46 SPECIES OF LARGER GENERA [Chap. II. 



of difference between the species is often exceedingly small. I have 

 endeavoured to test this numerically by averages, and, as far as my 

 imperfect results go, they confirm the view. I have also consulted 

 some sagacious and experienced observers, and, after deliberation, 

 they concur in this view. In this respect, therefore, the species 

 of the larger genera resemble varieties, more than do the species Oi 

 the smaller genera. Or the case may be put in another way, and it 

 may be said, that in the larger genera, in which a number of varie- 

 ties or incipient species greater than the average are now manufac- 

 turing, many of the 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. Undoubtedly 

 there is one most important point of difference between varieties 

 and species ; namely, that the amount of difference between varie- 

 ties, 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 denomi- 

 nations 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 

 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 acknow- 

 ledged varieties are recorded, and these range over 7'7 provinces ; 



