274 CLASS ASCOMTCETEAE 



isms do not rightly belong here but in the Pseudosphaeriales. Periphyses, 

 i.e., paraphysis-like threads at the edge of the hymenium but not inter- 

 mingled with the asci, are much more frequent. The asci may reach 

 maturity at different ages within the perithecium a phenomenon not rare 

 in the apothecial forms also. The ascospores may be expelled violently 

 through a pore (not an operculum) at the apex of the ascus or the osmotic 

 pressure within may rupture the ascus at its middle so that the upper half 

 is forced off, or the outer layer may break near the apex and contract, 

 allowing the inner layer to expand and finally burst, or the asci, paraph- 

 yses, etc., may be digested within the perithecium leaving the ascospores 

 embedded in the gummy mass. This absorbs water during a rain and 

 swells, emerging from the ostiole, where the gum is dissolved away and 

 the spores carried off by the currents in the film of rain water or splashed 

 off in the droplets caused by the striking rain drops. In some genera only 

 the ascus stalk digests, the resultant gummy mass containing the un- 

 changed bodies of the asci. Nannfeldt and some others before him have 

 suggested that in the true Sphaeriales the asci discharge their ascospores 

 through an apical pore and mostly do not undergo autodigestion and 

 that forms in which the latter occurs and no paraphyses are present 

 belong in the Aspergillales or some other order. 



The asci vary from cylindrical to club-shaped or obovate, sometimes 

 being drawn out below into a narrow stalk-like portion. The ascospores 

 may lie in one or more rows in the ascus or in a ball-like cluster. The num- 

 ber is mostly eight but in a few cases only four or even fewer spores are 

 formed and in others 16 to 32 or even as many as 256 or 512 are reported. 

 They vary exceedingly in size, shape, structure, and color. They may be 

 colored or hyaline, 1-celled, 2-celled, several-celled in one row (phrag- 

 mosporous), many-celled by both cross and longitudinal walls (muriform 

 or dictyosporous), long and slender, or even tetrahedral. The recurrence 

 of certain spore and ascus types in what the current classifications con- 

 sider to be widely distant families has led (and probably rightly) some 

 mycologists (e.g., Vincens, 1918, 1921; Julian Miller, 1928; von Hohnel, 

 1918; Wehmeyer, 1926; and others) to attempt to amend the classifica- 

 tion so as to bring together those forms with similar asci and spores. 



The current classifications place first in this order those families in 

 which the perithecia stand separately upon the surface of the substratum 

 or but slightly sunken in it. Two of these families have very thin peri- 

 thecial walls. These are the Firaetariaceae (Sordariaceae) with naked or 

 almost naked perithecia and the Chaetomiaceae with the i)erithecia 

 covered with long hairs and with a special tuft of much longer hairs about 

 the ostiole. The fungi in both families grow on dung or decaying plant 

 tissues. They are distinguished further by the fact that the asci of the 

 former expel the ascospores through the ostiole while in the latter the 



