202 



PLANT EELATIONS. 



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 



