CHAP. II.] RESEMBLE VARIETIES. 43 



species already manufactured still to a certain extent resemble 

 varieties, for they differ from each other by less than the usual 

 amount of difference. 



Moreover, the species of the larger genera are related to each 

 other, in the same manner as the varieties of any one species are 

 related to each other. No naturalist pretends that all the species 

 of a genus are equally distinct from each other ; they may generally 

 be divided into sub-genera, or sections, or lesser groups. As Fries 

 has well remarked, little groups of species are generally clustered 

 like satellites around other species. And what are varieties but 

 groups of forms, unequally related to each other, and clustered 

 round 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 be- 

 tween 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 differences between varieties tend 

 to increase into the greater differences between species. 



There is one other point which is worth notice. Varieties gene- 

 rally have much restricted ranges : this statement is indeed 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. Watson has marked for me in the well-sifted London Cata- 

 logue 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 acknow- 

 ledged 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 closely connected ; but the 



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