SCIENCE IN THE PLANT WORLD
“_Weak with nice sense, the chaste Mimosa stands,
From each rude touch withdraws her timid hands._”
Plants are profound scientists. Their knowledge may not be as broad and
far-reaching as that of man, but they are more successful workers than
he. With all his wonderful discoveries in physics and chemistry, man as
a class has not yet learned to conduct his own body so as to make it
yield the highest efficiency. In fact, members of the human race are
today wearing out their frames at a faster rate than ever before. Adept
at running huge mechanisms of steel, they are neglectful of those most
delicate and wonderful machines which are bound up with their own life
processes.
Plants are not so prodigal. Whenever they are given a chance, they
develop and expand their powers in the most marvelous way. They bring
out the latent strength in their beings and so conduct themselves as to
conserve their energies. Whether by instinct, reason or blind force
they always know just what to do and how to make the most of their
heredity and environment. Their efficiency rating is one hundred per
cent.
As the whole life of all plants is a scientific progression, we can
only consider in the brief limits of this chapter some of the more
startling instances of the marvelous sense they exhibit in dealing with
Nature’s forces.
Probably one of the reasons we do not always think of plants in the
human, sympathetic way we should, is that we are inclined to regard
them as quiet, static objects, playthings of every wind that blows
upon them. Such is far from the case. Life is motion and the plants
are very much alive and very much in motion. From the tiniest cell to
the largest tree they exhibit constant, pulsating movements. Many of
the movements are described through so small a space as ordinarily to
escape our notice, but a little observation makes them quite apparent.
They all have a well-directed, scientific purpose.
What is plant growth itself but motion upward and outward? If a
telescope or an instrument such as Sir Jaghadish Bose’s crescograph
be trained on a healthy plant, it is possible to see the growth
actually take place before the eye somewhat as it is managed in motion
pictures. Travelers aver that if a Banana Plant be cut off close to the
ground and the surrounding soil well supplied with water, the sturdy
creature will make such strenuous efforts to destroy the effects of its
mutilation that its growth may easily be perceived with the unaided
eye, and a full-sized leaf produced in a single day.
Leaves and flowers are usually quite mobile. When they go to sleep,
they droop and fold their edges together very carefully, sometimes to
such an extent as to make themselves almost invisible. Even such an
astute man as Linnaeus was once completely deceived by some sleeping
specimens of Lotus. They were very fine red flowers and he was proud
of them. Taking a friend to view them one evening by lantern-light,
what was his dismay to find that they had completely disappeared. He
concluded that they had been stolen or eaten by insects and went away,
only to find them in full array on his return the next morning. It
took several nocturnal visits to unravel the mystery and discover
that the flowers folded themselves and retired so adroitly into the
surrounding foliage each evening that they were completely hidden.
The Acacia is a plant which closes up at night; the same phenomenon is
very striking in the Oxalis. The common Bean sleeps standing: that is,
its leaves close upward instead of downward. The little blue Veronica
flower, so strikingly brilliant and attractive in the daytime, tucks
itself in so snugly at bedtime that it becomes quite inconspicuous. A
Marigold called _Calendula Pluvialis_ even contracts its corolla every
time the sun is veiled by a passing cloud. These sleep movements all
have a scientific purpose. Their main object, just as in animals, is
to reduce bodily activities to a low ebb and so to give the plant a
chance to recuperate for another day’s efforts. The contraction of all
surfaces cuts down the radiation of heat and moisture and presents less
resistance to outside elements. The plant is in a quiescent, somnolent
state.
There are other movements of leaves and flowers the object of which is
not quite so apparent. For instance, there is the _Hedysarum Gyrans_ or
Oscillating Sainfoin. Each of its leaves has three folioles. The center
one is very large and stands bolt upright, except at night, when it
condescends to bend its head in sleep. The two lateral folioles are in
perpetual oscillation both day and night. Nothing but a very hot sun
seems able to stop their movement. Possibly, this plant is a fresh air
fiend which requires a steady atmospheric flow upon its respiratory
surfaces! The two lateral folioles of each leaf are delegated to act as
fans and blow a constant supply of air upon their majestic brother.
Similar oscillations have been noticed in some Orchids, where a part of
the flower’s corolla rises and falls with a regular rhythm not unlike
the beating of a human pulse.
The stamens and pistils of flowers sometimes have the power of
movement. If an insect, wandering about in the flower of the Barberry
Tree (Berberis Vulgaris), happens to touch the base of a stamen,
it bends forward with a quick, spring-like motion and presently
straightens up again. The evident intent is to shower some pollen on
the little intruder with the hope that he may carry its vital principle
to some neighbour of the same species.
In the _Parnassia Palustris_, fortunate observers have sometimes seen
the five stamens bend forward and beat on the head of the pistil in
rotation as if on an anvil. Perhaps outside pollen-carrying agencies
have passed this particular flower by and, in desperation, it is
resorting to self-fertilization.
The _Junger Mania_, a plant allied to the Mosses, shows knowledge of
the laws of mechanics when it uses a natural spring coiled in a small
tube to project its seeds out into the world. Seeds of fresh-water
Algae swim about for a few hours after leaving their mother-plant,
vibrating their cilia with great rapidity. It is the ability of certain
one-celled plants to move about freely which causes considerable
discussion as to whether they are really not animals. The Diatoms are
examples. They propel themselves through the water by oscillating their
whole bodies from side to side. To reverse their direction they go
backward like a ferryboat.
The ancients as far back as Aristotle recognized the sensitiveness of
plants to light and their eager use of its life-giving properties. In
fact, one has only to watch the Sun-Flower follow the orb of day across
the heavens to realize that there must be something vital in sunlight
for the plants. What interests us is that they have the instinct or the
knowledge to so present their surfaces to the light that they receive
a maximum benefit from its influences. From the aristocratic indoor
potted plant to the wild trees and shrubs on the edge of a thicket, we
notice a vigorous straining toward the light. Each leaf is tilted at
just the right angle to receive the largest possible share of energy,
for the leaves are starch factories for which the sun furnishes the
motive power.
Botanists tell us that this heliotropism or turning motion toward the
light is due to the tendency of most leaves to arrange themselves
perpendicularly to the sun’s rays. Tendrils may be apheliotropic or
tend to turn away from the light. Morning Glories or Wistaria, which
climb up whatever support is handy, exhibit insensibility to light no
matter from what angle it strikes. Stems, flower and leaves of all
plants each give a different and scientific reaction to light in a way
which looks much like directing thought.
Nothing is more scientific than the skill with which plants co-operate
with gravity in constructing their root systems. The roots are often
trained to grow out horizontally and resist gravity for a certain
distance. Then they gracefully yield to its pulling power, and, curving
their tips downward, grow straight toward the center of the earth. Any
secondary roots which are sent out again start horizontally to repeat
the above process on a smaller scale. All this makes for an efficient,
well-balanced root-system.
A curious motion which is not thoroughly understood is a slight
gyratory movement observable in the tips of all living plants. It is
possible that it is connected in some way with the earth’s rotation or
is it merely a kind of groping, feeling gesture? In the case of roots,
where the same gyrations occur, it undoubtedly serves that purpose. A
revolving root tip makes a very efficient drill with which the hardy
plant may bore a way through refractory soil. It is claimed that the
great whirling sweeps made by tendrils of various climbers are merely
amplifications of the circumnutation occurring in all plant terminals.
Before leaving the subject of scientific movement in the plant world,
it will be of interest to briefly consider some of the vegetable
motions which are called forth by the stimulus of touch. Almost
everyone is familiar with the Sensitive Plant and its double rows of
tiny leaves. Touch any one of them and the whole group will instantly
begin to contract and bend toward the stalk. We say begin, for so
slow is the transmission of the impulse that one can readily see its
progress, as one after another of the leaves respond.
A motion which has forethought and design behind it occurs in the
leaves of the famous and crafty Venus Fly-Trap. Two sections of
leaves edged with teeth-like nerve-hairs form the two halves of an
enticing-looking bowl and cover. The slightest contact with one of
the delicate hairs will cause the trap to shut together and imprison
any sweet-toothed member of the insect world which has happened to
stray inside. An aquatic form of the same thing occurs in a species of
Bladderwort which spreads a leaf-net cunningly shaped to look like a
fish’s mouth. Frightened baby-fishes, accustomed to seek their mother’s
throat in time of danger, sometimes swim in and, brushing certain
nerve-hairs near the entrance, cause the lips to close and leave them
to slow dissolution. Both sinister and scientific are the movements of
carnivorous plants.
Far from being static or quiescent, the plant world is a kingdom of
energetic, vibratory motion--a motion which is cool and calculating
and which rarely fails to accomplish its purpose. Even the protoplasm
of microscopic plant cells is in constant movement. If a thin slice
of Sycamore bark be placed under a microscope, a regular circulation
of cell-liquid, suggestive of blood circulation in animals, can be
observed.
Plants show great skill in their use of water. It is their storage
of liquid in their cells which makes their soft bodies rigid and so
makes movement possible. This property sometimes called turgidity
was discovered by the scientist De Vries in 1877, the same year that
Pfeffer established the theory of osmosis. This latter is a phenomenon
which physicists find very difficult to explain and involves the
transmutation of one liquid into another through the medium of an
intervening membrane.
Some plants have acquired the faculty of storing water in their bodies,
on which, camel-like, they can subsist for long periods of time. A
certain large tree-cactus of the American desert sometimes stores up
as much as seventeen hundred pounds or five barrels of water in the
wet season. When drought comes, its roots dry up and it lives entirely
on its internal resources. It is said that an eighteen-foot specimen
can exist for a year on its stored-up liquid. A branch on such a plant
may live and bloom after the trunk is dead. Many ordinary plants, such
as Turnips, Carrots, and Beets, store water along with starch and
dextrose in their underground tubers. Such subterranean reservoirs are
preferable to those above ground.
Plants have paid particular attention to the manipulation of gases.
They maintain an internal atmosphere of their own composed of oxygen,
nitrogen and carbon dioxide in proportions varying greatly from those
of the outside air. If the stem of a Water Lily be broken below the
surface of a pond, gas bubbles will often be observed to issue from the
wound, indicating that the internal gas pressure of this particular
plant is greater than that of the external air. In other cases, the
reverse is true and we find partial vacuums within the bodies of plants.
Man long ago found it impossible to “live on air” but the plants have
solved the difficulty of aerial existence and have become creatures of
the air rather than the earth, so far as their food is concerned. The
great bulk of the largest tree is preponderantly composed of carbon,
which has been slowly and labouriously extracted from the air. The
mineral salts and water which have been filtered out of the ground by
the roots are essential but are present in a much lesser quantity.
It is well known that plants breathe in carbon dioxide and breathe out
oxygen. This can be graphically demonstrated by placing a plant in a
glass jar of carbon dioxide inverted in water. If its life processes
are quickened by exposure to sunlight, the plant will replace the CO₂
with oxygen in a day. A more striking example is furnished by any
aquatic plant accustomed to growing submerged in ponds and rivers.
Placed in a water-filled bottle inverted in a pan of water, it will
generate oxygen so rapidly that the bubbles can be seen forming on
the leaves when the sun is allowed to strike them fully. The bottle
will become filled with oxygen in a few hours, and its presence can be
demonstrated with the usual ember test.
Opposed to the absorption of carbon dioxide and the breathing out of
oxygen, which is really a digestive operation, the plants, queerly
enough, carry on a directly opposite process which involves the
absorption of oxygen and the breathing out of carbon dioxide. This
is a respiratory process akin to breathing in animals. It is carried
on in such a relatively small way that it does not seriously affect
the statement that “plants breathe in carbon dioxide and breathe
out oxygen” and so are purifiers of the air which man and animals
contaminate.
Besides this general use of gases common to nearly all plants, a few
of the members of the vegetable world specialize in the production
of protective and poisonous vapours of various composition. One of
the most interesting of these is the Gas Plant of the South American
jungles. This beautiful white-flowered inhabitant of the tropics is
entirely protected from leaf-destroying insects and birds by the
poisonous vapours it constantly pours forth.
The plants are expert chemists, and the reactions in which they engage
are, on the whole, much simpler than those which go on in the bodies
of animals. Vegetable tissue is largely carbon, hydrogen, oxygen and
nitrogen. It is a curious fact that instead of using the abundant
carbon compounds present in decomposed animal and vegetable matter of
the soil the plants get most of their carbon from the carbon dioxide
of the air. Inversely, they largely disregard the seventy-eight per
cent nitrogen of the air, and extract that element from the complicated
compounds found in the soil, or take it from the air only by aid of
certain Bacteria.
Certain plants manufacture lime and metallic oxides with which to
harden the protective armour they wear. Many others generate nitric
acid, carbonic acid and ammonia for use in their interior laboratories.
Roots nearly always secrete a fluid which aids in the absorption of
minerals from the earth. It is so powerful that quartz, flint and
limestone are often scratched and corroded by its action. Above and
below ground, plants are active chemical laboratories.
The differences of taste, smell and colour which characterize leaves,
blossoms and fruits are due to the presence of various organic
compounds. These are largely volatile oils which are more complex than
the substances involved in the simpler life processes. The slow or
rapid evaporation of these oils influences the strength and character
of an odour. When a flower or fruit passes through infinite gradations
of colour, we can give no adequate account of the chemical changes
involved. All we can do is to observe and to note. Sometimes infusions
of iron sulphate or other chemicals in the soil darken the hues of
flowers. Gardeners profit by this fact in the cultivation of certain
varieties of Hortensia.
The chemical activities of plants are of incalculable value to man.
They change air, water and mineral salts into forms easily assimilable
by the human system. Eliminate all the vegetable life from this planet,
and the animals, including man, would perish in a few months. Man has
also learned to make abundant use of plant substances for innumerable
purposes. Potash is an example of how the plants come to our aid in
furnishing us a valuable chemical. It is extracted from wood, Seaweed
and Banana stalks. These plants have discovered a way of getting it out
of its well-nigh insoluble earth combinations with silica. If it had
not been for certain industrious sea plants, man would probably never
have been aware of the important chemical twins, bromine and iodine, so
important in photography. These plants patiently filter them out of sea
water where they exist in microscopic quantities, and build them into
their bodies. Beer is possible because germinating grains transform
amylum or plant starch into sugar. We find ripe fruits palatable
because their acids change into sugar under the influence of sunlight.
Man seems to have outstripped the plants in the use of light, heat,
electricity, and other physical forces, but the plants have more
engineers among them than we imagine. In the fact that man has just
learned to extract nitrogen from the air by the agency of electrical
discharges, lies the probable explanation of how the plants have
been doing the same thing for years. It is believed that the minute
electrical discharges continually going on between the different air
strata make small quantities of nitrogen assimilable for the plants.
The micro-organisms which also furnish nitrogenous material to the
plants may get nitrogen from the air in the same way. It is quite
certain that the plants are affected by the chemical state of the
atmosphere.
Everyone knows what an important part light plays in plant physiology,
but the fact that certain plants produce their own lights, while
generally known, is not universally understood. The Austrian
naturalist, Heller, was the first to demonstrate that the glowing of
decayed wood at night is caused by emanations of light from Fungus
growing in the cavities. A similiar organism called Luminous Peridineas
(sometimes classed as an animal) is responsible for the phosphorescence
of the ocean and the night lights of many flowers.
About three hundred species of Bacteria and fifteen species of Fungus
are recognized to be luminous. The dead leaves of the tropical
Banibusa, Nephelium and Aglaia often glow at night with the light of
these tiny creatures. Ordinary dead Oak and Beech leaves are luminous,
sometimes shining in spots, but frequently glowing throughout with a
soft, white, steady light. These miniature incandescent lights often
shine for days, weeks and months, and with abundant nutriment at hand,
sometimes for years. The light is slight in intensity, but uniformly
steady and white, green or blue-green in colour. It is strong enough to
enable the plants on which the Fungus grows to photograph themselves by
long exposure to sensitized plates. The fungus light has also been used
to influence the heliotropic movements of plant seedlings. In fact, a
colony of Fungus has sometimes been placed in an electric light bulb
and made thus to serve as an illuminant.
No matter from what angle we study the plants, we find that they are
extremely scientific. They conduct themselves and all their activities
in a way to always get the best results. They show knowledge and
acquaintance with all of Nature’s laws, and they have learned to apply
many of them with startling success.
[Illustration: MODERN NATURE WORSHIPPERS]