ORGANIC LIFE--VEGETABLE.
The constituent elements that enter into vegetable life consist in
the main of three elementary substances. These essential elements
consist of oxygen, hydrogen, and carbon.
The secondary elementary bodies consist of nitrogen and earthy
elements, sulphur and phosphorus.
There are also found other elementary substances in lesser quantities
in vegetable structures, as potassium, sodium, calcium, magnesium,
silicon, aluminium, iron, manganese, chlorine, bromine, and iodine.
These are the materials of which vegetables are made. Vegetables derive
all the materials of their fabric from the earth and the air. Plants
can possess no simple elements which these do not supply. They may take
in, to some extent, almost every element which is thus supplied. The
elements above mentioned are not of universal occurrence, nor are
they all components of any one vegetable tissue.
Although plants and animals have no peculiar elements; though the
materials from which their bodies spring, and to which they return, are
common earth, water, and air, yet in them these elements are wrought
into something widely different from any form of lifeless mineral
matters, under the influence of what is usually termed the principle
of life. This may be said to consist of a favorable condition brought
about by the union of certain elements, under a moist atmosphere and
a high temperature, combined with other powerful forces in nature.
"When this terrestrial globe began to cool the matter predominating in
the atmosphere was water or its elements oxygen and hydrogen, carbonic
acid and nitrogen; under the influence of a high temperature, and
powerful sources of electricity, numerous combinations were produced
between the elements; first carburetted hydrogen, then a nitrogenous
combination, more or less analogous to the albuminous matter which
we know" (Huxley).
Among the innumerable combinations nature produced, during a series
of infinite ages, slowly undergoing transformation, the mixture of
these substances, acting chemically upon one another, generating and
regenerating at the expense of their surroundings, composed the first
living being. This being was of excessive simplicity, comparable to
the organisms which we call monera.
The sun's heat acting upon these elements, and the elements acting upon
one another, produced motion. Heat is motion, expansion, restrained
and acting in its strife upon the smallest particles of bodies.
The principles of life were first produced by the action of the
sun's heat upon these vitalizing elements, setting them in motion,
generating the required force. The surrounding condition being
favorable, the simplest form of physiological life was produced. Once
under the influence of what may now be termed the principle of life,
in connection with which alone such phenomena are manifested, the
three or four simple constituents effected peculiar combinations,
giving rise to a few organizable elements--as they are termed,
because of them the organized fabric of the vegetable or animal
kingdom is built up. This fabric is in a good degree similar in all
living bodies; the solid parts, or tissues, in all assuming the form
of membranes, arranged so as to surround cavities, or form the walls
of tubes, in which fluids are contained. Such a structure is called
organized structure, and the bodies so composed are called organized
bodies, because such fabrics consist of parts coöperating with one
another as instruments or organs adapted to certain ends, and through
which alone the living principle, under whose influence the structure
itself was built up, is manifested in the operations which the animal
or plant carries on. There is in every organic fabric, a necessary
connection between its conformation and the action it is destined to
perform. This is equally true of the minute structure, or tissue,
as revealed by the microscope, and of the larger organs which the
tissues form in all plants and animals of the higher grades, such as
a leaf, a petal, or a tendril, a hand, an eye, or a muscle. The term
organization formerly referred to the possession of organs in this
larger sense, that is, of conspicuous parts or membranes. It is now
applied as well to the intimate structure of these parts, themselves
made up of smaller organs through which the vital forces directly act.
Protoplasm, called by Huxley the basis of physical life, is nothing
more than a homogeneous albuminous matter. An isolated albuminoid
is not living any more than an acid or a base equally isolated is a
chemically active body. But a mixture of two or several albuminous
substances (a protoplasm contains at least two) might be living,
similarly as a mixture of an acid and a base demonstrates the chemical
activity of the two bodies. But, whereas in the combination of an acid
and a base, the formation of a new body puts an end to the dynamic
manifestations of the mixture; the albuminous matter which by its
union gives birth to a protoplasm, that is to say, to living matter,
is capable of generating itself at the expense of the medium in which
it is placed, and in proportion to the dynamic manifestations which
it produces, gives birth to some rejected excreta in its midst.
Living matter may be roughly compared to an electric pile, the
elements of which are capable of regenerating indefinitely. This
continual exchange of the elements of living bodies and the medium in
which they are placed, is one of the conditions of life. Life is the
continued organization, while the molecules constituting the organized
body (organism) are in a state of mobile equilibrium, or a continual
renovation. A grain of vegetation, or an animal (Rotifera) slowly
dried, might not manifest any vital property for a long time. Far from
constituting an example opposed to our definition, it on the contrary
goes to corroborate it. Whilst the chemical elements which compose it
could not act one upon the other, it was necessary that they should
be dissolved: Corpora non agunt nisi sulta. One might compare these
organisms to a pile where nothing except the fluid is wanting. The
eggs of certain animals (birds, etc.), that require a certain heat
in order to develop completely, furnish us a case analogous to those
chemical actions which could not be accomplished in a perfect manner
except by a sufficient elevation of temperature.
The long discussions that have taken place in the last few years on
this question, the attempted efforts to demonstrate or refute the
heterogenic doctrine, have but indifferently served the purposes of
science. They have made us at least to see more clearly the impotence
of chemistry and physiology alone to solve the biological problem. It
is impossible for anyone to study with care the organization of
the Infusoria, and even the Protista, and believe that beings so
complex are formed by spontaneous generation. The size of an animal
or a vegetable signifies nothing in this question. The imperfections
of the micrographic investigation have alone permitted the notion of
the creation of beings such as the Paramecia, the Mucidina, etc. Even
in the more inferior Protista, the Bacteria, and other Schizomycites,
the hypothesis of heterogeny is reversed by the simple observation that
these beings present a very complicated metamorphosis. An evolution,
that is to say a series of supposed forcible metamorphoses, a special
condition of the germ, resulting from heredity, consequently proves
a generation dependent on other than anterior organisms.
This reasoning, however, demonstrates in an unobjectionable manner that
the first living beings were formed independent of all preëxisting
organization, and that these beings were as little organized as
possible.
The latest progress in chemistry and in biology permits us to raise
the veil partly in recovering the obscure origin of living matter.
ANIMAL-VEGETABLES, PROTISTA.
When we behold the plants and animals that ordinarily surround us,
the distinction between the animal and vegetable kingdom is somehow
intuitive. And it seems a loss of time and trouble to indicate the
character which separates these two from each other. It is not the same
when we descend the scale of organisms. Then we arrive at an inferior
region where the distinction disappears gradually, and we soon conceive
the existence of a frontier zone between the animal and vegetable,
a neutral territory which has been designated the kingdom of Protista.
They reproach naturalists for admitting the kingdom of Protista,
accusing them of doubling the difficulty, instead of abolishing it;
since it is necessary to establish a distinction between Protista,
on the one part animal, on the other vegetable. That objection could
be made every time they established a new division in the organic
kingdom. It does not signify anything for those who know that all
divisions that trench on biology are purely subjective and that
nature does not bend to our strict system of classification. Natura
non facit saltus.
All living bodies can be decomposed into visible elements under
the microscope, and these have been named Plastides or Cells. That
word is employed in a more general sense. The most simple Plastide
is the Cytode, a simple mass of protoplasm without a nucleus or
membranous envelope. A cell in a restricted meaning of the word is
a Cytode presenting a nucleus, that is to say, a mass of protoplasm
in the midst of which is a distinct part of the substance ambient
differentiated by its aspect and its property.
1. Plants and animals are always produced under the influence of a
living body similar to themselves.
2. They develop from a germ or rudiment, and run through a course of
changes, to a state of maturity.
3. Plants increase by a process through which foreign materials are
taken, made to permeate their interior, and deposited interstitially
among the particles of the previously existing substance; that is,
they are nourished by food.
4. Plants and animals alone possess the power of assimilation, or the
faculty of converting the proper foreign materials they receive into
their own peculiar substance.
5. Connected with assimilation, as a part of the functions of
nutrition, is a state of internal activity and unceasing change
in living bodies; these constantly undergoing decomposition and
recomposition, particles which have served their turn being continually
thrown out of the system as new ones are brought in. This is true of
both plants and animals, but more fully of the latter.
6. The duration of living beings is limited. They are developed,
they reach maturity, they support themselves for a time, then perish
by death sooner or later.
Mineral bodies have no life to lose, and contain no internal principle
of destruction. Once formed, they exist until destroyed by some
external power. They lie passive under control of physical forces.
Life. The great characteristic of plants and animals is life,
which these beings enjoy, but minerals do not. We may safely infer
that life is not a product, or result, of the organization; but is
a force manifested in matter, which it controls and shapes into
peculiar forms--into an apparatus, in which means are manifestly
adapted to ends, by which results are reached that are in no other
way attainable. As we rise in the scale of organized structure from
plants through the various grades of the animal organization, the
superadded vital manifestations become more and more striking and
peculiar. But the fundamental characteristics of living beings--those
which all enjoy in common, and which necessarily give rise to all the
peculiarities above enumerated--are reducible to two, viz.: 1. The
power of self-support, that of nourishing themselves by taking in
surrounding mineral matter and converting it into their own proper
substance; by which individuals increase in bulk or grow, and maintain
their life; 2. The power of self-division or reproduction, by which
they increase in number and perpetuate the species.
A striking illustration may set both points in a strong light. The
larva of the flesh-fly possesses such power of assimilation that
it will increase its own weight two hundred times in twenty-four
hours, and such consequent power of reproduction that Linnæus did not
exaggerate when he affirmed that "Three flesh-flies would devour the
carcass of a horse as quickly as a lion."
The distinction between vegetable and mineral is therefore well
defined. But the line of demarcation between plants and animals is
by no means so readily drawn. Ordinarily, there can be no difficulty
in distinguishing a vegetable from an animal. All the questionable
cases occur on the lower confines of the kingdom, which exhibit
forms of the greatest simplicity of structure, and of a minuteness
of size that baffles observation. Even here the uncertainty may be
attributed rather to the imperfection of our knowledge, than to any
confusion of the essential characteristics of the two kinds of beings
(the kingdom of Protista above alluded to).
The essential characteristics of vegetables doubtless depend upon
the position which the vegetable kingdom occupies between the mineral
and the animal, and upon the general office it fulfills.
Plants are those organized beings that live directly upon the mineral
kingdom, upon the surrounding earth, air, water. They alone convert
inorganic, or mineral, into organic matter; whilst animals originate
none, but draw their whole sustenance from the organized matter which
plants have thus elaborated. Plants, having thus the most intimate
relations with the mineral world, are generally fixed to the earth,
or other substance upon which they grow, and the mineral matter upon
which they feed is taken directly into their system by absorption
from without, and is assimilated under the influence of light in
organs exposed to the air, while animals, endowed with volition and
capable of responding promptly to external impressions, have the power
of selecting the food ready prepared for their nourishment, which is
received into an internal reservoir or stomach. The permanent fabric
of plants is composed of only Carbon, Hydrogen, and Oxygen. The tissue
of animals contains an additional element, viz., Nitrogen. Plants,
as a necessary result of assimilating their inorganic food, decompose
carbonic acid and restore its oxygen to the atmosphere. Animals in
respiration continually recompose carbonic acid, at the expense of
the oxygen of the atmosphere and the carbon of plants.