LICHENS. 315 



typically unicellular, but often become divided up so as to be multi- 

 cellular when ripe (this also occurs in many Ascomycetes). In the 

 apothecia of both Ascomycetes and Lichens, the spores are often 

 forcibly thrown out to a distance, by the pressure due to the 

 swelling of the asei and paraphases, acting against thfi firmer rim of 

 the apothecium. 



Cut vertical sections of the apothecium of Ascobolus or 

 Peziza. The former occurs on horse or cow dung kept for 

 a few weeks under a bell-glass ; various species of Peziza 

 (often red or orange-coloured) occur on rotten twigs or 

 dead wood, P. stercorea on cow dung. Note (1) the densely 

 interwoven hyphae, forming on the lower side a compact 

 tissue from which attaching and absorbing hyphae run into 

 the substratum; (2) the hymenium, consisting of long 

 narrow paraphyses and thicker asci, each ascus with 

 eight spores ; (3) the compact sub-hymenial layer below 

 the hymenium. 



