202 



PLANT RELATIONS. 



•^i 



Pig. 169. Two species of Achillea on different soils. TIil' one to the Ic'ft was grown 

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



SciIIMPEK. 



extreme of leaf reduction has been reached hy tlic cactus 

 plants, Avhose leaves, so far as folia.i;'c is concerned, have 

 disappeared entirely, and the leaf work is done by the 



