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.