90 EVOLUTION OF BRITISH CATTLE 



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." l Let us view De Vries's discovery 

 as described by Professor Arthur Thomson 2 : 



" 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 dis- 

 appointingly conservative. It seemed as if most 



1 De Vries's "Species and Varieties," 1905, p. 16. 



2 "Heredity," 1908,^91. 



