1 66 



PYRENOMYCETES 



[CH 



approximate Diatrype, to the almost spherical cushions of "^ << 2 

 and the erect, simple, or branched stromata of Xyhna (fig. 124) and 

 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 often cover the young stroma with a whitish powder. 



Fig. 123. Hypoxylon coccineum Bull.; the smallest stroma bears conidia, the others perithecia; 

 after Tulasne. 



Poronia punctata 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 covered by a greyish-white 

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

 dots scattered over 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 obtain pure cultures, both from the asco- 

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

 of horse dung. 



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

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

 from both and sometimes also laterally ; the mycelium is at first much more 

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

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



