bulbils is shown in fig. 295.
545. Greenhouse ferns. — Some of the ferns grown in conservatories have
similar bulblets. Fig. 296 represents one of these which is found abundantly
on the leaves of Asplenium bulbiferum. These bulbils have leaves which are
very similar to the ordinary leaf except that they are smaller. The
bulbs are also much more firmly attached to the leaf, so that they do not
icadily fall away.
546. Plant conservatories usually furnish a number of very interesting
ferns, and one should attempt to make the acquaintance of some of them, for
FERNS.
26l
here one has an opportunity during the winter season not only to observe these
interesting plants, but also to obtain material for study. In the tree ferns
which often are seen growing in such places we see examples of the massive
trunks and leaves of some of the tropical species.
547. The fern plant is a sporophyte. — We have now studied
the fern plant, as we call it, and we have found it to represent
the spore-bearing phase of the plant, that is the sporophyte (cor-
responding to the sporogonium of the liverworts and mosses).
548. Is there a ga-
in etophyte phase in
ferns ? — But in the spor-
ophyte of the fern, which
we should not forget is
the fern plant, we have
a striking advance upon
the sporophyte of the
liverworts and mosses.
In the latter plants the
sporophyte remained
attached to the gameto-
phyte, and derived its
nourishment from it.
In the ferns, as we see,
tne sporophyte has a
root of its own, and is
attached to the soil.
Through the aid of root
hairs of its own it takes up mineral solutions. It possesses also
a true stem, and true leaves in which carbon conversion takes
place. It is able to live independently, then. Does a gametophyte
phase exist among the ferns ? Or has it been lost ? If it does
exist, what is it like, and where does it grow? From what we
have already learned we should expect to find the gametophyte
begin with the germination of the spores which are developed
on the sporophyte, that is on the fern plant itself. We should
investigate this and see.
Fig. 296.
Bulbil growing from leaf of asplenium (A , bulbiferum).
CHAPTER XXVII.
FERNS CONTINUED.
Gametophyte of ferns.
549. Sexual stage of ferns. — We now wish to see what the
sexual stage of the ferns is like. Judging from what we have
found to take place in the liverworts and mosses we should infer
Fig. 207.
Prothallium of fern, under side, showing rhizoids, antheridia scattered among and near
them, and the archegonia near the sinus.
that the form of the plant which bears the sexual organs is de-
veloped from the spores. This is true, and if we should examine
old decaying logs, or decaying wood in damp places in the near
262
FERNS.
vicinity of ferns, we should probably find tiny, green, thin, heart-
shaped growths, lying close to the substratum. These are also
found quite frequently on the soil of pots in plant conservatories
where ferns are grown. Gardeners also in conservatories usually
sow fern spores to raise new fern plants,
and usually one can find these heart-shaped
growths on the surface of the soil where
they have sown the spores. We may call
the gardener to our aid in finding them in
conservatories, or even in growing them for
us if we cannot find them outside. In some
cases they may be grown in an ordinary room
by keeping the surfaces where they are
growing moist, and the air also moist, by
placing a glass bell jar over them.
550. In fig. 297 is shown one of these growths enlarged.
Upon the under side we see numerous thread-like outgrowths,
the rhizoids, which attach the plant to the substratum, and which
act as organs for the absorption of nourishment. The sexual
organs are
borne on the
under side also,
and we will
study them
later. This
heart-shaped,
flattened, thin,
green plant is
Fig. 298.
Spore of Pteris serru-
lata showing the three-
rayed elevation along
the side of which the
spore wall cracks during
germination.
Pig. 299.
Fig. 300.
Spore of Aspidium
acrostichoides with
winged exospore.
Spore crushed to remove exospore and
show endospore.
the prothallium
of ferns, and we should now give it more careful study, be-
ginning with the germination of the spores.
551. Spores. — We can easily obtain material for the study of
the spores of ferns. The spores vary in shape to some extent.
Many of them are shaped like a three-sided pyramid. One of
these is shown in fig. 298. The outer wall is roughened, and
on one end are three elevated ridges which radiate from a given
264
MORPHOLOG Y.
point. A spore of the Christmas fern is shown in fig. 299. The
outer wall here is more or less winged. At fig. 300 is a spore
of the same species from which the
outer wall has been crushed, showing
that there is an inner wall also. If
possible we should study the germi-
nation of the spores of some fern.
552. Germination of the spores.
— After the spores have been sown for
about one week to ten days we should
Spores of asplenitm '; exospore re- mOUnt E few hl Watet f°r examination
moved from the one at the right. wjtn tiie microscope in order to study
the early stages. If germination has begun, we find that here
and there are short slender green threads, in many cases attached
to brownish bits, the old
walls of the spores.
Often one will sow the
sporangia along with the
spores, and in such cases
there may be found a
number of spores still
within the old sporan-
gium wall that are ger-
minating, when they will
appear as in fig. 302.
553. Protonema. —
These short green threads
are called protonemal threads, or protonema,
which means a first thread, and it here
signifies that this short thread only pre-
cedes a larger growth of the same object.
In figs. 302, 303 are shown several stages of
germination of different spores. Soon after
3°siores of the short germ tube emerges from the
a stU1 in the crack in the spore wall, it divides by the
FERNS. 265
formation of a cross wall, and as it increases in length other
cross walls are formed. But very early in its growth we see that
a slender outgrowth takes place from the cell nearest the old
spore wall. This slender thread
is colorless, and is not divided
into cells. It is the first rhizoid,
and serves both as an organ of
attachment for the thread, and for
taking up nutriment.
554. Prothallium. — Very soon,
if the sowing has not been so
crowded as to prevent the young
plants from obtaining nutriment
sufficient, we will see that the end
of this protonema is broadening,
as shown in fig. 303. This is done
by the formation of the cell walls
in different directions. It now
continues to grow in this way, the
end becoming broader and broader,
and new rhizoids are formed from
the under surface of the cells. The
growing point remains at the mid-
dle of the advancing margin, and
the cells which are cut off from*
either side, as they become old,
widen ;out. In this way the Voung prothauta£°of a fcm (nipho-
" wings," or margins of the bolus)-
little, green, flattened body, are in advance of the growing
point, and the object is more or less heart-shaped, as shown
in fig. 297. Thus we see how the prothallium of ferns is
formed.
555. Sexual organs of ferns. — If we take one of the prothal-
lia of ferns which have grown from the sowings of fern spores,
or one of those which may be often found growing on the soil
266
MORPHOLOG Y.
of pots in conservatories, mount it in water on a slip, with
the under side uppermost, we can then examine it for the
Fig. 304.
Male prothallium of a fern (niphobolus), in form of an alga or protonema. Spermato-
zoids escaping from antheridia.
sexual organs, for these are borne in most cases on the under
side.
556. Antheridia. — If we search among the rhizoids we see
small rounded elevations as shown in fig. 297 or 305 scat-
Fig- 305-
Male prothallium of fern (niphobolus), showing opened and unopened antheridid , section
of unopened antheridium ; spermatozoids escaping ; spermatozoids which did nut escape
from the antheridium.
FEXtfS.
267
tered over this portion of the prothallium.
theridia. Ifthepro-
thallia have not been
watered for a day or
so, we may have an
opportunity of see-
ing the spermato-
zoids coming out of
the antheridium, for
when the prothallia
are freshly placed in
These are the an-
gection of antheridla showing sperm cells, and spermato-
ids in the one at the right.
water the cells of the antheridium ab-
sorb water. This presses on the con-
tents of the antheridium and bursts the
cap cell if the antheridium is ripe, and
all the spermatozoids are shot out.
We can see here that each one is
shaped like a screw, with the coils at
Fig. 307.
Different views of spermatozoids; first close. But as the SpermatOZOid
in a quiet condition; in motion , •,. .,
(Adiantum concinnum). begins tO mOVC this COll Opens SOHie-
what and by the vibration of
the long cilia which are on the
smaller end it whirls away. In
such preparations one may often
see them spinning around for a
long while, and it is only when
they gradually come to rest
that one can make out their
form.
557. Archegonia. — If we now
examine closely on the thicker
part of the under surface of the
prothallium, just back of the
Fig. 308.
Archegonium of fem. Large cell in the
" Sinus, we may See longer venter is the egg, next is the ventral canal
cell, and in the canal of the neck are two
StOUt projections from the surface nuclei of the canal cell.
of the prothallium. These are shown in fig. 297. They are
268
MORPHOLOG Y.
the archegonia. One of them in longisection is shown in fig.
308. It is flask -shaped, and the broader portion is sunk in tne
sp
Fig. 309.
Mature and open archegonium of fern (Adiantum cuneatum) with spermatozoids making
their way down through the slime to the egg.
tissue of the prothallium. The egg is in the larger part. The
spermatozoids when they are swimming
around over the under surface of the pro-
thallium come near the neck, and here they
are caught in the viscid substance which
has oozed out of the canal of the arche-
gonium. From here they slowly swim
down the canal, and finally one sinks into
the egg, fuses with the nucleus of the latter,
and the egg is then fertilized. It is now
ready to grow and develop into the fe-n
plant. This brings us back to the sporj-
Fig. 310.
Campbell.)
phyte, which begins with the fertilized egg.
Sporophyte.
558. Embryo. — The egg first divides into two cells as shown in fig. 228, then
into four. Now from each one of these quandrants of the embryo a definite
part of the plant develops, from one the first leaf, from one the stem, from
one the root, and from the other the organ which is called the toot, and which
FEJ?NS.
269
attaches the embryo to the prothallium, and transports nourishment for the
embryo until it can become attached to the soil and lead an independent ex-
istence. During this time the wall of the archegonium grows somewhat to
accommodate the increase in size of the embryo, as shown in figs. 312, 313.
But soon the wall of the archegonium is ruptured and the embryo emerges,
the root attaches itself to the soil, and soon the prothallium dies.
The embryo is first on the under side of the prothallium, and the first leaf
Two-celled embryo of Pteris serrulata. Remnant of archegonium neck below.
and the stem curves upward between the lobes of the heart-shaped body, and
then grows upright as shown in fig. 314. Usually only one embryo is formed
on a single prothallium, but in one case I found a prothallium with two well-
formed embryos, which are figured in 315.
559. Comparison of ferns with liverworts and mosses. — In the ferns then
we have reached a remarkable condition of things as compared with that
which we found in the mosses and liverworts. In the mosses and liverworts
270
MORPHOLOG Y.
the sexual phase of the plant (gametophyte) was the prominent one,
and consisted of either a thallus or a leafy axis, but in either case it bore the
sexual organs and led an independent existence; that is it was capable of ob-
taining its nourishment from the soil or water by means of organs of absorp-
tion belonging to itself, and it also performed the office of photosynthesis.
560. The spore-bearing phase (sporophyte) of the liverworts and mosses,
on the other hand, is quite small as compared with the sexual stage, and it is
Fig. 312.
Young embryo of fern (Adiantum concinnum) in enlarged venter of the archegoniura. S,
stem ; L, first leaf or cotyledon ; R, root ; F, foot.
completely dependent on the sexual stage for its nourishment, remaining at-
tached permanently throughout all its development, by means of the organ
called a foot, and it dies after the spores are mature.
561. Now in the ferns we see several striking differences. In the first
place, as we have already observed, the spore-bearing phase (sporophyte) of
FERNS.
271
the plant is the prominent one, and that which characterizes the plant. It
also leads an independent existence, and, with the exception of a few cases,
does not die after the development of the spores, but lives from year to year
and develops successive crops of spores. There is a distinct advance here in
the size, complexity, and permanency of this phase of the plant.
562. On the other hand the sexual phase of the ferns (gametophyte), while
it still is capable of leading an independent existence, is short-lived (with very
few exceptions). It is also much smaller than most of the liverworts and
Fig. 313-
Embryo of fern (Adiantum concinnum) still surrounded by the archegonium, which has
grown in size, forming the " calyptra." L, leaf ; S, stem ; Jf, root ; F, foot.
mosses, especially as compared with the size of the spore-bearing phase.
The gametophyte phase or stage of the plants, then, is decreasing in size and
durance as the sporophyte stage is increasing. We shall be interested to see
if this holds good of the fern allies, that is of the plants which belong to the
same group as the ferns. And as we come later to take up the study of the
higher plants we must bear in mind to carry on this comparison, and see if
this progression on the one hand of the sporophyte continues, and if the
retrogression of the gametophyte c^.tinues also.
MORPHOLOG Y.
Fig. 314-
Young plant of Pteris serrulata still
attached to prothallium.
Fig. 3 1 5-
Two embryos from one prothallium of
Adiantum cuueatum.
CHAPTER XXVIII.
DIMORPHISM OF FERNS.
563. In comparing the different members of the leaf series
there are often striking illustrations of the transition from one
form to another, as we have noted in the case of the trillium
flower. This occurs in many other flowers, and in some, as in
the water lily, these transformations are always present, here
showing a transition from the petals to the stamens. In the bud
scales of many plants, as in the butternut, walnut, currant, etc.,
there are striking gradations between the form of the simple bud
scales and the form of the leaf. Some of the most interesting of
these transformations are found in the dimorphic ferns.
564. Dimorphism in the leaves of ferns. — In the common
polypody fern, the maidenhair, and in many other ferns, all the
leaves are of the same form. That is, there is no difference be-
tween the fertile leaf and the sterile leaf. On the other hand, in
the case of the Christmas fern we have seen that the fertile
leaves are slightly different from the sterile leaves, the former
having shorter pinnae on the upper half of the leaf. The fertile
pinnae are here the shorter ones, and perform but little of the
function of carbon conversion. This function is chiefly per-
formed by the sterile leaves and by the sterile portions of the
fertile leaves. This is a short step toward the division of labor
between the two kinds of leaves, one performing chiefly the labor
of carbon conversion, the other chiefly the labor of bearing the
fruit.
565. The sensitive fern. — This division of labor is carried to
an extreme extent in the case of some ferns. Some of our native
273
274
MOKPHOLOG y.
ferns are examples of this interesting relation between the leaves
like the common sensitive fern (Onoclea sensibilis) and the
ostrich fern (O. struthiopteris) and the cinnamon fern (Osmunda
cinnamomea). The sensitive fern is here shown in fig. 316.
The sterile leaves are large, broadly expanded, and pinnate, the
Fig. 316.
Sensitive fern ; normal condition of vegetative leaves and sporophylls.
pinnse being quite large. The fertile leaves are shown also in
the figure, and at first one would not take them for leaves at all.
But if we examine them carefully we see that the general plan
of the leaf is the same : the two rows of pinnae which are here
much shorter than in the sterile leaf, and the pinnules, or smaller
DIMORPHISM OF FERNS.
275
divisions of the pinnse, are inrolled into little spherical masses
which lie close on the side of the pinnae. If we unroll one of
these pinnules we find that there are several fruit dots within
protected by this roll. In fact when the spores are mature these
Fig. 317-
Sensitive fern ; one fertile leaf nearly changed to vegetative leaf.
pinnules open somewhat, so that the spores may be dissemi-
nated.
There is very little green color in these fertile leaves, and
what green surface there is is very small compared with that of
the broad expanse of the sterile leaves. So here there is practi-
cally a complete division of labor between these two kinds of
270 MORPHOLOG Y.
leaves, the general plan of which is the same, and we recognize
each as being a leaf.
566. Transformation of the fertile leaves of onoclea to
sterile ones. — It is not a very rare thing to find plants of the
sensitive fern which show intermediate conditions of the sterile
and the fertile leaf. A number of years ago it was thought by
some that this represented a different species, but now it is known
Fig. 318.
Sensitive fern, showing one vegetative leaf and two sporophylls completely transformed.
that these intermediate forms are partly transformed fertile leaves.
It is a very easy matter in the case of the sensitive fern to pro-
duce these transformations by experiment. If one in the spring,
when the sterile leaves attain a height of 12 to 16 cm (8— 10
inches), cuts them away, and again when they have a second
time reached the same height, some of the fruiting leaves which
develop later will be transformed. A few years ago I cut off the
DIMORPHISM OF FERNS.
277
sterile leaves from quite a large patch of the sensitive fern, once
in May, and again in June. In July, when the fertile leaves
were appearing above the ground, many of them were changed
partly or completely into sterile leaves. In all some thirty plants
Fig. 319.
Normal and transformed sporophyll of sensitive fern.
showed these transformations, so that every conceivable gradation
was obtained between the two kinds of leaves.
567. It is quite interesting to note the form of these changed
leaves carefully, to see how this change has affected the pinnae
and the sporangia. We note that the tip of the leaf as well as
the tips of all the pinnae are more expanded than the basal por-
278 MORPHOLOGY.
tions of the same. This is due to the fact that the tip of the
leaf develops later than the basal portions. At the time the
stimulus to the change in the development of the fertile leaves
reached them they were partly formed, that is the basal parts of
the fertile leaves were more or less developed and fixed and
could not change. Those portions of the leaf, however, which
were not yet completely formed, under this stimulus, or through
correlation of growth, are incited to vegetative growth, and ex-
pand more or less completely into vegetative leaves.
568. The sporangia decrease as the fertile leaf expands. —
If we now examine the sporangia on the successive pinnae of a
partly transformed leaf we find that in case the lower pinnae are
not changed at all, the sporangia are normal. But as we pass to
the pinnae which show increasing changes, that is those which are
more and more expanded, we see that the number of sporangia
decrease, and many of them are sterile, that is they bear no
spores. Farther up there are only rudiments of sporangia, until
on the more expanded pinnae sporangia are no longer formed,
but one may still see traces of the indusium. On some of the
changed leaves the only evidences that the leaf began once to
form a fertile leaf are the traces of these indusia. In some of
these cases the transformed leaf was even larger than the sterile
leaf.
569. The ostrich fern. — Similar changes were also produced
in the case of the ostrich fern, and in fig. 320 is shown at the
left a normal fertile leaf, then one partly changed, and at the
right one completely transformed.
570. Dimorphism in tropical ferns. — Very interesting forms
of dimorphism -are seen in some of the tropical ferns. One of
these is often seen growing in plant conservatories, and is known
as the staghorn fern (Platycerium alcicorne). This in. nature
grows attached to the trunks of quite large trees at considerable
elevations on the tree, sometimes surrounding the tree with a
massive growth. One kind of leaf, which may be either fertile
or sterile, is narrow, and branched in a peculiar manner, so that
it resembles somewhat the branching of the horn of a stag.
DIMORPHISM OF FERNS.
2/9
Below these are other leaves which are different in form and
sterile. The.se leaves are broad and hug closely around the roots
and bases of the other leaves. Here they serve to catch and
Fig. 320.
Ostrich fern, showing one normal sporophyll, one partly transformed, and one completely
transformed.
retain moisture, and they also catch leaves and other vegetable
matter which falls from the trees. In this position the leaves
decay and then serve as food for the fern.
CHAPTER XXIX.
HORSETAILS.
571. Among the relatives of the ferns are the
horsetails, so called because of the supposed resem-
blance of the branched stems of some of the species
to a horse's tail, as one might infer from the plant
shown in fig. 325. They do not bear the least re-
semblance to the ferns which we have been study-
ing. But then relationship in plants does not depend
on mere resemblance of outward form, or of the promi-
nent part of the plant.
572. The field equisetum. Fertile shoots. — Fig.
321 represents the common horsetail (Equisetum ar-
vense). It grows in moist sandy or gravelly places,
and the fruiting portion of the plant (for this species
is dimorphic), that is the portion which bears the
spores, appears above the ground early in the spring.
It is one of the first things to peep out of the recently
frozen ground. This fertile shoot of the plant does
not form its growth this early in the spring. Its
development takes place under the ground in the
autumn, so that with the advent of spring it pushes
up without delay. This shoot is from 10 to 20
cm high, and at quite regular intervals there are
slight enlargements, the nodes of the stem. The
cylindrical portions between the nodes are the
internodes. If we examine the region of the inter- ^^"' of
nodes carefully we note that there are thin mem-^jL^f^
branous scales, more or less triangular in outline, and ^"Osre1;shown^
connected at their bases into a ring around the stem. f^fnga"stike?
280
HORSE TA ILS. 28 1
Curious as it may seem, these are the leaves of the horsetail.
The stem, if we examine it farther, will be seen to possess numer-
ous ridges which extend lengthwise and which alternate with
furrows. Farther, the ridges of one node alternate with those
of the internode both above and below. Likewise the leaves
of one node alternate with those of the nodes both above and
below.
573. Sporangia. — The end of this fertile shoot we see pos-
sesses a cylindrical to conic enlargement. This is the fertile
spike, and we note that its surface is marked off
into regular areas if the spores have not yet been
disseminated. If we dissect off a few of these por-
tions of the fertile spike, and examine one of them
with a low magnifying power, it will appear like the
fig. 322. We see here that the angular area is a
Fig. 322. disk-shaped body, with a stalk attached to its inner
phyf/oVequSetum surface, and with several long sacs projecting from
Ing^p^ngiaTn its inner face parallel with the stalk and surrounding
the same. These elongated sacs are the sporangia,
and the disk which bears them, together with the stalk which
attaches it to the stem axis, is the sporophyll, and thus belongs to
the leaf series. These sporophylls are borne in close whorls on
the axis.
574. Spores. — When the spores are ripe the tissue of the
sporangium becomes dry, and it cracks open and the spores fall
out. If we look at fig. 323 we see that the spore is covered
with a very singular coil which lies close to the wall. When the
spore dries this uncoils and thus rolls the spore about. Merely
breathing upon these spores is sufficient to make them perform
very curious evolutions by the twisting of these four coils which
are attached to one place of the wall. They are formed by the
splitting up of an outer wall of the spore.
575. Sterile shoot of the common horsetail. — When the
spores are ripe they are soon scattered, and then the fertile
shoot dies down. Soon afterward, or even while some of the
fertile shoots are still in good condition, sterile shoots of the
282
MORPHOLOG Y.
plant begin to appear above the ground. One of these is shown
in fig. 325. This has a much more slender stem and is pro-
Fig. 323.
Spore of equisetum
with elaters coiled up.
Fig. 324.
Spore of equisetum with elaters un
coiled.
vided with numerous branches. If we ex-
amine the stem of this shoot, and of the
branches, we see that the same kind of
leaves are present and that the markings on
the stem are similar. Since the leaves of
the horsetail are membranous and not green,
the stem is green in color, and this per-
forms the function of photosynthesis. These
green shoots live for a great part of
the season, building up material which is
carried down into the underground stems,
where it goes to supply the forming fertile
shoots in the fall. On digging up some of
these plants we see that the underground
stems are often of great extent, and that
both fertile and sterile shoots are attached
to one and the same.
576. The scouring rush, or shave grass.
— Another common species of horsetail in
the Northern States grows on wet banks,
or in sandy soil which contains moisture
along railroad embankments. It is
the scouring rush (E. hyemale), so
called because it was once used for
polishing purposes. This plant like
all the species of the horsetails has
Fig. 325-
mt of horsetail (Equi-
HORSETAILS. 283
underground stems. But unlike the common horsetail, there is
but one kind of aerial shoot, which is green in color and fertile.
The shoots range as high as one meter or more, and are quite
stout. The new shoots which come up for the year are un-
branched, and bear the fertile spike at the apex. When the
spores are ripe the apex of the shoot dies, and the next season
small branches may form from a number of the nodes.
577. Garnet ophyte of equisetum. — The spores of equisetum have chloro-
phyll when they are mature, and they are capable of germinating as soon as
mature. The spores are all of the same kind as regards size, just as we
found in the case of the ferns. But they develop prothallia of different
sizes, according to the amount of nutriment which they obtain. Those
which obtain but little nutriment are smaller and develop only antheridia,
while those which obtain more nutriment become larger, more or less
branched, and develop archegonia. This character of an independent pro-
thallium (gametophyte) with the characteristic sexual organs, and the also
independent sporophyte, with spores, shows the relationship of the horsetails
with the ferns. We thus see that these characters of the reproductive
organs, and the phases and fruiting of the plant, are more essential in deter-
mining relationships of plants than the mere outward appearances.
CHAPTER XXX.
CLUB MOSSES.
578. What are called the "club mosses" make up another
group of interesting plants which rank as allies of the ferns.
They are not of course true mosses, but the general habit of
some of the smaller species, and especially the
form and size of the leaves, suggest a resem-
blance to the larger of the moss plants.
579. The clavate lycopodium. — Here is one
of the club mosses (fig. 326) which has a wide
distribution and which is well entitled to hold
the name of club because of the form of the up-
right club-shaped branches. As will be seen
from the illustration, it has a prostrate stem.
This stem runs for- considerable distances on
the surface of the ground, often partly buried in
the leaves, and sometimes even buried beneath
the soil. The leaves are quite small, are flat-
tened -awl -shaped, and stand thickly over the
stem, arranged in a spiral manner, which is the
usual arrangement of the leaves of the club
mosses. Here and there are upright branches
which are forked several times. The end of
one or more of these branches becomes pro-
duced into a slender upright stem which is
nearly leafless, the leaves being reduced to tum i^nch bearing two
J
mere scales. The end of this leafless branch , .
then terminates in one or several cylindrical sP°renear il-
heads which form the club.
Lycopodium c I a v a -
fruiting spikes ; at right
n°gpf°
284
CLUB MOSSES.
285
580. Fruiting spike of Lycopodium clavatum. — This club is
the fruiting spike or head (sometimes termed kstrobilus). Here
the leaves are larger again and broader, but still not so large as
the leaves on the creeping shoots, and they are paler. If we bend
down some of the leaves, or tear off a few, "we see that in the
axil of the leaf, where it joins the stem, there is a somewhat
rounded, kidney -shaped body. This is the spore-case or spo-
rangium, as we can see by an examination of its contents. There
is but a single spore-case for each of the fertile leaves (sporophyll).
When it is mature, it opens by a crosswise slit as seen in fig. 326.
When we consider the number of spore-cases in one of these club-
shaped fruit bodies we see that the number of spores developed
in a large plant is immense. In mass the spores make a very fine,
soft powder, which is used for some
kinds of pyrotechnic material, and for
various toilet purposes.
581. Lycopodium lucidulum. — Another com-
mon species is figured at 327. This is Lycopo-
dium lucidulum. The habit of the plant is quite
different. It grows in damp ravines, woods, and
moors. The older parts of the stem are prostrate,
while the branches are more or less ascending.
It branches in a forked manner. The leaves are
larger than in the former species, and they are
all of the same size, there being no appreciable
difference between the sterile and
fertile ones. The characteristic
club is not present here, but the
spore-cases occupy certain regions of
the stem, as shown at 327. In a
single season one region of the stem
may bear spore-cases, and then a
sterile portion of the same stem is
, developed, which later bears another
Lycopodium lucidulum, bulbils in axils of
leaves near the top, sporangia in axils of leaves series of spore-cases higher up.
below them. At right is a bulbil enlarged.
582. Bulbils on Lycopodium
lucidulum. — There is one curious way in which this club moss multiplies.
One may see frequently among the upper leaves small wedge-shaped or heart-
shaped green bodies but little larger than the ordinary leaves. These are little
286
MOKPHOLOGY.
buds which contain rudimentary shoot and root and several thick green leaves.
When they fall to the ground they grow into new lycopodium plants, just as
the bulbils of cystopteris do which were described in the chapter on ferns.
583. Note. — The prothallia of the species of lycopodium which have been
studied are singular objects. In L. cernuum a cylindrical body sunk in the
earth is formed, and from the upper surface there are green lobes. In L.
phlegmaria and some others slender branched, colorless bodies are formed
which according to Treub grow as a saphrophyte in decayed bark of trees.
Many of the prothallia examined have a fungus growing in their tissue which
is supposed to play some part in the nutrition of the prothallium.
The little club mosses (selaginella).
584. Closely related to the club mosses are the selaginellas.
These plants resemble closely the general habit of the club mosses,
but are generally smaller and the leaves more delicate. Some
species are grown in conservatories for ornament, the leaves of
Fig. 328. Fig. 329. Fig. 33°. Fig- 331-
Selaginella with Fruiting spike Large spo- Small spo-
three fruiting spikes, showing large and rangium. rangium.
(Selaginella apus.) small sporangia.
such usually having a beautiful metallic lustre. The leaves of some
are arranged as in lycopodium, but many species have the leaves
in four to six rows. Fig. 328 represents a part of a selaginella
plant (S. apus). The fruiting spike possesses similar leaves, but
they are shorter, and their arrangement gives to the spike a four-
sided appearance.
LITTLE CLUB MOSSES.
287
585. Sporangia. — On examining the fruiting spike, we find
as in lycopodium that there is but a single sporangium in the
axil of a fertile leaf. But we see that they are of two different
kinds, small ones in the axils of the upper leaves, and large ones
in the axils of a few of the lower leaves of the spike. The micro-
spores are borne in the smaller spore-cases and the macrospores
in the larger ones. Figures 329-331 give the details. There
are many microspores in a single small spore-case, but 3-4 ma-
crospores in a large spore-case.
586. Male prothallia. — The prothallia of selaginella are much
reduced structures. The microspores when mature are already
divided into two cells. When they grow into the mature pro-
thallium a few more cells are formed, and some of the inner ones
form the spermatozoids, as seen in fig. 332. Here we see that
Fig. 332.
Details of microspore and male prothallium of selaginella ; ist, microspore ; zd, wall re-
moved to show small prothallial cell below ; id, mature male prothallium still within the
wall ; 4th, small cell below is the prothallial cell, the remainder is antheridium with wall and
four sperm cells within ; 5th spermatozoid. After Beliaieff and Pfeffer.
the antheridium itself is larger than the prothallia. Only an-
theridia are developed on the prothallia formed from the
microspores, and for this reason the prothallia are called male
prothallia. In fact a male prothallium of selaginella is nearly
all antheridium, so reduced has the gametophyte become here.
587. Female prothallia. — The female prothallia are devel-
oped from the macrospores. The macrospores when mature have
a rough, thick, hard wall. The female prothallium begins to
develop inside of the macrospore before it leaves the sporangium.
The protoplasm is richer near the wall of the spore and at the
288
MORPHOLOG Y.
upper end. Here the nucleus divides a great many times, and
finally cell walls are formed, so that a tissue of considerable ex-
tent is formed inside the wall of the spore, which is very
different from what takes place in the ferns we have
studied. As the prothallium matures the spore is cracked
at the point where the three angles meet, as shown in
fig- 334- The archegonia are developed in this exposed
surface, and several can be seen in the illustration.
588. Embyro. — After fertilization the egg divides in such a way
that a long cell called a suspensor is cut off from the upper side,
Fig- 333- fig- 334-
Section of mature macrospore Mature female prothallium of
of selagmella, showing female selaginella, just bursting open
sela-
prothallium and archegonia. the wall of macrospore, exposing ginella still attached
After Pfeffer. archegonia. After Pfeffer. to the macrospore.
After Campbell.
which elongates and pushes the developing embyro down into the center of
the spore, or what is now the female prothallium. Here it derives -nourish-
ment from the tissues of the prothallium, and eventually the root and stem
emerge, while a process called the " foot " is still attached to the prothallium.
When the root takes hold on the soil the embyro becomes free.
Fig. 336.
CHAPTER XXXI.
QUILLWORTS (ISOETES).
589. The quillworts, as they
are popularly called, are very
curious plants. They grow in
wet marshy places. They receive
their name from the supposed
resemblance of the leaf to a quill.
Fig. 336 represents one of these
quillworts (Isoetes engelmannii) .
The leaves are the prominent
part of the plant, and they are
about all that can be seen except
the roots, without removing the
leaves. Each leaf, it will be
seen, is long and needle-like, ex-
cept the basal part, which is
expanded, not very unlike, in out-
line, a scale of an onion. These
expanded basal portions of the
leaves closely overlap each other,
and the very short stem is com-
pletely covered at all times. Fig.
338 is from a longitudinal sec-
tion of a quillwort. It shows
the form of the leaves from this
view (side view), and also the
Isoetes, mature plant, sporophyte stage, general outline of the short Stem,
which is triangular. The stem is therefore a very short object.
289
290
590. Sporangia of isoetes. — If we pull off some of the
leaves of the plant we see that they are somewhat spoon-shaped
as in fig. 337. In the inner surface of the expanded base we
note a circular depression which seems to be of a different text-
- 337-
Base of leaf of isoetes,
showing sporangium with
macrospores. (Isoetes en-
gelmannii.)
Fig. 338.
Section of plant of Isoetes engelmanii, showing cup-
shaped stem, and longitudinal sections of the sporan-
gia in the thickened bases of the leaves.
ure from the other portions of the leaf. This is a sporangium.
Beside the spores on the inside of the sporangium, there are
strands of sterile tissue which extend across the cavity. This is
peculiar to isoetes of all the members of the class of plants to
which the ferns belong, but it will be remembered that sterile
strands of tissue are found in some of the liverworts in the form
of elaters.
591. The spores of isoetes are of two kinds, small ones
(microspores) and large ones (macrospores), so that in this
respect it agrees with selaginella, though it is so very different in
other respects. When one kind of spore is borne in a sporan-
QUILLWORTS. 2gi
gium usually all in that sporangium are of the same kind, so that
certain sporangia bear microspores, and others bear macrospores.
But it is not uncommon to find both kinds in the same sporan-
gium. When a sporangium bears only microspores the number
is much greater than when one bears only macrospores.
592. If we examine some of the microspores of isoetes we see that they are
shaped like the quarters of an apple, that is they are of the bilateral type as
seen in some of the ferns (asplenium).
593. Male prothallia. — In isoetes, as in selaginella, the microspores de-
velop only male prothallia, and these are very rudimentary, one division of
the- spore having taken place before the spore is mature, just as in selagi-
nella.
594. Female prothallia. • — -These are developed from the macrospores. The
latter are of the tetrahedral type. The development of the female prothal-
lium takes place in much the same way as in selaginella, the entire prothal-
lium being enclosed in the macrospore, though the cell divisions take place
after it has left the sporangium. When the archegonia begin to develop
the macrospore cracks at the three angles and the surface bearing the arche-
gonia projects slightly as in selaginella. Absorbing organs in the form of
rhizoids are very rarely formed.
595. Embryo. — The embryo lies well immersed in the tissue of the pro-
thallium, though there is no suspensor developed as in selaginella.
CHAPTER XXXII.
COMPARISON OF FERNS AND THEIR RELATIVES.
596. Comparison of selaginella and isoetes with the ferns. — On compar-
ing selaginella and isoetes with the ferns, we see that the sporophyte is, as
in the ferns, the prominent part of the plant. It possesses root, stem, and
leaves. While these plants are not so large in size as some of the ferns,
still we see that there has been a great advance in the sporophyte of selagi-
nella and isoetes upon what exists in the ferns. There is a division of labor
between the sporophylls, in which some of them bear microsporangia with
microspores, and some bear macrosporangia with only macrospores. In the
ferns and horsetails there is only one kind of sporophyll, sporangium, and
spore in a species. By this division of labor, or differentiation, between the
sporophylls, one kind of spore, the microspore, is compelled to form a male
prothallium, while the other kind of spore, the macrospore, is compelled to
form a female prothallium. This represents a progression of the sporophyte
of a very important nature.
597. On comparing the gametophyte of selaginella and isoetes with that
of the ferns, we see that there has been a still farther retrogression in size
from that which we found in the independent and large^gametophyte of the
liverworts and mosses. In the ferns, while it is reduced, it still forms
rhizoids, and leads an independent life, absorbing its own nutrient materials,
and assimilating carbon. In selaginella and isoetes the gametophyte does
not escape from the spore, nor does it form absorbing organs, nor develop
assimilative tissue. The reduced prothallium develops at the expense of
food stored by the sporophyte while the spore is developing. Thus, while
the gametophyte is separate from the sporophyte in selaginella and isoetes,
it is really dependent on it for support or nourishment.
598. The important general characters possessed by the ferns and their
so-called allies, as we have found, are as follows: The spore-bearing part,
which is the fern plant, leads an independent existence from the prothallium.
and forms root, stem, and leaves. The spores are borne in sporangia on
the leaves. The prothallium also leads an independent existence, though in
isoetes and selaginella it has become almost entirely dependent on the sporo-
292
COMPARISON OF FERA'S. 293
phyte. The prothallium bears also well-developed antheridia and arche-
gonia. The root, stem, and leaves of the sporophyte possess vascular
tissue. All the ferns and their allies agree in the possession of these char-
acters. The mosses and liverworts have well-developed antheridia and
archegonia, and the higher plants have vascular tissue. But no plant of
either of these groups possesses the combined characters which we find in
the ferns and their relatives. The latter are, therefore, the fern-like plants,
or pteridophyta. The living forms of the pteridophyta are classified as fol-
lows into families or orders. (See page 295.)
294
MORPHOLOGY.
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FEXNS: CLASSIFICATION.
Classification of the Pteridophytes.
Of the living pteridophytes four classes may be recognized.
CLASS FILICINE.E.*
This class includes the ferns. Four orders may be recognized.
600. Order Ophioglossales. (One Family, Ophioglossacese). — This order
includes the grapeferns (Botrychium), so called because of the large
botryoid cluster of sporangia, resembling roughly a cluster of grapes; and
the adder-tongue (Ophioglossum), the sporangia being embedded in a long
tongue-like outgrowth from the green leaf. Botrychium and Ophioglos-
sum are widely distributed. The roots are fleshy, nearly destitute of root
hairs, and contain an endophytic fungus, so that the roots are mycorhiza.
The gametophyte is subterranean, and devoid of chlorophyll. In Botry-
chium virginianum, an endophytic fungus has been found in the prothal-
lium. Another genus (Helminthostachys) with one species is limited to
the East Indies.
601. Order Marattiales (One Family, Marattiaceae). — These are trop-
ical ferns, with only four or five living genera (Marattia, Danaea, etc.).
They resemble the typical ferns, but the sporangia are usually united, sev-
eral forming a compound sporangium, or synangium.
The Ophioglossales and Marattiales are known as eusporangiate ferns,
while the following order includes the leptosporangiate ferns.
602. Order Filicales. — This order includes the typical ferns. Eight
families are recognized.
Family Osmundacea. — Three genera are known in this family. Os-
munda has a number of species, three of which are found in the Eastern
United States; the cinnamon-fern (O. cinnamomea), the royal fern (O.
regalis), and Clayton's fern (O. claytoniana). No species of this family
are found on the Pacific coast.
Family Gleicheniacea. — These ferns are found chiefly in the tropics, and
in the mountain regions of the temperate zones of South America. There
are two genera, Gleichenia containing all but one of the known species.
Family Matoniacea.— One genus, Matonia, in the Malayan region.
Family Schizizacece. — These are chiefly tropical, but two species are
found in eastern North America, Schizaea pusilla and Lygodium palma-
tum, the latter a climbing fern.
Family HymenophyttacecB. — These are known as the filmy ferns because
of their thin, delicate leaves. They grow only in damp or wet regions,
mostly in the tropics, but a few species occur in the southern United States.
Family Cyatheacea. — These are known as the tree-ferns, because of the
* As class Filicales in Engler and Prantl.
296 MORPHOLOG Y.
large size which many of them attain. They occur chiefly in tropical moun-
tainous regions, many of them palm-like and imposing because of the large
trunks and leaves. Dicksonia, Cyathea, Cibotium, Alsophila, are some of
the most conspicuous genera.
Family Parkeriacea. — There is a single species in this family (Cera-
topteris thalictroides), abundant in the tropics and extending into Florida.
It is aquatic.
Family Polypodiacece. — This family includes the larger number of living
ferns and many genera and species are found in North America. Exam-
ples, Polypodium, Pteridium (=Pteris), Adiantum, etc.
603. Order Hydropterales (or Salviniales). — The members of this order
are peculiar, aquatic ferns, some floating on the water (Azolla, Salvinia),
while others are anchored to the soil by roots (Marsilia, Pilularia). They
are known as water ferns. The sporangia are of two kinds, one containing
large spores (macrospores) and the other small spores (microspores). They
are therefore heterosporous ferns.
Family Salviniacece. — There are two genera, Salvinia and Azolla.
Family Marsiliacece. — Two genera, Marsilia and Pilularia. In this family
the sporangia are enclosed in a sporocarp, which forms a pod-like structure.
CLASS EQUISETINEJE.*
604. Order Equisetales. — The single order contains a single family,
Equisetaceae, among the living forms, and but a single genus, Equisetum.
There are about twenty-four species, with fourteen in the United States (see
Chapter XXIX).
CLASS LYCOPODIINEJE.f
605. Order Lycopodiales. — The first two families of this order include
the homosporous Lycopodiineae, while the Selaginellacea? are heterosporous.
Family Lycopodiacece. — There are two genera. Lycopodium (club
moss) includes many species, most of them tropical, but a number in tem-
perate and subarctic regions. The gametophyte of many species is tuber-
ous, lacks chlorophyll, and in some there lives an endophytic fungus. Phyl-
loglossum with one species is found in Australia.
Family Psilotacea. — There are two genera. Psilotum chiefly in the
tropics has one species (P. triquetrum) in the region of Florida.
Family Selaginellacea. — These include the little club mosses, with one
genus, Selaginella (see Chapter XXX).
CLASS ISOETINEJE.
606. Order Isoetales, with one family Isoetaceae and one genus Isoetes
(see Chapter XXXI). There are about fifty species, with about sixteen in
the United States.
* As class Equisetales in Engler and Prantl.
f As class Lycopodiales in Engler and Prantl.
CHAPTER XXXIII.
GYMNOSPERMS.
The white pine.
607. General aspect of the white pine. — The white pine
(Pinus strobus) is found in the Eastern United States. In
favorable situations in the forest it reaches a height of about 50
meters (about 160 feet), and the trunk a diameter of over i
meter. In well-formed trees the trunk is straight and towering;
the branches where the sunlight has access and the trees are not
crowded, or are young, reaching out in graceful arms, form a
pyramidal outline to the tree. In old and dense forests the lower
branches, because of lack of sunlight, have died away, leaving
tall, bare trunks for a considerable height.
608. The long shoots of the pine. — The branches are of two kinds. Those
which we readily recognize are the long branches, so called because the
growth in length each year is considerable. The terminal bud of the long
branches, as well as of the main stem, continues each year the growth of the
main branch or shoot; while the lateral long branches arise each year from
buds which are crowded close together around the base of the terminal bud.
The lateral long branches of each year thus appear to be in a whorl. The
distance between each false whorl of branches, then, represents one year's
growth in length of the main stem or long branch.
609. The dwarf shoots of the pine. — The dwarf branches are all lateral
on the long branches, or shoots. They are scattered over the year's growth,
and each tears a cluster of five long, needle-shaped, green leaves, which
remain on the tree for several years. At the base of the green leaves are
a number of chaff-like scales, the previous bud scales. While the dwarf
branches thus bear green leaves, and scales, the long branches bear only
thin scale-like leaves which are not green.
297
298
MORPHOLOGY.
610. Spore-bearing leaves of the pine. — The two kinds of
spore-bearing leaves of the pine, and their close relatives, are
so different from anything which we have yet studied, and are
so unlike the green leaves of the pine, that we would scarcely
recognize them as belonging to this category. Indeed there is
great uncertainty regarding their origin.
611. Male cones, or male flowers. — The male cones are borne
in clusters as shown in fig. 339. Each compact, nearly cylindri-
Fig. 339-
Spray of white pine showing cluster of male cones just before the scattering of the pollen.
cal, or conical mass is termed a cone, or flower, and each arises
in place of a long lateral branch. One of these cones is shown
GYMNOSPERMS: WHITE PINE.
299
considerably enlarged in fig. 340. The central axis of each
cone is a lateral branch, and belongs to the stem series. The
stem axis of the cone can be seen in fig. 341. It is completely
covered by stout, thick, scale-like outgrowths. These scales
are obovate in outline, and at the inner angle of the upper end
Fig. 340. Fig. 341- Fig. 342-
Staminate cone of white Section of staminate Two sporo-
pine, with bud scales re- cone, showing sporangia, phylls removed,
moved on one side. showing open-
ing of sporangia.
there are several rough, short spines. They are attached by
their inner lower angle, which forms a short stalk or petiole,
and continues through the inner face of the scale as a "mid-
rib. ' ' What corresponds to the lamina of the scale-like leaf--
bulges out on each side below and makes the bulk of the scale.
These prominences on the under side are the sporangia (micro-
sporangia). There are thus two sporangia on a sporophyll
(microsporophyll). When the spores (microspores), which
here are usually called pollen grains, are mature each sporangium,
or anther locule, splits down the middle as
shown in fig. 342, and the spores are set free.
612. Microspores of the pine, or pollen
grains. — A mature pollen grain of the pine is
It is a queer-looking object,
possessing on two sides an air sac, formed by the
upheaval of the outer coat of the spore at these two points.
Fig. 343-
Pollen grain of shown in fig. T.AT,.
white pine.
300
MORPHOLOGY.
When the pollen is mature, the moisture dries out of the scale
(or stamen, as it is often called here) while
it ripens. When a limb, bearing a cluster
of male cones, is jarred by the hand, or by
currents of air, the split suddenly opens, and
a cloud of pollen bursts out from the numer-
ous anther locules. The pollen is
thus borne on the wind and some of
it falls on the
female flowers.
Fig. 345.
Mature cone of white pine
at time of scattering of the
seed, nearly natural size.
Fig. 344-
White pine, branch with cluster of
mature cones shedding the seed. A
few young cones four months old
are shown on branch at the left.
Drawn from photograph.
613. Form of the ma-
ture female cone. — A
cluster of the white-
pine cones is shown in
fig. 344. These are
mature, and the scales
have spread as they do when mature and becoming dry, in
order that the seeds may be set at liberty. The general out-
GYMNOSPERMS: WHITE PINE. 3OI
line of the cone is lanceolate, or long oval, and somewhat
curved. It measures about io-i$cm long. If we remove one
Fig. 346. Fig. 347- Fig. 348. Fig. 349. Fig. 35°-
Sterile scale. Scale with Seeds have Back of scale Winged
Seeds undevel- well- developed split off from with small cover seed free from
oped. seeds. scale. scale. scale.
Kigs. 346-350.— White pine showing details of mature scales and seed.
of the scales, just as they are beginning to spread, or before the
seeds have scattered, we shall find the seeds at-
tached to the upper surface at the lower end.
There are two seeds on each scale, one at each
lower angle. They are ovate in outline, and
shaped somewhat like a biconvex lens. At this
time the seeds easily fall away, and may be
freed by jarring the cone. As the seed is
detached from the scale a strip of tissue from
the latter is peeled off. This forms a " wing "
for the seed. It is attached to one end and is
shaped something like a knife blade. On the
back of the scale is a small appendage known
as the cover scale.
614. Formation of the female pine cone. — The female
flowers begin their development rather late in the spring
of the year. They are formed from terminal buds of
the higher branches of the tree. In this way the cone
may terminate the main shoot of a branch, or of the
Fig. 351. lateral shoots in a whorl. Aftergrowth has proceeded
Female cones of the for some time in the spring, the terminal portion begins
pine at time of pollina-
tion, about natural size, to assume the appearance of a young female cone or
3O2
MORPHOLOG Y.
flower. These young female cones, at about the time that the pollen is
escaping from the anthers, are long ovate, measuring about 6-iomm long.
They stand upright as shown in fig. 351.
615.
one of
Form of a " scale " of the female flower. — If we remove
the scales from the cone at this stage we can better study
it in detail. It is flattened, and oval in
outline, with a stout " rib," if it may be so
called, running through the middle line and
terminating in a point. The scale is in
two parts as shown in fig. 354, which is a
view of the under side. The small "out-
growth ' ' which appears as an appendage is
the cover scale, for while it is smaller in the
pine than the other portion, in some of
the relatives of the pine it is larger than its
mate, and being on the outside, covers it.
(The inner scale is sometimes called the ovu-
liferous scale, because it bears the ovules. )
616. Ovules, or macrosporangia, of the
pine. — At each of the lower angles of the
Fig. 352-
Section of female cone
of white pine, showing
young ovules (macrospo- erous scale.
rangia) at base of the ovu-
lif erous scales.
Fig. 353-
Scale of white pine with the
two ovules at base of ovulif-
Fig. 354-
Scale of white pine seen
from the outside, showing the
cover scale.
scale is a curious oval body with two curved, forceps-like pro-
cesses at the lower and smaller end. These are the macro-
sporangia, or, as they are called in the higher plants, the ovules.
These ovules, as we see, are in the positions of the seeds on the
GYMNOSPERMS: WHITE PINE.
303
mature cones. In fact the wall of the ovule forms the outer coat
of the seed, as we will later see.
617. Pollination. — At the time when the pollen is mature the
female cones are still erect on the branches, and the scales, which
during the earlier stages of growth were closely pressed against
one another around the axis, are now
spread apart. As the clouds of pollen
burst from the clusters of the male cones,
some of it is wafted by the wind to the
female cones. It is here caught in the
open scales, and rolls down to their bases,
where some of it falls between these
forceps-like processes at the
lower end of the ovule. At
Fig. 355-
Branch of white pine showing young female cones at time of pollination on the ends of
the branches, and one-year-old cones below, near the time of fertilization.
this time the ovule has exuded a drop of a sticky fluid in this
depression between the curved processes at its lower end. The
pollen sticks to this, and later, as this viscid substance dries up,
it pulls the pollen close up in the depression against the lower
304
MORPHOLOG Y.
Fig. 356.
end of the ovule. This depression is thus known as the pollen
chamber.
618. Now the open scales on the young female cone close up
again so tightly that water from rains is excluded. What is also
very curious, the cones, which up to this
time have been standing erect, so that
the open scale could catch the pollen,
now turn so that they hang downward.
This more certainly excludes the rains,
since the overlapping of the scales forms
a shingled surface. Quantities of resin
are also formed in the scales, which
exudes and makes the cone practically
impervious to water.
619. The female cone now slowly
grows during the summer and autumn,
increasing but little in size during this
time. During the winter it rests, that
is, ceases to grow. With the coming of
spring, growth commences again and
at an accelerated rate. The increase in
size is more rapid. The cone reaches maturity in September.
We thus see that nearly eighteen months elapse from the begin-
ning of the female flower to the maturity of the cone, and about
fifteen months from the time that pollination takes place.
620. Female prothallium of the pine. — To study this we must make care-
ful longitudinal sections through the ovule (better made with the aid of a
microtome). Such a section is shown in fig. 358. The outer layer of tis-
sue, which at the upper end (point where the scale is attached to the axis of
the cone) stands free, is the ovular coat, or integument. Within this integu-
ment, near the upper end, there is a cone-shaped mass of tissue. This
mass of tissue is the nucellus, or the macrosporangium proper. In the
lower part of the nucellus in fig. 356 can be seen a rounded mass of "spongy
tissue " (spt), which is a special nourishing tissue of the nucellus, or spo-
rangium, around the macrospore. Within this can be seen an axile row
of three cells (an : m). The lowest one, which is larger than the other
two, is the macrospore. Sometimes there are four of these cells in the axile
row. This axile row of three or four cells is formed by the two successive
pfr-
G YMNOSPERMS : WHITE PINE.
305
divisions of a mother cell in the nucellus.
three or four cells are all
spores.
Only one of them, however,
the lower one, develops; the
others are disorganized and
disappear. The nucleus of
the macrospore now divides
several times to form several
free nuclei in the now enlarg-
ing cavity, much as the nu-
cleus of the macrospore in
Selaeinella and Isoetes divides
So it would appear that these
Fig. 357.
. Pollen grains of pine. One of them germinat-
ing. pl and p2, the two disintegrated prothallial
Within the spore. The de- cells, = sterile part of male gametophyte; a.c.,
velopment thus far takes place ^U or°tul» n^deu" ofthe^rinri^SfS^rf
during the first summer, and antheridium ;s.g., starch grains. (After Ferguson.)
now with the approach of winter the very young female prothallium goes
into rest about the stage shown in
%• 358- The conical portion of
the nucellus which lies above is the
nucellar cap.
621. Male prothallia.— By the
time the pollen is mature the male
prothallium is already partly
formed. In fig. 343 we can see
two well-formed cells. Two other
cells are formed earlier, but they
become so flattened that it is diffi-
cult to make them out when the
pollen grain is mature. These are
shown in fig. 357, pl and p2, and
they are the only sterile cells of the
male prothallium in the pines. The
large cell is the antheridium wall,
its nucleus v.n. in fig. 357. The
smaller cell, a.c., is the central cell
of the antheridium. During the
summer and autumn the male
prothallium makes some farther
growth, but this is slow. The
Fig- 35g. larger cell, called the vegetative
Section of ovule of white pine. int. in- cell or tube cell, which is in reality
tegument; pc, pollen chamber; pt, pollen
tube: n, nucleus; m, macrospore cavity.
--n
-•m.
.
the wall of the antnendium, elon-
306
MORPHOLOG Y.
gates by the formation of a tube, forming a sac, known as the pollen tu1>c
It is either simple or branched. It grows down into the tissue of the nu
cellus, and at a stage represented in fig. 358, winter overtakes it and it
rests. At this time the central cell has divided into two cells, and the
vegetative nucleus is in the pollen tube.
822. The endosperm. — In the following spring growth of all these parts
Sf.1l
Fig. 359-
Section of nucellus and endosperm of white pine. The inner layer of cells of
the integument shown just outside of nucellus; arch, archegonium; en, egg nu-
cleus. In the nucellar cap are shown three pollen tubes, v n, vegetative nucleus
or tube nucleus; sic, stalk cell; spn, sperm nuclei, the larger one in advance is
the one which unites with the egg nucleus. The archegonia are in the endosperm
or female gametophyte. (After Ferguson.)
continues. The nuclei in the macrospore divide to form more, and event-
ually cell walls are formed between them making a distinct tissue, known
GYMNOSPERMS: WHITE PINE,
307
as the endosperm. This endosperm continues to grow until a large part of
the nucellus is consumed for food.
623. Female prothallium and archegonia. — The endosperm is the female
prothallium. This is very evident from the fact that severa* archegonia
are developed in it usually on the side toward the pollen chamber. The
archegonia are sexual organs, and since the sexual organs are developed on
the gametophyte, therefore, the endosperm is the female gametophyte, or
prothallium. In fig. 359 are represented two archegonia in the endosperm
and the pollen tubes are growing down through the nucellus. The arche-
gonia are quite large, the wall is a sheath or jacket of cells which encloses
the very large egg which has a large nucleus in the center.
624. Pollen tube and sperm cells. — While the endosperm (female pro-
thallium) and archegonia are developing the pollen tube continues its
growth down through the nucellar cap, as shown in fig. 359. At the same
time the two cells which were formed in
the pollen grain (antheridium) from the
central cell move down into the tube. One
of these is the "generative" cell, or "body"
cell, and the other is called the stalk cell,
though it is more properly a sterile half of
the central cell. The nucleus of the gener-
ative cell, about the time the archegonium
is mature, divides to form two nuclei,
which are the sperm nuclei, and the one
in advance is the larger, though it is much
smaller than the egg nucleus.
625. Fertilization. — Very soon after the
archegonia are mature (early in June in the
northern United States) the pollen tube
grows through into the archegonium and
empties the two sperm nuclei, the vegetative
nucleus and the stalk cell, into the proto-
plasm of the large egg. The larger of the
two sperm nuclei at once comes in contact
with the very large egg nucleus and sinks
down into a depression of the same, as
shown in fig. 361. These two nuclei, in the pi 6o
pines, do not fuse into a resting nucleus, but Last division 'of the egg in the
at once organize the nuclear figure for the whitf pil]f Cuttin8 off the ventral
- . . canal cell at the apex of the
nrst division of the embryo. Two nuclei archegonium. End, endosperm;
are thus formed, and these divide to form A
four nuclei which sink to the bottom of the archegonium and there organ-
--Areh
MORPHOLOG Y.
ize the embryo which pushes its way into the endosperm from which it
derives its food (fig. 362).
626. Homology of the parts of the female cone. — Opinions are divided as
to the homology of the parts of the female cone of the pine. Some consider
the entire cone to be homologous with a flower of the angiosperms. The
spn
en
Fig. 361.
Archegonium of white pine at stage of fertilization, en, egg nucleus; spn, sperm
nucleus in conjugation with it; no, nutritive bodies in cytoplasm of large egg;
cpt, cavity of pollen tube; vn, vegetative nucleus or tube nucleus; sc, stalk cell:
spn, second sperm nucleus: pr, portion of prothallium or endosperm; SK, starch
grains in pollen tube. The sheath of jacket cells of the archegonium is not shown.
(After Ferguson.)
entire scale according to this view is a carpel, or sporophyll, which is divided
into the cover scale and the ovuliferous scale. This division of the sporo-
phyll is considered similar to that which we have in isoetes, where the spo-
rophyll has a ligule above the sporangium, or as in ophioglossum, where the
leaf is divided into a fertile and a sterile portion.
Others believe that the ovuliferous scale is composed of two leaves situ-
ated laterally and consolidated representing a shoot in the axis of the bract.
There is some support for this in the fact that in certain abnormal cones
which show proliferation a short axis appears in the axil of the bract and
GYMNOSPERMS: WHITE PINE.
309
bears lateral leaves, and in some cases all gradations are present between
these lateral leaves on the axis and their consolidation into an ovuliferous
scale. In the normal condition of the ovuliferous scale the axis has disap-
peared and the shoot is represented only by the consolidated leaves, which
would represent then the
macrosporophylls (or carpels)
each bearing one macrospo-
rangium (ovule).
One of the most interesting
and plausible views is that
of Celakovsky. He believes "'-•
that the axial shoot is reduced
to two ovules, that the ovules
Fig. 362. Fig. 363. • Fig. 364-
Pine seed, section of. sc. Embryo of white Pine seedling just
seed coat ;«, remains of nu- pine removed from emerging from the
cellus; end, endosperm seed, showing ground.
(= female gametophyte); several cotyle-
emb, embryo = young spo- dons,
rophyte. Seed coat and
nucellus= remains of old
sporophyte.
have two integuments, but the outer integument of each has become pro-
liferated into scales which are consolidated. In this proliferation of the
outer integument it is thrown off from the ovule so that it only remains
attached to one side and the larger part of the ovule is thus left with only
one integument. This view is supported by the fact that in gingko, for
example (another gymnosperm), the outer integument (the "collar")
sometimes proliferates into a leaf. Ceiakovsky's view is, therefore, not
very different from the second one mentioned above.
310
MORPHOLOG y.
Fig- 365-
White-pine seedling casting seed coats.
CHAPTER XXXIV.
FURTHER STUDIES ON GYMNOSPERMS.
Cycas.
627. In such gymnosperms as cycas, illustrated in the front-
ispiece, there is a close resemblance to the members of the fern
group, especially the ferns themselves.
This is at once suggested by the form of
the leaves. The stem is short and thick.
The leaves have a stout midrib and
numerous narrow pinnae. In the center
of this rosette of leaves are numerous
smaller leaves, closely overlapping like
bud scales. If we remove one of these
at the time the fruit is forming we see that
in general it conforms to the plan of the
large leaves. There are a midrib and a
number of narrow pinnae near the free
end, the entire leaf being covered with
woolly hairs. But at the lower end, in
... Flg',?6n' t place of the pinnae, we see oval bodies.
Macrosporophyll of Cycas r
revoiuta. These are the macrosporangia (ovules)
of cycas, and correspond to the macrosporangia of selaginella,
and the leaf is the macrosporophyll.
628. Female prothallium of cycas. — In figs. 367, 368, are
shown mature ovules, or macrosporangia, of cycas. In 368, which
is a roentgen-ray photograph of 367, the oval prothallium can be
seen. So in cycas, as in selaginella, the female prothallium is
3"
312
MORPHOLOVY.
developed entirely inside of the macrosporangium, and derives
the nutriment for its growth from the cycas plant, which is the
Fi<r. ^7. Fig. 368.
Macrosporangium of Cycas revoluta Roentgen photograph of same, show-
ing female prothallium.
sporophyte. Archegonia are developed in this internal mass of
cells. This aids us in deter-
mining that it is the prothal-
lium. In cycas it is also called
endosperm, just as in the
pines.
629. If we cut open one of the
mature ovules, we can see the en-
dosperm (prothallium) as a whitish
mass of tissue. Immediately sur-
rounding it at maturity is a thin,
papery tissue, the remains of the
nucellus (macrosporangium), and
outside of this are the coats of the
ovule, an outer fleshy one and an
inner stony one.
630. Microspores, or pollen, of
cycas. — The cycas plant illustrated
in the frontispiece is a female plant.
Male plants also exist which have A sporophyll istamen) of cycas; sporangia in
Hi .1 ., , groups on the under side. />, group of sporangia:
small leaves m the center that bear * op£n sporangja. (From Warming.)
FURTHER STUDIES ON GYMNOSPERMS.
313
only microsporangia. These leaves, while they resemble the ordinary leaves,
are smaller and correspond to the stamens. Upon
the under side, as shown in fig. 369, the microspo-
rangia are borne in groups of three or four, and these
contain the microspores, or pollen grains. The ar-
rangement of these microsporangia on the under side
of the cycas leaves bears a strong resemblance to the
arrangement of the sporangia on the under side of
the leaves of some ferns.
631. The gingko tree is
another very interesting plant
belonging to this same group.
It is a relic of a genus which \ B / fll Fig. 370.
Zamia inte-
r ifolia.show-
f n g thick
stem, fern-like
leaves, and
cone of male
flowers.
flourished in the remote
past, and it is interesting
also because of the re-
semblance of the leaves
to some of the ferns like
adiantum, which sug-
gests that this form of
the leaf in gingko has
been inherited from some
fern-like ancestor.
632. While the resem-
blance of the leaves of
someofthegymnosperms
to those of the ferns sug-
gests fern-like ancestors
for the members of this
group, there is stronger
evidence of such ances-
try in the fact that a pro-
thallium can well be de-
tig. 371.
Two spermatozoids in end of pollen tube of cycas. (After termined m the ovules.
The endosperm with its
well-formed archegonia is to be considered a prothallium.
633. Spermatozoids in some gymnosperms. — But within the past two
years it has been discovered in gingko, cycas, and zamia, all belonging to this
MORPHOLOG Y.
group, that the sperm cells are well-formed spermatozoids. Tn zamia each
one is shaped somewhat like the half of a biconvex lens, and around the con-
vex surface are several coils of cilia. After the
pollen tube has grown down through the nucel-
lus, and has reached a depression at the end of
the prothallium (endosperm) where the arche-
gonia are formed, the spermatozoids are set
free from the pollen tube, swim around in a
liquid in this depression, and later fuse with
the egg. In gingko and cycas these spermato-
zoids were first discovered by Ikeno and Hirase
in Japan, and later in zamia by Webber in this
country. In figs. 371-374 the details of the
male prolhallia and of fertilization are shown.
634. The sporophyte in the gymnosperms. —
In the pollen grains of the gymnosperms we
easily recognize the characters belonging to the
spores in the ferns and their allies, as well as in
fusing the liverworts and mosses. They belong to the
Fig. 372
Fertilization i
small spermatozoid
---- Busing
with the larger female nu- . ,.
cleus of the egg. The egg same series of organs, are borne on the same
protoplasm fills the archego- phase or generation of the plant, and are practi-
mum. (rrom drawings by r
Hirase and Ikeno.) cally formed in the same general way, the
variations between the different groups not being greater than those within
a single group. These spores we have recognized as being the product of
the sporophyte. We are able then to identify the sporophyte as that phase
or generation of the plant formed from the fer-
tilized egg and bearing ultimately the spores.
We see from this that Ihe sporophyte in the
gymnosperms is the prominent part of the
plant, just as we found it to be in the ferns.
The pine tree, then, as well as the gingko, cycas,
yew, hemlock-spruce, black spruce, the giant
redwood of California, etc., are sporophytes.
. . \ i i ,
While the sporangia (anther sacs) of the male
flowers open and permit the spores (pollen) to be scattered, the sporangia of
the female flowers of the gymnosperms rarely open. The macrospore is de-
veloped within sporangium (nuccllus) to form the female prothallium (en-
dosperm).
635. The gametophyte has become dependent on the sporophyte. — In this
respect the gymnosperms differ widely from the pteridophytes, though we see
suggestions of this condition of things in Isoetes and Selaginella, where the fe-
male prothallium is developed within the niacrospore, and even in Selaginella
begins, and nearly completes, its development while still in the sporangium.
a tail.
Hirase.)
(After Ikeno and
FURTHER STUDIES ON GYMNOSPERMS.
3'5
In comparing the female prothallium of the gymnospenns with that of the
fern group we see a remarkable change has taken place. The female pro-
thallium of the gymno-
sperms is very much
reduced in size. Espe-
cially, it no longer leads
an independent existence
from the sporophyte, as
is the case with .nearly
all the fern group. It
remains enclosed = within
the macrosporangium (in
cycas if not fertilized it
sometimes grows outside
of the macrosporangium
and becomes green), and
derives its nourishment
through it from the sporo-
phyte, to which the latter
remains organically con-
nected. This condition
of the female prothallium
of the gymnosperms
Fig. 374- necessitated a special
Gingko biloba. A , mature pollen grain ; /?, germinating adaptation of the male
pollen grain, the branched tube entering among the cells m-nth-lHum ;n nrrler that
of the nucellus; Ex, exine (outer wall of spore); /^ pro- PrOtnallmm 11
thallial cell ; A^, antheridial cell (divides later to form stalk the sperm cells may reach
cell and generative cell) ; /'3, vegetal' ve cell ; l''a, vacuoles ;
Nc, nucellus. (After drawings by Hirase and Ikeno.) and fertilize the egg cell.
MO
Fig- 375-
Gingko biloba, diagrammatic representation of the relation of pollen tube to the arche-
;pnium in the end of the nucellus. //, pollen tube ; o, archegonium. (After drawing by
"irase and Ikeno.)
i!
636. Gymnosperms are naked seed plants. — The pine, as we have seen,
has naked seeds. That is, the seeds are not enclosed within the carpel, but
MORPHOLOG V.
are exposed on the outer surface.
Fig. 376-
Spermatoz <ids of
zamia in pollen tube;
pg, pollen grain; a, a,
spermatozoids. (After
Webber.)
coordinate with them,
as follows:
All the plants of the great group to
which the pine belongs have
naked seeds. For this reason
the name "gymnosperms"
has been given to this great
group.
637. Classification of gymno-
sperms.— The gingko tree has
until recently been placed with
the pines, yew, etc., in the order
Fig. 377. Finales, but the discovery of
Spermatozoid of za- the spermatozoids in the pollen
mia showing spiral ...
row of cilia. (After tube suggests that it is not
Webber.) closely allied with the Finales,
and that it represents an order
Engler arranges the living gymnosperms somewhat
Class Gymnospermae.
Order i. Cycadales; family Cycadaceae. Cycas, Zamia, etc.
Order 2. Gingkoales; family Gingkoaceae. Gingko.
Order 3. Finales (or Coniferae); family i. Taxaceae. Taxus, the common
yew in the eastern United
States, and Torreya, in the
western United States, are
examples.
family 2. Pinaceae. Sequoia (redwood of
California), firs, spruces, pines,
cedars, cypress, etc.
Order 4. Gnetales. Welwitschia niirabilis, deserts of southwest Africa;
Ephedra, deserts of the Mediterranean and of West
Asia. Gnetum, climbers (Lianas), from tropical
Asia and America.
FURTHER STUDIES ON GYMNOSPEKMS. 317
3 OF SPOROPHYTE AND GAMETOPHYTE IN THE PINE.
d
I
d
0
o
i
§
S
B
OH
X.
Q
U
3
J
a
8
js
13
s c.
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i « S g c
C CC C3 'Q ^
S S C^P-10H
II II II II II
dimentary male pro-
ary antheridium = Mature pollen grain,
ridium wall ?) = Vegetative cell of pollen grain.
= Small cell of pollen grain,
to form stalk cell and
im (male sexual organ) = Generative cell,
him divides to form
= Paternal cells, or generative cells.
= Ovuliferous scale (cover scale and carpellary
outgrowth); or three carpels united into
ovuliferous scale, the central one sterile
(in axil of cover scale),
d by integument = Nucellus covered by integument = ovule,
iporangium) = Large cell in center of nucellus which de-
velops embryo-sac and endosperm (remains
in nucellus).
porangium) = Endosperm, in nucellus.
il organs) = Corpuscula, in endosperm.
= Maternal cell, or germ cell.
= Germ cell.
= Pine embryo in nucellus and integument.
= Embryo 1
hyte = Endosperm l~.
= Nucellus
awth of old sporophyte = Integument J
W
—
H
O
2 g
43 '_.
.B T3
T3 'u
2 a
CL> C
in 3
e ><
g-
&
[OWING HOMOLOG
iMS CORRESPONDING TO TH
Sporophyte
Spore-bearing part
j Microsporophyll
1 Microsporangium
Microspore
Mature microspore is
thallium with rudim
c "2
CS '>
'C *>
D 43
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CHAPTER XXXV.
MORPHOLOGY OF THE ANGIOSPERMS : TRILLIUM;
DENTARIA.
Trillium.
639. General appearance. — As one of the plants to illustrate
this group we may take the wake-robin, as it is sometimes called,
or trillium. There are several species of this genus in the
United States ; the commonest one in the eastern part is the
"white wake-robin" (Trillium grandiflorum). This occurs in
or near the woods. A picture of the plant is shown in fig. 378.
There is a thick, fleshy, underground stem, or rhizome as it is
usually called. This rhizome is perennial, and is marked by
ridges and scars. The roots are quite stout and possess coarse
wrinkles. From the growing end of the rhizome each year the
leafy, flowering stem arises. This is 20— $ocm (8-12 inches) in
height. Near the upper end is a whorl of three ovate leaves,
and from the center of this rosette rises the flower stalk, bearing
the flower at its summit.
640. Parts of the flower. Calyx. — Now if we examine
the flower we see that there are several leaf-like structures.
These are arranged also in threes just as are the leaves. First
there is a whorl of three, pointed, lanceolate, green, leaf-like
members, which make up the calyx in the higher plants, and the
parts of the calyx are sepals, that is, each leaf-like member is a
sepal. But while the sepals are part of the flower, so called, we
easily recognize them as belonging to the leaf series.
318
ANGIOSPERMS: TRILLIUM.
641. Corolla. — Next above the calyx is a whorl of white or
pinkish members, in
are also leaf-like in form,
being usually somewhat
make up what is the
and each member of the
they are parts of the
their form and posi-
also belong to the leaf
642. Andrcecium. —
tion of the corolla is
of members which do not
form. They are known
As seen in fig. 379 each
ament), and extending
greater part of the length
side. This part of the
ridges form the anther
Soon after the flower is
ther sacs open also by a
along the edge of the
time we see quantities of
or dust escaping from the
Trillium grandiflorum, which
and broader than the sepals,
broader at the free end. These
corolla in the higher plants,
corolla is a petal. But while
flower, and are not green,
tion would suggest that they
series.
Within and above the inser-
found another tier, or whorl,
at first sight resemble leaves in
in the higher plants as stamens.
stamen possesses a stalk ( = fil-
along on either side for the
are four ridges, two on each
stamen is the anther, and the
sacs, or lobes,
opened, these an-
split in the wall
ridge. At this
Fig. 378. yellowish powder
Trillium grandiflorum. ruptured anther
locules. If we place some of this under the microscope we see
320
MORPHOLOGY.
that it is made up of minute bodies which resemble spores ; they
are rounded in form, and the outer wall is spiny. They are in fact
spores, the microspores
of the trillium, and here,
as in the gymnosperms,
are better known as pollen.
Fig. 379-
Sepal, petal, stamen, and pistil of Trillium
grandiflorum.
643. The stamen a sporo-
phyll. — Since these pollen
grains are the spores, we would
infer, from what we have
learned of the ferns and gym-
nosperms, that this member of
the flower which bears them is a sporophyll ;
and this is the case It is in fact what is called
the microsporophyll. Then we see also that the
anther sacs, since they enclose the spores, would
be the sporangia (microsporangia). From this
it is now quite clear that the stamens
belong also to the leaf series. They
are just six in number, twice the number
found in a whorl of leaves, or sepals,
or corolla. It is believed, therefore,
that there are two whorls of stamens in the flower of trillium.
644. Gyncecium. — Next above the stamens and at the center
of the flower is a stout, angular, ovate body which terminates in
three long, slender, curved points. This is the pistil, and at
Fig. 380.
Trillium gran-
diflorum, with
the compound
pistil expanded
into three leaf-
like members.
At the right
these three are
shown in detail.
A NGIOSPERMS : TRTL LIUM.
321
present the only suggestion which it gives of belonging to the
leaf series is the fact that the end is divided into three parts, the
number of parts in each successive whorl of members of the
flower. If we cut across the body of this pistil and examine it
with a low power we see that there are three chambers or cavi-
ties, and at the junction of each
the walls suggest to us that this
body may have been formed by the
infolding of the margins of three
leaf- like members, the places of
contact having then become grown
together. We see also that from
the incurved
margins of each
division of the
pistil there stand
out in the cavity oval bodies.
These are the ovules. Now the
ovules we have learned from our
study of the gymnosperms are the
sporangia (here the macrosporangia).
It is now more evident that this curious body, the pistil, is made up
of three leaf-like members which have fused together, each mem-
ber being the equivalent of a sporophyll (here the macrosporo-
phyll). This must be a fascinating observation, that
plants of such widely different groups and of such
different grades of complexity should have members
formed on the same plan and belonging to the same
series of members, devoted to similar functions, and
yet carried out with such great modifications that at
first we do not see this common meeting ground
Fig. 382. which a comparative study brings out so clearly.
s.amrenSo°frTriid 645 . Transformations of the flower of trillium. —
anther s'iocui"f If anything more were needed to make it clear that
on the margin. ^ parts Qf ^ flQwer Qf triuium belong to the leaf
series we could obtain evidence from the transformations which
Fig. 381.
Abnormal
trillium. The
nine parts of
the perianth
are green,
and the outer
whorls of
stamens are
expanded into
petal -like
members.
322 MORPHO LOGY.
the flower of trillium sometimes presents. In fig. 381 is a sketch
of a flower of trillium, made from a photograph. One set of
the stamens has expanded into petal-like organs, with the anther
sacs on the margin. In fig. 380 is shown a plant of Trillium
grandiflorum in which the pistil has separated into three distinct
and expanded leaf-like structures, all green except portions of
the margin.
Dentaria.
646. General appearance. — For another study we may take
a plant which belongs to another division of the higher plants,
the common "pepper root," or " toothwort " (Dentaria
diphylla) as it is sometimes called. This plant occurs in moist
woods during the month of May, and is well distributed in the
northeastern United States. A plant is shown in fig. 383. It
has a creeping underground rhizome, whitish in color, fleshy,
and with a few scales. Each spring the annual flower-bearing
stem rises from one of the buds of the rhizome, and after the
ripening of the seeds, dies down.
The leaves are situated a little above the middle point of the
stem. They are opposite and the number is two, each one
being divided into three dentate lobes, making what is called a
compound leaf.
647. Parts of the flower. — The flowers are several, and they
are borne on quite long stalks (pedicels) scattered over the ter-
minal portion of the stem. We should now examine the parts
of the flower beginning with the calyx. This we can see, look-
ing at the under side of some of the flowers, possesses four scale-
like sepals, which easily fall away after the opening of the flower.
They do not resemble leaves so much as the sepals of trillium,
but they belong to the leaf series, and there are two pairs in the
set of four. The corolla also possesses four petals, which are more
expanded than the sepals and are whitish in color. The sta-
mens are six in number, one pair lower than the others, and also
ANGIOSPERMS: DENTARIA. 323
shorter. The filament is long in proportion to the anther, the
latter consisting of two
lobes or sacs, instead of
four as in trillium. The
pistil is composed of two
carpels, or leaves fused
together. So we find in
the case of the pepper
root that the parts of the
flower are in twos, or
multiples of two. Thus
they agree in this respect
with the leaves; and
while we do not see
such a strong resem-
blance between the
parts of the flower
here and the leaves,
yet from the pres-
ence of the pollen
Fig. 384.
Flower of the toothwort (Dentaria
diphylla).
Fig. 383.
Toothwort (Dentaria diphylla).
324
MORPHOLOG Y.
(microspores) in the anther sacs (microsporangia) and of ovules
(macrosporangia) on the margins of each half of the pistil, we
are, from our previous studies, able to recognize here that all the
members of the flower belong to the leaf series.
648. In trillium and in the pepper root we have seen that the
parts of the flower in each apparent whorl are either of the same
number as the leaves in a whorl, or some multiple of that num-
ber. This is true of a large number of other plants, but it is not
true of all. A glance at the spring beauty (Claytonia virginiana,
and at the anemone (or Isopyrum biternatum, fig. 563) will
serve to show that the number of the different members of the
flower may vary. The trillium and the dentaria were selected
as being good examples to study first, to make it very clear that
the members of the flower are fundamentally leaf structures, or
rather that they belong to the same series of members as do the
leaves of the plant.
649. Synopsis of members of the sporophyte in angiosperms.
Higher plant.
Sporophyte phase
Root.
oiupnyie piiasc •<
(or modern phase). ( Shoot- j
Leaf.
Foliage leaves.
Perianth leaves.
Spore-bearing leaves
with sporangia.
(Sporangia sometimes
on shoot.)
Flower.
CHAPTER XXXVI.
pollen grain of tril-
lium. The sm
smaller
cell is the genera-
tive cell. the mother cell.
GAMETOPHYTE AND SPOROPHYTE OF ANGIO-
SPERMS.
650. Male prothallium of angiosperms. — The first division
which takes place in the nucleus of the pollen grain occurs, in
the case of trillium and many others of the angio-
sperms, before the pollen grain is mature. In the
case of some specimens of T. grandiflorum in
which the pollen was formed during the month
of October of the year before flowering, the divi-
Neariy mature sion of the nucleus into two nuclei took place
soon after the formation of the four cells from
The nucleus divided in the
young pollen grain is shown in fig. 385. After this takes
place the wall of the pollen grain becomes stouter, and minute
spiny projections are formed.
651. The larger cell is the vegetative cell
of the prothallium, while the smaller one, since
it later forms the sperm cells, is the generative
cell. This generative cell then corresponds
to the central cell of the antheridium, and the
vegetative cell perhaps corresponds to a wall
cell of the antheridium. If this is so, then the
male prothallium of angiosperms has become
reduced to a very simple antheridium. The
farther growth takes place after fertilization.
In some plants the generative cell divides into
the two sperm cells at the maturity of the pollen grain,
pollen grain. In other cases the generative cell divides in the pollen tube
after the germination of the pollen grain. For study of the pollen tube the
pollen may be germinated in a weak solution of sugar, or on the cut surface
325
(poll
ided
egetat
326
MORPHOLOG Y.
of pear fruit, the latter being kept in a moist chamber to prevent drying
the surface.
652- In the spring after flowering the pollen escapes from the anther sacs,
and as a result of pollination is brought to rest on the stigma of the pistil.
Here it germinates, as we say, that is, it develops a long tube which makes
its way down through the
style, and in through the
micropyle to the embryo sac,
where, in accordance with
what takes place in other
plants examined, one of the
sperm cells unites with the
egg, and fertilization of the
egg is the result.
653. Macrospore and embryo sac.
three carpels are united into one,
two carpels are also united into one
Simple pistils are found in many
in the ranunculaceas, the buttercups,
These simple pistils bear a greater
Fig. 387-
Section of pistil of tril-
lium, showing position of
ovules (macrosporangia).
— In trillium the
and in dentaria the
compound pistil,
plants, for example
columbine, etc.
resemblance to a
leaf, the margins of
which are folded
around so that they
meet and enclose
the ovules or spo-
rangia.
654. If we cut
across the com-
pound pistil of tril-
lium we find that
the infoldings of the
three pistils meet to
Fig. 388. r
Mandrake (Podo- ic-rm three partial
phyllumpeltatum). nnft,;t.;nncl wnich
extend nearly to the center, dividing off three spaces. In these
spaces are the ovules which are attached to the infolded margins.
If we make cross sections of a pistil of the May-apple (podo-
GAMETOPHYTE AND SPOROPHYTE.
327
phyllum) and through the ovules when they are quite young, we
shall find that the ovule has a structure like that shown in fig. 389.
At m is a cell much larger than the surrounding ones. This is
called the macrospore. The tissue surrounding it is called here the
nucellus, but because it contains the macrospore it must be the
macrosporangium. The two coats or integuments of the ovule are
yet short and have not grown out over the end of the nucellus.
This macrospore increases in size, forming first a cavity or sac
in the nucellus, the embryo sac. The nucleus divides several
Fig. 389.
Young ovule (macrosporangium) of podophyllum. n, nucellus containing the one-
celled stage of the macrospore; i.int, inner integument; o.int, outer integument.
times until eight are formed, four in the micropylar end of the
embryo sac and four in the opposite end. In some plants it
has been found that one nucleus from each group of four moves
toward the middle of the embryo sac. Here they fuse together
to form one nucleus, the endosperm nucleus or definitive nucleus
shown in fig. 390. One of the nuclei at the micropylar end is
the egg, while the two smaller ones nearer the end are the syner-
328
MORPHOLOG Y.
gids. The egg cell is all that remains of the archegonium in
this reduced prothallium. The three nuclei at the lower end
are the antipodal cells.
Fig. 390.
PodophyUum peltatum, ovule containing mature embryo sac; two synergids, and
eggs at left, endosperm nucleus in center, three antipodal cells at right.
655. Embryo sac is the young female prothallium.— In figs.
39I-393 are shown the different stages in the development of
the embryo sac in lilium. The
embryo sac at this stage is the
young female prothallium, and
the egg is the only remnant of the
female sexual organ, the arche-
gonium, in this reduced gameto-
phyte.
656. Fertilization. — When the
pollen tube has reached the em-
bryo sac (paragraph 652) it opens
Macrospore (one-celled stage) of lilium. an(J the two sperm Cells are emptied
near the egg. The first sperm nucleus enters the protoplasm
.surrounding the egg nucleus and uniting with the latter brings
about fertilization. The second sperm nucleus often unites
with the endosperm nucleus (or with one or both of the "polar
nuclei"), bringing about what some call a second fertilization.
Where this takes place in addition to the union of the first sperm
Fig. 391-
GAMETOPHYTE AND SPQROPHYTE.
329
nucleus with the egg nucleus it is called double fertilization. The
sperm nucleus is usually smaller than the egg nucleus, but often
grows to near or quite the size of the egg nucleus before union.
See figs. 394 and 395.
657. Fertilization in plants is fundamentally the same as
in animals. — In all the great groups of plants as represented by
spirogyra, cedogonium, vaucheria, peronospora, ferns, gymno-
Fig. 392-
Two- and four-celled stage of embryo-sac of lilium. The middle one shows
division of nuclei to form the four-celled stage. (Easter lily.)
sperms, and in the angiosperms, fertilization, as we have seen,
consists in the fusion of a male nucleus with a female nucleus.
Fertilization , then, in plants is identical with that which takes
place in animals.
658. Embryo. — After fertilization the egg develops into a short
row of cells, the suspensor of the embryo. At the free end the em-
bryo develops. In figs. 397 and 398 is a young embryo of trillium.
659. Endosperm, the mature female prothallium. — During
the development of the embryo the endosperm nucleus divides
330
MORPHOLOG Y.
into a great many nuclei in a mass of protoplasm, and cell walls
are formed separating them into cells. This mass of cells is the
endosperm, and it surrounds the
embryo. It is the mature female
prothallium, belated in its growth
in the angiosperms, usually de-
veloping only when fertilization
takes place, and its use has been
assured.
660. Seed. — As the embryo
PD
Fig- 393-
Mature embryo sac (young pro-
thallium) of lilium. /«, micropylar
end ; S, synergids ; £, egg ; /'«,
polar nuclei; Ant, antipodals.
(Easter lily.)
Fig. 394-
Section through nucellus and upper part of embryo
sac of cotton at time of entrance of pollen tube. E,
egg; S, synergids; l\ pollen tube with sperm cell in
the end. (Duggar.)
GAMETOPHYTE AND SPOROPHYTE.
33'
is developing it derives its nourishment from the endosperm (or
in some cases perhaps from the nucellus). At the same time
Sn-
male and female nu-
u's fusing. (Duggar.)
the integuments increase
in extent and harden as
the seed is formed.
661. Perisperm. — In tt
most plants the nucellus is '
all consumed in the devel-
opment of the endosperm,
so that only minute frag-
ments of disorganized cell
walls remain next the in-
ner integument. In some
plants, however, (the water-
lily family, the pepper
family, etc.,) a portion of
the nucellus remains in-
tact in the mature seed.
In such seeds the remain-
ing portion of the nucellus is the perisperm.
662. Presence or absence of endosperm in the seed. — In
many of the angiosperms all of the endosperm is consumed by
the embryo during its growth in the formation of the seed. This
is the case in the rose family, crucifers, composites, willows, oaks,
legumes, etc., as in the acorn, the bean, pea and others. In
some, as in the bean, a large part of the nutrient substance pass-
Fig. 396.
Diagrammatic section of ovary and ovule at time
of fertilization in angiosperm. f, funicle of ovule ;
», nucellus ; m, tnicropyle ; b, antipodal cells of
embryo sac ; e, endosperm nucleus ; k, egg cell and
synergids ; at, outer integument of ovule ; ii, inner
integument. The track of the pollen tube is shown
down through the style, walls of the ovary to the
micropylar end of the embryo sac.
332
MO RP HO LOG V.
ing from the endosperm into the embryo is stored in the cotyle-
dons for use during germination. In other plants the endosperm
Fig. 107- Fig. 598.
Section of one end of ovule of trillium, showing Embryo e n -
young embryo in endosperm. larged.
is not all consumed by the time the seed is mature. Examples of
1his kind are found in the buttercup family, the violet, lily, palm,
Fig 399-
Seed of violet, external view, and
section. The section shows the embryo
lying in the endosperm.
Fig. 400.
Section of fruit of pepper (Piper
nigrum), showing small embryo lying
in a small quantity of whitish endo-
sperm at one end, the perisperm oc-
cupying the larger part of the interior,
surrounded by pericarp.
jack-in-the-pulpit, etc. Here the remaining endosperm in the
seed is used as food by the embryo during germination.
663. Outer parts of the seed. — While the embryo is forming
ANGIOSPERMS: SEED. 333
within the ovule and the growth of the endosperm is taking
place, where this is formed, other correlated changes occur in
the outer parts of the ovule, and often in adjacent parts of the
flower. These unite in making the " seed, " or the " fruit. "
Especially in connection with the formation of the seed a new
growth of the outer coat, or integument, of the ovule occurs,
forming the outer coat of the seed, known as the testa, while
the inner integument is absorbed. In some cases the inner
integument of the ovule also forms a new growth, making an
inner coat of the seed (rosaceae). In still other cases neither
of the integuments develops into a testa, and the embryo sac
lies in contact with the wall of the ovary. Again an additional
envelope grows up around the seed; an example of this is
found in the case of the red berries of the " yew " (taxus), the
red outer coat being an extra growth, called an aril.
In the willow and the milkweed an aril is developed in the
form of a tuft of hairs. (In the willow it is an outgrowth of
the funicle, = stalk of the ovule, and is called a funicular aril ;
while in the milkweed it is an outgrowth of the micropyle, =
the open end of the ovule, and is called a micropylar aril. )
664. Increase in size during seed formation. — Accompany-
ing this extra growth of the different parts of the ovule in the
formation of the seed is an increase in the size, so that the seed
is often much greater in size than the ovule at the time of fer-
tilization. At the same time parts of the ovary, and in many
plants, the adherent parts of the floral envelopes, as in the apple;
or of the receptacle, as in the strawberry ; or in the involucre,
as in the acorn ; are also stimulated to additional growth, and v
assist in making the fruit.
334
MORPHOLOG Y.
Ripened ovule.
The seed.
665. Synopsis of the seed.
Aril, rarely present.
Ovular coats (one or two usually present), the
testa.
Funicle (stalk of ovule), raphe (portion of
funicle when bent on to the side of ovule),
micropyle, hilum (scar where seed was
attached to ovary).
Remnant o} the nucettus (central part of
ovule); sometimes nucellus remains as
. Perisperm in some albuminous seeds.
Endosperm, present in albuminous seeds.
Embryo within surrounded by endosperm when this is present,
or by the remnant of nucellus, and by the ovular coats which
make the testa. In many seeds (example, bean) the endo-
sperm is transferred to the cotyledons which become fleshy
(exalbuminous seeds).
666. Parts of the ovule. — In fig. 401 are represented three
different kinds of ovules, which depend on the position of the
Fig. 401.
A, represents a straight (orthotropus) ovule of polygonum; B, the inverted
(anatropous) ovule of the lily; and C, the right-angled (campylotropus) ovule of
the bean, f, funicle; c, chalaza; k, nucellus; ai, outer integument; «*, inner
integument; m, micropyle; em, embryo sac.
ovule with reference to its stalk. The funicle is the stalk of the
ovule, the hilum is the point of attachment of the ovule with
the ovary, the raphe is the part of the funicle in contact with
the ovule in inverted ovules, the chalaza is the portion of the
ovule where the nucellus and the integuments merge at the base
of the ovule, and the micropyle is the opening at the apex of
the ovule where the coats do not meet.
FLOWER: MEMBERS AND ORGANS, 335
Comparison of Organ and Member.
667. The stamens and pistils are not the sexual organs. —
Before the sexual organs and sexual processes in plants were
properly understood it was customary for botanists to speak
of the stamens and pistils of flowering plants as the sexual
organs. Some of the early botanists, a century ago, found .that
in many plants the seed would not form unless first the pollen
from the stamens came to be deposited on the stigma of the
pistil. A little further study showed that the pollen germinated
on the stigma and formed a tube which made its way down
through the pistil and into the ovule.
This process, including the deposition of the pollen on the
stigma, was supposed to be fertilization, the stamen was looked
on as the male sexual organ, and the pistil as the female sexual
organ. We have found out, however, by further study, and
especially by a comparison of the flowering plants and the lower
plants, that the stamens and pistils are not the sexual organs of
the flower.
668. The stamens and pistils are spore-bearing leaves.— The
stamen is the spore-bearing leaf, and the pollen grains are not
unlike spores; in fact they are the small spores of the angio-
sperms. The pistil is also a spore-bearing leaf, the ovule the
sporangium, which contains the large spore called an embryo sac.
In the ferns we know that the spore germinates and produces the
green heart-shaped prothallium. The prothallium bears the
sexual organs. Now the fern leaf bears the spores and the spore
forms the prothallium. So it is in the flowering plants. The
stamen bears the small spores — pollen grains — and the pollen
grain forms the prothallium. The prothallium in turn forms
the sexual organs. The process is in general the same as it is in
the ferns, but with this special difference: the prothallium and
the sexual organ of the flowering plants are very much reduced.
669. Difference between organ and member. — While it is
not strictly correct then to say that the stamen is a sexual organ,
336 MORPHOLOGY.
or male organ, we might regard it as a male member of the flower,
and we should distinguish between organ and member. It is an
organ when we consider pollen production, but it is not a sexual
organ. When we consider fertilization it is not a sexual organ,
but a male member of the flower which bears the small spore.
The following table will serve to indicate these relations.
Stamen = spore-bearing leaf = male member of flower.
Anther locule = sporangium.
Pollen grain = small spore = reduced male prothallium and
sexual organ.
So the pistil is not a sexual organ, but might be regarded as
the female member of the flower.
Pistil = spore-bearing leaf = female member of flower.
Ovule = sporangium.
Embryo sac = large spore = female prothallium containing the
egg-
The egg =a reduced archegonium=the female sexual organ.
Progression and Retrogression in Sporophyte and
Gametophyte.
670. Sporophyte is prominemt and highly developed. — In the angiosperms
then, as we have seen from the plants already studied, the trillium, dentaria,
etc. , are sporophytes, that is they represent the spore-bearing, or sporophytic,
stage. Just as we found in the case of the gymnosperms and ferns, this stage
is the prominent one, and the one by which we characterize and recognize the
plant. We see also that the plants of this group are still more highly special-
ized and complex than the gymnosperms, just as they were more specialized
and complex than the members of the fern group. From the very simple
condition in which we possibly find the Sporophyte in some of the algae like
spirogyra, vaucheria, and coleochsete, there has been a gradual increase in
size, specialization of parts, and complexity of structure through the bryo-
phytes, pteridophytes, and gymnosperms, up to the highest types of plant
structure found in the angiosperms. Not only do we find that these changes
have taken place, but we see that, from a condition of complete dependence of
the spore-bearing stage on the sexual stage (gametophyte), as we find it in the
liverworts and mosses, it first becomes free from the gametophyte in the mem-
bers of the fern group, and is here able to lead an independent existence.
The sporophyte, then, might be regarded as the modern phase of plant life,
PART III.
PLANT MEMBERS IN RELATION TO ENVIRONMENT.
CHAPTER XXXVIII.
THE ORGANIZATION OF THE PLANT.
I. Organization of Plant Members.*
689. It is now generally conceded that the earliest plants to
appear in the world were very simple in form and structure.
Perhaps the earliest were mere bits of naked protoplasm, not
* Suggestions to the teacher, — In the studv of the flowering plants in the
secondary school and in elementary courses three general topics are sug-
gested, ist, the study of the form and members of the plant and their
arrangement, as in Chapters XXXVIII-XLV. 2d, the study of a few
plants representative of the more important families, in order that the
members of the plant, as studied under the first topic, may be seen in corre-
lation with the plant as a whole in a number of different types. 3d, the
study of plants in their relation to environment, as in Chapter XLVI.
The first and second topics can be conducted consecutively in the class-
room and laboratory. The third topic can be studied at opportune times
during the progress of topics i and 2. For example, while studying topic i
excursions can be made to study winter conditions of buds, shoots, etc.,
if in winter period, or the relations of leaves, etc., to environment, if in
the growing period. While studying topic 2 excursions can be made to
study flower relations, and also vegetation relations to environment (see
Chapters XLVI-LVII of the author's "College Text-book of Botany").
It is believed that a study of these three general topics is of much more
value to the beginning student than the ordinary plant analysis and deter-
mination of species.
349
35° DELATION TO ENVIRONMENT.
essentially different from early animal life. The simplest ones
which are clearly recognized as plants are found among the
lower algae and fungi. These are single cells of very minute
size, roundish, oval, or oblong, existing during their growing
period in water or in a very moist substratum or atmosphere.
Examples are found in the red snow plant (Sphcerella nivalis),
the Pleurococcus, the bacteria; and among small colonies of
these simple organisms (Pandorina) or the thread-like forms
(Spirogyra, CEdogonium, etc.). It is evident that some of the
life relations of such very simple organisms are very easily ob-
tained— that is, the adjustment to environment is not difficult.
All of the living substance is very closely surrounded by food
material in solution. These food solutions are easily absorbed.
Because of the minute size of the protoplasts and of the plant
body, they do not have to solve problems of transport of food to
distant parts of the body. When we pass to more bulky organ-
isms consisting of large numbers of protoplasts closely com-
pacted together, the problem of relation to environment and of
food transport become felt; the larger the organism usually the
greater are these problems. A j>oint is soon reached at which
there is a gain by a differentiation in the work of different proto-
plasts, some for absorption, some for conduction, some for the
light relation, some for reproduction, and so on. There is also
a gain in splitting the form of the plant body up into parts so that
a larger surface is exposed to environment with an economy in
the amount of building material required. In this differentiation
of the plant body into parts, there are two general problems to
be solved, and the plant to be successful in its struggle for exist-
ence must control its development in such a way as to preserve
the balance between them, (i) A ready display of a large sur-
face to environment for the purpose of acquiring food and the
disposition of waste. (2) The protection of the plant from
injuries incident to an austere environment.
It is evident with the great variety of conditions met with in
different parts of the same locality or region, and in different
parts of the globe, that the plant has had very complex problems
ORGANIZATION PLANT MEMBERS. 35 *
to meet and in the solution of them it has developed into a great
variety of forms. It is also likely that different plants would in
many cases meet these difficulties in different ways, sometimes
with equal success, at other times with varied success. Just as
different persons, given some one piece of work to do, are likely
to employ different methods and reach results that are varied as
to their value. While we cannot attribute consciousness or
choice to plants in the sense in which we understand these qual-
ities in higher animals, still there is something in their " consti-
tution" or "character" whereby they respond in a different
manner to the same influences of environment. This is, per-
haps, imperceptible to us in the different individuals of the same
species, but it is more marked in different species. Because of
our ignorance of this occult power in the plant, we often speak of
it as an "inherent" quality.
Perhaps the most striking examples one might use to illustrate the dif-
ferent line of organization among plants in two regions where the environ-
ment is very different are to be found in the adaptation of the cactus or
the yucca to desert regions, and the oak or the cucurbits to the land condi-
tions of our climate. The cactus with stem and leaf function combined in
a massive trunk, or the yucca with bulky leaves expose little surface in
comparison to the mass of substance, to the dry air. They have tissue for
water storage and through their thick epidermis dole it out slowly since
there is but little water to obtain from dry soil.
The cucurbits and the oak in their foliage leaves expose a very large sur-
face in proportion to the mass of their substance, to an atmosphere not so
severely dry as that of the desert, while the roots are able to obtain an
abundant supply of water from the moist soil. The cactus and the yucca
have differentiated their parts in a very different way from the oak or the
cucurbits, in order to adapt themselves to the peculiar conditions of the
environment.
When we say that certain plants have the power to adapt themselves to
certain conditions of environment, we do not mean to say that if the cucur-
bits were transferred to the desert they would take on the form of the cactus
or the yucca. They could do neither. They would perish, since the change
would be too great for their organization. Nor do we mean, that, if the
cactus or yucca were transferred from the desert to our climate, they would
change into forms with thin foliage leaves. They could not. The fact is
that they are enabled to live in our climate when we give them some care,
but they show no signs of assuming characters like those of our vegetation.
352 RELATION TO ENVIRONMENT.
What we do mean is, that where the change is not too great nor too sudden,
some of the plants become slightly modified. This would indicate that the
process of organization and change of form is a very slow one, and is there-
fore a question of time — ages it may be — in which change in environment
and adaptation in form and structure have gone on slowly hand in hand.
690. Members of the plant body.— The different parts into
which the plant body has become differentiated are from one
point of view, spoken of as members. It is evident that the sim-
plest forms of life spoken of above do not have members. It is
only when differentiation has reached the stage in which certain
more or less prominent parts perform certain functions for the
plant that members are recognized. In the algae and fungi
there is no differentiation into stem and leaf, though there is an
approach to it in some of the higher forms. Where this simple
plant body is flattened, as in the sea-wrack, or ulva, it is a jrond.
The Latin word for frond is thallus, and this name is applied to
the plant body of all the lower plants, the algae and fungi. The
algae and fungi together are sometimes called thallophyles, or
thallus plants. The word thallus is also sometimes applied to
the flattened body of the liverworts. In the foliose liverworts
and mosses there is an axis with leaflike expansions. These
are believed by some to represent true stems and leaves; by
others to represent a flattened thallus in which the margins are
deeply and regularly divided, or in which the expansion has only
taken place at regular intervals.
In the higher plants there is usually great differentiation of
the plant body, though in many forms, as in the duckweeds, it is
in the form of a frond. While there is a great variety in the
form and function of the members of the plant body, they are
all reducible to a few fundamental members. Some reduce
these forms to three, the root, stem, leaf; while others to two, the
root, and shoot, which is perhaps the best primary subdivision,
and the shoot is then divided into stem and leaf, the leaf being
a lateral outgrowth of the stem, and can be indicated by the fol-
lowing diagram:
ORGANIZATION- PLANT MEMBERS,
353
Plant body
Shoot. .
Root.
Stem.
Leaf.
KINDS OF SHOOTS.
691. Since it is desirable to consider the shoot in its relation to
environment, for convenience in discussion we may group shoots
into four prominent kinds: (i) Foliage shoots; (2) Shoots with-
out foliage leaves; (3) Floral shoots; (4) Winter conditions of
shoots and buds. Topic (4) will be treated in Chapter XXXIX,
section IV.
692. (1st) Foliage shoots. — Foliage shoots are either aerial,
when their relation is to both light and air; or they are aquatic,
when their relation is to
both light and water. They
bear green leaves, and
whether in the air or water
we see that light is one of
the necessary relations for
all. Naturally there are
several ways in which a
shoot may display its leaves
to the light and air or
water. Because of the
great variety of conditions
on the face of the earth
and the multitudinous
kinds of plants, there is the
greatest diversity presented
in the method of meeting these conditions. There is to be con-
sidered the problem of support to the shoot in the air, or in
the water. The methods for solving this problem are funda-
mentally different in each case, because of the difference in the
density of air and water, the latter being able to buoy up the
plant to a great degree, particularly when the shoot is provided
with air in its intercellular spaces or air cavities. In the solu-
Fig. 413-
Lupinus perennis. Foliage shoot and floral
shoot.
354 RELATION TO ENVIRONMENT.
tion of the problem in the relation of the shoot to aerial en-
vironment, stem and leaf have in most cases cooperated ; * but
in view of the great variety of stems and their modifications, as
well as of leaves, it will be convenient to discuss them in separate
chapters.
693. (2d) Shoots without foliage leaves. — These are subter-
ranean or aerial. Nearly all subterranean shoots have also
aerial shoots, the latter being for the display of foliage leaves
(foliage shoots), and also for the display of flowers (flower shoots)..
The subterranean kinds bear scale leaves, i.e., the leaves not
having a light relation are reduced in size, being small, and they
lack chlorophyll. Examples are found in Solomon's seal, man-
Fig. 4130.
Burrowing type, the mandrake, a "rhizome."
drake (fig. 4130), etc. Here the scale leaves are on the bud at
the end of the underground stem from which the foliage shoot
arises. Aerial shoots which lack foliage leaves are the dodder,
Indian pipe-plant, beech drops, etc. These plants are sapro-
phytes or parasites (see Chapter IX). Deriving their carbo-
hydrate food from other living plants, or from humus, they do
not need green leaves. The leaves have, therefore, probably
been reduced in size to mere scales, and accompanying this
there has been a loss of the chlorophyll. Other interesting ex-
amples of aerial shoots without foliage leaves are the cacti where
* It is interesting to note that in some foliage shoots the stem is entirely
subterranean. See discussion of the bracken fern and sensitive fern in
Chapter XXXIX.
ORGANIZATION: PLANT MEMBERS. 355
the stem has assumed the leaf function and the leaves have
become reduced to mere spines. The various modifications
which shoots have undergone accompanying a change in their
leaf relation will be discussed under stems in Chapter XXXIX.
694. (3d) Floral shoots.— The floral shoot is the part of the
plant bearing the flower. As interpreted here it may consist of
but a single flower with its stalk, as in Trillium, mandrake, etc.,
or of the clusters of flowers on special parts of the stem, termed
flower clusters, as the calkin, raceme, spike, umbel, head, etc. In
the floral shoot as thus interpreted there are several peculiarities
to observe which distinguish it from the foliage shoot and adapt
it to its life relations.
The floral shoot in many respects is comparable to the foliage
shoot, as seen from the following peculiarities:
(1) It usually possesses, beside the flowers, small green leaves
which are in fact foliage though they are very much reduced in
size, because the function of the shoot as a foliage shoot is sub-
ordinated to the function of the floral shoot. These small leaves
on the floral shoot are termed bracts.
(2) It may be (a) unbranched, when it would consist of a
single flower, or (b) branched, when there would be several to
many flowers in the flower cluster.
(3) The flower bud has the same origin on the shoot as the
leaf bud; it is either terminal or axillary, or both.
(4) The members of the flower belong to the leaf series, i.e.,
they are leaves, but usually different in color from foliage leaves,
because of the different life relation which they have to perform.
Evidence of this is seen in the transition of sepals, petals, sta-
mens, or pistils, to foliage leaves in many flowers, as in the pond
lily, the abnormal forms of trillium, and many monstrosities in
other flowers (see Chapter XXXIV).
(5) The position of the members of the flower on its axis,
though usually more crowded, in many cases follows the same
plan as the leaves on the stem. •
The various kinds of floral shoots or flower clusters will be
discussed in Chapter XLII, on the Floral Shoot.
35^ RELATION TO ENVIRONMENT.
II. Organization of Plant Tissues.
695. A tissue is a group of cells of the same kind having a
similar position and function. In large and bulky plants differ-
ent kinds of tissue are necessary, not only because the work of
the plant can be more economically performed by a division of
labor, but also cells in the interior of the mass or at a distance
from the source of the food could not be supplied with food and
air unless there were specialized channels for conducting food
and specialized tissue for support of the large plant body. In
these two ways most of the higher plants differ from the simple
ones. The tissues for conduction are sometimes called collec
lively the mestome, while tissues for mechanical support are
called stereome. Division of labor has gone further also so that
there are special tissues for absorption, assimilation, perception,
reproduction, and the like. The tissues of plants are usually
grouped into three systems: (i) The Fundamental System,
(2) The Fibrovascular System, (3) The Epidermal System.
Some of the principal tissues are as follows:
1. THE FUNDAMENTAL SYSTEM.
696. Parenchyma. — Tissue composed of thin-walled cells which in the
normal state are living. Parenchyma forms the loose and spongy tissue in
leaves, as well as the palisade tissue (see Chapter IV); the soft tissue in the
cortex of root and stem (Fig. 414)^ as well as that of the pith, of the pith
rays or medullary rays of the stem; and is mixed in with the other elements
of the vascular bundle where it is spoken of as wood parenchyma and bast
parenchyma; and it also includes the undifferentiated tissue (meristem) in
the growing tips of roots and shoots; also the "intrafascicular" cambium
(i.e., between the bundles, some also include the cambium within the
bundle).
697. Collenchyma. — This is a strengthening tissue often found in the
cortex of certain shoots. It also is composed of living cells. The cells
are thickened at the angles, as in the tomato and many other herbs (fig.
414).
698. Sclerenchyma, or stone-tissue.— This is also a strengthening tissue
and consists of cells which do not taper at the ends and the walls are evenly
thickened, sometimes so thick that the inside (lumen) of the cell has nearly
disappeared. Usually such cells contain no living contents at maturity.
Sclerenchyma is very common in the hard parts of nuts, and underneath
ORGANIZATION: PLANT TISSUES.
357
the epidermis of stems and leaves of many plants, as in the underground
stems of the bracken fern, the leaves of pines (fig. 415), etc.
Fig. 414. Fig. 415-
Transverse section of portion of Margin of leaf of Pinus pinaster, transverse
tomato stem. ep, epidermis; ch section, c, cuticularized layer of outer wall
chlorophyll-bearing cells; co, collen- of epidermis; *, inner non-cuticularized
chyma; cp, parenchyma. layer; c', thickened outer wall of marginal
cell; g, i', hypoderma of elongated scle-
renchyma, p, chlorophyll-bearing paren-
chyma; pr, contracted protoplasmic con-
tents. X8oo. (After Sachs.)
699. Cork. — In many cases there is a development of "cork" tissue
underneath the epidermis. Cork tissue is developed by repeated division
of parenchyma cells in such a way that rows of parallel cells are formed
toward the outside. These are in distinct layers, soon lose their proto-
plasm and die; there are no intercellular spaces and the cells are usually
of regular shape and fit close to each other. In some plants the cell walls
are thin (cork oak), while in
others they are thickened
(beech). The tissue giving
rise to cork is called "cork
cambium," or phellogen, and
may occur in other parts of
the plant. For example,
where plants are wounded the
living exposed parenchyma
cells often change to cork
cambium and develop a pro-
tective layer of cork. The Fig. 416.
.,,,,, _ Section through a lenticel of Betula alba show,
walls Ot COIK cells contain a jng stoma at top, phellogen below producing rows
substance termed suberin, o£ flattened cells, the cork. (After De Bary.)
which renders them nearly waterproof.
RELATION TO ENVIRONMENT.
700. Lenticels. — These are developed quite abundantly underneath
stomates on the twigs of birch, cherry, beech, elder, etc. The phellogen
underneath the stoma develops a cushion of cork which presses outward
in the form of an elevation at the summit of which is the stoma (fig. 416).
The lenticels can easily be seen.
2. THE FIBROVASCTJLAR SYSTEM.
701. Fibrous tissue.* — This consists of thick-walled cells, usually with-
out living contents which are elongated and taper at the ends so that the
cells, or fibers, overlap. It is common as one of the elements of the vas-
cular bundles, as wood fibers and bast fibers.
702. Vascular tissue, or tracheary tissue. — This consists of the vessels or
ducts, and tracheides, which are so characteristic of the vascular bundle
(see Chapter V) and forms a conducting tissue for the flow of water. The
vascular tissue contains spiral, annular, pitted, and scalariform vessels and
tracheides according to the marking on the walls (figs. 58, 59). These are
all without protoplasmic contents when mature. There are also thin-
walled living cells intermingled called wood parenchyma. In the conifers
(pines, etc.) the tracheary tissue is devoid of true vessels except a few spiral
vessels in the young stage, while it is characterized by tracheides with pecu-
liar markings. These marks on the tracheides are due to the "bordered"
pits appearing as two concentric rings one within the other. These can be
easily seen in a longitudinal section of wood of conifers.
703. Sieve tissue. — This consists of elongated tubular cells connected at
the ends, the cross- walls being perforated at the ends. These are in the
phloem part of the bundle, and serve to conduct downwards the dissolved
substances elaborated in the leaves.
704. Fascicular cambium. — This is the living, cell -producing tissue in
the vascular bundle, which in the open bundle adds to the phloem on one
side and the xylem on the other.
3. THE EPIDERMAL SYSTEM.
705. To the epidermal system belong the epidermis and the various out-
growths of its cells in the form of hairs, or trichffmes, as well as the guard
cells of the stomates, and probably some of the reproductive organs.
706. The epidermis. — The epidermis proper consists of a single layer of
external cells originating from the outer layer of parenchyma cells at
the growing apex of the stem or root. These cells undergo various
modifications of form. In many cases they lose their protoplasmic
contents. In many cases the outer wall becomes thickened, especially
* Some fibers occur also very frequently in the Fundamental System,
forming bundle-sheaths, or strands of mechanical tissue in the cortex.
ORGANIZATION: PLANT TISSUES.
359
in plants growing in dry situations or when; they are exposed to drying
conditions. The epidermal cells generally become considerably flattened,
and are usually covered with a more or less well developed water-proof
cuticle, a continuous layer over the epidermis. In many plants the cuticle
is covered with a waxy exudation in the form of a thin layer, or of rounded
grains, or slender rods, or grains and needles in several layers. These
waxy coverings are sometimes spoken of as "bloom" on leaves and fruit.
707. Trichomes. — Trichome is a general term including various hair-
like outgrowths from the epidermis, as well as scales, prickles, etc. These
include root hairs, rhizoids, simple or branched hairs, glandular hairs,
glandular scales, etc. Glandular hairs are found on many plants, as
tomato, verbena, primula, etc.; glandular scales on the hop; simple-celled
hairs on the evening primrose, cabbage, etc.; many-celled hairs on the
primrose, pumpkin; branched hairs on the shepherd's purse, mullein, etc.,
stellate hairs on some oak leaves.
For stomates see Chapter IV.
4. ORIGIN OF THE TISSUES.
708. Meristem tissue. — The various tissues consisting of cells of dissimi-
lar form are derived from young growing tissue known as meristem. Meri-
stem tissue consists of cells nearly alike in form, with thin cell walls and
rich in protoplasm. It is situated at the growing regions of the plants.
In the higher plants these re-
gions in general are three in
number, the stem and root
apex, and the cambium cyl-
inder beneath the cortex.
Tissues produced from the
stem and root apex are called
primary, those from the cam-
bium secondary. In most
cases the main bulk of the
plant is secondary tissue,
while in the corn plant it is all
primary.
709. Origin of stem tissues.
point of stem-
periblem between.
Section through
— lust back of the apical dermatogen; p, plerome;
, (After De Bary.)
meristem in a longitudinal
section of a growing point it can be seen that the cells are undergoing a
change in form, and here are organized three formative regions. The
outer layer of cells is called dermatoge.n (skin producer), because later it
becomes the epidermis. The central group of elongating cells is the plerome
(to fill). This later develops the central cylinder, or stele, as it is called
360 RELATION TO ENVIRONMENT.
(fig. 417). Surrounding the plerome and filling the space between it and
the dermatogen is the third formative tissue called the periblem, which later
forms the cortex (bark or rind), and consists of parenchyma, collenchyma,
sclerenchyma, or cork, etc., as the case may be. It should be understood
that all these different forms and kinds of cells have been derived from
meristem by gradual change. In the mature stems, therefore, there are
three distinct regions, the central cylinder or stele, the cortex, and the
epidermis.
710. Central cylinder or stele. — As the central cylinder is organized from
the plerome it becomes differentiated into the vascular bundles, the pith,
the pith rays (medullary rays) which radiate from the pith in the center
between the bundles out to the cortex, and the pericycle, a layer of cells
lying between the central cylinder and the cortex. The bundles then are
farther organized into the xylem and phloem portions with their different
elements, and the fascicular cambium (meristem) separating the xylem
and phloem, as described in Chapter V. Such a bundle, where the xylem
and phloem portions are separated by the cambium is called an open bun-
Fig. 418.
Concentric bundle from stem of Polypodium yulgare. Xylem in the center,
surrounded by phloem, and this by the endodermis. (From the author's Biology
of Ferns.)
die (as in fig. 58). Where the phloem and xylem lie side by side in the same
radius the bundle is a collateral one. Dicotyledons and conifers are char-
acterized by open collateral bundles. This is why trees and many other
ORGANIZATION: PLANT TISSUES.
361
perennial plants continue to grow in diameter each year. The cambium
in the open bundle forms new tissue each spring and summer, thus adding
to the phloem on the outside and the xylem on the inside. In the spring
and early summer the large vessels in the xylem predominate, while in
late summer wood fibers and small vessels predominate and this part of
the wood is firmer. Since the vascular bundles in the stem form a circle in
the cylinder, this difference in the size of the spring and late summer wood
produces the "annual" rings, so evident in the cross-section of a tree trunk.
Branches originate at the surface involving epidermis, cortex, and the
bundles.
In monocotyledonous plants (corn, palm, etc.) the bundles are not regu-
larly arranged to form a hollow cylinder, but are irregularly situated through
the stele. There is no meristem, or cambium, left between the xylem and
phloem portions of the bundle and the bundle is thus closed, (as in fig. 60),
since it all passes over into permanent tissue. In most monocotyledons
there is, therefore, practically no annual increase in diameter of the stem.
711. Ferns. — In the ferns and most of the Pteridophytes an apical meri-
stem tissue is wanting, its place being taken
by a single apical cell from the several
sides of which cells are successively cut
off, though Isoetes and many species of
Lycopodium have an apical meristem
group. In most of the Pteridophytes also
the bundles are concentric instead of col-
lateral. Fig. 418 represents one of the
bundles from the stem of the polypody
fern. The xylem is in the center, this
surrounded by the phloem, the phloem by flff^jS^^SSSSSuA
the phloem sheath, and this in turn by sclerenchyma; a, thin - walled
. . sclerenchyma; par, parenchyma.
the endodermis, giving a concentric ar-
rangement of the component tissues. A cross-section of the stem (fig.
419") shows two large areas of sclerenchyma, which gives the chief mechan-
ical support, the bundles being comparatively weak.
712. Origin of root tissues. — A similar apical meristem exists in roots,
but there is in addition a fourth region of formative tissue in front of the
meristem called calyptrogen (fig. 420). This gives rise to the "root cap"
which serves to protect the meristem. The vascular cylinder in roots is
very different from that of the stem. There is a solid central cylinder in
which the groups of xylem radiate from the center and groups of phloem
alternate with them but do not extend so near the center (fig. 421). As the
root ages, changes take place which obscure this arrangement more or
less. Branches of the roots arise from the central cylinder. In fern
roots the apical meristem is replaced by a single four-sided (tetrahedral)
Fig- 419-
362
RELATION TO ENVIRONMENT.
apical cell, the root cap being cut off by successive divisions of the outer
face, while the primary root tissues are derived from the three lateral
faces.
Fig. 420.
Median longitudinal section of the
apex of a root of the barley, Hordeum
vulgare. k, calyptrogen; d, dermat-
ogen; c, its thickened wall; pr, peri-
blem; />/, pleronie; en, endodermis;
i, intercellular air-space in process of
formation; a, cell row destined to form
a vessel; r, exfoliated cells of the root
cap. (After Strasburger.)
Fig. 421.
Cross-section of fibrovascular bundle
in adventitious root of Ranunculus re-
pens, w, pericycle; g, four radial plates
of xylem; alternating with them are
grotips of phloem. This is a radial
bundle. (After De Bary.)
Function of the root cap. — The root cap serves an important function in
protecting the delicate meristem or cambium at the tip of the root. These
cells are, of course, very thin-walled, and while there is not so much danger
that they would be injured from dryness, since the soil is usually moist
enough to prevent evaporation, they would be liable to injury from friction
with the rough particles of soil. No similar cap is developed on the end
of the stem, but the meristem here is protected by the overlapping bud-
scales. One of the most striking illustrations of a root cap may be seen in
the case of the Pandanus, or screw-pine, often grown in conservatories (see
fig. 447). On the prop roots which have not yet reached the ground the
root caps can readily be seen, since they are so large that they fit over the
end of the root like a thimble on the finger.
ORGANIZATION: PLANT TISSUES.
363
713. Descriptive Classification of Tissues.
Epidermis.
Epidermal
System. . . .
Fibrovascular
System
Simple hairs.
Many-celled hairs.
Branched hairs, often stellate.,
Trichomes. \ Clustered, tufted hairs.
Glandular hairs.
Root hairs.
Prickles.
Guard-cells of stomates.
• Spiral vessels.
Pitted vessels
Scalariform vessels,
Xylem (wood) . • Annular vessels.
Tracheides.
Wood fibers.
Wood parenchyma.
Cambium (fascicular).
Phloem (bast).
Fundamental
System
Stem and root. •
Sieve-tubes.
Bast fibers.
Companion cells.
Bast parenchyma.
Cork.
Collenchyma.
Cortex. . . \ Parenchyma.
Fibers.
Milk tissue.
Pith-ray., j
Parenchyma.
Intrafascicular cambiurr
( Parenchyma.
Pith. ... 1
I Sclerenchyma.
Bundle-sheath.
Endodermis.
Palisade tissue.
Spongy parenchyma.
Leaves ]
. Reproductive Organs (mainly fundamental).
364 RELATION TO ENVIRONMENT.
714. Physiological Classification of Tissues.
Formative Tissue.
Thin-walled cells composing the meristem, capable of division and from
which other tissues are formed.
Protective Tissue.
Tegumentary System. — Epidermis, periderm, bark protecting the plant
from external contact.
Mechanical System. — Bast tissue, bast-like tissue, collenchyma, scler-
enchyma, afford protection against harmful bending, pulling, etc.
Nutritive Tissues.
Absorptive System. — Root hairs and cells, rhizoids, aerial root tissue,
absorptive leaf glands, absorptive organs in seeds, haustoria of para-
sites, etc.
Assimilatory System. — Assimilating cells in leaf and stem.
Conductive System. — Sieve tissue, tracheary tissue, milk tissue, conduct-
ing parenchyma, etc.
Food-storing System. — Water reservoir, water tissue, slime tissue, fleshy
roots and stems, endosperm and cotyledons, etc.
Aerating System. — Air spaces and tubes, special air tissue, air-seeking
roots, stomates, lenticels, etc.
Secretory and Excretory System. — Water glands, digestive glands, resin
glands, nectaries, tannin, pitch and oil receptacles, etc.
Apparatus and Tissues for Special Duties.
Holdfasts.
Tissues of movement, parachute hairs, floating tissue, hygroscopic tis-
sue, living tissue.
For perceiving stimuli.
For conducting stimuli, etc-
CHAPTER XXXIX.
THE DIFFERENT TYPES OF STEMS. WINTER
SHOOTS AND BUDS.
I. Erect Stems.
715. Columnar type. — The columnar type of stem may be
simple or branched. When branching occurs the branches are
usually small and in general subordinate to the main axis. The
sunflower (Helianthus annuus) is an example. The foliage part
is mainly simple. The main axis remains unbranched during
the larger part of the growth period. The principal flowerhead
terminates the stem. Short branches bearing small heads then
arise in the axils of a few of the upper leaves. In dry, poor soil,
or where other conditions are unfavorable, there may be only
the single terminal flowerhead, when the stem is unbranched.
The mullein is another columnar stem. The foliage part is
rarely branched, though branches sometimes occur where the
main axis has become injured or broken. The flower stem is
terminal. The corn plant and the Easter lily are good illustra-
tions also of the columnar stem.
Among trees the Lombardy poplar (Populus fastigiata) is at
excellent example of the columnar type. Though this is pro-
fusely branched, the branches are quite slender and small in
contrast with the main axis, unless by some injury or other cause
two large axes may be developed. As the technical name indi-
cates, the branching is fastigiate, i.e., the branches are crowded
close together and closely surround the central axis. The royal
Dalm and some of the tree ferns have columnar, simple stems,
365
366
RELATION TO ENVIRONMENT.
but the large, wide-spreading leaves at the top of the stem give
the plant anything but a cylin-
drical habit. Some cedars and
arbor-vitae are also columnar.
The advantages of the colum-
nar habit of stem are three: (i)
That the plant stands above
other neighboring ones of equal
foliage area and thus is enabled
to obtain a more favorable light
relation; (2) where large num-
bers of plants of the same species
are growing close together, they
can maintain practically the
same habit as where growing
alone; (3) the advantage gained
by other types in their neighbor-
hood in less shading than if the
type were spreading. The cyl-
indrical type can, therefore, grow
between other types with le"s
competition for existence.
716. The cone type.— This is
well exampled in the larches,
spruces, the gingko tree, some
of the pines, cedars, and other
gymnosperms. In the cone type,
the main axis extends through
the system of branches like a
tall shaft, i.e., the trunk is excur-
rent. The lower branches are
wide-spreading, and the branches
become successively shorter,
usually uniformly, as one ascends
the stem. The branching is of
two types: (i) the branches are in false whorls; (2) the branches
Fig. 422.
Cylindrical stem of mullein.
TYPES OF STEMS.
367
are distributed along the stem. To the first type belong the
pines, Norway spruce, Douglas pruce, etc. The white pine is
an exquisite example, and in
young and middle-aged trees
shows the style of branching to
very good advantage. The
branches are nearly horizontal,
with a slight sigmoid graceful
curve, while towards the top the
branches are ascending. This
direction of the branches is due
to the light relation. The few
whorls at the top are ascending
because of the strong light from
above. They soon become ex-
tended in a horizontal direction
as the main source of light is
shifting to the side by the shad-
ing of the top. The ascending
direction first taken by the upper
branches and their subsequent turning downward, while the ends
often still have a slight ascending direction gives to the older
branches their sigmoid curve.
The young vernal shoots of the pines show some very interest-
ing growth-movements. There are two growth periods: (i) the
elongation of the shoot, and (2) the elongation of the leaves.
The elongation of the shoot takes place first and is completed in
about six weeks or two months' time. The direction of the
shoot in the first period seems to be entirely influenced by geot-
ropism. It grows directly upward and stands up as a very
conspicuous object in strong contrast with the dark green foliage
of the more or less horizontal shoots. When the second period
of growth takes place, and the leaves elongate, the shoot bends
downward and outward in a lateral direction.
The rate of growth of the pines can be very easily observed
since each whorl of branches (between the whorls of long shoots
Fig. 423.
Conical type of larch.
RELATION TO ENVIRONMENT.
there are short shoots bearing the needle leaves), whether on
the main axis or on the lateral branches, marks a year, the new
branches arising each year at the end of the shoot of the previous
year. The rate of growth is sometimes as high as twelve to
twenty-four inches or more per year.
The spruces form a more perfect cone than the pines. The
long branches are mostly in whorls, but often there are interme-
diate ones, though the rate of growth per year can usually be
easily determined. In the hemlock spruce, the branching is
distributed. The larch has a similar mode of branching, but it
is deciduous, shedding its leaves in the autumn, and it has a tall,
conical form.
It would seem that trees of the cone type possessed certain
advantages in some latitudes or elevations over other trees,
(i) A conical tree, like the spruces and larches and the pines,
and hemlocks also, before they get very old, meets with less injury
during high winds than trees of an oval or spreading type. The
slender top of the tree where the force of the wind is greatest
presents a small area to the wind, while the trunk and short
slender branches yield without breaking. Perhaps this is
one reason why trees of this type exist in more northern latitudes
and at higher elevations in mountainous regions, and why the
spruce type reaches a higher latitude and altitude even than the
pines. (2) The form of the tree is such as to admit light to a
large foliage area, even where the trees are growing near each
other. The evergreen foliage, persistent for several years, on
the wide-spreading lower branches, probably affords some pro-
tection to the trees since this cover would aid in maintaining a
more equable temperature in the forest cover than if the trees
were bare during the winter. (3) There is less danger of injury
from the weight of snow since the greater load of snow would lie
on the lower branches. The form of the branches also, espe-
cially in the spruces, permits them to bend downward without
injury, and if necessary unload the snow if the load becomes too
heavy.
717. The oval type. — This type is illustrated by the oak, chest-
TYPES OF STEMS. 369
nut, apple, etc. The trees are usually deciduous, i.e., cast their
leaves with the approach of winter. The main axis is some-
times maintained, but more often disappears (trunk is deliques-
cent), because of the large branches which maintain an ascending
direction, and thus lessen the importance of the central axis
which is so marked in the cone type. Trees of this type, and in
fact all deciduous trees, exhibit their character or habit to better
advantage during the winter season when they are bare. Trees
of this type are not so well adapted to conditions in the higher
altitudes and latitudes as the cone type, for the reason given in
the discussion of that type. The deciduous habit of the oaks,
etc., enables them to withstand heavy winds far better than if
they retained their foliage through the winter, even were the
foliage of the needle kind and adapted to endure cold.
718. The deliquescent type. — The elm is a good illustration
of this type. The main axes and the branches fork by a false
dichotomy, so that a trunk is not developed except in the forest.
The branches rise at a narrow angle, and high above diverge
in the form of an arch. The chief foliage development is lofty
and spreading.
Trees possess several advantages over vegetation less lofty.
They may start their growth later, but in the end they outgrow
the other kinds, shade the ground and drive out the sun-loving
kinds.
II. Creeping, Climbing, and Floating Stems.
719. Prostrate type. — This type is illustrated by creeping or
procumbent stems, as the strawberry, certain roses, of which
a good type is one of the Japanese roses (Rosa wichuriana),
which creeps very close to the ground, some of the raspberries,
the curcubits like the squash, pumpkin, melons, etc. These
often cover extensive areas by branching and reaching out radi-
ally on the ground or climbing over low objects. The cucurbits
should perhaps be classed with the climbers, since they are capa-
ble of climbing where there are objects for support, but they
are prostrate when grown in the field or where there are no ob-
370
RELATION TO ENVIRONMENT.
jects high enough to climb upon. In the prostrate type, there
is economy in stem building. The plants depend on the ground
for support, and it is not necessary to build strong, woody trunks
for the display of the foliage which would be necessary in the
case of an erect plant with a foliage area as great as some of the
Fig. 424-
Prostrate type of the water fern (marsilia).
prostrate stems. This gain is offset, at least to a great extent,
by the loss in ability to display a great amount of foliage, which
can be done only on the upper side of the stem.
Other advantages gained by the prostrate stems are protec-
tion from wind, from cold in the more rigorous climates, and
some propagate themselves by taking root here and there, as in
certain roses, the strawberry plant, etc. Some plants have
erect stems, and then send out runners below which take root
and aid the plant in spreading and multiplying its numbers.
. 720. The decumbent type. — In this type the stem is first erect,
but later bends down in the form of an arch, and strikes root
where the tip touches the ground. Some of the raspberries
and blackberries are of this type.
TYPES OF STEMS. 3/1
721. The climbing type. — The grapes, clematis, some roses,
the ivies, trumpet creeper, the climbing bittersweet, etc., are
climbing stems. Like the prostrate type, the climbers economize
in the material for stem building. They climb over shrubs,
up the trunks of trees and often reach to a great height and
acquire the power of displaying a great amount of foliage by
sending branches out on the limbs of the trees, sometimes devel-
oping an amount of foliage sufficient to cover and nearly smother
the foliage of large trees; while the main stem of the vine may
be not over two inches in diameter and the trunk of the supporting,
tree may be three feet in diameter.
722. Floating stems. — These are necessarily found in aquatic
plants. The stems may be ascending or horizontal. The
stems are usually not very large, nor very strong, since the water
bears them up. The plants may grow in shallow water, or in
water 10-12 feet or more deep, but the leaves are usually formed
at or near the surface of the water in order to bring them near
the light. Various species of Potamogeton, Myriophyllum, and
other plants common along the shores of lakes, in ponds, slug-
gish streams, etc., are examples. Among the algae are exam-
ples like Chara, Nitella, etc., in fresh water; Sargassum, Macro-
cystis, etc., in the ocean. In these plants, however, the plant
body is a thallus, which is divided into stem-like (caulidium) and
leaf-like (phyllidiuiri) structures.
723. The burrowing type, or rhizomes. — These are horizon-
tal, subterranean stems. The bracken fern, sensitive fern, the
mandrake (see fig. .4130), Solomon's seal, Trillium, Dentaria,
and the like, are examples. The subterranean habit affords
them protection from the cold, the wind, and from injury by
certain animals. Many of these stems act as reservoirs for the
storage of food material to be used in the rapid growth of the
short-lived aerial shoot. In the ferns mentioned, the subterra-
nean is the only shoot, and this bears scale leaves which are
devoid of chlorophyll, and foliage leaves which are larger, and
the only member of the plant body which is aerial. The foliage
leaf has assumed the function of the aerial shoot. The latter if
372
RELATION TO ENVIRONMENT.
not necessary since flowers are not formed. The mandrake,
Solomon's seal, Trillium, etc., have scale leaves on the fleshy
underground stems, while foliage leaves are formed on the aerial
stems, the latter also bearing the flowers. Some of the advan-
tages of the rhizomes are protection from injury, food storage
for the rapid development of the aerial shoot, and propagation.
Many of the grasses have subterranean stems which ramify
for great distances and form a dense turf. For the display of
foliage and for flower and seed production, aerial shoots are
developed from these lateral upright branches.
III. Specialized Shoots and Shoots for Storage of
Food.*
724. The bulb.— The bulb is in the form of a bud, but the
scale leaves are large, thick, and fleshy, and contain stored in
them food products manu-
factured in the green aerial
leaves and transported to the
underground bases of the
leaves. Or when the bulb is
aerial in its formation, it is
developed as a short branch of
the aerial stem from which
the reserve food material is
transported. Examples are
found in many lilies, as Easter
Fig. 425. lily, Chinese lilies, onion, tulip,
etc. The thick scale leaves are
closely overlapped and surround the short stem within (also
called a tunicated stem). In many lilies there is a sufficient
* Besides these specialized shoots for the storage of food, food-substances
are stored in ordinary shoots. For example, in the trunks of many trees
starch is stored. With the approach of cold weather the starch is con-
verted into oil, in the spring it is converted into starch again, and later as the
buds begin to grow the starch is converted into glucose to be used for food
In many other trees, on the other hand, the starch changes to sugar on the
approach of winter.
TYPES OF STEMS.
373
amount of food to supply the aerial stem for the development
of flower and seed. There are roots, however, from the bulb
and these acquire water for the aerial shoot, and when planted
in soil additional food is obtained by them.
725. Corm. — A corm is a thick, short, fleshy, underground
stem. A good example
is found in the jack-in-the-
pulpit (Arisaema).
726. Tubers. — These
are thickened portions of
the subterranean stems.
The most generally known
example is the potato
tuber ("Irish" potato, not
the sweet potato, which
is a root). The "eyes" of
the potato are buds on the
stem from which the aerial
shoots arise when the po-
tato sprouts. The potato
tuber is largely composed
of starch which is used for
food by the young sprouts.
726a. Phylloclades. —
These are trees, shrubs, or
herbs in which the leaves are reduced to mere bracts and stems,
are not only green and function as leaves, but some or all of the
branches are flattened and resemble leaves in form as in Phyl-
lanthus, Ruscus, Semele, Asparagus, etc. The flowers are borne
directly on these flattened axes. The prickly pear cactus
(Opuntia) is also a phylloclade. Examples of phylloclades are
often to be found in greenhouses.
727. Undifferentiated stems are found in such plants as the
duckweed, or duckmeat (Lemna, Wulffia, etc. See Chapter III).
^
Fig. 426.
Conn of Jack-in-the-pulpit.
374
RELATION TO ENVIRONMENT.
IV. Annual Growth and Winter Protec-
tion of Shoots and Buds.*
728. Winter conditions. f — While herbs are
subjected only to the damp warm atmosphere
of summer, woody plants are also exposed dur-
ing the cold dry winter, and must protect them-
selves against such conditions. The air is dryer
in winter than in summer; while at the same
time root absorption is much retarded by the
cold soil. Then, too, the osmotic activity of
the dormant twig-cells being much reduced, the
water-raising forces are at a minimum. It is
easy to see, therefore, that a tree in winter is prac-
tically under desert conditions. Moreover, it has
been found by various investigators, contrary to
the general belief, tlfat cold in freezing is only indi-
rectly the cause of death. The real cause is the
abstraction of water from the cell by the ice crys-
tals forming in the intercellular spaces. Death
ensues because the water content is reduced below
the danger-point for that particular cell. It was
formerly thought that on freezing, the cells in the
tissue were ruptured. This is not so. Ice almost
never forms within the cell, but in the spaces
between. Freezing then is really a drying proc-
ess, and dryness, not cold, causes death in winter.
To protect themselves in winter, trees provide
various waterproof coverings for the exposed sur-
faces and reduce the activity of the protoplasm
so that it will be less easily harmed by the loss of
water abstracted by the freezing process. j
729. Protection of the twig. — Woody^ants
Fig. 427- protect the living cells within the twigs by the
of^ho^hiSS production of a dull or rough corky bark, or by a
showing buds and ___^__________
leaf scars. (A twig
with a terminal bud * This topic was prepared by Dr. K. M. Wiegand.
should have been se- . _ .. . , T-~ • r*i ir-r -.rr
lected for this figure.) t See discussion ot Aropophytes m Chapter XL VI.
TYPES OF STEMS. 375
thick glossy epidermis over the entire surface. At intervals
occur small whitish specks called lenticels, which here perform
nearly the same function as do stomates in the leaf.
730. Bark of trunk. — A similar service is performed by the
bark for the main trunk and branches of the tree. To admit of
growth in diameter the old bark is constantly being thrown off
in strips, flakes, etc., and replaced by a new but larger cylinder
of young bark. The external appearance thus produced enables
experienced persons to recognize many kinds of trees by the
trunk alone.
731. Leaf-scars and bundle-scars. — The presence of foliage
leaves during the winter would greatly increase the transpiring
surface without being of use to the plant; hence they are usually
thrown off on the approach of winter. The scars left by the
fallen leaves are termed leaf-scars. The small dots on the leaf-
scars left by the vascular bundles which extended through the
petiole into the twig are termed bundle-scars. Sometimes
stipule-scars are left on each side of the leaf -scar by the fallen
stipules.
732. Nodes and internodes. — The region upon a stem where
a leaf is borne is termed a node. The space between two nodes
is an internode.
733. Phyllotaxy. — Investigation of a horse-chestnut or willow twig will
show that the leaf-scars occupy definite positions which are constant for
each plant but different for the two species. The arrangement of the
leaves on the stem in any plant is termed phyllotaxy. In the horse-
chestnut we find two scars placed at the same node, but on opposite sides
of the stem. Somewhat higher up we find two more similarly placed, but
in a position perpendicular to that of the first pair. Such phyllotaxy is
termed opposite. If in any plant several leaves occur at a node, the phyl-
lotaxy is whorled. If but one at each node, as in the willow, the phyllotaxy
is alternate. The opposite and alternate types are very commonly met
with. Closer observation will show that in the willow, if a line be drawn
connecting the successive leaf-scars, it will pass spirally up the twig until
at length a scar is reached directly over the one taken as a starting-point.
Such spiral arrangement always accompanies alternate phyllotaxy. The
section of the spiral thus delineated is termed a cycle. We express the
nature of the cycle by the fractions J, £, f, f, fgi etc., in which the
376
RELA TION TO ENVIRONMENT.
Fig. 428. Fig. 429.
Fig. 428. — Shoot of butternut
showing leaf -scars, axillary buds,
and adventitious buds (buds com-
ing from above the axils).
Fig. 429. — Shoot and bud of
white oak-
numerator denotes the number of turns
around the stem in each cycle, and the
denominator the number of leaf-scars in
the same distance. In a general way we
find in plants only such arrangements as
are represented by the fractions given
above. These fractions show the curious
condition that the numerator and de-
nominator of each is equal to the sum
of the numerator or denominator of the
two preceding fractions. Much specula-
tion has been indulged in regarding the
significance of these definite laws of leaf-
arrangement. In part they may be due
to the desire that each leaf receive the
maximum amount of light. Only certain
definite geometrical conditions will insure
this. More likely it is due to the economy
of space alotted to the leaf-fundaments
in the bud. Here, again, geometiical
laws govern this economy. The phyllo-
taxy is nearly constant for a given species.
734. Buds. — The growing point
of the stem or branch together with
its leaf or flower fundaments and
protective structures is termed a
bud. Winter buds on woody plants
are terminal when inclosing the
growing point of the main axis of the
twig; lateral when the growing point
is that of a branch of the main
axis. Lateral buds are always axil-
lary, i.e., situated on the upper angle
between a leaf and the main axis.
735. Buds occupying special po-
sitions. — Several species of trees
and shrubs produce more than one
bud in each leaf-axil. The addi-
tional ones are termed accessory or
supernumerary buds. These may
TYPES OF STEMS. 377
be lateral to one another or they may be superposed as in the wal-
nut or butternut. In such cases some of the buds usually contain
simply floral shoots and are termed flower-buds. In some species
buds are frequently produced on the side of the branches and
trunk at some distance from the leaf-axils, and entirely without
regard for the latter; or more rarely may occur upon the root.
Such buds are termed adventitious, and are the source of the
feathery branchlets upon the trunks of the American elm.
736. Branching follows the phyllotaxy. — Since the lateral or
branch-producing buds are always located in the axil of a leaf,
the branches necessarily follow the same arrangement upon the
main axis as do the leaves. Since, however, many of the axil-
lary buds fail to develop, this arrangement may be more or less
obscured.
737. Coverings of winter-buds. — These are of two sorts, hair
and cork, or scales. Buds protected simply by dense hair or
sunk in the cork of the twig are termed naked buds, and are
comparatively rare. Most species protect their buds by the
addition of an imbricated covering of closely appressed scales,
the whole frequently being rendered still more water-proof by
the excretion of resin between the scales or over the whole sur-
face. The scales when studied carefully are found to be much
reduced leaves or parts of leaves. In some cases they represent
a modified whole leaf, when they are said to be laminar, or a
leaf-petiole, when they are petiolar, or stipular, when they are
much-specialized stipules of a leaf which itself is usually absent.
The latter type is much the less common. The form of the bud,
the nature and form of the scales, when combined with characters
furnished by the leaf- and bundle-scars, enable one to recog-
nize and classify the winter twigs of the various woody species.
738. Phyllotaxy of the bud-scales. — Since the bud-scales are
leaves, they follow a definite phyllotaxy. This may or may not
be the same as that of the foliage leaves. Twigs with opposite
leaves have opposite bud-scales, or if with alternate leaves, then
alternate bud-scales, but the fractions vary. If the scales are
stipular, then there are of course two at each node.
378
RELATION TO ENVIRONMENT.
739. Function of the bud-coverings.— It is popularly be-
lieved that the scales and hairy coverings serve to keep the bud
warm. Research, however, shows this
to be almost entirely erroneous, and
that the thin bud coverings are en-
tirely inadequate to keep out the cold
of winter. They cannot keep the
bud even a degree or two warmer than
the outside air, except when the
changes are very rapid. Experiment
also shows that the modifying effect
of the covering when the bud thaws
out is so slight -'as to be almost neg-
ligible. Indeed, a thermometer bulb
covered with scales taken from a
horse-chestnut bud warmed up more
rapidly than a naked one when ex-
posed to sunshine. The wool in the
horse-chestnut bud is not for the pur-
pose of keeping it warm, but to pro-
tect the young shoot from too great
transpiration after the bud opens the
following spring. Research has also
Bud of European elm in sec- shown that such tempering of the
lion, showing overlapping of
scales- heat conditions is not especially bene-
ficial to the plant, as was once thought. Neither can we find the
main function in the prevention of water from entering the bud.
This might be accomplished in much simpler ways, even if we
could demonstrate the desirability of keeping the water out at all.
The true functions of the bud-scales are two in number:
Firstly, the prevention of too great loss of water from the young
and delicate parts within; and secondly, the protection of these
same parts from mechanical injury. Without some such pro-
tection the delicate young structures would be beaten off by the
wind, or become the food for Vmnsjry birds during the long win-
ter months.
Fig. 430.
TYPES OF STEMS.
379
740. Opening of the buds. — When the young shoot begins to
grow in the spring, the bud-scales are forced apart or open of
their own accord. During the young condition the shoot is very
soft and brittle, and also possesses a very thin, little cutinized
epidermis. In this condition it is especially liable to mechanical
Fig. 431.
Opening buds of hickory.
injury and to injury from drying out. We find, therefore, a
tendency for the inner bud-scales to elongate during vernation,
thus forming a tube around the delicate tissue much like the
opening out of a telescope. The young leaves and internodes
380 RELATION TO ENVIRONMENT.
themselves are often provided with a woody or hairy covering
to retard transpiration. When the epidermis becomes more
efficient the hairy covering often falls away.
In the case of naked buds protection is afforded in other ways :
by the protection of hairy covering, by physiological adaptation of
the tissue, or in many cases by the late appearance of the shoot
in spring after the very dry April and May winds have ceased.
741. Bud-scars, and how to tell the age of the plant. — In gen
eral the bud-scales when they fall away in the spring leave scars
termed scale-scars, and the whole aggregate of scale-scars makes
up the bud-scar. The position of the buds of previous winters is,
therefore, marked. It becomes an easy matter to determine the
age of a branch, since all that is necessary is to follow back from
one bud-scar to another, the portion of the stem between repre-
senting, except in rare cases, one year's growth.
A woody plant grows in height only by the formation of new
sections of stem added to the apex or side of similar sections
produced the previous season, never, as is commonly supposed,
by the further elongation of the previous year's growth. Hence a
branch once formed upon a tree is fixed as regards its distance
from the ground. The apparent rise of the branches away from
the ground in forest trees is an illusion caused by the dying away
of the lower branches.
742. Definite and indefinite growth. — With the opening of
the buds in spring, growth begins. In some cases, when all the
members for the season were formed, but still minute, within the
bud, such growth consists solely in the expansion of parts already
formed; in others only a few members are thus present to ex-
pand, while new ones are produced by the growing point as the
season progresses. In most cases growth is completed by the
middle of July, soon after which buds are formed for next year's
growth. Such a method of growth is termed definite.
In a few woody plants, as, for example, sumach, locust, and
raspberry, growth continues until late in the autumn. In such
cases the most recently formed nodes and internodes are unable
to become ru.". riently "hardened" before winter sets in, and
TYPES OF STEMS.
381
On the outside is the
are killed back more or less. Next season's shoot is a branch
from some axillary bud. Such growth is termed indefinite.
743. Structure of woody stems. — If we make a cross-section of a woody
twig three general regions are presented to view,
rather soft,often greenish "bark,"
so called, made up of sieve-
tubes, ordinary parenchyma
cells, and in many cases long
fibrous cells composing the "fi-
brous bark." From a growing
layer in this region, termed the
phellogen, the true corky bark
of the older trunk is formed.
Next within the bark we find
the so-called "woody" portion
of the twig. This is strong and
resistant to both breaking and
cutting. The microscope shows
it to be composed of the ordi-
nary already known woody ele-
ments,* wood-fibers, for
strengthening purposes, pitted
and spiral vessels as conducting
tissue ; and intermixed with these
some living parenchyma cells.
A cross-section of the stem also
shows narrow radial lines through
the wood. These are pith-rays,
composed of vertical plates of
living parenchyma cells. These
cells, unlike the others in the
wood, are elongated radially,
not vertically. The height of the
pith-rays as well as their thick- annual rings-
ness varies with the species studied. In the older trunk only the outer por-
tion, a few inches in thickness, remains light-colored and fresh, and is called
sap-wood. The inner wood is usually darker and harder, and is termed
heart-wood. Living parenchyma cells, in general, are present only in the
sap-wood, and in this almost solely the ascent of sap occurs. Dyestuffs
and other substances are frequently deposited in the walls of the heart -wood.
The third region occupying the center of the twig is the pith. This
* Chapter V, and Organization of Tissues in Chapter XXXVIII.
Fig. 432-
Three-year-old twig of the American ash,
with sections of each year's growth showing
382 RELATION TO ENVIRONMENT.
is composed ordinarily of angular, little elongated, parenchyma cells,
when mature mostly without cell-contents and filled with air. The pith
region in different trees is quite diversified. It may be hollow, chambered,
contain scattered thick -walled cells, have woody partitions, or rarely be
entirely thick-walled.
The nature of the woody ring is rather perplexing at first; but its origin
is simple. We may conceive that it has developed from a stem-type like the
sunflower, in which the bundles, though separate, are connected by a con-
tinuous cambium ring. In the woody twigs the numerous bundles are
closely packed together, and only separated by the primary pith-rays ex-
tending from the pith to the cortex. Other secondary pith-rays are pro-
duced within each bundle, but they usually extend only part way from
the cortex to the pith. The wood represents the xylem of the bundle,
and the sieve-tubes of the bark, the phloem.
744. Growth in thickness. — Although the year's growth does not in.
crease in length after the first season has passed, it does increase in diam-
eter very much. From the size of an ordinary little twig it may at length
become a large tree trunk several feet in thickness. Only a portion of the
first year's growth is produced by the growing point. All the rest is a
product of the cambium, a cylinder of wood being added to the exterior
of the old wood each season. The cambium, here, as in the sunflower, lies
between the phloem and the xylem, forming a cylinder entirely around
the stem. In spring, when active, it becomes soft and delicate, thus en.
abling one to easily strip off the bark from some trees, such as willow, etc.,
at that season.
745. Annual rings in woody stems. — The wood produced by the cam.
bium each season is- not homogeneous throughout, but is usually much
denser toward the outer part of the yearly cylinder, wood-fibers here pre*
dominating. In the inner portion vessels predominate, giving a much
more porous effect. The transition from one year's growth to another
is very abrupt, giving rise to the appearance of rings in cross-section. Since
ordinarily in temperate climates but one cylinder of wood is added each
year, the number of rings will indicate the age of the trunk or branch.
This is not absolutely accurate, since in some trees under certain conditions
more than one ring may be produced in a summer. The porous part
of the ring is often termed "spring wood," and the denser portion "fall
wood," but since growth from the cambium ceases in most trees by the
middle of July, "summer wood" would be more appropriate for the latter.
It is mainly the alternation of the cylinders of the spring and summer
wood that gives the characteristic grain to lumber. Pith-rays play an
i.nportant part in wood graining only in a few woods, as, for instance, in
quartered oak. The reason for the production of porous spring wood
and dense summer wood is still one of the unsolved problems of botany.
CHAPTER XL.
FOLIAGE LEAVES.
I. General Form and Arrangement of Leaves.
746. Influence of foliage leaves on the form of the stem. —
The marked effect which foliage has upon the aspect of the plant
or upon the landscape is evident to all observers. Perhaps it is
usual to look upon the stem as having been developed for the
display of the foliage without taking into account the possibility
that the foliage may have a great influence upon the form or
habit of the stem. It is very evident, however, that the foliage
exercises a great influence on the form of the stem. For ex-
ample, as trees increase in age and size, the development of
branches on the interior ceases and some of those already formed
die, since the dense foliage on the periphery of the trees cuts
off the necessary light stimulus. The tree, therefore, possesses
fewer branches and a more open interior. In the forest also,
the dense foliage above makes possible the shapely, clean timber
trunks. Note certain trees where by accident, or by design, the
terminal foliage-bearing branches have been removed that foliage-
bearing branches may arise in the interior of the tree system.
Without foliage leaves the stems of green plants would develop
a very different habit from what they do. This development
could take place in three different directions under the influence
of light: (i) The light stimulus would induce profuse branch-
ing, so that there would be many small branches. (2) The stem
would develop fewer branches, but they would be flattened.
(3) Massive trunks with but few or no branches. In fact, all
383
384 RELATION TO ENVIRONMENT.
these forms are found in certain green stems which do not bear
leaves. An example of the first is found in asparagus with its
numerous crowded slender branches. But such forms in .our
climate are rare, since foliage leaves are more efficient. The
second and third forms are found among cacti, which usually
grow in dry regions under conditions which would be fatal to
ordinary thin foliage leaves.
747. Relation of foliage leaves to the stem. — In the study of
the position of the leaves on the stem we observe two important
modes of distribution: (i) the distribution along the individual
stem or branch which bears them, usually classed under the
head of Phyllotaxy; (2) the distribution of the leaves with refer-
ence to the plant as a whole.
748. Phyllotaxy, or arrangement of leaves. — In examining buds on the
winter shoots of woody plants, we cannot fail to be impressed with some
peculiarities in the arrangement of these members on the stem of the plant.
In the horse-chestnut, as we have already observed, the leaves are in
pairs, each one of the pair standing opposite its partner, while the pair
just below or above stand across the stem at right angles to the position of
the former pair. In other cases (the common bed-straw) the leaves are
in whorls, that is, several stand at the same level on the axis, distributed
around the stem. By far the larger number of plants have their leaves
arranged alternately. A simple example of alternate leaves is presented
by the elm, where the leaves 'stand successively on alternate sides of the
stem, so that the distance from one leaf to the next, as one would measure
around the stem, is exactly one half the distance around the stem. This
arrangement is one half, or the angle of divergence of one leaf from the
next is one half. In the case of the sedges the angle of divergence is less,
that is one third.
By far the larger number of those plants which have the alternate arrange-
ment have the leaves set at an angle of divergence represented by the frac-
tion two fifths. Other angles of divergence have been discovered, and
much stress has been laid on what is termed a law in the growth of the
stem with reference to the position which the leaves occupy. Singularly
by adding together the numerators and denominators of the last two fractions
gives the next higher angle of divergence. Example: -T-"li -Tl=— ;
3 + 5 8 S +° '3
and so on. There are, however, numerous exceptions to this regular
arrangement, which have caused some to question the importance of any
theory like that of the "spiral theory" of growth propounded by Goethe
and others of his time.
FOLIAGE LEAVES. 385
749. Adaptation in leaf arrangement. — As a result, however, of one
arrangement or another we see a beautiful adaptation of the plant parts
to environment, or the influence which environment, especially light, has
had on the arrangement of the leaves and branches of the plant. Access
to light and air are of the greatest importance to green plants, and one
cannot fail to be profoundly impressed with the workings of the natural
laws in obedience to which the great variety of plants have worked out
this adaptation in manifold ways.
750. Distribution of leaves with reference to the entire plant. — In this
case, as in the former, we recognize that it is primarily a light relation.
As the plant becomes larger and more branched the lower and inner leaves
disappear. The trees and shrubs have by far the larger number of leaves
on the periphery of the branch system. A comparison of different kinds
of trees in this respect shows, however, that there is great variation. Trees
with dense foliage (elm, Norway maple, etc.) present numerous leaves
on the periphery which admit but little light to the interior where leaves
are very few or wanting. The sugar maple and red maple do not cast
such a dense shade and there are more leaves in the interior. This is
more marked in the silver maple, and still more so in the locust (Gledit-
schia tricanthos).
751. Color of foliage leaves. — The great majority of foliage leaves are
green in color. This we have learned (Chapter VII) is due to the presence
of a green pigment, chlorophyll, in the chloroplastids thickly scattered in
the cells of the leaf. We have also learned that in the great majority of
cases, the light stimulus is necessary for the production of chlorophyll
green. There are many foliage leaves which possess other colors, as red
(Rosa rubrifolia), purple (the purple barberry, hazel, beech, birch, etc.),
yellow (the golden oak, elder, etc.); while many others have more or less
deep tints of pink, red, purple, yellow, when young. All of these leaves,
however, possess chlorophyll in addition to red, yellow, purple or other
pigment. These other pigments are sometimes developed in great quan-
tity in the cell-sap. They obscure the chlorophyll from view, but do not
interfere seriously with the action of light and the function of chlorophyll,
and perhaps in some cases serve as a screen to protect the protoplast.
752. Autumn colors. — Foliage leaves of many trees display in the autumn
gorgeous colors. These colors are principally shades of red or yellow,
and sometimes purple. The autumn color is more marked in some trees
than in others. In the red maple, the red and scarlet oak, the sourwood,
etc., red predominates, though sometimes yellow may be present with
the red in a single leaf. Sugar maples, poplars, hickories, etc., are prin-
cipally yellow in autumn. The sweet gum has a rich variety of color-red,
purple, maroon, yellow; sometimes all these colors are present on the same
tree
386 RELATION TO ENVIRONMENT.
The red and purple colors are found suffused in the cell-sap of certain
cells in the leaf much as we have found it in the cells of the red beet. The
yellow color is chiefly due to the disappearance and degeneration of the
chlorophyll while the leaf is in a moribund state. A similar phenomenon
is seen in the yellowing of crops when the soil becomes too wet, or in the
blanching of grass when covered with a board, or of celery as the earth
is ridged up over the leaves in late summer and autumn. A number of
different theories have been advanced to explain autumn coloring, i.e.,
the appearance of the red coloring-matter. It has been attributed to the
approach of cold weather, and this has likely led to the erroneous belief
on the part of some that it is caused by frost. It very often precedes frost.
Some have attributed it to the action of the more oblique light rays during
autumn, and still others to the diminishing water-supply with the approach
of cool weather. The question is one which has not met as yet with a
satisfactory solution, and is certainly a very obscure one. It is likely
that the low temperature or the declining activities of the leaf affect certain
organic substances in the leaf and give rise to the red color, and it is quitt
certain that in some years the display is more brilliant than in others.
The color 'is more striking in some regions than in others and the differenv
soil, as well as climate, has been supposed to have some influence. The
North American forests are noted for the brilliant display of autumnal
color. This is perhaps due to some extent to the great variety or number
of species which display color. It would seem that there is some specific
as well as individual peculiarities in certain trees. Some individuals,
for example, exhibit brilliant colors every autumn, while others near of
the same species are more subdued.
It has been shown by experiment that when sunlight passes through
red colors the temperature is slightly increased, and it has been suggested
that this may be of protection to the living substance which has ceased
working and is in danger of injury from cold. There does not seem to
be much ground for this suggestion, however. It certainly could not
protect the protoplasm of the leaf at night when the cold is more intense,
and during the day would only aggravate matters by supplying an in-
creased amount of heat, since extremes of heat and cold in alternation
are more harmful to plant life than uniform cold. Especially would this
be the case in alpine climates where the alternation of heat and cold be-
tween day and night is extreme, and brilliancy of the colors of alpine plants
is well known. It seems more reasonable to suppose that the red color
acts as a screen, as the chlorophyll is disappearing, to protect from the
injurious action of light, certain organic substances which are to be trans-
ferred back from the leaf to the stem for winter storage. So in the case
ot many stems in the spring or early summer when the young leaves often
have a reddish color, it is likely that it acts as a screen to protect the living
FOLIAGE LEAVES. 38?
substance from the strong light at that season of the year until the chloro-
phyll screen, which is weak in young leaves, becomes darker in color and
more effective, when the red color often disappears.
753. Function of foliage leaves. — In general the function of
the foliage leaf as an organ of the plant is fivefold (see Chapters
IV, VII, VIII, XI), (i) that of carbon-dioxide assimilation or
photosynthesis, (2) that of transpiration, (3) that of the synthesis
of other organic compounds, (4) that of respiration, and (5) that
of assimilation proper, or the making of new living substance.
While none of these functions are solely carried on in the leaf,
it is the chief seat of the first three of these processes, its form,
position, and structure being especially adapted to the purpose.
Assimilation proper, as well as respiration, probably take place
equally in all growing or active parts.
754. Parts of the leaf. — All foliage leaves possess a blade or
lamina, so called because of its expanded and thin character.
The blade is the essential part. Many leaves, however, are
provided with a stalk or petiole by which the blade is held out
at a greater or lesser distance from the stem. Leaves with no
petiole are sessile, the blade is attached by one end directly on
the stem. In some cases the base of the blade is wrapped partly
around the stem, or in others it extends entirely around the
stem and is perjoliate. Besides, many leaves have short append-
ages, termed stipules, attached usually on opposite sides of the
petiole at its junction with the stem. In some species of magnolia
the stipules are so large that each one envelops the entire portion
of the bud which has not yet opened. Many leaves possess out-
growths in the form of hairs, scales, etc. (See leaf protection.)
755. Simple leaves. — Simple leaves are those in which the
blade is plane along the edge, not divided. The edge may be
entire or indented (serrate) to a slight extent as in the elm. The
form of the simple leaf varies greatly but is usually constant
for a given species, or it may vary in shape in the same species
on different parts of the plant. Some of the terms applied to
the outline of the leaf are ovate, oval, elliptical, lanceolate,
linear, needle-like, etc., but it is idle for one to waste time on
388 RELATION TO ENVIRONMENT.
matters of minute detail in form until it becomes necessary for
those in the future who pursue taxonomic work. It is evident
that a simple leaf, except those of minute size, possesses advantages
over a divided leaf in the amount of surface it exposes to the
light. But in other respects it is at a disadvantage, especially
as it increases in size, since it casts a deeper shade and does
not admit of such a free circulation of air. It will be found,
however, in our study of the relation of leaves to light and air
that the balance between the leaf and its environment is ob-
tained in the relation of the leaves to each other.
756. Venation of leaves. — A very prominent character of the
leaf is its "venation. " This is indicated by the presence of numer-
ous " veins," indicated usually by narrow depressed lines on the
upper surface, and by more or less distinct elevated lines on the
under surface. There are two general types: (i) In the corn,
Smilacina, Solomon's seal, etc., the veins extend lengthwise of the
leaf and are nearly parallel. Such leaves are said to be parallel-
veined. It is generally, though not always, a character of mono-
cotyledenous plants. (2) In the elm, rose, hawthorn, maple, oak,
etc., the veins are not all parallel. The larger ones either diverge
from the base of the blade (palmate leaf, maple), or the mid-
vein extends through the middle line of the leaf, while other
prominent ones branch off from this and extend, nearly parallel,
toward the edge of the leaf (pinnate venation). The smaller
intermediate veins which are also very distinct extend irregularly
and branch and anastomose in such a fashion as to give the figure
of a net with very fine meshes. These are netted-veined leaves.
These are characteristic of most of the dicotyledenous plants.
It is evident from what has been said of the examples cited that
there are two types of netted-veined leaves, the palmate and pinnate.
NOTE. As we have already learned in Chapter V the veins contain the
vascular bundles of the leaf. Through them the water and food solutions
are distributed to all parts of the leaf, and the return current of food ma-
terial elaborated in the leaf moves back through the bast portion into the
shoot. The veins also possess a small amount of mechanical tissue. This
forms the framework of the leaf and aids in giving rigidity to the leaf and
FOLIAGE LEAVES.
389
in holding it in the expanded position. The mechanical tissue in the
framework alone could not support the leaf. Turgescence of the meso-
phyll is needed in addition.
757. Cut or lobed leaves. — In many leaves, the indentations
on the margin are few and
deep. Such leaves pre-
sent several lobes the pro-
portionate size of which
is dependent upon the
depth of the indentation
or "incision." Several
of the maples, oaks,
birches, the poison ivy,
thistles, the dandelion,
etc., have lobed leaves.
Where the indentation
reaches to or very near
the midrib the leaf is
said to be cut. A study
of various leaves will
show all gradations from
simple leaves with plane edges to those which are cut or divided, as
in compound leaves, and the lobes are often variously indented.
758. Divided, or compound leaves. — The rose, sumac, elder,
hickory, walnut, locust, pea, clover, American creeper, etc., are
examples of divided or compound leaves. The former are pin-
nately compound, and the latter are palmately compound. The
leaf of the honey-locust is twice pinnately compound or bipin-
nate, and some are three times pinnately compound.* It is
* Some of the different terms used to express the kinds of compound
leaves are as follows:
Unifoliate (for a single leaflet, as in orange and lemon where the com-
pound leaf is greatly reduced and consists of one pinna attached to the
petiole by a joint). Bifoliate for one with two leaflets; trifoliate for one
with three leaflets, as in the clover; plurifoliate for many leaflets. Odd
pinnate for a pinnate leaf with one or more pairs of leaflets and one odd
leaflet at the end.
Fig. 433-
Lobed leaves of oak forming a mosaic.
390
RELATION TO ENVIRONMENT.
evident that compound leaves are only extreme forms of lobed
or cut leaves and that the form of all bears a definite relation
to the primary venation. There has been a reduction of meso-
phyll and of the area of smaller venation.
759. These forms of leaves probably have some definite sig-
nificance. It is not quite clear why they should have developed as
they have; though it is
possible to explain several
important relations of these
forms to their environ-
ment, (i) The reduction
of the surface of the leaf,
with the retention of the
firmer portions, allows
freer movement of the air
and affords the leaf greater
protection from injury dur-
Fig ing violent winds, just as
Twice compound leaf. Leaflets arranged in the finely dissected leaVCS
one plane, but open spaces permit free circula-
tion of air through the large leaf. of Some water - plants
are less liable to injury from movement of the more dense
medium in which they live. It is possible that here we may
have an explanation of one of the factors involved in this
reduction of leaf surface. (2) In trees with compound leaves,
like the hickory, walnut, locust, ailanthus, etc., the midvein,
and in the case of the Kentucky coffee-tree (Gymnocladus) the
primary lateral veins also, serve in place of terminal branches
of the stem. By the increase in the outline of the leaf and
the reduction of its surface between the larger veins, the tree
has attained the same leaf development that it would were the
So leaves are palmately bifoliate, etc., pinnately bifoliate, etc. Decom-
pound leaves are those where they are more than twice compound, as
ternately decompound in the common meadow rue (Thalictrum).
Perfoliate leaves are seen in the bellwort (Uvularia), connate perfoliate,
as in some of the honeysuckles where the bases of opposite leaves are joined
together around the stem. F.quitant leaves are found in the iris, where the
leaves fit over one another at the base like a saddle.
FOLIAGE LEAVES. 39 1
larger veins replaced by stems bearing simple leaves. The tree
as it is, however, has the advantage of being able to cast off for
the winter period a layer of what otherwise would have been a
portion of the stem system, to retain which through the winter
would use more energy than with the present reduced stem
system, and the stouter stem is less liable to dry out. In the
case of herbaceous plants, in the case of plants like most of
the ferns where the stem is on the underground rootstock (Pteris) ,
or a very short erect stem, as in the Christmas fern, the leaf
replaces the aerial stem, and the division (or branching, as it is
sometimes styled) of the leaf corresponds to the branching of the
stem. This is more marked in the gigantic exotics like Cibo-
tium regale, and in the tree ferns which have quite tall trunks,
the massive compound leaves replace branches. In the palms
and cycads are similar examples. Those who choose to observe
can doubtless find many examples close at hand. (3) While
divided leaves have probably not been evolved in response to
the light relation, still their relation in this respect is an impor-
tant one, since if the leaf with its present size were entire, it
would cast too dense a shade on other leaves below.
760. General structure of the leaf. — The general structure of the leaf
has been already studied (see Chapters IV, V, VII). It is only necessary
to recall the main points. The upper and lower surfaces of the leaf are
provided with a layer of cells usually devoid of chlorophyll. The mesophyll
of the leaf consists usually of a layer of palisade cells beneath the epider-
mis, and the remainder consists of loose parenchyma with large intercel-
lular spaces. Through the mesophyll course the "veins," or fibre-vas-
cular strands, consisting of the xylem and phloem portions and serving
as conduits for water, salts, and foodstuffs. In the epidermis are the
stomata, each one protected by the two guard cells. The guard cells as
well as the mesophyll contain chlorophyll. The stomata and the com-
municating intercellular spaces furnish the avenues for the ingress and
egress of gases, and for the escape of water vapor.
761. Protection of leaves. — There are many modifications of the general
plan of structure in different leaves, many of them being adaptations for
the protection of the leaf under adverse or trying conditions. Many
leaves are also capable of assuming certain positions which afford them
protection. The discussion of this subject may be presented under two
general heads: Protective modifications; protective positions.
392 RELATION TO ENVIRONMENT.
II. Protective Modification of Leaves.
762. General directions in which these modifications have
taken place. — The usual type of foliage leaf selected is that of
deciduous trees or shrubs or of our common herbs. Such a
leaf is usually greatly expanded and thin in order to present as
great a surface as possible in comparison with its mass, since
the kind of work which the leaf has to do can be more effectu-
ally carried on when it possesses this form. This form of leaf
is best adapted for work in regions where there is a medium
amount of moisture such as exists in the temperate zones. But
since there are very great variations in the climatic and soil
conditions of these regions, and even greater changes in desert
and arctic regions, the type of leaf described is unsuited for
all. Its own life would be endangered, and it would also en-
danger the life of the plant. Modifications have therefore taken
place to meet these conditions, or at least those plants whose
leaves have become modified in those directions which are
suited to the surrounding conditions have been able to persist.
Excessive cold or heat, drought, winds, intense light, rain, etc.,
are some of the conditions which endanger leaves. The pro-
tective modifications of leaves may be grouped under four gen-
eral heads: (i) Structural adaptations; (2) Protective cover-
ing; (3) Reduction of surface; (4) Elimination of the leaf through
the complete assumption of the leaf function by the stem.
763. (i) Structural adaptations. — The general structure of
the leaf presents certain features which are protective. The pali-
sade layer of cells found usually beneath the upper epidermis
forms a compact layer of long cells which not only acts as a
light screen cutting off a certain amount of the light, since too
intense light would be harmful ; it also aids in lessening the loss
of water from the upper surface, where radiation is greater.
The stomata are usually on the under side of aerial leaves, and
the mechanism which closes them when the leaf is losing too
much water is protective. As a protection against intense light
the number of palisade layers is sometimes increased or the
FOLIAGE LEAVES.
393
cells of this layer are narrow and long. This is often beauti-
fully shown when comparing
leaves of the same plant grown
in strong light with those grown
in the shade. The compass
plant (Lactuca scariola) affords
an interesting example. The
leaves grown in the light are
usually vertical, so that the light
reaches both sides. Such leaves
often have all of the mesophyll
organized into palisade cells (fig.
435), while leaves grown in the
deep shade may have no palisade
cells.
764. (2) Protective covering.
— Epidermis and cuticle. — The
walls of the epidermal cells are
much thickened in some plants.
Sometimes this thickening occurs
in the outer wall, or both walls
may be thickened. Variation in
this respect as weir as the extent
of the thickening occur in dif-
ferent plants and are often corre-
lated with the extremes of conditions which they serve to meet.
The cuticle, a waxy exudation from the thick wall of the epider-
mis of many leaves, also serves as a protection against too great
loss of water, or against the leaf becoming saturated with water
during rains. The cabbage, carnation, etc., have a well-developed
cuticle. The effect of the cuticle in shedding water can be nicely
shown by spraying v/ater on a cabbage leaf or by immersing it in
water. Sunken stomata also retard the loss of water vapor.
Covers o] hair or scales. — In many leaves certain of the cells
of the epidermis grow out into the form of hairs or scales of
various forms, and they serve a variety of purposes. (Vhen
ll.S
Fig. 435-
Structure of leaf of Lactuca scariola.
Upper one grown in sunlight, palisade
cells on both sides. Lower one grown
in shade, no palisade tissue.
394 RELATION TO ENVIRONMENT.
the hairs form a felt-like covering as in the common mullein
some antennarias, etc., they lessen the loss of water vapor be-
cause the air-currents close to the surface of the leaf are retarded.
Spines (see the thistles, etc.) also afford a protection against
certain animals.
765. (3) Reduction of surface. — Reduction of leaf surface is
brought about in a variety of ways. There are two general
modes: (ist) Reduction of surface along with reduction of
mass; (2d) Reduction of surface inversely as the mass. Ex-
amples of the first mode are seen in the dissected leaves of many
aquatic plants. In this finely dissected condition the mass of
of the leaf substance is much reduced as well as the leaf surface,
but the leaf is less liable to be injured by movement of the water.
In addition it has already been pointed out that lobed and
divided aerial leaves are much less liable to injury from violent
movements of the air, than if a leaf with the same general out-
line were entire. The needle leaves of the conifers are also
examples, and they show as well structural provisions for pro-
tection in the thick, hard cell-walls of the epidermis. To off-
set the reduced surface there are numerous crowded leaves.
Reduction of surface inversely as the mass, i.e., the mass of
the leaf may not be reduced at all, or it may be more or less
increased. In other words, there is less leaf surface in pro-
portion to the mass of leaf substance. It is probable in many
cases, example: the crowded, overlapping small scale leaves of
the juniper, arbor vitae, cypress, cassiope, pyxidanthera, etc., that
there has been a reduction in the size of the leaf, and at the
same time an increase in thickness. This with the crowding
together of the leaves and their thick cell-walls greatly lessens
the radiation of moisture and heat, thus protecting the leaves
both in dry and cold weather. The succulents, like "live-for-
ever," have a small amount of surface in proportion to the mass
of the leaf. In the yucca, though the leaves are often large,
they are very thick and expose a • comparatively small amount
of surface to the dry air and intense sunlight of the desert regions.
The epidermal covering is also hard and thick. In addition,
FOLIAGE LEAVES. 395
such leaves, as well as those of many succulents, are so thick
they provide water storage sufficient for the plants, which radi-
ate so slowly from their surface.
766. (4) Elimination of the leaf. — Perhaps the most striking
illustration of the reduction of leaf surface is in those cases where
Fit;. 4.5<i-
A "Phylloclade," leaves absent, stems broadened to function as leaves, on the
edges numerous flowers are borne.
the leaf is either completely eliminated as in certain euphorbias,
or in certain of the cacti where the leaves are thought to be re-
duced to spines. Whether the cactus spine belongs to the leaf
series or not, the leaf as an organ for assimilation and trans-
piration has been completely eliminated and the same is true
in the phylloclades. The leaf function has been assumed by
the stem. The stem in this case contains all the chlorophyll;
is bulky, and provides water storage.
III. Protective Positions.
767. In many cases the leaves are arranged either in relation
to the stem, or to each other, or to the ground, in such a way
as to give protection from too great radiation of heat or moisture.
In the examples already cited the imbricated leaves of cassiope,
RELATION TO ENVIRONMENT
pyxidanthera, juniper, etc., come also under this head. In the
junipers the leaves spread out in the summer, while in the winter
they are closely overlapped. An interesting example of protective
position is to be seen in the case of the leaves of the white pine.
During quite cold winter weather the needles are appressed to
the stem, and sometimes the trees present a striking appear-
ance in contrast with the spreading position of the needles in
summer. On windy days in winter, the needles turn with the
wind and become rigid in that position so that they remain
in a horizontal position for some time, often until the wind
dies down, or until milder weather. The following day, should
there be a cold strong wind from the opposite direction, the
needles again assume a leeward direction. In quiet weather
appressed to the stem and in the form of a brush there is less
radiation of heat than if they diverged. In strong winds by
turning in the leeward direction the wind is not driven between
the needle bases and scales. Some plants, especially many
of those in arctic and alpine regions, have very short stems and
the leaves are developed near the ground, or the rock. Lying
close on the ground they do not feel the full force of the drying
winds, there is less radiation from them, and the radiation of
heat from the ground protects them. Many plants exhibit
movement in response to certain stimuli which place them in
a position for protection. Some of these examples have been
discussed under the head of irritability (see Chapter XIII). The
night position of leaves and cotyledons presented by many
plants, but especially by many of the Leguminosae, is brought
about by the removal of the light stimulus at evening. In many
leaves, when the light influence is removed, the influence of
growth turns the leaves downward, or the cotyledons of some
plants upward. In this vertical position of the leaf-blade there
is less radiation of heat during the cool night. The most strik-
ing cases of protection movements are seen in the sensitive
plant. As we have seen, the leaves of mimosa close in a verti-
cal position at midday if the light and heat are too strong. Ex-
cessive transpiration is thus prevented. At night the vertical
FOLIAGE LEAVES.
397
position prevents excessive radiation of heat. The vertical or
profile position of the leaves of the compass plant already re-
ferred to not only lessens transpiration, but the intense heat and
light of the midday sun is avoided. This profile position is
characteristic of certain plants in the dry regions of Australia,
and the topmost leaves of tropical forests.
IV. Relation of Leaves to Light.
768. It is very obvious from our study of the function of the
foliage leaf that its most important relation to environment is
that which brings it in touch with light and air. It is necessary
that light penetrate the leaf tissue that the gases of the air and
Fig. 437
Mosaic form by trailing shoots of Panicum variegatum, "ribbon grass."
plant may readily diffuse and that water vapor may pass out
of the leaf. The thin expanded leaf-blade is the most economi-
cal and efficient organ for leaf work. We have seen that leaves
respond to light stimulus in such a way as to bring their upper
sides usually to face the source of light, at right angles to it or
nearly so (heliotropism, see Chapter XIII). How fully this is
brought about depends on the kind of plant, as well as on other
elements of the environment, for as we have seen in our study of
leaf protection there is danger to some plants in any region,
398 RELATION TO ENVIRONMENT.
and to other plants in certain regions that the intense light
and heat may harm the protoplast, or the chlorophyll, or both.
The statement that leaves usually face the light at right angles
is to be taken as a generalized one. The source of the strongest
illumination varies on different days and again at different times
of the day. On cloudy days the zenith is the source of strongest
illumination. The horizontal position of a leaf, where there are
no intercepting lateral or superior objects would receive its
strongest light rays perpendicular to its surface. The fact is,
however, that leaves on the same stem, because of taller or
shorter adjacent stems, are so situated that the rays of greatest
illuminating power are directed at some angle between the
zenith and horizon. Many leaves, then, which may have their
upper sides facing the general source of strongest illumination,
no not necessarily face the sun, and they are thus protected
from possible injury from intense light and heat because the
direct rays of sunlight are for the most part oblique. This
does not apply, of course, to those leaves which "follow the
sun" during the day. Their specific constitution is such that
intense illumination is beneficial.
The leaf is adjusted as well as may be in different species of
varying constitution, and under different conditions, to a certain
balance in its relation to the factors concerned. The problem
then is to interpret from this point of view the positions and
grouping of leaves. Because of the specific constitution of dif-
ferent plants, and because of a great variety of conditions in the
environment, we see that it is a more or less complex question.
769. Day and night positions contrasted. — In many plants
the day and night positions of the leaves are different. At
night the leaves assume a position more or less vertical, known
as the profile position. This is generally regarded as a pro-
tective position, since during the cool of the night the radiation
of heat is less than if the leaf were in a vertical position. In
many of these plants, however, the leaves in assuming the night
position become closely appressed which would also lessen the
radiation. This peculiarity of leaves is largely possessed by
FOLIAGE LEAVES.
399
the members of the family Leguminoseae (clovers, peas, beans,
etc.), and by the sensitive plants.* But it is also shared by
some other plants as well (oxalis, for example). The leaves
of these plants are usually provided with a mechanism which
enables them to execute these movements with ease. There is
a cushion (pidvinus) of tissue at the base of the petiole, and in
the case of compound leaves, at the base of the pinnae and pin-
nules which undergoes changes in turgor in its cells. The col-
lapsing of the cells by loss of water into the intercellular spaces
causes the leaf to droop. When the cells regain their turgor
by the absorption of the water from the intercellular spaces th;.
leaf is raised to the horizontal, or day position. The light stinru
ulus induces turgor of the pulvinus, the disappearance of the stim-
Fig. 438.
Sunflower with young head turned toward morning sun.
ulus is accompanied by a loss of turgor. It is a remarkable
fact that in some sensitive plants, intense light stimuli are alarm
signals which result in the same movement as if the light stim-
* The most remarkable case is that of the "telegraph" plant (Des-
modium gyrans). Aside from the day and night positions which the
leaves assume, there is a pair of small lateral leaflets to each leaf which con-
stantly execute a jerky motion, and swing oro'.'nd in a circle like the second
hand of a watch.
400
RELATION TO ENVIRONMENT.
ulus were entirely removed. As we know also contact or pres-
sure stimulus, or jarring produces the same result in "sensitive"
plants like mimosa, some species of rubus, etc. In many plants
there is no well-developed pulvinus, and yet the leaves show
similar movements in assuming the day and night positions.
Examples are seen in the sunflower, and in the cotyledons of
many plants. A little observation will enable any one interested
to discover some of these plants.* In these cases the night
position is due to epinastic growth, and while this influence is
not removed during the day the light stimulus overcomes it
and the leaf is raised to the day position.
770. Leaves which rotate with the sun. — During the growth
period the leaves of the sunflower as well as the growing end
Fig. 439-
Same sunflower plant photographed just at sundown.
of the stem respond readily to the direct sunlight. The re-
sponse is so complete that during sunny days the leaves toward
the growing end of the stem are drawn close together in the
form of a rosette and the entire rosette as well as the end of the
* Seedlings are usually very sensitive to light and are good objects to
study.
FOLIAGE LEAVES.
401
stem are turned so that they face the sun directly. In the morn
ing under the stimulus of the rising sun the rosette is formed
and faces the east. All through the day, if the sun continues to
shine, the leaves follow it, and at sundown the rosette faces
squarely the western horizon. For a week or more the young
sunflower head will also face the sun directly and follow it all
day as surely as the rosette of leaves. At length, a little while
before the flowers in the head blossom, the head ceases to turn,
Fig. 440.
Same plant a little older when the head does not turn, but the stem and leaves do.
but the rosette of leaves and the stem also, to some extent, con-
tinue to turn with the sun. When the leaves become mature
they also cease to turn. This is well shown in all three photo-
graphs (figs. 438-439). The lower leaves on the stem being
older have assumed the fixed horizontal position usually char-
acteristic of the plant with cylindrical habit.
It is not true, as is commonly supposed, that the fully opened
sunflower head turns with the sun. But I have observed young
heads four or five inches in diameter rotate with the sun all day.
This is because the growing end of the stem as well as the young
head responds to the light stimulus. So there is some truth as
well as a great deal of fiction in the popular belief that the sun-
4O2 RELATION TO ENVIRONMENT,
flower head follows the sun. The young head will follow the
sun all day even if all the leaves are cut off, and the growing
stem will also if all the leaves as well as the flower head are cut
away. Young seedlings will also turn even if the cotyledons and
plumule are cut off.
This phenomenon of the rotation of leaves with the sun is
much more general than one would infer, as may be seen from
a little careful observation of rapidly growing plants on bright
sunny days. In Alabama I have observed beautiful rosettes of
Cassia marilandica rotate with the sun all day. The peculiarity
is very striking in the cotton plant, especially when the rows
extend north and south. In the forenoon or afternoon it is
most striking as the entire row shows the leaves tilted up facing
the sun. There are many of our weeds and common flowers
of field and garden which show this rotation of the leaves. Some
of these form rotating rosettes; while in others the leaves rotate
independently as in the sweet clover.
771. Fixed position of old leaves. — In many of the cases cited
in the preceding paragraph, the rotation of the leaf only occurs
on sunny days. During cloudy days the leaves of the sunflower,
for example, are in a nearly horizontal position, or the lower
ones may be somewhat oblique, since the stronger illumination on
such a plant would be the oblique rays rather than the zenith
rays. As the leaves reach maturity also the epinasitic growth is
equalized by hyponastic growth so that the growth movements
bring the leaf to stand in a nearly horizontal position, or that
position in which it receives the best illumination. In age, then,
many leaves have a fixed position and this corresponds with the
position assumed on cloudy days.
772. Position on horizontal stems. — On horizontal stems the
leaves have a horizontal position, and if such a stem is stood in
an erect position the appearance is very odd. If the leaf arises
directly from the horizontal stem, its petiole will be twisted part
way around in order to bring the face of the leaf uppermost.
It is interesting to observe the different relation of stem, petiole
and blade and the amount of twisting as the horizontal stem or
FOLIAGE LEA VES. 403
vine trails over irregularities in the surface, or climbs over and
through other vegetation.
773. Position of leaflets on divided leaves. — An interesting
comparison can be made with entire, lobed, divided and dis-
sected leaves. The entire leaf usually lies in one plane, since
usually the problem of adjustment is the same for the entire
surface. So the lobes of a leaf usually lie all in the same plane
as they would if the leaf were entire. We find the same is true
usually of the compound leaf. It forms an incomplete mosaic.
Some of the pieces having been removed allow much of the light
to pass through to leaves beneath. Leaves, especially those of
some size rarely lie in a flat plane. Some are more or less de-
pressed. Some curve downward. Compound leaves often
curve more or less and the leaflets often droop more or less in a
graceful fashion. It is interesting, however, that these far-sepa-
rated leaflets all lie in the same general plane. This is because
the area of the leaf, if not too large, makes the problem of posi-
tion with reference to light much the same as if the leaf were
entire. The leaflets or divisions, though separated, are laminate,
and they can work more efficiently facing the light. But suppose
we extend our observation to the finely dissected capillary leaves
of some of the parsley family (Umbelliferas), or to the upper
leaves of the fennel-leaved thoroughwort (Eupatorium fceni-
culaceum) among the aerial plants, and to Myriophyllum among
the aquatic plants. The divisions are threadlike or cylindrical.
One side of the leaflet is just as efficient when presented to the
light as another. As a result the leaflets are not arranged in
the same plane, but stand out in many directions.
Occasionally one finds a divided or compound leaf in such a
position that one portion, because of being shaded above, receives
the stronger light stimulus from the side, while the other portion
is lighted from above. If this relation continues throughout
the growth-period of the leaf the leaflets of one portion may lie
in a different plane from those of the other portion. In such
cases, some of the leaflets are permanently twisted to bring them
into their proper light relation.
404 RELATION TO ENVIRONMENT.
V. Leaf Patterns.
MOSAICS, OB CLOSE PATTERNS.
774. Where the leaves of a plant, or a portion of a plant, are
approximate and arranged in the form of a pattern, the leaves
fitting together to form a more or less even and continuous sur-
face, such patterns are sometimes termed "mosaics," since the
relation of leaves to one another is roughly like the relation of
the pieces of a mosaic. A good illustration of a mosaic is pre-
sented by a greenhouse plant Fittonia (fig. 441). The stems
Fig. 441.
Fittonia showing leaves arranged to form compact mosaic. The netted vena-
tion of the leaf is very distinctly shown in this plant. (Photo by the Author.)
are prostrate and the erect branches quite short, but it may
have quite a wide system by the spreading of the runners; the
branches of such a length that the leaves borne near the tips all
fit together forming a broad surface of leaves so closely fitted
together often that the stems cannot be seen. The advantage
of a mosaic over a separate disposition of leaves at somewhat
different levels is that the leaves do not shade one another. Were
all the light rays coming down at right angles to the leaves, there
would not be any shading of the lower ones, but the oblique
rays of light would be cut off from many of the leaves. In the
case of a mosaic all the rays of light play upon all the leaves.
Some of the mosaics which can be observed are as- follows:
FOLIAGE LEAVES.
405
775. Rosette pattern. — The rosette pattern is presented by
many plants with "radial" leaves, or leaves which arise in a
cluster near the surface
of the ground, and are
thus more or less crowded
in their arrangement on
the stem. The pretty
gloxinia often presents
fine examples of a loose
rosette. In the rosette
pattern the petioles of
the lower leaves are
longer than the upper
ones, and the blade is
thus carried out beyond
the inner 'eaves. The
leaves being so crowded
in their attachment to
the stem lie very nearly
in the same plane.
776. Vines and climbers. — Some of the most extensive mosaic
patterns are shown in creeping and climbing vines. A very
common example is that of the ivies trained on the walls of build-
ings, covering in some instances many square yards of surface.
Where the vines trail over the ground or clamber over other
vegetation, it is interesting to observe the various patterns, and
the distortion of petioles brought about by turning of the leaves.
Of examples found in greenhouses, the Pellonia is excellent, and
the trailing ribbon-grass often forms loose mosaics.
777. Branch patterns. — These patterns are very common.
They are often formed in the woods on the ends of branches by
the leaves adjusting themselves so as to largely avoid shading
each other. Figure 443 illustrates one of them from a maple
branch. It is interesting to note the way in which the leaves
fit themselves in the pattern, how in some the petioles have
elongated, while others have remained short. Of course, it
Fig. 442.
Rosette pattern of leaves.
406
RELATION TO ENVIRONMENT.
Fig. 443-
Spray of leaves of striped maple, showing different lengths of leafstalks.
Fig. 444.
Cedar of Lebanon, strong light only from one side of tree (Syria).
FOLIAGE LEAVES.
407
should be understood that the pattern is made during the growth
of the leaves.
778. The tree pattern. — Mosaics are often formed by the
exterior foliage on a tree, though they are rarely so regular as
some of those mentioned above. Still it is common to see in some
trees with drooping limbs like the elm, beautiful and large mo-
saics. The weeping elm sometimes forms a very close and
quite even pattern over the entire outer surface. In most trees
the leaf arrangement is not such as to form large patterns, but
is more or less open. While the conifers do not form mosaics
there are many interesting examples of grouping of foliage on
branch systems into broadly expanded areas, as seen in the
branches of white pine trees, especially in the edge of a wood,
or as seen in the arbor vitae.
OTHER PATTEENS.
779. Imbricate pattern of short stems. — This pattern is quite
common, and differs from the rosette in that the leaves are dis-
tributed further apart on
the stem so that the cen-
tral ones are consider-
ably higher up than in
the mosaic. The lower
petioles are longer, as in
the rosette, so that the
outer .Jower leaves ex-
tend further out. Some
begonias show fine im-
bricate patterns.
780. Spiral patterns.
— They are very common
on stems of the cylindrical
type, which are unbranched, or but little branched. The sun-
flower, mullein, chrysanthemum, as it is grown in greenhouses, the
Easter lily, etc., are examples. The spiral arrangement of the
leaves provides that each successive leaf on the stem, as one ascends
the stem, is a little to one side so that it does not cast shade on the
Fig. 445.
Imbricate pattern of leaves; Begonia.
408
RELATION TO ENVIRONMENT.
leaf just below. In some stems, according to the leaf arrange-
ment (or phyllotaxy), one would pass several times around in
ascending the stem before a leaf would be found directly above
another, which would be such a distance below that it would not
be shaded to an appreciable extent. Interesting observations
can be made on different plants to work out the relation of dis-
tance of leaves on the stem to length of the upper and lower
Fig. 446.
Palm showing radiate arrangement of leaves and the petiole of the leaf func-
tions as stem in lifting leaf to the light.
leaves; the number of vertical rows on the stem compared to
the width of the leaves; and the relation of these facts to the
problem of light supply. Related to the spiral pattern is that of
erect stems with opposite leaves. Here each pair is set at right
angles to the direction of the pair above or below.
781. Radiate pattern. — This pattern is present in many grasses
and related plants with narrow leaves and short stems. The
leaves are often very crowded at the base, but by radiating in
all directions from the horizontal to the vertical, abundant ex-
FOLIAGE LEAVES.
409
posure to light is gained with little shading. The dragon tree
screw-pine, and plants grown in greenhouses also illustrate this
Fig. 447-
Screw pine.(Pandanus) showing prop roots and radiate pattern of leaves.
type. It is also shown in cycads, palms, and many ferns, although
these have divided leaves.
782. Compass plants. — These plants with vertical leaf arrange-
ment, and exposure of both surfaces to the lateral rays of light
have been mentioned in other sections (Lactuca scariola).
783. Open patterns. — Open patterns are presented by divided
or "branched" leaves. Where the leaves are very finely dis-
sected, they may be clustered in great profusion and yet admit
sufficient light for some depth below. Where the leaflets are
broader, the leaves are likely to be fewer in number and so
arranged as to admit light to a great depth so that successive
leaves below on the same or adjacent stems may not be too much
shaded. On such plants, often the leaves lying next the ground
-are entire or less divided.
CHAPTER XLI.
THE ROOT
I. Function of Roots.
784. The most obvious function of the roots of ordinary plants
are two: ist, To furnish anchorage and partial support, and
2d, absorption of liquid nutriment from the soil. The environ-
mental relation of such roots, then, in broad terms, is with the
soil. It is very clear that in some plants the root serves both
functions, while in other plants the root may fulfil only one of
these requirements.
The problems which the plant has to solve in working out
these relations are:
(1) Permeation of the soil or substratum.
(2) Grappling the substratum.
(3) A congenial moisture or water relation.
(4) Distribution of roots for the purpose of reaching food-
laden soil.
(5) Exposure of surface for absorption.
(6) The renewal of the delicate structures for absorption.
(7) Aid in preparation of food from raw material.
(8) The maintenance of the required balance between the
environment as a whole and the increasing or changing require-
ments of the plant.
785. (i) Permeation of the soil or substratum. — The funda-
mental divergence of character in the environmental relations of
root and stem are manifest as soon as they emerge from the
germinating seed. Under the influence of the same stimulus
(gravity) the root shows its geotropic character by growing down-
410
ROOTS. 411
ward, while the geotropic character of the stem is shown in its
upward growth.
The medium which the root has to penetrate offers consider-
able resistance, and the form of the root as well as its manner of
growth is adapted to overcome this difficulty. The slender,
conical, penetrating root-tip wedges its way between the minute
particles of soil or into the minute crevices of the rock, while
the nutation of the root enables it to search for the points of least
resistance. The root-tips having penetrated the soil, the older
portions of the root continue this wedge action by growth in
diameter, though, of course, elongation of the old parts of the
root does not take place. It is the widening growth of the taper-
ing root that produces the wedge-like action. The crevices of
the rock are sometimes broadened, but the resistance here is so
great, the root is often greatly flattened out.
786. (2) Grappling the substratum. — The mere penetration
of a single root into the soil gives it some hold on the soil and it
offers some resistance to a "pull" since it has wedged its way in
and the contact of soil particles offers resistance. The root-hairs
formed on the first entering root growing laterally in great num-
bers and applying themselves very closely to the soil particles,
increase greatly the hold of the plant on the soil, as one can
readily see by pulling up a young seedling. Lateral roots are
soon formed, and as these continue to extend and ramify in all
directions, the hold is increased until in the case of some of the
larger plants the resistance their hold would offer would equal
many tons. Even in some of the smaller shrubs and herbs the
resistance is considerable, as one can easily test by pulling with
the hand. To obtain some idea of the amount of resistance the
roots of these smaller plants offer, they can be tested by pulling
with the ordinary spring scales.
787. (3) A congenial moisture, or water relation. — In gen-
eral, the roots seek those portions of the soil provided with a modi-
cum of moisture. Usually a suitable moisture condition is present
in those portions of the soil containing the plant food. But if por-
tions of the soil are too dry and very nearby other portions con-
412 RELATION TO ENVIRONMENT.
taining moisture, the roots grow mainly into the moist substratum
(hydrotropism). If the soil is too wet, the roots grow away from
it to soil with less water, or in some cases will grow to and upon
the surface of the soil.
The roots need aeration, and where the supply of water is too
great, the air is shut out, and we know that corn, wheat, and
many other plants become "sickly" in low and undrained soil
in wet seasons. This can only be said in the case of our ordinary
dry land plants, i.e., those that occupy an intermediate position
between water-loving plants and dry-conditioned plants. This
phase of the subject must be reserved for special treatment.
(See Chapter XLVI.)
788. (4) Distribution of roots for the purpose of reaching
food-laden soil. — This is one of the essential relations of the root
in the case of the land plant, and probably accounts for the very
extensive ramification of the roots. To some extent it also
explains the different root systems in some plants. The pines,
spruces, etc., usually grow in regions where the soil is very shal-
low. The root system does not extend deeply into the soil. It
spreads laterally and extends widely through the shallow surface
soil and presents a very different aspect from the stem system in
the air. The root-system of the broad-leaved trees usually extends
more deeply into the soil, while of course, extending laterally
to great distances. The hickory, walnut, etc., especially have
strong tap roots which extend deeply into the soil, and the root
system of such a tree is more comparable in aspect, if it were
entirely uncovered, to the stem system in the air. The tap-root
is more pronounced in some trees than in others. It may be that
in the hickory and walnut the deep tap-root is important in
supplying the tree with water in dry seasons, especially when
growing on dry, gravelly soil which does not retain moisture on
the surface nor hold it within two or three feet of the surface.
Experiment has demonstrated, by pot culture of plants, that-
where soil rich in plant food lies adjacent to poor soil, no matter
in what part of the pot the rich soil is, the greatest growth and
branching of roots is in the rich soil.
ROOTS. 413
789. (5) Exposure of root surface for absorption. — The prin-
cipal part of root absorption takes place in the young root and
the root hairs growing near the root-tip. The root-tips and
root-hairs in their relation to the root systems on which they are
borne are not to be compared morphologically with the leaves
and stem system. But the root-tip, and hairs are absorbing
organs of the roots while the main root system supports them,
brings them into relation with the soil and moisture, and con-
ducts food and other substances to and from them. One of the
important relations of the leaf is that of light, and since the source
of light is restricted, i.e., it is not equally strong from all sides,
an expanded and thin leaf-blade is more effective than an equal
expenditure of plant material in the form of thread-like out-
growths. It is different, however, with the plant food dissolved
in the soil water. It is equally accessible on all sides. A greater
surface for absorption is exposed with the same expenditure of
material by multiplication of the organs and a reduction in their
size. Numerous delicate root-hairs present a greater absorbing
surface than if the same amount of material were massed into
leaflike expansions. There is another important advantage
also. Its slender roots and thread-like root-hairs allow greater
freedom of circulation of water, food solutions, and air than if
the absorbing organs of the roots were broadly expanded.
790. (6) The renewal of the delicate structures for absorp-
tion.— The delicate root-hairs are easily injured. The thin
cell-walls through which food solutions flow become more or less
choked by the gradual deposit of substances in solution in the
water, and continued growth of the root in diameter forms a
firmer epidermis and cortex through which the solutions taken
up by the root-hairs would pass with difficulty. For this reason
new root-hairs are constantly being formed on the growing root-
tip throughout the growing season, and in the case of perennial
plants, through each season of their growth.
791. (7) Aid in preparation of food from raw materials. — For
most plants the food obtained from the soil is already in solution in
the soil water. But there are certain substances (examples, some
RELATION TO ENVIRONMENT.
of the chemical compounds of potash, phosphoric acid, etc.) which
are insoluble in water. Certain acids excreted by the roots aid
in making these substances soluble (see Chapter III). In a n,um-
ber of plants the roots have become associated with fungus or
bacterial organisms which assist in the manufacture of nitro-
genous food substances, or even in the absorption of ordinary
food solution from the soil, or in making use of the decaying
humus of the forest (see Chapter IX).
792. (8) The maintenance of the required balance between
the environment and the increasing or changing requirements
of the plant. — In this matter the entire plant participates. Men-
tion is made here only of the general relation which the root
sustains to its own environment and the increased burden placed
upon it by the shoot. The increase in the root system keeps
pace with the increasing size of the stem system. The roots
become stronger, their ramifications wider, and the number of
absorbing rootlets more numerous. The observation is some-
times offered that the correlation between the root system of a
plant, and the form of the stem system and position of the leaves,
is of such a nature that plants with a tap-root system have their
leaves so arranged as to shed the water to the center of the sys-
tem, while plants with a fibrous root system have their leaves so
arranged as to shed the water outward. In support of this
attention is called to the radiate type of the leaf system of the
dandelion, beet, etc. In the second place the imbricate type as
manifested in broad-leaved trees, and in the overlapping branch
systems of many pines, etc. One should note, however, that in
the former class the leaves are often arranged to shed as much
water outward as inward. As to the latter class, there is need
of experiment to determine whether these empirical observations
are correct, for the following reasons: ist, Root and leaf distri-
bution are governed by other and more important laws, the root
being influenced by the location of food in the soil which usually
forms a very thin stratum while the shoot and leaf is mainly in-
fluenced by light, and root distribution is much wider in a lateral
direction than that of the branches, ad, In light rains the leaf
ROOTS. 4*5
surface holds back practically all the rain which is then evap-
orated into the air and lost to the root systems. 3d, In heavy
and long-continued rains the water breaks through the leaf
system to such an extent that roots under the tree would be as
well supplied as those outside, and the ground outside being
saturated anyway, the roots do not need the small additional
water which may have been shed outward. 4th, It is the habit
of plants where left undisturbed (except in rare cases), to grow
in more or less dense formations or societies. Here there is no
opportunity for any appreciable centrifugal distribution of rain-
fall and yet the root distribution is practically the same, except
that the root systems of adjacent plants are interlaced.
II. Kinds of Roots.
793. The root system. — From the foregoing, it will be under-
stood that the roots of a plant taken together form the root sys-
tem of that plant. In soil roots in general we usually recognize
two kinds of root systems.
794. The fibrous-root system. — Roots which are composed of
numerous slender branching roots resembling " fibers," are
termed fibrous, or the plant is said to have a fibrous-root system.
The bean, corn, most grasses, and many other plants have fibrous-
root systems.
795. The tap-root system. — Plants with a recognizable cen-
tral shaft-like root, more or less thickened and considerably
stouter than the lateral roots, are said to have tap roots, or they
have a tap-root system. The dandelion, beet, carrot (see crown
tuber) are examples. The hickory, walnut, and some other
trees have very prominent tap-roots when young. The tap-root
is maintained in old age, but the lateral roots often become
finally as large as the tap-root. Besides tap-roots and fibrous-
roots, which include the larger number, several other kinds of
roots are to be enumerated.
796. Aerial roots. — Aerial roots are most abundantly devel-
oped in certain tropical plants, especially in the orchids and
aroids. Many examples of these nlants are grown in conserva-
RELATION TO ENVIRONMENT.
tories. The amount of moisture is so great in these tropical
regions that the roots are abundantly supplied without the soil
relation. Certain of the roots hang free in the air and are pro-
vided with a special sheath of spongy tissue called the velanien,
through which moisture is absorbed from the air. Other roots
attach themselves to the trunk or branches of the tree on which
ihe orchid is growing, and furnish the support to the epiphyte,
as such plants are often called. Among the tangle of these
clinging roots falling leaves are caught. Here they decay and
nourishing roots grow from the clinging roots into this mass of
decaying leaves and supply some of the plant food. Aerial
roots sometimes possess chlorophyll.
There are a number of plants, however, in temperate regions
which have aerial roots. These are chiefly used to give the stem
support as it climbs on trees or on walls. They are sometimes
called clinging roots. A common example is the climbing poison
ivy (Rhus radicans), the trumpet creeper, etc. Such aerial roots
are called adventitious roots.
797. Bracing roots, or prop roots. — These are developed in a
great variety of plants and serve to brace or prop the plant where
the fibrous-root system is in-
sufficient to support the heavy
shoot system, or the shoot sys-
tem branches so widely props
are needed to hold up the
branches. In the common In-
dian corn several whorls of
bracing roots arise from the
nodes near the ground and ex-
tend outward and downward to
the ground, though the upper
whorls do not always succeed in
reaching the ground. The
screw-pine so common in
greenhouses affords an excellent example of prop roots. The
roots are quite large, and long before the root reaches the soil the
Fig. 448.
Bracing roots of Indian corn.
ROOTS.
417
large root-cap is evident. The banyan tree of India is a classic
example of prop roots for supporting the wide-reaching branches.
The mangrove in our own subtropical forests of Florida is a
nearer example.
798. Buttresses are formed at the junction of the root and
trunk, and therefore are part root and part stem. Splendid
Fig. 449. ,
Buttresses of silk-cotton tree, Nassau.
examples of buttresses are formed on the silk-cotton tree. They
are sometimes formed on the elm and other trees in low swampy
ground.
799. Fleshy roots, or root tubers. — These are enlargements of
the root in the form of tubers, as in the sweet potato, the dahlia,
etc. They are storage reservoirs for food. Portions of the roots
become thick and fleshy and contain large quantities of sugar,
as in the sweet potato, or of inulin (a carbohydrate) in the root-
tubers of the dahlia and other composites.
800. Water roots and roots of water plants. — These are roots
which are developed in the water, or in the soil. Water-roots
are sometimes formed on land plants where the root comes in
41 8 RELATION TO ENVIRONMENT.
contact with a body of water, or a stream. Water-roots usually
possess no root-hairs, or but a few, as can be seen by comparing
water-roots with soil-roots, or by comparing roots of plants
grown in water cultures. The greater body of water in contact
with the root and the more delicate epidermis of the root render
less necessary the root-hairs. The duck-meats (Lemna) are
good examples of plants having only water-roots. Other aquatic
plants like the potamogetons, etc., have true roots which grow
into the soil and serve to anchor the plant, but they are not devel-
oped as special organs of absorption, since the stem and leaves
largely perform this function.
801. Holdfasts. — These are organs for anchorage which are
not true roots. These are especially well developed in some of
the algae (Fucus, Laminaria, etc.). They are usually called
holdfasts. The holdfasts of the larger algae are mainly for
anchoring the plant. They do not function as absorbing organs,
and the structure is different from that of true roots.
802. Haustoria or suckers is a name applied to another kind
of holdfast employed by parasitic plants. In the dodder the
haustorium penetrates the tissue of the host (the plant on which
the parasite grows), and besides furnishing a means of attach-
ment, it serves as an absorbing organ by means of which the
parasite absorbs food from its host. The parasitic fungi like
the powdery mildews which grow on the surface of their hosts
have simple haustoria which serve both as organs of attachment
and absorption, while in the rusts which grow in the interior of
their hosts the haustoria are merely absorbing organs.
803. Rootlets, or rhizoids. — Many of the algas, liverworts and
mosses have slender, hair-like organs of attachment and absorp-
tion. These plants do not have true roots. Because of the
slender form and small size of these organs, they are called
rhizoids, or rootlets. In form many of them resemble the root-
hairs of higher plants.
CHAPTER XLII.
THE FLORAL SHOOT.
I. The Parts of the Flower.
THE portion of the stem on which the flowers are borne is
the flower shoot or axis, or taken together with the flowers, it is
known as the Flower Cluster.
804 The flower. — The flower is best understood by an exam-
ination, first of one of the types known as a "complete"' flower,
as in the buttercup, the spring beauty, the bloodroot, the apple,
the rose, etc.
There are two sets of organs or members in the complete
flower — (i) the floral envelope; (2) the essential or necessary
members or organs.
The floral envelope when complete consists of — ist, an outer
envelope, the calyx, made up of several leaflike structures
(sepals), very often possessing chlorophyll, which envelop all
the other parts of the flower when in bud ; 2d, an inner envelope,
the corolla, also made up of several leaflike parts (petals'), usu-
ally bright colored and larger than the sepals. The outer and
inner floral envelopes are usually in whorls (though in close spirals
in many of the buttercup family, etc.), and for reasons discussed
elsewhere (Chapter XXXIV) represent leaves. The essential
or necessary members of the flower are also usually in whorls
and likewise represent leaves, but only in rare cases is there any
suggestion, either in their form or color, of a leaf relationship.
These members are in two sets: (i) The outer, or androecium,
consisting of a few or many parts (stamens'); (2) the inner set,
the gynoecium, consisting of a few or many parts (carpels').
419
42O RELATION TO ENVIRONMENT.
805. Purpose of the flower. — While the ultimate purpose of all
plants is the production of seed or its equivalent through which
the plant gains distribution and perpetuation, the flower is the
specialized part of the seed plant which utilizes the food and
energies contributed by other members of the plant organization
for the production of seed. In addition to this there are definite
functions performed by the members of the flower, which come
under the general head of plant work, or flower work.
806. The calyx, or the sepals. — These are chiefly protective,
affording protection to the young stamens and carpels in the
flower bud. Where the corolla is absent, sepals are usually
present and then assume the function of the petals. In a few
instances the calyx may possibly ultimately join in the formation
of the fruit (examples: the butternut, walnut, hickory).
807. The corolla, or petals. — The petals are partly protective
in the bud, but their chief function where well developed seems
to be that of attracting insects, which through their visits to the
flower aid in "pollination" especially "cross pollination."
808. The stamens. — The stamens ( = microsporophylls) are
flower organs for the production of pollen, or pollen-spores
( = microspores). The stalk (not always present) is the filament,
the anther is borne on the filament when the latter is present
The anther consists of the anther sacs or pollen sacs (microspo-
rangium) containing the pollen-spores, and the connective, the
sterile tissue lying between and supporting the anther sac. The
stamens are usually separate, but sometimes they are united by
their filaments, or by their anthers. When the pollen is ripe
they open by slits or pores and the pollen is scattered; or in
rarer cases the pollen mass (polHnium) is removed through the
agency of insects (see Insect pollination, Chap. XLIII).
809. The pistil.— The pistil consists of the "ovary," the style
(not always present), and the stigma. These are well shown in
a simple pistil, common examples of which are found in the
buttercup, marsh marigold, the pea, bean, etc. The simple
pistil is equivalent to a carpel ( = macrosporophyll), while the
compound pistil consists of two or several carpels joined, as in
THE FLORAL SHOOT. 421
the tooth wort, trillium, lily, etc. The ovary is the enlarged part
which below is attached to the receptacle of the flower, and con-
tains within the ovules. The style, when present, is a slender
elongation of the upper end of the ovary. The stigma is sup-
ported on the end of the style when the latter is present. It is
often on a capitate enlargement of the style or extends down one
side, or when the style is absent it is usually seated directly on
the upper end of the ovary. The stigmatic surface is glutinous
or "sticky," and serves to hold the pollen-spores when they
come in contact with it.
The ovules are within the ovary and are arranged in different
ways in different plants. The pollen-grain (or better pollen-
spore = micrpspo re), after it has been transferred to the stigma,
"germinates," and the pollen tube grows down through the
tissue of the stigma and style, or courses down the stylar canal
until it reaches the ovule. Here it usually enters the ovule
(macrosporangium) at the micropyle (in some of the ament-
bearing plants it enters at the chalaza), and the sperm-cells are
emptied into the embryo sac in the interior of the ovule.
810. Fertilization. — One of the sperms unites with the egg in
the embryo sac. This is fertilization, and from the fertilized
egg the young embryo is formed still within the ovule. Double
fertilization, — the other sperm-cell sometimes unites with one
or both of the "polar" nuclei which have united to form the
"definitive" or "endosperm" nucleus. As a result of fertiliza-
tion, the embryo plant is formed within the ovule, the coats of
which enlarge by growth forming the seed coats, and altogether
forming the seed. (See Chapters XXXIV, XXXV, XXXVI.)
II. Kinds of Flowers.
811. Absence of certain flower parts. — The complete flower
contains all the four series of parts. When any one of the series
of parts is lacking, the flower is said to be incomplete. Where only
one series of the floral envelopes is present the flowers are said to
be apetalous (the petals are absent), examples: elm, buckwheat,
422 RELATION TO ENVIRONMENT.
etc. Flowers which lack both floral envelopes are naked. When
pistils are absent but stamens are present the flowers are stami-
nate, whether floral envelopes are present or not; and so when
stamens are absent and pistils pre ent the flower is pistillate. It
both stamens and pistils are absent the flower is said to be sterile
or neutral (snowball, marginal or showy flowers in hydrangea).
Flowers with both stamens and pistils, whether or not they have
floral envelopes, are perfect (or hermaphrodite), so if only one
of these sets of essential organs of the flower is present the flower
is imperfect, or diclinous. Scmetimes the imperfect, or diclinous,
flowers are on the same plant, and the plant is said to be monoe-
cious (of one household). When staminate flowers are on cer-
tain individual plants, and the pistillate flowers of the same
species are on other individuals, the plant is dioecious (or of two
households). When some of the flowers of a plant are diclinous
and others are perfect, they are said to be polygamous.
Many of these variations relating to the presence or absence of
flower parts in one way or another contribute to the well-being
of the plant. Some indicate a division of labor; thus in the
neutral flowers of certain species of hydrangea or viburnum, the
showy petals serve to attract insects which aid in the pollination
of the fertile flowers. It must not be understood, however, that all
variations in plants which results in new or different forms of flowers
is for the good of the species. For example, under cultivation
the flowers of viburnum and hydrangea sometimes are all neu-
tral and showy. While such variations sometimes contribute to
the happiness of man, the plant has lost the power of developing
seed. In diclinous flowers cross pollination is necessitated.
812. Form of the flower. — The flower as a whole has form.
This is so characteristic that in general all flowers of the different
individuals of a species are of the same shape, though they may
vary in size. In general, flowers of closely related plants of dif-
ferent species are of the same type as to form, so that often in the
shape of the flower alone we can see the relationship of kind,
though the form of the flower is not the most important nor
always the sure index of kinship. Since many flowers resemble
THE FLORAL SHOOT.
423
certain familiar objects, names are often used which relate to
these objects.
Flowers are said to be regular, or irregular. In a regular
flower all of the parts of a set or series are of the same shape and
size, while in irregular flowers the parts are of a different shape
or size in some of the sets. The flowers of the pea family (Papi-
/ionacece), of the mint family (Labiates), of the morning glory,
larkspur, monkshood, etc., are irregular (fig. 450). The corolla
usually gives the characteristic form to the flower, and the name
is usually applied to the form of the corolla.
Some of the different forms are wheel-shaped or rotate corolla
when the petals spread out at once like the spokes of a wheel, as
in the potato, tomato, or bittersweet; salver-shaped when the
Fig. 450.
Several forms of flowers. Regular flowers, wh, wheel-shaped corolla; 5a,
salver-shaped; tub, tubular-shaped. Irregular flowers, pa, butterfly or papilio-
naceous; per, personate or masked flower; lab, gaping or ringent corolla. The
two latter are called bilabiate flowers.
petals spread out at right angles from the end of a corolla tube,
as in the phlox; bell-shaped, or campanulate, as in the harebell
or campanula; funnel-shaped, as in the morning glory; tubular,
when the ends of the petals spread but little or none from the
end of the corolla tube, as in the turnip flower or in the disk
florets of the composites. The butterfly, or papilionaceous cor-
olla is peculiar as in the pea or bean. The upper petal is the
"banner," the two lateral ones the "wings," and the two lower
the "keel."
The labiate corolla is charcteristic of the mint family where
the gamosepalous corolla is unequally divided, so that the two
424 RELATION TO ENVIRONMENT.
upper lobes are sharply separated from the three lower forming
two "lips." The labiate corolla of the toadflax, or snapdragon
is personate, or masked, because the lower lip arches upward
like a palate and closes the entrance to the corolla tube; that of
the dead nettle (Lamium) is ringent or gaping, because the lips
are spread wide apart. In some plants the labiate corolla is not
very marked and differs but slightly from a regular form.
The ligulate or strap-shaped corolla is characteristic of the
flowers of the dandelion or chicory, or of the ray flowers of other
composites (fig. 451). The lower part of the gamosepalous
corolla is tubular, and the upper part is strap-shaped, as if that
part of the tube were split on one side and spread out flat.
These forms of the flower should be studied in appropriate
examples.
813. "Union of flower parts. — In the buttercup flower all the
parts of each series are separate from one another and from
other series of parts. Each one is attached to the receptacle of
the flower, which is a very much shortened portion of the flower
axis. The calyx being composed of separate and distinct parts
is said to be polysepalous, and the corolla is likewise polypejal-
ous. The stamens are distinct, and the pistils are simple. In
many flowers, however, there is a greater or lesser union of parts.
814. Union of parts of the same series or cycle. — The parts
coalesce, either slightly or to a great extent. Usually they are
not so completely coalesced but what the number of parts of
the series can be determined. Where the sepals are united the
calyx is gamosepalous, when the petals are united the corolla is
gamopetalous.
Union of the sepals or of the corolla is quite common, but
union of the stamens is rare except in a few families where
it is quite characteristic. When the stamens are united by
their anthers, they are syngenoesions. This is the case in
most flowers of the composite family. When all the stamens
are united into one group by their filaments, they are mona-
delphons (one brotherhood), as in holy hock, hibiscus, cotton,
THE FLORAL SHOOT. 42$
marsh-mallow, etc. When they are united by their filaments in
two groups, they are diadelphous (two brotherhoods), as in the
pea and most members of the pea family. In most species of
St. John's wort (Hypericum), the stamens are united in threes
(triadelphous).
815. The carpels are often united. — The pistil is then said to
be compound. Where the pistils are consolidated, usually the
adjacent walls coalesce and thus separate the cavity of each
ovary. Each cavity in the compound pistil is a locule. In
some cases the adjacent walls disappear so that there is one com-
mon cavity for the compound pistil (examples: purslane, chick-
weeds, pinks, etc.). In a few cases there is a false partition
(example, in the tooth wort and other crucifers). The compound
pistil is very often lobed slightly, so that the different pistils can
be discerned. More often the styles or stigmas are distinct, and
thus indicate the number of pistils united.
816. Union of the parts of different series. — While in the
buttercup and many other flowers, all the different parts are
inserted on the torus or receptacle, in other flowers one series of
parts may be joined to another. This is ddnation of parts, or
the two or more series are adnate. In the morning glory the
stamens are inserted on the inner face of the corolla tube; the
same is true in the mint family, and there are many other ex-
amples. The insertion of parts, whether free or adnate, is usually
spoken of in reference to their relation to the pistil. Thus,
in the buttercup the floral envelopes and stamens are all free
and hypogynous they are below the pistil. The pistil in this
case is superior. In the cherry, pear, etc., the petals and stamen?
are borne on the edge of the more or less elevated tube of the
calyx, and are said to be perigynous, i.e., around the pistil.
In the cranberry, huckleberry, etc., the calyx is for the most
part united with the wall of the ovary with the short calyx limbs
projecting from the upper surface. The petals and stamens
are inserted on the edge of the calyx above the ovary; they are,
therefore, epigynous, and the ovary being under the calyx, as
it were, is inferior.
426 RELATION TO ENVIRONMENT.
III. Arrangement of Flowers, or Mode of Inflores-
cence.
817. Flowers are solitary or clustered. — Solitary flowers are
more simple in their arrangement, i.e., it is easier for us to deter-
mine and name their relation to each other and to other parts
of the plant. They are either axillary, i.e., on short lateral
shoots in the axils of ordinary foliage leaves, or they are terminal,
i.e., they are borne on the end of the main axis of an ordinary
foliage shoot. In either case they are so far separated, and the
foliage leaves are so prominent, they do not form recognizable
groups or clusters. The manner cf arrangement of flowers on
the shoot is called inflorescence, while the group of flowers so
arranged is the flou'er cluster.
Two different modes of inflorescence are usually recognized
in the arrangement of flowers on the stem, (i) The corymbose,
or indeterminate inflorescence (also indefinite inflorescence), in
which the flowers arise from axillary buds, and the terminal bud
may continue to grow. (2) The cymose or determinate inflor-
escence (also definite inflorescence) in which the flowers arise
from terminal buds. This arrests the growth of the shoot in
length.
There are several advantages to the plant in the different
modes of inflorescence, chief among which is the massing of the
flowers, thus increasing the chances for effective pollination.
A. FLOWEB CLUSTERS WITH INDETERMINATE INFLORESCENCE.
818. The simplest mode of indeterminate inflorescence is
where the flowers arise in the axils of normal foliage leaves,
while the terminal bud, as in the florist's smilax, the bellwort,
moneywort, apricot, etc., continues to grow. The flowers are
solitary and axillary. In other cases which are far more numer-
ous, the flowers are associated into more or less definite clusters
in which are a number of recognizable types. The word type
used in this sense, it should be understood, does not refer to an
THE FLORAL SHOOT. 427
original structure which is the source of others. It merely refers
to a mode of inflorescence which we attempt to recognize, and
about which we group those forms which have a resemblance to
one another. There are many forms of flower clusters which
do not conform to any one of our recognized types, and are very
puzzling. The evolution of the flower clusters has been natural,
and we cannot make them all conform to an artificial classifica-
tion. These types are named merely as a matter of convenience
in the expression of our ideas. The types usually recognized
are as follows:
819. The raceme.— The flower-shoot is more or less elongated,
and the leaves are reduced to a minute size termed bracts, while
the flowers on lateral axes are solitary in the axils of the bracts.
The reduction in the size of the leaves and the somewhat limited
growth of the shoot in length, makes the flowers more prominent,
and brings them into closer relation than if they were formed in
the axils of the leaves on the ordinary foliage shoot. The choke
cherry, currant, pokeweed, sourwood, etc., are examples of a
raceme (fig. 569). In most plants with the raceme type, while
the inflorescence is indeterminate, and the uppermost flowers
(those toward the end of the main shoot) are younger, still the
period of flowering is somewhat restricted and the raceme stops
growing. In a few plants, however, as in the common "shep-
herd's purse," the raceme continues to grow throughout the
summer, so that the lower flowers may have ripened their seed
while the terminal portion of the raceme is still growing and
producing new flowers. Compound racemes are formed when
by branching of the flower-shoot there are several racemes in a
cluster, as in the false Solomon's seal (Smilacina racemosa).
820. The panicle. — The panicle is developed from the raceme
type by the branching of the lateral flower-axes forming a loose
open flower cluster, as in the oat.
821. The thyrsus is a compact panicle of pyramidal form, as
in the lilac, horsechestnut, etc.
822. The corymb. — The corymb shows likewise an easy tran-
sition from the raceme type, by the shortening of the main axis
428 RELATION TO ENVIRONMENT.
of inflorescence, and the lengthening of the lower, lateral flower
peduncles so that the flower cluster is more or less flattened on
top. This represents the simple corymb. A compound corymb
*s one in which some of the flower peduncles branch again form-
ing secondary corymbs, as in the mountain ash. It is like a
panicle with the lower flower stalks elongated.
823. The umbel. — The umbel is developed from the raceme,
or corymb. The main flower-shoot remains very short or unde-
veloped with several flowers on long peduncles arising close to-
gether around this shortened axis, in the form of a whorl or clus-
ter. Examples are found in the milkweed, water pennywort
(Hydrocotyle), the oxheart cherry, etc. A compound umbel is
one in which the peduncles are branched, forming secondary
umbels, as in the caraway, parsnip, carrot, etc.
824. The spike. — In the spike the main axis is long, and the
solitary flowers in the axils of the bracts are usually sessile, and
often very much crowded. The plaintain, mullein (fig. 422),
etc., are examples. The spike is a raceme, only the flowers are
sessile and crowded. In the grasses the flower cluster is branched,
and the branchlets bearing a few flowers are spikelets.
825. The head. — When the flower axis is very much short-
ened and the flowers crowded and sessile or nearly so, forming a
globose or compressed cluster, it is a head or capiMum. The
transition is from a spike by the shortening of the main axis, as
in the clover, button bush (Cephalanthus), etc., or in the short-
ening of the peduncles in an umbel, as in the daisy, dandelion,
and other composite flowers. In these the head is surrounded
by an involucre, which in the young head often envelopes the
mass of flowers, thus affording them protection. In some other
composites (Lactuca, for example) the involucre affords pro-
tection for a longer period, even while the seeds are ripening.
826. The spadix. — When the main axis of the flower cluster
is fleshy, the spike or head forms a spadix, as in the Indian tur-
nip, the skunk cabbage, the calla, etc. The spadix is usually
more or less enclosed in a spathe, a somewhat strap-shaped leaf.
827. The catkin. — A spike which is usually caducous, i.e.,
THE FLORA!. SffOOT.
420
falls away after the maturity of the flower or fruit, is called &
catkin, or an ament. The flower clusters of the alder, willow,
(fig. 555), poplar, and the staminate flower clusters of the oak,
hickory, hazel, birch, etc., are aments. So characteristic is this
Fig. ^51.
Head of sunflower showing centripetal inflorescence of tubular flowers. (Photo
by the Author.)
mode of inflorescence that the plants are called amentijerous, or
amentaceous.
828. Anthesis of flowers with indeterminate inflorescence. —
In the anthesis of the raceme as well as in other corymbose forms
the lower (or outer) flowers being older, open first. The open-
ing of the flowers then takes place from below, upward; or from
the outside, inward toward the center of inflorescence. The
anthesis, i.e., the opening of the flowers of corymbose forms is
said to be centripetal, i.e., it progresses from outside, inward.
The anthesis of the fuller's teazel is peculiar, since it shows both
types. There are several distinct advantages to the plant where
430
RELATION TO ENVIRONMENT.
anthesis extends over a period of time, as it favors cross pollina-
tion, favors the formation of seed in case conditions should be
Fig. 452.
Heads of fuller's teazel in different stages of flowering.
unfavorable at one period of anthesis, distributes the drain on
the plant for food, etc.
B. FLOWER CLUSTERS WITH DETERMINATE INFLORESCENCE.
829. The simplest mode of determinate inflorescence is a
plant with a solitary terminal flower, as in the hepatica, the tulip,
etc. The leaves in these two plants are clustered in the form of a
rosette, and the aerial shoot is naked and bears the single flower
at its summit. Such a flower-shoot is a scape. As in the case
of the indeterminate inflorescence, so here the larger number
of flower-shoots are more, complex and specialized, resulting in
the evolution of flower clusters or masses. Accompanying the
association of flowers into clusters there has been a reduction in
leaf surface on the flower-shoot so that the flowers predominate
in mass and are more conspicuous. Among the recognized
modes of determinate inflorescence, the following are the chief
ones:
830. The cyme. — In the cyme the terminal flower on the main
axis opens first and the remaining flowers are borne on lateral
shoots, which arise from the axils of leaves or bracts, below.
THE FLORAL tffOOT.
431
Thes£ lateral shoots usually branch and elongate so that the
terminal flowers on all the brandies reach nearly the same height
as the terminal flower on the main shoot, forming a somewhat
flattened or convex top of the flower cluster. This is illustrated
A SB o
Fig. 453-
Diagrams of cymose inflorescence. A, dichasium; B, scorpioid cyme; C, heli-
coid cyme. (After Strasburger. )
in the basswood flower. The anthesis of the cyme is centrifugal,
i.e., from the inside outward to the margin. But it is often more
or less mixed, since the lateral shoots if they bear more than one
flower are dimunitive cymes and the terminal flower opens before
the lateral ones. Where the flower cluster is quite large and
the branching quite extensive, compound cymes are formed, as
in the dogwood, hydrangea, etc.
831. The helicoid cyme. — Where successive lateral branch-
ing takes place, and always continues on the same side a curved
flower cluster is formed, as in the forget-me-not and most mem-
bers of the borage family. This is known as a helicoid cyme
(fig. 453, C). Each new branch becomes in turn the "false"
axis bearing a new branch on the same side.
832. The scorpioid cyme. — A scorpioid cyme (fig. 453, B) is
formed where each new branch arises on alternate sides of the
"false" axis.
833. The forking cyme is where each "false "'axis produces
two branches opposite, so that it represents a false dichotomy
(example, the flower cluster of chickweed).
834. Some of these flower clusters are peculiar and it is diffi-
432 RELATION TO ENVIRONMENT.
cult to see how the helicoid, or scorpioid, cymes are of any
advantage to the plant over a true cyme. The inflorescence of
the plant being determinate, if the flowering is to be extended
over a considerable period a peculiar form would necessarily
result. In the helicoid cyme continued branching takes place
on one side, and the result in the forget-me-not is a continued
inflorescence in its effect like that of a continued raceme (com-
pare shepherd' s-purse). But we should not expect that all
of the complex and specialized structures from simple and gen-
eralized ones are beneficial to the plant. In many plants we
recognize evolution in the direction of advantageous structures.
But since the plant cannot consciously evolve these structures,
we must also recognize that there may be phases of retrogression
in which the structures evolved are not so beneficial to the plant
as the more simple and generalized ones of its ancestors. Varia-
tion and change do not result in advancing the plant or plant
structures merely along the lines which will be beneficial. The
tendency is in all directions. The result in general may be dia-
gramed by a tree with divergent and wide-reaching branches.
Some die out; others remain subordinate or dormant; while
still others droop downward, showing a retrogression. But in
this backward evolution they do not return to the condition of
their ancestors, nor is the same course retraced. A new down-
ward course is followed just as the downward-growing branch
follows a course of its own, and does not return in the trunk.
CHAPTER XLIII.
POLLINATION.
Origin of heterospory, and the necessity for
pollination.
835. Both kind* of sexual organs on the same prothallium. — In the ferns, as
we have seen, the sexual organs are borne on the prothallium, a small, leaf-like,
heart-shaped body growing in moist situations. In a great many cases both
kinds of sexual organs are borne on the same prothallium. While it is per-
haps not uncommon, in some species, that the egg cell in an archegonium
may be fertilized by a spermatozoid from an antheridium on the same pro-
thallium, it happens many times that it is fertilized by a spermatozoid from
another prothallium. This may be accomplished in several ways. In the
first place antheridia are usually found much earlier on the prothallium than
are the archegonia. When these antheridia are ripe, the spermatozoids es-
cape before the archegonia on the same prothallium are mature.
836. Cross fertilization in monoecious prothallia. — By swimming about in
the water or drops of moisture which are at times present in these moist situa-
tions, these spermatozoids may reach and fertilize an egg which is ripe
in an archegonium borne on another and older prothallium. In this way
what is termed cross fertilization is brought about nearly as effectually as if
the prothallia were dioecious, i.e. if the antheridia and archegonia were all
borne on separate prothallia.
837. Tendency toward dioecious prothallia. — In other cases some fern pro-
thallia bear chiefly archegonia, while others bear only antheridia. In these
cases cross fertilization is enforced because of this separation of the sexual
organs on different prothallia. These different prothallia, the male and
female, are largely due to a difference in food supply, as has been clearly
proven by experiment.
838. The two kinds of sexual organs on different prothallia. — In the horse-
tails (equisetum) the separation of the sexual organs on different prothallia has
become quite constant. Although all the spores are alike, so far as we can
determine, some produce small male plants exclusively, while others produce
433
434 RELATION TO ENVIRONMENT.
large female plants, though in some cases the latter bear also antheridia. It
has been found that when the spores are given but little nutriment they form
male prothallia, and the spores supplied with abundant nutriment form
female prothallia.
839. Permanent separation of sexes by different amounts of nutriment sup-
plied the spores. — -This separation of the sexual organs of different prothallia,
which in most of the ferns, and in equisetum, is dependent on the chance
supply of nutriment to the germinating spores, is made certain when we come
to such plants as isoetes and selaginella. Here certain of the spores receive
more nutriment while they are forming than others. In the large sporangia
(macrosporangia) only a few of the cells of the spore-producing tissue form
spores, the remaining ceils being dissolved to nourish the growing macro-
spores, which are few in number. In the small sporangia (microsporangia)
all the cells of the spore-producing tissue form spores. Consequently each
one has a less amount of nutriment, and it is very much smaller, a micro-
spore. The sexual nature of the prothallium in selaginella and isoetes, then, is
predetermined in the spores while they are forming on the sporophyte. The
microspores are to produce male prothallia, while the macrospores are to
produce female prothallia.
840. Heterospory. — This production of two kinds of spores by isoetes,
selaginella, and some of the other fern plants is heterospory, or such plants
are said to be heterosporous. Heterospory, then, so far as we know from liv-
ing forms, has originated in the fern group. In all the higher plants, in the
gymnosperms and angiosperms, it has been perpetuated, the microspores being
represented by the pollen, while the macrospores are represented by the em-
bryo sac; the male organ of the gymnosperms and angiosperms being the
antherid cell in the pollen or pollen tube, or in some cases perhaps the pollen
grain itself, and the female organ in the angiosperms perhaps reduced to
the egg cell of the embryo sac.
841. In the pteridophytes water serves as the medium for conveying the
sperm cell to the female organ. — In the ferns and their allies, as well as in
the liverworts and mosses, surface water is a necessary medium through
which the generative or sperm cell of the male organ, the spermatozoid, may
reach the germ cell of the female organ. The sperm cell is here motile.
This is true in a large number of cases in the algae, which are mostly aquatic
plants, while in other cases currents of water float the sperm cell to the
female organ.
842. In the higher plants a modification of the prothallium is necessary.
— As we pass to the gymnosperms and angiosperms, however, where the
primitive phase (the gametophyte) of the plants has become dependent solely
on the modern phase (the sporophyte) of the plant, surface water no longe/
serves as the medium through which a motile sperm cell reaches the egg cell
to fertilize it. The female prothallium, or macrospore, is, in nearly alJ
POLLINATION. 435
cases, permanently enclosed within the sporangium, so that if there were
motile sperm cells on the outside of the ovary, they could never reach the
egg to fertilize it.
843. But a modification of the microspore, the pollen tube, enables the
sperm cell to reach the egg cell. The tube grows through the nucellus,
or first through the tissues of the ovary, deriving nutriment therefrom.
844 But here an important consideration should not escape us. The pol-
len grains (microspores) must in nearly all cases first reach the pistil, in
order that in the growth of this tube a channel may be formed through which
the generative cell can make its way to the egg cell. The pollen passes from
the anther locule, then, to the stigma of the ovary. This process is termed
pollination.
Pollination.
i
845 Self pollination, or close pollination. — Perhaps very few of the ad-
mirers of the pretty blue violet have ever noticed that there are other flowers
than those which appeal to us through the beautiful colors of the petals.
How many have observed that the brightly colored flowers of the blue violet
rarely "set fruit"? Underneath the soil or debris at the foot of the plant
are smaller flowers on shorter, curved stalks, which do not open. When the
anthers dehisce, they are lying close upon the stigma of the ovary, and the
pollen is deposited directly upon the stigma of the same flower. This
method of pollination is self pollination, or close pollination. These small,
closed flowers of the violet have been termed " cleistogamous" because they
are pollinated while the flower is closed, and fertilization takes place as a
result.
But self pollination takes place in the case of some open flowers. In some
cases it takes place by chance, and in other cases by such movements of the
stamens, or of the flower at the time of the dehiscence of the pollen, that it
is quite certainly deposited upon the stigma of the same flower.
846. Wind pollination. — The pine is an example of wind-pollinated flowers.
Since the pollen floats in the air or is carried by the "wind," such flowers are
anemophilons . Other anemophilous flowers are found in other conifers, in
grasses, sedges, many of the ament-bearing trees, and other dicotyledons.
Such plants produce an abundance of pollen and always in the form of
"dust,'1 so that the particles readily separate and are borne on the wind.
847. Pollination by insects — A large number of the plants which we have
noted as being anemophilcus are monoecious or dioecious, i.e. the stamens
and pistils are borne in separate flowers. The two kinds of flowers thus formed,
the male and the female, are borne either on the same individual (monoe-
cious) or on different individuals (dioecious). In such cases cross pollination.
436
RELATION TO ENVIRONMENT.
i.e. the pollination of the pistil of one flower by pollen from another, is
sure to take place, if it is pollinated at all. Even in monoecious plants cross
pollination often takes place between flowers of different individuals, so that
Fig. 4S4-
Viola cucullata ; blue flowers above, cleistogamous flowers smaller and curved below
Section of pistil atj-ight.
more widely different stocks are united in the fertilized egg, and the strain
is kept more vigorous than if very close or identical strains were united.
848. But there are many flowers in which both stamens and pistils are pres-
ent, and yet in which cross pollination is accomplished through the agency of
insects.
859. Pollination of the bluet. — In the pretty bluet the stamens and
styles of the flowers are of different length as shown in figures 455, 4^6.
The stamens of the long-styled flower are at about the same level as the
stigma of the short-styled flower, while the stamens of the latter are on
POLLINA TION.
437
about the same level as the stigma of the former. What does this interesting
relation of the stamens and pistils in the two different flowers mean ? As the
butterfly thrusts its "tongue" down into the tube of the long-styled flower
Fig. 453'
Dichogamous flower of the bluet (Houstonia ccerulea), the long-styled form.
for the nectar, some of the pollen will be rubbed off and adhere to it. When
.now the butterfly visits a short-styled flower this pollen will be in the right
position to be rubbed off onto the stigma of the short style. The positions of
Fig. 456.
Dichogamous flower of bluet (Houstonia ccerulea), the short-styled form.
the long stamens and long style are such that a similar cross pollination will
be effected.
850. Pollination of the primrose. — In the primroses, of which we have
examples growing in conservatories, that blossom during the winter, we
have almost identical examples of the beautiful adaptations for cross polli-
nation by insects found in the bluet. The general shape of the corolla is
43^ RELATION TO ENVIRONMENT.
the same, but the parts of the flower are in fives, instead of in fours as ii,
the bluet. While the pollen of the short-styled primulas sometimes must
fall on the stigma of the same flower, Darwin has found that such pollen is
Fig- 45 7-
Dichogamous flowers of primula.
not so potent on the stigma of its own flower as on that of another, an ad-
ditional provision which tends to necessitate cross pollination.
In the case of some varieties of pear trees, as the bartlett, it has been
found that the flowers remain largely sterile not only to their own pollen, or
pollen of the flowers on the same tree, but to all flowers of that variety.
However, they become fertile if cross pollinated from a different variety of
pear.
851. Pollination of the skunk's cabbage. — In many other flowers cross
pollination is brought about through the agency of insects, where there is a
difference in time of the maturing of the stamens and pistils of the same
flower. The skunk's cabbage (Spathyema fcetida), though repulsive on
account of its fetid odor, is nevertheless a very interesting plant to study for
several reasons. Early in the spring, before the leaves appear, and in many
cases as soon as the frost is out of the hard ground, the hooked beak of the
large fleshy spathebf this plant pushes its way through the soil.
If we cut away one side of the spathe as shown in fig. 459 we shall have
the flowering spadix brought closely to view. In this spadix the pistil of
each crowded flower has pushed its style through between the plates of
armor formed by the- converging ends of the sepals, and stands out alone
with the brush-like stigma ready for pollination, while the stamens of all the
flowers of this spadix are yet hidden beneath. The insects which pass from
the spadix of one plant to another will, in crawling over the projecting
stigmas, rub off some of the pollen which has been caught while visiting a
plant where the stamens are scattering their pollen. In this way cross pollin-
ation is brought about. Such flowers, in which the stigma is prepared
POLL1NA TION.
439
Fig. 458.
Skunk's cabbage.
Fig. 459. 440
Proterogyny in skunk'8 cabbage. (Photograph by the author.)
'P0LLINA TION.
441
Fig. 460.
Skunk's cabbage ; upper flowers proterandrous, lower ones proterogynous.
442 RELATION TO ENVIRONMENT.
for pollination before the anthers of the same flower are ripe, are prater-
ogynous.
852. Now if we observe the spadix of another plant we may see a condi-
tion of things similar to that shown in fig. 460. In the flowers in the upper
part of the spadix here the anthers are wedging their way through between
the armor-like plates formed by the sepals, while the stvies of the same
flowers are still beneath, and the stigmas are not ready for pollination. Such
flowers are proterandrous, that is. the anthers are ripe before the stigmas of
the same flowers are ready for pollination. In this spadix the upper flowers
are proterandrous, while the lower ones are prolerogynous, so that it might
happen here that the lower flowers would be pollinated by the pollen falling
on them from the stamens of the upper flowers. This would be cross pol-
lination so far as the flowers are concerned, but not so far as the plants are
concerned. In some individuals, however, we find all the flowers proter-
androus.
853 Spiders have discovered this curious relation of the flowers and in-
sects.— On several different occasions, while studying the adaptations of the
flowers of the skunk's cabbage for cross pollination, I was interested to find
that the spiders long ago had discovered something of the kind, for tne>
spread their nets here to catch the unwary but useful insects. I have not
seen the net spread over th$ opening in the spathe, but it is spread over the
spadix within, reaching from tip to tip of either the stigmas, or stamens, or
both. Behind the spadix crouches the spider-trapper. The insect crawls
over the edge of the spadix, and plunges unsuspectingly into the dimly
lighted chamber below, where it becomes entangled in the meshes of the
net.
Flowers in which the ripening of the anthers and maturing of the stigmas
occur at different times are also said to be dichogamous.
854. Pollination of jack in-the-pulpit. — The jack-in-the-pulpit (Arisaema
triphyllum i has made greater advance in the art of enforcing cross pollina-
tion. The larger number of plants here are, as we have found, dioecious, the
staminate flowers being on the spadix of one plant, while the pistillate flowers
are on the spadix of another. In a few plants, however, we find both
female and male flowers on the same spadix.
855 The pretty bellflower (Campanula rotundifolia) is dichogamous
and proterandrous (fig. 462). Many of the composites are also dichoga-
mous.
856. Pollination of orchids. — But some of the most marvellous adaptations
for cross pollination by insects are found in the orchids, or members of the
orchis family. The larger number of the members of this family grow in the
tropics. Many of these in the forests are supported in lofty trees where the)
are brought near the sunlight, and such are called "epiphytes." A numbei
of species of orchids are distributed , .1 temperate regions.
POLLINA TION.
443
857. Cypripedium, or lady-slipper. — One species of the lady-slipper is
.?hown in fig. 468. The labcllum in this genus is shaped like a shoe, as one
Fig. 461.
A group of jacks.
can see by the section of the flower in fig. 468. The stigma is situated at st,
while the anther is situated at a, upon the style. The insect enters about
the middle of the boat-shaped labellum. In going out it passes up and out
444
RELATION TO ENVIRONMENT.
at the end near the flower stalk. In doing this it passes the stigma first and
the anther last, rubbing against both. The pollen caught on the head of
rig. 462.
Proterandry in the bell-flower (campanula). Left figure shows the syngenoecious stamens
surrounding the immature style and stigma. Middle figure, shows the immature stigma being
pushed through the tube and brushing out the pollen ; while in the right-hand figure, after
the pollen has disappeared, the lobes of the stigma open out to receive pollen from another
flower.
the insect, will not touch the stigma of the same flower, but will be in posi-
tion to come in contact with the stigma of the next flower visited.
858. Epipactis. — In epipactis the action of the pollinia, which move
downward, is described in fig. 469.
Fig. 463.
Kalmia latifolia, showing position of anthers before insect visits, and at the right the
scattering of the pollen when disturbed by insects. Middle figure section of flower.
849 . In some of the tropical orchids the pollinia are set free when the insect
touches a certain part of the flower, and are thrown in such a way that the
disk of the pollinium strikes the insect's head and stands upright. By the
time the insect reaches another flower the pollinium has bent downward suffi-
POL LIN A TSOM
445
ciently to strike against the stigma when the insect alights on the labellum.
In the mountains of North Carolina I have seen a beautiful little orchid, in
which, if one touches a certain part »f the flower with a lead-pencil or other
suitable object, the pollinium is set free suddenly, turns a complete somer-
sault in the air, and lands with the disk sticking to the pencil. Many of the
Fig. 464-
Spray of leaves and flowers
of cytisus.
orchids grown in conservatories can be used to demonstrate some of these
peculiar mechanisms.
860. Pollination of the canna. — In the study of some of the marvellous
adaptations of flowers for cross pollination one is led to inquire if, after all,
plants are not intelligent beings, instead of mere automatons which respond
Fig. 465
Flower of cytisus grown in conservatory. Same flower scattering pollen.
to various sorts of stimuli. No plant has puzzled me so much in this respect
as the canna, and any one will be well repaid for a study of recently opened
flowers, even though it may be necessary to rise early in the morning to
unravel the mystery, before bees or the wind have irritated the labellum.
The canna flower is a bewildering maze of petals and petal-like members.
446
RELATION TO ENVIRONMENT.
The calyx is green, adherent to the ovary, and the limb divides into three,
lanceolate lobes. The petals are obovate and spreading, while the stamens
have all changed to petal-like members, called staminodia. Only one still
shows its stamen origin, since the anther is seen at one side, while the fila-
ment is expanded laterally and upwards to form the staminodium.
Fig. 466.
Spartium, showing the dustinr, of the pollen through the opening keels on Uie under side
ot au insect. (From Ktvner and Oliver.)
861 The ovary has three locules, and the three styles are usually united
into a long, thin, strap-shaped style, as seen in the figure, though in some
cases three, nearly distinct, filamentous styles are present. The end of this
strap-shaped style has a peculiar curve on one side, the outline being some-
POLLINA TION.
447
times like a long narrow letter S. It is on the end of this style, and along
the crest of this curve, that the stigmatic surface lies, so that the pollm
leu
Fig. 468.
Section of flower of cypripedium. st,
stigma ; a, at the left stamen. The insect
enters the labellum at the center, passes
under and against the stigma, and out
through the opening b, where it rubs
against the pollen. In passing through
another flower this pollen is rubbed off
on the stigma.
must be deposited on the stigmatic end or margin
in order that fertilization may take place.
Fig. 467. 862. If we open carefully canna-flower buds
Cypripedium. which are nearly ready to open naturally, by
unwrapping the folded petals and staminodia, we shall see the anther-bearing
Fig. 469.
Epipactis with portion of perianth removed to show details. /, labellum ; st, stigma ; r,
rostellum ; /, polfinium. When the insect approaches the flower its head strikes the disk
of the pollinium and pulls the pollinium out. At this time the pollinium stands up out of the
way of the stigma. By the time the insect moves to another flower the pollinia have moved
downward so that they are in position to strike the stigma and leave the pollen. At the
right is the head of a bee, with two pollinia (a) attached.
448
RELATION TO ENVIRONMENT.
staminodium is so wrapped around the flattened style that the anther lies
closely pressed' against the face of the style, near the margin opposite that
on which the stigma lies.
863. The walls of the anther locules which lie against the style become
changed to a sticky substance for their entire length, se that they cling
firmly to the surface of the style
and also to the mass of pollen
within the locules. The result is
that when the flower opens, and
this staminodium unwraps itself
from the embrace of the style, the
mass of pollen is left there de-
posited, while the empty anther is
turned around to one side.
668. Why does the flower de-
posit its own pollen on the style ?
Some have regarded this as the act
of pollination, and have concluded,
therefore, that cannas are neces-
sarily self pollinated, and that
cross pollination does not take
place. But why is there such evi-
dent care to deposit the pollen on
the side of the style away from the
If we visit the
Fig. 470.
Canna flowers with the perianth removed to
show the depositing of the po.len on the style by stlgmatlC margin f
the stamen. cannas some morning, when a
number of the flowers have just opened, and the bumblebees are humming
around seeking for nectar, we may be able to unlock the secret
864. We see that in a recently opened canna flower, the petal which
directly faces the style in front stands upward quite close to it, so that the
flower now is somewhat funnelshaped. This front petal is the labellum, and
is the landing place for the bumblebee as he alights on the flower. ^ Here
he comes humming along and alights on the labellum with his head so close
to the style that it touches it. But just the instant that the bee attempts to
crowd down in the flower the labellum suddenly bends downward, as shown
in fig. 468. In so doing the head of the bumblebee scrapes against the
pollen, bearing some of it off. Now while the bee is sipping the nectar it is
too far below the stigma to deposit any pollen on the latter. When the bum-
blebee flies to another newly opened flower, as it alights, some of the pollen
of the former flower is brushed on the stigma.
865. One can easily demonstrate the sensitiveness of the labellum of
recently opened canna flowers, if the labellum has not already moved down
in response to some stimulus. Take a lead-pencil, or a knife blade, or even
POLLINA TION.
449
the finger, and touch the upper surface of the labellum by thrusting it
between the latter and the style. The labellum curves quickly downward.
866. Sometimes the bumblebees, after sipping the nectar, will crawl up
over the style in a blundering manner. In this way the flower may be pol-
Fig. 47i.
Pollination of the canna flower by bumblebee. Canna flower. Pollen on style, sta-
men at left.
linated with its own pollen, which is equivalent to self pollination. Un-
doubtedly self pollination does take place often in flowers which are adapted,
to a greater or less degree, for cross pollination by insects.
CHAPTER XLIV."
THE FRUIT.
I. Parts of the Fruit.
867. After the flower comes the fruit. — With the perfection of
the fruit the seed is usually formed. This is the end towards
which the energies of the plant have been directed. While the
seed consists only of the ripened ovule and the contained em-
bryo, the fruit consists of the ripened ovary in addition, and in
many cases with other accessory parts, as calyx, receptacle, etc.,
combined with it. The wall of the ripened ovary is called a
pericarp, and the walls of the ovary form the walls of the fruit.
868. Pericarp, endocarp, exocarp, etc. — This is the part of
the fruit which envelops the seed and may consist of the carpels
alone, or of the carpels and the adherent part of the receptacle,
or calyx. In many fruits the pericarp shows a differentiation
into layers, or zones of tissue, as in the cherry, peach, plum, etc.
The outer, which is here soft and fleshy, is exocarp, while the
inner, which is hard, is the endocarp. An intermediate layer is
sometimes recognized and is called mesocarp. In such cases
the skin of the fruit is recognized as the epicarp. Epicarp and
mesocarp are more often taken together as exocarp.
In general fruits are dry or fleshy. Dry fruits may be
grouped under two heads. Those which open at maturity and
scatter the seed are dehiscent Those which do not open are
indehiscent.
450
THE FRUIT.
451
Fig. 472-
Seed, or akene,
of buttercup.
II. Indehiscent Fruits.
869. The akene. — The thin dry wall of the ovary encloses
the single seed. It usually does not open and free the seed
within. Such a fruit is an akene. An akene is
a dry, indehiscent fruit. All of the crowded but
separate pistils in the buttercup flower when ripe
make a head of akenes, which form the fruit of
the buttercup. Other examples of akenes are
found in other members of the buttercup family,
also in the composites, etc. The sunflower seed
is a good example of an akene.
870. The samara. — The winged fruits of the maple (fig. 574),
elm, etc., are indehiscent fruits. They are sometimes called
key fruits.
871. The caryopsis is a dry
fruit in which the seed is con-
solidated with the wall of the
ovary, as in the wheat, corn,
and other grasses.
872. The schizocarp is a
dry fruit consisting of several
Fig. 473. locules (from a syncarpous
Fruit of red oak. An acorn. gytUEcium). At maturity the
carpels separate from each other, but do not themselves dehisce
and free the seed, as in the carrot family, mallow family.
873. The acorn. — The acorn fruit consists of the acorn and
the "cup" at the base in which the acorn sits. The cup is a
curious structure, and is supposed to be composed of an involucre
of numerous small leaves at the base of the pistillate flower,
which become consolidated into a hard cup-shaped body. When
the acorn is ripe it easily separates from the cup, but the hard
pericarp forming the "shell" of the acorn remains closed. Frost
may cause it to crack, but very often the pericarp is split open at
the smaller end by wedge-like pressure exerted by the emerging
radicle during germination.
452 RELATION TO ENVIRONMENT.
874. The hazelnut, chestnut, and beechnut. — In these fruits a
crown of leaves (involucre) at the base of the flower grows around
Fig. 474-
Germinating acorn of white oak.
the nut and completely envelops it, forming the husk or burr.
When the fruit is ripe the nut is easily shelled out from the husk.
In the beechnut and chestnut the burr dehisces as it dries and
allows the nut to drop out. But the fruit is not dehiscent, since
the pericarp is still intact and encloses the seed.
875. The hickory-nut, walnut, and butternut. — In these fruits
the "shuck" of the hickory-nut and the "hull" of the walnut
and butternut are different from the involucre of the acorn or
hazelnut, etc. In the hickory-nut the "shuck" probably con-
sists partly of calyx and partly of involucral bracts consolidated,
probably the calyx part predominating. This part of the fruit
splits open as it dries and frees the "nut," the pericarp being
very hard and indehiscent. In the walnut and butternut the
"hull" is probably of like origin as the "shuck" of the hickory
nut, but it does not split open as it ripens. It remains fleshy.
The walnut and butternut are often called drupes or stone fruits,
but the fleshy part of the fruit is not of the same origin as the
fleshy part of the true drupes, like the cherry, peach, plum, etc.
III. Dehiscent Fruits.
876. Of the dehiscent fruits several prominent types are rec-
ognized, and in general they are sometimes called pods. There
is a single carpel (simple pistil), and the pericarp is dry (gynce-
THE FRUIT. 453
cium apocarpous) ; or where there are several carpels united the
pistil is compound (gyncecium syncarpous).
877. The capsule. — When the capsule is syncarpous it may
dehisce in three different ways: ist. When the carpels split
along the line of their union
with each other longitudi-
nally (septicidal dehiscence),
as in the azalea or rhodo-
dendron. ad. When the Fig. 475.
1 ,7., t ,T .j Diagrams illustrating three types (in cross-
Carpels SpM down the mid- section) of the dehiscence of dry fruits. Loc,
77 7- /; 7--J7 j i • loculicidal; Sep, Septicidal, Septifragal.
die line (locuhcidal dehis-
cence), as in the fruit of the iris, lily, etc. 3d. When the carpels
open by pores (poricidal dehiscence), as in the poppy. Some
syncarpous capsules have but one locule, the partitions between
the different locules when young having disappeared. The
"bouncing-bet" is an example, and the seeds are attached to a
central column in four rows corresponding to the four locules
present in the young stage.
878. A follicle is a capsule with a single carpel which splits
open along the ventral or upper suture, as in the larkspur, peony.
879. The legume, or true pod, is a capsule with a single carpel
which splits along both sutures, as the pea, bean, etc. As the pod
ripens and dries, a strong twisting ten-
sion is often produced, which splits the
pod suddenly, scattering the seeds.
880. The silique.— In the toothwort,
shepherd's-purse, and nearly all of the
plants in the mustard family the fruit
consists of two united carpels, which
separate at maturity, leaving the par-
tition wall persistent. Such a fruit is
a silique; when short it is a silicle, or
pouch.
881. A pyxidium, or pyxis, is a cap-
sule which opens with a lid, as in the
Fruit c/sweeYpW: apod.
454
RELATION TO ENVIRONMENT.
IV. Fleshy and Juicy Fruits.
882. The drupe, or stone-fruit.— In the plum, cherry, peach,
apricot, etc., the outer portion (exocarp) of the pericarp (ovary)
becomes fleshy, while the inner portion (endocarp) becomes hard
and stony, and encloses the seed, or "pit." Such a fruit is known
as a drupe, or as a stone-fruit. In the almond the fleshy part
of the fruit is removed.
883. The raspberry and blackberry. — While these fruits are
Fig. 477-
Drupe, or stone-fruit, of plum.
known popularly as " berries," they are not berries in the tech-
nical sense. Each ovary, or pericarp, in the flower forms a single
small fruit, the outer portion being fleshy and the inner stony, just
as in the cherry or plum. It is a drupelet (little drupe). All of
the drupelets together make the " berry," and as they ripen the
separate drupelets cohere more or less. It is a collection, or
aggregation, of fruits, and consequently they are sometimes called
collective fruits, or aggregate fruits. In the raspberry the fruit
separates from the receptacle, leaving the latter on the stem,
while the drupelets of the blackberry and dewberry adhere to
the receptacle and the latter separates from the stem.
THE FRUIT.
455
884. The berry. — In the true berry both exocarp (including
raesocarp) and endocarp are fleshy or juicy. Good examples
are found in cranberries, huckleberries, gooseberries, currants,
snowberries, tomatoes, etc. The calyx and wall of the pistil
are adnate, and in fruit become fleshy so that the seeds are im-
bedded in the pulpy juice. The seeds themselves are more or
less stony. In the case of berries, as well as in strawberries, rasp-
berries, and blackberries, the fruits are eagerly sought by birds
and other animals for food. The seeds being hard are not
digested, but are passed with the other animal excrement and
thus gain dispersal.
V. Reinforced, or Accessory, Fruits.
When the torus (receptacle) is grown to the pericarp in fruit,
the fruit is said to be reinforced. The torus may enclose the
pericarps, or the latter may be seated upon the torus.
885. In the strawberry the receptacle of the flower becomes
Fig. 478.
Fruit of raspberry.
larger and fleshy, while the "seeds," which are akenes, are sunk
in the surface and are hard and stony. The strawberry thus
RELATION TO ENVIRONMENT.
differs from the raspberry and blackberry, but like them it is
not a true berry.
886. The apple, pear, quince, etc. — In the flower the calyx,
corolla, and stamens are perigynous, i.e., they are seated on the
margin of the receptacle, or torus, which is elevated around the
pistils. In fruit the receptacle becomes consolidated with the
wall of the ovary (with the pericarp). The torus thus rein-
forces the pericarp. The torus and outer portion of the pericarp
become fleshy, while the inner portion of the pericarp becomes
papery and forms the "core." The calyx persists on the free
end of the fruit. Such a fruit is called a pome. The receptacle,
or torus, of the rose-flower, closely related to the apple, is in-
structive when used in comparison. The rose-fruit is called a
"hip."
887. The pepo. — The fruit of the squash, pumpkin, cucum-
ber, etc., is called a pepo. The outer part of the fruit is the recep-
tacle (or torus), which is consolidated with the outer part of the
three-loculed ovary. The calyx, which, with the corolla and
stamens, was epigynous, falls off from the young fruit.
VI. Fruits of Gymnosperms.
The fruits of the gymnosperms differ from nearly all of the
angiosperms in that the seed formed from the ripened ovule is
naked from the first, i.e., the ovary, or carpel, does not enclose
the seed.
888. The cone-fruit is the most prominent fruit of the gymno-
sperms, as can be seen in the cones of various species of pine,
spruce, balsam, etc.
889. Fleshy fruits of the gymnosperms. — Some of the fleshy
fruits resemble the stone-fruits and berries of the angiosperms.
The cedar "berries," for example, are fleshy and contain several
seeds. But the fleshy part of the fruit is formed, not from peri-
carp, since there is no pericarp, but from the outer portion of
the ovules, while the inner walls of the ovules form the hard
stone surrounding the endosperm and embryo. An examination
THE FRUIT. 457
of the pistillate flower of the cedar (juniper) shows usually three
flask-shaped ovules on the end of a fertile shoot subtended by as
many bracts (carpels?). The young ovules are free, but as they
grow they coalesce, and the outer walls become fleshy, forming
a berry-like fruit with a three-rayed crevice at the apex marking
the number of ovules. The red fleshy fruit of the yew (taxus)
resembles a drupe which is open at the apex. The stony seed
is formed from the single ovule on the fertile shoot, while the red
cup-shaped fleshy part is formed from the outer integument of
the ovule. The so-called "aril" of the young ovule is a rudi-
mentary outer integument.
The fruit of the maidenhair tree (ginkgo) is about the size of
a plum and resembles very closely a stone-fruit. But it is merely
a ripened ovule, the outer layer becoming fleshy while the inner
layer becomes stony and forms the pit which encloses the em-
bryo and endosperm. The so-called "aril," or "collar," at the
base of the fruit is the rudimentary carpel, which sometimes is
more or less completely expanded into a true leaf. The fruit
of cycas is similar to that of ginkgo, but there is no collar at the
base. In zamia the fruit is more like a cone, the seeds being
formed, however, on the under sides of the scales.
VII. The "Fruit" of Ferns, Mosses, etc.
890. The term " fruit " is often applied in a general or popu-
lar sense to the groups of spore-producing bodies of ferns (jruit-
dots, or sori), the spore-capsules of mosses and liverworts, and
also to the fruit-bodies, or spore-bearing parts, of the fungi and
algae.
CHAPTER XLV.
SEED DISPERSAL
891. Means for dissemination of seeds. — During late summer or autumn
a walk in the woods or afield often convinces us of the perfection and variety
of means with which plants are provided for the dissemination of their
seeds, especially when we discover that several hundred seeds or fruits of
different plants are stealing a ride at our expense and annoyance. The hooks
and barbs on various seed-pods catch into the hairs of passing animals and
the seeds may thus be transported
considerable distances. Among the
plants familiar to us, which have such
contrivances for unlawfully gaining
transportation, are the beggar-ticks
or stick- tights, or sometimes called
Fig. 479.
Bur of bidens or bur-marigold, show-
ing barbed seeds.
Fig. 480.
Seed pod of tick-treefoil (desmodium) ; at the
right some of the hooks greatly magnified.
bur-marigold (bidens), the tick-treefoil (desmodium), or cockle-bur (xanthi-
um), and burdock (arctium).
892. Other plants like some of the sedges, etc., living on the margins of
streams and of lakes, have seeds which are provided with floats. The wind
or the flowing of the water transports them often to distant points.
458
SEED DISPERSAL.
459
893. Many plants pos ess attractive devices, and offer a substantial
reward, as a price for the distribution of their seeds. Fruits and berries are
devoured by birds and other animals ; the seeds within, often passing un-
harmed, may be carried long distances. Starchy and albuminous seeds and
Fig. 481.
Seeds of geum showing the booklets where the end of the style is kneed.
grains are also devoured, and while many such seeds are destroyed, others
are not injured, and finally are lodged in suitable places for growth, often
remote from the original locality. Thus animals willingly or unwillingly
become agents in the dissemination of plants over the earth. Man in the
development of commerce is often responsible for the wide distribution of
harmful as well as beneficial species.
894. Other plants are more independent, and mechanisms are employed
for violently ejecting seeds from the pod or fruit. The unequal tension of
the pods of the common vetch (Vicia sativa) when drying causes the valves
to contract unequally, and on a dry summer day the valves twist and pull in
opposite directions until they suddenly snap apart, and the seeds are thrown
forcibly for some distance. In the impatiens, or touch-me-not as it is better
known, when the pods are ripe, often the least touch, or a pinch, or jar, sets
the five valves free, they coil up suddenly, and the small seeds are thrown
for several yards in all directions. During autumn, on dry days, the pods
of the witch hazel contract unequally, and the valves are suddenly spread
apart, and the seeds are hurled away.
Other plants have seeds provided with tufts of pappus, or hair-like
masses, or wing-like outgrowths which serve to buoy them up as they
460
RELATION TO ENVIRONMENT.
are whirled along, often miles away In late spring or early summer
the pods of the willow burst open, exposing the seeds, each with a tuft
of white hairs making a mass of soft down. As the delicate hairs dry,
Fig. 482.
Touch-me-not (Impatiens fulva) ; side and front view of flower below ; above unopened
pod, and opening to scatter the seed.
they straighten out in a loose spreading tuft, which frees the individual seeds
from the compact mass. Here they are caught by currents of air and float
off singly or in small clouds.
895. The prickly lettuce. — In late summer or early autumn the seeds of
the prickly lettuce (Lactuca scariola) are caught up from the roadsides by
the winds, and carried to fields where they are unbidden as well as unwel-
come guests. This plant is shown in fig. 483.
896. The wild lettuce. — A related species, the wild lettuce (Lactuca cana-
densis) occurs on roadsides and in the borders of fields, and is about one
meter in height. The heads of small yellow or purple flowers are arranged
in a loose or branching panicle. The flowers are rather inconspicuous, the
rays projecting but little above the apex of the enveloping involucral bracts,
which closely press together, forming a flower-head more or less flask-
shaped.
At the time of flowering the involucral bracts spread somewhat at the
apex, and the tips of the flowers are a little more prominent. As the flowers
then wither, the bracts press closely together again and the head is closed.
As the seeds ripen the bracts die, and in drying bend outward and down-
ward, around the flower stem below, or they fall away. The seeds are
SEED DISPERSAL.
461
thus exposed. TJie dark brown achenes stand over the surface of the recep-
tacle, each one tipped with the long slender beak of the ovary. The "pap-
pus," which is so abundant in many of the plants belonging to the composite
family, forms here a
pencil-like tuft at the
tip of this long beak.
As the involucral bracts
dry and curve down-
ward, the pappus also
dries, and in doing so
bends downward and
stands outward, brist-
ling like the spokes of
a small wheel. It is an
interesting coincidence
that this takes place
simultaneously with
the pappus of all the
seeds of a head, so
that the ends of the
pappus bristles of ad-
joining seeds meet,
forming a many-sided
dome of a delicate and
beautiful texture. This
causes the beaks of the
achenes to be crowded
apart, and with the
leverage thus brought to
bear upon the achenes
they are pried off the
receptacle. They are
thus in a position to
be wafted away by the
gentlest zephyr, and
they go sailing away
on the wind like a
miniature parachute.
As they come slowly
to the ground the seed Fig- 483-
,. Lactuca scariola.
is thus carefully low-
ered first, so that it touches the ground in a position for the end which
contains the root of the embryo to come in contact with the soil.
RELATION TO ENVIRONMENT.
I
897. The milkweed, or silkwoed. — The common milkweed, or silkweed
(Asclepias cornuti), so abundant in rich grounds, is attractive net only
Fig. 484.
Milkweed (Asclepias cornuti) ; dissemination of seed.
because of the peculiar pendent flower clusters, but also for the beautiful
floats with which it sends its seeds skyward, during a puflfof wind, to finally
lodge on the earth.
898. The large boat-shaped, tapering pods, in late autumn, are packed
with oval, flattened, brownish seeds, which overlap each other in rows like
shingles on a roof. These make a pretty picture as the pod in drying splits
along the suture on the convex side, and exposes them to view. The silky
tufts of numerous long, delicate white hairs on the inner end of each seed,
in drying, bristle out, and thus lift the seeds out of their enclosure, where
they are caught by the breeze and borne away often to a great distance,
where they will germinate if conditions become favorable, and take their
places as contestants in the battle for existence.
899. The virgin's bower. — The virgin's bower (Clematis virgimana), too,
clambering over fence and shrub, makes a show of having transformed its
SEED DISPERSAL.
463
exquisite white flower clusters into grayish-white tufts, which scatter in the
autumn gusts into hundreds of arrow-headed, spiral plumes. The achenes
Fig. 485.
Seed distribution of virgin's bower (clematis).
have plumose styles, and the spiral form of the plume gives a curious twist
to the falling seed (fig. 485).
CHAPTER XLVI.
VEGETATION IN RELATION TO ENVIRONMENT.*
I. Factors Influencing Vegetation Types.
900. All plants are subject to the influence of environment
from the time the seed begins to germinate until the seed is
formed again, or until the plant ceases to live. A suitable amount
of warmth and moisture is necessary that the seed may germi
nate. Moisture may be present, but if it is too cold, germination
will not take place. So in all the processes of life there are
several conditions of the environment, or the "outside" of plants,
which must be favorable for successful growth and reproduction.
Not only is this true, but the surroundings of plants to a large
extent determine the kind of plants which can grow in particular
localities. It is also evident that the reaction of environment
on plants has in a large measure caused them to take on certain
forms and structures which fit them better to exist under local
conditions. In other cases where plants have varied by muta-
tion (p. 338) some of the new forms may be more suited to the
conditions of environment than others and they are more apt
to survive. These conditions of environment acting on the
plant are factors which have an important determining influence
on the existence, habitat, habit, and form of the plant. These
factors are sometimes spoken of as ecological /actors, and the
study of plants in this relation is sometimes spoken of as ecology, f
* For a fuller discussion of this subject by the author see Chapters XLVI-
LV1I of his "College Text-book of Botany" (Henry Holt & Co.).
f OIKO $ = house, and Xoyo 5 = discourse.
464
FACTORS INFLUENCING VEGETATION TYPES. 465
which means a study of plants in their home or a study of the
household relations of plants. These factors are of three sorts:
ist, physical factors; 2d, climatic factors; 3d, biotic factors.
901. Physical factors. — Some of these factors are water, light,
heat, wind, chemical or physical condition of the soil, etc. Water
is a very important factor for all plants. Even those growing on
land contain a large percentage of water, which we have seen is
rapidly lost by transpiration, and unless water is available for
root absorption the plant soon suffers, and aquatic plants are
injured very quickly by drying when taken from the water.
Excess of soil water is injurious to some plants. Light is impor-
tant in photosynthesis, in determining direction of growth as
well as in determining the formation of suitable leaves in most
plants, and has an influence in the structure of the leaf according
as the light may be strong, weak, etc. Heat has great influence
on plant growth and on the distribution of plants. The growth
period for most vegetation begins at 6° C. (=43°F.), or in the
tropics at io°-i2°C., but a much higher temperature is usually
necessary for reproduction. Some arctic algae, however, fruit
at i.8°C. The upper limit favorable for plants in general is
45°-5o° C., while the optimum temperature is below this. Very
high temperatures are injurious, and fatal to most plants, but
some algae grow in hot springs where the temperature reaches
8o°-90° C. Some desert plants are able to endure a temperature
of 70° C., while some flowering plants of other regions are killed
at 45° C. Some plants are specifically susceptible to cold, but
most plants which are injured by freezing suffer because the
freezing is a drying process of the protoplasm (see p. 374). Wind
may serve useful purposes in pollination and in aeration, but
severe winds injure plants by causing too rapid transpiration,
by felling trees, by breaking plant parts, by deforming trees and
shrubs, and by mechanical injuries from "sand-blast." Ground
covers protect plants in several ways. Snow during the winter
checks radiation of heat from the ground so that it does not
freeze to so great a depth, and this is very important for many
trees and shrubs. It also prevents alternate freezing and thaw-
466 RELATION TO ENVIRONMENT.
ing of the ground, which "heaves" some plants from the soil.
Leaves and other plant remains mulch the soil and check evapora-
tion of water. The influence of the chemical condition of the
soil is very marked in alkaline areas where the concentration
of salt in the soil permits a very limited range of species. So
the physical and mechanical conditions of the soil influence
plants because the moisture content of the ground is so closely
dependent on its physical condition. Rocky and gravelly soil,
other things being equal, is dry. Clay is more retentive of
moisture than sand, and moisture also varies according to the
per cent of humus mixed with it, the humus increasing the per-
centage of moisture retained.
902. Climatic factors. — These factors are operative over very
wide areas. There are two climatic factors: rainfall or atmos-
pheric moisture, and temperature. A very low annual rainfall
in warm or tropical countries causes a desert; an abundance of
rain permits the growth of forests; extreme cold prevents the
growth of forests and gives us the low vegetation of arctic and
alpine regions.
903. Biotic factors. — These are animals which act favorably
in pollination, seed distribution, or unfavorably in destroying or
injuring plants, and man himself is one of the great agencies
in checking the growth of some plants while favoring the growth
of others. Plants also react on themselves in a multitude of
ways for good or evil. Some are parasites on others; some in
symbiosis (see p. 85) aid in providing food; shade plants are
protected by those which overtop them; mushrooms and other
fungi disintegrate dead plants to make humus and finally plant
food; certain bacteria by nitrification prepare nitrates for the
higher plants (see p. 83).
II. Vegetation Types and Structures.
904. Responsive type of vegetation. — In studying vegetation
in relation to environment we are more concerned with the
form of the plants which fits them to exist under the local con-
VEGETATION TYPES AND STRUCTURES. 467
ditions than we are with the classification of plants according
to natural relationships. Plants may have the same vegetation
type, grow side by side, and still belong to very different floristic
types. For example, the cactus, yucca, three-leaved sumac,
the sage-brush, etc., have all the same general vegetation type
and thrive in desert regions. The red oaks, the elms, many
goldenrods, trillium, etc., have the same general vegetation type,
but represent very different floristic types. The latter plants
grow in regions with abundant rainfall throughout the year,
where the growing season is not very short and temperature
conditions are moderate. Some goldenrods grow in very sandy
soil which dries out quickly. These have fleshy or succulent
leaves for storing water, and while they are of the same floristic
type as goldenrods growing in other places, the vegetation type
is very different. The types of vegetation which fit plants for
growing in special regions or under special conditions, they have
taken on in response to the influence of the conditions of their envi-
ronment. While we find all gradations between the different types
of vegetation, looking at the vegetation in a broad way, several
types are recognized which were proposed by Warming as follows:
905. Mesophytes. — These are represented by land plants
under temperate or moderate climatic and soil conditions. The
normal land vegetation of our temperate region is composed
of mesophytes, that is. the plants have mesophytic structures
during the growing season. The deciduous forests or thickets
of trees and shrubs with their undergrowth, the meadows, pas-
tures, prairies, weeds, etc., are examples. In those portions
of the tropics where rainfall is great the vegetation is mesophytic
the year around.
906. Xerophytes. — These are plants which are provided with
structures which enable them to live under severe conditions
of dryness, where the air and soil are very dry, as in deserts or
semideserts, or where the soil is very dry or not retentive of
moisture, as in very sandy soil which is above ground water, or
in rocky areas. Since the plants cannot obtain much water
from the soil they must be provided with structures which will
468 RELATION TO ENVIRONMENT.
enable them to retain the small amount they can absorb from
the soil and give it off slowly. Otherwise they would dry out
by evaporation and die. Some of the structures which enable
xerophytic plants to withstand the conditions of dry climate
and soil are lessened leaf surface, increase in thickness of leaf,
increase in thickness of cuticle, deeply sunken stomates, compact
growth, also succulent leaves and stems, and in some cases loss
of the leaf. Evergreens of the north temperate and the arctic
regions are xerophytes.
907. Hydrophytes, — These are plants which grow in fresh
water or in very damp situations. The leaves of aerial
hydrophytes are very thin, have a thin cuticle, and lose water
easily, so that if the air becomes quite dry they are in danger of
drying up even though the roots may be supplied with an abun-
dance of water. The aquatic plants which are entirely submerged
have often thin leaves, or very finely divided or slender leaves,
since these are less liable to be torn by currents of water. The
stems are slender and especially lack strengthening tissue, since
the water buoys them up. Removed from the water they droop
of their own weight, and soon dry up. The stems and leaves
have large intercellular spaces filled with air which aids in aera-
tion and in the diffusion of gases. Some use the term hygrophytes.
908. Halophytes. — These are salt-loving plants. They grow
in salt water, or in salt marshes where the water is brackish,
or in soil which contains a high per cent of certain salts, for example
the alkaline soils of the West, especially in the so-called "Bad
Lands" of Dakota and Nebraska, and in alkaline soils of the
Southwest and California. These plants are able to withstand
a stronger concentration of salts in the water than other plants.
They are also found in soil about salt springs.
909. Tropophytes.* — Tropophytes are plants which can live as
mesophytes during the growing season, and then turn to a
xerophytic habit in the resting season. Deciduous trees and
shrubs, and perennial herbs of our temperate regions, are in
this sense tropophytes, while many are at the same time mesophytes
* Term used by Schimper.
PLANT FORMATIONS. 469
if they exist in the portions of the temperate region where rain-
fall is abundant. In the spring and summer they have broad
and comparatively thin leaves, transpiration goes on rapidly,
but there is an abundance of moisture in the soil, so that root
absorption quickly replaces the loss and the plant does not
suffer. In the autumn the trees shed their leaves, and in this
condition with the bare twigs they are able to stand the drying
effect of the cold and winds of the winter because transpiration
is now at a minimum, while root absorption is also at a minimum
because of the cold condition of the soil. Perennial herbs like
trillium, dentaria, the goldenrods, etc., turn to xerophytic habit
by the death of their aerial shoots, while the thick underground
shoot which is also protected by its subterranean habit carries
the plant through the winter.
910. While these different vegetation types are generally
dominant in certain climatic regions or under certain soil con-
ditions, they are not the exclusive vegetation types of the regions.
For example, in desert or semidesert regions the dominant
vegetation type is made up of xerophytes. But there is a
mesophytic flora even in deserts, which appears during the
rainy season where temperature conditions are favorable for
growth. This is sometimes spoken of as the rainy-season flora.
The plants are annuals and by formation of seed can tide over
the dry season. So in the region where mesophytes grow there
are xerophytes, examples being the evergreens like the pines,
spruces, rhododendrons; or succulent plants like the stonecrop,
the purslane, etc. Then among hydrophytes the semiaquatics
are really xerophytes. The roots are in water, and absorption
is slow because there are no root hairs, or but few, and the aerial
parts of the plant are xerophytic.
III. Plant Formations.
911. The term plant formation is applied to associations of
plants of the same kind, though there is a great difference in the
use of the word by different writers which leads to some con-
47° RELATION TO ENVIRONMENT.
fusion.* It is sometimes applied to an association of individuals
of a species, or of several species occupying a rather definite area
of ground where the soil conditions are not greatly different
(individual formation); by others it is applied to the plants of
a definite physiographic area, as a swamp, moor, strand, or
beach, bank, rock hill, clay hill, ravine, bluff, etc. (principal for-
mation) ; and in a broad sense it is applied to the plants of climatic
regions, of those in bodies of water, etc. (general formations).
Space here is too limited to discuss all these kinds of formations,
but the nature of the general formations will be pointed out.
The general formations may be grouped into four divisions:
i st. Climatic formations.
2d. Edaphic formations.
3d. Aquatic formations.
4th. Culture formations.
912. Climatic formations. — Climatic influences extend over
wide regions, so that climate controls the general type of vegeta-
tion of a region. In the sense of control there are two climatic
factors, temperature and moisture, especially soil moisture.
Temperature exerts a controlling influence over the vegetation
type only where the total heat during the period of growth and
reproduction is very low. This occurs in polar lands and at
high elevations where the climate is alpine. In the temperate
and tropical regions of the globe moisture, not heat, controls
the general vegetation type. These vegetation types in general
are coincident with rainfall distribution, and Schimper recognizes
here three types, which with the arctic-alpine type would make
four climatic formations as follows:
i st. The woodland formation. — This formation is characterized
by trees and shrubs, and it is what is called a close formation.
By this it is meant that so far as the climate is concerned the
conditions are favorable for the development of trees and shrubs
in such abundance that they become the dominant vegetation
type of the region and grow close together. Other plants, as
* See the author's "College Text-book of Botany." Chapter XLIX.
PLANT FORMATIONS. 471
herbs, grasses, etc., occur, but they grow as subordinate elements
of the general vegetation type, and as undergrowth. The
land portion of the globe, therefore, outside of arctic and alpine
regions, where the annual precipitation is 40 to 60 or more inches,
is the area for woodland formation. In some places, the
eastern part of England, for example, the annual precipitation
is 25 to 30 inches, but the cool temperature permits a forest
growth. It is true there are places where forests do not grow, —
where man cuts them down, for example. But if cultivated lands
in this region were allowed to go to waste, they would in time grow
up to forest again. So there are swamps where the soil is too
wet for trees, or sandy or rocky areas where there is not a suf-
ficient amount of soil or water to support forest trees. But
here it is the soil conditions, not climatic conditions, which pre-
vent the development of the forest. But we know that swamps
are being filled in and the ground gradually becoming higher
and drier, and that soil is slowly accumulating in rocky areas,
so that in time if left to natural forces these places would become
forested. So this area of heavy annual rainfall is a potential
forest area. These areas are determined by warm currents of
moisture-laden air from the ocean moving over cooler land areas
where the moisture is precipitated. In general these areas are
along the coasts of great continents and on mountains. There-
fore the interior of a continent is apt to be dry because most
of the moisture has been precipitated before it reaches the interior.
Deserts or steppes are therefore usually near the interior of
continents. Some exceptions to this general rule are found:
central South America, which is a region of exceptional rainfall
because the moisture-laden winds here come from the warmest
part of the ocean ; the desert region west of the Andes mountains,
where the winds are not favorable; southern California, where
the winds come chiefly from a cooler portion of the Pacific ocean
nnd move over an area of high temperature, etc.
2d. Grassland formation. — Grasses form the dominant vege-
lation type where the annual rainfall is approximately 15 to 25
inches. In true grasslands the formation is a dose one since
4/2 RELATION TO ENVIRONMENT.
there is still a sufficient amount of moisture to provide for all
the plants which can stand on the ground. Yet there is not
enough moisture to permit the growth of forest as the dominant
type without aid and protection by man. The so-called prairie
regions are examples. Trees and shrubs do occur, but they
cannot compete successfully with the grasses because the climatic
Fig. 486.
Typical prairie scene, a few miles west of Lincoln, Nebraska. (Bot. Dept., Univ.
Nebraska. )
conditions are favorable for the latter and unfavorable for the
former. On the border line between forest and prairie the line
of division is not a clear-cut one because conditions grade from
one to the other. The two formations are somewhat mixed,
like the outpos.ts of contending armies, arms of the forest or
prairie extending out here and there. In the United States the
prairies extend from Illinois to about the looth meridian, and
beyond this to the foothills of the Rockies and southwest to the
Sonora Nevada desert the region is drier, the rainfall varying
from 10 to 20 inches. This is the area of the Great Plains,
and while grasses of the bunch type are dominant, they make
PLANT FORMATIONS.
473
a more or less open formation because the moisture is not suf-
ficient to supply all the plants which could be crowded on the
ground, each individual tuft needing an area of ground surround-
ing it on which it can draw for moisture. Such a formation is
an open one, and in this respect is similar to desert formations.
3d. Desert formations. — These occur where the annual rain-
fall is still lower, 10 to 4 inches or even less, 2 to 3 inches, while
in one place in Chili it is as low as J inch. In the great Sahara
desert it is about 8 inches, while in the Sonora Nevada desert
Fig. 487.
Winter range in northwestern Nevada, showing open formation; white sage
(Eurotia lanata) in foreground, salt-bush (Atriplex confertifolia) and bud:sage
(Artemisia spinescens) at base of hill, red sage (Kochia americana) on the higher
slope. (After Griffiths, Bull. 38, Bureau Plant Ind., U. S. Dept. Agr.)
in the southwestern United States it is 4 to 8 inches. Here
the formation is an open one. In the forest and prairie forma-
tions the plants compete with each other for occupancy of the
ground, since climatic conditions are favorable, so that the struggle
against climate is not severe. But in the desert plants do not com-
pete with each other; since the climate is so austere, the struggle
is against the climate. Hence plants stand at some distance from
each other because the roots need the moisture from the ground
for some distance around them. There is not enough moisture
for all the plants that begin, and those which get the start take
474
RELATION TO ENVIRONMENT.
the moisture away from the intervening ones, which then die.
Since the struggle is against the adverse conditions of climate
and not a competition between plants to occupy the ground,
no one floristic type dominates as in the case of the grasses and
forests of the grassland and woodland formations, but grass-
land and woodland types grow together. So we find grasses,
trees, and shrubs growing without competition in the desert.
The dominant vegetation type is xerophytic.
4th. Arctic-alpine formation. This formation extends from
the limit of tree growth to the region of perpetual ice and snow.
Fig. 488.
Northern limit of tree growth, Alaska. (Copyright, 1899, by E. H. Harriman.)
The forest here comes in competition with climate, with the
severe cold of the long winter night, so that tree growth is limited,
and on the border line with the woodland formation the trees
are stunted, bent to one side by the heavy snows, or the tops are
killed by the cold wind. The arctic zone of plant growth is
sometimes spoken of as the "cold waste," since conditions here
are somewhat similar to those in the desert, the extreme cold
PLANT SOCIETIES. 475
exercising a drying effect on vegetation, and the vegetation type
then is largely xerophytic.
913. Edaphic * formations. — Edaphic formations may occur
in any of the climatic-formation areas. They are controlled by
the condition of soil or ground. The condition of the soil is
unfavorable for the growth of the general vegetation type of
that region, or is more favorable for another vegetation type, so
that soil conditions overcome the climatic conditions. These
areas include swamps, moors, the strand or beach, rocky areas,
etc., as well as oases in the desert, warm oases in the arctic zone,
river bottoms in the prairie and plains region, alkaline areas, etc.
The edaphic formations may be close or open according to the
nature of the soil. The edaphic formations then are infiltrated
in the climatic formations, the different vegetation types fitting
together like pieces of mosaic, which can be seen in some places
from a mountain top, or if one could take a bird's-eye view of
the landscape or from a balloon.
914. Aquatic formations. — These are made up of 'water
plants and are of two general kinds: fresh-water plant forma-
tions in ponds, lakes, streams; and salt-water plant formations
in the ocean and inland salt seas.
915. Culture formations. — Culture formations are largely
controlled by man, who destroys the climatic or edaphic forma-
tion and by cultivation protects cultivated types, or by allowing
land to go to "waste" permits the growth of weeds, though
weeds are often abundant in the culture areas. In general the
culture formations may be grouped into two subdivisions: ist, the
vegetation of cultivated places; and 2d, the vegetation of waste
places, as abandoned fields, roadsides, etc.
IV. Plant Societies.
916. Plant societies are somewhat definite associations of
the vegetation of an area marked by physiographic conditions.
A single plant society is nearly if not altogether identical with a
ground.
4/6 RELATION TO ENVIRONMENT.
" principal formation" but is a more popular expression, and
besides includes all the plants growing on the area, while in the
use of the term "principal formation" we have reference mainly
to the dominant plants and the most conspicuous subordinate
species.
917. Complex character of plant societies. — In their broadest
analysis all plant societies are complex. Every plant society
has one or several dominant species, the individuals of which,
because of their number and size, give it its peculiar character.
The society may be so nearly pure that it appears to consist of
the individuals of a single species. But even in those cases
there are small and conspicuous plants of other species which
occupy spaces between the dominant ones. Usually there are
several or more kinds in the same society. The larger individuals
come into competition for first place in regard to ground and
light, the smaUer ones come into competition for the intervening
spaces for shade, and so on down in the scale of size and shade
tolerance. Then climbing plants (lianas) and epiphytes (lichens,
algae, mosses, ferns, tree orchids, etc.) gain access to light and sup-
port by growing on other larger and stouter members of the society.
Parasites (dodder, mistletoes, rusts, smuts, mildews, bacteria,
etc.) are present, either actually or potentially, in all societies,
and in their methods of obtaining food sap the life and health
of their hosts. Then come the scavenger members, whose
work it is to clean house, as it were, the great army of saprophytic
fungi (molds, mushrooms, etc.), and bacteria ready to lay hold
on dead and dying leaves, branches, trunks, roots, etc., disin-
tegrate them, and reduce them to humus, where other fungi
change them into a form in which the larger members of the
plant society can utilize them as plant food and thus continue
the cycle of matter through life, death, decay, and into life again.
Mycorhiza (see Chapter IX) or other forms of mutualistic
symbiosis occur which make atmospheric nitrogen available for
food, or shorten the path from humus to available food, or the
humus plants feed on the humus directly. Nor should we
leave out of account the myriads of nitrate and nitrite bacteria
PLANT SOCIF.TfRS. 477
(see Chapter IX) which make certain substances in the soil avail-
able to the higher members of the society. Most plant societies
are also benefited or profoundly influenced in other ways by
animals, as the flower-visiting insects, birds which feed on
injurious insects, the worms which mellow up the soil and cover
dead organic matter so that it may more thoroughly decay. In
short, every plant society is a great cosmos like the universe
itself of which it is a part, where multitudinous forms, processes,
influences, evolutions, degenerations, and regenerations are at
work.
918. Forest Societies.* — Each different climatic belt or region
has its characteristic forest. For example, the forests of the
Hudsonian zone in North America are different from those of
the Canadian zone, and these in turn different from those in
the transition zone (mainly in northern United States). The
forests of the Rocky mountains and of the Pacific coast differ
from those of the Alleghanian, Carolinian (mainly middle United
States) or Austroriparian (southern United States) areas.
Finally, tropical forests are strikingly different from those of
other regions. Similar variations occur in the forests of other
regions of the globe. The character of these forests depends
largely on climatic factors. The character of the forest varies,
however, even in the same climatic area, dependent on soil
conditions, or success in seeding and ground-gaining of the
different species in competition, etc.
919. General structure of the forest. — Structurally the forest
possesses three subdivisions: the floor, the canopy, and the
interior. The floor is the surface soil, which holds the rootage
of the trees, with its covering of leaf-mold and carpet of leaves,
mosses, or other low, more or less compact vegetation. The
canopy is formed by the spreading foliage of the tree crowns,
which, in a forest of an even and regular stand, meet and form
a continuous mass of foliage through which some light filters
down into the interior. Where the stand is irregular, i.e., the
* For a full discussion of forest societies see Chapter L in the author's
"College Text-book of Botany."
478
RELATION- TO ENVIRONMENT.
trees of different heights, the canopy is said to be "compound"
or "storied." Where it is uneven, there are open places in
the canopy which admit more light, in which case the under-
growth may be different. The interior of the forest lies between
the canopy and the floor. It provides for aeration of the floor
and interior occupants, and also room for the boles or tree trunks
Fig. 489.
Mature forest of redwood (Sequoia sempervirens). (Bureau of Forestry U S.
Dept. Agr., Bull. 38.)
(called by foresters the wood mass of the forest) which support
the canopy and provide the channels for communication and
food exchange between the floor and canopy. The canopy
manufactures the carbohydrate food and assimilates the mineral
and proteid substances absorbed by the roots in the soil; and
also gets rid of the surplus water needed for conveying food
materials from the floor to the place where they are elaborated.
It is the seat where energy is created for work, and also the
place for seed production.
PLANT SOCIETIES. 479
920. Longevity of the forest. — The forest is capable of self-
perpetuation, and, except in case of unusual disaster or the action
of man, it should live indefinitely. As the old trees die they
are gradually replaced by younger ones. So while trees may
come and trees may go, the forest goes on forever.
921. Autumn colors. — One of the striking effects produced
by the deciduous forests is that of the autumn coloring of the
leaves. It is more pronounced in the forests of the United States
than in corresponding life zones in the eastern hemisphere because
of the greater number of species. With the disintegration of
the chlorophyll bodies, other colors, which in some cases were
masked by the green, appear. In other cases decomposition
products result in the formation of other colors, as red, scarlet,
yellow, brown, purple, maroon, etc., in different species. These
coloring substances to some extent are believed to protect the
nitrogenous substances in the leaf from injury. The colors
absorb the sun's rays, which otherwise might destroy these
nitrogenous substances before they have passed back through
the petiole of the leaf into the stem, where they may be stored
for food. The gorgeous display of color, then, which the leaves
of many trees and shrubs put on is one of the many useful adapta-
tions of the plants.
922. Importance of the forest in the disposal of rainfall. — The
importance of the forest in disposing of the rainfall is very great.
The great accumulation of humus on the forest floor holds back
the water both by absorption and by checking its flow, so that
it does not immediately flow quickly off the slopes into the drain-
age system of the valley. It percolates into the soil. Much
of it is held in the humus and soil. What is not retained thus
filters slow\y through the soil and is doled out more gradually
into the valley streams and mountain tributaries, so that the
flood period is extended, and its injury lessened or entirely pre-
vented, because the body of water moving at any one time is
not dangerously high. The winter snow is shaded and in the
spring melts slowly, and the spring freshets are thus lessened.
The action of the leaves and humus in retarding the flow of the
480 RELATION TO ENVIRONMENT.
water prevents the washing away of the soil; the roots of trees
bind the soil also and assist in holding it.
923. Absence of forest encourages serious floods. — The great
floods of the Mississippi and its tributaries are due to the rapidity
with which heavy rainfall flows from the rolling prairies of the
west, and from the deforested areas west of the Alleghany system.
The serious floods in recent years in some of the South Atlantic
States are in part due to the increasing area of deforestation in
the Blue Ridge and southern Alleghany system.
924. The prairie and plains societies. — These are to be found
in the grassland formation. In the prairies "meadows" are
formed in the lower ground near river courses where there is
greater moisture in soil. The grasses here are principally "sod-
formers" which have creeping underground stems which mat
together, forming a dense sod. On the higher and drier ground
the "bunch" grasses, like buffalo-grass, beard -grass, or broom-
sedge, etc., are dominant, and in the drier regions as one
approaches desert conditions the vegetation gradually takes on
more the character of the desert, so that in the plains sage-
brush, the prickly-pear cactus, etc., occur. Besides the dominant
vegetation of the society there are subordinate species, and the
societies are especially marked by a spring and autumn flora of
conspicuous flowering plants which are mixed with the grasses.
925. Desert societies. — These are composed of plants which
possess a form or structure which enables them to exist in a
very dry climate where the air is very dry and the soil contains
but little moisture. The true desert plants are perennial. The
growth and flowering period occurs during the rainy season, or
those portions of the rainy season when the temperature is favor-
able, and they rest during the very dry season and cold. Charac-
teristic desert plants are the cacti with thick succulent green
stems or massive trunks, the leaves being absent or reduced to
mere spines which no longer function in photosynthesis; yuccas
with thick, narrow and long leaves with a firm and thick cuticle;
small shrubs or herbs with compact rounded habit and small
thick gray leaves. All of these structures conserve moisture.
PLANT SOCIETIES.
481
The mesquite tree is one of the common trees in portions of the
Sonora Nevada desert. Besides the true desert plants, desert
societies have a rainy-season flora consisting of annuals, which
Fig. 490.
Desert vegetation, Arizona, showing large succulent trunks of cactus with shrubs
and stunted trees. Open formation. (Photograph by Tuomey.)
can germinate, vegetate, flower, and seed during the period of
rain and before the ground moisture has largely disappeared,
and these pass the resting period in seed.
926. Arctic-alpine societies. — The most striking of the arctic
plant societies are the "polar tundra," extensive mats of vegeta-
tion largely made up of mosses, lichens, etc., only partially
decayed because of the great cold of the subsoil, and perhaps
also because of humus acid in the partially decayed vegetation.
These tundras are brightened by numerous flowering plants
which are characterized by short stems, a rosette of leaves near
the ground, and by large bright-colored flowers. Heaths, saxi-
frages, and dwarf willow abound. Alpine-plant societies are
similar to the arctic, although some of the conditions are more
482 RELATION TO ENVIRONMENT.
severe than in the arctic region. This is principally due to the
Fig. 491.
Polar tundra with scattered flowers, Alaska. (Copyright by E. H. Harriman.)
fact that during the summer while the plants are growing they
Fig. 492.
Perennial rosette plant from alpine flora ot the Andes, showing short stem.
rosette of leaves, and large flower. (After Schimper.)
are subject to a high temperature during the day and a very low
PLANT SOCIETIES. 483
temperature at night, whereas during the summer in arctic regions
while the plants are growing there is continuous warmth for growth
and continuous light for photosynthesis. Five types of alpine
plants are recognized by some. ist. Elfin tree; This type has
short, gnarled, often horizontal stems, as seen in pines, birches,
and other trees growing in alpine heights. 2d. The alpine shrubs.
In the highest alpine belts they are dwarfed and creeping, richly
branched and spreading close to the ground, while at lower belts
they are more like lowland shrubs. 3d. The cushion type.
The branching is very profuse and the branches are short and
touch each other on all sides, forming compact masses (examples
saxifrages, androsace, mosses, etc.). 4th. Rosette plants. These
are perennial, short stems and very strong roots, and play an
important part in the alpine meadows. 5th. Alpine grasses.
These usually have much shorter leaves than grasses of the low-
lands and consequently form a low sward.
927. Edaphic plant societies. — These are equivalent to edaphic
plant formations, and the vegetation is of course controlled by
the peculiar conditions of the soil. There are a number of
different kinds of edaphic plant societies determined by the
character of the physiographic areas, ist. Sphagnum moors.
These are formed in shallow basins originally with more or less
water. The growth of the sphagnum moss along with other
vegetation and its partial decay in the water builds up ground
rapidly so that in course of time the pond may be completely
filled in. This filling in proceeds from the shore toward the
center, and in the early stages of course there would be a pond
in the center. The partial decay of vegetation creates an excess
of humus acid which retards absorption by the roots. The
conditions are such, then, as require aerial structures for retarding
the loss of water, and plants growing in such moors are usually
xerophytes. Some of the plants are identical with those growing
in the arctic tundra. 2d. Sand * strand of beach. The quantity
of sand with very little or no admixture of humus or plant food
makes it difficult for plants to obtain a sufficient amount of
* See Chapter LIV of the author's "College Text-book of Botany."
484 RELATION TO ENVIRONMENT.
water even where rainfall is abundant. The same may be said
of the sand dunes farther back from the shore. The plants
of these areas are then usually xerophytes. Some of the plants
accustomed to growing in such localities are American sea-rocket,
seaside spurge, bugseed, sea-blite, sea-purslane, the sand-
cherry, dwarf willow, marram-grass, certain species of beard-
grass, etc. 3d. Rocky shores or areas. Here lichens and mosses
first grow, later to be followed by herbs, grasses, shrubs, and
trees, as decayed plant remains accumulate in the rock crevices.
4th. Shores of ponds, or swamp moors. Here the vegetation
often takes on a zonal arrangement if the ground gradually
slopes to the shore and out into the pond. In Fig. 493 is shown
Fig. 493.
Macrophytes in the upper zone of the photic region. Ascophyllum and Fucus
t low tide, Hunter's Island, New York City. (Photograph by M. A. Howe.)
zonal distribution of plants. The different kinds of plants are
drawn into these zones by the varying amount of ground water
in the soil, or the varying depth of the water on the margin of
the pond as one proceeds from the land towards the deeper
water. On the border lines or tension lines between the different
zones the plants are struggling to occupy here ground which is
suitable for each adjacent individual formation. Other edaphic
societies are those of marl ponds, alkaline areas, oases in deserts,
PLANT SOCIETIES.
485
486 RELATION TO ENVIRONMENT.
warm oases in arctic lands, the forested areas along river bottoms
in prairie or plains regions, etc.
928. Aquatic plant societies — In general we might distinguish
three kinds, ist. Fresh-water plant societies, with floating algae
like spirogyra, cedogonium, etc., the floating duck-meats, riccias;
the plants of the lily type with roots and stems attached to the
bottom and leaves floating on the surface, like the water-lily
and certain pondweeds, and finally the completely submerged
ones like certain pondweeds, the bassweed (Chara), etc.
2d. Marine plant societies, which are made up mostly of the
red and brown algae or "seaweeds," though some green algae
and flowering plants also occur. 3d. The salt marshes where
the water is brackish and there is usually a luxuriant growth of
marsh-grasses.
CHAPTER XLVIL
CLASSIFICATION OF THE ANGIOSPERMS.
Relation of Species, Genus, Family, Order, etc.
929. Species. — It is not necessary for one to be a botanist in
order to recognize, during a stroll in the woods where the tril-
lium is flowering, that there are many individual plants very
like each other. They may vary in size, and the parts may
differ a little in form. When the flowers first open they are
usually white, and in age they generally become pinkish. In
some individuals they are pinkish when they first open. Even
with these variations, which are trifling in comparison with the
points of close agreement, we recognize the individuals to be of
the same kind, just as we recognize the corn plants, grown from
the seed of an ear of corn, as of the same kind. Individuals of
the same kind, in this sense, form a species. The white wake-
robin, then, is a species.
But there are other trilliums which differ greatly from this one.
The purple trillium (T. erectum) shown in fig. 495 is very different
from it. So are a number of others. But the purple trillium
is a species. It is made up of individuals variable, yet very like
one another, more so than any one of them is like the white
wake-robin.
930. Genus. — Yet if we study all parts of the plant, the
perennial root-stock, the annual shoot, and the parts of the
flower, we find a great resemblance. In this respect we find
that there are several species which possess the same general
characters. In other words, there is a relationship between
487
488
CLASSIFICATION OF ANGIOSPERMS.
these different species, a relationship which includes more than the
individuals of one kind. It includes several kinds. Obviously,
then, this is a relationship
with broader limits, and
of a higher grade, than
that of the individuals of
a species. The grade next
higher than species we
call genus. Trillium,
then, is a genus. Briefly
the characters of the genus
trillium are as follows:
931. Genus trillium. — Perianth of
six parts: sepals 3, herbaceous, per-
sistent; petals colored. Stamens 6 (in
two whorls), anthers opening inward.
Ovary 3-loculed, 3-6-angled; stig-
mas 3, slender, spreading.
Herbs with a stout per-
ennial rootstock, with ^^
fleshy, scale-like leaves,
from which the low annual
shoot arises, bearing a terminal flower and 3 large netted-veined
leaves in a whorl.
Note. — In speaking of the genus the present usage is to say
trillium, but two words are usually employed in speaking of the
species, as Trillium grandiflorum, T. erectum, etc.
932. Genus erythronium. — The yellow adder-tongue, or
dogtooth violet (Erythronium americanum), shown in fig. 496,
is quite different from any species of trillium. It differs more
from any of the species of trillium than they do from each
other. The perianth is of six parts, light yellow, often spotted
near the base. Stamens are 6. The ovary is obovate, tapering
at the base, 3-valved, seeds rather numerous, and the style is
elongated. The flower stem, or scape, arises from a scaly bulb
deep in the soil, and is sheathed by two elliptical-lanceolate,
Fig. 495.
Trillium erec-
tum (purple
form), two
plants from one
rootstock.
GENUS. FAMILY, ETC.
489
mottled leaves. The smaller plants have no flower and but
one leaf, while the
bulb is nearer the
surface. Each year
new bulbs are
formed at the end
of runners from a
parent bulb. These
runners penetrate
each year deeper
into the soil. The
deeper bulbs bear
the flower stems.
933. Genus lil-
ium. — While the
lily differs from
either the trillium
or erythronium, yet
we recognize a re-
lationship when we
compare the peri-
anth of six col-
ored parts, the 6
stamens, and the
3 -sided and long
3-loculed ovary.
934. Family Liliacese. — The relationship between genera, as
between trillium, erythronium, and lilium, brings us to a still
higher order of relationship, where the limits are broader than in
the genus. Genera which are thus related make up the family.
In the case of these genera the family has been named after the
lily, and is the lily family, or Liliacece.
935. Order, class, group. — In like manner the lily family,
the iris family, the amaryllis family, and others which show
characters of close relationship are united into an order which
has broader limits than the family. This order is the lily order,
Fig. 496.
Adder-tongue (erythronium). At left below pistil,_an(l
three stamens opposite three parts of the perianth,
at the right.
Bulb
490
CLASSIFICATION OF ANGIOSPERMS.
or order Liliales. The various orders unite to make up the class,
and the classes unite to form a group.
936. Variations in usage of the terms class, order, etc. —
Thus, according to the system of classification adopted by some,
the angiosperms form a group. The group angiosperms is then
divided into two classes, the monocotyledones and dicotyledones.
(It should be remembered that all systematists do not agree in
assigning the same grade and limits to the classes, subclasses,
etc. For example, some treat of the angiosperms as a class,
and the monocotyledons and dicotyledons as subclasses; while
others would divide the monocotyledons and dicotyledons into
classes, instead of treating each one as a class or as a subclass.
Systematists differ also in usage as to the termination .of the
ordinal name; for example, some use the word Liliales for Lilii-
florce, in writing of the order.)
937. Monocotyledones. — In the monocotyledons there is a
single cotyledon on the embryo; the leaves are parallel veined;
the parts of the flower are usually in threes; endosperm is usu-
ally present in the seed; the vascular bundles are usually closed,
and are scattered irregularly through the stem as shown by a
rm
Fig. 497.
A. Cross-section of the stem of an oak tree thirty-seven years old, showing the
annual rings. rm, the medullary rays; m, the pith (medulla). B. Cross-section
of the stem of a palm tree, showing the scattered bundles.
cross-section of the stem of a palm (fig. 497), or by the arrange-
ment of the bundles in the corn stem (fig. 57). Thus a single
character is not sufficient to show relationship in the class (nor
ORDER, CLASS, GROUP. 49 1
is it in orders, nor in many of the lower grades), but one must
use the sum of several important characters.
938. Dicotyledones. — In the dicotyledons there are two
cotyledons on the embryo; the venation of the leaves is reticu-
late ; the endosperm is usually absent in the seed ; the parts of the
flower are frequently in fives; the vascular bundles of the stem
are generally open and arranged in rings around the stem, as shown
in the cross-section of the oak (fig. 497). There are exceptions
to all the above characters, and the sum of the characters must
be considered, just as in the case of the monocotyledons.
939. Taxonomy. — This grouping of plants into species,
genera, families, etc., according to characters and relationships
is classification, or taxonomy.
To take Trillium grandiflorum for example, its position in
the system, if all the principal subdivisions should be included
in the outline, would be indicated as follows:
Group, Angiosperms.
Class, Monocotyledones.
Order, Liliales.
Family, Liliaceze.
Genus, Trillium.
Species, grandiflorum.
In the same way the position of the toothwort would be indi-
cated as follows:
Group, Angiosperms.
Class, Dicotyledones.
Order, Papaverales.
Family, Cruciferae.
Genus, Dentaria.
Species, diphylla.
But in giving the technical name of the plant only two of
these names are used, the genus and species, so that for the
toothwort we say Dentaria diphylla, and for the white wake-
robin we say Trillium grandiflorum.
940. Kingdom and Subkingdom. — Organic beings form alto-
gether two kingdoms, the Animal Kingdom and the Plant King-
492 CLASSIFICATION.
dom. The Plant Kingdom is then divided into a number of
subkingdoms as follows: ist, Subkingdom Thallophyta, the
thallus plants, including the Alga? and Fungi; 2d, Subkingdom
Bryophyta, the moss-like plants, including the Liverworts and
Mosses; 3d, Subkingdom Pteridophyta, the fern-like plants,
including Ferns, Lycopods, Equisetum, Isoetes, etc.; 4th, Sub-
kingdom Spermatophyta, the seed-plants, including Gymno-
sperms and Angiosperms. Subkingdoms are divided into groups
of lower order down to the classes. So there are subclasses,
subfamilies or tribes, subgenera, and even subspecies. But
taking the principal taxonomic divisions from the greater to the
lesser rank, the order would be as follows:
Plant Kingdom.
Subkingdom, Spermatophyta.
Group (not used in a definite sense).
Class, Gymnospermae.
Order, Finales.
Family, Pinaceae.
Genus, Pinus.
Species, strobus, or, in full,
Pinus strobus, the white pine.
Group Angiospermae.
I. CLASS MONOCOTYLEDONES.
941. Order Pandanales. — Aquatic or marsh plants. The
cattail flags (Typha) and the bur- reeds (Sparganium), each rep-
resenting a family. The name of the order is taken from
the tropical genus Pandanus (the screw-pine often grown in
green-houses).
942. Order Naiadales. — Aquatic or marsh herbs. Three
families are mentioned here.
The pondweed family (Naiadaceae) , named after one genus,
Naias. The largest genus is Potamogeton, the species of which
are known as pondweeds. Ruppia occidentalis occurs in
OKDEXS OF ANGIOSPERMS, 493
saline ponds in Nebraska, and R. maritima along the seacoast
and in saline districts in the interior.
The water-plantain family (Alismaceae) includes the water-
plantain (Alisma) and the arrow-leaves (Sagittaria).
The tape-grass family (Vallisneriaceae) includes the tape-grass,
or eel-grass (the curious Vallisneria spiralis).
943. Order Graminales. — Two families.
The grass family (Gramineae), the grasses and grains.
The sedge family (Cyperaceae), the sedges.
944. Order Palmales, with one family, Palmaceae, includes
the palms, abundant in the tropics and extending into Florida.
Cultivated in greenhouses.
945. Order Arales.
The arum family (Araceae). Flowers in a fleshy spadix. Ex-
amples: Indian turnip (Arisaema), sweet-flag (Acorus), skunk-
cabbage (Spathyema).
The duckweed family (Lemnaceae). (Examples: Lemna,
Spirodela, Wolffia. See paragraphs 51-53.)
946. Order Xyridales, from the genus Xyris, the yellow-
eyed grass family (Xyridaceae). Species mostly tropical, but
a few in North America. Other examples are the pipewort
family (Eriocaulaceae, example, Eriocaulon septangulare) , the
pineapple family (Bromeliaceae, example, the pineapple culti-
vated in Florida) ; the Florida moss or hanging moss (Tillandsia
usneoides); the spiderwort family (Commelinaceae), including
the spiderwort (Tradescantia, several species in North America) ;
the pickerel- weed family (Pontederiaceae), including the genus
Pontederia in borders of ponds and streams.
947. Order Liliales. — Some of the families are as fol-
lows :
The rush family (Juncaceae, example, Juncus), with many
species, plants of usually swamp habit.
The lily family (Liliaceae, examples: Lilium, Allium = Onion,
Erythronium, Yucca).
The iris family (Iridaceae, examples: Iris, the blue-flag,
fleur-de-lis, etc.).
494 ' CLASSIFICATION.
The lily-of-the- valley family (Convallariaceae, examples: lily-
of-the-valley, Trillium, etc.)
The amaryllis family (Amaryllidaceae, examples: Narcissus,
the daffodil; Cooperia, in southwestern United States).
948. Order Scitaminales. — This order includes the large
showy cultivated Canna of the canna family.
949. Order Orchidales. Example, the orchid family (Orchi-
daceae) with Cypripedium, Orchis, etc.
II. CLASS DICOTYLEDONES.
SERIES i. CHORIPETAL.E. Petals wanting (Apetalae, or
Archichlamydae of some authors), or present and distinct from
one another (Polypetalae, or Metachlamydae).
950. Order Casuarinales, confined to tropical seacoasts
(example, Casuarina).
951. Order Piperales includes the lizard's-tail family (Sau-
ruraceae), Saururus cernuus, lizard's-tail, in the eastern United
States.
952. Order Salicales. — Shrubs or trees, flowers in aments.
Includes the willows and poplars (Salix and Populus of the
willow family, Salicaceae.
953. Order Myricales. — Shrubs or small trees. Includes the
sweet-gale (Myrica gale) in wet places in northern United States
and British North America, Myrica cerifera forming thickets
on sand-dunes along the Atlantic coast, and the sweet-fern
(Comptonia peregrina = C. asplenifolia) in the eastern United
States in dry soil of hillsides.
954. Order Leitneriales. — Shrubs or trees. Includes the cork-
wood, Leitneria floridana (Leitneriaceae).
955. Order Juglandales. — Trees, staminate flowers in aments.
The walnut family (Juglandaceas, examples: walnut, butternut,
etc. Juglans; hickory, Hicoria = Carya.
956. Order Fagales. — Trees and shrubs. Flowers in aments,
or the pistillate ones with an involucre which forms a cup in
fruit, as in the acorn of the oak.
ORDERS OF ANGIOSPERMS. 495
The birch family (Betulaceae, examples: Betula, birch; Cory-
lus, hazelnut; Alnus, alder, etc.).
The beech family (Fagaceae = Cupuliferae, examples: Fagus,
beech; Castanea, chestnut; Quercus, oak.
957. Order TJrticales. — Trees, shrubs, or herbs. Examples:
the elm family (Ulmaceae), the mulberry family (Moraceae), and
the nettle family (Urticaceae).
958. Order Santalales, herbs or shrubs, mostly parasitic.
The mistletoe family (Loranthaceae) , with the American
mistletoe (Phoradendron flavescens), parasitic on deciduous
trees in the South Atlantic, Central, and Gulf States (N. J.
to Ind. Ter.).
The sandalwood family (Santalaceae, example, the bastard
toad-flax, Comandra umbellata), widely distributed in North
America.
959. Order Aristolochiales. — Herbs or vines with heart-
shaped or kidney-shaped leaves. The birthwort family (Aris-
tolochiaceae, example, Aristolochia serpentaria, the Virginia
snake-root, eastern United States; wild ginger, or heart-leaf,
Asarum canadense, eastern North America.)
960. Order Polygonales. — Examples: the buckwheat family
(Polygonaceae), including buckwheat (Fagopyrum), and numer-
ous species of Polygonum, known as smartweed, water-pepper,
tear-thumb, bindweed, knotweed, prince's-feather, etc.
961. Order Chenopodiales. — Herbs. There are several fam-
ilies; one of the largest is the goosefoot family (Chenopodiaceae).
The genus Chenopodium includes many species, known as goose-
foot, lamb's-quarters, etc. Here belong also the Russian thistle
(Salsola tragus) and the saltwort (S. kali). The former is some-
times a troublesome weed in the central and western United States,
naturalized from Europe. The latter occurs along the Atlantic
coast on seabeaches. Atriplex occurs in salty or alkaline soil,
also the glasswort (Salicornia herbacea), the bugseed (Cori-
spermum). The pokeweed family (Phytolaccaceae), the Amaranth
family (Amaranthaceae), the purslane family (Portulacaceae,
including the purslane or "pursley," Portulaca oleracea, and
496 CL A SSI PICA TION.
the spring-beauty, Claytonia virginica), and the pink family
(Caryophyllaceae) , belong here.
962. Order Ranales. — Herbs, shrubs, or trees. Examples are :
The water-lily family (Nymphaeaceae) , with the yellow water-lily
(Nymphaea advena = Nuphar ad vena) and the white water-lily
(Castalia odorata= Nymphaea odorata).
The magnolia family (Magnoliaceas), including the mag-
nolias (Magnolia) and the tulip-tree (Liriodendron). The crow-
foot family (Ranunculaceae) , with the buttercups, hepatica, clem-
atis, etc.
963. Order Papaverales. — Mostly herbs. Examples are:
The poppy family (Papaveraceas), including the opium or
garden poppy (Papaver somniferum), the blood-root (Sangui-
naria canadensis), the Dutchman's-breeches (Bicuculla cucul-
laria = Dicentra cucullaria), squirrel's-corn (Bicuculla canaden-
sis =D. canadensis).
The mustard family (Crucif era;) , including the toothwort
(Dentaria), shepherd 's-purse (Bursa bursa-pastoris = Capsella
bursa-pastoris, the cabbage, turnip, etc.
964. Order Sarraceniales. — Insectivorous plants.
The pitcher-plant family (Sarraceniaceae). Examples: Sarra-
cenia purpurea, the pitcher-plant, in peat-bogs, northern and
eastern North America.
The sundew family (Droseraceae) . Examples: Drosera rotun-
difolia, and other sundews.
965. Order Resales. — Herbs, shrubs or trees. Seventeen
families are given in the eastern United States. Examples:
The riverweed family (Podostemaceae), containing the river-
weed (Podostemon).
The saxifrage family (Saxifragaceae), containing a number of
species. Example, Saxifraga virginiensis.
The gooseberry family (Grossulariaceae), including the wild
and the cultivated gooseberry.
The witch-hazel family (Hamamelidaceae) , including the
witch-hazel (Hamamelis), in eastern North America, and the
sweet-gum (Liquidambar styraciflua).
ORDERS OF ANGIOSPERMS. 497
The plane-tree family (Platanaceae) , with the plane-tree, or
buttonwood (Platanus occidentalis), eastern North America.
(Other species occur in western United States.)
The rose family (Rosaceae), including roses, spiraeas, rasp-
berries, strawberries, the shrubby cinquefoil (Dasiphora fruti-
cosa), etc.
The apple family (Pomaceae), including the apple, mountain-
ash, pear, June-berry (or shadbush, also service-berry), the haw-
thorns (Crataegus).
The plum family (Drupaceae), including the cherries, plums,
peaches, etc.
The pea family (Papilionaceae) , including the pea, bean,
clover, vetch, lupine, etc., a very large family.
966. Order Geraniales. — Herbs, shrubs, or trees. Nine
families in the eastern United States. Examples:
The geranium family (Geraniaceae), with the cranesbill (Gera-
nium maculatum) and others.
The wood-sorrel family (Oxalidaceae), with the wood-sorrel
(Oxalis acetosella) and others.
The flax family (Linaceaa). Example, flax (Linum vul-
garis).
The spurge family (Euphorbiaceae). Plants with a milky
juice, and curious, degenerate flowers. Examples: the castor-
oil plant (Ricinus), the spurges (many species of Euphorbia).
967. Order Sapindales. — Mostly trees or shrubs. Twelve
families in the eastern United States. Example :
The sumac family ( Anacardiaceae) , containing the sumacs in
the genus Rhus. (Examples: the poison-ivy (R. radicans), a
climbing vine, in thickets and along fences, in eastern United
States. Sometimes trained over porches. The poison - oak
(R. toxicodendron), a low shrub. Poison-sumac or poison-alder
(R. vernix=R. venenata), sometimes called "thunderwood,"
or dogwood, is a large shrub or small tree, very poisonous. The
smoke-tree (Cotinus cotinoides) belongs to the same family, and
is often planted as an ornamental tree. The maple family (Ace-
raceae), including the maples (Acer).
498 CLASSIFICATION.
The buckeye family (Hippocastanaceae) , including the horse-
chestnut (^sculus hippocastanum), much planted as a shade
tree along streets. Also there are several species of buckeye in
the same genus.
The jewelweed family (Balsaminaceae) , including the touch-
me-not (Impatiens biflora and aurea) in moist places. The
garden balsam (Imp. balsamea) also belongs here.
968. Order Rhamnales. — Shrubs, vines, or small trees. There
are two families, the buckthorn (Rhamnaceae), the grape family
(Vitaceae), including the grapes (Vitis), the American ivy (Par-
thenocissus quinquefolia=Ampelopsis quinquefolia), in woods
and thickets, eastern North America, and much planted as a
trailer over porches. The Japanese ivy (P. tricuspidata=A.
veitchii) used as a trailer on the sides of buildings belongs
here.
969. Order Malvales. — Herbs, shrubs, or trees.
The linden family (Tiliaceae). Example, the basswood or
American linden (Tilia americana.)
The mallow family (Malvaceae), including the hollyhock, the
mallows, rose of Sharon (Hibiscus), etc.
970. Order Parietales, with seven families in the eastern
United States. The St.-John's-wort (Hypericum) and the vio-
lets each represent a family. The violets (Violaceas) are well-
known flowers.
971. Order Opuntiales. — These include the cacti (Cactaceae),
chiefly growing in the dry or desert regions of America.
972. Order Thymeleales, with two families and few
species.
973. Order Myrtales. — Land, marsh, or aquatic plants.
The most conspicuous are in the evening primrose family
(Onagraceae), including the fireweeds, or willow herbs (Epilobium),
and the evening primrose (Onagra biennis = (Enothera bien-
nis).
974. Order Umbellales. — Herbs, shrubs, or trees, flowers in
umbels.
The ginseng family (Araliaceae). This includes the spikenards
ORDERS OF ANGIOSPERMS. 499
and sarsaparillas in the genus Aralia, and the ginseng (or " sang"),
Panax quinquefolium.
The carrot family (Umbelliferae). This family includes the
wild carrot (Daucus carota), the poison-hemlock (Cicuta), the
cultivated carrot and parsnip, and a large number of other genera
and species.
The dogwood family (Cornaceae). The flowering dogwood
(Cornus florida), abundant in eastern North America, is an
example.
SERIES 2. GAMOPETAL^ ( = Sympetalae or Metachla-
mydae). Petals partly or wholly united, rarely separate or wanting.
975. Order Ericales. — There are six families in eastern
United States. Examples:
The wintergreen family (Pyrolaceae), including the shin-leaf
(Pyrola elliptica).
The Indian-pipe family (Monotropaceae), with the Indian-
pipe (Monotropa uniflora) and other humus saprophytes. (See
paragraphs 182-191.)
The heath family (Ericaceae). Examples: Labrador tea
(Ledum), in bogs and swamps in northern North America.
The azaleas, with several species widely distributed, are beauti-
ful flowering shrubs, and many varieties are cultivated. The
rhododendrons are larger with larger flower-clusters, also beau-
tiful flowering shrubs. R. maximum in the Alleghany Moun-
tains and vicinity, from Nova Scotia to Ohio and Georgia. R.
catawbiense, usually at somewhat higher elevations, Virginia
to Georgia. The mountain laurel (Kalmia latifolia) and
other species rival the rhododendrons and azaleas in beauty.
The trailing arbutus (Epigaea repens) in sandy or rocky woods is
a well-known small trailing shrub in eastern North America.
The sourwood (Oxydendrum arboreum) is a tree with white
racemes of flowers in August, and scarlet leaves in autumn.
The spring or creeping wintergreen (Gaultheria procumbens) is
a small shrub with aromatic leaves, and bright red spicy berries.
The huckleberry family (Vaccinaceae) includes the huckle-
berries (example, Gaylussacia resinosa, the black or high-
5 00 CLA SSIFICA TION.
bush huckleberry, eastern United States), the mountain cran-
berry (Vitis-Idaea vitisidaea=Vaccinium vitisidaea) in the north-
ern hemisphere; the bilberries and blueberries (of genus Vacci-
nium) ; the cranberries (examples : the large American cranberry,
Oxycoccus macrocarpus and the European cranberry, Oxycoc-
cus oxycoccus, in cold bogs of northern North America, the
latter also in Europe and Asia).
976. Order Primulales. — Two families here. The primrose
family (Primulaceae) contains the loosestrifes (Steironema), star-
flower (Trientalis), etc.
977. Order Ebenales.— Of the four families, the ebony fam-
ily (Ebenaceae) contains the well-known persimmon (Diospyros
virginiana) and the storax family (Styracaceae) with the silver-
bell, or snowdrop tree (Mohrodendron carolinum).
978. Order Gentianales.— Herbs, shrubs, vines, or trees.
Six families in the United States.
The olive family (Oleaceae) includes the common lilac (Syrin-
ga), the ash trees (Fraxinus), the privet (Ligustrum).
The gentian family (Gentianaceae) among other genera in-
cludes the gentians (Gentiana).
The milkweed family (Asclepiadaceae) contains plants mostly
with a milky juice. Asclepias with many species is one of the
most prominent genera.
979. Order Polemoniales. — Mostly herbs, rarely shrubs and
trees. Fifteen families in the eastern United States.
The morning-glory family (Convolvulaceae) includes the
bindweeds (Convolvulus), the morning-glory (Ipomaea), etc.
The dodder family (Cuscutaceae) includes the dodders, or
"love- vines." There are nearly thirty species in the United
States. The stems are slender and twine around other plants
upon which they are parasitic (see paragraph 179).
The phlox family (Polemoniaceae). The most prominent
genus is Phlox. Over forty species occur in North America.
The borage family (Boraginaceas) includes the heliotrope
(Heliotropium), the hound's-tongue (Cynoglossum), the forget-
me-not (Myosotis), and others.
ORDERS OF ANGIOSPERMS. 5OI
The vervain family (verbenaceae) contains the verbenas.
The mint family (Labiatae) contains the mints (Mentha), skull-
cap (Scutellaria), dead-nettles (Lamium).
The potato family (Solanaceae) includes the ground-cherry
(Physalis), the nightshades (Solanum), the tomato (Lycoper-
sicon), tobacco (Nicotiana).
The figwort family (Scrophulariaceae) includes the common
mullein (Verbascum), the monkey-flower (Mimulus), the toad-
flax (Linaria), turtle's-head (Chelone), and many other genera
and species.
The bladderwort family (Lentibulariaceae) includes the curi-
ous bog or aquatic plants with finely dissected leaves, and with
bladders in which insects are caught (Utricularia).
The trumpet-creeper family (Bignoniaceae) includes the trum-
pet-creeper (Bignonia), the catalpa tree, and others.
980. Order Plantaginales with one family (Plantaginaceae)
includes the plantains (Plantago).
981. Order Rubiales with three families is represented by
The madder family (Rubiaceae) with the bluets (Houstonia),
the button-bush (Cephalanthus), the partridge-berry (Mitchella),
the bedstraws (Galium), etc.
The honeysuckle family (Caprifoliaceae) with the elder (Sam-
bucus), the arrowwoods and cranberry trees (Viburnum), the
honeysuckles (Lonicera), etc.
982. Order Valerianales with two families includes
The teasel family (Dipsacaceae). Example, Fuller's teasel
(Dipsacus).
983. Order Campanulales with five families, the corolla
usually gamopetalous.
The gourd family (Cucurbitaceae) includes the pumpkin,
squash, melon, and a few feral species. Example, the star-
cucumber (Sicyos angulatus), in moist places in eastern and
middle United States.
The bell-flower family (Campanulaceae) includes the hare-
bells or bell-flowers (Campanula), the lobelias (example, Lobelia
cardinalis, the cardinal-flower), etc.
502 CLASSIF1CA TION.
The chicory family (Cichoriaceae) includes the chicory or
succory (Cichorium intybus, known also as blue-sailors), the
oyster-plant or salsify (Tragopogon porrif olius) , the dandelion
(Taraxacum taraxacum =T. densleonis), the lettuce (Lactuca),
the hawkweed (Hieraceum), and others.
The ragweed family (Ambrosiaceae) includes the ragweeds
(Ambrosia), the cockle-bur (Xanthium), and others.
The thistle family (Compositae) includes the thistle (Carduus),
asters (Aster), goldenrods (Solidago), sunflowers (Helianthus),
eupatoriums or joepye- weeds, thorough worts (Eupatorium),
cone-flowers or black-eyed Susans (Rudbeckia), tickseed (Core-
opsis), bur-marigold or beggar-ticks or devil's-bootjack (Bidens),
chrysanthemums, etc.
INDEX.
Absorption, 13, 22-28
Aceraceae, 497
Acorn, 451
Acorus, 493
^cidiomycetes, 218
^cidiospore, 189
^Esculus hippocastanum, 498
Agaricaceae, 199, 219
Agaricus arvensis, 206
Agaricus campestris, 200-207
Akene, 451
Albumen, 98
Albuminous, 98, 108
Alder, 495
Algae, 136-176
Algae, absorption by, 22
Alismaceae, 493
Alpine formation, 474
Alpine plant societies, 483
Amanita phalloides, 207, 208
Amaranth, 495
Amaryllidacese, 494
Aments, 429
American mistletoe, 495
Ampelopsis, 498
Ancylistales, 215
Andreales, 249
Andrcecium, 319, 419
Anemophilous, 435
Angiosperms, morphology of, 318-
348; classification, 487
Antheridiophore, 227
Antheridium, 144, 149, 155, 176, 223,
228, 240, 245, 246, 266, 287, 433
An thesis, 429
Anthoceros, 240, 241
Anthocerotales, 242
Anthocerotes, 242
Apogamy, 346
Apogeotropic (ap"o-ge"o-trop'ic) ,
126
Apogeotropism (ap"o-ge-ot'ropism),
126
Apple, 456, 497
Apple family, 497
Aquatic formations, 475
Aquatic plant societies, 486
Araceae, 493
Archegonia (ar-che-go'ni-a), 223,
229, 233, 241, 244-246, 267, 288,
29 *> 3°7, 3°8
Archegoniophore, 229
Archegonium, 433
Archesporium (ar"che-spo'ri-um),
235
Archidiales, 249
Arctic formation, 481
Aril, 457
Arisaema, 493
Arisaema triphyllum, 442, 443
Aristolochiales, 705
Arrow leaf, 492
Arum family, 493
Asclepias, 500
Asclepias cornuti, 462
Ascomycetes (as-co-my<e'tes), 195-
198, 216-218
Ascus, 190, 213
Ash of plants, 79, 80
Ash tree, 500
Aspidium acrostichoides, 253, 257
Assimilation, 67, 109
Aster, 502
Atriplex, 495
Auric ulariales, 218
Autotrophic plants, 85
Azalea, 499
Azolla, 296
Bacteria, 164, 165
Bacteria, nitrite and nitrate, 83
Bacteriales, 164, 165
5°3
504
INDEX.
Bacteroid, 93
Bangiales, 175
Basidiomycetes (ba-sid"i-o-my-ce'-
tes), 199—208, 218
Basidium, 201, 213
Bast, 50-52
Batrachospermum, 171-173, 175
Bazzania, 25
Beard-grasses, 480
Bedstraws, 501
Beechnut, 452
Beet, osmose in, 15, 16, 17, 18
Begonia, 407
BellfloWer, 501
Berry, 454, 455, 456
Betulaceae, 495
Bicuculla, 496
Bidens, 458
Bignonia, 501
Bilberries, 500
Biotic factors, 466
Birch, 495
Bird's-nest fungi, 220
Blackberry, 454
Black fungi, 198
Bladderwort, 501
Blasia, 164, 236
Bloodroot, 496
Bluets, 436, 437, 501
Boletus, 209
Boletus edulis, 209
Boraginaceae, 500
Botrychium, 295
Botrydiaceae, 162
Botrydium granulatum, 146, 162
Broom sedge, 480
Blown algae, 167-170
Bryales, 349
Buds, winter condition of, 374-
377
Buckeye family, 498
Buckthorn, 498
Buckwheat, 495
Buffalo-grass, 480
Bug seed, 495
Bulb, 372
Bunch-grasses, 480
Butternut, 452, 494
Buttonbush, 501
Buttonwood, 497
Cacti, 395, 498
Callithamnion, 173
Calyptrogen, 361
Cambium, 50, 52, 358, 363
Campanula rotundifolia, 442, 4/1
5io
Campanulales, 501
Canna, 445-449, 494
Capsella bursa-pastoris, 496
Capsule, 453
Carbohydrate, 71, 75, 80, 90
Carbon dioxide, 62-67, 110-113
Cardinal flower, 501
Carpogonium, 172, 176
Carrot family, 799
Caryophyllaceae, 496
Caryopsis, 451
Cassia marilandica, 402
Cassiope, 395
Castalia odorata, 496
Castor-oil plant, 497
Catalpa, 501
Catkin, 428
Cattail-flag, 492
Caulidium, 371
Cedar apples, 194
Cell, 3; artificial 30
Cell sap, 3, 40
Ceratopteris thalictroides, 296
Chaetophora, 151, 162
Chaetophoraceae, 162
Chara, 176
Charales, 176
Chemical condition of soil, 466
Chemosynthetic assimilation, 109
Chenopodiales, 495
Chenopods, 495
Chestnut, 452, 494
Chicory family, 502
Chlamydomonas, 159, 160
Chlamydospores, 180
Chloral hydrate, 65, 87
Chlorophyceae, 158
Chlorophyll, 2, 67, 72
Chloroplast, 68, 69, 71
Christmas fern, 25^1-253
Chromoplast, 71
Chromosomes, 342-345
Chroococcaceae, 163
Chrysanthemum, 502
Chytridiales, 215
Cichoriaceae, 502
Cichorium intybus, 502
Clavaria botrvtes, 212
Clavariaceae, 210, 219
Claytonia virginica, 496
Cleistogamous, 435
INDEX.
505
Clematis virginiana, 462, 463, 706
Climatic factors, 466
Climatic formations, 470
Clostridium pasteurianum, 93
Clover, 497
Club mosses, 284, 289
Coccogonales, 163
Cocklebur, 502
C old wastes, 474
Coleocluetaceffi, 162
Coleochffite, 153-156, 226
Collenchyma, 356, 363
Comandra, 495
Compass plants, 409
Compositae, 502
Comptonia asplenifolia, 494
Cone fruit, 456
Confervoideae, 162
Coniferae, 316
Conjugation, 137, 141, 160, 162,
179
Convallariaceae, 494
Cooperia, 494
Cordyceps, 218
Coreopsis, 502
Cork, 357, 363
Corm, 373
Cortex, 50
Corymb, 427
Cotyledon, 99-101
Cranberry, 500
Crataegus, 497
Crowfoot family, 496
Cruciferae, 496
Cryptonemiales, 175
Cucurbitaceae, 501
Culture formations, 470, 475
Cultures, water, 28, 29
Cup fungi, 109
Cupuliferae, 495
Cuscuta, 83, 500
Cushion type of vegetation, 483
Cuticle, 43
Cyanophyceae, 163
Cyatheaceae, 295
Cycadales, 316
Cycas, 311, 312, 457
Cyclosis, 9, 10
Cyclosporales, 171
Cyme, 430, 432
Cyperaceae, 493
Cypripedium, 443, 447, 494
Cystocarp, 174
Cystopteris bulbifera, 260
Cystopus, 215
Cytase, 92, 108
Cytisus, 445
Cytoplasm (cy'to-plasm), 5
Dacryomycetales, 219
Dahlia, 108
Dandelion, 502
Dasiphora fruticosa, 497
Daucus carota, 499
Dehiscence, 453
Dentaria, 322-324
Dentaria diphylla, 496
Dermatogen, 359
Desert formation, 473
Desert societies, 480
Desmodium, 458
Desmodium gyrans, 399
Diadelphous (di "a-del'phous),
425
Diageotropism (di"a-ge-ot'ro-pism),
126
Diahelio tropic (di"a-he"li-o-trop'-
ic), 127
Diaheliotropism (di"a-he"li-ot'ro-
pism), 127
Diastase, 77, 78, 108, 116
Diatoms, 166
Dichogamous (di-chog'a-mous), 437,
442
Dicentra, 496
Dicotyledons, 494
Dictyophora, 219
Diffusion, 13—20
Digestion, 107, 108, 109
Dimorphism of ferns, 273-280
Dicecious, 435
Dionasa muscipula, 133
Dipodascus, 216
Dipsacus, 501
Discomycetes, 217
Dodder, 83, 84, 500
Dogwood, 499
Dothicliales, 218
Downy mildews, 185
Drosera rotundifolia, 133, 496
Drupaceae, 497
Drupe, 454
Duckweeds, 26, 28
Dudresnaya, 175
Dunes, 484
Ebenales, 500
Ecological factors, 464
506
INDEX.
Ecology (sometimes Written .oecol-
ogy), 464
Ectocarpus, 167
Edaphic formations, 475
Elaphomyces, 217, 218
Elder, 501
Elm family, 495
Elodea, 61—63
Embryo of ferns, 269—272
Embryo sac, 326—328
Empusa, 215
Endocarp, 450
Endomyces, 216
Endosperm, 103, 105, 107, 306, 309;
nucleus, 327, 329-334
Entomophthorales, 215 ,
Enzyme, 92, 98, 116, 117
Epidermal system, 358
Epidermis, 358, 359, 363
Epigaea repens, 499
Epigynous, 425
Epilobium, 498
Epinastic (ep-i-nas'tic), 129
Epinasty (ep'i-nas-ty), 129
Epipactis, 444, 447
Epiphegus, 84
Epiphytes, 416
Equisetales, 296
Equisetineae, 296
Equisetum, 280-283
Ericaceae, 499
Ericales, 499
Erythronium, 493
Etiolated plants (e'ti-o-la"ted), 68
Euascomycetes, 217
Eubasidiomycetes, 219
Eupatorium, 403, 502
Euphorbiaceae, 497
Eurotium oryzae, 78
Evening primrose family, 498
Exalbuminous, 108
Exoascus, 217
Exobasidiales, 219
Exocarp, 450
Fagales, 494
Fehling's solution, 75, 76
Ferment, 98, 108, 116
Ferns, 251-279, 292, 457; classifica-
tion of, 295
Fertilization, 307, 308, 328, 329, 140,
145, 169, 172, 174, 197, 421
Fibrovascular bundles, 49-54
Figwort family, 501
Filicales, 295
Filicineae, 295
Fittonia, 404
Flagellates, 83, 165
Flax, 497
Flower cluster, 419
Flower, form of, 422; parts 0^419;
union of parts, 424
Flowers, arrangements of, 426;
kinds of, 421
Follicle, 453
Forest, formations 471; societies,
477
Forests, relation to rainfall, 479
Fresh-water societies, 486
Frond, 352
Fruit, 450-457; parts of, 450
Frullania, 25, 236
Fucus, 168-170
Fungi, absorption by, 22; classifica-
tion of, 213-222 ; nutrition of, 86-
90; respiration in, 115
Gametangium (gam"et-an'gi-um),
140
Gamete (gam'ete), 138, 139
Gametophore (gam'et-o-phore), 230,
248
Gametophyte (gam'et-o-phyte), 225,
226, 244, 245, 250, 262, 270, 283,
292, 294, 3°S» 314, 3i7» 336-339.
340-348, 434
Gamopetalous (gam"o-pet'a-lous),
424
Gamosepalous (gam-o-sep'a-lous),
424
Gas in plants, 60—64
Gasteromycetes, 219
Gemmae, 179, 235
General formations, 470
Gentian, 500
Geotropism (ge-ot'ro-pism), 125-
127, 410
Geraniaceae, 497
Geraniales, 497
Geranium family, 497
Germ, 459
Gigartinales, 175
Gingko, 313-315. 457
Gingkoales, 316
Ginseng, 499
Glasswort, 495
Gleicheniaceae, 295
Glucose, 108. See sugar.
INDEX.
Gne tales, 316
Gonidia, 118, 143, 172, 174, 178-
184
Gonidiangium (go"nid-an'gi-um),
178
Gonidium, 213
Gooseberry, 496
Goosefoot family, 495
Gracilaria, 173, 174, 175
Graminales, 492
Gramineae, 492
Grape, 498
Grass family, 492
Grassland formation, 471
Green algae, 158
Growth, 118-124, 380
Gulf weed, 170
Gymnosperms, 311, 456
Gymnosporangium, 194
Gyncecium, 320, 419, 451, 452
Gyrocephalus, 219
Halophytes, 468
Harpochytrium, 214, 215
Haustorium, 87, 88
Hawkweed, 502
Hawthorn, 497
Hazelnut, 452, 495
Head, 428
Heart leaf, 495
Heath family, 499
Heliotrope, 500
HeKotropism (he-li-ot'ro-pism),
127-131, 133, 397
Helvellales, 217
Hemiascomycetes, 216
Hemibasidiomycetes, 218
Hepaticae, 242
Heterospory (het"er-os'po-ry), 434
Heterothallic, 180
Heterotrophic plants, 85
Hickory, 494
Hickory nut, 452
Hilum, ioi, 102
Hippocastanaceae, 498
Holdfasts, 418
Hollyhock, 498
Homothallic, 180
Honeysuckle, 501
Hormogonales, 163
Horse-chestnut, 498
Horsetails, 280-283
Houstonia coerulea, 437
Huckleberry, 499
Humus saprophytes, 85, 91
Hybridization, 338
Hydnaceae, 210, 219
Hydnum coralloides, 210
Hydnum repandum, 211
Hydrocarbon, 75
Hydrodictyaceae, 161
Hydrophytes, 468
Hydropterales, 295
Hydrotropism (hy-drot'ro'pism),
133. 134, 412
Hygrophytes, 468
Hymeniales, 219
Hymenogastrales, 219
Hymenomycetes, 219
Hymenomycetineae, 219
Hymenophyllaceae, 295
Hypericum, 498
Hypocotyl (hy'po-co"tyl), ioi
Hypocreales, 217
Hypogenous, 425
Hyponastic (hy-po-nas'tic), 129
Hyponasty (hy'po-nas-ty), 129
Hysteriales, 217
Impatiens, 498
Impatiens fulva, 460
Indian-pipe, 499-
Indian-turnip, 493
Indusium, 252
Inflorescence, 426
Insectivorous plants, 133, 496
Integument, 304
Intramolecular respiration, 113, 114
Inulase, 108
Inulin, 108, 417
Iodine, 65
Ipomoea, 500
Iridaceas, 493
Iris, 493
Irritability, 125-135
Isoetales, 296
Isoetes, 289-291, 292
Isoetineae, 296
Ivy, 498
Jack-in-the-pulpit, 373
Jewelweed, 498
Juglandales, 494
June-berry, 497
Jungermanniales, 242
Kalmia latifolia, 444
Karyokinesis, 341-344
50$
INDEX.
Kelps, 1 68
Kingdom, 492
Labiatae, 423, 501
Laboulbeniales, 218
Labrador tea, 499
Lactuca canadensis, 460
Lactuca scariola, 409, 460, 461
Lagenidium, 214, 215
Laminaria, 168, 169
Lamium, 424, 501
Larch, 367
Laurel, 499
Leaf patterns, 404
Leathesia difformis, 168
Leaves, form and arrangement, 383-
391; function of, 3_8jj; protective
modifications of, 392; protective
positions," 395; reduction of sur-
face, 394; relation to light, 397;
structure of, 40-43. I3I. 39 r> 393
Legumes, 92, 93, 453
Leguminosae ( = Papilionaceae), 396,
399
Leitneria floridana, 494
Leitneriales, 494
Lemanea, 171, 173, 175, 492
Lemna, 418
Lemna trisulca, 26, 27
Lenticel, 357, 358
Lepiota naucina, 208
Lettuce, 502
Leucoplast, 71
Lichens, 86, 93-95, 220, 221
Light, 465
Liliaces, 490, 493
Liliales, 490, 493
Lilium, 489-493
Linaria vulgaris, 501
Linden, 498
Linum vulgaris, 497
Lipase, 108
Liquidambar, 496
Liriodendron, 496
Live-forever, 394
Liverworts, 222-239; absorption by,
23-25; classification of, 242
Lobelia, 501
Lupinus perennis, 353
Lycoperdales, 220
Lycopodiaceae, 296
Lycopodiales, 296
Lycopodiineae, 296
Lycopodium, 284-286
Macrosporangium, 94, 302, 304, 311.
312, 321
Macrospore, 287, 290, 326-328, 434
Magnolia, 496
Mallow family, 498
Malvales, 498
Maple family, 497
Marchantia, 24, 226-236
Marchantiales, 242
Marine plant societies, 486
Marratiales, 295
Marsilia, 370
Marsiliaceae, 296
Matoniaceae, 295
Medicago denticulata, 92
Medulla, 50
Members of the flower, 335
Members of the plant, 349—353
Meristem, 359
Mesocarp, 450
Mesophytes, 467
Microsporangia, 294, 299
Microspore, 287, 290, 299, 312,
435
Microsporophylls, 299, 320, 420
Milkweed family, 500
Mimosa, 132, 396
Mimulus, 501
Mint family, 501
Mistletoe, 84, 495
Mitchella, 501
Mixotrophic plants, 85
Mnium, 243-246
Molds, nutrition of, 86-90
Molds, water, 181
Monadelphous, 424
Monoblepharidales, 215
Monoblepharis, 215
Monocotyledons, 490, 492
Monoecious, 435
Monotropa uniflora, 499
Morchella, 198, 199
Morel, 198, 199
Morning-glories, 500
Mosaics, 405
Mosses, 243-248, 457; absorption
by, 25; classification of, 248
Mucor, 6, 7, 15, 118, 119, 177-180,
215
Mucorales, 215
Mulberry, 704
Mullein, 366, 394, 501
Mushrooms, 199-208
Mustard family, 496
INDEX.
509
Mutation, 338
Mutualism, 95
Mycelium, 6, 86-90
Mycetozoa, 213, 214
Mycorhiza, 86, 91, 92, 217
Myosotis, 500
Myrica cerifera, 494
Myrica gale, 494
Myricales, 494
Myriophyllum, 403
Myrtales, 498
Myxobacteriales, 165
Myxomycetes, 83, 213, 214
Naiadaceae, 492
Naiadales, 492
Naias, 492
Nemalion, 171, 172, 175
Nemalionales, 175
Nettle, 495
Nicotiana, 501
Nidulariales, 220
Nitella, 8, 9, 176
Nitrobacter, 83
Nitrogen, 92, 93
Nitromonas, 83
Nostocaceae, 164
Nucellus, 304
Nucleus, 3, 4; morphology of, 340-
345
Nuphar advena, 496
Nutation, 123, 124
Nymphaea odorata, 496
Oak, 495
Oak family, 495
CEdogoniaceae, 162
CEdogonium, 147—151, 350
CEnothera biennis, 498
(Enothera gigas, 338
CEnothera lamarkiana, 338"
Olpidium, 214, 215
Onagar biennis, 498
Onagraceae, 498
Onoclea sensibilis, 254, 273-278
Oogonium, 144, 150, 155
Oomycetes, 214, 215
Ophioglossales, 295
Ophioglossum, 295
Opuntiales, 498
Orchidaceae, 494
Orchidales, 494
Orchids, 442
Oscillatoriaceae, 163
Osmosis, 13-20
Osmundaceae, 295
Ostrich fern, 279
Ovule, 302, 321, 334, 421
Oxalis, 497
Oxycoccus, 500
Oxydendrum arboreum, 501
Oxygen, 63, 110-113
Palisade cells, 41, 43
Palmaceae, 493
Palmales, 493
Palms, 408
Pandanales, 492
Pandanus, 492
Pandorina, 160, 350
Panicle, 427
Papaverales, 496
Papilionaceae, 423, 497
Parasites, 83, 84, 86
Parasitic fungi, nutrition of, 86-90
Parenchyma, 50, 356, 363
Parietales, 498
Parkeriaceae, 296
Parmelia, 96
Parthenogenesis, 184
Partridge berry, 501
Pea, 497
Pea family, 497
Pear, 456
Pediastrum, 161
Pellia, 164
Pellonia, 405
Peltigcra, 94, 95
Pepp, 456
Pericycle, 360
Peridineae, 166
Perigynous, 425
Perisperm, 331, 332
Perisporiales, 217
Peronospora, 183, 215
Peronosporales, 215
Persimmon, 500
Pezizales, 217
Phacidiales, 217
Phaeophyceae, 167
Phaeosporales, 171
Phallales, 219
Phloem, 50-52, 360, 361, 363
Phlox family, 500
Phoradendron flavescens, 495
Photosynthesis, 67, 68, 70, 117
Phycomycetes (Phy"co-my-ce'tes)j
214, 215
5io
INDEX.
Phyllidium, 371
Phylloclades, 373, 395
Phyllotaxy, 375, 384
Physical condition of soil, 465
Physical factors, 465
Phytolaccaceae, 495
Phytomyxa leguminosarum, 92
Phytophthora, 182, 184, 215
Pickerel weed, 493
Pilularia, 296
Finales, 216
Pine, white, 297-310
Piperales, 494
Pitcher-plant, 496
Pith, 50
Plant-food, sources of, 81
Plant-formations, 496
Plant-substance, analysis of, 79,
80
Plantaginales, 501
Plantago, 501
Plasmolysis (plas-mol'y-sis), 19
Plasmopara, 183, 215
Plectascales, 217
Plectobasidiales, 220
Pleurococcaceae, 161
Pleurococcus, 161
Plum family, 497
Plumule, 99
Podostemon, 496
Poison-hemlock, 499
Poison-ivy, 497
Poison-oak, 497
Poisonous mushrooms, 207, 208
Poison-sumac, 497
Pokeweed, 495
Polemoneales, 500
Pollen-grain, 299, 305
Pollination, 303, 304, 420, 430, 433-
449
Pollinium, 420
Polygonales, 495
Polygonum, 495
Polypodiaceae, 296
Polyporaceae, 209, 219
Polyporus, 209, 210
Polyporus mollis, 92
Polyporus sulphureus, 209
Pomaceae, 497"
Pondweeds, 492
Poppy, 496
Porella, 237
Portulaca, 495
Potamogeton, 492
Potato, 501
Powdery mildews, 195-198, 217
Primrose, 498, 500
Primula, 438
Primulales, 500
Procarp, 172, 174, 175
Progeotropism (pro"ge-ot'ro-pism),
126
Promycelium (pro"my-ce'li-um), 192
Proterandrous, 441, 442
Proterandry, 444
Proterogenous, 441, 442
Proterogeny, 440
Prothallium, 265, 287, 288, 291, 292,
304, 3°5» 3", 325> 328, 335. 433.
434
Protoascales, 216
Protoascomycetes, 216
Protobasidiomycetes, 218
Protococcoideae, 158, 621
Protodiscales, 217
Protomyces, 216
Protonema (pro"to-ne'ma), 248, 264
Protoplasm, 1-12, 42-43, 342; move-
ment of, 7-1 1
Psilotaceae, 296
Pteridophytes, 295, 434
Pteris cretica, 346
Puccinia, 187
Puff-balls, 220
Pumpkin, 501
Purslane, 495
Pyrenoid, 2, 3
Pyrenomycetes, 217
Pyrola, 499
Pyxidium, 453
Quercus, 495
Quillworts, 289-291
Quince, 456
Raceme, 427
Radicle, 99
Ragweed, 502
Rainy-season flora, 481
Ranales, 496
Ranunculaceae, 496
Raspberry, 454, 455
Red algae, 171, 628; uses of, 175
Reproduction, 137, 143, 149, 154,
155, 179, 185, 186
Respiration, 110-116, 117
Rhamnales, 498
Rhizoids, 24-26
INDEX.
Rhizome, 354
Rhizomorph (rhi'zo-morph), 89
Rhizophidium, 214, 215
Rhizopus, 177-180, 215
Rhododendron, 499
Rhodomeniales, 175
Rhodophyceae, 171
Rhus radicans, 416, 497
Riccia, 23, 164, 222-226
Ricinus, 497
Riverweed, 496
Root, function of, 410-418
Root-hairs, absorption by, 19, 30,
32
Root-hairs, action on soil, 82
Root pressure, 33, 34, 45
Root, structure of, 30, 361 362
Root tubercles, 92
Roots, kinds of, 415
Rosaceae, 497
Resales, 496
Rose family, 497
Rosette, 405
Rosette plants, 483
Rubiales, 501
Rudbeckia, 502
Rusts, 187-194
Salicaceae, 494
Salix, 494
Salsify, 502
Salviniaceae, 296
Samara, 451
Sandalwood, 495
Sanguinaria, 496
Santalales, 495
Sap, rise of, 53, 54
Sapindales, 497
Saprolegnia, 181-184
Saprolegniales, 215
Saprophytes, 83-85
Sargassum, 170
Sarraceniales, 496
Sarsaparilla, 499
Saxifrage, 496
Schizaeaceae, 295
Schizocarp, 451
Schizomycetes, 164
Schizophyceae, 163
Sclerenchyma, 356-357, 361, 363
Scouring-rush, 282
Screw-pine, 409, 492
Scrophulariaceae, 501
Sedge family, 492
Seed, dispersal of, 458-463
Seed plants, 338
Seed, s'ructure of, 98, 102
Seedlings, 97-107
Seeds, 330-334
Selaginella, 286-288, 292
Selaginellaceae, 296
Sensitive fern, 273
Sensitive plants, 132, 396, 399
Sexual organs, 144, 147
Shadbush, 497
Shepherd's-purse, 496
Shoot, floral, 419, 432
Shoots, 353-355; types of, 365-
373; winter condition of, 374-
377
Sieve tissue, 358, 363
Sieve tubes, 52, 53
Silique, 453
Silk -cotton tree, 417
Silver bell, 500
Siphoneas, 146, 162
Skunk's cabbage, 439-442
Slime molds, 83
Smoke- ree, 497
Societies, 475
Solanum, 501
Solidago, 502
Sourwood, 499
Spadix, 428
Spartium, 446
Spathyema fcetida, 438, 493
Spermagonia, 190
Spermatophytes, 338
Sphacelaria, 168
Sphaerella lacustris, 158, 159
Sphaerella nivalis, 158, 350
Sphaeriales, 218
Sphagnales, 248
Sphagnum, 164
Spiderwort, u, 493
Spike, 428
Spirodela polyrhiza, 27
Spirogyra, 1-5, 13, 14, 60, 72, 136-
140, 35°
Sporangia, 178-182
Sporangium, 253-258, 281, 290
Spores, 225, 256-258, 263, 264,
281
Sporocarp, 173
Sporogonium (spo"ro-go'ni-um),
224, 231, 233, 234, 237, 238, 239,
241, 246, 247, 248
Sporophyll, 274, 281, 292
512
INDEX.
Sporophyte (spo'ro-phyte), 225, 226,
232, 234, 237-239, 241, 242, 250,
261, 268, 270, 283, 292, 294, 314,
3J5> 31?, 336-339, 340-348 434
Spurge family, 497
Squash, 501
Staminodium, 446
Starch, formation of, 68, 70-74;
changed to sugar, 77, 78; translo-
cation of, 73; digestion of, 75
Stems, types of, 365-373
Stems, woody, structure of, 381-382
Stoma (pi. stomata) (sto'ma-ta), 42-
44, 46
Strawberry, 455, 497
Sugar, test for, 75, 76
? imac, 497
Sundew, 133, 496
Sunflower, 399-401, 502
Sweet gum, 496
Symbiosis, 85, 86, 92-95
Synergids (syn'er-gids), 327, 330
Syngencesious, 424
Synthetic assimilation, 67
Tape-grass, 493
Taraxacum densleonis, 502
Teasel, 501
Telegraph-plant, 399
Teleutospore, 188
Temperature, 134, 135, 465
Tetrasporacese, 161
Tetraspores, 173, 174
Thallophytes, 352
Thallus, 352
Thelephoracese, 219
Thistle family, 502
Thunderwood, 497
Thyrsus, 427
Tilia, 498
Tillandsia, 493
Tissue, tensions of, 57-59
Tissues, classification of, 363, 364;
kinds of, 356-359; organization
of, 356-362
Toad-flax, 501
Tomato, 501
Tradescantia, 493
Tragopogon, 502
Trailing arbutus, 499
Trametes pini, 90
Transpiration, 35-46
Tremellales, 218, 219
Triadelphous, 425
Trillium, 318-322, 494
Trumpet-creeper, 501
Tuberales, 217
Tubers, 373
Tundra, 481
Turgescence, 14, 15
Turgor, 20; restoration of, 56, 57
Typha, 493
Ulmacese, 495
Ulmus americana, 495
Ulothrix, 162
Ulotrichaceae, 162
Ulvaceae, 162
Umbel, 428
Umbellales, 498
Uredinales, 218
Uredineae, 187-194, 218
Uredospore, 189
Uromyces caryophyllinus, 87
Urticales, 495
Ustilaginales, 218
Ustilagineae, 218
Utricularia, 501
Vaccinium, 499
Vacuoles, 7, 8
Valerianales, 501
Vallisneria spiralis, 493
Variation, 338
Vascular tissue, 358, 363
Vaucheria, 142-146
Vaucheriaceae, 162
Vegetation types, 464
Venus' flytrap, 133
Verbascum, 501
Verbena, 501
Vessels, 52, 53
Vetch, 92, 497
Viburnum, 501
Vicia sativa, 459
Viola cucullata, 436
Violaceae, 498
Virgin's-bower, 462, 463
Viscum album, 84
Vitaceae, 498
Volvocaceae, 158
Walnut, 452, 494
Water, 465 ; flow of, in plants, 53, 54
Water-lilies, 496
Water-plantain, 493
White pine, 396
Wild carrot, 499
INDEX.
5'3
Willow family, 494
Wind, 471
Wintergreen, 499; leaf of, .43
Witch-hazel, 496
Wolffia, 28
Woodland formation, 470
Xerophytes, 467
Xylem/50, 52, 360, 361, 363
Xylogen, 92
Xyridales, 493
Yeast, 216; fermentation of, 115,
116
Yucca, 480, 493
Zamia, 313, 316, 457
Zoogonidia, 143, 149, 178-184
Zoospore, 149, 154
Zygomycetes, 215
Zygospore, 2, 138-140, 157, 160, 179,
180
Zygote (zy'gote), 138, 179
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