Microsphaera Alni (LILAC MILDEW) 



A. Classification: 

 Division I. Thallophyta. 



Subdivision B. Fungi. 



Class IV. Ascomycetes (Sac Fungi). 

 Order. Perisporiales. 

 Family. Erysiphaceae. 

 Genus. Microsphaera. 

 Species. Alni (Wallr.) Wint. 



B. Habitat: 



i. Examine the specimens available, and record what 

 kinds of trees and other plants are affected by this 

 common fungous disease. What is the significance 

 of the specific name Alni? 



C. Naked-eye Characters: 



1. What causes the dusty or "mildewed" appearance 

 of the infected leaves? Are both sides of the leaf 

 affected? Describe the distribution of the infec- 

 tion over the leaf-surface. 



2. What are the minute yellowish or blackish bodies 

 seen among the white threads? Make a drawing 

 (natural size) to illustrate your observations. 



D. Microscopic Characters: 



i. Scrape off some of the whitish fungous threads 

 (the mycelium), and examine with low and high 

 powers. Strip off the epidermis and try to find the 

 sucker-like organs (haustoria) which grow down into 

 the epidermis and absorb nourishment. Draw 

 them, if found. 



1 See footnote, p. 135. 



136 



