172 The Origin of Species by Mutation. 



mi nation of the limits of these groups the systematist 

 is guided almost entirely by the gaps which have arisen 

 by the disappearance of more or less numerous sub- 

 species. 



With regard to the nomenclature, it would perhaps 

 be better if the binary system were replaced by a ternary; 

 to retain the Linnean specific names as much as possible 

 and to write after them the name of the elementary 

 form.i The idea of a variety should be strictly confined 

 to cultivated forms. ^ 



§ 22. SPECIES IN NATURE. 



The species of the systematist are compound species; 

 they consist of a greater or smaller number of subspecies 

 which breed true when tested. The larger the geograph- 

 ical area inhabited by a species, the larger is the number 

 of component subspecies : they are concentrated in the 

 center of the area and become scattered towards its per- 

 iphery. 



In local floras therefore as a rule each species con- 

 sists of only one or very few elementary species.^ The 

 species of such local floras do not exactly agree in neigh- 

 boring districts.^ From France alone Jordan brought 



^ This course is adopted by Waagen in Benecke, Geognostisch- 

 paldontologische Beitragc , 1876, Vol. 2, p. 187. — An example: any one 

 can guess the meaning of Draba verna leptophylla whilst Erophila 

 leptophylla has no meaning except to the initiated. 



^ Subspecies are not to be regarded as subsidiary to, nor as de- 

 rived from the species ; for each species consists of a group of sub- 

 species. The only thing that can be said in favor of the conventional 

 assumption of a forma genuina is that it is convenient. 



^ Only one elementary species of Draba verna so far as I can 

 find occurs round Amsterdam and the towns in its neighborhood: 

 it agrees with Jordan's D. leptophylla. 



■* For example Senecio Jacohaea is common in the neighborhood 

 of Haarlem, but always without ray-florets, whereas in the adjoin- 

 ing dunes near Leiden it is only found with these florets. 



