Chap. II.] KESEMBLE VARIETIES. 73 



species, and in so far resemble varieties, often have 

 much restricted ranges. For instance, Mr. H. C. 

 Watson has marked for me in the well-sifted London 

 Catalogue of plants (4th edition) 63 plants which are 

 therein ranked as species, but which he considers as so 

 closely allied to other species as to be of doubtful 

 value : these 63 reputed species range on an average 

 over 6*9 of the provinces into which Mr. Watson has 

 divided Great Britain. Now, in this same Catalogue, 

 53 acknowledged varieties are recorded, and these 

 range over 7 '7 provinces ; 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. 



Summary. 



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, 

 notwithstanding that they cannot be rlosely 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 



