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.