By choosing seeds from a plant that pleases him, the breeder may be able, under given conditions, to produce numbers of plants with more or less of the desired qualities; from the best of these, he may again choose; and so on until the race becomes greatly improved (Figs. 5, 6, 7). This process of continuously choosing the most suitable plants is known as =selection=. A somewhat similar process proceeds in wild nature, and it is then known as =natural selection=. [Illustration: FIG. 6.--FLAX BREEDING. _A_ is a plant grown for seed production; _B_, for fiber production. Why?] [Illustration: FIG. 7.--BREEDING. _A_, effect from breeding from smallest grains (after four years), average head; _B_, result from breeding from the plumpest and heaviest grains (after four years), average head.] SUGGESTIONS.--=6.= Every pupil should undertake at least one simple experiment in selection of seed. He may select kernels from the best plant of corn in the field, and also from the poorest plant,--having reference not so much to mere incidental size and vigor of the plants that may be due to accidental conditions in the field, as to the apparently constitutional strength and size, number of ears, size of ears, perfectness of ears and kernels, habit of the plant as to suckering, and the like. The seeds may be saved and sown the next year. Every crop can no doubt be very greatly improved by a careful process of selection extending over a series of years. Crops are increased in yield or efficiency in three ways: better general care; enriching the land in which they grow; attention to breeding. CHAPTER IV PLANT SOCIETIES In the long course of time in which plants have been accommodating themselves to the varying conditions in which they are obliged to grow, _they have become adapted to every different environment_. Certain plants, therefore, may live together or near each other, all enjoying the same general conditions and surroundings. These aggregations of plants that are adapted to similar general conditions are known as =plant societies=. Moisture and temperature are the leading factors in determining plant societies. The great geographical societies or aggregations of the plant world may conveniently be associated chiefly with the moisture supply, as: _wet-region societies_, comprising aquatic and bog vegetation (Fig. 8); _arid-region societies_, comprising desert and most sand-region vegetation; _mid-region societies_, comprising the mixed vegetation in intermediate regions (Fig. 9), this being the commonest type. Much of the characteristic scenery of any place is due to its plant societies. Arid-region plants usually have small and hard leaves, apparently preventing too rapid loss of water. Usually, also, they are characterized by stiff growth, hairy covering, spines, or a much-contracted plant-body, and often by large underground parts for the storage of water.