Aetiolb YL— Parasitic Fungi of Illinois. Part II. By T. 

 J. BuREiLL and F. S. Eaklb. 



ERYSIPHE^, Mv. 

 (Ann. Sci. Nat, Ser. III., Tome XV.) 



On living plants. Mycelium superficial, consisting of 

 numerous branching, septate, usually white, much interwoven 

 threads, which extend widely over the epidermis of the host, 

 adhering to it by means of haustoria; conidia simple, color- 

 less, cylindrical, oval or ovate, borne one above the other, 

 on erect, simple, septate colorless hyphae; perithecia seated 

 singly on the mycelium, membranaceous, indehiseent, globose 

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

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

 like appendages; asci arising from the base of the perithecium, 

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

 ular, usually pedicellate, containing 2-8 spores; spores (except 

 in Saccardia) simple, colorless, granular, oblong or oval. 



The Erysiphece, commonly known as "white mildews" 

 or "blights," may be easily recognized by the white, dusty 

 or web-like coating they form on the, leaves, or other succu- 

 lent parts, of many common plants. They frequently grow 

 throughout the summer, but, usually, only reach their full 

 development in the fall, when the perithecia, or little fruit- 

 balls, may be seen like minute black or dark brown dots scat- 

 tered over the whitened surface of the leaves. 



The very abundant mycelium consists of numerous slender, 

 white or colorless, septate threads, that branch widely, and ex- 

 tend over the leaf in every direction, frequently crossing and 

 interlacing. These threads are usually pressed close to the 

 host, but they do not themselves enter it.* They send out at 

 intervals, however, short special branches called haustoria, that 



* It is, held by some writers that in Sphseroiheca pannosa, L(5v., the 

 jnycelium does sometimes enter the tissues of the host, but this is not 

 satisfactorily proven. 

 1. 



