170 ASCOMYCETES. 



vellaceae. All these groups include forms parasitic on plants, 

 except the last, which is saprophytic. 



(/i/uuioasciis and Ctc/wmi/crs are forms intermediate to the 

 (Jymnoasci and Carpoasci ; they have the asci enclosed in a 

 slimy envelope of mycelial tissue. We place them along with 

 tlie former group, although Brefeld puts them in tlie latter. 



PERISPORIACEAE. 



The I'erisporiaceae are distinguished by having an ascocarp 

 or perithecium which never opens, so that the asci are only 

 e.vposed by decay of the envelope. It includes three families, 

 the Erysipheae, Perisporieae, and Tuberaceae. 



ERYSIPHEAE. 



The members of this family all live as parasites on the 

 outer surface of plant-organs, and have a much-branched, 

 white, septate mycelium, which derives nourishment from tlie 

 interior of the epidermal cells of the host by means of 

 haustoria of various forms. 



The Erysipheae or Mildews appear as white spots and 

 coatings, on which the ascocarps or perithecia appear later as 

 black points. On microscopic examination, the perithecia 

 will Ije found to contain one or many asci, while externally 

 they are beset with thread-like appendages of a definite form 

 and definitely arranged, so tliat they are of great use in 

 determining the various species. 



The fungus passes through the winter l)y means of the 

 ascospores. These do not ripen till spring, when, liberated by 

 decay of tlie ascocarp, they are carried to plants, where they 

 germinate, especially on the leaves, and form a mycelium. In 

 addition, the fungus is propagated throughout the summer Ijy 

 means of conidia produced on special conidiophores hi acropetal 

 series or cliains, of which the distal terminal conidium (acrospore) 

 is the oldest and largest. The ripe conidia fall ofi' and 

 ]troduce a mycelium which is at once fixed in place by the 

 fnriii;iti<iii (.f haustoria. 



Prevention. " Sulphuring " is the method chiefiy used for 

 combating mildew. This consists in dusting powdered sulphur 

 (flowers of sulphur) over the plant threatened with attack. 



