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.