1 66 



PYREXOMYCETES 



[CH. 



approximate Diatrv/'i.to the almost spherical cushions of //i/'(U;i7(VM fig. 123) 

 and the erect, simple, or branched stromata oi Xrlaria (fig. 124) and its 

 allies. The perithecia are arranged just below and at right angles to the 

 surface of the stroma; their development may be preceded by the formation 

 of conidia which otten co\er the \'oung stroma with a whitish powder. 



Fig. 123. Ilypcxyhti LOicijuurn Hull.; ihc -<m.-illcst ^'lonKi lit:ir^ C'jnitJia, the iiiliLr^ j>t.'rillieci,^ ; 



after Tiila>ne. 



Poroiiia piiiictata occurs on old horse dung; the stromata are about 

 I cm. in height, stalked and expanded above into a cup or disc (fig. 125), 

 which, in the earlier stages of development, is cox'ered b\- a gre}ish-white 

 film of conidia; later the ostioles of the numerous perithecia appear as black 

 dots scattered o\"er the surface of the disc (fig. 126). The asci, when ripe, 

 protrude through the ostiole so that the dark brown spores are shed outside 

 the perithecium. 



Dawson was able readily to nbtain pure cultures, both from the asco- 

 spores and from the conidia, on 10 per cent, gelatine made up with flecoction 

 of horse dung. 



The ascospore forms a single lateral germ-ttibe, which develops septa 

 and branches freely. The conidia produce germ-tubes from cither end or 

 from both and sometimes also laterally; the m_\celium is at first much more 

 delicate than that derived from the ascospores but soon becomes indistin- 

 guishable from it. Branches arise fn.un points just below the cross walls; 



