3. SPH.ERIACK.ti. roritliceiii mostly with a distinct (»stioliiiii, 

 of vnrioiis odiisistciicc, Uiit not ciiriiosc or ii.c'iiilti'iiiiiictMM'iiriiosc. Iti-own 

 or Itliicix. Slroiua. wiicn picsont. not rai'nosc, dnrli colored outside, 

 and ol'ttJii white within. 



4. I)()THIDE.\('K.t]. .^tionia always present, not fleshy, Idack, 

 or dark-c<dored. Perithocia mostly reduced to mere cells in the 

 stroma, und not separaldo from it. Ostiolum always present. 



PERISPORIACE.E. 



This suiujrdor is divided into two lamilies. The Enj^iphcm and 



FAMILY. ERYSIPHE.*:, Lev. 



Ann. Sci. Nat. Str. III. Tome XV. 



On livinir plants. ^lycelium sn|terlicial, consisting' of nunioroui* 

 l»ranchin<>', septate, usually white, much intei'woven threads, which ox- 

 tend widely over the epidermis of the host, adherinji' to it liy means (jf 

 lisiustoria. Conidia simple, colorless, cylindrical, oval or ovate, liornc 

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

 thocia seated singly on the mycelium, memltranaceous, indehiscent, 

 globose or sometimes dej)ressed, at first colorl(»ss, then yellow, becom- 

 ing dark blown or black when mature, bearing various thi'ead-like, 

 radiating appendages. Asci arising from the Itase of the perithecium. 

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

 usually i)edicellate, containing 2-8 sporidia, which arc simple, color- 

 less, granular, oblong or oval. 



The Et't/Htpheie, commoidy known as "white mildews" or 

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

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

 mon plants. They freijuently grow throughout the summer, but 

 usually oidy reach their full development in the fall, when the j)eri- 

 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, freiiuently 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, sj)ecial 

 branches called haustoria, that penetrate the epidermal cells, serving 

 for the secure attachment of the fungus, and j)robably also for its* 



