XEROrilYTE SOCIETIES 



197 



Fig. 174. Two specicB of Achillea on difEerent soils. The one to tlie left ^\■as growa 

 in drier conditions and shows an abundant development of hairs.— After 



8CHIMPER. 



extreme of leaf reduction has been reached hy the cactus 

 phmts, whose leaves, so far as foliage is concerned, have 

 disappeared entirely, and the leaf "work is done by the 



