PLATE III 



Fig. I. — Cystopus candidus on Lepidium virginicum. This plant was chopped out 

 of the frozen ground on February 22, 1911, and brought into the greenhouse. There 

 days later white pustules of Cystopus candidus began to appear on the leaves. 



Fig. 2. — A, The two leaves at the left show the amount of sporulation of Peronospora 

 parasitica on leaves of Lepidium virginicum; B, the two leaves at the right show Cystopus 

 candidus fruiting on leaves of Capsella bursa pastoris. The pustules developed from 

 mycelium alive in the plants in the winter of 191 1. 



Fig. 3. — Peronospora viciae on Vicia sepium. A systematic infection of the dowTiy 

 mildew collected on April 15, 19 14, in the District of .Columbia. This plant was 

 badly infected when coming through the ground. 



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