May, 1910.] The Ohio Powdery Mildews. 167 



Key to the Genera (After Ellis & Everhart). 



Class — AscoM ycetae . 



Order — Perisporiales. 



Family — Erysiphaceae. 



1 . Appendages of perithecia simple, and similar to the mycelium 2 



Appendages different from the myceliuin 3 



2. Only on ascus in the perithecium Spacrotheca 



Several asci in the perithecium Erysiphe 



3. Appendages coiled at tip Uncinula 



Appendages branched at tip 4 



Appendages not branched, swollen at base, with tip straight. . . . 



Phyllactiyiia 



4. Only one ascus in perithecium Podosphaera 



Several asci in perithecium Micros phaera 



Sphaerotheca, Sw. 



Key to the Ohio Species. 



1 . ]klycelium thick, forming persistent patches containing the perithecia 2 

 Mycelium thin or not persistent 3 



2. Mycelium brown. Outer and inner walls of perithecium not 



separating inors-uvae 



3. Perithecia 60-70 /i in diameter; ascus 60 x 42 to 70 x 50 /£, inner 



and outer walls of perithecium readily separating, .phytoptophila 

 Perithecia 58-120 ix in diameter; ascus 45 x 50 to 72 x 90 /i, 

 inner and outer walls of perithecium separating with 

 difiticulty 4 



4. Cells of perithecium averaging 15 /t huntiili 



Cells of perithecium averaging 25 [i hmnuli var. fuliginia 



Sphaerotheca humuli (DC) Burr. Perithecia 58-1 20,« in 

 diameter; cells lU to 2U /«; appendages usually long, straight, sep- 

 tate, dark brown ; ascus usually without stalk, 45 x 50 to 72 x 90 /z; 

 spores 8, 12 X 20 to 18 X 25 /i.' 



Host plants in Ohio Herbarium; Geum canadense, Medina Co., Rubus 

 odoratus, Cuyahoga Co., E. Claassen; Rosa (cult), Columbus, J. G. Sanders; 

 Taraxacum taraxacum, Auglaize Co., J. D. Simkins; Agrimonia eupatoria, 

 Lancaster, W. A. Kellerman. 



Sphaerotheca humuli fuliginea (Schl.) Salm. Perithecia 



averaging smaller than humuli; cells averaging 25 p.; spores 



12 X 20-15 X 25 p. 



Host plants in Ohio Herbarium: Prenanthes alba, Cuyahoga Co., E. 

 Claassen; Bidens frondosa, Columbus, F. L. Stevens, Cuyahoga Co., E. 

 Claassen; Taraxacum taraxacum, Cuyahoga Co., E. Claassen, Columbus, 

 F. L. Stevens. 



Spharotheca mors uvae (Schw.) B. & C. MyceHum dense; 

 perithecia abundant, 75-110 ix in diameter; cells 10-25 /i; appen- 

 dages few, pale, brown, tortuous, length 1-5 times diameter of 

 perithecium; ascus 50 x 70-62 x 92 /t: spores 12 x 20-15 x 25 fx. 



Common on cultivated gooseberries throughout Ohio. 



(luIlibrar 



