Chap. II. RESEMBLE VARIETIES. 07 



is one most important point of dilFerencc between varieties and 

 species ; namely, that the amount of diflerencc between varieties, 

 M'hen compared with each other or with their parent-species, is 

 much less than that betw'een the species of the same genus. But 

 ■when WG come to discuss the principle, as I call it, of Diver- 

 gence of Character, we shall see how this may be explained, 

 and how the lesser diiferences between varieties tend to in- 

 crease 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 thaii that of its sujiposed parent-species, 

 their denominations would be reversed. But there is also 

 reason to believe that those species which are very closely 

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

 have much-restricted ranges. For instance, Mr. II. C. Watson 

 has marked for me, in the well-sifted London Catalogue of 

 plants (fourth edition), G3 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 G.9 of the provinces into which Mr. 

 Watson has divided Great Britain. Now, in this same cata- 

 logue, 53 acknowledged varieties are recorded, and these range 

 over 7.7 jirovinces ; whereas, the species to Avhich these vari- 

 eties belong range over 14.3 provinces. So that the acknowl- 

 edged varieties have very nearly the same restricted average 

 range as have those very closely allied forms, marked for me 

 liy Mr. Watson as doubtful species, but which are almost uni- 

 versally ranked by British botanists as good and true species. 



Summart/. 



Finally, then, varieties caimot be distinguished from species 

 — except, first, by the discovery of intermediate linking forms; 

 and, secondly, by a certain indefinite amount of difference be- 

 tween them ; for two forms, if differing very little, are gener- 

 ally ranked as varieties, notwithstanding that they cannot be 

 closely 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 uncfiually, allied together. 



