CHAPTER XVII 

 MILDEWS AND RELATED FUNGI 



Suborder D. Perisporiineae. — The mycelium of the fungi which 

 belong to this suborder is filamentous, superficial, light- or dark- 

 colored, rarely forming a stroma. The fruit bodies are superficial, 

 spheric to egg-shaped without a pore and break up irregularly. Peri- 

 thecia are usually dark-colored and in many cases surrounded by 

 accessory hyphae, or suffulcra. The asci are spheric, egg-shaped, or 

 elongated, and range within the closed perithecia from one to many 

 in number. Paraphyses are usually absent. The following families 

 are recognized: 



A. Perithecium spheric, poreless or breaking irregularly at the top. 



(a) Aerial mycelium white, perithecium with appendages or suffulcra ; 

 accessory spores belonging to the genus Oidium. 



I. Erysiphaceae. 



(b) Aerial mycelium absent, or dark-colored, perithecia without 

 appendages or suffulcra, accessory spores not belonging to 

 Oidium. 



2. Perisporiace^. 



B. Perithecium peltate flat, opening at top by a round pore. 



3. MlCROTHYRIACE^. 



Family i. Erysiphace^. — The fungi of this family are popularly 

 called "white" or "powdery mildews." During the summer their 

 conidial fructifications (Oidium) are found on hops, maples, peas, 

 roses and vines imparting to the surface of the host a dusty appearance, 

 due to the white conidiospores. Later in the summer, the globular 

 dark brown, or black, perithecia appear and these are provided usually 

 with appendages, or suffulcra, which are frequently branched in a way 

 characteristic of the different genera of the family. The white 

 mycelium upon which the fruit bodies arise is truly parasitic, for short 

 haustoria are formed which pierce the wall of the epidermal cells, and 

 swell out into a bladder-like form for absorptive purposes. The haus- 



i.'54 



