Elementary Species in Nature 51 



simultaneous or successive. According to the 

 geographic distribution, the place of common 

 origin must probably be sought in the southern 

 part of central Europe, perhaps even in the 

 vicinity of Lyons. Here we may assume that 

 the old Draba verna has produced a host or a 

 swarm of new types. Thence they must have 

 spread over Europe, but whether in doing so 

 they have remained constant, or whether some 

 or many of them have repeatedly undergone 

 specific mutations, is of course unknown. 



The main fact is, that such a small species as 

 Draba verna is not at all a uniform type, but 

 comprises over two hundred well distinguished 

 and constant forms. 



It is readily granted that violets and whitlow- 

 grasses are extreme instances of systematic 

 variability. Such great numbers of elementary 

 species are not often included in single species 

 of the system. But the numbers are of second- 

 ary importance, and the fact that systematic 

 species consist, as a rule, of more than one inde- 

 pendent and constant subspecies, retains its al- 

 most universal validity. 



In some cases the systematic species are man- 

 ifest groups, sharply differentiated from one 

 another. In other instances the groups of ele- 

 mentary forms as they are shown by direct ob- 

 servation, have been adjudged by many authors 



