Article VI. — Parasitic Fungi of Illinois. Part TT. By T. 

 J. BuRRiLL and F. S. Earle. 



ERYSIPHE.E, Lev. 



(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, indehiscent, 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 Sarcardia) 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 Spluvrotheca pannosa, Lev., the 

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

 satisfactorily proven. 



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