Selection of Elementary Species 119 



Nature has constituted them as groups of 

 slightly different constant forms, quite in the 

 same way as wheat and oats and corn. Assum- 

 ing that this happened ages ago somewhere in 

 central Europe, it is of course probable that 

 the same differences in respect to the influence 

 of climatic conditions will have prevailed as 

 with cereals. Subsequent to the period which 

 has produced the numerous elementary spe- 

 cies of the whitlow-grass came a period of wide- 

 spread distribution. The process must h,ave 

 been wholly comparable with that of acclimati- 

 zation. Some species must have been more 

 adapted to northern climates, others to the soils 

 of western or eastern regions and so on. These 

 qualities must have decided the general lines of 

 the distribution, and the species must have 

 been segregated according to their respective 

 climatic qualities, and their adaptability to soil 

 and weather. A struggle for life and a natural 

 selection must have accompanied and guided 

 the distribution, but there is no reason to as- 

 sume that the various forms were changed 

 by this process, and that we see them now en- 

 dowed with other qualities than they had at the 

 outset 



Natural selection must have played, in this 

 and in a large number of other cases, quite the 

 same part as the artificial method of variety- 



