Theories of Evolution 13 



planting one in a garden, varietal differences 

 at once arise and are often designated in sys- 

 tematic works under different varietal names. 

 Secondly all individual differences which are of 

 a fluctuating nature are to be combined into a 

 group. But with these we shall deal later. 



Apart from these minor points the subdi- 

 visions of the systematic species exhibit two 

 widely different features. I will now try to 

 make this clear in a few words, but will return 

 in another lecture to a fuller discussion of this 

 most interesting contrast. 



Linnaeus himself knew that in some cases all 

 subdivisions of a species are of equal rank, to- 

 gether constituting the group called species. 

 No one of them outranks the others; it is not 

 a species with varieties, but a group consisting 

 only of varieties. A closer inquiry into the 

 cases treated in this manner by the great master 

 of systematic science, shows that here his varie- 

 ties were exactly what we now call elementary 

 species. 



In other cases the varieties are of a deriva- 

 tive nature. The species constitutes a type that 

 is pure in a race which ordinarily is still grow- 

 ing somewhere, though in some cases it may 

 have died out. From this type the varieties are 

 derived, and the way of this derivation is usual- 

 ly quite manifest to the botanist. It is ordina- 



