FUNGI.— ASCOMYCETES. 



'03 



section. In all other Ascomycetes a fructification of more or less complex structure and 

 composed of numerous hyphae is formed on the mycelium. It consists of two essen- 

 tially distinct parts, a sterile part which is sometimes of considerable size, and a fertile 

 part which produces the spores. If the hyphae in the fertile part form a continuous 

 layer, this is called the hymenium. In it are usually found, together wiih the asci, a num- 

 ber of unicellular or multicellular hair-like 

 sterile branches of the hyphae, called para- 

 physes. The Ascomycetes may be subdivided 

 according to the character of the fructifica- 

 tion. In the Discomycetes the fructification 

 is a roundish often stalked disk or bowl 

 (Fig. 64, A) in which the hymenium forms 

 the exposed concave upper surface. The 

 fructifications, on the contrary, of the Py- 

 renomycetes are not exposed but open 

 only by a narrow canal or aperture to the 

 outside, and consist of an outer wall and 

 an interior part chiefly composed of hyme- 

 nial tissue lining the inner surface of the 

 wall. In a third subdivision, the Cleis- 

 tocarpous Ascomycetes, the asci are inside 

 the closed envelope of the fructification 

 and are set free by its decay or in some 

 other way. Finally, the Tuberaceae are 

 known by their subterranean tuberous 

 fructifications in which the hymenium is 

 inclosed in sinuous cavities {Tuber). 



The number of spores formed in an 

 ascus varies much ; in the Truffles there are 

 two to three, in other kinds four, most fre- 

 quently eight spores. The ascospores have 

 always a firm cuticularised outer membrane, 

 the exosporium, which is usually beset 

 with small protuberances, raised ■edges, or 

 spike-like projections. An inner mem- 

 brane, the endosporium, bursts or breaks 

 through the exosporium in germination 

 and developes one germ-tube or several to- 

 gether, and these give rise to the mycelium. 

 The mycelium in many cases produces go- 

 nidiophores, as in the Peronosporeae, on 



which gonidia are formed and abscised ; and several of our commonest moulds are 

 nothing but gonidial forms of Ascomycetes, among them PetiiciUium glauciim, Euro- 

 ihiin Aspergillus glauciis, and Botrytis cinerea, which last belongs to Peziza Fuckeliana. 

 Besides the gonidiophores certain special receptacles are often found with or on the 

 fructifications, in which gonidia of varying size are produced {stylospores in pyctiidid, 



Fig. 64. Peziza convexida. A vertical section through 

 the whole fructification ; h hymenium, 5' sterile tissue sur- 

 rounding the hymenium like a cup at the margin q. At its 

 base fine filaments grow out between the particles of the 

 soil. B a small portion of the hymenium ; sh subhyn enial 

 layer of closely woven hyphae ; a—f asci of different ages, 

 between them thinner filaments (the paraphyses) containing 

 red granules. .4 magn. about 20 times, B 550 times. 



