CH.V] MENDELIAN HEREDITY . 53 



occupied almost solely with the discussion of the 

 * Origin of Species,' his work attracted no attention 

 at the time, and only became celebrated on its 

 rediscovery in 1900. One cannot avoid speculating 

 on the possible effects on biological thought, had 

 the experiments and conclusions of his now famous 

 contemporary ever come to the knowledge of 

 Darwin. 



The method which led Mendel to his great 

 discovery was to experiment with plants exhibiting 

 discontinuous characters, and to consider each char- 

 acter separately. Previous workers in the same 

 field had made many laborious experiments in 

 crossing different races of plants or animals [7], but 

 had always regarded the individual as the unit, and 

 hence arose the belief that mongrels or hybrids were 

 usually intermediate between the parents, resembling 

 one in some features, the other in others, but with 

 no regular rule ; and further, that when hybrids were 

 bred together the offspring were often almost infinitely 

 variable, extending in a series from some closely 

 approaching one original parent through a diversity 

 of intermediate or new forms to others like the second 

 parent. So grew up the belief that the crossing 

 of distinct races or breeds is a potent cause of 

 variability, which, however, except when ' reversion 

 on crossing' took place, seemed to fall under no 

 ascertainable law. 



