io Raymond J. Pool 



species of the genus by its pannose, satiny patches of persistent 

 mycelium in which the perithecia are usually completely im- 

 mersed. S\ pannosa is our very common "rose mildew." It 

 occurs commonly upon the leaves of various wild species and 

 cultivated varieties. Those plants growing in moist or shady 

 situations are most commonly infected. The disease is rarely 

 destructive to any degree with us, but may become so under es- 

 pecially favorable conditions. 



Spaerotheca mors-uvae (Schwein.) B. & C. 



Erysiphe mors-uvae Schwein. 

 Sphaerotheca pannosa Lev. 



Amphigenous; mycelium persistent, when mature forming 

 dense patches composed of sparingly branched, more or less 

 rlexuous, brown hyphae, becoming dark brown and thick-walled ; 

 perithecia gregarious, more or less immersed in the persistent 

 mycelium, sub-globose, 75-110^ in diameter, cells large, at first 

 well defined then becoming obscure, usually about 15-20//,; appen- 

 dages usually few, pale brown, short and tortuous, sometimes 

 more numerous and longer, up to five times the diameter of the 

 perithecium ; ascus elliptical to sub-globose, 70-92 X $0-62^ ; 

 spores 20-25 X 12-15^. 



On: Ribcs aurcnm, R. floridum, R. grossulariae, R. rotundi- 

 folium. 

 Anselmo, Calloway, Grand Island, Lincoln, Loup City, St. Paul, 

 Weeping Water, Wood River. 



This species may become of considerable importance as a 

 disease of cultivated gooseberries and currants during especially 

 favorable seasons. 



Sphaerotheca humuli (DC.) Burrill. 



Erysiplic hum nil DC. 

 Sphaerotheca pruinosa C. & P. 

 Sphaerotheca castagnei Lev. (partim). 



Amphigenous ; mycelium usually evanescent, rarely forming 

 white, orbicular or irregular patches on the upper surface of the 

 leaf ; perithecia scattered or somewhat gregarious, or caespitose, 

 55-120,11 in diameter, cells small, averaging 15^ wide; appen- 

 dages very variable, few to numerous, usually long, often nine 

 times the diameter of the perithecium, more or less straight, sep- 



68 



