II HISTORICAL IS 



of species, and questioned whether the accepted ideas of 

 variation and heredity were after all in consonance with 

 the facts. Speaking generally, species do not grade grad- 

 ually from one to the other, but the differences between 

 them are sharp and specific. Whence comes this preva- 

 lence of discontinuity if the process by which they have 

 arisen is one of accumulation of minute and almost imper- 

 ceptible differences? Why are not intermediates of all 

 sorts more abundantly produced in nature than is actually 

 known to be the case ? Bateson saw that if we are ever 

 to answer this question we must have more definite know- 

 ledge of the nature of variation and of the nature of the 

 hereditary process by which these variations are trans- 

 mitted. And the best way to obtain that knowledge was 

 to let the dead alone and to return to the study of the liv- 

 ing. It was true that the past record of experimental 

 breeding had been mainly one of disappointment. It 

 was true also that there was no tangible clue by which 

 experiments might be directed in the present. Neverthe- 

 less in this kind of work alone there seemed any promise 

 of ultimate success. 



A few years later appeared the first volume of de Vries' 

 remarkable book on The Mutation Theory. From a pro- 

 longed 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 



