The process of germination is essentially a chemical one. The seed is placed in the soil, excluded from the light, supplied with a due quantity of moisture, and maintained at a certain temperature, which must be above that at which water freezes; air must have free access to the seed, which if placed so deep in the soil as to prevent the permeation of the atmosphere never germinates. Under favorable circumstances, the life-quickening processes begin; the starch, which is a compound of carbon and oxygen, is converted into sugar by the absorption of another equivalent of oxygen from the air; and we have an evident proof of this change in the sweetness which most seeds acquire in the process, the most familiar example of which we have in the conversion of barley into malt. The sugar thus formed furnishes the food to the now living creation, which, in a short period, shoots its first leaves above the soil; and these, which rising from their dark chamber are white, quickly become green under the operations of light.
In the process of germination a species of slow combustion takes place, and—as in the chemical processes of animal life and in those of active ignition—carbonic acid gas, composed of oxygen and charcoal, or carbon, is evolved. Thus, by a mystery which our science does not enable us to reach, the spark of life is kindled—life commences its work—the plant grows. The first conditions of vegetable growth are, therefore, singularly similar to those which are found to prevail in the animal economy. The leaf-bud is no sooner above the soil than a new set of conditions begin; the plant takes carbonic acid from the atmosphere, and having, in virtue of its vitality, by the agency of luminous power, decomposed this gas, it retains the carbon, and pours forth the oxygen to the air. This process is stated to be a function of vitality; but as this has been variously described by different authors, it is important to state with some minuteness what does really take place.
The plant absorbs carbonic acid from the atmosphere through the under surfaces of the leaves, and the whole of the bark; it at the same time derives an additional portion from the moisture which is taken up by the roots, and conveyed “to the topmost twig” by the force of capillary attraction, and another power, called endosmosis, which is exerted in a most striking manner by living organic tissues. This mysterious force is shown in a pleasing way by covering some spirits of wine and water in a wine-glass with a piece of bladder; the water will escape, leaving the strong spirit behind.
Independently of the action of light the plant may be regarded as a mere machine; the fluids and gases which it absorbs, pass off in a condition but very little changed—just as water would strain through a sponge or a porous stone. The consequence of this is the blanching or etiolation of the plant, which we produce by our artificial treatment of celery and sea-kale—the formation of the carbonaceous compound called chlorophyle, which is the green coloring-matter of the leaves, being entirely checked in darkness. If such a plant is brought into the light, its dormant powers are awakened, and, instead of being little other than a sponge through which fluids circulate, it exerts most remarkable chemical powers; the carbonic acid of the air and water is decomposed; its charcoal is retained to add to the wood of the plant, and the oxygen is set free again to the atmosphere. In this process is exhibited one of the most beautiful illustrations of the harmony which prevails through all the great phenomena of nature with which we are acquainted—the mutual dependence of the vegetable and animal kingdoms.
In the animal economy there is a constant production of carbonic acid, and the beautiful vegetable kingdom, spread over the earth in such infinite variety, requires this carbonic acid for its support. Constantly removing from the air the pernicious agent produced by the animal world, and giving back that oxygen which is required as the life-quickening element by the animal races, the balance of affinities is constantly maintained by the phenomena of vegetable growth. This interesting inquiry will form the subject of another essay.
The decomposition of carbonic acid is directly dependent upon luminous agency; from the impact of the earliest morning ray to the period when the sun reaches the zenith, the excitation of that vegetable vitality by which the chemical change is effected regularly increases. As the solar orb sinks toward the horizon the chemical activity diminishes—the sun sets—the action is reduced to its minimum—the plant, in the repose of darkness, passes to that state of rest which is as necessary to the vegetating races as sleep is to the wearied animal.
These are two well-marked stages in the life of a plant, germination and vegetation are exerted under different conditions; the time of flowering arrives, and another change occurs, the processes of forming the alkaline and acid juices, of producing the oil, wax, and resin, and of secreting those nitrogenous compounds which are found in the seed, are in full activity. Carbonic acid is now evolved and oxygen is retained; hydrogen and nitrogen are also forced, as it were, into combination with the oxygen and carbon, and altogether new and more complicated operations are in activity.
Such are the phenomena of vegetable life which the researches of our philosophers have developed. This curious order—this regular progression—showing itself at well-marked epochs, is now known to be dependent upon solar influences; the
“Bright effluence of bright essence increate”
works its mysterious wonders on every organic form. Much is still involved in mystery; but to the call of science some strange truths have been made manifest to man, and of some of these the phenomena must now be explained.