Germination is a chemical change which takes place most readily in darkness; vegetable growth is due to the secretion of carbon under the agency of light; and the processes of floriation are shown to involve some new and compound operations: these three states must be distinctly appreciated.
The sunbeam comes to us as a flood of pellucid light, usually colorless; if we disturb this white beam, as by compelling it to pass through a triangular piece of glass, we break it up into colored bands, which we call the spectrum, in which we have such an order of chromatic rays as are seen in the rainbow of a summer shower. These colored rays are now known to be the sources of all the tints by which nature adorns the surface of the earth, or art imitates, in its desire to create the beautiful. These colored bands have not the same illuminating power, nor do they possess the same heat-giving property. The yellow rays give the most LIGHT; the red rays have the function of HEAT in the highest degree. Beyond these properties the sunbeam possesses another, which is the power of producing CHEMICAL CHANGE—of effecting those magical results which we witness in the photographic processes, by which the beams illuminating any object are made to delineate it upon the prepared tablet of the artist.
It has been suspected that these three phenomena are not due to the same agency, but that, associated in the sunbeam, we have LIGHT, producing all the blessings of vision, and throwing the veil of color over all things—HEAT, maintaining that temperature over our globe which is necessary to the perfection of living organisms—and a third principle, ACTINISM, by which the chemical changes alluded to are effected. We possess the power, by the use of colored media, of separating these principles from each other, and of analyzing their effects. A yellow glass allows light to pass through it most freely, but it obstructs actinism almost entirely; a deep-blue glass, on the contrary, prevents the permeation of light, but it offers no interruption to the actinic, or chemical rays; a red glass, again, cuts off most of the rays, except those which have peculiarly a calorific, or heat-giving power.
With this knowledge we proceed in our experiments, and learn some of the mysteries of nature’s chemistry. If, above the soil in which the seed is placed, we fix a deep, pure yellow glass, the chemical change which marks germination is prevented; if, on the contrary, we employ a blue one, it is greatly accelerated; seeds, indeed, placed beneath the soil, covered with a cobalt blue finger-glass, will germinate many days sooner than such as may be exposed to the ordinary influences of sunshine:—this proves the necessity of the principle actinism to this first stage of vegetable life. Plants, however, made to grow under the influences of such blue media present much the same conditions as those which are reared in the dark; they are succulent instead of woody, and have yellow leaves and white stalks—indeed, the formation of leaves is prevented, and all the vital energy of the plant is exerted in the production of stalk. The chemical principle of the sun’s rays, alone, is not therefore sufficient; remove the plant to the influence of light, as separated from actinism, by the action of yellow media, and wood is formed abundantly—the plant grows most healthfully, and the leaves assume that dark green which belongs to tropical climes or to our most brilliant summers. Light is thus proved to be the exciting agent in effecting those chemical decompositions which have already been described; but under the influence of isolated light it is found that plants will not flower. When, however, the subject of our experiment is brought under the influence of a red glass, particularly of that variety in which a beautifully pure red is produced by oxide of gold, the whole process of floriation and the perfection of the seed is accomplished.
Careful and long-continued observations have proved that in the spring, when the process of germination is most active, the chemical rays are the most abundant in the sunbeam. As the summer advances, light, relatively to the other forces, is largely increased: at this season the trees of the forest, the herb of the valley, and the cultivated plants which adorn our dwellings, are all alike adding to their wood. Autumn comes on, and then heat, so necessary for ripening grain, is found to exist in considerable excess. It is curious, too, that the autumnal heat has properties peculiarly its own—so decidedly distinguished from the ordinary heat, that Sir John Herschel and Mrs. Somerville have adopted a term to distinguish it. The peculiar browning or scorching rays of autumn are called the parathermic rays: they possess a remarkable chemical action added to their calorific one; and to this is due those complicated phenomena already briefly described.
In these experiments, carefully tried, we are enabled to imitate the conditions of nature, and supply, at any time, those states of solar radiation which belong to the varying seasons of the year.
Such is a rapid sketch of the mysteries of a flower; “Consider the lilies of the field, how they grow; they toil not, neither do they spin; and yet I say unto you, Solomon in all his glory was not arrayed like one of these.”
Under the influence of the sunbeam, vegetable life is awakened, continued, and completed; a wondrous alchemy is effected; the change in the condition of the solar radiations determines the varying conditions of vegetable vitality; and in its progress those transmutations occur, which at once give beauty to the exterior world, and provide for the animal races the food by which their existence is maintained. The contemplation of influences such as these realizes in the human soul that sweet feeling which, with Keats, finds that
A thing of beauty is a joy forever;
Its loveliness increasing, it will never