14 MENDELISM CHAP, n 



Nevertheless in this kind of work alone seemed there 

 any promise of ultimate success. 



A few years later appeared the first volume of 

 de Vries' remarkable book on The Mutation Theory. 

 From a prolonged study of the evening primrose 

 (Oenothera) de Vries concluded that new varieties 

 suddenly arose from older ones by sudden sharp 

 steps or mutations, and not by any process involving 

 the gradual accumulation of minute differences. The 

 number of striking cases from among widely different 

 plants which he was able to bring forward went far 

 to convincing biologists that discontinuity in varia- 

 tion was a more widespread phenomenon than had 

 hitherto been suspected, and not a few began to 

 question whether the account of the mode of evolu- 

 tion so generally accepted for forty years was after 

 all the true account. Such, in brief, was the outlook 

 in the central problem of biology at the time of the 

 rediscovery of Mendel's work. 



