84 



Forest Club Annual 



Fig. 13. Uncinula macrospora on the Elm. Notice the 

 colonies showing radial growth. 



Erysiphaceac : 



These parasitic fungi are commonly known as "Powdery 

 Mildews" because of the powdery nature given by them to the 

 surface of the infected tissues. The "powder" is in reality com- 

 posed of myriads of the asexual conidiospores that are formed 

 in chains on simple scattered conidiophores. The filamentous, 

 silky- white, septate mycelium often forms conspicuous colonies 

 over the leaves of some of our forest trees such as the Elm, 

 Willow, and Cottonwood. See fig. 13. Upon the same mycelium 





