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LIVING PLANTS AND THEIR

PROPERTIES

PLANT OF WILD LETTUCE

The left hand figure as seen from the east, the other figure as
seen from the south, showing the compass-like habit of adajust-
ing the leaves in the meridional plane.

OB iure a

NEW YorRK
BOTANICAL

x

SARDEN:

LIVING PLANTS AND THEIR
PROPERTIES

A COLLECTION OF ESSAYS

BY:

JOSEPH CHARLES ARTIIUR Sc. D.
PROFESSOR OF VEGETABLE PHYSIOLOGY AND PATHOLOGY

IN PURDUE UNIVERSITY

DANIEL TREMBLY MAC DOUGAL PH. D.

ASSISTANT PROFESSOR OF BOTANY IN CHARGE OF PLANT
PHYSIOLOGY IN THE UNIVERSITY OF MINNESOTA

NEW YORK
BAKER AND TAYLOR
MINNEAPOLIS: MORRIS AND WILSON
1898

OAKS |
AT

COPYRIGHT BY
J.C. ARTHUR AND D. T. MAC DOUGAL
1898

UNIVERSITY PRESS OF MINNESOTA
MINNEAPOLIS

PREFACE

The essays comprised in this book are selected from
popular addresses and articles presented by the authors
within the last five years. The unequal conditions of
the original preparation have made it necessary to revise
and rewrite certain articles in order to meet the require-
ments of their juxtaposed position. The occasion has
been seized to omit portions less relevant in the present
connection, and to amplify others to meet the demands
of continuity, clearness, and harmony with current bo-
tanical thought. The original presentation of each sub-
ject is denoted by a foot-note under the title. The au-
thors are separately responsible for the chapters to
which their names are signed in the table of contents.

The publication of this volume, it is believed, is justi-
fied by the appreciation accorded the essays, upon
their first appearance; and it is the hope of the authors
that it may stimulate an interest in the phases of botany
covered, both among general readers and also among
workers in the co-ordinate branches of animal biology.

March, 1898. THE AUTHORS.

TABLE OF CONTENTS

I. THE SPECIAL SENSES OF PLANTS, J. C. ARTHUR..... 1
Eighteenth century opinions—Application of terms—
Knowledge of mechanism—Primary unity with great di-
versity—What constitute special senses—Sense of con-
tact—Trend of sense development—Free and fixed organ-
isms-——Discovery of gravity sense—Movement connected
with growth—Transmission of impulses—Sensitiveness
to light—Chemical sense—Moisture sense.

Il. THE DEVELOPMENT OF IRRITABILITY, D. T. Mac-

JL) [0 y 6 Dime I eed oe Ebene ek eae pices vuntivacbwumeues a LS)
Derivation of existing forms—Chlorophyll and sunlight—
Pollination—Organization of shoot—Distribution of nu-
tritive factors—Sensory and motor zones—Development
of root functions—Nutritive factors in soil—Organization
of roots.

III. Witp Lerrucr as WEED AND Compass Piant, J.

C: AB THER... 1¢caxscnciess sainappaclehes sabcguiti sais Uactts! WO:
Likeness to cultivated lettuce—General characters and
habit—First appearancein America—Fifteen years of con-
quest—Seeds and their distribution—How to be asuccess-
ful weed—Even a weed may be interesting—The habit of
poiarity—Another compass plant—Explanation of the
peculiar trait.

Viii LIVING PLANTS

IV. Mimosa: A Typical SENSITIVE PLant, D. T. Mac-

PQ G AT isis acts cancscsscensepseasremieasessaeehei tae 47
Uses of movement—Power of movement—Characteristics
of mimosa—Organization—Day position of leaves—Night
position of Leaves—Reaction to shock, ete.—Transmis-
sion of stimuli—Repetition of stimuli—Methods of trans-
mission—Purpose of reaction to shock.

V. UNIVERSALITY OF CONSCIOUSNESS AND Pain, J. C.

AUDI: svc cnect Svisse se nad ieascedimenccdmasbanpes Speen sueane 63
Unity in nature—Superstition of the mandrake—Can
a mandrake feel—Meaning of consciousness—Examiples
of consciousness—Definition of terms—General irritabil-
ity—Welfare of the organism—Adaptive movements im-
ply consciousness—Pain a factor in evolution—Action of
plants difficult to interpret—Plants not degenerates.

VI. How Coin AFFEcTs Piants, D.T. MacDouGat. 85
Varying reaction to cold—Appearance of frozen plants—
Ice in the tissues—Relation of cell to cold—Relation of
organism to cold—Death above freezing point—Adapta-
tions against cold.

VII. Two Opposinc Factors OF INCREASE, J. C. AR-

BIER ce dean Jn peas denser escape sisissipa se qonaseaeekey eaaeeeeeaeen 59
Two sides to plants—Nutrition and development—Effect
of soil fertility— Provision for perpetuity—Size of seeds—
Early growth—Final yield—Superiority of large seeds—
Vegetative and fruiting parts compared—External and
internal factors.

VIII. CHLOROPHYLL AND GrowTH, D.T. MacDovuGat. 121
Historical—Methods of experimentation—Growth inthe
absence of carbon dioxide—Effect of darkness—Total re-
sults with Arisema—Results with Calla—Results with
Zea—Results with Phoenix—Ordinary course of growth
—Growth with insufficient nutrition—Conclusions

IX. LEAVES IN SPRING, SUMMER, AND AUTUMN, D. T.

BV AC DOUG AU asec seccnnseeesscsceses ansencdcasnscopeeeeee eee 145
Importance of chlorophyll—Properties of chlorophyll—
Varying tints—Synthesis of food—Acquisition of chloro-
phyil—Autumnal leaf-fall—Withdrawal of leaf-substance
—Color as a protecting screen—Separation layer—Ever-
green leaves.

CONTENTS “ix

X. THE SIGNIFICANCE OF CoLor, D.T. MacDouGav..165
Early views—Sprengel’s discoveries—Ecological consider-
ations—Enumeration of colors—Chlorophyll—Etiolin—
The lipochromes—Anthocyans—Relation of anthocyan
to light—The screen theory—Promotion of metabolism
—Promotion of transpiration—Red seaweeds—Mark-
ings not due to color—Silvery areas—Velvety surfaces
—Conclusions.

XI. THE RIGHT TO LIVE, J. C. ARTHUR...... asacexuendocees 193
Aggressiveness of plants—Likeness of plants and animals
—Possible rate of increase—Weeds as examples—Prolifi-
eacy of other plants—lIllustrative similes—A world of
strife—Destruction of life for a dinner—Natural right to
food—Logic of good fortune—Object of living—Death not
essential to life—Plants are born to live—Right to life
should be respected.

XII. DISTINCTION BETWEEN PLANTS AND ANIMALS,
| © SRR sadeaxcebee poche fhetaniienseecnenae 209

Learned vagaries—Ancient opinions—M odern opinions—
Anintermediate kingdom—Blending of the two kingdoms—
Characters from structure and function—Various physio-
logical distinctions—The most universal structures—
Characters to be taken from the active organism—Repro-
ductive states to be ignored—Animals and plants defined
—Chemical features of cell walls—Physical features of
cell walls—The test applied.

STE: = ERDEX TOCP ANT NABEES? .iseccoesSecakss scence nu enseuce 229

|

THE SPECIAL SENSES OF PLANTS.*

Aside from the tales of travelers, the varied
plant myths, and the inventions of story
writers, there have been fancies and beliefs
held by learned men in past ages, which in-
vested plants with specific powers differing
from those of animals only in clearness of
manifestation. Not until the middle of the
present century, however, did the commonly
observed movements of plants receive any
genuine interpretation. Aristotle and his fol-
lowers to the time of Cesalpino (1583),
vaguely ascribed a soul to plants which di-
rected their vital operations and distinguished
them from lifeless nature. Jung, a contem-
porary of Kepler, Galileo and Descartes, who
dominated botanical thought in Germany
during the seventeenth century, expressed his

*Condensed from a presidential address before the Indiana
Academy of Sciences, December 27, 1893.

Eighteenth
century
opinions

2 LIVING PLANTS

view in the sentence: ‘‘Planta est corpus viv-
ens non sentiens.’’ A hundred years later
Linneus gave his famous definition of the
three kingdoms of nature: ‘‘Minerals grow,
plants grow and live, animals grow, live and
feel.’ These great leaders of scientific thought
inclined to deny sentience to plants as a mat-
ter of definition, but did not wholly discoun-
tenance some of the vagaries of their predeces-
sors.

At the beginning of the present century gen-
eral students of plant life were inclined to
admit greater range of the plant’s powers.
Sir J. E. Smith, in his “Introduction to
Botany,” a work which met with such favor
as to pass through seven editions within
twenty-six years, has voiced the uncertainty
of the period regarding the plant’s status in
the form of a query: ‘‘As they possess Uife, ir-
ritability and motion, spontaneously direct-
ing their organs to what is natural and bene-
ficial to them, and flourishing according to
their success in gratifying their wants, may
not the exercise of their vital functions be at-
tended with some degree of sensation, how-
ever low, and some consequent share of hap-
piness?”’ Erasmus Darwin, a few years be-
fore, and J. E. Tupper, a few years later, ex-
pressed similar sentiments in works that met
with popular recognition and approval.

SPECIAL SENSES 3

The passing of the present century has seen
an increasing tendency toward the serious
use of terms for plant activity borrowed from
the volitional and neural manifestations of
animals. These, in part, are suggested by
purely superficial analogy, and intended sole-
ly to lend greater attractiveness to thenarra-
tive, asin Charles Darwin’s description of a
twining plant, whose horizontal extremity
repeatedly slid past the support which tem-
porarily arrested its progress as it swung
slowly around in a circle. ‘‘This movement
of the shoot had a very odd appearance,’ he
Says, ‘‘as if it were disgusted with its failure,
but was resolved to try again.”’ Yet in part
there is implied an obscure but real analogy,
as when the same author in another work
sums up his studies of the root tip with the
assertion that in its power to direct move-
ment in the adjoining parts it ‘‘acts like the
brain of one of the lower animals.”

So long as the comparison of animal and
vegetable activities rested largely upon exter-
nal appearances, with very limited under-
standing of the changes within the organism
by which they are brought about, no consid-
erable advance was possible. At first the in-
terpretation was necessarily based upon
human and animalanalogies. As Julius Sachs
has admirably said in his “History of

Application
of terms

Knowledge
of mechanism

Zo LIVING PLANTS

Botany,” “from our own vital motions we
argue to those of the higher animals, which
we comprehend immediately and instinctively
from their conduct; by aid of these the mo-
tions of the lower animals also become intel-
ligible to us, and further conclusions from
analogy lead us finally to plants, whose vi-
tality is only in this way made known tous.”’

An illustration of such reasoning is admira-
bly set forth by G. H. Lewes, the eminent
English psychologist, in his volume on the
object, scope and method in the study of psy-
chology. He says: ‘‘Touch the eye of a frog,
and there is at once the response of a reflex
closure of the eyelid. Touch the hairs of a
venus fly-trap (Dionoea muscipula), and there
is at once the response of a reflex closure of
the leaf. Confine the frog and the dioncea
undera glass shade, and place there a sponge,
over which ether has been sprinkled. Both
plant and animal breathe this air in which
there is vapor of ether, and as this vapor pen-
etrates to their tissues we observe a gradual
cessation of all sensibility; first the reflex
actions cease, then the irritability of the par-
ticular tissues ceases. Stuporhas supervened
for both. Now remove the glass shade; the
vapor dissipates, the fresh air penetrates to
the tissues in exchange for the vitiated air,
and both frog and dioncea slowly recover

SPECIAL SENSES 5

their sensibility.” From this experiment he
justly concludes ‘‘that the animal and plant
organisms have with their common structure
common properties, andif we call one of these
properties sensibility in the animal, we must
call it thus in the plant.”

Modern investigations have more and
more confirmed the fundamental unity of
the primary functions of animals and plants,
but at the same time have increasingly em-
phasized the great divergence they have ob-
tained in developing along lines of specific
adaption to the needs of the energy-liberating
animal on the one hand, and of the energy-
conserving plant on the other hand. Until
recently the difficulty of interpreting the
movements of plants without recourse to the
assumption of astructural device in some way
comparable to the neuro-muscular mechanism
of animals has seemed very great. But the
wonderful advance in studying the plant’s
minute structure and general physiology dur-
ing the last few decades has revealed unsus-
pected and ample vegetal methods of bringing
about movement as the result of stimulation,
which bear no analogy and nocounterpart to
those of animals, but have been developed
with a trend as different as the physical basis
of tissues in the plant is different from that in
the animal.

Primary
unity
with great
diversity

What constitute
special senses

Sense of
contact

6 LIVING PLANTS

If we ask ourselves what could properly be
considered as constituting special senses in
plants, it will be necessary to remember that
in the broadest ecological import the special
senses of animals are the conspicuous ways
in which they respond to particular kinds of
external stimuliin promoting their well-being,
and that the same must be true of plants.
Knowing that irritability is a fundamental
property of all living matter, let us see what
advantages the animal and the plant could
secure by its special development.

It is unquestionable that the paramount
necessity of every organism is self-preserva-
tion. To secure food, to avoid injury, and to
obtain the requisite supply of light, heat,
moisture and air, may beconsidered the funda-
mental necessities of every living being,
whether man or monad, tree or microbe. It
is in these directions, therefore, that we must
look for special senses.

The animal has developed a quick response
tocontact. This is probably the most univer-
sal of all the senses, and in its lowest forms
is little removed from simple irritability. It
primarily contributes to the animal’s safety,
as it gives warning of the proximity of uncon-
genial or dangerous objects, and is also an
important factor in the operation of securing
food, and in many minor operations. Itis a

SPECIAL SENSES £6

characteristic sense in wellnigh every animal,
and in the larger number is especially devel-
oped and intensified in certain organs that
may beappropriately termed organs of touch.
If we return to plants, we find this simplest
and most generalized of senses, with some
notable exceptions, practically absent. In a
few instances, as in the tendrils of certain
plants, there is a marked, sometimes a mar-
velous sensitiveness to touch, but it is con-
nected neither with the attainment of safety
nor of food. Only in the very few and excep-
tional cases of insectivorous plants, like the
sundews, has the plant acquired a sense of
touch to aid it indetecting and grasping food.
But sensitiveness to contact is not a common
property of plants.
_ Aninquiry into the conspicuous difference
between the attitude of the animal and the
plant toward objects external to itself must
reveal some of the reasons underlying the
trend of sense development. And first of all
it must be noted, that when the animal de-
tects something inimical to its safety, it
moves away from the offending object, a pro-
cedureimpossible to the plant with its anchor-
ageofroots. Were the aspen quaking through
fear of impending calamity, itcould not escape
by flight, or by the displacement of its body
by so much as aninch. In another, and even

Trend of sense
development

Free and fixed
organisms

8 LIVING PLANTS

more important particular, does the animal
with its power of locomotion show the need
of a different set of senses from those of the
plant. The ingestion of a large amount of
solid food requires the animal to search for a
suitable supply; while the plant, partaking
only of food in solution and in comparatively
small quantities, is enabled to secure it by
slender feeders extending into the surround-
ing medium. In securing food and protecting
itself from injury the animal makes use of
three important senses: smell, hearing and
sight. The plant with its fixed position and
simpler requirements does not need these
senses; they would be useless to it, and have
not been developed.

We may safely conclude that in so far as
animals and plants respond in a marked
manner to stimulation, it is along two dis-
tinct lines, to correspond with the necessities
of free organisms on the one hand, and of
fixed organisms on the other.

For a fixed organism orientation is of prime
necessity. The roots of a plant must pene-
trate the soil and its foliage be spread to the
air.

Yet the root or shoot has no power to de-
viate from extension in a straight line unless
it is acted on by some external force, no more
than a cannon ball or otber moving body has

SPECIAL SENSES 9

power to vary from a straight line. Ifa seed
in germinating lies in sucha position that the
roots point upwards and the stem down-
wards, some method is needed by which the
plantlet may readjust itself, either by turning
over bodily, or changing the direction of its

Fic. 1.—A clinostat. Germinating seeds are pinned on the
cork disc, and are kept moist by dipping into water as they
revolve. One revolution is made in about twenty minutes.
Under these conditions the primary root and stem grow
straight in whatever position they are fastened.

growing parts. As every one knows, the lat-
ter alternative is adopted, and theroots bend
-down and penetrate the earth, while thestem
bends up and lifts its foliage into the air. It
is so apparently a matter of course that
stems grow up and roots grow down, that
we may never have given a thought to an
explanation of the process. Even botanists
have only recently felt the full necessity for
an explanation of the fact, as it has been less
than two decades since V6chting announced
his theory of rectipetality, or the inherent

Discovery of
gravity sense

10 LIVING PLANTS

tendency of growing organs to extend in a
straight line unless acted upon by outside force.

There is only one force known that acts uni-
formly in the direction of the center of the
earth, that is gravity; and it was the genius
of Andrew Knight, an Englishman, to demon-
strate as long ago as 1806, that this force
does furnish the directive influence in securing
verticality to plants. He grew plants on re-
volving wheels, and found that they respond-
ed to centrifugal force, and that when the
wheel was placed horizontally and revolved
at a speed that made the centrifugal force
equal to that of gravity, both roots and
stems grew obliquely, taking the position of
a resultant of the two forces, that is, of forty-
five degrees to the vertical.

But this discovery by Knight was not imme-
diately fruitful, forno one could tell how grav-
ity produced the effect ascribed to it. If it
pulled the root down, why did it push the
stem up? The stem is as heavy as the root,
why arenot bothattracted toward thecenter
of the earth? It was a curious paradox to
say the same force acted now one way and
now exactly the reverse on different parts of
the same plant; as if pulling and pushing
were the same thing. It was supposed that
gravity acted upon the root as it does upona
mass of taffy candy, drawing it downward.

SPECIAL SENSES otal

But Sachs showed in 1878 that the root of a
bean fixed horizontaJly over mercury could
penetrate the mercury in assuming a vertical
position. As mercury is about thirteen times
as heavy as the tissues of a young root, it is
evident that far more force was expended in
penetrating the mercury thancould have been
derived from the physical action of gravity,
that is, from the simple weight of the root.
Theexperiment hassince been tried in another
and more obvious way by harnessing a root
tip lying horizontal to a weight suspended
over a pulley, the weight being raised as the
root bends downward in response to gravity.
From these experiments we must conclude
that gravity doesnot act physically but phys-
iologically to induce the curvature, that is, it
acts asastimulus. Itisa small spark that
fires the gun. ‘fhespark will fire a pistol or
a cannon, theresult depending solely upon the
amount and arrangement of the explosive
material. So in theroot, if thereis the proper
mechanism and storage of force, gravity will
release this force and cause the bending, the
amount of work done being enormously out
of proportion to the initial expenditure of
energy.

But when the bending takes place, will it be
upward or downward? If it were a purely
mechanical device, it is evident that by know-

Movement
connected

with growth

12 LIVING PLANTS

ing the structure of the organ, one could pre-
dict the direction of movement under stimu-
lation. But we shall have to look beyond
and above simply mechanical laws for an ex-
planation, for the living organism acquires
specific powers of adaptation and heredity.
Although the force which a plant can exert
amounts to several atmospheres, it is only in
the young tender portions, usually at theends
of the branches of the stem and root, that
this force can be successfully applied to secure
movement of the whole organ. It therefore
comes about that movement in plants is
oftenest associated with growth. This ar-
rangement permits each root tip and growing
stem to have its own kind and degree of sen-
sitiveness. Thus we find by experiment that
while the first root which starts from a seed,
the tap root, is sensitive to gravity in sucha
way that it places itself parallel to the direc-
tion of the impinging force and points directly
downward, the secondary roots, which
branch from it, are sensitive after a different
fashion, and instead of growing parallel to
the force, grow at an angle to it, the exact
angle being different for different kinds of
plants,” The tertiary roots, or next set of
branches, are usually very little sensitive to
gravity, or if they are sensitive they assumea
neatly horizontal position. The stems react

SPECIAL SENSES 13

in a similar way, except that the general
direction is upward instead of downward,
and in consequence of the diversity of sensi-
tiveness of the primary andsecondary shoots,
the branches are spread out to the air and
light, imparting to each species of tree and
herb its characteristic appearance.

But if there is no nerve-like communication
between one root tip and another, or between
one stem and another, there is sometimes a
distinct transmission of impulse from the cells
receiving the stimulation to the cells a short
distance away where the movement is con-
summated. Thus, in the tip of the primary
root Darwin found that only the cells at the
very tip were sensitive. Ifso small a piece as
one millimeter be removed from the end of the
root by cutting or burning, all power of
movement is lost. This remarkable localiza-
tion has been denied by Sachs and Detlefsen,
whocharacterize Darwin’s claim as sensation-
al, but the fact has been fully verified by Wies-
ner, who found that if the root is weakly
sensitive, the seat of irritability coincides
with the zone of most rapid growth, but if
highly sensitive, it will beat a distance.

To sum up the characteristics of the gravity
sense: Itis localized in or near the ends of
growing roots,stems and other organs of the
plant; it is developed in varying strength in

Transmission
of impulse

Sensitiveness

to light

14 LIVING PLANTS

different organs; it sets up movement of the
organin response to stimulation ; the direction
of movement will depend upon the specific
kind of sensibility acquired by that organ;
the direction of the movement will always
bear some definite relation to the vertical
without regard to the position of the plant.

But, what other senses have plants? Next
to a proper position, most plants need a suit-
able exposure to light. I shall not attempt

to show the nu-
LG AA
oT,

fa merous and inter-

esting ways in
which plants re-
spond to light.
Everyone knows
how plants light-
ed from one side,
as when placed
before a window,
_ bend toward the
light. This isa

= true sensitiveness,

light and the roots away from it. bringing about
definite movement.

The stems place themselves parallel to the di-
rection of the incident rays—that is, point to-
ward the window, while the leaves place them-

selves at right angles to the direction of the

SPECIAL SENSES 15

light—that is, with their upper surfaces to the
window. Leaves and stems, therefore, show

Fic. 3.—Day and night positions of the leaves of redbud
Cercis Canadensis).

Chemical sense

16 LIVING PLANTS

sensitiveness characteristic of each. Some
stems, however, like those of the Virginia creep-
er, turn away from light, enabling them to
cling to dark walls. Roots which are general-
ly buried in the soil, rarely exhibit sensitive-
ness to light, and when they do, it is usually
to turn fromit. If light comes to the organ
from two directions, it will bend toward the
source of the stronger light, and differences
which will affect the plant are far more minute
than can be detected by the eye.

As in the case of roots, certain stems place
themselves not parallel with the direction of
the light, but at some particular angle to it,
in accordance with some inherent necessity.
Not as large a part of the plant, asa rule, is
as sensitive to light as to gravity, but the de-
gree of sensitiveness is often greater.

Plants also possess a chemical sense, a kind
of taste, by which they detect certain sub-
stances in solution fitted for their nutrition.
By this means parasitic fungi starting to
grow upon the surface of other plants find
their way into the stomata from which the
acid juices of the tissues diffuse, and thus gain
entrance into the host. Roots exhibit sensi-
tiveness to many nutritive substances, al-
though not as a rule to the same extent that
fungido. It enables them to turn and grow
in the direction of the best food supply, and

SPECIAL SENSES 5 lg

accounts for the popular notion that roots
seek rich soil.

Moisture also exerts a directive influence
upon roots, and sometimes upun other parts
of the higher plants, as well as upon the or-
gans of many lower plants. Usually the
movement is toward the moister side. It is
evidently beneficial to the plant in keeping its
absorbing organs bathed in the greatest
available supply of fluid.

Plants are thus seen to react sensitively to
gravity, light, solutions, moisture and con-
tact. Each isa special kind of sensitiveness,
having its own method of reaction. Two or
more kinds of sensitiveness may reside in the
same organ, when its position will be a re-
sultant of the several forces. There are no
exclusive organs of sense in plants, although
there is more or less localization in certain
parts; and there are no nerves although the
motor impulse may be transmitted some dis-
tance, even as far as seventy centimeters or
more in very vigorous sensitive plants, for
example in mimosa. To complete the com-
parison I should say there are no muscles in
plants, although they execute movements of
very considerable amplitude. Their motor
mechanism is operated by devices having no
counterpart in the animal organization, but
is the outcome of specific adaptation.

Moisture sense

18 LIVING PLANTS

Aristotle’s notion, which is still too preval-
ent, of an ascending complexity in vital phe-
nomena from plants to man, should be whol-
ly abandoned. The only way of viewing or-
ganic nature, to secure proper interpretation,
is that of two diverging lines of development,
one through motile forms, and the other
through fixed forms. Each line of develop-
ment has worked out peculiarities of its own.
If the special senses of animals show wonder-
ful adaptations, the special senses of plants,
although very dissimilar, will, when better
known, appear quite as remarkable.

The observation of Sachs, the learned pro-
fessor of Wiirzburg, and one of the most far-
seeing of physiological botanists, is particu-
larly pertinent in this connection. ‘We have
no necessity,’’ he says, ‘‘to refer to the physi-
ology of nerves in order to obtain greater
clearness as to the phenomena of irritability
in plants; it will, perhaps, on the contrary,
eventually result that we shall obtain from
the process of irritability in plants data for
the explanation of the physiology of nerves,
and this, although it is as yet a distant hope,
gives a special attraction to the study of the
irritable phenomena of plants.”

II
THE DEVELOPMENT OF IRRITABILITY

The economical acquisition of nutritive sub-
stance in proper amount is a fundamental ne-
cessity of every organism, and to the condi-
tions attendant upon the performance of the
nutritive functions must be ascribed the chief
causes underlying the development of the plant
body. The chlorophyll processes have, there-
fore, been the paramount factors in the devel-
opment of the shoot, and the absorptive pro-
cesses haveruled the differentiation of the root
system.

In an early stage of the existence of the an-
cestors of our present plant population they
were doubtless thalloid organisms, unicellular
or multicellular, floating in the water, and
were perhaps in many instances endowed with

*Given in an address before the Botanical Club of the Univer-
sity of Chicago, Jan. 18, 1897.

Derivation o
existing forms

Chlorophyll
and sunlight

20 LIVING PLANTS

the power of locomotion. All of the cells con-
tained chlorophyll and shared in the work of
food formation, and since more or less of the
surface of each cell was bathed by the fluid in
which it lived, all absorbed the mineral salts
in solution in the surrounding medium, and
all of the cells participated in the reproductive
processes.

It will not be profitable here to follow the
direction or possibilities of morphological dif-
ferentiation into detail,except to say that the
organism soon found it more economical to
be attached to a fixed point rather than to
float at random or swim through the water
which contained the mineral salts in equal
diffusion, and in which the necessary intensity
of light bore a direct relation to the distance
from the surface. Then in consequence of this
newly acquired habit of fixation, and the re-
cession of the water from the substratum occu-
pied, some distinct and important physiolog-
ical changes ensued to meet the new condi-
tions attendant upon the nutritive processes.

The sunlight impinging upon the portion of
the plant containing chlorophyll no longer
came filtering down through layers of water
of varying depth, but beat upon it from all
points inan arc of one hundred andeighty de-
grees. The greater amount of energy thus
available to the aerial shoot could only be

IRRITABILITY 21

made of use to the plant by the arrangement
and division of its chlorophyll areas, and
the morphological necessities will account
for the method of differentiation of the
shoot, and the very great degree of segmen-
tation and branching which it has attain-
ed. The segmentation of the shoot has made
possible not only the profitable display of
ever-increasing areas of chlorophyll-bearing
tissues, the proper elevation, orientation and
isolation of the reproductive organs, but also
a separation of the minor functions and the
differentiation of special organs for their per-
formance. The separation of nutritive, repro-
ductive and other functions has been accom-
panied by a contemporaneous separation and
development of the special forms of irritabil-
ity which are concerned with the forces dealt
with by each organ. Thus, for example, the
most important factor in the processes carried
on by the leaf is the radiant energy derived
from the sun. Asa necessary concomitant of
the advantageous use of this energy, the leaf
has developed a strongly marked irritability
to light and heat rays.

By these special powers it is enabled to
move its chlorophyll-bearing areas in the
leaves into such position that theexact inten-
sity of light and heat rays suitable to its
specific constitution will be received and as a

Pollination

Organization
of shoot

22 LIVING PLANTS

result of the relations of the organ to the ho-
rizon in response to its helictropism and ther-
motropism, it has also acquired in some in-
stances a trace of geotropism. The elimina-
tion of all but nutritive functions from the
leaves has made it possible for these organs
to perform such functions with greater eco-
nomy, and made superfluous aiso the pres-
ence of any other forms of irritability which
would direct the position of the leaf.

In the accomplishment of the reproductive
process, an incidental condition is the trans-
ferance of the pollen from its place of forma-
tion to the surface of the stigma in the same
or other flowers. In a great majority of in-
stances the relation of the line adjoining the
anther and the stigma to the vertical or hori-
zon, is of the utmost importance, whether
the pollinationis accomplished automatically,
by air currents, or by insects, and a well
marked geotropic reaction is therefore gen-
erally exhibited by flowers with the motor
zone located in the peduncle. These organs
also show minor heliotropic reactions.

The same process of analysis may be
applied to the entire shoot, with the general
result that each organ will be found to re-
spond to a number of forces generally limited
to two or three, though of course, instances
are not lacking where a greater number of

IRRITABILITY 23

forms of irritability are found to reside in the
same organ, as for example, in tendrils. In
such instances, however, the excessive num-
ber of the forms of irritability have beeen de-
veloped to meet special ecological conditions,
bearing upon both the nutritive and repro-
ductive processes either directly or indirectly.
Furthermore, the organs of the shoot may
also acquire the power of special reactions to
internal forces or stimuli, such for example,
as the carpotropic movements.

In a consideration of the localization and
distribution of the property of irritability,
attention is to be called to the fact, that the
conditions concerned in thenutritive processes
of the shoot show an invariably wide diffu-
sion. Carbon dioxide exists everywhere in
the atmosphere in uniform proportions and
bathes every part of the shoot. Sunlight is
bounded only by the horizon line and may
reach any surface of the shoot in diffuse form.
The chlorophyll processes may then be carried
on by the sub-epidermal tissues in any por-
tion of the shoot, and as a consequence, a
greater proportion of the peripheral proto-
plasm of the shoot has developed an irrita-
bility to sunlight, although it may not al-
ways be manifested by organic or external
movement, or other response.

The researches of Rothert have shown that

Distribution
of nutritive
factors

Sensory and
motor zones

24. LIVING PLAN'S

a large part of the surface of the leaf of Ave-
na and Phalaris exhibits a heliotropic sensi-
bility, and that thelamine of dicotyledonous
leaves exhibit an equal distribution of sensi-
tiveness over their entire surface, and that the
leaflets in a compound organ are strictly co-
ordinate and equal with respect to their irri-
tability. Those branches of the shoot that
have developed special, or ecological adapta-
tions exhibit an extension of the irritable
surface corresponding to the limited diffusion
or occurrence of possible stimuli, modified to
some extent by the character and inclusive-
ness of the reaction.

Before further progress is made in the dis-
cussion, the chief facts in the organization of
the irritability of leaves should be recalled.
The portion of a leaf which is capable of re-
ceiving light and converting it into some
other force which will set upa reaction is
termed the sensory zone. The portion of the
organ in which motion ensues is termed the
motor zone. Now as may be seen by the pre-
ceding paragraph the sensory zone is located
in the blade of the leaf, and if the movements
of the leaves of the bean or mimosa are ob-
served, the motor zones will be found at the
base of the petioles. Lightstriking the blade
of the leaf sets in actionasecond force, which
is transmitted to the motor zone wherea third

IRRITABILITY 25

ae ee ee a EE

force causes the movement. The leaf then is
a living machine the movements of which are
directed by two forces—light and heat (some-
times gravity), while the root is directed by
many forces.

Although the motor zones of the shoots do
not include as large proportions of the plant
as the sensory zones, yet the distribution is
fairly general throughout growing regions.
It is possible to induce curvatures in some
stems in which growth has almost entirely
ceased. The curvature is accompanied by a
revival of the growth activity, however.

Having followed the shoot to its ultimate
and present form wemay retrace our steps to
the beginnings of the root-system. The primi-
tive function of the root of the plant emerging
from an aquatic habit was of course purely
mechanical and consisted in holding the or-
ganism in place. With the recession of the
water the plant no longer found solutions
of mineral salts bathingits surface. Its rudi-
mentary anchoring organs were, it is true,
left in contact with small quantities of fluid,
but the amount of surface was by no means
adequate or proportional to the now rapidly
enlarging shoot. Under such circumstances
it might do but one thing—extend the root-
system and thereby increase its absorbing
surface.

Development
of root
functions

26 LIVING PLANTS

The functions of the root are not so numer-
ous as those of the shoot, and while the effi-
cient performance of the necessary amount
of absorption, to keep pace with the increase
in mass and surface of the shoot, has de-
manded a repeated branching, yet no seg-
mentation like that of theshoot has occurred.
The less important function of the root, fixa-
tion, is purely mechanical, and the separation
of the two functions has not been effected by
a localization of the functions in different
organs, butis an incident to the stage or
degree of development of these organs. Phys-
iologically the basal portion of roots sustains
a relation to the absorptive system similar to
that of the basal portions of typical stems to
the chlorophyll-bearing and reproductive
organs.

In the earlier stages of growth any given
portion of the rootis purely directive, next
absorptive and in the later periods, is exclu-
sively fixative. Only in certain special classes
of aerial and other plants does a separation
or isolation occur. The stem, on the other
hand, is at first directive, and then fixative,
and does not in any stage of its existence as-
sume the relative importance which is to be
ascribed to every portion of the root in one
period of its development.

In explanation of this method of develop-

IRRITABITITY 27

ment, so widely different from that of the
shoot, it is to be said that roots have taken
on fewer functions, and have always been sur-
rounded by much more uniform conditions
than the shoot, and in consequence have met
the necessity of a much narrower range of
adaptive modifications. But, while the rapid-
ity of variation of outward conditions affect-
ing roots has been much less than that of the
shoot, yet the greater number of the factors
concerned and the inequalities of diffusion and
distribution of the nutritive substances are
much greater than those affecting the shoot.
Water and food substances lie below the sur-
face of the substratum and the root has de-
veloped a highly marked form of geotropism,
which enables it to penetrate the soil. Water
and food substances are by no means so uni-
formly distributed as sunlight and carbon di-
oxide, however. While water exhibits a fairly
horizontal distribution in quantity, yet so far
as its actual availability is concerned, differ-
ences corresponding to the physical character-
istics of the soil are to be found. The vertical
distribution is modified in the same manner.
The mineral food substances present no sys-
tem or uniformity of distribution whatever.
As a matter of fact the masses of food sub-
stances may and do lie in all possible direc-
tions from the absorbent zone of the apical

Nutritive
factors in soil

Organization
of roots

28 LIVING PLANTS

portion of the root. In order to reach such
irregularly distributed masses of nutritive
substances, it is evidently necessary that the
root should develop an irritability to a much
greater number of forces than any member of
the shoot, and furthermore it is evident that
all theforms of irritability thus acquired must
be located in the apical portion of the root,
the proper directive activity of which only
can result in facilitating the absorptive pro-
cesses. The coincidence of several forms of
irritability within such narrow limits has ne-
cessitated differentiations in another direction
from that offered by the shoot. The differen-
tiation of the shoot resulted in a tendency to
separate the different forms of irritability
with their attendant mechanisms. The in-
crease of the efficiency of the root has resulted
in the acquisition of a constantly increasing
number of forms of which the mechanism
must necessarily be identical. Still further,
this has resulted, of course, in the differentia-
tion of the separate parts of the mechanism,
and increase of its delicacy of reaction. This
may be held to apply to all similar arrange-
ments, especially in the ecological adaptations
exhibited by certain members of the shoot.
Thus if an examination of the mechanism
of irritability of the root is made, it will be
found that only an extremely small portion

IRRITABITITY 29

of the organ may receive a stimulus from grav-
ity, light, temperature, moisture, running
water, chemicals, electricity, contact or injury.
This sensory zone consists of amass of cells in
the shape of a cylinder beginningimmediately
back of the growing point and not more than
one millimeter in length. The portion of the
root in which curvature ensues lies immedi-
ately back of the sensory zone.

The root is a generalized type of the mech-
anisms by which plants respond to external
directive stimuli, and the shoot is a special-
ized type. The same mechanism in the root
is capable of response to eight different classes
of stimuli, while in the shoot but two or three
may act upon any given organ, in such man-
ner as to secure a responsive movement.

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GavaA GHLOWTOUN V NI SGHAM

HiT.
WILD LETTUCE AS WEED AND COMPASS PLANT*

The prickly lettuce is a plant closely resem-
bling the common garden lettuce, especially
the narrow leaved Cos varieties. The simi-
larity is more striking if we compare them
after the flower stalks have begun to appear.
There are in fact good grounds for believing
that the garden forms were derived from the
wild lettuce: a view held at one time by Bis-
choff, De Candolle, and other authorities, who
wrote the Latin name of the garden forms
Lactuea Scariola var. sativa, instead of L.
sativa, as adopted by Linnzeus and adhered
to by most of recent writers.

The plant is an annual, coming from seed
each year. Occasionally the seed germinates
in the fall, the plant making some growth be-

*A portion of Bulletin No.52 of the Indiana Experiment Sta-
tion, issued November 10, 1894.

Likeness to
cultivated
lettuce

General
characters
and habits

32. LIVING PLANTS

fore the cold weather. In this form it passes
the winter, thus becoming a winter annual.
The term is applied to distinguish such plants
from true biennials. It is in flower from July
to September.

The height of the plant is from a few inches
in poor soil up to five or six feet, or more, in
rich soil. As seen along fence rows and in
meadows it stands asarule about three or
four feet high. In general the plant possesses
a centralstraight shaft, branched only above.
The lower half or two-thirds of the stalk is
clothed with leaves of quite uniform width,
four to six inches long by one to two inches
wide, while the upper half or third of the stalk
sends out spreading, rather bare branches,
much subdivided, and ultimately bearing in-
conspicuous yellow flowers. Each flower
(capitulum) gives rise to about a dozen dark
brown (so-called) seeds of similar shape to
those of the garden lettuce, but somewhat
shorter. Each seed (in reality a fruit, con-
sisting of a dry capsule inclosing the solitary
small seed, like all members of the composite
family) bears a slender rigid stalk as long as
itself, in turn supporting a white, filmy para-
chute, like that of the dandelion seed, only
smaller, which serves to buoy up the ripe seed
and waft it long distances on currents of air.

The whole plant has a pale, pea-green color.

WILD LETTUCE 33

Its specially characteristic feature is the pres-
ence of a row of soft prickles along the edges
of the leaf and arow down the midrib beneath.
There are also a few prickles scattered over
the stem, particularly the lower portion.
With these exceptions the plant is smooth.
These prickles are from an eighth to a quarter
inch long, and although scarcely stiff enough
to penetrate the flesh, yet give the plant a
rough and disagreeable character when hand-
led. The juice of the plant is milky.

The prickly lettuce is a native of southern
Europe, northern Africa, and the temperate
part of middle Asia. At the present time it
occurs as a weed in nearly all arable parts of
Europe and Asia, except the colder regions.
In England and northern Europe it is only an
occasional weed along roadsides and in waste
places, and is not troublesome to the culti-
vator.

Prickly lettuce made its advent in this
country not far from thirty-five years ago;
the exact date and place have not yet been
ascertained. It is supposed to have come in
with packing, ballast and other wastage. So
far as can be inferred from available data, the
plant gained a foothold insome Atlantic port.
After having become established it was car-
ried to the larger cities of the West, and from
them scattered in all directions by the rail-

First appear-
ance in

America

34: LIVING PLANTS

roads. To be more specific, it appears to
have first been seen in Cambridge, Mass.,
about 1863, and about fifteen or twenty
years later to have appeared in several of the
larger cities along the great lakes and the
Mississippi river. It is probable that the fact
that these cities are upon water-ways had
little to do with the matter, but being great
railway centers must have been animportant
factor.

The earliest record in American literature is
in the edition of Gray’s Manual of Botany
issued in the year 1867, where the plant is
said to occur in waste ground and along road-
sides in Cambridge, Mass. In the editions of
1866 and earlier it is not mentioned. .It was,
however, to be found in Cambridge at least
four years earlier than the published record,
as specimens exist in the Gray Herbarium of
Harvard University, collected by Mr. D. Mur-
ray, in both 1863 and 1864. It was found
upon ballast ground near New York City in
1879, but not seen in previous years. The
ballast grounds of Philadelphia, which have
received much attention from local botanists,
do not appear to have yielded a specimen of
the plant until 1883. Along the Atlantic sea-
board the plant is still comparatively uncom-
mon, and does not become an abundant weed

WILD LETTUCE 35

anywhere in the region east of the Alleghany
mountains.

Aithough the plant did not find an especial-
ly congenial soil and climate when it landed
upon our shores in its emigration venture,
yet it was able to maintain itself and to
spread. In the course of fifteen years it had
penetrated into the Mississippi valley, prob-
ably making the longer distances as the hobo
travels, by clinging to freight trains, for it is
first recorded as seen in St. Louis in 1877. It
was afterward detected in Toledo, Chicago,
St. Paul and other cities. In three or four

Fic. 4.—Map of the distribution of wild lettuce, as reported
to the U. S. Department of Agriculture up to October, 1895.
The comparative rarity of the weed in the Atlantic states,
where first introduced, and its abundance in the central states,
are conspicuously shown. (After Dewey.)

years it was an abundant weed in almost
every large city of the central west. At the

Fifteen years
of conquest

36 vi Seteile LIVING PLANTS

present time it is especially abundant in this
part of the country, not only in cities and
towns, but on farm lands and along high-
ways.

The inference appears well founded that the
plant has found its most congenial domain
between the Alleghany and Rocky mountains,
and between the fortieth and forty-third par-
allels. The region in which it has become so
well established and so abundant as to take
on the character of a prominent weed em-
braces the northern half of the states of Ohio,
Indiana, Illinois, the southern parts of Mich-
igan and Wisconsin, and part of Iowa. Out-
side of this region it occurs locally in every
direction so that its distribution may now be
said in general to extend throughout the
United States.

Probably no one thing about this plant im-
presses the observer more that the appear-
ance of having ‘‘come to stay,’’ an expression
used by many of those who have recorded
their first acquaintance withit. It is a weed
not only because it is a ‘‘plant out of place,”’
but because it possesses certain attributes
that enable it to maintain itself wherever a
seed finds moisture and soil enough for the
forthcoming plantlet to gain a foothold.

Before discussing this pre-eminent trait of
the plant, however, it will be well to mention

WILD LETTUCE 37

some lesser features that go to help it in its
conquest of the land. In this connection the
number and ease of distribution of its seeds is
an important item. Eachsmall head of flow-
ers ripens about twelve seeds (1. e. seed-like
fruits), and a plant of medium size, according
to an estimate made by Miss Freda Detmers,
bears 688 heads, or 8,526 seeds. Each seed is
well constructed and protected toenable it to
withstand a siege of the elements, and is like-
ly to reach the succeeding springtime in good
germinating condition, unless devoured by the
birds. This contingency is not, however, of
much moment, for the seeds are enclosed by a
close wrapping of green scales until entirely
ripe; they are then fully exposed only a short
time, being carried away by the first breeze;
and when they drop to the ground, aftera
longer or shorter sail through the air, they
become almost invisible, their color being that
of dry soil.

Each seed, as it leaves the mother plant, is
supported from a white, feathery parachute,
about half an inch across, which enables it to
keep afloat upon currents of air for a long
time, and ensures the plant a wide and rapid
dissemination.

The flowers, which are yellow and small,
only open a short time on clear days, and
then close until the seed is ripe, and in the

Seeds and their
distribution

How to be
a successful
weed

38 LIVING PLANTS

meantime look almost like young, unopened
buds. This deceptive appearance may lead
the cultivator to think he is cutting the weed
in the bud before it has blossomed, when in
reality it is loaded with young seeds, which
will ripen as the plant dies, and be discharged
to start another crop, almost as effectively as
if the plant had been left standing.

The plant finds protection from herbivorous
animals and boring insects through its bitter
milky juice. For although like the garden
lettuce, itis tender and palatable when young,
it becomes exceedingly disagreeable to the
taste after the flower stalks start up.

The prickles also, although weak and not
very abundant, havea protective value to the
plant by restraining animals from eating it.

Although the plant, by its milky and bitter
juice, and by its prickles, renders itself dis-
tasteful and unattractive as food for animals,
and by prodigality of seeds, with their, ample
means for distribution and self-protection, in-
sures a rapid and wide dissemination, thereby
securing great advantages asa dominant and
ever-present member of every area of vegeta-
tion, yet it is the possessor of another attri-
bute belonging to a successful weed of even
more importance, and that is its ability to
grow and seed whatever the character of the
soil and surroundings. Stone heaps, weed-

WILD LETTUCE 39

choked corners of fences and yards, alongside
gutters and roadways, a crevice in the pave-
ment, beaten paths, all are acceptable places
in which to flourish. But such poverty and
ill usage are by no means essential factors in
its success, for it also springs up in meadows,
gardens and cultivated fields. Still the power
to extract sufficient moisture and food from
compacted and sun-beaten earth, and thus to
overtop competitors, and inthe less favorable
spots to grow where few plants could live,
place it in the first rank of noxious annual
weeds.

Where it can maintain life, seed will be
formed, even when conditions are unfavor-
able for full development. Thus one will
often find in very dry soil plants only a few
inches high bearing a number of flower heads
and fully formed seeds. If by any accident
the upper part of the plant is removed,
branches at once start from below, and bear
leaves and flowers.

The tenacious hold upon life which the wild
lettuce exhibits is remarkable. It may be
broken down, trod upon, cut off, and yet it
puts out new shoots from below and flourishes
again; its roots may be in the driest gravel,
the most compact clay, or squeezed into the
crevices of wallsor pavements where moisture
almost fails, and yet it grows. But all this

40 LIVING PLANTS

tenacity of life is only displayed as long as
the roots remain undisturbed. A plant of
wild lettuce once pulled up dies as quickly as
any other plant. When mowed, the top that
is cut off dies as soon as ragweed, cocklebur,
horseweed or thistles do; it possesses none of
the live-for-ever quality of purslane. Neither
has the root any recuperative force in itself.
If the stem be cut away well down into the
root, the whole plant dies, no shoots ever
starting up from the roots in the soil.

The various characteristics enumerated
largely explain the success of the plant as an
introduced weed. In the central west, itis a
formidable rival of ragweed, horseweed,
cocklebur, jimsonweed, pigweed and other
tall-growing annual weeds, especially during
dry seasons. In July and August the plant
becomes most obnoxious, for then it sends up
the seed stalks. The heat and dryness which
are likely to occur at this season and retard
the growth of other plants, killing the small
and weak ones, give the conditions which
enable wild lettuce to gain the mastery and
flourish in disheartening luxuriance.

Not only has the plant the properties of a
weed, but it has the appearance of one. It
looks weedy. There is nothing about it that
will ever give it an esthetic value. To city-
bred and country-bred observers alike it will

WILD LETTUCE 41

be only a weed, and nothing of the nature of
the transformation of ox-eye daisies into
marguerites will ever befall it.

Although wild lettuceis an uncompromising
weed, with no beauty of flower or leaf, yet it
possesses some points of much interest to the
student of plant life. ‘‘A garden in which
nothing thrives has charms that soothe the
rich possessor,’’ asserts Cowper; and if we
turn in such a spirit of expectancy to this
weed tramp, although annoying us by its un-
welcome presence in our yards and fields, we
will find it to have characteristics worthy of
study.

The mechanical and biological causes which
determine the time and manner of opening
and closing of the flower heads must be a fer-
tile subject of inquiry. The construction and
expansion of the airy parachute also deserves
attention. Numerous other things about the
plant may well engage the scrutiny of the
careful student.

Only one of these features need occupy usat
the present time, however. The species is
characterized in the various manuals as pos-
sessing vertical leaves. As nearly al] plants
hold their leaves horizontal, 1. e., with the
edges right and left, this peculiarity of the
edges of the leaves being presented up and
down, that is, at right angles to the custom-

Even a weed
may be
interesting

The habit
of polarity

4.2 LIVING PLANTS

ary position, may repay closer examination.
A little scrutiny shows that the leaf is set
upon the stem in the normal manner, and the
vertical position attained by a quarter turn
near the base. Some leaves turn one way,
and some the opposite way, to gain the de-
sired uprightness.

This in itself is odd enough, but a further
examination shows all the leaves on a plant
to stand for the most part in one plane. If
the plant is looked at from a certain point of
view, one sees the flat surfaces of the leaves,
partly upper and partly under surfaces, while
seen at right angles to the former direction
the leaves present their edges only. The
leaves of each plant, in fact, lie approximate-
ly in a single plane.

Even stranger yet, the plane in which the
leaves lie is that of the meridian, that is, the
leaves of the prickly lettuce present their
edges north and south. The species, in fact,
is a so-called compass plant, and exhibits one
of the most curious and interesting cases of
physiological adaptation to be met with in
plants. Its polarity was first observed by
Dr. Stahl, professor of botany at Jena, who
published a very full account of the matter
in 1881.

There are two species known which are pre-
eminently entitled to becalled compass plants:

WILD LETTUCE 43

one is the subject of this article, the prickly
lettuce, a native of the old world, the other is
the rosin weed, which is indigenous to the
new world. The latter (Silphium lacinatum
L.) occurs on the western prairies from Ohio
tothe Rocky mountains. It isa large,coarse
plant, but yet an attractive one, with sun-
flower-like heads. It is usually known as
rosin weed, from the resinous exudation,
which children gather and convert into a
white palatable chewing-gum.

So strong is the polarity of the leaves of this
plant that it has repeatedly served a very
useful purpose in providing travelers with
their bearings when lost on the prairies during
dark nights or cloudy days. This character-
istic was familiar to pioneers long before Gen.
Alvord of the U.S. Army made it known to
the scientific world in 1842. Longfellow,
upon hearing of the plant and its service to
travelers, made it the basis of some lines in
Evangeline:

“Look at this vigorous plant that lifts its head from
the meadow,

See how its leaves are turned to the north, as true as
the magnet;

This is the compass flower, that the finger of God has
planted

Here in the houseless wild, to direct the traveler’s jour-
ney

Over the sea-like, pathless, limitless waste of the des-
ents?

Unfortunately the poet at first misappre-
hended the real character of the plant, with

Another com-
pass plant

Explanation
of the pecul-
iar trait

AL LIVING PLANTS

its coarse, rigid stem, and wrote, ‘‘Look at
this delicate flower * * * that the finger of
God has suspended here on its fragile stalk,”
but in later editions of the poem changed the
wording as above.

The compass plant of the prairies and the
compass plant of the highways differ, in that
the former exhibits polarity chiefly in the rad-
ical leaves (large, coarse leaves, a foot ortwo
long), and the latter in the stem leaves.
Otherwise the phenomenon in the two plants
is practically identical.

There was much conjecture for a long time
as to the cause of this unique behavior. It
was suggested that the magnetic currents of
the earth acted upon iron oxide in the leaves,
or that the abundant resin in the plant
brought about electrical disturbances. But
both theories failed when put to the test, and
others stood no better until the relation to
light was observed. It was found that plants
grown in boxes, if turned one quarter round,
readjusted their leaves to again point north
and south. This occurred when the plants

- were grown in bright light, but not when

grownindarkness. It was also found that
the number of stomata (breathing pores) was
essentially the same on both surfaces of the
leaf, while ordinarily there are very many
more below than ahove, Further uniformity

WILD LETTUCE 45

of structure between the two sides of the leaf
was also found to exist.

It is unnecessary to point out all the rea-
sons for the conclusion finally reached, that
compass plants are endowed with an organi-
zation which enables the leaves, as the mid-
day sun becomes unpleasantly bright, to turn
part way around and present less surface to
the action of its rays. Figuratively, one
might say the plant turns a cold shoulder to
the sun, when he becomes too ardent.

Ordinary leaves permit the sun to shine up-
on the upper surface only, having that side
constructed to bear the light and heat with-
out injury, while the under side, having a
more delicate organization, is turned from the
sun. When the compass plant adjusts its
leaves in the only position possible by which
equal illumination is secured for the two sides
during the middle of the day, the under side
of the leaf is evidently in danger of injury un-
less reorganized. Such a change does in fact
come about. As the palm of the hand is cal-
loused by repeated rough usage, so the lower
surface of the leaf is inured to the sun’s action
by exposure, the change consisting of a pro-
found alteration of the underlying tissues as
well as of the superficial portion. Physiolog-
ically there is no longer an upper and a lower
surface to the meridional leaf, but simply a

46 LIVING PLANTS

—

right and a left surface; both sides function
alike.

Some time ago the writer made the obser-
vation that the garden lettuce also shows
polarity of the stem leaves, although not so
marked asin the wildplant. It is strongerin
the plain narrow leaves of the Cos and Deer-
tongue varieties than in the curled leaves of
the more common varieties.

Both the wild and garden forms show no
vertical adjustments of the basal or so-called
root leaves, the edible part of the cultivated
plant. In feral plants these leaves are not
called upon to endure the hot sun of July and
August, having already performed their office
during spring and early summer, and died.
The compass plant of the prairies (Si/phium),
on the contrary, retains its root leaves
throughout the torrid season. It is evident
that the device is primarily a midsummer ad-
justment, only developedinsuch foliar organs
as are destined to endure the fiercest insola-
tion.

There are eight or nine species of wild let-
tuce indigenous to North America, but none
of them has yet been observed to show po-
larity. The species that are most at home in
the western prairie regions, such as Lactuca
Ludoviciana, are most likely to show tendency
toward the habit.

IV.
MIMOSA: A TYPICAL SENSITIVE PLANT.*

Movement as an adjustment to variations
in temperature and light is one of the most
necessary and most highly useful adaptations
made by leaves. The species that can accom-
plish the movements most economically will
have a great advantage in the struggle for
existence where the solar factors are most in-
tense. In fact it is to be said that no plantin
the tropics exposes its leaves to the perpen-
dicular rays of the noonday sun. In the
species incapable of producing the movement,
the adjustment is secured less perfectly by the
passive drooping of the leaves. In the tem-
perate zone active movements of leaves are
exhibited by species of Leguminose, Oxalide,
Malvacee, Tiliaceze and Marsiliacee only, but
in the tropics the number is enormously mul-

*Adapted from a lecture on ‘‘Movements of Plants’’ given
betore the Institute of Jamaica, June 19, 1897.

Uses

of movement

Power
of movement

Characteristics
of mimosa

48 LIVING PLANTS

tiplied and includes among other families the
Euphorbiaceze and Marantacee. Thegroups
mentioned have shown a peculiar fitness for
tropical environment. One genus alone,
Cassia, includes four hundred and fifty species,
nearly all of which are at home in countries
near the equator. One of the northern repre-
sentatives, Cassia chamecrista, has acquired
the name of the ‘Wild Sensitive Plant’’
throughout the middle and northern states,
while Cassia nictitans is similarly designated
in New England. Southward the number of
species increases with that of the other legum-
inous plants until near the equator, represen-
tatives of the group form a very large propor-
tion of the total mass of vegetation.

Mimosa pudica the ‘Sensitive Plant’’ or
‘‘Shameweed’”’ of the West Indies is one of
the most attractive members of this group,
since in addition to the typical adjustments of
the leaves, which it performs with great ra-
pidity and delicacy, it also exhibits reactions
to other and unusual stimuli. The move-
ments of plants are generally so slowly made
as to be incapable of detection except by re-
peated or long continued observation. M1-
mosa, however, is one of the small number
which is capable of rapid movement of large
organs. This fact, and the great degree of ir-
ritability shown, drew the attention of the

MIMOSA 49

earlier botanists, and it has been the object
of a succession of investigations for more
than a century. The plant has become a
classical illustration in botanical literature,
and a drawing showing positions taken by
the leaves after movement, made by Duchar-
tre many years ago, is still reproduced in text
books.

The equatorial zone is the home of an enor-
mous number of species. The island of Ja-
maica, with an area of about 6,000 square
miles, about that of Connecticut, furnishes
approximately four-fifths as many species of
flowering plants as are to be found in the
United States east of the Mississippi river.
The advent of modern man into the teeming
tropical areas, and the facilities he afforded
intentionally and unintentionally for distri-
bution has led to a wholesale emigration and
intermingling of tropical forms.

Mimosa pudica was originally an inhabi-
tant of the plains of Brazil and Venezuela, but
it has accompanied man in his journeys
around the world in the equatorial regions.
It has become a virile pest in fields, gardens
and pastures in warm countries, and is culti-
vated in greenhouses in latitudes as high as
55° N.

It is a low, spreading, prostrate, woody
plant in the tropics. The forms seen in north-

Organization

50 LIVING PLANTS

ern greenhouses show an erect stem because
of insufficient light and are ‘‘drawn’’ in the
language of the gardener. The scattered
leaves consist of a long petiole bearing two
or four leaflets, which are divided into eight
to twelve pairs of small ovate pinnules. The
bases of the stalks of the pinnules, the leaflets
and the petiole are developed in the form of
thick cylindrical swellings (pulvini). The
woody, mechanical tissue in the stalks is in
the form of a hollow cylinder, but in passing
through the pulvinus to join thestem it comes
together forming a solid rod. The central
cylinder of mechanical tissue is surrounded by
a thick layer of thin walled motile cells which
are capable of rapid changes inform. Such
alterations are due to variationsin the hydro-
static pressure in the cells. When the cells of
one side of the pulvinus give off water which
passes into the spaces between the cells, a
curvature toward this side results from the
unchanged pressure of the turgid cells of the
opposite side. The sinking of a leaf upon its
petiole is due to the relaxation of the cells of
the lower side of the pulvinus. When these cells
reabsorb the water from the intercellular
spaces, their former size and shape is slowly
regained and the leaf is returned to its former
position.

MIMOSA 51

The continuous observation of half a dozen
healthy plants through the course of a mid-
summer’s day will reveal the greater number
of reactions exhibited by this plant.

Early in the morning the pinnules are seen
to occupy a horizontal position with the
blades fully exposed to the light. The petioles
are slightly elevated above the horizontal.
As the sun mounts toward the noonday posi-
tionits rays increase in intensity, and their ef-
fect on horizontal leaf-blades will increase cor-
respondingly. Atsometime, however, before
therays strike the surface perpendicularly, the
regulatory mechanism of the plant sets up
movements in the pinnules by which their
surfaces are directed upward at an acute
angle. The angle increases as the sun nears |
and passes the zenith until the edges of the
blades are directed almost exactly toward
the sun, and its rays exercise an actual effect
on the leaf not much greater than in the
early forenoon. If this adaptation were not
made, the fierce rays would strike through
the leaf-blades so strongly as to injure the
chlorophyll and evaporate more water than
could be supplied by the roots, thus causing
wilting.

As the sun declines toward the west, the
blades return once more to the horizontal Night positions
position, but the approach of night brings 0 leaves

Day positions
of leaves

LIVING PLANTS

52

BB, night

.
,

AA, normal position
fter shock.

iona

CC, posit

ition ;

Fic. 5:—Mimosa
posi

MIMOSA 53

another danger to the plant, consisting in an
extremely rapid radiation of heat and accom-
panying loss of water. This threatened in-
jury is again avoided by deflection of the
blades from the horizontal to the perpen-
dicular. The movement begins at or near
sunset and the laminz slowly rise until their
upper surfaces are appressed. The evapora-
ting surface is thus reduced exactly one-half,
while the radiation of heat is much less from
a vertical plane than a horizontal one. Ref.
erence to the accompanying illustrations will
show that minor movements have occurred.
A movement of the pulvinus at the base of the
petiole results in placing that member hori-
zontally.

The ‘‘night,”’ ‘“‘sleep’’ or nyctitropic move-
ments occur daily while
those to avoid the ef-
fects of the hot sun are
exhibited only when a
certain intensity is at-
tained. The regular
daily recurrence of the
conditions which cause
the nyctitropic move-
ments has fixed them
so firmly in the plant
that they occur at

Fic. 6.—Hot sun position j 1
Spa rhythmic intervals re-

Reaction
to shock, etc.

54 LIVING PLAN'S

gardless of the surroundings of the plant.
The “‘sleep’’ of the plant on any given night
is not the direct result of the absence of light
at that time but of the darkness of previous
nights. Ifa healthy individual is placed in
continuous light or darkness, it continues to
‘‘so to sleep’’ at regular intervals for several
days, but finally sickens or adjusts itself to
the new conditions imposed upon it. The
habit is regained on restoration to normal
conditions.

The sleep position may be produced in the
middle of the day by suddenly excluding the
sun’s rays, but the normal position will soon
be regained unless the temperature is greatly
reduced. Mimosa is one of the plants in
which the night position is wholly a response
to low temperatures.

If ascreened plant is suddenly exposed to
the sun’s glare in the middle of the day, the
leaves sink and the pinnules close as if struck
or jarred. Many interesting deviations from
these typical reactions have been observed.
Thus, if a healthy plant is placed in a dry
room at 15° Centigrade the blades will be
found extended in the morning, while the pe-
tioles have assumed and retained a depressed
position. The reactions described above are
not especially characteristic of mimosa, since
they are exhibited by many hundreds of spe-

MIMOSA 55

cies and may be easily observed in the bean,
oxalis, locust, cassia, and other leguminous
species.

It has other forms of irritability, not at all
common or widely distributed. Thus if one
should lightly touch, or blow the breath upon,
the expanded leaflets of mimosa at ordinary
temperatures, the pinnules or ultimate divi-
sions of the leaf would: rise up above the mid-
ribs upon which they are borne, closing in
pairs. Ifthe shock were given with sufficient
force or if a blow of the pencil be given upon
the stem all the leaves will erect the pinnules
and sink on the petioles. A flame held near
the leaflet, or the fumes of acid, ammonia, or
chloroform, will cause the movement also,
while an electric current applied to almost
any part of the plant has a similar effect.
More correctly speaking, the breaking of the
current is the true stimulus. The plant re-
sponds to chemical, mechanical, thermal
and electrical stimuli. An interesting differ-
ence between the reactions of mimosa and
those of the tendrils of climbing plantsis that
the latter move when pressed by asolid body,
but not when struck. Mimosa, on the other
hand, responds to a blow orshock, butnotto
a steady pressure, as the leaves may be given
a steady pressure by the thumb and finger
without results.

56 LIVING PLANTS

A careful analysis
of the above reac-
tions will yield many

interesting results.
If a quick snipis giv-
en with scissors
to the terminal
pair of pinnules
in one of the upper
leaves, the pinnules
disturbed will close
rapidly and then the
other pairs will react
in succession until
the base of the leaflet
is reached. After a
short interval the
basal pairs of pin-
nules of the neigh-
boring leaflets close
and thepairs toward
the apices in succes-
sion. Before the mo-
tion has been taken
up by all of the leaf-
lets the pulvinus at
the base€s0d sie

Fic. 7.—Successive positions of mimosa after stimulation at
the tip of a leaflet. a, position a few seconds after a flame is
applied at f. b, the impulse has reached the base of the leaf.
c, the impulse has traversed nearly the entire shoot and is near-
ing the leaf-tips of the last leaf reached.

MIMOSA 57

main leafstalk acts, and the entire leaf
sinks. If the stimulus has been given with
sufficient force, or by means of a match flame
instead of the forceps or scissors, the move-
ment will be taken up in turn by the leaves
above and below the one treated. The reac-
tion of the plant is most rapid in specimens
growing vigorously, and standing in moist
air at a temperature of 30—35° centigrade.

It may be noticed that a short time elapses
between the action of the stimulus from the
scissors or flame and the reaction of the leaf-
let. This is termed the latent period and
amounts to slightly less or more than a sec-
ond according to conditions. The experi-
ments also have demonstrated that theeffects
of a force applied to one part of the plant
may be transmitted over its entire body, which
is often a yard or a meter in length. If care-
ful note of the time is made between the appli-
cation of the stimulus to the plant and the
reactions in different portions of the plant,
together with accurate measurements, it will
be found that the impulse or force set in mo-
tion by the stimulus travels at the rate of
eight to twenty-five millimeters (4 to 1 inch)
per second under favorable circumstances.

As the plant stands in the quiet atmosphere
on a warm morning, a breath of air or the
smallest drops of water striking the blades

Transmission
of stimuli

Repetition
of stimuli

58 LIVING PLANTS

will cause reactions. If the movement of the
air is continuous and freshens to a breeze, or
the drops of water are followed by a steady
rain, the plant finally replaces the pinnules in
the original position, though blown about or
beaten bytherain. The plant is enabled todo
this by its great power of accommodation to
any force acting upon it. The real stimulus
is not the force in itself but consists in changes
in the forces acting upontheplant. Thismay
be demonstrated if a specimen is subjected to
a spray of water forming an artificial rain-
storm in a greenhouse. After a time it be-
comes accustomed to the falling water and
resumes the normal position. If now the
force of the spray is suddenly increased, a re-
action is shown, and the pinnules are closed.
After exposure to the heavier spray for atime
it once more resumes the nurmal attitudeand
the experiment may be repeated with similar
results. A specimen of mimosa grown in a
pot may be carried on a journey in a wagon
or railroad train, and may be seen to resume
the normal position after it has become accus-
tomed to the jarring from the vehicle, if the
temperature and light are favorable. While -
an individual may thus accommodate itself
to an unusual intensity of any force, it is as
delicately sensitive to other stimuli as usual.
Thus one may stand some distance from a

MIMOSA 59

plant exposed to an artificial rainfall and
cause a reaction by a puff of the breath.

When a plant has become accustomed toa
continuously acting force, the amount of ia-
crease necessary to secure a reaction is a defi-
nite and fixed proportion of the continuously
acting force. The formula which expresses
this proportion has been found to apply to
the reactions of both plants and animals.

The manner in which impulses are trans-
mitted from one part of a plant to another
forms a problem, the solution of which has
baffled investigation for more than a century.
Many interesting experiments looking to-
ward a determination of the question have
been made.

It has been found that when a section of a
stem has been girdled by the removal of the
bark and cambium the transmission of an 1m-
pulse is in nowise hindered, thus proving
that the path lies through the wood, which
in this plant is composed of cells which die on
attaining normal size. The fact is proven
more positively by the removal of the wood
from another section, the living tissues and
bark being allowed to remain. In this in-
stance no transmission occurs.

If a short section of a stem is killed by
means of a bandage of cloth kept saturated
with boiling water for several minutes, trans-

Method

of transmission

60 LIVING PLANTS

mission is not hindered and a stem may be so
treated as to consist of alternate dead and
living portions and still transmit the effects
of stimulation. This set of experiments dispos-
es of the idea that the transmission of impulses
is in any sense a function of living matter in
mimosa.

The presence of a system of elongated cylin-
drical cells in the outer part of the woody tis-
sue, containing glucosides and water under
pressure, led to the formulation of the theory
that these tubes were the paths of transmis-
sion and that impulses consisted of simple hy-
drostatic disturbances traversing the system,
as the pulsations of the forcing engines are
transmitted through the mains and pipesof a
city water system.

The mere presence of these tubes can have
no especial significance, because they are found
in hundreds of species of Leguminosz in which
transmission does not occur. It is to be ad-
mitted of course that the tubes might serve
such use in mimosa, though not in any other
plant. When sudden disturbances areinduced
in the contents of the tubes by means of
powerful pumps, abrupt pressure, the appli-
cation of heated rods to the stem or strong
chemical solutions to cut surfaces, no reac-
tions follow, and it is difficult in face of such
results to maintain that an impulse is a hy-

MIMOSA 61

drostatic disturbance. As a matter of fact
impulses have been conducted through air-dry
wood of the stem in which hydrostatic trans-
mission would be impossible, and the only
pathway would be the water of imbibition in
the cell wall. Information as to the condi-
tion of water in the wall is not sufficient to
make the formulation of any reasonable
theory based on this assumption possible.

The reaction of mimosa to impact and
injury is supposed to be a protection against
drouth and damage from grazing animals.
A recent writer says: ‘‘When a browsing
animal approaches a clump of mimosa and
agitates any part of it at all strongly the
green appearance disappears at once, and only
an apparently withered clump in which the
hard and prickly stems are most conspicuous
remains; the consequence being that the ani-
mal either turns away or passes through the
clump toless bewildering pasturage.”’

As the plant has not been studied in its
habitat in Venezuela and Brazil it is not
definitely known whether it is ravaged by
grazing animals or not. The theory was
once proposed and widely reiterated that the
contact irritability of mimosa was developed
as a protection against hailstorms, regardless
of the fact that the plant never encounters
such dangers in the torrid zone. As has been

Purpose
of reaction
to shock, etc.

62 LIVING PLANTS

shown it is not a protection against rain, be-
cause the plant soon becomes accustomed to
the falling drops, and opens. The fact that
many plants of the temperate zone, among
which is the ordinary locust (Robinia pseud-
acacia), exhibit irritability to impact leads to
the suggestion that the plant must be very
delicately poised to be able to avoid the dan-
gers of changes in temperature, and that any
shock sets the protoplasmic machinery in
motion.

The movements of mimosa in response to
the action of ether, chloroform and other an-
esthetics, as well as electricity, is due to the
direct action of these agents on the motor tis-
sues. A similar instance is afforded by the
action of changes in temperature upon ten-
drils. |

Equipped with an irritable organization of
such a high degree of complexity, mimosacan
easily hold its ownin the swarm of competing
organisms in tropical climates. A similar or-
ganization would be highly disadvantageous
as well as impossible in high latitudes.

V.

UNIVERSALITY OF CONSCIOUSNESS AND PAIN*

“Tt is my faith that every flower that blows
Enjoys the air it breathes!’’
Wordsworth.

It is the glory of modern science to have
shown that the phenomena of the universe are
capable of being grouped into classes and sub-
classes, and that throughall the ramifications
runs anessential nexus, or genetic association.
In the organic world the development of
plants and animals has been shown to be
governed by similar laws tor both, and their
special ways of maintaining the funderment-
al characteristics of their existence is being
found more and more to be based upon like
properties.

In the following pages the writer hopes to
present a generalization that throws a some-
what different light upon the life of plants

*Read before the Parlor Club, an organization devoted to
literary and scientific culture; Lafayette, Ind., Sept. 20, 1896.

Unity

in nature

Superstition
of the
mandrake

Can a man-
drake feel?

64 CONSCIOUSNESS AND PAIN

from that usually entertained, and yet he
does not wish to claim more than well-estab-
lished facts and reasonable analogy will up-
hold.

An old superstition ascribed to the man-
drake, acommon plant of the Mediterranean
region, a supersensitiveness that caused it to
utter such cries of pain when drawn from the
earth ‘‘that living mortals, hearing them, yo
mad.’ This marvelous anthropomorphic ex-
hibition was associated, so it was said, with
an equally marvelous resemblance of the plant
to a human body wherein lay the reasonable-
ness of the plant’s behavior.

By logical extension of modern deductions
regarding the nature of the physical basis of
life and the unity of ecological methods in its
expression, it is not too much to claim that a
more genuine agreement exists between man-
drakes and man than the superficial one of
form that appealed so powerfully to the
ancients; in fact, as is well known at present,
the representatives of both kingdoms not
only grow, breath and require food, but they
respond to changes in environment by being
irritable. On the one hand the irritability
rises, especially among the higher animals, to
a clear exhibition of feeling, capable of induc-
ing suffering; what is there in the logic of the
situation that prevents us from assuming

CONSCIOUSNESS AND PAIN 65

that plants also feel? I venture to say that
they do feel, and that the mandrake, or any
other plant,isreally hurt when pulled forcibly
from the ground, suffering its modicum of
pain, although unaccompanied by signs that
make the fact patent to oursenses. Ifa plant
can feel a bodily hurt, it must necessarily pos-
sess consciousness, for pain without conscious-
ness is inconceivable. Hence the thesis: all
living organisms, whether animal or plant,
arecapable of conscious pain to a degree com-
mensurate with the requirements of their
nature.

At the outset it must be clearly recognized
that the word consciousness, as used in this
connection, contains no reference to self-con-
sciousness, which implies introspection. Self-
consciousness, it may be said in passing, is
necessary that the individual may, for in-
stance, be aware of its own identity, or may
reflect upon a given sensation, which powers
belong, undoubtedly, not to all classes of be-
ings, but only to the more highly organized,
and especially to those with a centralized ner-
vous system.

General consciousness, on the other hand,
implies arecognition of the impact of stimuli;
the individual knows that the uniformity of
the conditions of its existence is disturbed,
sometimes pleasurably, sometimes painfully.

Meaning of
consciousness

Examples of
consciousness

66 LIVING PLANTS

Recognition does not come, however, with all
changes in external conditions, they must
reach a certain violence, or intensity, before
consciousness is aroused; and the degree re-
quired for efficiency will vary with the organ-
ism.

The state of consciousness and the usual
accompanying reaction of the organism can
be illustrated by the well known effects of a
thrust. Let us suppose that the organism in
question is a man, and the thrust is received
from the proboscis of a mosquito. The man
may be especially sensitive to mosquito bites
and retaliate with a violent blow of the hand.
However, being a rational being, he may first
reflect upon the probability of getting the
greatest satisfaction from his effort, and take
certain precautionary measures to secure
deadly aim. If the same invasion of per-
sonal rights be attempted with the man’s
canine companion, the reactionary effects are
similar in every essential; but being a far less
rational being than his master, the dog will
give little or no thought to the manner of the
removal of the offending insect. As we go
down the scale of organized life the mosquito
bite will continue to meet withcounteraction,
taking on more and more the character of a
simple sensitive response to an irritation.

CONSCIOUSNESS AND PAIN 67

In order to carry our observation further
and have the trials under better control, sup-
pose a splinter of wood, or a feather, be used
as the irritating object. If now thisawaken-
er of consciousness be cautiously applied to
the back of the neck of an unsuspecting per-
son, it will arouse reaction, provided the fric-
tion has been sufficient to be felt. Suppose
we tickle the nose of a dog, who is taking a
siesta with his eyes shut; there is not sufficient
difference in the results to require comment.
If the back of a caterpillar or worm next be
tested, a wriggling of disapproval takes
place. Now touch the mantle of the lazy
clam, and make sure that your fingers are not
too near to be caught between the jaws of
the shell as it springs together. Try a sea-
anemone and watch the speedy infolding and
packing away of its whole garniture of bril-
liant fringes. Proceed, if you choose, to the
bell-animalcule, the amoeba, and others of
lowest and simplest animals.

But we need not stop with animals. Try
the same test on theleaf of the Venus’ fly-trap,
and note the astonishingly quick interlocking
of the rat-trap edges of the leaf-blade, a
movement that has brought mortal surprise
to many a fly. Brush the inner surface of a
tendril of the wild cucumber and notice how
it begins in a moment to slowly coil up.

Definition
of terms

68 LIVING PLANTS

Touch the leaf of a sensitive plant and see it
shrink away into the smallest compass at-
tainable.

What do all these animal and plant move-
ments mean, except it be that the individual
has felt something and acts responsively, ac-
cording to its ability. And yet it may be ob-
jected that while man and some of the higher
animals may possess genuine feeling, that is,
to be more explicit, may experience conscious
pain, yet the lower animals and all plants
only react mechanically upon stimulation,
such as frictional contact, shock, light, heat,
electricity, etc. To illustrate: when a dog
howls upon being hit with a stone, it will
generally be admitted that it is because he
suffers pain; but when an earthworm strug-
gles as the angler threads it upon the hook, a
question arises whether the movement is in-
dicative of pain or whether it 1s simply reac-
tionary, like the quivering of a mass of jelly
when struck; and when a twig is pulled from
a tree no more thought of pain is connected
with the act than in the breaking of a stone.

In discussing asubject like this considerable
difficulty is found in using terms in such a
way that they will convey an exact and uni-
form meaning. In the task I have essayed,
nothing is easier than to upset the whole ar-
gument by employing the words feeling,

CONSCIOUSNESS AND PAIN 69

pleasure, pain, etc., in some of their several
legitimate meanings, whichare not, however,
those suitable for the topic, and ignoring the
meanings which alone can lead to clear no-
tions. To show the diversity of usage in em-
ploying the word ‘‘feeling”’ I will quote Ward
in the Encyclopedia Britannica (xx, 40),
who observes that “it is plain that further
definition is requisite for a word that may
mean (1) a touch, as feeling of roughness, (2)
an organic sensation, as feeling of hunger, (3)
an emotion, as feeling of anger, (4) feeling
proper, as pleasure or pain.”’ It is inthis last
sense only that I wish to employ it. And it
is well to bear in mind in the same connec-
tion, that in simple organisms, feeling, like
other functions, will have but a simple and
feeble development, while in complex beings,
it will take on a diversity commensurate with
the degree of organic attainment, preserving,
however, throughout the whole gamut of var-
iation, the same fundamental quality of
physical pain and pleasure.

No less diversity exists as to the use of the
terms pain and pleasure. Ina recent volume
on the subject (Marshall: Pain, pleasure and
zesthetics, 1894, p. 169) I findit stated that
the ‘‘activity of the organ of any content if
efficient is pleasurable, if inefficient is pain-
ful,’ which is nearly in accord with the

70 LIVING PLANTS

philosophy of Lester F. Ward, who says that
“the supply of tissue is attended with pleas-
ure,’ and ‘‘the destruction of tissue results in
pain’’ (Monist, v, 253). But both these ob-
servations, it seems to me, carry the analysis
too far. I am inclined to agree with Paul
Carus, who says that although ‘‘It is gener-
ally assumed that pleasure is an indication
of growth and pain of decay, it has never
been proven, and after a careful consideration
of this theory I have come to the conclusion
that it is based upon an error. Growth is
rarely accompanied with pleasure and decay
is mostly painless.’”” He goes on to remark
that the most optimistic philosophers look
upon pleasure as positive and pain as nega-
tive, while the greatest pessimist, Schopen-
hauer, turns the tables and says pain 1s posi-
tive and pleasure is negative. He adds as his
own opinion that ‘an impartial considera-
tion of the subject will show that both pleas-
ure and pain are positive. Pain is felt when-
ever disturbances take place, pleasure is felt
whenever wants are satisfied’’ (Monist, 1,
559). This definition accords so well with
the usual mode of thinking and use of terms
that I deem it unnecessary to elaborate it. If
now it be admitted that pain results from a
more or Jess violent interruption or altera-
tion of the normal functional state of the or-

CONSCIOUSNESS AND PAIN yall

ganism, we shall only have to make sure
that the organism knows that it is suffering
the pain, and the basis of the argument will
have been established. It must be remember-
ed, however, that a sensation which would be
called pain, if of sufficient intensity, when
very slight might be called simply discom-
fort.

This leads us to a consideration of what is
to be understood by consciousness. It is in-
advisable to attempt an extended exposition
of this much treated and intricate question,
both for want of space and because meta-
physical subjects are proverbially tedious. It
seems to me sufficient in order to make my
position intelligible, to say that when the
organism is aware of a feeling of pleasure or
pain, or of any other sensation, knowing that
the same is located within its own organs, it
is possessed of consciousness. This is whatis
usually known as simple sense-perception, the
simplest type of consciousness. In the higher
and more complex forms, memory plays a
constantly increasing part; and judgment,
the formation of concepts, and all the intrica-
cies of mental activity finally enter into the
problem.

It is usual to begin with man, and say with
Noah Porter that consciousness is ‘‘the
power by which the soul knows its own acts

72 LIVING PLANTS

and states” (‘“‘Human Intellect,”’ par. 67), or
with Locke that it is ‘‘the perception of what
passes in a man’s own mind” (‘Human Un-
derstanding,”’ II, i, 19), and then to pass
down the scale of being and admit the posses-
sion of consciousness in such animals as are
thought to be endowed with a “soul” or
‘“mind,’’ according to the definition these
words are permitted to bear. Anatomical
structure is made to furnish considerable evi-
dence in this connection. Perhaps Grant Al-
len’s remarks about the earwig in his lucubra-
tion on ‘‘thicroscopic brains’’ present sufh-
ciently well theattitude of most writers atthe
present time. ‘Of course miost insects have
no real brains,’’ he says. ‘‘The nerve sub-
stance in their heads is a mere collection of ill-
arranged ganglia directly connected with
their organs of sense. Whatever man may be,
an earwig at least is a conscious, or rather
a semi-conscious automaton. Hehas just a
few knots of nerve-cells in his little pate, each
of which leads straight from his dim eye, or
his vague ear, or his indefinite organs of
taste; and his muscles obey the promptings
of external sensations without possibility of
hesitation or consideration, as mechanically
as the vaive of a steam-engine obeys the gov-
ernor-balls” (‘‘Evolutionist at Large,” 2).
Again in speaking of slugs and snails hesays:

CONSCIOUSNESS AND PAIN 73

“Their nerves are so rudely distributed in
loose knots all over the body, instead of being
closely bound into a single central system as
with ourselves, that they can scarcely possess
a consciousness of pain at all analogous to
our own” (ibid, 12). Ofcourse, if animals of
as high an organization as insects and snails
are thought to be meagerly endowed with
sensibility, animals of still lower grade, and
those especially that are without nerves must
be quite outside the bounds of consideration,
to say nothing of plants.

But there is another way in which to ap-
proach the matter; and one, it seems to me,
that leads to results more in accord with our
present understanding of the unity of nature
and the evolution of organic forms. Living
protoplasm is a very unstable substance.
Living organisms of even the lowest type
have but a fighting chance for continued ex-
istence. Life, asks the poet, what is it?

“A frail and fickle tenement it is;
Which, like the brittle glass which measures time,
Is broke ere half its sands are run.”’
—Notes and Queries, 1863.

The smallest and most structureless being,
as well as the largest and most intelligent,
must guard itself against bodily accidents of
all kinds, it must look out for its daily means
of subsistence, and furthermore, it must main-
tain itself against the encroachments of fel-

General
irritability

74 LIVING PLANTS

low beings. The struggle for existence is by
no means a fiction, even with an amoeba.
What is the provision, the device, the method
by which the organism is enabled to success-
fully meet the destructive and levelling ten-
dencies of the world outside itself? Itis tobe
found, without question,in that general prop-
erty of all living matter usually designated
as irritability. If a bit of the leaf of water-
weed, the hair from a pumpkin stem, an
amoeba, or any similar vegetable or animal
structures be placed under the microscope
and irritated in some manner, say by a light
tap or shock, sudden change of temperature,
aninterruptedcurrent of electricity, etc., the
soft protoplasmic portion will shrink and
change form in a characteristic way that
thoroughly justifies us in saying that it makes
a sensitive response to the stimulus. Aftera
time the normal form and activity are regain-
ed, and another irritation will be followed by
another visible response. If, however, the ir-
ritation be too severe—if the tap be too
strong, the change of temperature too great,
or the electric shock too intense—the convul-
sion which follows will be mortal, and no fav-
orable environmental conditions or supply of
energy will again restore the life that has dis-
appeared. The protoplasm or animalcule is
as genuinely dead as the man who has been

CONSCIOUSNESS AND PAIN 75

knocked over with a mortalblow. Every or-
ganism, except when in a special state of re-
pose—for instance, during the hibernation of
some animals and the period of a plant’s ex-
istence when enclosed in a seed—every organ-
ism of whatever grade of development is
possessed of sensitiveness of essentially the
same character as that of the simplest bit of
protoplasm revealed by the microscope. As
the organism rises in the scale of being,
irritability takes on a correspondingly varied
development. And it may be asserted that
the recoil when I accidentally press my hand
against a thorn 1s of the same essential
nature as that of an amoeba or slime-mold
when pierced with a sharp point; or that the
so-called instinct of the dog which urges him
to follow up the scent of a rabbit when hun-
gry, has its basis in the same fundamental
property of living matter as that which
causes the lively spores of the salmon-fungus
(Saprolegnia) to swim toward the spot from
which there is a slight emanation of decaying
fish, or the leaf-mildew to turn and grow
toward the breathing pore of a grape leaf, in-
to which it desires to enter and find acongen-
ial place of development, because it detects a
slight escape of vegetable acids from that di-
rection.

Irritability in its various forms must, there-

Welfare of

the organism

758 LIVING PLANTS

fore, be considered the property of living
beings by which they defend themselves
against injury, secure food, and obtain the
best conditions for existence. But there is no
efficiency in irritability unless the organism is
enabled to change its position or the position
of some of its organs upon stimulation, that
is, it must be capableof molar motion. How
molar motion originated is a question into
which [ shall not enter, although a most im-
portant one in a full exposition of the subject;
neither shall Itouch upon the origin of organs
and some other related matters of philosoph-
ical importance. It will suffice in this con-
nection to point out that the preliminary
to every vital movement, not automatic, 1s
aneffort. That all plant and animal move-
ments, not accidental, are related to the wel-
fare of the organism isa proposition that will
be generally admitted; and such movements
may consequently be classed as adaptive.
That all movement having significance must
at first have been adaptive seems to be sufh-
ciently clear, and therefore automatic move-
ments must necessarily have been derived from
conscious ones. This, l am aware, is the re-
verse of the usual course of reasoning, and as
the form in which I have stated it is too con-
cise to be readily apprehended, it will be best
to give a few lines to its elaboration,

CONSCIOUSNESS AND PAIN FT|

That an adaptive movement requires effort,
and that etfort implies consciousness is the
first step in the argument; that automatic
movements must have been derived from con-
scious movements, in order to avoid the ab-
surdity that actions can be directed toward
an end by pure chance, is the second step in
the argument. These steps can probably be
illustrated by a concrete example better than
by abstract statement; andI shall take a
familiar example although the complexity of
the conditions give many opportunities for
being misunderstood, rather than select an
illustration from the less familiar domain
of simple organisms. The man who is being
tormented by a mosquito, that is, receiving a
stimulus giving rise to pain, must put forth
an effort in order to moveahand to crush the
offender. That effort must be a conscious
effort, or else the blow would be aimless and
futile and stand in no relation to the cause.
Butif the man were preoccupied, he might aim
a well directed blow at the mosquito and yet
not realize that any such thing had occurred.
In this case it is evident enough that it was
not the first time that he had performed a
similar act. The first time such a movement
was made,it must have been a conscious one,
and for many times afterward, until it could
be performed without conscious effort. All

Adaptive move-
ments imply
consciousness

78 WIVING PLANTS

other automatic movements may be similarly
explained. In reference to the involuntary
movements of the heart and other viscera,
Cope has suggested that they ‘‘were organ-
ized in primitive and simple animals in suc-
cessive states of consciousness, which stimu-
lated voluntary movements, which ultimately
became rhythmie”’ (Organic Evolution, 511).
He goes on to observe that “‘the structure of
the infusoria offers the structural conditions
for such a process,’’ and proceeds to illustrate
how the contractile vesicle might have thus
arisen, and from it the mammalian heart.
But we need not follow him.

Lester F. Ward has said that ‘‘pleasure and
pain are the conditions to the existence of
plastic organisms, pleasure leading to those
acts which insure nutrition and reproduction,
and pain to those which will insure safety”’
(Psychic Factors of Civilization). Cope has
elaborated theideainto a well maintained hy-
pothesis, which he calls archesthetism. He
defines it thus: ‘‘It maintains that conscious-
ness, as well as life, preceded organism, and
has been the primum mobile in the creation
of organic structure. This conclusion also
flows from a due consideration of the nature
of life. I think it possible to show,” he goes
on to say, ‘‘that the true definition of life is
energy directed by sensibility, or by a mechan-

CONSCIOUSNESS AND PAIN 79

ism which has orifiinated under the direction
of sensibility”’ (1. c. 513). With this view of
the role of consciousness the writer fully
agrees.

Let us now stop and see where weare. I
have tried to show that all organisms, even
to the very simplest, whcther plant or animal,
from the very nature of life and the struggle
for its maintenance, must be endowed with
conscious feeling, pleasure and pain being its
simplest expression. I have attempted to
show that consciousness is not a function
superimposed upon, or evolved from an ad-
vanced state of organic development, but is
co-extensive with life.

The hypothesis would likely meet with con-
siderable adherence were it not for plants,
which all writers seem to think present an
insurmountable difficulty. Paul Carus, the
learned editor of the Monist and author of
many important philosophical treatises, as-
serts that ‘‘pleasure and pain are undoubtedly
important factors in the evolution of the ani-
mal world, but the kingdom of plants demon-
strates that theexistence of plastic organisms
with complex systems of nutrition and repro-
duction and also devices for safety is possible
without pleasure and pain” (Monist, iv. 624).
Cope has tried to get around the difficulty in
his work on the primary factors of organic

Pain a factor
in evolution

Action of
plants difficult
to interpret

sO LIVING PLANTS

evolution by assuming that plants are won-
derfully degenerate, having little cause for
exertion, aud behave in this respect like para-
sites. ‘‘We can understand,” he says, “how
by parasitism or other modeof getting a live-
lihood without exertion, the adoption of new
and skillful movements would become unnec-
essary, and consciousness itself would be sel-
dom aroused. Continued repose would be
followed by subconsciousness, and later by
unconsciousness. Such appears to be the
history of the entire vegetable kingdom” (l.c.
509). The writer believes that such opinions
as just quoted are the outcome of ignorance
of the present status of botanical science;
not the botany that teaches about plants—
their names, and the ways of identifying the
different kinds—but the botany that intro-
duces the learner to a knowledge of their
modes of living, their habits and their physi-
ology. Plantsaremore difficult to study and
understand than animals, because they are
so much more unlike ourselves. Vegetable
activities are very different from animal ac-
tivities; they have been developed along dif-
ferent lines. It is only recently that we have
begun to understand them atall. And yet
already, the elucidation of plant movements
is providing a key to the study of animal
movements. Recently an investigator at the

CONSCIOUSNESS AND PAIN 81

Zoological Station at Naples has shown that
wher a moth flies into a flame it is attracted
in essentially the same way that the window
plant is whenit turns to the light. One must
go to the tropics to see the highest develop-
ment of movement in plants, on account of
the high and uniform temperature, and pos-
sibly other environmentalconditions. I have
been told that in Java, as one walks through
a tangle of sensitive plants, they will drop
down in their deprecating way for yards on
either side, as if suddenly aroused into life
only to be again transformed into lifeless
sticks by some unseen power.

It is because plant movements are so slow,
as a rule, that we get the erroneous idea that
they are rare. Have you ever noticed that
beans and clover put their leaves into a differ-
ent position at night, the same as a sensitive
plant does; and that locusts, lindens, red-bud,
and many other trees and shrubs do thesame?
Suppose a seed falls upon the ground and
germinates: if it has no sensitiveness by
which it feels the action of gravity, the
chances are that it will speedily perish, for
the root would not otherwise find its way in-
to the soil, except throughaccident. There is
one excellent reason why plants rarely re-
spond visibly to bodily injury, and that lies
in the fact that they are, for the most part,

82 LIVING PLANTS

fixed objects. They have not been required to
learn to move out of the way of danger, or
to recoil when nurt, because the character of
their structure makes movement difficult,
their limbs and organs are not sufficiently
plastic, and their attachment to the earth re-
strains them, like Prometheus bound.

This leads me to say, that as arule we do
not expect the right things of plants; we do
not understand them. Our point of view is
not well chosen. Animals are free moving
beings, with their soft parts in considerable
masses, while plants are fixed to one spot all
their lives, and have their soft parts infinitely
divided, each particle being encased in a
rather rigid envelope. How can they act
alike? And yet both are organized from the
same character of living matter, which is
obedient to the same general laws.

In another respect plants differ widely from
animals. They have no nervous organiza-
tion, and no co-ordinating centers for deter-
mining the character of movements. The
movement that follows a stimulus is there-
fore confined usually to the near vicinity of
the point of stimulation. If they experience
pain, as I think they may, it can rarely ex-
tend to the whole organism, but the injured
organ suffers without its fellows being
affected.

CONSCIOUSNESS AND PAIN 83

Plants as a class are not degenerates. In
their way they have reached a high state of
development, but it is not the development
of animals. As their movements are slow,
and poorly co-ordinated, it must be assumed
that their pains and pleasures are correspond-
ingly feeble; not but that they are genuine,
nevertheless, and to them mean as much as
ours dotous. If another man who is inferior
to ourselves, if a horse, a dog, a bird may be
made to suffer, and in consequence ought to
have considerate treatment, so may the sim-
plest animals and so may all plants.

I will close with a quotation from Grant
Allen,andacomment thereon. ‘‘Hoeing among
the flower beds on my lawn this morning, for
I ama bitof agardener in my way,” he writes,
“T have had the ill luck to maim a poor yellow
slug, who had hidden himself among the en-
croaching grass on the edge of my little par-
terre of sky-blue lobelias. This unavoidable
wounding and hacking of worms and insects,
despite all one’s care,is no small drawback to
the pleasures of gardening in propria persona.
Vivisection for genuine scientific purposes in
responsible hands, one can understand and
tolerate, even though lacking the heart for it
one’s self; but the useless and causeless vivi-
section which can not be prevented in every
ordinary piece of farm work, seems a gratu-

Plants not
degenerates

84. LIVING PLANTS

itous blot upon the face of beneficent nature.
My only consolation lies in the half-formed
belief that feeling among these lower crea-
tures is indefinite and that pain appears to
effect them far less acutely than it effects
warm-blooded animals.’’ To which I have to
addthat heshould have embraced plants, and
then conciuded that i proportion to their de-
gree of organization they are hurt, and to the
same degree deserve consideration.

We

HOW COLD AFFECTS PLANTS.*

If one should carefully note the exit of his
floral acquaintances in the autumn he would
find that not allof themsuccumb to the rigors
of the cold season at the same time. Some
of the members of the plant communities pe-
culiar to meadows, woods and slopes will
give over activity at the first suggestion of
frost, while others endure a long succession
of freezing nights before they finally perish.

Still others, the conifers and evergreens, the
thick beds of mosses, and the thin green layers
formed by the liverworts and the grayish
coating formed by the lichens, live through
arctic winters without great apparent change,
except indeed thatsome grow and fruit in and
under the snow.. Between the groups which

*Given before the Botanical Seminar, University of Minne-
sota, Nov. 13th, 1897.

Varying
reaction
to coli

86 LIVING PLANTS

are killed by the winter, and the evergreens
which withstand it without any great altera-
tions in outward form, stand the deciduous
trees, which cast their leaves, and herbaceous
plants with thickened underground stems,
which withdraw the living substance from
the leaves and stems to the underground
structures, leaving the entire shoot to perish
in the winter storms.

The degree of cold necessary to ensure the
death of any species depends entirely upon the
specific constitution of the protoplasm and
the stage of development, or stage of activity
of the organism at the time it is subjected to
the low temperature.

According to numerous tests made during
the last half century, it has been found that
many delicately leaved, rapidly growing spe-
cies are killed by a temperature above the
freezing point, others native to the Arctic zone
are not injured when the air and the soil in
which they grow fallto seventy degrees centi-
grade below the freezing point. Well matured
and air dried seeds in the resting stage have
been subjected without injury for prolonged
periods to the extremest low temperatures
that can be produced in the laboratory. In
one series of experiments seeds were immersed
in liquid air at a temperature of about two
hundred degrees centigrade for several hvurs

EFFECTS OF COLD 87

with no resulting damage. From this last
series of tests, it may be safely said that the
protoplasm of plants when in the proper rest-
ing stage is practically indestructible by cold.
Not only have seeds great power of resistance
to cold, but they are capable of carrying on
growth at low temperatures. The seeds of
several common cereals will germinate on
blocks of ice at a temperature of one or even
two degrees below the freezing point.

If frozen leaves are taken in the hand and
crushed or bent, they retain the form given
them. During the crushing, the breaking of
the ice can be heard distinctly. Frozen plants
do not regain their elasticity upon thawing.
Upon the contrary, they become limp, partly
transparent, and exhibit changes of color
chiefly due to the destruction of the chloro-
phyll. The entire body of the plant has lost
its consistency, and the different tissues may
be easily stripped apart. When exposed to
the sun, the leaves shrivel and assume arusty
brown or black color. They entirely resemble
charred leaves, and the farmer says that the
frost has ‘‘burned them.”

It is not to be taken for granted that all of
the cells of a plant are equally resistant to
cold. Thus it is known that hairs and the
guard cells of stomata remain active when the

Appearance
of frozen
plants

Ice in the
tissues

88 LIVING PLANTS

remainder of the plant is frozen solidly, With-
out doubt other differences also exist.

To understand these appearances one must
recall the salient features in the structure of
the leaf: that it is composed of a mass
of loosely-arranged, thin-walled, globular,
cylindrical or irregular sacs lined with pro-
toplasm and containing seventy to ninety
percent of their volume of water. The loosely-
arranged cells are held in position by the
strong mechanical tissue of the ribs or nerves,
and the whole enclosed by the single layer of
epidermal cells: that of the lower side has
openings (stomata) which permit the escape
of watery vapor accumulating in the spaces
among the inner cells.

If now a section is made of a frozen leaf, it
will be found that the spaces between the cells
usually containing air are filled almost solidly
with ice crystals. From whence is thisice de-
rived? It will be remembered that the cell
contains a large proportion of water, some
of which is in the form of a solution of acids,
salts, etc., in the cavities of the cell, and some
in the form of water of imbibition in the pro-
toplasm and in the cell wall. The water of
imbibition may be imagined as filling up the
minute spaces between the groups of mole-
culesin the cell walland the protoplasm. Now
it is a well known principle in physics that

EFFECTS OF COLD 89

water in a solution and water in capillary
spaces, or water of imbibition will not freeze
until the temperature falls a certain amount
below the freezing point; and it will be perti-
nent to state at this point that the tempera-
ture of small plant bodies is approximately
the same as the surrounding air, with the ex-
ception of the flowers of certain aroids and
other plants. Ice then may not be formed
until the temperature of a plant has fallen
more or less below the freezing point, amount-
ing to two or even six degrees below in some
instances. The exact point will vary withthe
specific constitution of the plant, as it does
insolutions of different substances.
Protoplasm even in its simplest forms is
highly automatic, and self-regulating. When
the cells of a leaf are subjected to a low tem-
perature, they contract and a portion of the
water contained is driven out into the inter-
cellular spaces where it isfrozen. By this pro-
vision the proportion of the waterin the cells
is reduced and the danger of ice formation
and consequent destruction is averted. If
now the temperature is again lowered an ad-
ditional amount of water is forced into the
intercellular spaces, rendering the cell solu-
tions still more concentrated, and less easily
crystallized into ice. This process may con-
tinue until the greater part of the water has

Relation of
the cell to cold

90 LIVING PLANTS

been driven out of the cell sap, protoplasm
and wall, and may be seen piled up in the
spaces in the form of small pillars or discs, in
many instances completely filling up the space
between the cells and forcing them apart,
but not injuring the protoplasm or the cell
wall by the crystallization of water in their
interstices. It is thus to be seen that the ex-
trusion of water into the intercellular spaces
is a protective device of the protoplasm. In
many instances the amount of ice formed in
the spaces among the cells may be so great as
to split the tissues completely apart. This is
especially noticeable in trees, and the sudden
yielding of the firm wood to the pressure of
the ice crystals within is accompanied by
startling reports familiar to those who fre-
quent the forests in the early days of winter.
In many of the herbaceous plants the split-
ting of the stems is followed by the formation
of very delicate and fantastically arranged
sheets of ice crystals, which are commonly
known as “‘frost flowers.”’

The excretive power of protoplasm is not
always sufficient to enable it to reduce the
percentage of water in the celltosucha degree
as to escape freezing. In such instances, iceis
formed inside the cell, and the withdrawal of
practically all of the water in the protoplasm
to form the crystals results in the architec-

EFFECTS OF COLD 91

tural disintegration of the living substance.
It is as if all of the mortar used in the con-
struction of a building had been irregularly
withdrawn, leaving only a toppling, ruinous
pile of bricks.

FiG.8. Spirogyra magnified 300 times: a, intact; b, frozen
in ice: the cells are shrunken but no ice is formed in the cells;
c, thawed: the protoplasm is contracted upon the chlorophyll
bands, and the nucleus is disorganized. Aiter Molisch

Relation of
the organism
to cold

Death above
freezing point

92 LIVING PLANTS

The formation of ice in the plant does not
imply its death. Ifthe temperature falls to a
certain point characteristic of each species a
disorganization of the protoplasm will ensue,
and the plant dies regardless of subsequent
treatment. On the other hand it is well
known that many plants may be frozen and
recover normal appearance, and that the
death of others may be averted by practices
known to the gardener. Thus some frozen
plants, if submerged in water a few degrees
above freezing and allowed to thaw, will en-
tirely recover. If such plants are placed in
warm air to recover, the ice in the intercellu-
lar spaces gradually melts and a large pro-
portion of it evaporates into the air, while
the protoplasm absorbs only asmallamount.
All of this ice was in the cell originally, and
its return is necessary for the welfare of the
cell and the plant. A frozen plant, thawed in
the open air, therefore, is sometimes killed by
loss of water which might be prevented if the
plant were immersed in a vessel of the fluid.
If ice be actually formed inside the cells,
however, the plant dies whether thawed
slowly or quickly, in dry or moist media.

The death of plants by low temperature
above freezing point is due to related causes.
Acanthus, coleus, basils, melons, tobacco
plants, etc., blacken and die if exposed toa

EFFECTS:OF COLD 93

temperature of three or four degrees above
freezing point for a single night. In such in-
stances the death of the leaves is due to the
fact that the chilling of the roots decreases
their ability to absorb water from the soil as
fast asitis needed by the leaves, which shrivel,
blacken and dry up in consequence. If one of
these plants is placed in a pot and the earth
about the roots not allowed to approach
within fourteen degrees of the freezing point,
the shoot and leaves may be exposed to air
near the freezing point withoutinjury. As has
been shown elsewhere the casting of autumn
leaves is a provision of deciduous plants,
whereby the leaves are cut away at the time
when the absorbing capacity of the roots
and the water supply is decreased.

The power of excretion of water from the
cells by protoplasm is the primary means of
protection against death by cold, and is pos-
sessed by all plant protoplasm. It is evident,
however, that this is a method designed pri-
marily for the safety of each individual cell.
The organism as a whole may be expected to
exhibit adaptations to shield the cells from
the extremes of low temperature. The most
common device for escaping cold consists of a
deeply penetrating rootsystem and the devel-
opment of underground stems. The rootsare
sent down to a depth at which the tempera-

Adaptations
against cold

94 LIVING PLANTS

ture does not reach the freezing point, or does
so slowly, and rises again so gradually that
no harm is done. The primary purpose of the
roots is of course to penetrate the soil in such
manner as to fix the plant and obtain a sup-
ply of mineral salts, and in so doing a region
not subject to the rigors of low temperature
is reached. Somelowly-growing plants avail
themselves of the blanket-like coverings of
leaves and snow which fall upon them before
the extremest rigors of the winter areat hand.
Many plants native in alpine regions are
specially adapted to take advantage of this
means of protection. Among them are some
of the rhododendrons, dwarf junipers and
pines.

The stem of Pinus humilis of the higher
mountain slopes, althougheight or ten inches
in diameter and strong enough to stand erect
and sustain the ample crown, grows almost
parallel with the surface anda few inches
above it. The branches which are ordinarily
erect are very flexible and easily bent down-
ward, and when weighted spread themselves
along the ground. This is true of branches
which stand upto the height of a yard or
more. When the early storms set in, and the
ever increasing layer of snow settles down
over everything, the branches slowly bend
under the constantly augmented weight, and

EFFECTS OF COLD 95

finally are pressed against the soil under many
feet of snow. In this position they are also
secure from the shearing action of moving
masses of ice and snow above them. When
the snow melts in the spring the elastic
branches return to the upright position, and
the early climber may see the old leaves plas-
tered over with earth, and small stones ad-
hering to the twigs and branches. The gar-
dener imitates the action of these pines when
he bends rose bushes and small shrubs to the
ground andcovers them withearthand straw.

A very interesting method of avoiding
death by cold is afforded by many aquatic
plants. Species which float on the surface of
water owe their buoyancy to small bubbles
of gas in or between the cells. On the ap-
proach of winter, the gas is given off, and the
plant sinks to the bottom, either in the form
of spores or the entire vegetative body of the
plant.

In such forms as the water lily, the leaves
and flowers die down and the main stem of
the plant, a bulky rhizome loaded with food,
is securely imbedded in the mud below the
freezing line. At the beginning of eachseason
new leaves and flower-stalks are sent to the
surface.

Perhaps the most interesting adaptation is
that offered by such aquatic plants as the

96 LIVING PLANTS

pondweeds, bladderworts and stoneworts
which root in the mud at a few feet below the
surface. With the approach of autumn the
tips of the stems grow in the form of a thick
shoot with short, crowded leaves which are
termed hibernacula. The hibernacula finally
break loose from the stem, which dies, and
sink to the bottom before ice formation sets

Fic. 9.—a. Hibernaculum of Utricularia in October. b. Ter-
minal portion of stem insummer. c. Hibernaculum of Philo-
tria Canadensis (Elodea Canadensis). d. Terminal portion of
stem insummer: photographed in the air.
in, and lie quiescent during the winter. After
the spring thaws, if one rows over the shal-
lows near a lake shore, he may see the hiber-
nacula resting on the bottom, and as soon as
the sun’s rays have warmed the water suf-
ficiently to allow growth, a few rise to the
surface, and all begin to send out roots from

the lower end, and stems form at the upper

EFFECTS OF COLD 97

end, with the result that the entire plant is
reproduced within a short period. Some
species form a hibernaculum at the tip of each
branch, with the result of multiplying the
plant by this method.

Some plants as a whole avoid low temper-
atures by growing in such a manner as to be
covered with a protecting blanket of leaves
and snow; and others retire toa depth below
the frost line in the medium in which they live.

Winter buds are of course devices for the
protection of growing tips against sudden
changes of temperature and moisture, as well
as from mechanical injuries due to wind, sleet,
snow or ice.

As a conclusion to be derived from the fore-
going paragraphs it is to be seen that proto-
plasm seeks to avoid danger of disorganiza-
tion from the formation of ice inits interstices
by getting rid of a portion of its water when
the temperature falls, and the death of a plant
does not necessarily follow ‘‘freezing.’’ Death
by cold may be due to the direct action of
cold, or to the consequent desiccation of
the tissues. When due to the latter cause it
may be brought about by temperatures above
the freezing point.

That temperature has been a most impor-
tant factor in the evolution of the vegetable
kingdom, as well as in the distribution of the

98 LIVING PLANTS

separate forms, is evident when one considers
the vegetation of a mountain from its base
with its warm breezes and soft sunshine to
the bleak summit with icy winds, cold nights
and ravines filled with snow.

Vari:

TWO OPPOSING FACTORS OF INCREASE.*

The energies of the plant are used for two
general purposes: the development and main-
tenance of the vegetative parts, and the for-
mation of special reproductive bodies. In
some respects the efforts of the plant in these
two directions are antagonistic. The vegeta-
tive part consists of root, stem, foliage, etc.,
and at first, and sometimes for a long period
in the life of the individual, the energies of the
plant are wholly absorbed in increasing the
size and promoting the functional activities of

*Condensed from two articles: one in collaboration with
Miss Katherine E. Golden, entitled ‘‘Weight of the Seed in Re-
lation to Production,”’ published in Agricultural Science, May.
1891; and another entitled ‘‘A New Factor in the Improve-
ment of Crops,’’ read before the Society for the Promotion of
Agricultural Science, August, 1893, and published in its Pro-
ceedings and in Agricultural Science, September, 1893.

Two sides
to plants

100 LIVING PLANTS

these organs, all being connected with the
welfare of the individual plant. After a time
special reproductive structures are developed,
consisting of seeds or spores and the accom-
panying parts that aidin their protection and
dissemination. They find their use in continu-
ing the race, that is, in providing for another
generation of individuals.

The formation of the vegetative part and
the formation of the fruiting part may be
treated as separate tendencies in plant life.
They rarely proceed pari passu, for usually if
one is favored, the otheris less favored. This
is popularly expressed by saying that the
plant runs to leaves, or runs to vine, or on
the other hand thatit runs to seed, or it over-
bears.

The portion of the plant having economic
value for food belongs sometimes to the vege-
tative, sometimes to the reproductive side.
Most fodders, and many culinary vegetables,
such as cabbage, radish, lettuce and aspara-
gus, belong to the vegetative part, while the
grains, fruits and such vegetables as peas,
beans, tomatoes and egg plant, belong to the
reproductive side. The object of cultivation
is to increase the size and quality of the part
used, and it is evident, therefore, that one re-
quirement of the husbandman must be to
learn the conditions which promote the de-

FACTORS OF INCREASE 101

velopment of the particular side of the plant
to which the crop in question belongs.

But it is not from the standpoint of the cul-
tivator that the present article was written,
but rather from that of the evolutionist, al-
though the illustrations being drawn from
cultivated plants make it easy to see prac-
tical applications of the conclusions.

It has been pointed out that among the
lower animals, a sudden check to growth in-
creases reproduction. I wish to expand that
statement into the much broader and more
widely applicable generalization that a de-
crease in nutrition during the period of growth
of an organism favors the development of the
reproductive parts while abridging the vege-
tative parts. The converse, that an increase
in nutrition favors the vegetative parts while
abridging the reproductive parts, is equally
SCie:

Unimpeachable statistics arenot abundant,
for experiments bearing directly upon the
problem have not been undertaken, and ser-
viceable data culled from the supplementary
records of other experiments are not very
complete or numerous. Enough are obtain-
able, however, to lend very material aid to-
ward establishing the generalization.

The cultivator employs no method so fre-
quently for enhancing the value of his harvest

Nutrition and
development

Effect of
soil fertility

102 LIVING PLANTS

as increasing the fertility of the soil. Itisa
method of giving the plants a greater supply
of nutriment, whereby they grow larger and
yield more. Ifthe principle just stated holds
true, however, the increase will be greater
proportionally for the stems, leaves and roots
than for the seeds and fruits. The data pro-
vided by Latta from experiments conducted
in Indiana bear this out. Wheat grown
upon fertilized and unfertilized areas, averag-
ing the results of three seasons, 1889-91,
showed a decided gain in both straw and
grain due to the richer soil; but upon exam-
ining into the relative increase of straw and
grain, it is very evident that while the increase
in yield of grain was considerable, it was by
no means so great as the increase of straw,
and that the proportion of straw to grain
was, in spite of the increased yield, in reality
lessened. (See table 1., page116.) Essentially
the same results are evident in data obtained
by Caldwell in Pennsylvania with corn, aver-
aging the results of ten years, 1882690;
(omitting 1887, the crop being destroyed by
insects). (See table m1.)

A very different method of increasing yield
is the treatment of seed grain before sowing
to a short bath in hot water. It is especially
interesting to find that this method develops
the same reciprocal relations between the

FACTORS OF INCREASE 103

vegetative and reproductive parts of the har-
vest asin the preceding cases. In a crop of
wheat (see table m) thus treated it was
found, that while the total weight of straw
and grain was both asa wholeand separately
increased by the hot water treatment, the
yield of grain was lessened as compared with
the yield of straw.

If we turn from the statistical method of
demonstration and appeal to general obser-
vation, an overwhelming array of facts can
be brought to bear.

It is acommon observation that plants in
too rich soil run to leaves instead of fruit.
Every farmer knows that he can expect little
or no grain from an excessively rich spot of
ground, although the plants grow far taller
and larger. The orchardist root-prunes his
trees to bring them into bearing, when they
prove to be unusually backward; the florist
permits his plants to become pot bound to in-
duce them to flower more freely; certain
slow acting diseases, e. g., peach yellow, and
cotton rust, increase and hasten the fruiting.
A wide range of such general facts could be
cited, familiar to every one having experience
in such lines. In this connection Professor
Atkinson, of Cornell University, has called
attention to the longer time that elapses be-
fore spores are formed when certain bacteria

104 LIVING PLANTS

are provided with more abundant food mater-
ial. A customary culture gave a crop of
spores in 15-20 hours, a culture with fewer
germs (second dilution) in 36 hours, and one
with still fewer germs (third dilution) in 48—
72 hours.

The prolificacy of weeds in sterile soilis a
matter of common observation. The great
ragweed in poor soil produces a crop of seeds
when but a few inches high, and the same is
true of other weeds, especially noticeable in
normally tall ones. Wild plants rooted in
thin soil on rocks often bear single flowers as
large asall the remainder of the plant. Anal-
ogous development may beseenin some alpine
plants.

As a summary of the evidence already
brought forward it is plain that the environ-
mental conditions of plant existence have a
disproportionate effect upon the two sides of
plant life, the vegetative and the reproductive.
An increase in available supply of food, as
when the farmer fertilizes his fields, an earlier
and stronger start in spring as in the case of
wheat treated to a bath in hot water before
sowing, the larger amount of food as when
fewer and fewer bacteria are placed in same
amount of culture media, all show a favoring
action upon the vegetative part greater than
obtains with the reproductive part. On the

FACTORS OF INCREASE 105

other hand, checking growthby root pruning
or by keeping plants in undersized pots, re-
ducing the general vitality by slow disease,
and depriving the plant of sufficient soil and
moisture, show a favoring action upon the
reproductive part in hastening and multiply-
ing the formation of flower and seed far in
excess of the development attained by the
vegetative part.

As a factor to insure perpetuity this law is
evidently important in guarding against ex-
termination, for the poorer the conditions for
growth, the more effort the organism puts
forth toward seed-bearing. One cannot fail
to be impressed by the thought, however,
that if this be a general law of nature, it
would seem to imply that the weakest and
least favored individuals, being most fruitful,
are most likely to be perpetuated, which is in
evident contradiction to the accepted theory
of natural selection and to common observa-
tion.

There is, however, another factor which
comes into play here, as a corrective of this
tendency to deterioration of the race. and it
is to this law that special attention will now
be directed.

In all the methods of increase in rate of
growth, so far brought forward, the change
has been due in the main to external agencies,

Provision for
perpetuity

Size
of seeds

106 LIVING PLANTS

and the increased growth was found to be
correlated with decrease in amount of repro-
duction. There are, however, methods of in-
crease in rate of growth, arising from causes
inherent within the organism, that tend in
quite a different direction, in fact, are opposed
to those already cited. The best illustration,
and the only one to be given in this article, is
that shown by the size of seeds. It may be
stated as a general law that large seeds pro-
duce stronger plants with a greater capacity
for reproduction than small seeds of the same
kind.

That larger seeds produce stronger plants,
that is, plants possessing both heavier veg-
etative parts and larger yield of fruit, can be
shown by abundant experimental data.

To be sure there is quite a common belief
that the size of the seed has no material effect
upon the product; that, provided a due re-
gard be paid to vitality, any size of seed will
answer the purpose of propagation. This be-
lief is one of long standing, and is also held
by some men of eminence. Sir Joseph Banks,
one of the leaders in agriculture of a hundred
years ago, advocated the use of small seed as
answering the purpose of the farmer ‘‘as effect-
ually as the largest.’? Hehad wheat especial-
ly in mind, and as the largest grains contain
the most flour, the use of the large instead of

FACTORS OF INCREASE LOW

the small seed for sowing seemed to him ‘‘un-
necessary waste of human subsistence.” In
recent years the distinguished scientist, Hab-
erlandt, has given expression to essentially
the same opinion. He believes it ischiefly the
strain and the favorable conditions for growth
that influence the product, and not the weight
of the seed. He doubtless represents the opin-
ions of alarge percentage of cultivators of the
present time, inclusive of many good thinkers.
Probably a fair statement of the general opin-
ion would be thatif astrain isto be kept up to
its full vigor, or if improvement is desired,
careful selection of the largest seed is indis-
pensable, but that the difference between the
use of the large and small seed will not beno-
ticeable in the first year’s crop. This view is
not, however, borne out by experiment, as
we will see.

The amount and strength of the early
growth from the seed has been studied by
Marek, who experimented with beans and
peas. The seeds were laid between moist
blotting paper for seventeen days, and then
measurements were taken of the length and
diameter of the primary and lateral roots and
of thestem. The figures all stood higher for
the largeseeds than for the small seeds, except
for the length of the pea stem. Similar ex-
periments werecarried out by von Tautphéus,

Early growth

Final yield

108 LIVING PLANTS

who used from two to four sizes each of wheat,
barley, rye, oats, corn, beans and peas. He
measured the lengths of the plumule and
radicle from day to day for two weeks. His
conclusion was that the larger and
heavier the seed, the stronger the develop-
ment. He found, however, an apparent
exception in peas, as did Marek, in which the
main root and stem are shorter the larger the
seed. Butin this case it was noted that the
extra strength is expended in lateral growth,
forming athicker stem and more side rootlets,
thus bringing the apparent anomaly into line.
A subsequent experiment by Marek was car-
ried somewhat further. Threesizes of English
beans were planted April 24th, and their
growth noted upto maturity, July 12th, with
the result that the larger the seed the taller
the stems and the more numerous and larger
the leaves. It also occurred to him to test the
force exerted by roots of seedlings in piercing
the sail, and in this respect also the off-
spring of large seedshowed marked superior-
ity over those from small seed.

Taking into account now the harvest, we
find some excellent experiments with clear re-
sults. Trial of large and small seed roughly
separated by sifting was made by Goff with
onion, cauliflower, turnip and cabbage, with
some gain in favor of the large seed in all but

FACTORS OF INCREASE 109

the last,and also made by Latta with wheat,
who also obtained gain for the large seed.

Lehmann separated peas into three grades,
large, medium and small, and planted 528
seeds of each. The germination showed that
the larger seeds were possessed of greater in-
herent strength than the smaller, the number
of seeds growing from each lot being 480, 478
and 423 respectively. The yield in peas, pods
and vines, taken separately or together, and
estimated per plant or as total weight, gave
the largest figures for the product of the largest
seed, and intermediate figures for the product
of the medium seed. (See tables rv and vu.)

An experiment in this line with corn was
conducted by the writer in 1889. Thirty ker-
nels from asingle ear of white dent corn were
separately weighed of which six grew that
were over 400 milligrams each, and nine that
were under 300 milligrams each. The pro-
duct of these fifteen plants gave a greater
average weight of ears for the large than for
the small seed, which was also true of the
cobs and kernels taken separately. (See
table v).

The accompanying graphic illustration of
these results brings out the differences in the
weight of the kernels even more strikingly.
The solid line indicates the product from large
seed and the interrupted line from small seed.

110 LIVING PLANTS

The diagram as a whole shows the variation
at different parts of the ear, the butt being to

_ the left and the tip to the right.
Thus far we have given the results of ex-
periments in all of which the seed was pro-
vided the same ground space without regard

acannon anna

SONIA ARAAAN ee ie

Se a3 sis rae =a 2222S

3 2 4 mM 1 2 3 4 5 6 7 & 9) 4008 ore

Fic. 10.—Illustrating the product from largeand small seeds
of corn. Data for the curves were obtained by weighing the
kernels on each ear of the product by fifties from base to tip.
The heaviest lot of fifty came not far from the base. These
maxima were averaged and marked ‘‘M,’’ and the next fifties
right and left in succession were averaged in the same way.
Figures along the bottom of the diagram show position of
each fifty seeds, and along the side the average weight in
grams. The position of the ear of corn above corresponds to
the curves.

to size, and the datashow that the largeseeds
give larger returns than the small seeds. It
would be natural to suppose that if the small

FACTORS OF INCREASE atnlal

seeds were placed correspondingly closer to-
gether, or in other words, if the seeds were
planted according to weight instead of num-
ber, the results might be reversed. For it is
evident that the same weight or measure of
seed will contain a much larger number in
case of small seeds than of large, and in plant-
ing the small seeds will require less ground
area for development, and consequently a
greater number of plants can mature upon an
equal space.

This phase of the question has been tested
by Lehmann. He pianted 188 grams each of
large, medium and small peas upon equal
sized plats of ground, and although there
were more than twice as many small seeds as
large, and nearly once and a half as many
medium seeds as large, still the harvest was
greatly in favor of the larger seeds, both per
area and per plant. (Data in table vi., page
148).

A practical lessonis very pointedly brought
out here, that in sowing farm seeds the
amount of the harvest depends quite as much,
and it may be more, upon the quality (size)
of the individual seeds as upon the weight or
measure sown per acre.

Is it not apparent that large seeds show
great superiority over small seeds in numer-
ous requirements that enter into successful

Superiority of
large seeds

a a LIVING PLANTS

plant life? In the first place, alarger propor-
tion germinate, and this evidence of the pos-
session of greater strength is followed up by
more vigorous growth and the display of in-
creased capacity for overcoming obstacles.
The resulting plants attain to greater de-
velopment, as the size of leaf, length of stem —
and weight of any part or of the whole plant
abundantly proves. It isespecially noticeable
that in this display of greater vigor both
vegetative and reproductive parts are benefit-
ted; and while the individual plants are
making a more successful fight in promoting
their present welfare, they areenabled to pro-
vide more abundantly for the next generation,
by producing a better crop of seeds.
Although the proposition in relation to size
of seed, with which we started, has been illus-
trated and established so far as present space
permits, yet in order to compare more fully
the tendency of the powers of the plant derived
from the two sources, which for convenience
we may call acquired and hereditary, the for-
mer coming from food, light, warmth, and
other external conditions, and the latter from
the energy stored in the seed, it is necessary
to bring forward still other data. We may
venture to formulate this proposed extension
ofthelaw relating to the size of seed thus: /arge
seeds give rise to plants with a greater deve-

FACTORS OF INCREASE AAS

lopment of the reproductive parts, and less
of vegetative parts, than small seeds do.

It is intended here to directly compare the
reciprocal relations of the two sides of the
plant as influenced by the parent seeds. The
data may be taken by weighing the fruiting
portion and comparing it with the weight of
all the remainder of the plant, both done
when at their best development; or other
methods may be used.

Excellent data are supplied from the re-
searches of Lehmann (see table vur). He
grew large, medium and small peas, over 400
of each lot, and obtained plants that were
heavier for the larger seed in both their vege-
tative and their reproductive parts, i. e., the
leaves and stalks for the vegetative part and
the peas and pods for the reproductive part.
And yet when the weight of the vegetative
portion is compared with that of the repro-
ductive portion of each lot, it isclear that the
fruiting part has attained a stronger devel-
opment in comparison to the remainder of
the plant in the lots from larger seeds. To
state the facts in another way, the larger
seeds not only grow larger plants, but those
which have fruiting parts more strongly de-
veloped than the associated vegetative parts.

Interesting dataare furnished by Birnerand
Troschke using oats and peas, and by Marek

Vegetative and
fruiting parts
compared

114 LIVING PLANTS

with peas. The last investigator found that
the weight of peas of first quality was nearly
three-fourths of the whole harvest raised from
large seeds, and only about one-third of that
from small seeds. (See table wn.) In this
case, therefore, the large seeds not only gave
a much better total yield, but far more seed
material of high grade with which to con-
tinue the strain.

Marek, in Germany, experimenting with
wheat (see table 1x), and Plumb, in the Uni-
ted States, with oats (see table x), have
demonstrated the same fact. Both have pro-
vided data which show that the amount of
grain in comparison with the straw was
greater in case of large seeds than of small
ones.

Statistical evidence of this kind might be
greatly extended, although observations have
rarely, if ever, been instituted with this par-
ticular end in view. Casual observations
give no aid to this part of the inquiry, as the
differences are obscured by other factors which
stand out more prominently. What the eye
cannot detect, however, is readily and unmis-
takably revealed by the rule and balance.

So far as data can be marshalled at present,
there appears good reason to believe that
large seeds, besides giving rise to larger and
more fruitful plants, also possess an inherent

FACTORS OF INCREASE 115

tendency to accentuate the reproductive side
of the resulting development. If peas are
sown, the largest seeds not only give rise to
the largest plants, with the greatest weight
of pods and of seeds, but to an excess of
fruitage when compared with the remainder
of the plant; and ina similar way with other
kinds of plants, the largest parent seeds give
the greatest returns of fruit and daughter
seeds, both absolutely and alsoin comparison
with the growth of leaf, stem and root. It is
to be understood, of course, that we are not
attempting to deal with single plants, but
with sufficiently large numbers to neutralize
individuality and small accidents, which some-
times produce most unaccountable variations.

If we consider the bearing of all the data
now brought forward, it seems reasonable
to assume that in the ultimate analysis we
are dealing with acquired and inherited tend-
encies. In the one case the impulse or stim-
ulus to development comes from without; it
is environmental, and acts more strongly up-
on the somatogenic portion of the plant,
while in the other case it is inherent in the or-
ganization of the secd and derived from the
parent plant. Whatever the explanation of
the origin may be, however, it seems certain
that these two opposing factors of increase
play an important role in the economy of

External and
internal factors

116 LIVING PLANTS

nature. As the food supply is lessened, a
greater effort is made on the part of the
parent plant to enhance the chances for
perpetuity; but at the same time the largest
seeds, having the greatest potentiality, stand
the best chance in the future struggle; and
although the best nourished plants produce
the fewest seeds, their greater size gives them
decided advantages over seeds from starved
plants. The two laws acting together, there-
fore, aid in maintaining the perpetuity of the
species and its full measure of vigor.

TABLES.

TI. YIELD OF WHEAT ON FERTILIZED AND UNFERTILIZED

GROUND.

(Weights calculated to the acre.)

Weight of | Weight of | Proportion

Treatment. straw in grain in of straw
pounds. pounds. to grain.
Water EUIZEG io ss.0ct--1-c50re) ees) 2813 1602 1:0.56
Commercial Fertilizer....{ ee eT Gao
Waite Gertz eG vse. ce ses an sexe scces PAT PAT 1506 1:30:55
f 3699 1818 1:0.49
Stable mianure:. <...0c.ccn00e \ 3361 1728 1:0.51
Wfeetiized Foicice eis osesverss 2894 [ 1512 1:0.52
Average unfertilized........ 2811 | 1540 1:0.55

Average fertilized............. 3880 | 1842 1:0.48

FACTORS OF INCREASE 3 la br
II. YIELD OF CORN AND WHEAT ON FERTILIZED AND
UNFERTILIZED GROUND.
(Weights calculated to the acre.)
Weight of | Weight of | Proportion
Crop Treatment. stalks in grainin | of stalks to
pounds. pounds. grain.
Wheat { Unfertilized ... 1367 958 £0.70
partes VRertiized= s... 2119 1246 1:0.59
Gorm fUnfertilized ... 24.30 3498 1:1.44
aes EB erilizede.-. 3144 3966 fete 26
III. YIELD OF WHEAT WITH AND WITHOUT HOT WATER

‘TREATMENT.

(Weights calculated to the acre.)

Weight Weight

Treatment.
of straw. of grain.
Wntreateds235.-..eccasteees cae BTS 1716
Blot water bathe ces. 4.555 1908

Proportion
of straw
to grain.

1:0.46
1:0.42

118 LIVING PLANTS

IV. PRODUCT FROM LARGE AND SMALL PEAS.

a Z Zz
a o ©
ha se ° ° Wt. of harvest in grams.
HH = rh
SIZE. Sn 3,0 ‘J
PS D5 ne
ge | 82 | 38
2% @ a” | Peas. | Pods.| Vine. | Total.
: a 5
Matees...- 273 528 480 | 1814 437 | 3170 | 5421
Medium..| 221 528 478 | 1495 357 | 2630 | 4482
Small...... 160 528 423 998 280 | 2010 | 3288

V. YIELD OF INDIAN CORN FROM LARGE AND SMALL SEED.

Av. Wt. of Av. Wt. of

SIZE. kernels cobs
in milligrams. in grams.
ates ONC acactandeelcene des cee cenesenceerels 312 Dee
Sra elie oc Saas saeco sae cen eweceeeceee cers 268 47

VI. PRODUCT FROM LARGE AND SMALL PEAS.

Peas harvested in grams.
No. of No. of
SIZE. peas in plants |—

188 grms| grown.
| Per area. Per plant.
Wate vinstssuereee 384 360 2307
Mredititn <.25,-4--4- 530 505 2224 4.40
Sina base forsee ess 780 680 1590

FACTORS OF INCREASE 119

VII. PRODUCT OF LARGE AND SMALL PEAS.

Size of |Wt. of peas in grams} Wt. of Wt. of | Proportion
—_—____—___—_—__—_——_| pods in |} vine in of vine
Seed. | 1st qual-{ 2d qual- | grams grams to fruit

ity. ity.
Large ons 554 1519 4185 1:0.83
Small 540 1045 1405 4074 OSG
VIII. PRODUCT OF LARGE AND SMALL PEAS.

Size of |Aver. wt. Wt. of | Wt. of peas|Proportion
of single | No. of vine and pods of vine
seed seeds plants | per plant} per plant to fruit

in grams in grams} in grams

Large PAG 480 6.60 4.69 ONT
Medium 2.21 478 DOO 3.87 1=0.70
Small 1.60 423 4.75 3.02 1:0.64

IX. YIELD OF WHEAT FROM LARGE AND SMALL SEED.

Size Weight Weight Proportion

of of straw in of grain in of straw to
seed grams grams grain
Large 2411 3039 11526
Small 2211 2456 a Ca Ba) WE

LIVING PLANTS

YIELD OF OATS FROM LARGE AND SMALL SEED.

120
>. &
Size Wet. of seeds
of sown pr.1000
seed in grams
Large 35.4
Small 15.9

Weight Weight | Proportion
of straw in| of grainin} of straw

ounces ounces to grain
556 190 1:0.34
518 143 1:0:28

MELT:

CHLOROPHYLL AND GROWTH.*

The adult leaf manufactures about ninety-
seven per cent of the food of the plant from
water and carbon dioxide of the air. In the
study of its functions and development it is
of the greatest importance to know whether
the plant can build up a leaf from food stored
within its body, or the products of other
leaves, or whether the products of the ma-
turing leaf itself are necessary to enable it to
complete growth.

In recognition of this fact it was one of the
earlier questions taken up in the study of the
physiology of the plant, and it has engaged
the attention of a number of authors of the
first rank. It would not be possible to recount

*Adapted from a lecture on ‘‘The Relation of the Growth of
Leaves and the Chlorophyll Function” before the Linnean So-
ciety of London, June 18, 1896.

Historical

Methods of
experimenta-
tion

122 LIVING PLANTS

here the exact results attained by each one,
except to note that the first investigation of
the subject was made by de Saussure in 1804,
and from his experiments upon leafy shoots
of woody plants he was led to assert that
leaves may not carry out full development,
or maintain normal existence when the food-
forming processes were inhibited. Subse-
quently in dealing with various phases of the
question Boehm, Kraus, Rauwenhoff, Stebler
and Véchting arrived at results in harmony
with those of de Saussure. On the other
hand Batalin, Vines, and Jost have reached
results quite to the contrary. Corenwinder
made two series of experiments, one series re-
sulting positively, the other negatively.

The experiments which would be of value
in the decision of this question consist in al-
lowing young leaves of many species of plants
to develop under suchcondaitions that no food
can be formed.

To place leaves under such conditions that
the chlorophyll-bearing cells may notcarry on
the formation of food, and that all growth
must be carried on by means vf food brought
from a distant portion of the plant, several
methods may be used, viz.: the leaf may be
enclosed in a dark chamber consisting of a
small box which will exclude all rays of light
from the leaf, without which the chlorophyll

CHLOROPHYLL AND GROWTH 25

is inactive, or one side of this box may con-
sist of a sheet of blue glass which would
permit only the blue-violet rays to pass and
thus allow but a small amount of food to be
formed ; the plant may be grown ina substra-
tum, or nutritive solution, from which iron
salts have been omitted, and as a consequence
no chlorophyll would beformed in theleaves ;
the shoot or the entire plant may be placed in
atmosphere made free from carbon dioxide by
means of chemical reagents. Of these meth-
ods chief reliance is to be placed upon those
in which light is excluded from the plant, and
in which carbon dioxide is excluded from the
leaves.

The former method induces such profound
disturbances of the chemical processes and
regulatory mechanism as to place the plant
under highly pathological conditions. The
more conclusive experiments are those by
which branches, or entire plants are intro-
duced into a sealed chamber, which is kept
free from carbon dioxide by means of solu-
tions of potassium hydrate, and the ventil-
ating openings were guarded with tubulures
similarly provided. The exact method of
dealing with the plant may be illustrated by
the following description of the treatment of
Ariseema triphyIlum.

The large tuberous corms were gathered

124 LIVING PLANTS

from the soil in woods in October, and placed
in a cold house until February 1st, when they
were placed in a temperate room, beginning
growth two weeks later. - Ordinarily the
plant sends up one or two leaf-stalks thirty
to fifty centimeters in height bearing the tri-
foliate lamina, with an area of one hundred
to two hundred and fifty square centimeters
and a scape twenty to forty centimeters in
height, bearing a spadix enclosed by a hooded
spathe. The hood contains a large proportion
of chlorophyll and sustains in greater part
the functional activity of theleaf, and exhibits
similar reactions to light and modified atmo-
spheres. The correlation of growth is such
that the scape and inflorescence attain full
size within ten days from the opening of the
bud, and the greater part of the leaf-expansion
follows in the nextten days. During the first
ten days thestarch stored in thecormis drawn
upon to furnish an increasing amount of ma- —
terial for the growth of the aerial organs;
during the next ten daysa decreasing amount
is drawn from the corm, and usually after
that time a stream of plastic material sets in
the opposite direction from the laminz, which
is in part stured in the corm and in part used
in the development of the lateral offshoots,
which begin development at this time.

Buds which had attained the height of ten

CHLOROPHYLL AND GROWTH 125

em. were brought through an opening ina
glass plate allowed to rest upon the top of
the pot in which the plant was grown. The
opening around the bud was securely sealed
by means of wax, molding clay, or the fol-
lowing device: A cork stopper was perfor-
ated with an opening larger than the ulti-
mate size of the sheathing petioles, and the
upper part of the opening was enlarged to
form a cup-shaped cavity. After the cork had
been saturated with paraffin it was placed in
the glass plate and enclosing the bud, the
bottom of the cup-shaped cavity covered with
a loose layer of asbestos or glass-wool, and
over this was poured a layer of mercury five
millimeters in thickness, which was covered
with water to prevent injurious action of the
metal.

This method of sealing exerted no harmful
pressure on the plant and allowed it to ex-
pand in a normal manner—a very important
consideration in experiment where soft-
stemmed herbaceous plants were used. The
plants werecovered with a bell-jar of a capac-
ity of four to eight liters sealed to the glass
plate, and provided with two tubulures. To
one tubulure was fitted a series of potassium
tubes or vessels containing potassium hy-
drate in solid form, and saturating a mass of
asbestos fiber, The second tubulure wascon-

126 LIVING PLANTS

POS ISORI TIES ETT IMTS TTS TTT ST

Fic. 12.—Apparatus for growing plants in an atmosphere
free from carbon dioxide: 1. Dish containing solution of po-
tassium hydrate. 2. Specimen of Arisema triphyllum 10
days after opening of bud. 3. Receiver of 10 liters capacity.
4. Outlet-tube connected with aspirator. 5. Sticks of potas-
sium hydrate and moist asbestos fiber. 6-9. Detail of method
for sealing plant in receiver. 6. Cork. 7. Asbestos fiber.

8. Mercury. 9. Stem of plant. 10. Sponge saturated with
water,

CHLOROPHYLL AND GROWTH 127

nected with an aspirator, by which the air was
occasionally renewed. Several vessels con-
taining two to five grams of solid potassium
hydrate were placed inside of the bell-jar.
The potassium absorbed water rapidly and
soon dissolved. To provide against the dry-
ness of the inclosed air thus induced a large
sponge saturated with water was placed near
the plant. These precautions furnish normal
conditions except in the composition of the
air,from which almost all of the carbon diox-
ideis taken. Itis of course understood that
the plant is constantly giving off this sub-
stance as a result of its oxidation processes,
and it may be imagined as forming a diffuse
stream from the plant to the vessels contain-
ing the potassium solutions. Theamountac-
tually present in the bell-jar at any time how-
ever must have been quite small. The potas-
sium solutions were renewed once each week.

Plants of Ariseema grown in the apparatus
described above exhibited a normal develop-
ment during the opening of the bud, and the
preliminary stages of the unfolding of the
leaves, which are crumpled in the bud during
a period of two to four days. The develop-
ment process was arrested, however, at a
very early stage, and the lamine were un-
folded only so far as toexpose the ventral sur-
face, and the crumpled appearance was not

Growth in the
absence of
carbon dioxide

128 LIVING PLANTS

lost. In ten to fourteen days after the begin-
ning of the experiment, the laminz assumed
a yellowish color, as a result of the decom-
position of the chlorophyll, and other signs of
deterioration appeared ending in the death of
the organ a few days later.

The structure and arrangement of the tis-
sues had undergone but little differentiation
from the forms present in the folded condition,
and differed from the normal forms by thesize
of the single layer of palisade cells and the
globular form of the spongy parenchyma, and
seemed moreover to be in a state of hunger.
It is to be noted that the sheathing spathe
also undergoes similar abnormalities, but
since it is never folded, and since its develop-
ment consists principally of a longitudinal ex-
pansion of the cylindrical sheath and hooded
tip, the more apparent deviation is one of size.
The thickness is such as to preventcrumpling.
It is to be noted moreover that the develop-
ment of the spathe is usually accomplished
before the leaves have begun maximal growth
under normal conditions. If mature leaves
were sealed into an apparatus similar to the
above, no changes were discernible until fif-
teen to twenty days later. At this time the
starch, and other carbohydrates with which
they were richly loaded, having been used, a
shrinkage was noticeable and the leaf was

CHLOROPHYLL AND GROWTH 129

found to be in astateof hunger. On restor-

Ss

.
x

7

Fic. 13.—Ariszeema triphyllum grown in open air.

ation to a normal atmosphere before decay

Effect of
darkness

130 LIVING PLANTS

had begun they were restored to a normal
condition.

In order to cultivate plants in darkness but
under otherwise approximately equal condi-
tions, a bottomless chamber of galvanized iron
was constructed, and allowed to rest ona
metal bench covered with a layer of moist
sand. This dark chamber was placed in such
position that the sun’s rays did not strike it,
and was attached to a simple pulley, by
which it might be raised and lowered to allow
an occasional examination of the plants.

Awakening plants with corms five centime-
ters long, when placed in this chamber,
showed a greatly exaggerated development
of the bud scales, a rapid elongation of the
scapes and petioles attaining a length near-
ly double the normal in five to eight days.
The daily increase of these organs in some
instances amounted to twelve centimeters.
The laminz sometimes were carried com-
pletely or almost completely through the un-
folding stage, but were rarely able to attain
a full extension, or area, much in excess of the
folded condition, and owing to the absence of
the directive influence of light, assumed var-
ious positions with respect to the horizontal.
The process of decay did not begin until fifteen
to twenty days after the beginning of the ex-
periments, and if the plants, after unfolding,

CHLOROPHYLL AND GROWTH 131

were brought into diffuselight with gradually
increasing intensity, the normal appearance

a

Fic. 14.—Arisema tri-
phyllum grown in an at-
mosphere free from car-
bon dioxide.

ff

was fi-
nally
resum-
ed): The
z= cCOlor of
Ede eti-
olated
leaves was of the cus-
tomary waxy yellow,
upon which the reddish pur-
ple color areas characteris-
tic of the external tissue
were boldly apparent. The
spathe exhibited great vari-
ety of reaction, but in gen-
eral it did not attain full
development. This was
the invariable result if this
member alone was enclosed
in a covering excluding
light. And although not
responsive to the directive
action of light or gravity,
it assumed an upright or
outwardly recurved posi-
tion in darkness.

If plants with mature

leaves were placed in the dark chamber a re-

132 LIVING PLANTS

newed activity of the petioles occurred, last-
ing two to three days, and in four or five
days the laminz began to bleach and decay.

Plants grown in a diffuse light exhibited
features of development in general analogous
to those shown in darkness. Elongation of
the petioles, and scape, and dwarfing of
the spathe especially of the overarching hood
occurred. Still more marked, however, was
the restriction of the area of the laminz, cor-
responding to the intensity of the light.

In order to determine how far the diversion
of food from certain members, and its concen-
tration in one might affect its development,
recourse was had to the removal of two of
the three aerial members of plants grown ina
dark chamber. If theleaves were removed no
changes resulted in the development of the
scape or spathe. The latter organ was
dwarfed, although not more than thirty cen-
timeters from thestored food in thecorm. If
the scape and one leaf were removed from a
plant emerging from the bud in a dark cham-
ber, the remaining leaf exhibited a develop-
ment quite similar to those of entire plants
under similar circumstances, except that the
petiole reached a length much in excess of
those on an entire plant. The laminz were
extended in such manner as to cause the dis-
appearance of the angles of the leaf-folding in

CHLOROPHYLL AND GROWTH 133

+
a

Fic. 15.—Arisema tri-
phyllum grown in darkness.

ff thebud. They soon

became recurved at
the margins, and only a
small increase in size oc-
curred after unfolding.

The removal of one
leaf and the scape, from
plants grown in an air

free from carbon dioxide,
resulted in a somewhat
more complete develop-
ment of thelaminz than
in an entire plant under
the same circumstances.
The angles taken on in
the bud completely dis-
appeared, an approxi-
mately normal green col-
or, and a position quite

Total results
with Arisaema

134 LIVING PLANTS

similar
of

in free
ass um-
The a-
of food
able for devel-
have been two
great as that
single leaf. In
days, however,
to exhibit signs
but a “at ths
moved from the
placed in -tire
mal condition
development
usual manner.
the result of the
ments that the
plant of Arisz-
of development,
ing stage in an
from carbon di-
the three aerial
moved, the re-
attain a more
development.
tioles are great-
the laminz un-

to that
plants
air was
ed.

mount
avail -

opine ni mamass
or three times as
usually afforded a
twelve to fourteen
the laminz began
of deterioration ;
time they were re-
apparatus and
open air the nor-
was regained and
proceeded in the

It is to be seen as

foregoing experi-
leaves on an entire
ma are incapable
beyond the unfold-
atmosphere free
oxide. If two of
members are: re
maining one may
advanced stage of
In darkness the pe-
ly elongated, and
fold, but no expan_

Fic. 16.—Arisema triphyllum with flower stalk and one
leaf cut away, in an atmosphere free from carbon dioxide.

CHLOROPHYLL AND GROWTH 135

sion of their area ensues. The removal of
concurrent members results in an exaggerat-
ed extension of the petiole, but has no effect
on the laminez. A similar result is obtained
with the spathe under both conditions. It
is to be noted thatin light the removal of
concurrent organs results in an increased
development of the laminz, and in darkness
of the petiole. .

Calla palustris is a plant consisting of a
creeping rhizome one to two centimeters in
thickness, from the apex of which arise a few
cordate leaves with petioles fifteen to twenty
centimeters long and one or more solitary
scapes eight to fifteen centimeters high. The
relatively large rhizomes are filled with stored
food.

Plants brought into a warm house and
placed under the apparatus described above
exhibited a development of the petioles and
lamine during a period of ten to twelve days
that resulted in the formation of perfect leaves.
The continued existence of the plant, however,
under such conditions wasimpossible because
of the destruction of the stored food by fer-
mentation.

In the dark chamber the slight extension of
the petioles occurred while the lamine attained
a size equal to those in the open air, although
they wererecurved at the margins. No effects

Results
with Calla

Results
with Zea

136 LIVING PLANTS

were obtained by the removal of the concur.
rent members.

Seedlings of Zea mais, with theshoot emerg-
ing from the cotyledon, were placed entirely
inside of the apparatus, where they remained
for a period of eight to twelve days without
carbon dioxide. In such experiments the
plant evidently could carry on the extension
of the shoot only so long as food could be ob-
tained from the seed. To determine the ac-
tual constructive value of the stored food
in the seed, plants were allowed to remain in
the apparatus until the leaves exhibited indi-
cations of deterioration, which was eleven to
fourteen daysafter the beginning of the exper-
iment. The plants were moreslender and the
leaves narrower than in control plants. A
small amount of starch was still to be ob-
served in the seeds, both in the plants grown
in the air free from carbon dioxide and in
normally grown plants of the same age.

In darkness the stems areelongated and the
etiolated leaves are much narrower than in
normal plants.

Specimens of Phoenix dactylifera were ob-
tained by the germination of the seeds of the
commercial date, a process requiring from
twenty to thirty days. The seed consists
largely of reserve cellulose, and according to
Haberlandt is sufficient to allow the forma-

CHLOROPHYLL AND GROWTH 137

tion of a primary root more than a meter in
length, before the unfolding of the first foliage
leaf in the natural habitat of the plant. In
planting the seeds in moist soil this excessive
development of the roots was useless, and
foliage leaves began to unfold when the root
had attained a length of a few centimeters.

The seedlings grown in small pots were
placed inside the apparatus and kept free from
carbon dioxide for a period of thirty to forty
days. The leaves, which at the beginning of
the experiment were emerging from thesheath-
ing scale, exposing a tip one to two centi-
meters in length, attained a length of fifteen
centimeters and a complete normal expansion
corresponding to that of organs grown in the
open air. Such leavesusually attain a length
of twenty to thirty centimeters by a slow
process of growth lasting several months, and
my experiment, therefore, covers only the
earlier stages of development.

Specimens placed in a dark chamber during
a period of thirty to forty days exhibited an
exaggerated elongation of the cotyledonary
and leaf scales, as well as the leaf itself, which
retained its lamina in the plicately folded
position. The increase in length amounted
to twenty to thirty per cent more than in
control plants.

It is safe to conclude that the development

Results
with Phoenix

138 LIVING PLANTS

of seedlings of corn and date may proceed
so long as the necessary amount of plastic
material is available.

In such manner many specimens each of
Arisema triphyllum, Calla palustris, Lilium
splendidum, Trillium erectum and T. erythro-
carpum, Isopyrum biternatum, Oxalis flori-
bunda and O. vespertilionis, Justitia sp., H1-
biscus rosa-sinensis, Zea mais and Phoenix
dactylitera were grown. Of these it was
found that leaves of Ariseema perish in an air
free from carbon dioxide at the beginning of
the unfolding stage; leaves of Calla, Lilium
and Trillium attain normal stature but are
incapable of further existence. Leaves of Zea
carry on normal development during a period
of ten to twelve days, but in this time attain
each a stature inferior to that of control
plants, and then begin todeteriorate. Leaves
of Oxalis, Isopyrum, Hibiscus, and Justitia
attained normal stature, and were capable of
continued existence at the expense of food de-
rived from storage tracts, or active chloro-
phyll-bearing tissues.

In the ordinary course of leaf development
growthis carried from the rudimentary stage
to the unfolding of the lamina at the expense
of food derived from storage organs or from
the main axis. Ordinarily the supply of food
transported to the developing leaf is supple-

CHLOROPHYLL AND GROWTH 139

mented early in the unfolding stage, by food
formed by the young lamina. Inashort time
the supplementary amount from the leaf is
entirely sufficient for its own needs for con-
structive purposes; and at this time the re-
serve food transported to the leaf has under-
gone great diminution. Whena leaf is placed
under such conditions that the laminais inac-
tive, the amount of reserve material which
can be transported to the leaf will, in many
instances, be found insufficient for its needs.
This will be best understood when it is
stated that the amount used at this time is
many times greater than that needed in the
earlier stages, and moreover, that the difficul-
ties of translocation have vastly increased.
Thus by the elongation of the petioles—
amounting from two to ten centimeters daily
in Arisema—the distance between the stored
food in thecorm and the point of consumption
in the leaf-blade has been greatly exaggerated.
Then again the amount of stored food has
been materially reduced by consumption and
the intervention of destructive fermentations.

It is apparent without recourse toa further
recital of the detail of the experiments, that,
if at a time when the available food supply is
diminishing to aminimum, and the difficulties
attendant on translocation are becoming
greater, the needs of the leaf should suddenly

Ordinary course
of growth

Growth with
insufficient
nutrition

140 LIVING PLANYS

mount to a maximum, the supply may be
found insufficient, unless supplanted by the
food-forming activity of the lamina, and de-
terioration of the tissues, due to starvation,
must ensue.

The stage in which the translocated food
becomes inadequate is not identical in all
species. Thus it appears from my experi-
ments that relatively small leaves, or those
with less rapid development, or with a read-
ily available supply of food material, may
attain a much more advanced stage than
those in which the contrary conditions pre-
vail. The conditions may be so favorably
disposed as to allow not only of the cornplete
development of the leaf, but also of its contin-
ued maintenance under conditions of func-
tional inactivity with respect to the chloro-
phyll.

It is to be noted that the phrase, ‘‘function-
al inactivity,’’ is used in a relative, not an
absolute sense. The portion of the plant en-
closed in the apparatus isconstantly emitting
carbon dioxide; which is rapidly absorbed by
the potassium solutions. Under such circum-
stances the carbon dioxide may be imagined
as forming a diffuse stream from the plant to
the potassium, and the amount actually
available by the chlorophyll-bearing cells at
any one time must be extremely small. Some

CHLOROPHYLL AND GROWTH 141

doubt still exists as to the cause of the rapid
deterioration of inactive leaves. It is held by
some that it is due to the harmful substances
set free in the decomposition of chlorophyll,
while it is asserted on the other hand that the
breaking up of the chlorophyll is a result of
starvation and functional inactivity.

Finally it may he said that in order to ac-
count for the reactions of inactive leaves in
light and in darkness it is necessary to predi-
cate the intervention of the regulatory mech-
anism in a manner almost entirely specific.
Such action has been described in Ariszema,
which on the removal of concurrent members,
develops laminz in the light and petioles
in darkness. That is to say, it should not be
taken for granted that all of the changes de-
scribed in the above plants are due simply to
disturbances of the nutritive processes, but
represent to some extent an irritable respanse
of the plant to the unusual conditions under
which it is placed and from which it attempts
to free itself. Thus the excessive elongation
of the stems and petioles in darkness seems
very clearly an adaptive modification for lift-
ing the leaf-blades and chlorophyll out of ob-
scurity and into sunlight, and may not be
accounted for on any other grounds. (This
theory of elongation as an adaptive modi-
fication was originally proposed by Godlew-

Conclusions

142 LIVING PLANTS

ski in 1873.) The results of the foregoing
discussion may be briefly summarized in the
following paragraphs.

The relation of the growth of leaves to their
food-forming power, is such that some are
able to carry development no further than
the beginning of the unfolding stage of the
laminze; others are able to carry the develop-
ment to an approximately normal stature;
and others are capable not only of the devel-
opment to normal stature but also of con-
tinued maintenance under conditions of en-
forced inactivity.

This varying reaction of leaves is dependent
upon a series of conditions which may be in-
cluded in the phrase ‘‘availability of the food
supply.”

The deterioration of certain leaves under
conditions of forced inactivity is due to insuf-
ficient nutrition and is accompanied by the
disintegration of the chlorophyll.

The behavior of inactive leaves in light ex-
hibits no similarities or correspondence, in
simple growth or upon the intervention of
correlation processes, to their behavior in
darkness.

Material constructed in active chlorophyll
areas and stored in special organs may be
transported to inactive chlorophyll-bearing
organs in some plants in light and in dark-

CHLOROPHYLL AND GROWTH 143

ness, and be used in such manner as to allow
of the perfect development of these organs.

The removal of concurrent membersin dark-
ness may have no effect, may cause an exag-
gerated development of the petioles, or may
result in the perfect development of the entire
leaf. The nature of theregulatory mechanism
in each instance is entirely specific.

It is possible for some plants to form perfect
leaves in darkness, when some of the branch-
es only are darkened, and for others when
the entire plant is etiolated. It is thusshown
that no invariable connection exists between
the phototonic condition and _leaf-develop-
ment.

Placing a leaf under such conditions that
it cannot construct food sets in motion
the specific regulatory mechanism of the or-
ganism in such a manner that the plastic
material may be withdrawn, and the organ
cast off. An exaggerated development of the
petioles may be induced in darkness by this
mechanism.

The excessive elongation of the stems and.
petioles in darkness is to be regarded as a
phenomenon of adaptation by which the
leaf surfaces would be placed beyond any ob-
- ject intervening between them and the light.

IX

LEAVES IN SPRING, SUMMER AND AUTUMN.*

The yearly miracle of the appearance of in-
numerable shades and hues of green in awak-
ening vegetation, exerts a mysterious influence
amounting to fascination over the human
race. A fascination made strong by the in-
herited experience of untold generations of
forest-dwelling ancestors, reaching backward
the entire present geologic period, and which
grows in intensity as we creep from the crea-
tion to millenium.

Our vague and emotional inherited interest
in the annual revivification of the vegetable
world becomes vividly intense and direct,
however, when itis learned that the universal
blush of green is due to the most important
coloring substance in the world—chlorophyll.

*Adapted from ‘‘Green Color of Plants,’’ Harper’s Magazine,
April, 1897, and “‘Autumn Leaves,’’ same journal, October,
1897.

Importance of
chlorophyll

146 LIVING PLANTS

It is literally true that the existence of every
living thing is ultimately dependent upon the
activity of plant-green.

The actual conditions are as follows: the
elements which enter into the construction of
protoplasm are carbon, nitrogen, oxygen, hy-
drogen and phosphorus. These elements are
found in the form of free gases or simple com-
pounds in the soil and atmosphere, and can-
not be used by protoplasm until built up into
the form of complex compounds. The con-
struction of compounds indispensable for the
nutrition of plants and animals does not re-
sult from mere proximity of the elements,
since those most highly desirable are chem-
ically inactive to one another, and will unite
only under the influence of energy from with-
out. The substances are selected and ab-
sorbed in their elemental condition by the
plants, and in the crucible of the cell, glowing
with potentiality absorbed from sunlight, are
fused together and made ready for assimila-
tion by protoplasm.

The most important synthetic process is
that which results in the formation of carbon
hydrates from carbon dioxideand water. If
this process were carried on by means of en-
ergy furnished by the activity of the proto-
plasm, the expenditure entailed would over-
balance the benefits gained by the assimilation

LEAVES IN SEASONS 147

of the substances formed. It is clearly ap-
parent, therefore, that the organism must
receive energy from some external source and
must be able to convert this energy into the
forms necessary to promote chemical synthe-
sis. Sunlight is a universal source of energy
and green plants are the only organism capa-
ble of converting its rays into available ener-
gy. The transformation is effected by means
of chlorophyll.

It is true that a few lower forms, inclusive
of the ‘‘sulphur” and “iron” bacteria among
plants and some of the lower forms among
animals, are able to accomplish the construc-
tion of carbohydrates, but the total result
of their activity is indefinitely unimportant,
and is doubtless at the cost of energy furnish-
ed by complex compounds derived from other
plants and animals.

Animals and non-green plants are therefore
dependent, directly or indirectly, upon the
substances formed by the green plants for
food. This physiological characteristic has
led a recent German writer to classify the
fungi (mushrooms, toadstools, molds, etc.)
among animals. A classification that would
work privation to the vegetarian if seriously
accepted.

The action of chlorophyll may best be un-
derstood when its physical properties are

Properties of
chlorophyll

148 LIVING PLANTS

demonstrated. In order to do this asolution
of the substance is obtained by placing a
gram of chopped leaves of grass or geran-
ium in a few cubic centimeters of alcohol for
an hour. The solution will be a bright, clear
green color, and when the vessel containing it
is held in such a manner that the sunlight is
reflected from the surface of the liquid it will
appear blood-red, due to its property of fluor-
escence, that of changing the wave lengths of
the violet end of the spectrum in such a man-
ner as to make them coincide with those of
the red end. Itis by examination of light
which has passed through a solution of chlor-
ophyll, however, that the greatest insight
into its physical proverties may be obtained.
Ifsuch aray is passed through a prism and
spread upon a screen, it may be seen that
there are several intervals of dark bands in
the spectrum. The rays which would have
occupied these spaces have been absorbed by
the chlorophyll and converted into heat and
other forms of energy. This energy is directly
available to the protoplasm containing the
chlorophyll. Asa necessary concomitant of
its physical properties, chlorophyll is usually
only to be found in organs exposed to the
light. It would not only be useless but dan-
gerous elsewhere, as it disintegrates in dark-
ness into substances hurtful to the organism.

LEAVES IN SEASONS 149

It is found in greatest quantity in leaves in
layers of special cells beneath the epidermis.
It is not distributed throughout the entire
cell, but occurs in the masses of protoplasm
which the botanist terms chloroplasts. The
chloroplasts are sponge-like structures, and
the chlorophyll is to be found in solution in
an oil in the interstices of the protoplasmic
sponge.

Chlorophyll is an extremely complex sub-
stance and correspondingly unstable. Hence
as soon as the chemist extracts it from the
plant in the attempt to make an analysis,
disintegration sets in and he is no longer
dealing with chlorophyll, but with the sub-
stances derived from it by decomposition.
Investigation upon the nature and activity
of plant-green has beenin progress more than.
a century, yet its exact chemical composition
is unknown. It contains carbon, oxygen,
hydrogen, nitrogen, magnesium and phos-
phorus, butthe proportions and arrangement
of the atoms of each element in the molecule
of chlorophyll have not been exactly ascer-
tained.

The beautiful and striking colors of autum-
nal foliage are due in greater part to sub-
stances formed by the disintegration of chlo-
rophyll. The many thousands of tints of
green leaves are due to a number of causes,

Varying tints

Synthesis
of food

150 LIVING PLANTS

In some cases the outer layers of cells of the
the leaf, or merely the walls of the celJs, may
contain coloring matter. The number and
size of the chloroplasts, and consequently the
amount of the chlorophyll, may be greater in
some leaves than in others. Besides, the chlo-
roplasts may be moved about in the cell and
their distance from the surface of the leaf
altered, or they may be placed in lines perpen-
dicular or parallel to the surface. In this
manner the infinite and elusive variations of
color, so fascinating to the lover of nature,
are produced in vegetation. The color ofa
leaf may vary momentarily throughout the
day, as indeed does that of the entire land-
scape to the puzzled artist.

The cell sap which bathes thechloroplast in
the leaves contains carbon dioxide absorbed
from the air. When the sun shines upon a
leaf therays pass through the epidermis and
penetrate the cells containing the chloroplasts.
The chlorophyll converts a large proportion
of the light into heat and other forms of en-
ergy. With this energy as a motive power
the protoplasm of the chloroplast withdraws
water and carbon dioxide from thesurround-
ing cell sap and combines them in such man-
ner that a substance known as formic alde-
hyde is formed and oxygen is liberated. In
a second stage the atoms of carbon, hy-

LEAVES IN SEASONS 151

drogen and oxygen in six molecules of
formic aldehyde are rearranged in one com-
plex molecule forming sugar, from which the
other carbohydrates are easily derived. Pro-
toplasm may not be formed from sugar alone,
since nitrogen is a very important constituent
of living substance. It is probable that nitro-
genous substances are sometimes formed by a
variation in the earlier stages of the process
described above, by which nitrogen is substi-
tuted for oxygen in the molecule of formic
aldehyde. Such a substitution would result
in the formation of hydrocyanic acid. The
recent discovery of this deadly acid in the
leaves of a tropical palm lends favor to the
hypothesis. It may be formed in many green
leaves, but, like the earlier substances in the
synthesis of sugar may undergo instant trans- '
formation and thus escape detection.

The absorption of carbon dioxide from the
air, and the excretion of oxygen by vegeta-
tion is sufficient to balance the opposite
processin animals, and hence thecomposition
of the atmosphere remains unchanged. It is
a notable fact that plants thrive in an atmo-
sphere containing a much larger proportion
of carbon dioxide than is found in the atmo-
sphere at the present time. Normal air con-
tains but one-twenty-fifth of one per cent of
this gas, and the food-forming power of the

Acquisition of
chlorophyll

152 LIVING PLANTS

plant is greatest inan atmosphere containing
two hundred times as much, seven to ten per
cent by volume. The power of using larger
proportions of carbon dioxide was doubtless
acquired in anearlier geologic period, and was
adapted to the conditions then prevalent.

The botanist finds himself lost in a maze of
conjecture if he endeavors to trace backward
the development of plants and determine the
point at which they gained the power to form
chlorophyll. Itis quitecertain that the simpler
ancestral forms, which consisted of simple
masses of protoplasm, were not able to con-
struct and maintain a substance so complex
and unstable as chlorophyll. The advent of
this substance into the living world marked
the attainment of a comparatively advanced
stage of development. A tinge of probability
lends itself to the theory that the protoplasm
of all simple organisms which: existed in a far
distant age of the world’s history were able
to accomplish the synthesis of complex from
simple compounds, and that the ‘‘sulphur”’
and “iron” bacteria are but remnants of this
primitive physiological type.

Still another problem is to be found in the
presence of chlorophyll in a number of the
lower forms of animals. A fact which renders
the task of making categorical distinction be-
tween plants and animals still more difficult,

LEAVES IN SEASONS 1538

The chlorophyll isnot found in the organisms
where the two kingdoms meet, but occurs in
animals which have attained a high degree
of development, such as the vorticella, and
fresh-water sponges. It is supposed that the
chloroplasts in these animals are descended
from others derived from unicellular plants
captured by the animals in an earlier stage
of the development.

To a naturalist one of the striking and
spectacular features in the history of living
things is the manner in which vegetation puts
on, wears, and discards its leafy coverings of
green. The season begins with the assump-
tion of an all prevalent, delicate green cover-
ing, composed of millions of irregular laminz
of every conceivable form, which hide the
roughnesses of gnarled and crooked branches,
the flinty soil and ragged moor. With the
advancement of the leaves toward maturity,
the earlier and more delicate tint deepens into
a rich satisfying green that fills the eye, and
then fades away in the long summer heat to
dull gray and bluish greens, dust-colored and
bearing the marks of many subduing strug-
gles with wind and storm. The first breath
of frost is the signal for a change on slopes,
valleys, forests and meadows, by which the
dull monotones are at once converted into a

Autumnal

leaf-fall

154 LIVING PLANTS

harmonious magnificence of color, as if by
magic.

The splendor of the colored markings of the
plants and animals of the tropics is a well
worn theme with amateurs, but it does not
stand comparison with the beauty of the au-
tumnal tints of foliage of the north temperate
zone. either in variety or richness of tone.
Furthermore it may be said that the display
offered by the forests east, west and south of
the Great Lakes in North America is not du-
plicated on any part of the globe. The vege-
tation of the valleys and mountain slopes of
the basins of the Rhine and Danube gives an
exhibit which is only less beautiful because of
the smaller number of species, and which is
less remarked because of its shorter duration.

On some portions of the earth’s surface
within the tropics, where no great or sharply
defined alterations in seasons occur, vegeta-
tion pursues a fairly even course all the year
round. Eachleaf retains its place onthestem
until the full limit of its usefulness or endur-
ance has been reached, and then withered and
woody it fallsto the ground incompany with
such of its fellows as may have reached a
similar stage at the same time. Of the myr-
iads of leaves borne-by any tree, not so many
are cast at one time, as to bare the branches
or make any apparent diminution of their

LEAVES IN SEASONS 155

number, and many plants exhibit flowers and
fruit as well during the year. Such favorable
conditions for growth are found only in certain
circumscribed areas, as a large proportion of
the earth’s surface within the tropics has a
supply of moisture during one part of the
year wholly insufficient for the needs of grow-
ing vegetation, and on the approach of this
dry season the plants in rich regions discard
allor a greater part of their leaf surfaces.
This shedding of leaves is not attended by
many of the more prominent features of au-
tumnal leaves, however.

A portion of the year in the temperatezone
is characterized by a protracted low temper-
ature whichis unfavorable to even thesimpler
forms of activity of protoplasm, and renders

the presence of a great expanse of leaf surface

not only useless but dangerous to plants
growing in those zones, and provision is made
for the economical disposition of the foliage.

Plants growing in regions with this alter-
nation of seasons have modified the primitive
rhythm of protoplasm in such manner that
they manifest annual periods of rest and ac-
tivity. While this yearly period has been ac-
quired in somewhat recent time perhaps, yet
it is most firmly fixed in the constitution of
the plant as may be demonstrated if an at-
tempt is made to grow a deciduous tree or

Yearly rhythm

Activity
of leaf

156 LIVING PLANTS

shrub in a conservatory after removal from
its native forest.

The full significance and real causes of the
phenomena attendant upon the fall of leaves
in autumn may only be comprehended, when
the uses subserved by the leaf, and the forms
of activity carried on underneath its surfaces
are recalled.

All the summer long the green surfaces have
been lifted to the sunlight and by the magic
of its potent touch have taken in carbon
dioxide from the air and combined it with
water in such manner as to form highly plas-
tic substances, which flowing steadily to dis-
tant portions of the plant have by the subtle
alchemy of protoplasm become converted into
wood, fiber, and cork, hard, firm and light
as such things only may be.

The scene of activity in the leaf is laidin the
columnar and variously distorted cells con-
taining the green color bodies (chloroplasts)
and these cells are rich in protoplasm, albu-
minoids and sugar. A steady stream of wa-
ter is sucked up by the minute hairs on
the rootlets, and containing mineral salts
in solution, has poured upward into these cells
during the entire season. Asmall amount of
the water has been used in combination with
carbon dioxide in forming food, but by far the
greater proportion has been evaporated

LEAVES IN SEASONS 157

through the membranous walls into the air-
spaces, and passes outward through the
breathing pores (stomata) into the open air
in the form of vapor. The quantity of water
poured into a thirsty sky in the heat of a mid-
summer day is by no means inconsiderable,
even in smaller plants, and in a full-grown
poplar tree may amount toabarrel. As the
water enters the roots it contains from one-
ten-thousandth to a thousandth part of its
weight of potassium, calcium, and magnesium
salts in solution, and it evaporates into the
air leaving the mineral compounds in the
plant. The minerals serve important uses in
building up protoplasm, and facilitating the
diffusion of food substances from one part of
the plant to another. Eventually a large
proportion of these substances accumulate in
layers on or in the cell wall, or as crystals in
the cell cavity, particularly in the leaf, insuch
condition as to be of but little use to the or-
ganism, and it would be benefited by being
freed from this superfluous matter. Besides
the inward condition of the leaf, changes in
the environmental conditions make it highly
important that the plant should dispense
with its leafy extensions.

With the approach of the close of the grow-
ing season, the outward conditions have un-
dergone a gradual and thorough change and

Cause of
leaf-fall

158 LIVING PLANTS

the tree finds its enormous leaf surface throw-
ing water into the surrounding dry atmo-
sphere much faster thanit may be taken from
the soil by the delicate absorbing organs.
The approach of autumn brings cool nights
and a consequent great radiation of heat
from the soil. The chilled root hairs in the
soil are unable to take the necessary supply
of water, and whenever the supply of moisture
coursing upward through the sinuous roots
and tall stems becomes less than that evapo-
rated, adjustment must be made or damage
will ensue. The plant is a most delicately
self-regulating organism. It cannot increase
the water supply, butit may and does decrease
the evaporating surface by casting or shed-
ding the leaves, a reaction which it exhibits
to other conditions as well. Like the true
seaman, however, the plant does not shorten
sail by cutting away its canvas, but by a de-
liberate and well-timed series of processes,
withdraws all of the substances from the leat
which may be useful to it, back into its body
beforeit discards the empty sheets of cells and
woody fibers of the petiole and lamina.
Before proceeding to a description of the
mechanism of leaf-fall, it may be well to call
attention to the popular and erroneous idea
that the coloring and casting of autumnal
leaves is due to the action of frost. It is true

LEAVES IN SEASONS 159

that the phenomena of autumnal leaf-fall are
due to low temperatures, but as may be seen
from the above, the defoliation of the plant is
not areaction to the cold, but is an adjust-
ment to the limited water supply furnished by
the chilled roots. The reduction of the water
supply and the beginning of the processes
leading to defoliation occur a long time before
the temperature of the air is depressed to the
freezing point, or the formation of frost. The
influence of low temperatures upon the plant
is illustrated by the manner in which leaves of
tobacco and melon plants blacken and die as
the result of cool nights before the occurrence
of frost. These plants transpire a relatively
large amount of water from the broad leaves,
and if the temperature of the soil descends to
forty degrees Fahrenheit, the roots are unable
to take up the necessary supply of water, and
the leaves are literally dried out, though they
are incorrectly described as frozen or frosted
by gardeners.

The casting of the leaf is not a sudden and
quick response to any single depression of the
temperature, but is brought about by a
complex interplay of processes begun days or
perhaps weeks before any external changes
are to be seen. The leafis rich in two classes
of substances, one of which is of no further
benefit to it, and another which it has con-

Withdrawal of
leaf-substance

160 LIVING PLANTS

structed at great expense of energy, and which
is in a form of the highest possible usefulness
to the plant. To this class belong the com-
pounds in the protoplasm, the green color
bodies, and whatever surplus food may not
have been previously conveyed away. The
substances which the plant must needs dis-
card are in the form of nearly insoluble crys-
tals, and, by remaining in position in theleaf,
drop with it to the ground and pass into
that great complex laboratory of the soil
where by slow methods of disintegration, use-
ful elements are set free and once again may
be taken up by the tree and travel their
devious course through root hairs along the
sinuous roots and up through million-celled
columns of the trunk out through the twigs
to the leaves.

The plastic substances within theleaf which
would be a loss to the plant if thrown away,
undergo quite a different series of changes.
These substances are in the extremest parts
of the leaf, and to pass into the plant body,
must penetrate many hundreds of membranes
by diffusion into the long conducting cells
around the ribs or nerves, and then down
into the twigs and stems. The successful re-
treat of this great mass of valuable matter is
not asimple problem. These substances con-
tain nitrogen as a part of their compounds

LEAVES IN SEASONS 161

and as a consequence are very readily broken
down when exposed to the sunlight. In the
living normal leaf the green color forms a most
effectual shield from the effects of the rays,
but when the retreat is begun, one of the first
steps results in the disintegration of the chlor-
ophyll. This would allow the fierce rays of
the September sun to strike directly through
the broad expanses of the leaf, destroying all
within, were not other means provided for
protection. In the first place, when the
chlorophyll breaks down, cyanophyll (blue-
green) is formed, antbocyan (blue-red) is
constructed by the pretoplasm, and at the
same time the yellow lipochromes present in
the cells, chiefly xanthophyll, become visible
and takeashare in protecting the plastic sub-

stances, which absorh the sun’s rays in the |

same manner as the chlorophyll, so that the
leaf exhibits outwardly a gorgeous panoply
of color in reds, yellow, and bronzes that
makes up the autumnal display. From the
wild riot of tints shown by a clump of trees
or shrubs, the erroneous impression might be
gained that the colors are accidental in their
occurrence. Thisisfar from the case, however.
The key-note of color in any species is con-
stant, with minor and local variations. The
birches area golden yellow, oaks vary through
yellow-orange to reddish brown, thered maple

Color as a pro-
tecting screen

162 LIVING PLANTS

a dark red, the tulip tree a light yellow, haw-
thorn and poison oak become violet, while the
sumacs and vines take ona flaming scarlet.
These colors exhibit some variation in accord
with the character of the soil on which the
plants stand.

From the above it is to be seen that the
color of autumnal leaves is a screen under
cover of which the protoplasm retreats into
the main stem, carrying with it such other
substances as may be of use to the plant.
With the coming of spring the advance of
living matter in the form of leaves and shoots
is protected in the same manner by layers of
reddish violet, or reddish brown coloring mat-
ter, which disappears on the appearance of
the green coloring matter.

It is of special interest to learn in this
connection that leaves whicharecovered with
a dense growth of silky, woolly or branching
hairs do not usually exhibit any marked au-
tumnal colors. The presence of the screen is
unnecessary in such instances because of the
protection afforded by the matted or felted
hairs on the surfaces.

At a time previous to the beginning of the
withdrawal of the contents of the leaf, or the
formation of the autumnal colors, prepara-
tions had been steadily in progress for cutting
away the leaf when the proper time should

LEAVES IN SEASONS 163

arrive. At some point near the base of the
leaf stalk, the formation of a layer of special
tissue had begun between the woody cylinder
in the center and the thin epidermis. When
the time for the casting of the leaf arrives
this special tissue grows rapidly, pushing
apart or cutting the cells which have held the
leaf rigidly in position, in such manner that
finally the leaf stalk consists of the brittle
cylinder of wood surrounded by the loosely
adherent cells of this newly formed layer of
separation. The merest touch or breath of air
will split the layer of separation, break the
wood, and allow the leaf to fall to the ground.
After the layer of separation has been formed,
a frost or freeze would help to break away
the fragile strand holding the leaf in place,
but exercises no other direct influence on the
process.

Many plants make provision for cutting
away the leaf at more than one point. The
vine forms two layers of separation, one at
the base of the leaf-stalk, and the other at the
upper end below theblade. Layers of separa-
tion are formed at the base of the main leaf-
stalk and at the base of the separate leaflets
in such compound leaves as those of the Vir-
ginia creeper, horse chestnut and Ailanthus.

It is to be remembered, of course, that all
plants do not discard their leaves on the ap-

Separation
laver

Evergreen
leaves

164 LIVING PLANTS

proach of the inclement season. The leaves
of evergreens are so organized that they may
withstand the periods of drought or frost
through several years. Before such leaves
enter upon a period of inactivity, alterations
are carried on in the cells, among which are
the reduction of the proportion of water pres-
ent, and chemical changes which result in the
formation of substances not affected by low
temperatures. The changes of color are not
so marked as to attract general attention,
and they are brought about by the withdrawal
of the chlorophyll bodies toward the inner
ends of the cells, and the formation of small
proportions of yellowish or reddish coloring
substances. The retention of the foliage is
made possible by adaptations in form and
structure, and is a result of the morphologi-
cal nature of the plants involved.

xX
THE SIGNIFICANCE OF COLOR.*

The colors exhibited by the roots, stems,
leaves and flowers of plants must have been
used by man as distinguishing marks in the
selection of food at quite an early stage in his
development. Doubtless masses and combt-
nations of the cruder colors afforded gratifi-
cation to his dawning sense of the beautiful
in these earlier times. Later he became im-
bued with the idea that man was the center
of the universe and that everything, plants
included, was meant to bear a good or evil
relation to the human race. In the deter-
mination of the aspect of any plant, color
and form were taken into account, and were
held to be indicative of magical curative or
poisonous properties.

* Adapted from ‘‘The Physiology of Color in Plants,’’ Pop-
ular Science Monthly, May, 1896.

Early views

Sprengel’s
discoveries

166 LIVING PLANTS

The last-named aspect of plant colors re-
ceived its greatest attention during the prev-
alence of the practices of the Grecian Rhizo-
tomoi and Pharmakopoli, and later in the
‘doctrine of signatures.’’ The doctrine of
signatures supposed that the color and form
of plants indicated their relations, good or
evil, to the human race, in reference to which
they were especially created. This crude su-
perstition attained greatest favor in the six-
teenth century, andisstill prevalentin obscure
form among the lower classes in certain por-
tions of Europe. The use of colors as a dis-
tinguishing mark between species, families,
and groups began quite early in the history
of attempts at classification, and still forms
a minor character in modern systems.

A consideration of the plant as an independ-
ent organism, and of colors with respect to
the possible uses to the species forming them
was first given by Konrad Sprengel near the
close of the eighteenth century. In his won-
derful book, Das Entdeckte Geheimniss der Na-
tur im Bau und der Befruchtung der Blumen,
published in 1793, he brought out the view
that the colors of flowers are for the pur-
pose of attracting animals which would
carry pollen from one individual to another.

The facts involved interest many classes of
naturalists, and observations have been ex-

COLOR 167

tended in every direction by trained and un-
trained workers until the aggregate mass of
results is nothing short of colossal. The con-
clusions advanced by Sprengel have been ex-
tended until effort has been made to show,
that not only does the plant use color to at-
tract useful insects to flowers, but that it also
displays luring areas of color and stores of
nectar on distant bracts and stems to lead
unwelcome and harmful visitors away from
the neighborhood of the reproductive mem-
bers. Still further, many plants aresupposed
to exhibit colors in mimicry of some danger-
ous animal, or which would serve as a signal
of warning to the ravaging animal of the
presence of weapons or chernicals hurtful to
it. In the highly speculative consideration
given the subject the general principal has
been drawn upon to furnish solutions to com-
plicated or unusual arrangements of color, in
a manner highly improbable and unscientific,
and in many instances verging upon the im-
possible and ridiculous. That it can not be
assumed a priori that the colors exhibited by
the flowers or any other organ of the plant
are devices to attract and guide or repel ani-
mal visitors is becoming more and more ap-
parent.

Recent researches have demonstrated that
a color sense is almost wholly lacking except

Ecological
considerations

168 LIVING PLANTS

among the higher insects, and that the form
and odor of the flower are the features most
effective in securing the attention of pollen-
carrying animals.

It is of course undeniably proven that some
colors do attract insects to flowers, and that
pollination is accomplished as a result of the
visit. If, however, the coloris supposed to be
developed as an adaptation, guided by the
selective agency of theanimal, some difficulties
arise. In the first place, it is to be said that
the selective power of the insect has been ex-
ercised only in comparatively recent times—
since it developed the sense of color. Secondly
the red, yellow, and white fioral markings
of leaves and flowers, as wellas of other mem-
bers, are due to katabolic or breaking down
processes, and originate as well in injured or
deteriorated organs in which the food-forming
capacity has suffered diminution. In some
instances, asin the screen of colored leaves,
the formation of the pigments is due to the
regulatory action of the plant, and serves the
purpose of checking the diminution of the
food-forming power, and hinders the disin-
tegration of plastic substances, to which it
owes its origin.

With all of the probabilities taken into ac-
count it can only be said that the selective
power of animals toward plant colors may

COLOR 169

have accentuated the development of these
substances in certain directions in lines deter-
mined by inherent physiological properties,
the origin as well as the continuation of
which are entirely independent of the prefer-
ences of the animal. If insects and birds do,
in certain instances, show a preference for any
color or color scheme it merely converts an
indifferent to a useful property. This is true
of attractiveas well as of warningcolors. By
a recent series of experiments with a number
of 'tropical plants which have a color scheme
resembling that of a poisonous snake, which
has been supposed to shield them from attack
by animals, it has been found that the degree
of hunger of the animals—snails, rabbits, an-

telopes, etc.—chiefly determines the choice of

food, and that warning devices serve no ac-
tual use so far as has been actually demon-
strated.

It will be found most convenient to discuss
thechemical nature and physiological uses of
the more prominent coloring substances, under
the heads of chlorophyll, etiolin, lipochromes,
anthocyan or erythrophyll, and various spec-
ial colors both red and yellow, to be found
within the limits of families, or ecological
groups. The manner of occurrence and their
universal unstability are such that it has

Enumeration
of colors

Chlorophyll

170 LIVING PLANTS

been impossible to determine their exact chem-
ical composition.

Chlorophyll is perhaps the most important
coloring substance in the world, for upon this
substance depends the characteristic activity
of plants, the synthesis of complex compounds
from carbon dioxide and water—a process
upon which the existence of all living things
is ultimately conditioned. Onlyin a very few
unimportant forms devoid of chlorophyll can
the synthesis of complex from simple com-
pounds, or from theelements, be accomplished.
The function of chlorophyll may only becom-
prehended when its chief physical properties
areunderstood. These may bebestillustrated
if a solution of the substance is obtained by
placing a gram of chopped leaves of grass
or geranium in a few cubic centimeters of
strong alcohol for an hour. Sucha solution
will be of a bright, clear green color, and
when the vessel containing it is held in such a
manner that the sunlight is reflected from the
surface of the liquid it will appear blood-red,
due to its property of fluorescence, that of
changing the wave length of the rays of light
of the violet end of the spectrum in such
manner as to make them coincide with those
of the red end. Itis by examination of light
which has passed through asolution of chloro-
phyll, however, that the greatest insight into

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. os
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Red Yellow Green Blue Indigo Violet

Fic. 17.—CuRVES SHOWING SYNTHETIC, THERMAL AND DISINTEGRAT-
ING EFFECTS OF THE REGIONS OF THE SOLAR
SpectTRUM. After Pfeffer.

Synthesis. ------------- Heat. —--—--—Disintegration.
Gg h
!
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ai -

II.

III.

Fic. 18.—I. SPECTRUM OF CHLOROPHYLL WITH SEVEN ee
SORPTION BANDS. The two in the red-yellow between B and D,
and the three in the blue-violet, beyond F, blended in the dia-
gram, are the most important and characteristic.

II. SPECTRUM OF AMARANTH-RED. All the rays except those
falling between B and D have been absorbed.

1II. SPECTRUM OF AUTUMNAL COLOR OF LEAVES OF AMPELOP-
sis. All the rays except a part of those falling between C and D

have been absorbed.

172 LIVING PLANTS

its physical properties may be gained. If
such a ray of light is passed through a prism
and spread out on a screen, it may be seen
that there are several large intervals or dark
bands in the spectrum. The rays of light
which would have occupied these spaces have
been absorbed by the chlorophyll, and con-
verted into heat and other forms of energy.
This energy is directly available to the proto-
plasm containing the chlorophyll, and by
means of it the synthesis ofcomplex substances
may beaccomplished. Moreover, the amount
of synthesis accomplished by plants exposed
to separate portions of the spectrum will be
directly proportional to the amount of that
portion which can be absorbed and converted
into useful forms of energy. The amount of
synthesis is shown to be greatest in the red
rays between B and C, where the most com.
plete absorption takes place.

Chlorophyll is a very complex and highly
unstable substance, and during the absorp-
tion of light it is slowly broken down, but or-
dinarily it is rebuilt by the protoplasm as
fast as it is decomposed. If, however, the
chlorophyll and the leaf containing it are ex-
posed to a light of such intensity that the
chlorophyll is decomposed faster than it can
be rebuilt, then damage must ensue, which if
sufficiently extensive will result in the death

COLOR 173

of the entire leaf. The intensity of the light
which induces a maximum of activity in any
plant, and which it may receive without dam-
age, is determined by its specific constitution.

Fic. 19.—TRANSVERSE SECTIONS THROUGH THE FROND OF
LEMNA TRISULCA (DUCKWEED), SHOWING DIFFERENT POSI-
TIONS OF CHLOROPHYLL BopIEs. A, position in diffuse light;
B, in strong light striking the surface perpendicularly; C, in
darkness. After Stahl.

In the greater majority of plants the efficien-
cy of the chlorophyll increases in tempera-
tures up to 35° centigrade, varies from 35 to

174 LIVING PLANTS

40C, and steadily decreases from 40 to 50°C.
where activity wholly ceases. The intensity
of light falling on a plant in an open plain
during twenty-four hours ranges from almost
total darkness to the blaze of the noonday
sun, and varies almost momentarily. As an
adjustment to this condition the intensity of
the light impinging on the chlorophyll-bearing
masses of protoplasm is varied by altering the
position of the surfaces of the leaves by active
and passive movements. In others in which
this movement is not possible—such, for ex-
ample, as the leaflike duckweeds which float
on the surface of the water—the intensity of
the light received is regulated by alterations
in the position and distance of the chlorophyll
from the surface of the organ.

In many plants growing in the bright glare
of the sun a thickened cuticle or a heavy coat
of hairs serves to protect the chlorophyll
against the more intense action of the rays.
Then, as will be shown later, other colors are
often developed in the external layers of the
leaf as a protection against intense illumina-
tion.

Chlorophyll is generally formed in special
sponge-like masses of protoplasm ( chloro-
plasts) in the peripheral layers in the cell, and
is most abundant in Jeaves.

As arule the chloroplasts may form chloro-

COLOR 175

phyll only in sunlight, though several instan-
ces are known in which the green color is to
be found in tissuesincomplete darkness. The
presence of iron in the cell is necessary for the
formation of chlorophyll, although it does
not enter into the composition of the pigment.

When aplantis grownin complete darkness
it assumes a pale waxy yellow color, the or-
gans are usually abnormal in size and form,
and are said to beetiolated. The yellow color
of etiolated plants is etiolin which resembles
chlorophyll in general chemical composition
and physical properties. Many writers be-
lieve that etiolinis formed in the earlier stages
of the construction of the chlorophyll mole-
cules. In support of this view it has been no-

ticed that plants grown in darkness and con-.

taining large quantities of etiolin turn green
on exposure to light much more rapidly than
those in which but little etiolin was found.
Etiolin is not to be confused with the yellow
colors of fruits and flowers, which are due to
an entirely different class of pigments next to
be considered.

The lipochromes are a series of substances
varying through yellow and red, devoid of
nitrogen, and which absorbcertain blue violet
rays of sunlight. These substances occur in
company with chlorophyll in leaves and else-
where in bacteria, alge, fungi, as well as in

Etiolin

The lipo-
chromes

176 LIVING PLANTS

the flowers and fruits of the seedforming
plants. The lipochromes constitute the pig-
ments of many animals also. Examples in
the two groups are offered by the yellow color
of the yolk of a hen’s egg, and by the reddish
yellow of the carrot, or the sulphur yellows
of certain fungi. These substances occur in
various forms, in oily drops in the fungi, ina
diffused state throughout the plasma in bac-
teria, and in crystalloids in the carrot and in
flowers. In leaves the lipochromes are sup-
posed to occur in the chloroplasts. If an
equal amount of kerosene or benzole is added
to a solution of chlorophyll in alcohol and the
mixture is shaken and allowed to stand for a
few hours, the alcohol containing a yellowish
lipochrome, xanthophyll, will separate from
the kerosene or benzole solution. The yel-
low and yellow-red tints of autumn leavesare
due to the lipochromes which become visible
after the decomposition of the chlorophyll.

In leaves the lipochromes are supposed to
act as ascreen in preventing the disintegrat-
ing action of light on nitrugenous substances.
Since the lipochromes disappear during the
germination of the spores of fungi it is sug-
gested that a function as reserve substance is
alsosubserved. Colored bacteria in which the
pigment is a lipochrome of which, Bacillus
brunneus, B. cinnbareus, Micrococcus agilis

COLOR a LY G7

and Sarcina rosea offer examples, have the
power of occluding oxygen from the air, which
may be given off under partial pressure. The
pigment is the oxygen carrier and may act in
asimilar manner after it has been extracted
from the organism. The green and purple
bacteria of which Bacterium viride and B. pho-
tometricum are examples, contain two pig-
ments one of which resembleschlorophyll and
the other the red coloring matter of the alge.

The anthocyans comprise a series of sub-
stances soluble in water varying from red to
blue and violet according to the acid or alka-
line nature of the cell sap in which they are
always found in solution. Thusa portion of
a plant of a blue color from the presence of
anthocyan may be changed to a red by im-

mersion in an acid solution and theoperation —

may be reversed. Similar changes are often
brought about in the petals of flowers by
chemical processes set up within the cell. Ex-
amples of changes of this character areshown
by Pulmonaria, Mertensia, Symphytum and
willows.

The anthocyans occur in stems, petioles,
flowers, leaves, unfolding shoots, organs ex-
posed to low temperatures, and in injured
regions. It is quite generally accepted that
the pigments embraced in this group are de-

Anthocyans

Relation of an-
thocyan to light

178 LIVING PLANTS

rived from the tannins. The colors which
attract animals belong chiefly to this group.
Several theories have been proposed in the
last decade to account for the functions of
anthocyan. Engelmann found that red pig-
ment permits 90 per cent of the orange rays,
10 to 30 per cent of the green and yellow, 50
per cent of the blue and 80 per cent of the
violet to be transmitted unchanged. Miiller
has plotted the absorption spectrum of aJarge
number of anthocyans, with the result that
while Engelmann’s results hold good in the
main, some also absorb the lower red rays.
As a natural result of such physical character-
istics it is found that anthocyan converts
lightinto heat, a portion of theconverted light

- being the disintegrating rays of the blue violet

endofthespectrum. That the anthocyan does
partially retard the disintegration of chlor-
ophyll by light may be seenif two vessels con-
taining solutions of chlorophyll are so ar-
ranged that the light which strikes on one of
them shall first pass through a parallel-walled
vessel containing water, and that which
strikes the other through a similar vessel con-
taining a solution of anthocyan. The chlor-
ophyllin the first will soon become much more
discolored than in the second, which has re-
ceived light transmitted through anthocyan.
That the disintegrating rays may be convert-

COLOR £79

ed into heatis demonstrated by the following
ingenious experiment designed by Kny.
Three similar glass vessels with parallel walls
are filled with distilled water. In one vessel
a number of green leaves of canna are placed,
and in another such number as to offer the
same amount of surface as those in the first,
but which contain a large amount of antho-
cyan. The third vessel is left unchanged, and
all are placed in sunlight of equal intensity.
A certain rise in temperature naturally ensues
in the water in the third vessel; agreater rise
occurs in the first, showing that chlorophyll
converts a portion of the light into heat,
while the greatest increase takes place in the
second, where, in addition to the action of
the chlorophyll, the converting power of the
anthocyan is exerted. The difference between
the temperature of the vessels containing the
green and red leaves often amounts to 4° C.,
which is due entirely to the action of the
anthocyan.

The ‘‘screen theory”’ supposes that the chief
purpose of anthocyanis to protect chlorophyll
and other nitrogenous and unstable sub-
stances in transit and in situ from being
broken down by the too intense action of
light rays. A second theory holds that the
development of heat and energy from a layer
of anthocyan is an aid to the translocation

The screen
theory

180 LIVING PLANTS

of carbohydrates and other substances from
one part of the plant to another, notably
starch, from theleaves to the stem. The third
theory consists of the idea that the heat de-
veloped by anthocyan serves chiefly as an aid
in promoting transpiration. Many facts are
at hand supporting both the first and last
named speculations, though the argument in
either case has not advanced to the stage of
absolute proof. As for the second, many
plants growing in cold situations are un-
doubtedly ableto carry on metabolism to bet-
ter advantage because of the heat derived
from light by layers of anthocyan present.
The ‘“‘screen”’ theory receives support from
the fact that the upper layers of leaves of
plants growing in intense sunlight and in ex-
posed Alpine situations are furnished with
layers of color on the upper or illuminated
surfaces of the leaves, as are also the leaves
of many shade-loving plants when grown in
free sunlight. It is likewise asserted that
plants devoid of color growing in the low-
lands will develop anthocyan in the leaves
when transplanted to Alpine elevations. Ker-
ner transplanted the summer savory (Satur-
eja hortensis) from lowland to a height of
3,200 meters and found that it developed a
very strong layerof anthocyan. Ewart found
that the plants on the summit of the moun-

COLOR 181

tain Geddeh, 4500-6500 feet, in Java, with
a very moist air have but little anthocyan
while on Pangerango, at a height of 10,000
feet, with a dry atmosphere the presence of red
coloring matter was very marked. The pow-
er of absorbing the photochemical rays pos-
sessed by moist air would preclude the need
of a protective coloring in the first instance.
The writer has noticed that the young and
pendant leaves of the mango (Mangifera) are
but slightly colored in the lowland habitats
of the tree in Jamaica but on the mountain
sides, near 1000 feet, the young bunches show
a perfect blaze of color especially in dry reg-
ions. Here, asin the highly colored young
leaves of the maple, oak, grape, sumac, alder
and others, the red coloring matter doubtless
serves as a protection against the penetrating
rays of the sun. At the same time it is to be
borne in mind that the low temperatures of
the elevations mentioned, or of the spring
season may be the direct cause of the forma-
tion of the anthocyan.

The most satisfactory proofs of the forma-
tion of anthocyan as a screenare given bythe
exposure to daylight of plants growing in
darkness. Under such circumstances the
pearly white rhizomes of Dentaria bulbifera
become violet. Plants of Philotria canaden-
sis (Elodea) and Utricularia vulgaris grown

182 LIVING PLANTS

in weak sugar solutions in strong light
formed anthocyan, while other specimens in
water and exposed to diffuse light did not,
showing that the color is formed when needed
only, and not accidentally, although its oc-
currence asin underground organs or in the
center of massive tissues must be accidental
and not useful.

Anthocyan as a screen is not always con-
fined to the upper layers of the leaf. The
leaves of the banana (Musa) are vertical and
rolled up with the ventral surfaces outermost
when young. One species develops color on
the under side, which disappears as the leaf
unrolls and comes down to a horizontal posi-
tion. Uncaria, Alpina, Belemcanda, and other
plants afford similar instances. The pinnules
of Mimosa pudica are provided with a red-
dish coloring matter in the surfaces of the
lower sides which are exposed when closed
together in the “hot sun”’ position.

The coloring matter in the pistils of anemo-
philous plants such as Populus, Salix, Plata-
nus, Ulmus, Ostrya, Carpinus, Corylus, Alnus,
Acer, Fraxinus, Rumex, and others in which
itcan haveno possible significance for animals,
also serves as a screen against the effects of
light. The growth of the pollen tube down
through the pistil would be very much hindered

COLOR 183

by the action of light, which is prevented by
the screening anthocyan.

The demonstrations of the useful properties
of anthocyan asa developer of heat for pro-
moting the chemical processes are not nearly
so numerous. The opening of the flowers
of some of the alpine grassesis brought about
by the rapid elongation of thecolored anthers
under the influence of sunlight. Itissuggested
that the energy for the rapid growth is de-
rived from the sunlight by the coloring mat-
ter. Itis quite true that the heat from any
source will cause these flowers to open quickly.
The red color of certain gymnospermous flow-
ers may accelerate their opening in the same
manner.

The presence of layers of color in the lower
sides of rosettes, and in leaves and rapidly
growing organs in the deep recesses of jungles
and swamps, admits of no interpretation ex-
cept that such arrangements are useful in
promoting transpiration by means of the
heat developed. Ifared and green leaf of the
same species are placed with their bases in
sunlight with the bases of the petioles placed
in calibrated cylinders full of water it will be
found that the transpiration is most rapid
from the colored leaf since it absorbs the
greatest amount of water. A very obvious
demonstration may also be made if the base

Promotion of
metabolism

Promotion of
transpiration

184 LIVING PLANTS

of the petiole of a leaf containing patches or
spots of color is placed in an aniline solution.
The dye will pass most quickly and rapidly to
the regions containing anthocyan, indicating
that the loss of water has been greatest from
these areas.

The maintenance of a transpiration stream,
laden with mineral salts, to leaves and rapid-
ly growing shoots in an already moist and
warm atmosphere is a matter of some diff-
culty andimportance. If the temperature of
a plant is higher than the surrounding atmo.
sphere it may continue to carry on transpira-
tion because of the greater tension of the
aqueous vapor in the heated air of the inter-
cellular spaces than in the surrounding med-
ium. The presence of anthocyan would be
almost a necessity to leaves under such cir-
cumstarices.

In connection with the heat producing prop-
erties of anthocyan itis to besaid that it may
increase the amount of odorous substances
volatilized from fragrant flowers, and thus in-
directly aid pollination. It is also possible
that the actual warmth of organs containing
anthocyan may serve as a lure to animals.

A number of pigments of limited distribu-
tion occur in the citrus fruits, colored algze
and bacteria, which are but little known so

COLOR 185

far as composition and use are taken into ac-
count.

The color of the red seaweed is due to the
presence of phyco-erythrophyll which is pres-
ent in the protoplasm associated with chloro-
phyll. Itis to be noted here that the antho-
cyans are dissolved in theceil sapof the plants
in which they occur. The gradation of the
amount of phyco-erythrophyll at different
depths suggests that the color serves the pur-
pose of converting light into heat useful in
promoting metabolism. The presence of a
red pigment in Hematococcus and the resting
spores of many algz is doubtlessa protection
against the disintegrating effect of light on
chlorophyll and protoplasm.

Effects quite as marked as those produced
by colors may be brought about by the pres-
ence or mechanical arrangement of certain
-cells. The shade of green presented by a leaf
will be determined by the number and posi-
tion of the chlorophyll bodies with respect to
the surface. Coatings of wax, mineral salts,
and hairs also, bring about modifications.
The silvery or silver gray or whitish appear-
ance of surfaces is due to the loose arrange-
ment of the sub-epidermal cells forming great
intercellularspaces. The multifold refractions
offered by the numerous free walls of the cells
prevents the penetration of the leaf by light.

Red sea-weeds

Markings not

due to color

186 LIVING PLANTS

(J

Fic. 20.—1. Transverse section of a velvety leaf of Eran-
themum Cooperi. The epidermal cells of the upper side are
furnished with elongated papillose extensions for entrapping
sunlight. The extremities of some cells are converted into
hairs. The epidermis of the lower side contains anthocyan.

2. Diagram showing the manner in which light enters the
epidermal cells of velvety surfaces,

COLOR 187

The tissues underneath such regions are usu-
ally free from chlorophyll. The leaf might be
compared to a sheet of tinted glass which per-
mits the passage of the greater part of the light
which falls upon it while intact. When
crushed into fragments the mass of minute
fragments reflects back the rays at thousands
of points.

Plants such as the aloe, growing in the
fierce light of a tropical desert, avoid burning
and drying of the tissues by such arrange-
ments. The silvery areas warm up much
more slowly than a typical leaf. At the same
time this feature is also of use to plants grow-
ing in moist, tropical climates, in the promo-
tion of transpiration at night.

The silvery areas not only warm up slowly
but they also radiate heat less rapidly thana
typical leaf, and the higher temperature of
these areas after sunset promotes transpira-

3. Transverse section of a velvety leaf of Piper porphyr-
aceum. A layer of aqueous tissue lies next theepidermis of the
upper and lower sides. The anthocyan is in the lower half of
the leaf.

4, Mottled leaf of Begonia faleata. a. Transverse section
of a brownish green velvety shining portion of lamina. The
epidermal cells of the upper side are furnished with papillose
extensions. The epidermal and sub-epidermal layers are joined
without intercellular spaces. The epidermis of the lower side
and the spongy parenchyma contain anthocyan. b. Trans-
verse section through a silvery portion. The outer walls of
the epidermis are plane. Large air spaces are present between
the epidermis and the cells containing chlorophyll.

5. Transverse section of a bright spot on the leaf of Ranun-
culus ficarioides. The sub-epidermal cells, a, contain a few
small chloroplasts, and are separated from the layer beneath
by large air-spaces.

6. Papillose epidermal cells of Begonia imperialis, var.
smaragdina, seen from above by refracted light. After Stahl,

Silvery areas

Velvety surfaces

188 LIVING PLANTS

tion at a time when itisata minimum in nor-
mal leaves. This is an adaptation of great
importance in certain regions as is indicated
by the great number of species in which it is
found. Begonia, Anthurium, Draczena, Tra-
descantia, and Geranium offer examples of
this arrangement.

The relation of silvery areas to light may
be demonstrated if the lower side of a mottled
leaf of Begonia or Anthurium is coated with
cocoa butter or lard and allowed to cool. If
the upper side is exposed to sunlight, the oily
substance will melt under the green areas be-
fore that beneath the silvery regions is effected.
If the experiment is continued until all of the
substance is melted and then taken into a
shaded place to cool it will be found that the
butter opposite the silvery areas remains
melted after that on the green portions has
solidified. The silvery areas of the leaves
carry on food-formation less rapidly than the
green regions because of the great obstruction
to penetration by light.

Many leaves exhibit a rich velvety surface
that is also due to structural modifications ;
when combined with underlying layers of
color as in Cissus, the effect is very striking.
The velvety appearance is due chiefly to the
papillose extension of the outer walls of the
epidermal cells. The conical and convex

COLOR 189

outer walls act as lenses in directing all rays
of light, which strike the surface at any angle,
into the interior, and in some instances actu-
ally focusses them upon the chloroplasts.
Such an arrangement is to be found chiefly in
plants native to moist climates, and gener-
ally growing in diffuse light. Oxalis aceto-
sella, Cissus discolor, Fucshia triphylla, Mar-
anta zevlina, and some begonias are exam-
ples showing this adaptation.

A plant or even a single leaf may exhibit
colors due to several causes. Thus the leaf
of Begonia falcata has silvery areas of the
usual structure, brownish green patches in
which the epidermal cells of the upper side are
outwardly convex, and those of the lower side
contain anthocyan. Arrangements of this
character are most frequent in the foliage of
tropical plants. The contents of the foregoing
paper may be briefly summarized in the fol-
lowing paragraphs.

Colors may serve as an attractive or guid-
ing device to lure animals to flowers or away
from them. Physiological causes have played
the principal part in the development of pig-
mented regions, and this development may
have been modified by the selective power of
animals to some extent. The color sense is
lacking in some pollen carrying insects, and
when present has been acquired in a compar-

Conclusions

190 LIVING PLANTS

atively recent period in the history of plants.
Form and odorare much more efficient agents
than color in the attraction of animals.

Chlorophyll converts light into energy by
the aid of which the protoplasm which con-
tains it is able to build up complex foods.

The lipochromes are found in leaves and
other organs, associated withchlorophyll un-
der the name of xanthophyll, in citrus fruits,
in some underground members and in fungi
and bacteria. The yellow tints of autumn
leaves are due to lipochromes. These sub-
stances may occur in solid crystalloids in the
cell or diffused throughout the protoplasm or
suspended in oily drops. The ltpochromes
probably serve as reserve substances in some
plants and in others as a screen against in-
tense illumination. Bacteria furnished with
a lipochrome pigment are able to occludecom-
paratively large quantities of oxygen which
may be given off under partial pressure. Cer-
tain green and red bacteria are able to carry
on food formation by means of a pigment re-
sembling chlorophyll in physical and chemi-
cal properties. A second pigment which has
some of the characteristics of the red color of
the algze is also present in these forms. The
pigments of the bacteria have been the subject
of but little investigation.

COLOR nA

Anthocyan is the most widely distributed
coloring substance. It occurs in solution in
cell sap, varies from red to blue and violet and
may be present in any part of the plant. It
may serve as a screen against the disintegrat-
ing action of light on chlorophyll and
other nitrogenous substances. By its heat-
developing power metabolism and transpira-
tion may be promoted.

The coloring matter in marine alge may
act asa screen against light and promote
metabolism and growth by the development
of heat.

The silvery or white appearance of organs
is due to the loose arrangement of the cells.
This arrangement serves as a protection
against intense sunlight andis found in plants
growingin heated deserts. Thesamearrange-
ment may promote transpiration in plants
growing in moist shady situations with cool
nights or frequent rains.

The velvety appearance of surfaces is due to
the papillose extensions of the outer walls of
the epidermis. The extended walls serve as
lenses to entrap sunlight and focus it upon
the chloroplasts. This adaptation is most
useful to plants growing in diffuse light.

Besides all of the occurrences of pigments
noted above, colored substances often are
found in the walls of dead cells, as in the

192 LIVING PLANTS

wood of Hematoxylon (logwood) and
other plants, in excretions and elsewhere in
such manner as to have no physiological sig-
nificance. The color in such instances is to be
regarded as a by-product in the necessary
chemical processes of the organism.

¥. GE

THE RIGHT TO LIVE.*

When we come to think of it, it is strikingly
patent that the world was not fashioned to
especially promote the convenience and happi-
ness of individuals. Should we assume suchan
hypothesis what explanation could be offered
for the prevalence of parasitism, by which the
individuals of one species of animal or plant
live upon, and at the expense of the individu-
als of another species, or what could be said
in extenuation of the carnivorous habit, or
even of the herbivorous habit? We find that
plants as well as animals are no respecters of
personal liberty. The glittering tentacles of
the sundews encompass the struggling fy, and
reduce the exquisitely developed body to a
reeking paste, and bring to nought its enjoy-

*Read before the Parlor Club, an organization devoted to
literary and scientific culture, Lafayette, Ind., Sept. 17, 1897.

Aggressiveness
of plants

Likeness of
plants and
animals

194 LIVING PLANTS

ment of air and light and fragrance. And
there is a travesty upon humancruelty enact-
ed by those curious swamp plants of North
Carolina, when they clasp their bristling leaves
together over the incautious insect with the
same blasting results to the mortal life of the
prisoner as befell the unfortunate victims of
inquisitorial times who succumbed to the
deadly embrace of the etserne Jungfrau. When
standing in the castle tower at Nuremberg,
viewing this torture weapon of medizeval in-
genuity, onecan not but feel that here the God-
like powers of man dropped perilously near
the blind forces of lower nature.

In all the essentials that go to constitute a
living organism of whatever degree of com-
plexity, that is, the ability to take food, to
grow, to respond to stimulation and to ex-
hibit spontaneous and directive energies, the
plant is the Ishmaelitic branch of the same
great world’s family in which the animal has
acquired a higher standing by superior aware-
ness. In other words, the plant and the ani-
mal, in ultimate essentials are of like consti-
tution. It is evident, therefore, that the argu-
ment for natural rights may be supported
from either branch of the organic phylon;
bearing in mind, however, that in shifting
from the animal to the plant, or from the

LEE RIGEEE TO; Elve 195

plant to the animal, the alluring quicksands
of bare analogy must be sedulously avoided.
Turning from the dramatically tragic phases
of plant life, let us look at theeveryday condi-
tions of existence. Two prominent factors in
plant as well as in animal life, are the rate of
increase and the supply of food. In regard to
these some simple calculations will be helpful,
although they may prove a cabala that will
disenchant and spread before us a different
panorama from the quiet, pastoral repose,
which we confidently anticipate when we

‘*Go forth under the open sky, and list
To Nature’s teachings.’’

Linnzeus computed the progeny of an an-
nual plant, from which only two seeds grew
into plants the second year, and from each of
these two plants two others sprung up the
third year, and so on for twenty years. This
is a very low rate of increase, yet at the end
of the second decade the one original plant
would be represented by a million offspring.
A computation made by Huxley gives asome-
what clearer illustration of the real tendency
of plant life. By the terms of his supposition
fifty seeds are able to make a successful
growth from each plant of the preceding year,
and a plant for full development is permitted
to have one square foot of ground. Now es-
timating that the whole land area of the

Possible rate
of increase

Weeds as

examples

196 LIVING PLANTS

world in round numbers is fifty-one million
square miles, and supposing for the sake of
the illustration, that every foot of this ground
is free from all encumbrance and equally
capable of supporting plant life, we shall
arrive at the astounding result that a single
parent plant by the tenth year will have
given rise to enough plants to occupy every
foot of this great area, and over five hundred
thousand billions besides. This means that
an annual plant, increasing at afifty-fold rate.
has the capacity to supply a plant for every
eight square inches of land surface of the
whole globe within one decade.

Such marvelous results of fecundity are al-
most past belief, and it is worth while to
inquire if any facts exist that give counten-
ance to such deductions. The ubiquity and
prolificacy of weeds are proverbial, but upon
closer acquaintance even the popular fancy
seems scarcely to reach the reality, to judge
from the records. Sturtevant found that a
plant of sbepherd’s purse, one of the most
common and mostinsignificant of weeds, bore
fully 12,000 seeds, that a plant of burdock
had 40,000 seeds, and that a number of other
common weeds were equally fertile. But the
list that he examined reached its climax in
the purslane, a plant which by its obtrusive-
ness and pertinacity has become the symbol

THE RIGHT TO LIVE LOZ,

of offensiveness—‘‘as mean as pusley,’’ the
saying goes. A single plant of this species
bore over two million seeds, surely a marvel-
ous prodigality. And yet even these great
numbers are certainly not the full measure of
the plant’s capacity, for some seeds may have
dropped off before the time of counting, and
many more might still have ripened if the in-
terests of science, or other untoward circum-
stances, had not cutshorta flourishing career.

But weeds are not the only plants to show
a superfluity of seeds. How many seeds do
you think, are borne on a single beech tree,
oreven an oak? Certainly many hundreds
more than ever grow into trees. And the
grasses, and climbers, and shrubs, and the
numerous wayside plants that individually
affect our lives so little that we do not know
them by name, does it not seem safe to
‘assume that they are potentially capable, to
be conservative, of a fifty-fold annualincrease,
rising in not a few instances to many thous-
and-fold, and sometimes to a million-fold ?
But the productive spots are already occu-
pied, and outside of cultivated lands largely
with perennial plants, so that there is little
chance of even one out of the large number of
offspring finding conditions for average devel-
opment. What becomes of the other 49, or
999, or 999,999? Many never find the op-

Prolificacy of
other plants

Illustrative

similes

198 LIVING PLANTS

portunity for germination and perish without
feeling conscious life; but many others do
start and attain some size only to be starved
and smothered out of existence.

The condition of the plant world may be
likened to the American struggle for riches;
a very few become millionaires, a small mi-
nority attain financial independence, but the
great majority die without knowing thecom-
forting security of a competence. It has
become customary to speak of this over-
whelming failure to attain a favorable posi-
tion in the world as a warfare, and to some
extent the term is applicable; it is an un-
organized warfare, the fighting of a mob
where there is no leadership, or to select a yet
better simile, the frantic efforts of individuals
under the excitement of a panic where action
is controlled by the single desire to find per-
sonal safety. Darwin’s striking phrase, ‘the —
struggle for existence,’’ which has been so
much used, and also greatly abused, seems
applicable enough when we think that for
each plant that attains normal development
thousands perish. As in the panic, it is the
strongest ones, or those having most advant-
ageous positions, or who are most apt in
adapting themselves to passing conditions,
that survive; and in this sense Herbert Spen-
cer’s twin phrase, the ‘‘survivalof the fittest”’

THE RIGHT TO LIVE 199

finds its application. It is the same in all
essential particulars with animals as with
plants, there is a constant struggle for a
suitable porticn of food and a comfortable
amount of space, the fortunate few succeed-
ing, while multitudes perish. To this general,
coércive law of the organic world man finds
in himself no exemption, except in so far as
the humanizing principle of altruism has
effect. Thus throughout the world the truth
in the refrain of Grant Allen’s ‘‘ Ballade of
Evolution’’ finds confirmation:

“*For the fittest will always survive,
While the weakliest go to the wall.”’

All are aware of the substantial use Darwin
made of facts regarding nature’s prodigality
in animate forms, and the resulting competi-
tion between them, in establishing his theory
of the origin of species. The logical result of
the theory requires the subordination of the
individual to the good of the race. As of all
the myriad individuals only the fittest survive,
the race is inconsequence gradually improved.
The battle is to the strong, and the weak are
mercilessly shoved aside, oppressed, and an-
nihilated. There seems no escape from the
conclusion that the ethics of nature make
right and might synonymous terms. Individ-
uals not only crowd and overpower individ-
uals of the same species, but they prey upon

A world
of strife

200 LIVING PLANTS

those of other species to an extent scarcely
conceivable. All the tribes of parasitic
fungi draw their sustenance from the liv-
ing host, and give rise to the long category
of plant ills known as rusts, smuts, mildews,
rots, molds and blights. The minutest veg-
etable parasites, the bacteria, attack and
bring low the largest and most noble forms
of both kingdoms, especially being man’s
most insidious and deadly enemies. With
comparatively few exceptions animals of
high and low degree, of all sizes, forms and
habits, whether inhabiting water, earthor air,
from the microscopic amoeba to the bear and
the elephant, seize upon and devourin part or
in whole other living beings, in order to main-
tain their own existence. Not only does the
lion kill other beasts of the jungle, the wolf
seize the lamb, the owl eat the mouse, and the
robin the earthworm, but the ox feeds upon
the living grass, the sparrow gourmandizes
upon myriads of young plants in the seed
stage, and the caterpillar defoliates trees.
With the exception of the carrion beetle, the
house fly, the nectar-feeding humming bird,
and some others, the animal world finds its
daily food by destroying the life of other
weaker beings, sometimes animal, sometimes
plant life being preferred. In this wholesale
destruction of life man lends a ready hand.

Ee, RIGHT Oe L ivi: 201

He has introduced the refinement of refrain-
ing from eating his fellow man, but he usually
does not scruple to partake of any other
kind of flesh that suits his palate, and never
thinks of hesitating when plant life is in ques-
tion. He has advanced so far as to cook
much of his food, but he still enjoys a live
oyster, and munches live celery, radishes and
lettuce with a satisfaction that denotes utter
absence of sensitiveness regarding the exercise
of his rights. It occurred to me to notice
how many individual lives were destroyed
to furnish me a dinner to-day. The beef
and the fowl required two animal lives.
There were over a hundred lima beans, some
six or seven hundred kernels of green corn,

part of two or three Irish and sweet potatoes,.

many hundred grains of wheat for the bread,
and still greater numbers of yeast cells to
lighten it. I did not count the number of
seeds in the sliced tomato, and do not know
how many grains were required for the cup
of coffee, neither can I well estimate the num-
ber of bacteria that took part in flavoring
my piece of cheese, and which were smother-
ed in the curing process. It was a simple re-
past, and yet to supply it required the saert-
fice of a thousand or more individual lives,
exclusive of the yeast and bacteria.

Was there anything wrong in this destruc-

Destruction of
life for a dinner

Natural right
to food

Logic of
good fortune

202 LIVING PLANTS

tion of life to furnish a meal for one individu-
al? Would it have been any more or any less
wrong to have eaten only animal food, or
only vegetable food? Is there anything
wrong in the owl eating a mouse or in the
rabbit eating herbage? Evidently the an-
swer is clear and direct. Every being is enti-
tled by the very law of its nature, and by the
constitution of the organic world, to the food
needed for its sustenance, and animal life per
se is no more sacred than vegetablelife. This
destruction of one being by another is in fact
the only method by which the balance of life
on the earth can be maintained; indeed, all
existence is vicarious, many lives aresacrificed
to maintain the few.

The evolutionary argument, whichhas now
been illustrated, runs along two lines pointed
out by Malthus nearly a century ago, neither
favoring the individual. On the one hand ex-
cessive increase, and on the other, necessity for
food, cause a dire struggle for existence, in
which the race is benefited, but the individual
is generally worsted. From this point of view
the only right to live that an individual being
canclaim is vested in its chance possession of
strength and opportunity; it lives merely
through good fortune.

If we inquire into the object of living, we
shall find that the evolutionists, the pre-evo-

THE RIGHT ITO LIVE 203

lutionists and the creationists are essentially
united in opinion. The chief end of existence
is to bear offspring that the race may be per-
petuated, they all say directly or indirectly.
From the highest forms to the lowest, through
both the plant and animal series, this is held
to be sufficiently patent. Again the individual
is sacrificed to the good of the race. Inregard
to plants this seems to have always been
accepted as a matter of course. I might
quote confirmatory statements without end,
but will only give two. Cesalpino, one of the
wisest of early botanists, said that ‘the
final purpose of plants consists in that pro-
pagation which is effected by the seed,” and
it would be difficult to find any author who

disagreed with him from that time to the.

present. It is so generally accepted that one
should not be surprised that it is taught to
children as an unquestioned fact. In one of
Mrs. William Starr Dana’s recent nature
books for young readers, a whole chapter is
devoted to the topic, ‘‘ What a plant lives for,”
with the terse conclusion that ‘‘a plant lives
to bear seed.”’

Here is the philosophy of the ages regarding
earthly existence in a nutshell; but to me it is
a very unsatisfactory philosophy. I do not
see why one may not argue that it is founded
upon an absurdity, for it is equivalent to say-

Object
of living

204 LIVING PLANTS

ing that the chief reason for living is to die
that another may live, and that other must
in turn do the same; thus true fruition, com-
plete realization, is never attained, but is
always in the unreachable future.

A misconception prevails, it appears to me,
in regard to the place that death and repro-
duction hold in the economy of the world,
which has thrown us upona wrong track.
We may safely assume that much of the di-
versity in the mode and form in which life is
presented tous hasresulted from the changea-
bleness and uncertainty ofexternalconditions.
If moisture, warmth and food could be, and
especially if they had always been, supplied
to every organism in uniform and ample
amount, the struggle forexistence would pre-
sent altogether another phase from its present
day aspect.

If the moisture of air and soil were of ap-
proximately unvarying percentage from day
to day, and year to year,andif warmth were
maintained at the genial glow of a summer
day without interruption, the provisions
against drouth and cold, shown in seeds,
tubers, bulbs, resting spores, sclerotia and
similar protective devices, would be largely
purposeless, and could not long persist, in
fact might never have developed. Undersuch
favorable conditions for continuous growth,

THE RIGHT TO LIVE 205

without the necessity of providing for the in-
terpolation of inhibiting periods of winter
cold or summer dryness, the larger part of
productive activity would doubtless disap-
pear, and with it much of the fierce strife for
place.

If added to other favorable conditions for
existence an adequate supply of food were
available, we can well believe that organisms
might become potentially immortal, that is,
they might live indefinitely unless killed by
pure accident. Such a happy environment
would be a true vale of Avalon:

“Where falls not hail, orrain, or any snow,

Nor ever wind blows loudly; butit lies
Deep-meadow’d, happy, fair with orchard lawns
And bowery hollows crown’d with summer sea.”’

It would, however, be a land of continuous
youth, a Ponce de Leon realization, rather
than a haven for effete King Arthurs.

Weismann finds an argument leading to the
like conclusion in the fission reproduction of
many unicellular animals, by whichno part of
the organism dies during the process of mul-
tiplication, but each part expands into the
perfection of an individual. A not materially
dissimilar process among higher members in
the vegetable kingdom is the ready propaga-
tion by successive branching of such rhizo-
matous plants as certain ferns, iris and
grasses. As the burrowing plant body pushes

206 LIVING PLANTS

forward in its growth the living contents
of the rear cells are gradually withdrawn,
and the effete skeleton of cell-walls disinte-
erates; and in a similar way the appendages
of leaf and root serve their purpose and are
discarded, as a stag sheds his antlers. Al-
though leaf and root and posterior part of
stem repeatedly disappear the plant retains
its identity as an individual. When the drop-
ping away of the end of the rhizome has
involved a branch, the two advancing ends
become entirely separate individuals, a method
of increase that some species find so efficient
that they rarely or never produce seeds or
even flowers. It is no fiction to say that such
a plant never dies. It is compelled to drop its
appendages and hibernate during the incle-
ment season, but its physiognomy remains
the same whatever age it may attain.

It has been shown in a previous essay (page
101), that increasing the food supply, or of
other external factors favorable to growth,
tends to prolong the life of the individual
and to decrease the amount of reproduction.
This is evidently moving, although but a step,
in the direction of ideal conditions for the
even display of vital energy.

These and other reasons which can not find
place here lead us to think that both senility
and excessive increase are riot inherent char-

Tip RIGHT LO LIVE 207

acteristics of life, but have arisen to meet the
demands of existence in a too changeable
world, and that even death is a ‘concession
to the outer conditions of life.” Natural
death may be regarded as a phylogenic inci-
dent, and accidental death as an ontogenic
incident.

The argument here outlined, but which can
not be adequately developed, is intended to
show that reproduction is partly, and death
wholly an adaptation, and that these can no
more be said to be the purposes of living
than can other adaptations, such as the an-
nual production of winter buds on trees, and
on such herbaceous plants as the tiger lily.
Furthermore, the logic of excessive increase
and consequent inadequacy of food does not

warrant us in assuming that present forms

of existence do not possess a natural right to
the greatest longevity and fullest develop-
ment which their individual opportunities
permit them to secure. The individual is lim-
ited in the duration of its active period andin
the expenditure of its energies by theinherited
adaptations imposed by the conditions under
which its ancestry has lived, and these limita-
tions are necessarily passed on to its off-
spring, but its right to the full measure of its
opportunities for self-development can not
therefore be withheld. It must be true that

Death not
essential to life

Plants are
born to live

Right to life
should be
respected

208 LIVING PLANTS

being, everyday existence, is an end in itself.
‘Plants are born to live, not to die,” says L.
H. Bailey in his work on the survival of the
unlike, and the same is undoubtedly true of
animals and of man.

If l have made good my argument, the in-
dividual has a right to its life, it has a right
to live, although under the present conditions
it must maintain its position and its life by
force. And if the individual has a right to its
life, and if the purpose of that life is primarily
to give enjoyment to the possessor, there is
after alla sacredness about life that makes it
wrong to destroy it needlessly. Not only the
animal, but also the plant is entitled to con-
sideration.

“Life is not to be bought with heaps of gold,
Not all Apollo’s Pythian treasures hold,

Or Troy once held, in peace and pride of sway,
Can bribe the poor possession of a day.”’

XII.

THE DISTINCTION BETWEEN ANIMALS AND PLANTS.*

No classes of natural objects seem to the
general apprehension more distinct and im-
miscible than animals and plants. The free
moving intelligent animal appears immeas-
urably removed from the fixed insentient
plant.

Yet, underlying this seeming distinctness,
there usually lurks some vague feeling of
analogy between the hidden springs of life in
the two classes of beings. Strange flights of
the imagination have imposed themselves
upon belief in all ages, that are hard to ac-
count for unless we take this general feeling
of a unity, or possibility of transference be-

_*A paper read before the joint session of the sections of
botany and zoology of the American Association for the Ad-
vancement of Science, at the Springfield meeting, September 2,
1895, and printed inthe American Naturalist, November, 1895;
somewhat revised and extended.

Learned

vagaries

210 LIVING PLANTS

tween the essential natures of the two classes
of objects, to be deep-seated and almost unt-
versal. Only two or threecenturies ago there
were even learned men who believed in the
Scythian lamb, that grew on the topofa

ZZ
2
ZG

sn

Fic. 21.—The Scythian lamb, that vegetated like a tree,
but ate herbage. It was reputed to flourish on the salt plains
west of the Volga. Cut reproduced from Claude Duret’s ‘‘His-
torie des Plantes,’’ 1605.
small tree-trunk in place of foliage, and in the
wonderful tree of the British Isles, whose fruit
turned to birds when it fell upon the ground,
and +o fishes when it fell into water. In still
earlier times, even more astonishing vagaries
were accepted as common knowledge, es-
pecially when vouched for by travelers.

But naturalists and others, who withheld

PLANTS AND ANIMALS 211

1 =
fe Se

: .
WPT

Fic. 22.—The tree of the British Isles, producing both fishes
and birds. Gerarde and other eminent naturalists describe
it with confidence. Cut reproduced from Duret’s ‘‘Historie
des Plantes,’’ 1605.

Ancient
opinions

212 LIVING PLANTS

belief in the fabulous tales about strange be-
ings in far off lands, such as Pliny describes
in his Natural History, and were able to keep
their love of the marvelous within bounds,
and to found their conceptions so far as pos-
sible upon verifiable observations, held more
rational and clearer views of the two king-
doms. As aconsequence of direct, although
not extended, observation the separation of
the higher animals and plants appeared to
most persons of bygone times, as well as of
today, simple enough. The free, independent
movements of animals, well directed toward
evident ends, and plainly originating from in-
ternal impulses, have from such a standpoint
fully entitled them to be called animate ob-
jects; while plants, deprived of the power of
moving about, seemingly without feeling, and
to all appearance incapable of conscious re.
action, could only be described as living, as
animate, only by an extension of terms, and
certainly not as sentient.

It does not take a very wide acquaintance
with living nature, however, to become aware
that freedom of movement and fixity of posi-
tion are not distinctive characters of animals
and plants respectively, and that even the
possession of feeling doesnot wholly separate
them. Many centuries ago, as we learnfrom

PLANTS AND ANIMALS 213

Aristotle and other ancient writers, it had
been observed that sponges grow attached
firmly to rocks by root-like extensions, yet
possess some feeling. that sea-cucumbers
(Holothuria) and sea-slugs (Ctenophora ),
although having | : |

ment, seem to lack
feeling, andin this
respect behave
like plants, that
sea-anemones are
fixed- objects, yet
are sensitive like
animals, andthat
many other living
things have char-
acteristics that
make them in like
manner uncertain
of classification.
Aristotle’s conclu-
sion from these .
facts, that ‘tna. Fic. 23.—A sea-cucumber with

extended branched tentacles.
ture passes grad- (after Claus.)

ually from the insentient over to the sentient
through forms that truly live but are not
animals,’’ only needs the substitution of
Mycetozoa and some Flagellata for the Po-

Modern

opinions

An intermed-
iate kingdom

214 LIVING PLANTS

rifera and Coelenterates as its foundation to
make it acceptable to some students of the
present day.

The citation of a few opinions held by
modern savants regarding the ultimate dis-
tinction between animals and plants, although
necessarily brief and without thesetting which
the authors considered the justification for
their conclusions,
will indicate how
numerous and
vain have been the
attempts to find ;
some character of 4%
universal diag- oF
nostic value. To |
some minds the
task of properly ,,

Fig. 24.—A mycetozoan (Arcyria
tans) in the resting state, attached
placing the ani-to bark. Part of the spore masses

1-lik 1 ts removed, leaving their bases. En-
mai-ike plants larged three diameters. (After Engler

and plant-like an- and Prantl.)

imals has been

well enough disposed of by creating an
intermediate kingdom. This was first done
by the Englishman Wotton at the beginning
of the active period that followed the intel-
lectual stupor of the middle ages. In his
work on the distinguishing characters of
animals, ‘‘De differentiis animalium,’’ pub-

PLANTS AND ANIMALS 215

lished in 1552, he established the group of
plant-animalsor zoophytes. These organisms
were subsequently shown to possess but a
superficial analogy to plants, being thor-
oughly animal in all important respects.
Most zoologists and botanists since the time
of Wotton have been content to share the
problematical forms, either in common or by
sufference, permitting them to be carried into
one camp or the other at the convenience or
pleasure of the student. A few years ago,
however, Heckel advocated an arrangement
that met with some favor. He proposed to
place the simple intermediate forms together
under the heading Protista, a plan that time
shows has added nothing to clearness of con-
ception or convenience of study.

Many writers believe that no characters

can be found that are universally diagnostic.
Dr. Asa Gray once said (1860) in connection
with an argument in justification of Dar-
winian evolution, that in regard to the two
classes of organisms, ‘‘no absolute distinc-
tion whatever is now known between them.
It is quite possible that the same organism
may be both vegetable and animal, or may
be first the one and then the other.’’ The
learned Dr. Claus,in his prorectoral address
before the University of Marburg in 1863 on

Blending of the
two kingdoms

Characters
from structure
and function

216 LIVING PLANTS

the limits of animal and plant life, after care-
fully reviewing the whole subject, says in his
concluding sentence that ‘‘a fast and abso-
lute boundary between animals and plants
does not exist.’ The last sentence of Profes-
sor Huxley’s lecture, delivered in London in
1876 upon the border territory between the
animal and the vegetable kingdoms, breathes
the same sentiment. It was his opinion that
‘the difference between animal and plant is
one of degree rather than of kind, and that
the problem whether, in a given case, an
organism is an animal or a plant, may be
essentially insoluble.”’

The positive statements of such leaders of
thought require no additional evidence to
show that finding crucial tests to apply
under all circumstances is well nigh hopeless.
And yet the writer believes that the last word
is not said, and that a clue will yet be found
leading to a reasonably clear solution of the
problem.

It has long been recognized that characters
drawn from structure are far more reliable in
determining relationship than characters
drawn from function. The latter respond
more readily to changes in the environment,
and therefore forms having little affinity may
possess the same physiological adaptations.

PLANTS AND ANIMALS 217

Profound changes in the environment event-
ually bring about changes in structure; but
they follow so slowly that rudimentary or-
gans and various vestigial structures reveal
the true affinities where all other characters
fail.

In all serious attempts to fully distinguish
the two kingdoms, so far as they have come
to my notice, the characters selected have
been essentially physiological, and not struc-
tural. Some of the most noted of these may
be briefly mentioned. Linnzeus leads with his
classical aphorism: ‘‘Lapides crescunt, veget-
abilia crescunt et vivunt, animalia crescunt,
vivunt et sentient,’’ with which he opened his
work on philosophical botany in 1751.
Cuvier, in the second edition of his ‘‘Regne.
animal,’ issued in 1828, elaborated four
reasons for the ‘division of organized beings
into animals and vegetables:’’ viz., the pos-
session by animals of (1) organs foringestion
of food, (2) circulatory system, (3) nitrog-
enous structure and (4) true respiration, of
which the first seemed to him mostimportant,
and did, indeed, survive the longest. The
distinction advocated by Dangeard (1887),
Minot (1895), and others, that only animals
are capable of receiving solid food into the
body, may be considered the latest phase of

Various
physiological
distinctions

218 LIVING PLANTS

Cuvier’s first proposition. Sedgwick and
Wilson in their “Biology” (1886), find the
sole characteristic of animals to be depend-
ence upon proteid food. Von Siebold in a
dissertation upon this subject published in
1844, believed he had found a criterion in the
contractility of tissues. Some have brought
forward the chlorophyll function, or the pro-
duction of starch, cellulose, etc. The latest
suggestion is probably that of Conway Mac-
Millan (1895), who sees a fundamental dif
ference between animals and plants in the
dynamic, energy-liberating nature of the for-
mer, expressed morphologically in cephaliza-
tion, and in the static, energy-fixing nature
of the latter, expressed morphologically in
sporophytization.

Whatever the characters that are selec
for our crucial test, it is evident that they
must apply equally to the highest and most
complex forms, to the simplest unicellular
forms, and to all intermediate grades. What
structure or structures are there so universal,
so indispensable to the simplest and to the
most complex, to animaland plant alike, from
which characters can be drawn of universal
application? The least complex organisms
are likely to furnish most readily the clue to
the answer. Setting aside physiological con-

PLANTS AND ANIMALS 219

siderations, and having in mind the simplest
organism, it is evident as soon as mentioned,
that the first structure likely to be present,
aside from the indispensable cytoplasm and
nucleus, would be a cell wall. The cell wallis
the shield, the armor, the enveloping cloak,
that the organism throws about itself to pro-
tect the living, delicate protoplasm from the
rough contact and harmful influence of the
outer world. Some protection is well nigh
indispensable upon the free surfaces. For the
unicellular organisms it is a cell wall; for the
multicellular organisms the walls about the
cells of part or all of the tissues persist, or else
only the general free surfaces develop walls.
It is in the nature of this almost universal in-

vestment that it is proposed to point out a.

fundamental distinction between animals and
plants.

In attempting to distinguish animals and
plants by means of definite characters, there
is, however, another point that first needs
attention. Diagnostic characters can only be
drawn between like things, and in so far as
the characters are also fundamental they
must be based uvon fundamentalfeatures. In
searching for essential points of resemblance
or dissimilarity, it cannot be denied that the
normal individual in possession of its full

The most uni-
versal structure

Characters to be
taken from the
active organism

Reproductive
states to be
ignored

Animals and
plants defined

220 LIVING PLANTS

powers is the real and genuine organism to
which attention is to be directed. Secondary
characters may be drawn from adaptive and
more or less incidental structures, but not so
the primary ones. Of all adaptive or ecolo-
gical features of the organism the reproduc-
tive organs and processes are most prominent,
and have naturally attracted great attention.
Botany has been popularly styled the study
of flowers, although flowers are only the dec-
orated vestibule to the real sanctuary of the
science. In trying to discover the innermost
reasons for establishing a criterion between
the two great classes of beings, only the nor-
mal vegetative state of organisms need, there-
fore, be considered, and the reproductive state,
when the organism disports as a new-born
entity of naked protoplasm, or is reduced to
a spore or an egg, or hibernates in seed or
cyst with protective and dispersive append-
ages, may be ignored. We are to keep in view
only the vegetative organism, and not the
mode in which a succession of individuals is
maintained.

The fundamental characters of animals and
plants may, in accordance with what has
been said, be given as follows:

PLANTS are organisms possessing a carbo-
hydrous investment.

PLANTS AND ANIMALS 221

ANIMALS are organisms possessing a nitro-
genous investment.

These characters hold good for the active
individual only, and have no necessary appli-
cation to reproductive stages. They are diag-
nostic characters and are not tobe cotisidered
as in anywise defining the powers or func-
tions of the two classes.

In cellular organisms the investment may
extend to each protoplasmic unit, as is usual
in plants, or to the units of certain tissues, as
is usual in animals, or be developed only upon
the general exterior, as is specially the case in
coenocytic organisms, like some of the com-
mon molds and sea-weeds (Mucorinz and
Siphonacez).

By designating the constitution of the pro-
tective investment, it is intended to cover
only the original or basic substance of which
it is composed, without reference to subse-
quent depositions or infiltrations, of what-
ever character they may be. Thus in the
walls of grasses and Equiseti there is often a
great amount of silica, in certain seaweeds
(Corallina) much lime, in tunicates so much
cellulose that it sometimes amounts to one-
fourth of the dry weight, and yet, in the case
of the plants named, the original and funda-

Chemical
features of

cell walls

Physical
features of
cell walls

222 LIVING PLANTS

mental substance of the wall iscarbohydrous,
and in the animals nitrogenous.

The carbohydrousinvestment of organisms,
chemically considered, is probably always
some form of cellulose. There are primary
and compound celluloses, and various modifi-
cations of these. In some instances nitrogen
seems to be associated with the cellulose, as
Winterstein has recently claimed in the case
of certain fungi, but of the nature of this asso-
ciation nothing is definitely known; the facts
can have little bearing upon the fundamental
proposition here laid down.

The nitrogenous investment is chemically
always of the nature of a non-protoplasmic
proteid, of very complex molecular structure,
undoubtedly varying much in different organ-
isms.

Both the carbohydrous and nitrogenous
vestural substances are very likely chemically
analogous, as maintained by Elsberg some
fifteen years ago. Quite recently Cross and
Bevan in their treatise on cellulose suggested
that the substance of the proteid cell wall
“may prove to be of similar carbon configur-
ation to that of cellulose.”’

But in physical characters the two kinds of
cell investiture are widely different, and espec-
ially so in their degree of elasticity. Carbo-

PLANTS AND ANIMALS 223

hydrous membranes stretch but little, while
nitrogenous membranes are highly extensible;
and herein lies the basis of the wonderful di-
vergence in mobility shown by animals and
plants. The power of free movement, which
characterizes the animal and has rendered
possible its great and varied development,
depends primarily upon the nature of the in-
vestment, just as the rigidity of plant bodies
and their slow adjustments also depend by
restriction upon the investment. It is no
doubt possible in ultimate analysis to trace
many of the
prominent phy-
siological char-
acters of both
kingdoms’ to
this difference
in structure.

In applying
the crucial test,
some organ-
isms_ present
special difficult-
ies. Someforms

es their vegeta- Fig. 25.—A mycetozoan in its vegeta-
tive state con- tive or plasmodial state, much magni-

i fied. (After Cienkowski.
sist of so-called %°¢: ‘Attet Cienkowski.)

naked protoplasm, of which themostcon

The test
applied

224. LIVING PLANTS

Fig. 26.—A mycetozoan (Dictydi-
um cernuum) in its resting state,

showing four fruiting stalks attached
to a piece of bark. Enlarged ten di-
ameters. (After Engler and Prantl.)

about the plasmodium,
which by its chemical reac-
tion is shown to be non-
protoplasmic, and it may
be inferred that careful ex-
amination will find it pres-
ent in most of the species,
and thatitcan be considered
as potential or undeveloped
in the others. . They. are,
therefore, distinctly animal
in their fundamental char-
acteristic. Although usu-
ally treated in botanical
text-books and studied hy
botanists, they were shown
by DeBary, as long ago as
1864, to have more points
of agreement with animals

uous and well-
known examples
are the mycetozo-
ans. Many spe-

3 cies of these fun-

gus-animals
(Pilzgethrere)
possess a dis-

tinet nitrog-
enous envelope

Fig. 27.—One fruiting
stalk from above. En-
larged fifty diameters.
(After Engler & Prantl.)

PLANTS AND ANIMALS 225

than with plants, and he believed them to be
‘‘outside the limits of the vegetable kingdom.”
This separation by DeBary was made without
reference to a nitrogenous membrane, which
may, however, be considered the crucial diag-
nostic character.

Another set of organisms, with apparently
naked protoplasm during the vegetative
stage, are the endophytic parasites belonging
to the group
of genera
represented
by Synchyt-
rium, Woro-
nina, Olpidi-
opsis, Rozel-
la and Rees-
ia. Whether

t h ey ever Fig. 28.—An amceba (Ameeba proteus).
4 Theclearspotisa pulsating vacuole. Greatly

possess any enlarged. (After Leidy.)
demonstrable nitrogenous envelope has not

been ascertained, hut it is known with much
certainty that they have nocellulose envelope;
they are, therefore, not plants, and must, in
consequence, be animals. This disposition of
them has already been made by Zopf on the
ground that a “‘plasmodial character of the
vegetative condition is entirely foreign to the
Eumycetes.”” The Chytridiaceze, which are

226 LIVING PLANTS

usually associated with the Synchytria, have
a much reduced but demonstrable mycelium
formed of cellulose, and are, therefore, unmis-
takable plants.

Among the lowest forms, as generally clas-
sified, the Rhizopods, including Amceba, and
the far simpler Monera, show no distinct en-
velope, either nitrogenous or carbohydrous,
but as the other affinities appear to be with
animals rather than with plants, they are
doubtless rightly placed in the animal king-
dom. It is reasonable to expect that more
careful examination will, in some cases, show
a simple or imperfectly formed nitrogenous
envelope.

The crucial diagnostic character, which is
here proposed, has in its favor the separation
of plants and animals upon a line which ac-
cords well with the consensus of opinion of
thoughtful students, both botanists and zo-
ologists, an opinion which has been formed
froma variety of structural, physiological and
developmental data. Full relationship must
necessarily beadduced from a study of the life-
history of organisms; diagnostic characters
only form points of departure.

INDEX TO PLANT NAMES

INDEX TO PLANT NAMES.

ASN AVES cece otcesaceteacecu cept sewasmoasttiias sansen© cee cedeetersscucessecers 92
ACER QUA PIE) hic.eceseceoececiosvoscaeeeeomnsces Desa aiais es | oeencaracetcenes 182
ASAI CHT S)oces neces aso acees neato nus seca oaran eae ce shes tose toes wosuadenedecees 163
PNG Cipcccaye cues. cates cok vise canan eee sgeease wapettion te sas eceates se lave suaneacers 181
Pre cone vads cose siesraeeleaserdessccecnsaueeeee 175,184, 185, 190,191
ANAS CAIGECI) =. scar inacaecs iiactacersscetecetedeisscuwtevswes webboaneat are 182
A Oras se eccc sec ne canes Saeeie ce eee seb hcs aeons sea Der eR sen wae ees. Heasaseeceenane cess 187
AIST Ae oso cisteatecicice vie Snieuieativeieeseinice een caaaesenecsae ses tedsdcecccuesesle eaee 182
TAVARES oo eck ewe ewer foen came waceee Soeeene eo aeaeeeaad sib ea cecietes ds one's ATE:
WAIN PElOPSIS sees ches sestesedsesees teens a Shaceeticelaudecerosatrsetesscosreseses a rab
AMEN TAI 7, sc cetesevsccccte oc tencaccsctcéevevessetissstacdsoscencecsenseces dass 188
Arisema triphyllum............... L235, 126; W277, 129, tsi, 133

134, 138, 139, 141
AE OIA Sesecnncsesaiecovedeker tonee sone center cate sneesecrcectl avenseus seesst essa 89
PASPALAL US sacesiacess avadeesaccs ase sinceceacatae sess sesscesacsse esoseeaaes 100
TENSY ES BRS COS CR EB SURE BORE UUCEG IEUC BOSCO BOS IOUCE ESS aL BUC GHEE CIC bat Saree Tf
ARV CHA: COATES) esse st cness ieee caceesce acest nsececcavanradesecieusverceamenecnses 24

BA Cre EUS] BiRUNIN EW Si ciiaeccss sete seccstadaneal nee eteneveds 176
Bacillus (GinnaDareus. .2.:.cssccccesseseseecsost, coeesosdaerdelnccsacesness 176
IBAGteri@s.s.ccs ce sceess 0s 103, 104, 152, 175, 184, 190, 200, 201
Bacteria pnotometric¢hins...2-.5.s2-..5--0<sessrccecnansnsteessecess alr Zi

a WPI Coiccccsceccctvcnddecteecerecse ccs secu cmaenecaseeecasescccs sacs a ery
SAMA a cccccesetscccerccscssncnstcnecsss ecscstiveccsnaaeoecsetsareetesacsesues 182
ABI CY ceuccav tes cnrs cusscennors sects ssccaceconcectcnn sor etotenecacwesacre cnctasts 108
| EIST (Re ne a ay ce Er eR se abi ee Be nis me era 92
SCA isc s ote ccccwcesceus sncedudeete coveuses esos it oo. hOO! 167, Los, 20m
CECH occa tac cecsetace ciescscnaceach dene celeisedulucenetinisncsoncseee oeecdscowre 197
CE OMI Ae eee occ ae cone case oe cases cn ccc cael vancisevacawesavsdsecdsiiccNes 188, 189

pee ALCUL A edo fen: acksccnascnsscassss sdie05eesssescelecee « isevee 187, 189

Me tEIN CRIBS accecaesces ese c aes ecccsces Hone oo tceveneseeacesescne snes 187
ECTS GANG Alrec cass nse: cen ovelesnc ate ccesisancdteceneciecsinedesdau nes ceerpmewss 182
PRUE ceca retiree toe e nae vaiek oa banaue de wan snssestimaacsmaneaccmsoeauctistebecse 161
Bladderwort (Utrictlaria) |x. si4:sciesccdsvscstsusewscescadsducseyesset 96
BRT Na ee coc cn ccc nae aa o ca eceecie da ccaase cat cedars sods taadi cha eleee een aa eS 200

230 LIVING PLANTS

CB Pe Be aa saive dese ont sens eaccn cosy vidn=ndien toades cheese 100, 108
STE: PRIGETIB | iiss occ dade scans sungsnedebisesteckeel eee 135, 138
CANN Dios sens cencs vcepdcscacatsdvcsucussesesdepeassanttotens 22s Cena 179
Carpinus (water beech) ......5.5.05. scece.s0ecet0cceosessaeeserecaaemen 182
MC ATTOC vo csacsscccecsecessecssccdssedocbacs! osenccs eee eesecease Een 176
CASSIE Bi cleeus cca ccisivess sccanasucshaness Reconestecset saan tee ee 48, 55

“© CRAM ZECLISEA 2. is. s.05 ced cna oneovscws a0cneecesseusee ete eee 48

© “SMICUICANS 5. ....evcrsscdeess ecocsccenss oeceeh castceesen eae emma 48
Cattaltfl 0 Wi iescscviscccsveness cessed scsecsss ovnc svat coeces Coote eee 108
Cercis Canadensis (redbud)......0:.:0:.c.<s0+2s-secesseeeeneeeeaeeee 15
Charlock (Brassica Sinapistrum)) .....icc:1--sscsecesse see eee 14
CHYETIGIA CEE Ss fois sens vccncncksevsesveaddscon stercedesonteetee a ae 225
RSMISEIB acini etn weevaead ons sina odab caries caucu vneucs enue esa ae vane lee
Cnicus discolor (thistle) ...;...:.......s0..ssceses.sssees eee ee eater 189
Cocklebur (CX anthitim) ....:s0c.<0.csces-eocsneocesdssacncee eee eee 40
COMCE goicccpvidecscaseucsocdeshocdekeacdeesssse ceed seeaeette eee ee 201
COIOUS 6 i055 scepncss Seats eonesenacen ansods anodes; acsve tte eee 92
Compass) Platits.cyes.cccnsses.sec0cso07 senansectessedet teen 42,44, 46
COMMETB so ioc ccecucesccssesccseacactesenssaeissctecossdcbe secu eee eee 84
C OF ATA 0003 vs cosedissveccede> cet encse sé0de0ee0caeess e028 eee 221
Coat (76a WAIS) ce cattcctcecke ss s0s. 102, 108 109 110, 119, 201
Corylus! (NaZel)).. 2. .c.c.cc0 5° sco0es00-secesceessecas see saateen eee emeeeee 182
COECON FUSE ya. in 52 cre cs csca ccs eccecs vbaveenecs ores coeesenaee cee 103

ID ASTIE soscccocesccccseccictes coocista its cisaceneodnotsnteee nthe ee 136
Dentaria: Dilbifera. o.oo s.ccccs<leccc.0ssconcesecales seco eee 181
Didnoea MiuUseipulas i235. 0685 20s les0dihs 0c sdecedent eee 4,188
Wyck weeds coos oie. bcc aces vce cee baade dae Lae es eee 173, 174

BGG PEANUT... ccc cscocscexssewsss tavesunastscones so saette texte eee 100
Elodea: Canadensiss: %. ccccciesocssssoesestanes eens eee ee 96,181
FEQUISCEHIMN, 4.5.05.d5003 coseedsedsdedecsobcondevens seeeeee eee eee ee 221
Branthemtin:.; ..:..3:.cccsecaseceasseeesvecsoe scene eee 186
TIL Y COLES, «0 occccicec ss teecedeoeescesecetaessassesipeeete tate ee 225
Buphorbiace2e . i. ...505:0ss00s0 00s cnecdssdces<sdewaane: Soseeee eee 48

VEE RUNS i eovatencecccscscesccdeceensoccetece cotsvecnceeae dees deen eee aaa 205
Praxis (agi)).i7.5...cccscccesssconsssgecdsoces0ceeescesseet ae 182
Pachsia triphylla... 2.002. .cc.05 ic. cesseet ce caceass ccedees sane 186
ESSE a ere eires sriccce casa ceavoca carn cn ter ecramenules 147, 175, 175, 190, 200

GEER AUN UO MEs sdesidecvenesssoees- ince sleds eooceseiees neat 170, 188

TT ALMATO COC CUS. i. accsncs 000d doncee nencensed gestae 185
PASM AL OKVION 56.02. 00ce scccvcnsceecacasccancnnseeeenniteser pee mete meena 192

Hawthorne (Crateeous) 0 .ccsics..ccscocdcenacssasessoscee see 162

EIS ISCTIS SEOSA-SINE NSIS soos, one cowacencaatehs nsec tiencccthbassssesaebeess 138
ELGESEIGHESEHGTEG(C277,S CTIILIGN jconeneccnc cecw acetic ceenss odewaubasas-Setnedes 163
Horseweed) (Atm brosia frida). .nciccce cecesseesesasccdsestacs tes 40

De aS eee cents tae entncs near Sons aes sieeacceuetensesacbecndesseceesecesenasts 205
TSO MY HEIN DLCCENA CUI soe: oes cess cases. sce. sceccene see ccecceceesscnssauses 138
JIMSONWEED, (Datura StramoOniii).......<.2.c000.ceveseceee 40
SIREIIT CI oo essence vace a oh ac coe nae sen seGcee senso tone ee s Sokncacw eae cdteuseaee 94
SUIS EMCI es bcos conan cehepncucee re toetaeeee TOA eco ook be gunn acasanitiesse 138
PCR Wie AG EAU) POW GAMING AS cenecerct «sec ecs ene cdeseveneanesvees om 46
NP ACEHCAGS AEN V Aico ac caer ace eee eRe ase enon Savane (vowel eceaeeadssedsennes 3!

Se SGA EEO ene eee eee ete aan on oniceint bow bevevencenseoee ot

i byerch Ere oi (6 (2h pn eee an ree at ae a Sh 2 Ae Ae ee 75
GCSE MEPS ZO oe soe 2s ck noeaban ees tiene see te asec Ua sGeveVausuesas avertcaans 47,60

IY CAMS Aig GEES CLC Risser ose s oso Sones sh evcmauicoeacdotees oes tevececees oot eeasatee 173
WELENCE 25 seccac0: d daclodtcdendadeaeestavecpaccssneeretceccsecse 31, 38, 46, 100

1 ba Te) ET DSRS SR ARe nC RBCEe = TRan angen SL cer CORREO SDE Ode CSAC Dann eCenee 85
MTS GO PEk pit cove. occ: ncceceasce as ake sacea esse usscundeseseesoTs erases 138
FMEA, ATM ECEICATID) hes on. ccec~cneonssorkestuesssaaacss ses stones ce 81

AV CBG OES aa sae ee So ceel cae ran at nie baba sak aveveaedeeeedcgantndnasases aces te 85
LOcHSt (RODIN PSCHGACACIA) «......<.<0.cecsn0cceccecseese 55, 62, 81

NE OP WOO Moiese ee oak cote ee arma eee ae ae wacnas cin oe ubics Secesenccsaccenes 192
MAL V A: C Ey AB: ccssecscves SPF CAE al ae wats d's base Leet ereneeaoe 47
WWE 91 CRANK Cha aasaa ak sonata ee Ses saben abe bie sdb ee oust odeeeRor eaters 64,65

IMG AN fet Als Fteaas nc cns ase eaton sacsedais tadeddsesecsSceees setecsecesderaiserese 181
Mango: (REAR STICLA) Fo ccsack eovancess gdvescecededdddcsececsesbeeseessacuss 181

IMB ales, fvcceccnssccceccceecieeddcscetgsesdsssciedsasdcdcetseccccecsesetscsececeses 161

NEA PAE ACCA oes coeee eaten cca ae ean sab oals ebeicue owas sateatoren cea etace 48
IME ATE Z CEI Aisi oss. dscne se asecde bases ve ostcenoseascensecedteeneccaesecas 189
Marcierntte (lh écan them iit) \s. 030355: ccccecSacasnccessceseacressance 41
INGAAS E ACESS ceo Sr disccessccnsediss tues de sede codscuened pace cea wetescaseacere 47
WGI OR oeiec ccc scacavtsvsedssecdesodtsngessvcsecsnars docdsn voce oUsecesestis ss 92,159
NMGCH ECT SIGs Soe case tn comnc te eaters cere cn me nee eo dees cat taaionenes 177
INFIECEOCOCCUS ARTIS cae c cen sccen dence snscdncesonegeseacecassscusccbessesooss 176
MAVEN CLES WG wcie roca ecco oe tate cin dose cae ones seme anc ode eases res odece ec seees 200
MiamnOSA BU GICA sco. vocencres.ccosccrnecees-+scrsncseetnese 17,47, 48, 182
IVIOVAS2 22 5.252<05% bad RAEN EY ah aD NN REE SOE AEE 147, 200, 221
INNO SSEStrras ecco ceo a esa feces das ademas od on dutienciotinsiecaisls Neducadeveasasepecs 84

TY APE BE pt SE ap et Sa SR ee Sn een A Aun ARE Se 27, Zou

INE TIS ieee Sasa terecac ete nated s ces tee Soeucaccucktecwan cattus covatessneerscesees 182
WAS TOOT Scc heer: asec ser ccccscaeetecness cdsucestuevsewereneebavedaeceses se 147
COVASER OPEL CUS 2 ee ce cov ass. sos shored ces nennaeisnecar oun ae) acpiens AGL St Tor

WAS CA VEMAL SALIVA) nos se <nasctpese hans esos es LOS, 113) 134-220

232 LIVING PLANTS

OIPIGIO PSIS vec. 00s cceves.ccssee cos cccceedowodeays coed sin eresna tren mmmen 225
OniON scien. iewedbeadecancseceeeousdsencsvs duusan ils Dayka w stil neem 108
OStL¥A. ALON WOO )....660.00000) s0ces sever. sevee sees ov eeed laMnaneisuaes 182
Oxalidg:...... 1S) ecdahabeueneduuelle vans esdccslacces senses es teae emte eimai 47
ORAS no cchasacecacvessassiuevisarvessese sisinge tee eee vedawaeatoe Fees 15)
Se ACOLOSEI] oi.0ccc ve ceccosenaanestonesansioase dence ane onp eae i 189

"6 AlOTIDUNG Aissscsscccddedsceeces nvetew sow cvss aoa se stanea seen te aetna 138

66 VESPeCLrtiliONiS;...<ccesccsc.conneseavended navensadaaddeddoaevenunaal 138
Ox-eye AaiSy (Leucanthemum)........ccccccsee cosesecsscsccncsceece 41
PAS re ee eee cracan sue eceees 100, 107; 108, 109) 201; ta) tise
Peach VeElO WS). vc ccsc0ccocecrecdfosccsecccosonevsosae-aee sen secensens eaten 103
IPR AIATISE Pioe ees ce cureses «sah cosa teehweresep ee . a ead/ob- 3 These ceelene eae 24.
Philotria ‘Canadensis «2... ccc<0c..csececess vee sce eee 96, 181
Phoentx dactylitera, (date)..-....:-.:-.ssr se aedin clea cdaecccate 136, 138
Pigweed (Amaranthus retroflexus) ..........0006 seeeeee wetdeaies 40
PATE Fo. 15 odaeecaedss <Oasoencscs aes ca sanddaaenale teoeniae eles ta ee eee re 94.
TIS ES MS seen s one seca a cos ecnosaeeeesoaaee vis bine 6? wenanas ee dena aeaemnee 94.
Piper POTPHYLaceuM........5.0. cecececscsenscee-ceenneeeneosscssecsedwor 187
Platanus (Sycamore)............ </o.aea aie » olsievelle\en’s elo eialaiete eee 181
Poison oak (RAUS tOXICOGENALOM) . 01... «004-ceovese- sero -saneataies 162
IPOnd weed CE IOGER) sa.d0.0 osecscs000asecine <ie5scasis sone aeee eee 96,181
PO PUA Kis caccepecvnncswanscicecenescociecacses «onan cin Sanne je say See rn a Lag
POPS. cscecccc0cscececsscescsececndncescesinesciscsvcecaiataeta geste see ete ae 182
12.f0 821) 910) peep Co pa R ae Ee Ee SarEOREDEREC nee Scecaocetnonn cocoon. >. ita acdaa totes. 201
rte lstiysl@GEACC vers os0sc-<-cse2) a -2 2/5 eaeee en onacade acter 31, 33, 43
PrulmOna Trias 255 sec eecds soda in cace dane ceGaadnec 50 yee eee eee aL TE
Pumpkin (Cucurbita PepO).....c...2.20.0 socencosass cnnpsecseiaconse 74:
Purslane (Portulaca Ol€fAcea) oc 2.2.20... ono saaedactadeeee as 40,196
526) 08 Ro S ee ae ner ere nnn O PY st eriacor oan cipouer-Seoreccriow wa. 100
Ragweed (Ambrosia artemisiZ@tOlia) ........cccscscreseseneneeees 40
RAnUNCuUIUS TCATIOIGES®: ...e5 6s -0. 02 conee oeeiraie es ooneemeaannn 186, 187
Red bud (\CercisS) < icccsdicscse see ceasncias se octets cecisere cetera eae ae 5, Si
Red MAPle ss ....6c.cicccsseecesnctencsseae sevecene seme senctan > eenaaae maa see 185
Red Se a=W Ce iis. ides vase occas eee ses ce asltcet nig tacts nec nae eee nr 185
VRRECSIA Ss ccnerccccsbes siscsle occ tewoavceets ceweves, oc rune aa rtiea nage eee 225
RHOGOGEN ETON Fe ois kc ene: vace og tsi acdc nicer pelvee pe cues ak eee 94.
Robinia PSCHGACACIAL. 1c. scccccns wnces ase vcsasn eos andneet deen 62
Rosin weed (Silphium laciniatum).............c.ccrersecsessersers 43
WR OES oe tai io sedicas vse cale saws tuwewcawdine ttememeses sed = nale este ean ann 200
FROZEN ai avs wc siaaie.sie's & -rotcarbisc'ecit o's stare Stel cie he ate stotclo he od sla ale’ oh etal 225
Ramex (GOCK) oie. 5 se ceccie «cinieiee otncresin alesia vsie e.s''s.c'e'0is’e'Ve/a/slolele ieee areas 182
Dn Cy See EE eros eOC I COCOON Lh cw noe 200
RRS ios ode Teich acts oGitlelsareld slo'c'eeis'elcbiniess’siviele Chuo elec uibigie oiarate oles cafes are(etele tae a aan 108

ON PON eu CUM NN oe dh noe esdseev as ontssiacaccdecsembanrad dae 182
Salm on-fanguss .............cccccssecsesesecceecensccserencssseseassvsescees ao
WerOlepniad....-c..2.sce.cesee +s NOR eee ake coe SRO, oe Uae ca des 75
SAECLMAULO SEH near raa eer inca ca ecn cone ener tiens avs esas eoeeuseseace a Ur (er
SALULE] AMM OGCEMSIS Hiss dees sccuies cece ae eicn cnanen seat cise cote sedeosenseders 180
WEE WEEUS so stceece nen ei caen aet ees ea ne daeste Iti Goeacdews ae maeasnadesensa 221
SENSILLVE SIAN, pe ucsetia cases cde aceceensatecer 17, 47, 48, 68, 81, 182
SSMANITE NVC Cesar sin te cceeectos cesta ee net omen eee eeaccak cslechocsepueecases 48
SHEDUEEG’S PUNSEsse sere ace eee hoes eee aet ces fesse sins ane sececieaeeseee 196
Sil Ohi a Cinacsb eins sseeceee celeeoeeete al cee sees oa. ccescsesoneseceses 43, 46
SIPHO MA CELE artes sores ee aoe eee ras xc delst ose oc eanswseees 211
SLi MME=t OLE acc sere ec ed ove ece eens ce deocn nen sien sees) ec etucecs™ soamesae ‘Gs
SSPULG OVA ae ck ee as ose steste sae ond meee ae eeccscseeon vs: eseseneans 91
SOME MOLE (GUAGE ne seece ered caterer aces erinenesSsseconaen= acinwsoue 96
SIAC RCS POTD OL Al) tree necse ater eee cr tae eesien haw (atacsoeases ca terae cise 162
SUMAITET SAV Olay sncsscees oeretocseac onsen Macey caccar ses aciseseteicacceseseese 180
SSRI (6 (Oa aaa ot ane mab peas Bocniatone ertenorecoOncnn cama cHeE= S oneveceues felts
SNVAEty 0) oa EU rl Gace spodeacocacccnbodeb . ostee cdsqnaasecupe PepbareDcrlo nC snqaanccne a (Ce
WiPMIC MivaCt lt tli su.psecenee este. nctercca= se ciesae re eose Scdsecawensta ces 225. 226

A ES Ee Si (CRICUS) enor eect aasesc ee = Baath oe enddescieaner wdancnenweees 40
Miser Niliyso.c. sccsece<e seus eee ae aroe oa omdoolsins snenaoae enon sls ehies 207
MW OAGSEO OISH sec ccecec ser inc ene Seater mrnton neleaecclobscisvesseleedsmclowsls 147
Alita) SAY UC Reece aeriac rR aOSEOOCT an Hen OACOdd os ncaLicC REC SR DE BADU BED Ca ber neat 92, 1159
AM OUIVAA Otccsachccccesces ceetnec cen orton coer Tease oO He saw sianiseceeaeine 100, 201
eal eESCA MEAs cael eac eer tee ene oe een ee nasa caxcawenss seeacus secerseae 188
ALAN t1ti1 CLECCEUMIIS, ose. sese sate ocee ew acce roe cine sss decane dsenesissserens 138
Trillium erythrocarpumd..............0.0.sseccccsceeserscscovoeccececes 138
Tulip tree (Liriodendron tulipifera)..........0.2.ceeeeeeeevenees 162
MAGEE eceeacece ens cee ccc asa « sida aaa dconebeicins sons esleeesisenuesmiac assess 108

WEL NIN WES a (elise ac ccscceccasscecatiemcnuecbs onsceccsaasess Maasmecatiliesteisice =i 182
WnCariaval ma oicc.<s cc-0ees-.t ossesa) eo eee sea sceenerenereresmarasnesecass 182
LOGS a VECO Fe i Ch a OA bade SHORE EDEL acccae. iEdccODaAcnauattan 96
WELCH ATA Wt SATIS. 2.0 cocreniset ene ecacsseine sees ceactieree smoen ss ssosarts 181

Wa INGO Se Y= Ree Pe Soe cole cic ca cnnaietvia vse avicisieuleainalenseciasieWiesciecicisivonnins 4,61
DVIS GU TTAS)) cee ecnee ces ceuens coucseocccca conse ct csids ew osiclosias “cians 162, 163
Virginia creeper (AmMPElODPSIS)...........0eceeeseeeeeee eee vee 163, 191

SS ACtIS Ee DB WW GN peeing ae) 20, 2} candace bestece <osaeesrwaas CreeReanioe 95
Water-weed (Elodea Canadensis)............ccececeneeeseceeeesees 74
Wheat....102, 103, 104, 106, 108, 109, tA atG ato 2Or
Wild cucumber (Echinocystis lODAata) ......cceceseeeeeeeeeeee ees 67
Wal le ERUCE Seno arcnscncsuessessoseencpatsacesssacee ses 30, 31, 35, 41
Wild sensitive plant...........cccececesesercneeeecserersersereeeecsenscees 48

Willow, CSAIEX) 5 isccc.tceccsncccevesecsercsesbseceseseenscavecesctescerones detia

234 LIVING PLANTS

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