The evolutionist believes that change of conditions and diversity of environment necessitates corresponding, or all changes and unlikeness there is in plant and animal life.

We find most plants can be propagated by either divisions or seed, while it is only the lowest order of animals that multiply by divisions. It is, also, only in the earliest or lowest order of plants that multiply only by divisions and offsets. Plants which multiply by divisions are subject to but little change in the surroundings; to continue its kind, growth must be continuous, and as M. De Quatrefages says, this is rather a form of growth than true generation. Such plants when they become subject to greater climatic changes, and could not adjust themselves would become extinct; while some by these changes, which either exhaust or obstruct growth, would be forced into bloom and seed. By this creation or differentiation of sex, seeds were developed which contained all the characteristic of the parent plant, and could lay dormant through the storms of winter and be forced into life by the heat of summer, and thus many species would be preserved through their sexual attributes. During these variations of climate in which seed is matured, the seed is subject to different conditions from those in which growth was maintained, and the seedlings could in time resist greater extremes, and thrive under conditions quite unlike those of its ancestors.

Again, seedling plants of the same parent by growing in different soils and different elevations and climate, would vary from the parent. The recrossing of these would produce offspring quite unlike the parent, and in time distinct species All this is brought about without any object or design by the simple laws of growth and adjustment, by action and reaction.

Darwin, in his work on Plants and Animals under Domestication, quotes Gallesio, "that seedling oranges in Italy were larger, more productive, and hardier than former kinds raised by grafts; and more was effected for the naturalization of oranges in Italy by the accidental production of new kinds during a period of sixty years than in many ages previous, by grafting old varieties."