36 



ASCOMYCETES 



[CH. 



number of spores is increased. There are sixteen or thirty-two in the species 



of Rhyparobius, sixteen to 

 sixty-four in Podospora pleio- 

 spora, and in Podospora curvi- 

 colla one hundred and twenty- 

 eight. 



The arrangement of the 

 spores in the ascus is usually 

 constant for a given species ; 

 they may be uniseriate, in a 

 single row; biseriate, in two 

 rows somewhat irregularly 

 placed, in which case they are 

 often uniseriate when young; 

 fasciculate if long narrow 

 spores are arranged in a pa- 

 rallel bundle; or inordinate if 

 they show no regular arrange- 

 ment. In the simplest forms 

 the spores are liberated by the 

 decay of the ascus walls, and, 

 where a definite fruit body is 

 present, they remain for a 

 time enclosed by its outer 

 layers. In other cases, in- 

 cluding the majority of Dis- 

 comycetes and Pyrenomy- 

 cetes, the ascus opens explosively either by an irregular tear or by dehiscence 

 along a definite line, and the spores are shot out in a jet of liquid while the 

 deflated ascus sinks back to about half its size (figs. 4, 5). In forms with an 

 explosive mechanism the ascus often elongates considerably during the latter 

 part of its development; the spores are arranged at the upper end and either 

 float suspended in the fluid contents of the ascus, or are attached to the 

 apex and to one another by cytoplasmic strands (Sordaria, Podospora, 

 fig. 2 e). 



The explosive ejection of spores from different asci may be simultaneous 

 or successive ; in a certain number of forms with an exposed hymenium 

 of parallel asci (Pezizales, Helvellales, Exoascales) successive discharge 

 takes place under moist conditions, but any disturbance leading to rapid 

 loss of water causes the simultaneous liberation of a number of spore 

 masses, so that the cloud of spores is visible even to the naked eye. This 

 phenomenon, which is known as "puffing," may be brought about under 



Fig. 3. Humaria rutilans (Fr. ) Sacc; hymenial layer 

 showing asci and paraphyses in various stages of develop- 

 ment, x 400. 



