ASCOMYCETES EUASCI PERISPORIALES 



269 



parasitic fungi, like the powdery mildew of the grape (Uncinula spiralis), 

 mildew of lilac (Microsphaera Alni), mildew of sunflower (Erysiphe Cichor- 

 acearum}, mildew of cherry (Podosphaera tridactyla). 



Erysiphe. (Hedw.) 



Perithecium containing several asci, appendages with simple threads, sim- 

 ilar to and frequently interwoven with the mycelium. A small genus of 20 

 species of wide distribution. 



Erysiphe communis. (Wallr.) 



Amphigenous, mycelium abundant, persistent, or sometimes evanescent ; 

 perithecia variable in size and reticulate, appendages variable in length, often 

 long; asci 4-8 or more, ascospores 4-8. 



Distribution. Found on a large variety of different hosts but common on 

 plants of the order of Leguminosae, especially the forage plants like the pea 

 (Vicia satira), bean, clover and other members of the clovers. 



Fig. 91. Powdery Mildews. 1-3. Sphaerotheca Castagnei on Hop. 1. Part of leaf 

 of hop with perithecia shown in the form of dots. 2. Perithecia with tortuous appendages 

 (ap) x 175. 3. Ascus with spores within the ascospores x 380. 4. Powdery Mildew on 

 Cherry (Podospliaera tridactyla), conidiophore bearing conidia (c). 5-7. Microthyriwm 

 microscopicum. 5. On leaf. 6. Perithecium, greatly magnified. 7. Ascus and ascospores. 

 1 after Wettstein. 2-4 after Tulasne. 5 after Lindau. 6-7 after Winter. 



