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Life in the world is represented by the Vegetable and Animal kingdoms. Plants and animals, unlike minerals, grow from germs, and develop into individuals with definite forms and organs. After a limited existence they die, their species being perpetuated by seed or offspring. The functions of plants and animals in nature are, however, entirely unlike. Plants are rooted in the soil; animals are free to move over the land, through the water or air. The plant, moreover, transforms the lifeless, inorganic elements (earth and air) into organic matter and thus prepares food for the animal. In its quiet, steady growth it gathers a store of force which the animal uses up in action. Thus the distribution of vegetation regulates that of animal life. Besides, vegetation clothes the surface of the land with that rich mantle of verdure and flowers which is its greatest ornament.

All living things are termed organisms, and the science which takes account of them with special regard to their common characteristics is termed Biology, or Life-lore. The classification and life-history of plants are the objects of that part of biology known as Botany. That part similarly occupied with the study of animals is known as Zoology.

Throughout the entire realm of nature, in the animal world as well as in the vegetable, the development of life increases in energy, and in the variety and perfection of the types, with the increasing intensity of light and heat, from the poles to the equator.