The Erysiphaccac of Nebraska 17 



Burwell, Crete, Grand Island, Lincoln, Long Pine, Red Cloud, 

 Roca, Scotia, Valentine, Wabash, Weeping Water. 



Microsphaera grossulariae (Wallr.) Lev. 



Alphitronwrpha grossulariae Wallr. 

 Erysiphc grossulariae (Lev.) De Bary. 



Epiphyllous or amphigenous ; mycelium evanescent, or sub- 

 persistent, thin and effused on the upper surface of the leaf ; peri- 

 thecia scattered or densely gregarious, globose-depressed, very 

 variable in size, 60— 130//, in diameter, cells 14-20/1 wide; appen- 

 dages 5-22, i-if times the diameter of the perithecium, color- 

 less, aseptate, tip 4-5 times closely and regularly dichotomously 

 branched, branches of the first and second orders very short, all 

 of the segments deeply divided, ultimate branches forming a 

 narrow fork, tips not recurved ; asci 4-10, broadly ovate or ob- 

 long, usually with a very short pedicel, 46-62 X 28-38/1 ; spores 

 4-6, variable in size, 20-28 X 12-16/x. 



On: Sambucus canadensis. 

 Crete, Fremont, Grand Island, Weeping Water. 



While with us M. grossulariae is confined to the elder, Sambu- 

 cus canadensis, in Europe it attacks the cultivated goose-berry, 

 and sometimes becomes quite destructive. It has not been re- 

 ported on Ribes from Nebraska as yet. Our common goose- 

 berry mildew is Sphacrotheca mors-uvae. 



Erysiphe Hedw. 



.Perithecia globose, or globose-flattened; asci several, 2—8- 

 spored ; appendages floccose, simple or obscurely branched, usu- 

 ally more or less similar to the mycelium and interwoven with it. 



KEY TO THE SPECIES 



I. Mature perithecia not containing spores on the living host. 



1. Perithecia large, 140-280/*, in diameter, more or less immersed 



in the lanuginose, persistent mycelium .... E. graminis 



2. Perithecia smaller, 80-140 M, not immersed in the mycelium. 



1) Haustoria lobed, asci 8-spored E. galcopsidis 



2) Haustoria not lobed, asci 2-spored E. cichoracearutn 



II. Mature perithecia containing spores on the living host. 



3. Appendages often interwoven with the mycelium, 



E. polygoni 



4. Appendages densely interwoven with the mycelium, haustoria not 



lobed E. cichoracearum 



75 



