106 A Monograph of the Erysiphaceae 



Hypophyllous, rarely amphigenous ; mycelium evanescent, or 

 subpersistent on the upper surface of the leaf and sometimes forming 

 definite spots ; perithecia usually scattered, sometimes gregarious, 

 rounded-lenticular, 160-225 11 in diameter, rarely only 125-160 

 p., averaging 190 /j, cells obscure, irregular, 10-14 /^ wide; ap- 

 pendages very numerous, usually densely crowded, just falling 

 short of the diameter of the perithecium, simple, smooth, aseptate, 

 rather delicate, about 5 fi wide, thin-walled and hyaline throughout^ 

 apex simply uncinate; asci 9-26, usually about 15, narrowly 

 ovate or cylindrical, sometimes ovate -oblong, with or without a 

 short stalk, 68-86 x 29-40 ii; spores 8, sometimes 7, 18-22 x 

 10-14 <"• 



Hosts.— -Acer dasycarpwn, A. Pennsylvanicum (60), A. rnbrum, 

 A. saccharhuim, A. spicatinn. 



Distributioji. — North America : United States Mai 



M 



M 



M 



{Z^l), Iowa. Canada — Ontario. 



"This species is related to U. biconiis \_U. aceris], from which 

 it is distinguished by its hypogenous habit, more numerous spo- 

 rangia and always simple appendages. It usually occupies the 

 whole under-surface of the leaf" (Peck, 25 Rep.) 



This distinct and endemic species, which apparently takes the 

 place of the European 17. aceris on the maples of North America, 

 \s somewhat intermediate between U. aceris and U. salicis, agree- 

 ing with the former species in the S-spored asci and large perithecia, 

 and with the latter in the numerous, simple, thin-walled appen- 

 dages. From U. aceris, var. Tulasnei it differs in the more or less 

 evanescent mycelium, and thin-walled appendages. When well- 

 developed the appendages cover the whole of the upper half of the 

 perithecium. 



7. U. parvula Cooke & Peck 



U. parznda Cooke & Peck, Journ. of Bot. II. i ; 170. 1872; 

 Burr & Earle, Bull. 111. State Lab. Nat. Hist. 2 : 409. 1887 ; Sacc. 

 Syll. Fung. 9 : 367. 1891 ; Atkins. Journ. Elisha Mitch. Sci. Soc. 

 7: 67. 1891 ; Burr.; Ell. & Everh. N. Amer. Pyren. 18. 1892. 



U. 



7: 215. 1872. 



Amphigenous ; mycelium evanescent ; perithecia usually hypo- 



86- 



eter, averaging 98./^ cells about 10 fx wide; appendages numer- 



