104 



INTRODUCTION TO THE STUDY OF FUNGI 



partially and obscurely known, rather from their results than 

 from their own nature. 



The second type of reproductive structure is the ascigerous, 

 in which the spores are not produced naked at the extremities 

 of sporophores, but are enclosed within special membranaceous 

 cylinders or sacs called asci, without sporo- 

 phores, and are dispersed by rupture of the asci 

 when mature (Fig. 46). Generally they are all 

 included under one term as Ascomycetes, but 

 three subdivisions are recognised as furnishing 

 important distinctions, which may be referred 

 to with advantage in a general purview. The 

 largest subdivision is that in which the re- 

 ceptacle which encloses the fructification is 

 always closed during growth and development, 

 and only perforated or ruptured at maturity 

 for the dispersal of the spores. The typical 

 form consists of a minute, subglobose receptacle 

 or perithecium, which may be fleshy, mem- 

 branaceous, leathery, or carbonaceous, and 

 either superficial or immersed. Externally 

 they are often black or dark-coloured, and are 

 seated upon a more or less distinct mycelium. 

 In some cases a number of them are associated 

 together, and sunk beneath the surface of a 

 common stroma, which is consequently larger 

 and more conspicuous. In all cases the 

 interior of the receptacle is filled with a 

 mass of parallel tubes, closed at each extremity, 

 and containing normally eight, but sometimes 

 four or sixteen, or rarely a larger number of minute spores 

 or sporidia. Side by side with these tubes or asci will 

 commonly be found a great number of thread-like filaments, 

 possibly abortive asci, but known as paraphyses. The upper 

 extremity of the receptacle is sometimes elongated into a neck 

 which is perforated, or the neck is suppressed and the apex 

 of the perithecium is , perforated to admit of the discharge of 

 the mature sporidia. This subdivision goes by the name of the 

 Pyrenomycetes. 



Asci and 



Fig. 46, 



paraphyses. 



