No. 496] ASPECTS OF THE SPECIES QUESTION 237 



From Darvviii, UrijAiii ol" Siiccies, new edition, from tlie 

 sixth English edition, New York, \). 33, 1883. 

 No one definition has satisfied all naturalists; yet every 

 naturalist knows vaguely what he means when he speaks 

 of a species. . . . The term variety is almost equally 

 difficult to define; ])ut here community of descent is 

 almost universally implied, though it can rarely be 

 proved. 



From Britton and Brown, Illustrated Flora 1: VI., 18!)(;. 

 A species is composed of all the individuals of a kind 

 capable of continuous successive propagation among 

 themselves. 



From De Vries, Species and Varieties, p. 32, 1905, under 



Elementary Species in Nature. 



''What are species?" Species are considered as the 

 true units of nature by the vast majority of biologists. 

 They have gained this high rank in our estimation prin- 

 cipally through the influence of Linnaeus. They have 

 supplanted the genera which were the accepted units 

 before Linnaeus. They are now to be replaced, in their 

 turn, by smaller types, for reasons which do not rest 

 upon comparative studies but upon direct experimental 

 evidence. 



2. Discussion 



Any method of evolution makes difficult the establish- 

 ment as a general conclusion, that all the progeny of a 

 species must belong to that species. The paleontologists 

 have always faced this difficulty; their species have of 

 necessity been assumptions, and theoretically, at least, 

 if the complete representation of any line of descent 

 could be assembled it would be seen at once that the 

 whole series of forms were in some way connected. The 

 induced mutation effected by MacDougal in Raimannia 

 odorata, in which plants so different from their imme- 

 diate parent as to appear, at least, specifically distinct 



