250 PROBLEMS OF GENETICS 



to which their successors may possibly want to refer, and gen- 

 erally by subdividing their material into as many species as 

 they can induce any responsible society or journal to publish. 

 Between Jordan with his 200 odd species for Erophila, and 

 Grenier and Godron with one, there is no hesitation possible. 

 Jordan's view, as he again and again declares with vehemence, is 

 at least a view of natural facts, whereas the collective species is a 

 mere abstraction, convenient indeed for librarians and beginners, 

 but an insidious misrepresentation of natural truth, perhaps 

 more than any other the source of the plausible fallacies regarding 

 evolution that have so long obstructed progress. 



Nevertheless though we have been compelled to retreat from 

 the speculative position to which scientific opinion had rashly 

 advanced, the prospect of permanent progress is greatly better 

 than it was. With the development of genetic research clear 

 conceptions have at length been formed of the kind of knowledge 

 required and of the methods by which it is to be attained. If 

 we no longer see how varieties give rise to species, we may feel 

 confident that a minute study of genetic physiology of varieties 

 and species is the necessary beginning of any critical perception 

 of their inter-relations. It is little more than a century since 

 no valid distinction between a mechanical mixture and a chemical 

 combination could be perceived, and in regard to the forms of 

 life we may well be in a somewhat similar confusion. 



As yet the genetic behaviour of animals and plants has only 

 been sampled. When the work has been done on a scale so 

 large as to provide generalisations, we may be in a position to 

 declare whether specific difference is or is not a physiological 

 reality. 



