The Gain of Responsiveness.
So also is there responsiveness when we look upon the life of plants in the large. As the traits of a shrub or tree are borne into its seed many a thousand impulses are merged and mingled. Little wonder that their delicate accord and poise should be slightly different from those of the seeds from which the parents sprang. Let us suppose these parents to be cactuses, and that the offspring displays an unusually broad stem, of less surface comparatively than any other plant in its group. In a soil seldom refreshed by rain, this cactus has the best foothold and maintains it with most vigor. Sandstorms which kill brethren less sturdy, strike it in vain, so that its kind is multiplied. Wherever such a new character as this gives a plant an advantage, it holds the field while its neighbors perish. Thus arises a high premium on every useful variation, be it in new stockiness of form, an acridity which repels vermin, or a strength which readily makes a way through sun-baked earth. Hence such new traits are, as it were, seized upon and become points of departure for new varieties, and in the fullness of time, for new species. About a hundred years ago a gardener imagined a tuberous begonia, and then proceeded step by step toward its creation by breeding from every flower that varied in the direction he desired. This man, and all his kindred who have added to our riches in cultivated blooms, have no more than copied the modes of nature which, at the end of ages, bestows as free gifts every wildflower of the field and hedgerow. If the botanist of to-day is the master of a plastic art, so is the cattle-breeder who chalks on a barn-door the outline of a beeve he wishes to produce, and then straightway plans the matings which issue in the animal he has pictured. Artificial selection, such as this, is after all only imitation of that natural selection which has derived the horse from a progenitor little larger than a fox, in response, age after age, to changing food, climate, enemies, and the needs of his human master.