282 Darwin, and after Darwin. 



and even also cross-sterile with allied varieties — it is 

 only some three or four living botanists who for these 

 reasons advocate the elevation of such varieties to 

 the rank of species. In short, as we are not engaged on 

 any abstract question touching the principles on which 

 species ought to have been constituted by their makers, 

 but upon the actual manner in which they have been, 

 the criterion of heredity must needs be disregarded in 

 the present discussion, as it has been in the work of 

 systematists. And the result of this is, that any 

 objection to our introducing the facts of climatic varia- 

 tion in the present discussion is excluded. In par- 

 ticular, so far as any question of heredity is concerned, 

 all these facts are as assuredly as they are cogently 

 relevant. It is perfectly certain that there is " a large 

 proportional number ' of named species — particularly 

 of plants — which further investigation would resolve 

 into climatic varieties. With the advance of know- 

 ledge, "bad species" are always increasing at the 

 expense of "good species," so that we are now justified 

 in concluding with Kerner, Hackel, and other naturalists 

 best qualified to speak on this subject, that if we could 

 know as much about the past history and present rela- 

 tions of the remaining good species as we do about the 

 bad, all the former, without exception, would become 

 resolved into the latter. In point of fact, and apart 

 altogether from the inductive experience on which this 

 conclusion is based, the conclusion follows " as a neces- 

 sary deduction " from the general theory of descent. 

 For this theory essentially consists in supposing 

 either the past or the present existence of interme- 

 diate varietal forms in all cases, with the consequence 

 that " good species '' serve merely to mark lacunae in 



