As yet, the effects of actinism have been more studied in the inanimate than the organic creation. Still, in the vegetable kingdom, its power is known to be of the utmost importance. A seed exposed to the entire sunbeam will not germinate; but bury it in the earth, at a depth sufficient to exclude the light, yet enough to admit actinism, which, like heat, penetrates the earth to some distance, and soon a chemical change will take place; the starch contained in the seed is converted into gum and water, forming the nutriment of the young plant; the tiny root plunges downward, the slender stem rises to the light, the first leaves, or cotyledons, then unfold, and now fully expand to the light, and a series of chemical changes of a totally different nature commence, which we have before noticed, when speaking of light. Experiments clearly prove that this change is to be attributed to actinism, and not to heat. Glass has been interposed of a dark blue color, which is transparent to actinism, though opaque to light and heat, and germination has been thereby quickened. Gardeners have long known this fact practically, and are accustomed to raise their cuttings under blue shades. There is no doubt that actinism exercises a powerful and beneficent influence on plants during their whole existence, but science has yet to demonstrate its nature; and it is curious to observe that the actinic element is most abundant in the sunbeam in the spring, when its presence is most essential in promoting germination--in summer the luminous rays are in excess, when they are most needed for the formation of woody fibre--and in autumn the heat-rays prevail, and ripen the golden grain and the delicious fruit; in each day the proportions of the different rays vary--in the morning the actinic principle abounds most, at noon the light, and at eventide the heat. The influence of actinism on the animal world is not well known; but it is probable that many of the effects hitherto referred to light are in reality due to actinism. It has the strange power of darkening the human skin, causing the deep color of those tribes who inhabit the sunniest regions of the earth; and even in our own country, in summer, that darkening of the skin called sun-burning. Doubtless, more careful investigation will discover this principle to be equally important to the life and health of animals as either of its closely allied powers of light and heat.