The Erysiphaceae of Nebraska g 



as occurring on Mains mains. In other sections it at- 

 tacks seedlings in the nursery and at such times often 

 causes damage of considerable extent. Nurserymen 

 should watch for its appearance, and adopt means for its 

 control should it become troublesome. 



Sphaerotheca Lev. 



Perithecia sub-globose ; ascus ovate, globose, or elliptical ; 

 spores eight; appendages floccose, not much different from the 

 mycelium, often closely interwoven with the mycelium, brown or 

 colorless, simple or obscurely branched. In some species (S. 

 pannosa) thick-walled, interwoven hyphae form a persistent pan- 

 nose covering for the more or less immersed perithecia. 



KEY TO THE SPECIES 



I. Mycelium persistent, thick ; perithecia more or less immersed in dense 

 patches of the mycelium. 



1. Mycelium shining, white to pale brown S. pannosa 



2. Mycelium dark brown, hyphae tortuous 5". mors-uvac 



II. Mycelium evanescent, not thick and dense, or sometimes more or less 



persistent. 



3. Perithecia scattered or densely gregarious S". humuli 



Sphaerotheca pannosa (Wallr.) Lev. 



Alphitromorpha pannosa Wallr. 

 Erysiphe pannosa Fr. 



Mycelium persistent on the stem calyx, petioles, and sometimes 

 on the mid-ribs of the leaves in dense satiny patches, at first 

 shining white, then gray to buff or light brown, composed of 

 densely interwoven thick-walled hyphae ; perithecia more or less, 

 or completely immersed in the persistent mycelium, globose to 

 sub-pyriform, 80-120/x in diameter, usually about 100/x, cells ob- 

 scure, about i2/x wide; appendages few, sometimes lacking alto- 

 gether, very short, tortuous, septate, pale brown ; ascus broadly 

 oblong to globose, 85-11 5/*, averaging 100X60-70^; spores 8, 

 20-27 X 12-15/*. 



On : Amygdalus persica, Bidcns cermia, Rosa arkansana, R. 

 in ul ti flora, Taraxacum taraxacum 

 Lincoln, Pleasant Dale, Red Cloud, Roca, Weeping Water. 



This species has been quite commonly confused with 5". humuli. 

 The present species is however quite well set off from all other 



67 



