696 Mutations 



tematic type. Still others are more distant or 

 even belong to different genera. The latter, 

 and even the diverging though rarely allied ele- 

 mentary species, are not adequate to give evi- 

 dence in any direction. They may well have 

 lived together with their actual characters in 

 the long ages before the separation of the now 

 widely distant floras, or have sprung from a 

 common ancestor living at that time, and subse- 

 quently have changed their habits. After ex- 

 cluding these unreliable instances, a good num- 

 ber of species remain, which are quite the same 

 in the arctic and alpine regions and on the sum- 

 mits of distant mountain-ranges. As no trans- 

 portation over such large distances can have 

 brought them from one locality to the other, no 

 other explanation is left than that they have 

 been wholly constant and unchanged ever since 

 the glacial period which separated them. Ob- 

 viously they must have been subjected to widely 

 changing conditions. The fact of their stability 

 through all these outward changes is the best 

 ^ proof that the ordinary external conditions do 

 not necessarily have an influence on specific evo- 

 lution. They may have such a result in some 

 instances, in others they obviously have not. 

 Many arctic forms bearing the specific name of 

 alpinus justify this conclusion. Astragalus al- 

 pinus, Phleum alpinum, Hieracium alpinum and 



