— 404 — 



impression of the habitat, and it also coincides with the results 

 that might be expected from the geological structure of the ground 

 on the habitats. 



In table I, pag. 378, the habitats are arranged according to 

 the degree of acidity in the soil: basic, neutral, acid; 3 habitats 

 that only gave a very faintly acid reaction are inserted in a special 

 class. 



When the habitats F, T and U are excepted, the isoreagents 

 are distributed as follows: 



On basic ground: parv, albid (pure arvensis), populations A — E. 



On acid ground: grand, viol (pure tricolor), populations P — S. 



On neutral-f aintly acid ground: all the combinations: parr, 

 albid; parv, viol; grand, albid and grand, viol (pure arvensis 

 and pure tricolor and the intermediate combinations), popu- 

 lations G — O. 



This result is in accordance with Ferdinandsen's above 

 mentioned. 



The cause of the many types present on neutral — faintly acid 

 soil is certainly that both the extreme combinations (arvensis 

 and tricolor) meet on this soil, and therefore there is a possibility 

 of crosses. 



Even if the reaction of the soil is not the only distributing 

 factor, it is surely one of the most important. The geographical 

 distribution of arvensis and tricolor in Jutland is certainly rather 

 due to the reaction of the soil in East- and West- Jutland than 

 to any special geographical causes. This is evident from the fact 

 that the composition of the populations can change within very re- 

 stricted areas parallel to the changes in the reaction of the soil. 

 A diagram of the route from Viborg to Hobro will show it: 



faintly 

 acid 



M 



[neutral] 



faintly 

 acid 



[parv, albid — grand, viol 

 and intermediates 



[basic; 



faintly 

 acid 



> A — 



-> Ai (not 





parv, albid 





"all combi-" 





alone 





nations 



At On sild (A) the populations suddenly changed. All the 

 large blue flowers disappeared coinciding with the fact that seed 

 and grass became markedly more vigorous. The explanation of 



