3. SPHJ3RIACEJ). Perithccia mostly with a distinct ostiolum, 

 of various consistence, hut not carnose or membranaceo-carnose, brown 

 or black. Slroma, when present, not carnose, dark colored outside, 

 and often white within. 



4. DOTHIDEACEJ]. Stroma always present, not fleshy, black, 

 or dark-colored. Perithecia mostly reduced to mere cells in the 



/ 



stroma, and not separable from it. Ostiolum always present. 



PERISPORIACEJ]. 



This suborder is divided into two families. The ErysipJiece and 

 Perisporiece. 



FAMILY. ERYSIPHE.E, Lev. 



Ann. Sci. Nat. Ser. Ill, Tome XV. 



On living plants. Mycelium superficial, consisting of numerous 

 branching, septate, usually white, much interwoven threads, which ex- 

 tend widely over the epidermis of the host, adhering to it by means of 

 haustoria. Conidia simple, colorless, cylindrical, oval or ovate, borne 

 one above the other, on erect, simple, septate, colorless hyphae. Peri- 

 thecia seated singly on the mycelium, membranaceous, indeluscent, 

 globose or sometimes depressed, at first colorless, then yellow, becom- 

 ing dark brown or black when mature, bearing various thread-like, 

 radiating appendages. Asci arising from the base of the perithecium, 

 delicate, thin-walled, colorless, oblong, oval, ovate or suborbicular, 

 usually pedicellate, containing 2-8 sporidia, which are simple, color- 

 less, granular, oblong or oval. 



The Erysiphece, commonly known as "white mildews" or 

 1 (lights," may be easily recognized by the white, dusty or web-like 

 coating they form on the leaves, or other succulent parts of many com- 

 mon plants. They frequently grow throughout the summer, but 

 usually only reach their full development in the fall, when the peri- 

 thecia, or little fruit-balls, may be seen by good unaided eyes, scattered 

 over the whitened surface of the leaves. 



The very abundant mycelium consists of numerous slender, white 

 or colorless, septate threads that branch widely, and extend over the 

 leaf in every direction, frequently crossing and interlacing. These 

 threads are usually pressed close to the host, but they do not them- 

 selves enter it. They send out at intervals, however, short, special 

 branches called haustoria, that penetrate the epidermal cells, serving- 

 for the secure attachment of the fungus, and probably also for its 



