Chap. V] 



THE SOIL 



105 



this dissimilar relation by means of the example of Achillea atrata and 

 A. moschata. 



Achillea moschata excludes A. atrata from a silicious soil and is itself excluded by 

 the latter from a calcareous soil. On the other hand, either of them grows equally 

 well in the company of A. Millefolium. Evidently the two first-mentioned plants, as 



if;} 



Fig. 55. I. Achillea atrata. Calciphilous. 2. Achillea moschata. Calciphobons. Natural size. 



hey are externally extremely alike, make analogous demands on the environment. 

 V Millefolium, however, which sj-stematically is further removed from either, does 

 lot compete with them, because it is dependent on other conditions of existence, 

 f either of the two species be absent, the other becomes indifferent as regards its 

 hoice of soil. 

 'In Bernina-Heuthal (Upper Engadine), A. moschata, A. atrata, and xV. Millefolium, 



