PLASMOPARA. 



131 



PI. vibumi, Peck. On Viburnum (U.S. America). 

 PI. densa (Eabh.). On Scrophularineae (Britain). 

 PI. ribicola (Schroet.). On Ribes ruhrum (U.S. America). 

 PI. epilobii (Eabh.). On Epilobium palustre, and S. parvifolium. 

 PI. obducens (Schroet.). On cotyledons of Impatiem (U.S. America). 

 PI. geranii (Peck.). On Geraniums in America. 



PI. Halstedii, Berl. and de Toni. On Silphium, Rudheckia, Helianthus, 

 and many other American Compositae. 



Sclerospora. 



Mycelium intercellular in living plant-tissues, and deriving 

 nourishment by means of haustoria. The conidiophores are 

 thick, short, and divide at their apices into short broad branches, 

 from each of which a single conidium is abjointed. The conidia 

 in germinating discharge swarming cells. One oospore is formed 

 in each oogonium. 



Sclerospora ^aminicola (Sacc.) lives in several species of 

 Setaria (U.S. America). 



Bremia. 



Mycelium intercellular in higher plants, and nourished by 

 little button-like haustoria. The conidiophores are branched, 

 and at their apical ends 

 become swollen in a char- 

 acteristic manner, so as to 

 resemble a hand held cup- 

 like with the fingers project- 

 ing separately upwards, like 

 the tentacles of Hydra. The 

 conidia are abjointed singly 

 from the tentacle-like pro- 

 cesses, and germinate, emit- 

 ting a germ-tube through a 

 definite thin spot in their 

 coat. Oospores originate 

 singly in oogonia. 



Bremia lactucae, Eeg. 

 {Peronospora ganglioniformis 

 Berk.i) (Britain and U.S. America). The richly-branched conidio- 

 phores appear singly on attacked parts of plants. This fungus 

 ^Cornu, Compt. rend., 1878. 



Fig. ii.— Bremia lactucae. (v. Tuteuf del.) 



