134 



COMPARATIVE MORPHOLOGY OF FUNGI 



In the simplest case, these fructifications form an undifferentiated 

 mass of tissue, a stroma, on or in which the asci are formed. A fructifica- 

 tion of this sort is called ascostroma or ascoma; it corresponds approxi- 

 mately to the sporodochium and acervulus of the fructifications of the 

 imperfect forms. 



In the higher forms, the hyphal tissue of the stroma undergoes many 

 differentiations both in form and histological structure, and develops to 

 fructifications which form the basis for the systematic classification of 

 the Ascomycetes. All these higher fructifications are referred to two 

 basic forms, perithecium and apothecium. 



The perithecia (Fig. 82) consist of a solid, often pseudoparenchyma- 

 tous, wall and a cavity containing the asci. The more primitive types 



are usually spherical ; the asci lie irregularly 

 in the interior and are only liberated at the 

 decay of the perithecial wall; thus the lower 

 forms are cleistocarpous. In the higher 

 types, they are generally flask shaped; at 

 their top, there is formed by the periclinal 

 arrangement of the hyphal elements during 

 the course of development, a special open- 

 ing (ostiole) whose canal is often closely 

 covered with hyphal ends, periphyses (Fig. 

 82, e). Between the asci (generally basal), 

 there are arranged sterile, haploid, hyphal 

 branches, the paraphyses, which serve 

 chiefly to nourish the growing asci. While 

 young they are rich in reserve materials; 

 during development of the fructification 

 they become vacuolate and in some forms 

 finally disappear. 



The liberation of the ascospores from 

 these flask-shaped perithecia takes place in 

 various ways. In many forms, they are 

 liberated into the interior of the perithe- 

 cium by the disintegration of the asci and are then gradually pushed out. 

 In other forms, they are actively shot out. A good example was described 

 by Zopf (1883), for two relatives of Podospora fimiseda {PI cur age fimi- 

 seda) shown here, P. minuta and P. curvula, which, because of their 

 transparent perithecia, allow one to follow under the microscope the 

 course of spore discharge in the unaltered living perithecium. The asci 

 are cylindrical and at the beginning of the discharge period their upper 

 third broadens. Hereupon one ascus after another elongates, penetrates 

 the opening of the perithecium and projects above the ostiole. Then it 

 bursts and shoots off its top, with ascospores firmly attached to it and to 



in> 



Fig. 82.- — Podospora fimiseda. 

 Perithecium. e, periphyses ; o, asci ; 

 s, ascospores; m, hyphae. (After 

 Tavel, 1892.) 



