40 Elementary Species 



aid of insects, and is widely dispersed in culti- 

 vated fields. The third form, V. alpestris, 

 grows in the Alps, but is of lesser importance 

 for our present discussion. 



Anywhere throughout the central part of 

 Europe V. tricolor and F. arvensis may be seen, 

 each occupying its own locality. They may be 

 considered as ranging among the most common 

 native plants of the particular regions they in- 

 habit. They vary in the color of the flowers, 

 branching of the stems, in the foliage and other 

 parts, but not to such an extent as to consti- 

 tute distinct strains. They have been brought 

 into cultivation by Jordan, Wittrock and others, 

 but throughout Europe each of them constitutes 

 a single type. 



These types must be very old and constant, 

 fluctuating always within the same distinct and 

 narrow limits. No slow, gradual changes can 

 have taken place. In different countries their 

 various habitats are as old as the historical 

 records, and probably many centuries older. 

 They are quite independent of one another, the 

 distance being in numerous cases far too great 

 for the exchange of pollen or of seeds. If slow 

 and gradual changes were the rule, the types 

 could not have remained so uniform throughout 

 the whole range of these two species. They 

 would necessarily have split up into thousands 



