202 



CLASS ASCOMYCETEAE 



Qa 



B 



Fig. 67. Ascomyceteae. Types of dehiscence of ascus. (A) Typical operculum. 

 (B) Bilabiate opening, modification of operculum. (C) Inoperculate opening by 

 softening and bursting of apex. (D-G) Contraction of external wall and expansion and 

 lateral rupture of inner wall and discharge of spores in Pyrenophora. (H, I) Ascus of 

 Myriangium duriaei Mont. & Berk. (H) Unexpanded. (I) Inner wall expanded, outer 

 wall contracted. (A-C, after Seaver: The North American Cup-fungi (Inoperculates). 

 D-G, after Atanasoff: Mycologia, 11(3):]25-128. H-I, after Fetch: Brii. Mycol. Soc. 

 Trans., 10:45-80.) 



a typical hymenium, the asci absorb water as they reach maturity and 

 become considerably distended. At the apex there is an area which under- 

 goes softening and stretching until the wall suddenly gives way under 

 the pressure from within the ascus, permitting the escape of the epiplasm, 

 ascospores, and vacuolar liquid while the ascus wall contracts. The asco- 

 spores may be shot off for a distance of several centimeters, many times 

 the length of the ascus. In the family Pezizaceae the apex of the ascus 

 develops a little lid (operculum) which is forced out, often remaining 

 attached by one edge like a trap door. In many Ascomyceteae the whole 

 ascus undergoes digestion at maturity, thus setting free the ascospores in 

 a mucilaginous liquid. Other methods of ascus dehiscence or rupture have 

 been reported by Atanasoff (1919), Falck (1916, 1923), Ziegenspeck 

 (1926), and other investigators. (Fig. 67.) 



The spore fruits of the Ascomyceteae may be classified in general 

 as either apothecia or perithccia or as stromatic structures not referable 

 to either of these forms. In addition there are structures which fit none 

 of these categories such as the naked asci of the order Saccharomycetales 

 and the spore fruits of the order Laboun)eniales. 



In the typical apothecium we find a disk or saucer-shaped or even 



