XEEOPHYTE SOCIETIES 
197 
FIG. 174. Two species of Achillea on different soils. The one to the left was grown 
in drier conditions and shows an abundant development of hairs. After 
SCHIMPER. 
extreme of leaf reduction has been reached by the cactus 
plants, whose leaves, so far as foliage is concerned, have 
disappeared entirely, and the leaf work is done by the 
