GROUP I. THALLOPHYTA: FUNGI: ASCOMYCETES. 299 



formed round the developing ascus by the growth round it of hyphae 

 from the adjacent mycelium, which cohere to form a layer of 

 parenchymatous tissue. 



In the majority of forms the development of the ascocarp is in- 

 direct. The archicarp gives rise to a greater or smaller number 

 of filaments, branched or unbranched, the ascogenous hyphce (which 

 closely correspond to the ooblastema-filaments of the Rhodophyceae, 

 see p. 270), from which the asci are formed as branches, and which 

 together form a compound sporophore. The asci are developed 

 close together, forming a hymenial layer or group, and may or may 

 not be enclosed, either completely or partially, by an investment 

 formed from the surrounding mycelium. In the latter case, vege- 

 tative hyphae grow in among the ascogenous hyphae and terminate 

 in a number of sterile filaments, the 

 paraphyses, which are situate in the . 

 hymenial layer between the asci. 



The following forms of ascocarp 

 may be distinguished amongst 

 those which have a cellular invest- 

 ment : the cleistothecium ; the in- 

 vestment remains closed until it 

 decays and ruptures to permit of F j &.2O9.A Ascocarp of UntinuU U- 



the escape of the aSCOSpOreS (see cornis (Erysiphese), slightly magnified : 

 1TI . onn cn-t\ J.T- VT m mycelium; / cleistothecium; h in- 



1 igs. 209, 211) : the periihecium ; a yesting filaments . B An ascus from the 



narrow aperture is developed Op- cleistothecium, containing eight asco- 



posite to the hymenial layer (see *Pres (more highly magnified). 

 Fig. 212) : the upotheciutn ; the investment is somewhat saucer- 

 shaped, so that the hymenial layer is fully exposed (see Fig. 213). 



The ascus is in all cases unicellular. It may be either spherical 

 (e.g. Eremascus, Eurotium), or oval, or club-shaped (e.g. Peziza) 

 in form. In some cases the ascospores are ejected with consider- 

 able force ; in others they are set free on the mucilaginous degene- 

 ration of the wall of the ascus. 



The ascopores are formed by free cell-formation (see Fig. 80, p. 122) 

 from a portion only of the protoplasmic contents of the ascus, pre- 

 ceded by nuclear division. The unused portion of the protoplasm is 

 termed the epiplasm, and is rich in a carbohydrate called glycogen. 

 In nearly all cases eight ascospores are formed ; in some cases each 

 of the eight spore-rudiments undergoes division to form a com- 

 pound spore (e.g. Hysterium, Pleospora, etc.), the cells of which 

 may either separate or remain coherent. The form of the asco- 



