Page:The Evolution of British Cattle.djvu/102

 oblivion till years after both discoverers were dead. As it is, we must now go back, and partially, at least, revise some of Darwin's conclusions.

One of Darwin's main contentions was that races of animals vary, but, as he thought, slowly and constantly; that, to take a homely case, the neck of a giraffe is slightly longer than his father's, that his father's is slightly longer than his grandfather's, and so on backwards: thus, that the differences between a set of animals and their descendants a hundred generations younger are really the sum of all the small accretions added on (or taken off, for that matter) by each successive generation.

But De Vries has shown that sudden and observable changes take place among plants, and that these changes may be inherited: " Varieties have often been observed to appear at once, and quite unexpectedly in horticulture and agriculture." Let us view De Vries 's discovery as described by Professor Arthur Thomson : —

"In 1886 De Vries began hunting about around Amsterdam for a plant which would show hints of being in what we may call a changeful mood. He tried over a hundred species, bringing them under cultivation, but almost all were disappointingly conservative. It seemed as if most