No. 496] 



ASPECTS OF THE SPECIES QUESTION 



257 



vegetative features alone are present in the blue-green 

 algae and many of the fungi. It is evident that the 

 method of morphologic differences greatly facilitates the 

 provisional cataloguing of a flora, but it suffers from 

 a universal and serious fault. This is the use of a few 

 herbarium specimens in lieu of a large number of field 

 individuals. Practically every collector selects a few 

 individuals that appear typical, while for the purpose of 

 scientific species-making he should collect as complete a 

 series as possible of divergent individuals. Even if this 

 were done, the ecologist must continue to regard the 

 method as a mere preliminary, which serves to arrange 

 the material and hence to facilitate the real study of 

 species. 



Closely connected with morphologic difference is the 

 question of the absence of intermediate forms. This 

 appears to have played a more important part in zoology 

 than in botany. In the latter case, at least, it seems 

 often to have been taken for granted as a necessary con- 

 sequence of structural differences. At best, it has regu- 

 larly been a question of intermediate forms in the her- 

 baria and not in the field. 



Constancy as a criterion of species is also but another 

 phase of morphologic di (Terence. As such it seems to 

 have been used chiefly to designate uniformity of differ- 

 ence throughout the individuals concerned. The con- 

 stancy of a structure from one generation to another, or 

 from one habitat to another has been given little atten- 

 tion in species-making. Yet it is precisely these which 

 are of fundamental importance. This fact, however, 

 makes it at once evident that constancy is something that 

 can only be determined by combining the most extensive 



various habitats. This makes it clear that our present 

 knowledge of constancy is almost purely theoretical, and 

 that it is profitless to discuss it in our present ignorance 

 of it. 



To the ecologist, then, the usual bases for distinguish- 



