Chap. II/J RESEMBLE VARIETIES. 47 



whereas, the species to which these varieties belong range over 14 - 3 

 provinces. So that the acknowledged varieties have nearly the same 

 restricted average range, as have the closely allied forms, marked 

 for me by Mr. Watson as doubtful species, but which are almost 

 universally ranked by British botanists as good and true species. 



Finally, varieties cannot be distinguished from species, — except, 

 first, by the discovery of intermediate linking forms ; and, secondly, 

 by a certain indefinite amount of difference between them ; for two 

 forms, if differing very little, are generally ranked as varieties, not- 

 withstanding that they cannot be closely connected; but the amount 

 of difference considered necessary to give to any two forms the rank 

 of species cannot be defined. In genera having more than the average 

 number of species in any country, the species of these genera have 

 more than the average number of varieties. In large genera the 

 species are apt to be closely, but unequally, allied together, forming 

 little clusters round other species. Species very closely allied to 

 other species apparently have restricted ranges. In all these respects 

 the species of large genera present a strong analogy with varieties. 

 And we can clearly understand these analogies, if species once 

 existed as varieties, and thus originated ; whereas, these analogies 

 are utterly inexplicable if species are independent creations. 



We have, also, seen that it is the most flourishing or dominant 

 species of the larger genera within each class which on an average 

 yield the greatest number of varieties ; and varieties, as we shall 

 hereafter see, tend to become converted into new and distinct 

 species. Thus the larger genera tend to become larger ; and through- 

 out nature the forms of life which are now dominant tend to become 

 still more dominant by leaving many modified and dominant 

 descendants. But by steps hereafter to be explained, the larger 

 genera also tend to break up into smaller genera. And thus, the 

 forms of life throughout the universe become divided into groups 

 subordinate to groups. 



