No. 507] DARWIN'S " ORIGIN OF SPECIES » 



167 



. . . Complex organs . . . have been perfected ... by the accumula- 

 tion of innumerable slight variations. 



He also says : 



It is, no doubt, extremely difficult to conjecture by what ynulntiuns 

 many structures have been perfected ... (p. 404). 

 Again, on pp. 413-414: 



As natural selection acts solely by accumulating slight successive, 

 favorable variations, it can produce no great or sudden modifications; 

 it can act only by short and slow steps. 



I think that it is evident from Darwin's discussion 

 of varieties of oaks that he would not have regarded 

 such work as that of DeVries on the evening primrose 

 as making a revision of the foregoing sentence necessary. 

 Even if DeVries 's mutants are what he thinks them to 

 be, that is, elementary species, still evolution of species 

 by that means must be by "short, slow steps." 



Even if it should be shown that species originate only 

 by mutation, the following sentence might be permitted 

 to stand: 



New species have come on the stage slowly and at successive inter- 

 vals, and the amount of change after equal intervals of time, is widely 

 different in different groups (p. 417). 



2. By the following quotations I shall attempt to show 

 the role which that kind of variation, now called muta- 

 tion, plays in the evolution of species according to Dar- 

 win's view. 



When it is noted that DeVries makes use of facts 

 recorded by Darwin in support of his views, it will be 

 seen that there is some reason for suspecting that some 

 of the facts which in Darwin's day were thought to be 

 of the grade of fluctuating variations were really of the 

 kind now believed by many to be something quite dif- 

 ferent. 



On page 22 is this statement : 



Some varieties useful to him (man) have probably arisen suddenly, 

 or by a step. 



Examples are cited, e. g., the fuller's teasel, the turn- 

 spit dog, etc. DeCandolle's memoir on the oaks of the 



