iv ON PLANT LIFE 151 



INFLUENCE OF SOIL 



The character of the vegetation is of course 

 greatly influenced by that of the soil. In this 

 respect granitic and calcareous regions offer 

 perhaps the best marked contrast. 



There are in Switzerland two kinds of 

 Rhododendrons, very similar in their flowers, 

 but contrasted in their leaves : Rhododendron 

 hirsuturn having them hairy at the edges as 

 the name indicates ; while in R. ferrugineum 

 they are rolled, but not hairy, at the edges, 

 and become ferrugineous on the lower side. 

 This species occurs in the granitic regions, 

 where R. hirsutum does not grow. 



The Yarrows (Achillea) afford us a similar 

 case. Achillea atrata and A. moschata will 

 live either on calcareous or granitic soil, but 

 in a district where both occur, A. atrata grows 

 so much the more vigorously of the two if the 

 soil is calcareous that it soon exterminates 

 A. moschata; while in granite districts, on 

 the contrary, A. moschata is victorious and 

 A. atrata disappears. 



