176 THE FUNGI WHICH CAUSE PLANT DISEASE 



The species is cosmopolitan and among its numerous hosts are 

 the economic genera Dipsacus, Fragaria, Humulus, Phlox, Pyrus, 

 Rosa, Ribes, Rubus, Scabiosa, Spirea and Viola. 



It is a common rose mildew of America and England and is also 

 especially destructive on the strawberry. 

 S. humili var. fuliginea. (Schl.) Sal. 



Perithecia usually smaller than in the last, sometimes only 50 n 

 in diameter, wall usually harder and more brittle, cells larger, ir- 

 regularly shaped, averaging 25 fi; 

 appendages usually short, pale 

 brown; spores 20-25 x 12-15 /i. 



Throughout Europe, Asia and 

 North America. 



It is recorded on Arnica, 

 Calendula, Coreopsis, Fragaria, 

 Gaillardia, Impatiens, Phlox, 

 Scabiosa, Taraxacum, Verbena, 

 Viola, and several other non- 

 economic genera. 

 S. pannosa (Wallr.) I^v.'"'^ 

 Fio. 126.^. mors-uvffi, a perithecium MyceUum persistent, forming 



discharging its single ascus which . ' ^ 



contains eight spores. After Long- dense satmy patches on the 



stem, calyx, petiole, and rarely 

 on leaves, at first shiny white, then becoming gray, buff or 

 rarely brown; perithecia more or less (usually completely) im- 

 mersed in the persistent mycelium, globose to pyriform, 85-120 fi 

 in diameter, usually about 100 >; cells obscure, about 10 n wide; 

 appendages few, often obsolete, very short, tortuous, pale brown, 

 septate; ascus broadly-oblong to globose, 88-115 n, averaging 

 100 X 60-75 fi; spores 20-27 x 12-15 /i. 



Conidia (=Oidium leucoconium) ovoid, 20-30 x 13-16 fi, 

 hyaline; conidiophores short. 



Hosts: peach and rose; cosmopolitan. 



The conidia are very common on the rose, but the perithecia 

 are rare. What often passes for this species on roses in America 

 is in reality S. humili." 



S. mors-uvae (Schw.) B. & C.^^^ 



The mycelium at first white, is exceptional among the Erysipheae 



