64 The Different Modes of Origin of new Species. 



a but with /? and are therefore considered as having been 

 derived from a Forma typica or gennina and not as being 

 of equal vakie with this. Evidently the principle on 

 which they are classified is borrowed from a consideration 

 of horticultural varieties. This proceeding, however, is 

 only justified in the relatively rare cases in which horti- 

 cultural varieties can be demonstrated to be younger than 

 the species. Besides this the geographical distribution 

 of the forms in question is often employed to decide 

 which is the species, and which are the varieties. If one 

 particular form is wide-spread and another only local 

 or sporadic in its appearance it is obvious that the former 

 will be regarded as the older and therefore as the species. 

 Often this fits in conveniently with the fact that the 

 species was discovered earlier than the variety, so that 

 instead of disturbing the classification in the system all 

 that had to be done was to range the variety under the 

 species. 



The exigencies of space prevent me from going into 

 further detail here. What I have already said may suffice 

 to show that the systematic term "variety" means two 

 fundamentally different things to Linnaeus and the 

 later svstematists: 



1. Homonomous Forms, amongst which even Lin- 

 naeus could not select one as a type for the others ; 

 "Elements de I'espece" (De Candolle) or ele- 

 mentary species. 



2. Derived Forms, which are distinguished from the 

 type of the species only by the decreased or in- 

 creased development of a particular quality; or 

 by its complete absence: True varieties.^ 



^ Amongst these, again, the simple invariable types are to be 

 distinguished from the intermediate or eversporting races. (See 

 §§3-4.) 



