follows. A plant that varied favourably has been chosen, and a vast number of plants have been reared from slips cut from it, the process being repeated through any number of pseudo-generations. In this way a single plant with a favourable variation is multiplied into many similar plants, and the variation is preserved for an indefinite time. Seeds reared from such plants generally develop into inferior plants, but exceptionally a superior plant develops, and is then propagated as before by means of slips. The parent variety is then ignored for breeding purposes and is used only for stock on which to engraft the newer variety. The more improved variety thus takes the place of the variety which is less improved. This process, the repetition of which has resulted in such extreme examples of rapid evolution as the peach and garden rose, is therefore a tremendously stringent process of selection. Practically speaking the most favourable individual of a species has been chosen and multiplied by means of slips, the rest of the species being eliminated; and in each new seminal generation the same process has been followed. It is as though, in an endeavour to increase the height of men, we chose the tallest man in the world, eliminated the rest of his species, multiplied him—not by seminal generation, but by some process analogous to the multiplication of plants by slips—into thousands of men and women as tall as himself, chose the tallest individual among the children of these, and repeated the process, and continued to do so through several seminal generations. The process of selection under which the cultivated rose and the peach have been evolved has therefore been, as I say, tremendously severe—a thousand times more severe than it is possible to make it among annual plants and among the higher animals; and their evolution has therefore been extremely rapid—even
