NO. 



PARASITES M ETC ALF 



25 



intermediate and definitive, necessary for each species of rust, present 

 a most interesting condition for distributional studies. The necessity 

 for two hosts in the Hfe cycle of a rust, presents a complication, but 

 one which makes the evidence from the rusts and their hosts more 

 than doubly significant. On the other hand the rusts lack one ad- 



FiG 2— The Pacific Ocean and the adjacent land areas. The dotted lines indicate 

 2000 fathoms depth. (Modified from a map by W. & A. K. Johnston.) 



vantage— their taxonomy is not well understood. This disadvantage is 

 only partly compensated by their large number of forms and their 

 numerous and diverse hosts. When the rusts are more widely and 

 more thoroughly known they will present data of peculiar value in 

 host-parasite studies. 



The smitts of grasses, especially of uncultivated grasses, might 

 furnish data; so also the powdery mildews (Erisiphaceae) and the 

 downy mildews (Peranosporaceae), especially those infesting unculti- 

 vated species. 



