CYSTOPUS 



131 



germination, these fungi can only infect plants during the 

 presence of a certain amount of moisture. All are parasites 

 on plants. 



White rust of crucifers. This fungus (Cystopus candidus, 



FlG. 29. Cystopus candidus. 1, fungus on shepherd's purse ; 2, conidial 

 form of fruit ; 3, oospore ; 4, Cystopus portulacae, conidia and oospores in 

 various stages of development ; 5, Cystopus trogopogonis, on leaf of goat's- 

 beard ; 6, oospore of same. Figs. 1 and 5, nat. size ; remainder highly 

 mag. 



Lev.) attacks nearly all plants belonging to the crucifer 

 family, in every part of the world. Among species of 

 economic value may be enumerated : horse-radish, radish, 



