74 ORIGIN OF SPECIES 



certain forms — that is, round their parent-species? Un- 

 doubtedly there is one most important point of difference 

 between varieties and species; namely, that the amount of 

 difference between varieties, when compared with each other 

 or with their parent-species, is much less than that between 

 the species of the same genus. But when we come to discuss 

 the principle, as I call it, of Divergence of Character, we 

 shall see how this may be explained, and how the lesser dif- 

 ferences between varieties tend to increase into the greater 

 differences between species. 



There is one other point which is worth notice. Varieties 

 generally have much restricted ranges : this statement is in- 

 deed scarcely more than a truism, for, if a variety were 

 found to have a wider range than that of its supposed parent- 

 species, their denominations would be reversed. But there 

 is reason to believe that the species which are very closely 

 allied to other species, and in so far resemble varieties, often 

 have much restricted ranges. For instance, Mr. H. C. Wat- 

 son 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 "j provinces ; whereas, the species to which these 

 varieties belong range over 14 "3 provinces. So that the ac- 

 knowledged varieties have nearly the same restricted aver- 

 age 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 closely connected; but the amount of difference 



