The Erysiphaceae of Nebraska 7 



Podosphaera Kunze. 



Perithecia globose or somewhat flattened ; ascus globose to 

 obovate; spores eight; appendages confined to a small apical 

 group or scattered over the upper half of the perithecium, dich- 

 otomously branched at the tip, branches simple and straight, or 

 more commonly in our species swollen and knob-like. 



KEY TO THE SPECIES 



I. Appendages of one kind. 



1. Appendages more or less scattered over the upper half of the 



perithecium P. oxyacanthae 



2. Appendages confined to a small group near the apex of the 



perithecium P. tridactyla 



II. Appendages of two kinds P. leucotricha 



Podosphaera oxyacanthae (DC.) De Bary. 



Erysiphe oxyacanthae DC. 

 Podosphaera kunzei Lev. 



Amphigenous ; mycelium variable, persistent in patches, or 

 wholly evanescent; perithecia scattered, or more or less clustered 

 in close groups, sub-globose, 60-90/t in diameter, cells 10-18/* 

 wide ; appendages spreading, sometimes equatorially placed, 5-30 

 in number and from | — 10 times the diameter of the perithe- 

 cium, dark brown for about half their length, septate, tips 2-4 

 times dichotomously branched, branches usually short and equal, 

 ultimate branches swollen and more or less knob-like, ascus 

 broadly obovate, oblong, or globose, variable in size 58-90 X 

 45-75^ thick-walled; spores 8, variable in size 18-30 X 10-17/x. 



On: Amelachier botryapium, Primus americana, P. besseyi, 

 P. cerasus, P. demissa, P. scrotina, P. virginiana. 

 Bloomington, Crete, Ewing, Grand Island, Johnstown, Lincoln, 

 Long Pine, Spencer, Naponee, Wabash, Weeping Water, 

 Orleans, Valentine, Callaway, Red Cloud. 



This is our most common mildew on wild and cultivated forms 

 of Primus. On Prunus ccrasus the perithecia are usually hy- 

 pophyllous, but on the other hosts they are usually epiphyllous 

 or amphigenous. 



Podosphaera tridactyla (Wallr.) De Bary. 



Alphitromorpha tridactyla Wallr. 

 Podosphaera kunzei Lev. (partim) 



65 



