CHAPTER XXII 



PEZIZALES 



In the Pezizales are grouped all fleshy Discomycetes. They are 

 characterized by the special structure of the fructifications which, as 

 briefly mentioned in the introduction to the Ascomycetes, are called 

 apothecia. A diagrammatic cross-section of a lichen apothecium is 

 given in Fig. 208. 



This discoid fertile layer (the ascus hymenium or thecium) is desig- 

 nated as t. It generally lies free in the later stages of development, as 



— m 



Fig. 208. — Section of the apothecium of Physcia pulverulenta. (After Nienburg, 1913.) 



shown in Fig. 208 ; in the early stages it is arched over by a special cover 

 layer which appears approximately in the direction of the dotted line in 

 Fig. 208 and only later, with the expansion of the hymenium, is reduced 

 to threads. Forms which, like these, begin their development angio- 

 carpously and end gymnocarpously are called hemiangiocarpous. 



Histologically, the fertile layer is composed of asci which form the 

 ascospores Sp and of the paraphyses p. The asci belong to the diplont, 

 but the paraphyses and the rest of the fructification to thehaplont. The 

 paraphyses show their haploid nature in teratological cases, e.g., Fabraea 



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