Chap. II.] RESEMBLE VARIETIES. 



73 



and in so far resemble varieties, often have much re- 

 stricted 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 prov- 

 inces into which Mr. Watson has divided Great Britain. 

 Now, in this same Catalogue, 53 acknowledged varie- 

 ties 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 difEerence between them; for two forms, if 

 differing very little, are generally ranked as varieties, 

 notwithstanding that they cannot be closely connected; 

 but the amount of difEerence 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 



