V] 



SPHAERIALES 



169 



The perithecium is initiated by the development of a coil of large, 

 deeply-staining cells forming the archicarp. It arises amongst the vegetative 

 filaments of the stroma, forms a couple of loops and is continued towards 

 the surface of the stroma as a. slender multicellular trichogyne (fig. 127 a). 

 At an early stage the coiled portion becomes surrounded by a knot of small, 

 densely-staining hyphae ; later the trichogyne disappears, degeneration 

 progressing from the base to the apex ; the investing filaments grow more 

 actively on the side of the archicarp towards the surface of the stroma, so 

 that the young perithecium becomes pear-shaped' (fig. i2j b, c); further 

 growth renders it hollow, and the upper part becomes lined with delicate 

 periphyses (fig. 127 d). At the base of the developing perithecium is a group 



Fig. 127. Poronia punctata (L.) Fr. ; u. archicarp, x 275 ; b. t. and d. young perithecia, x 205; 



after Dawson. 



of stout, deeply-staining hyphae, from which the asci arise and which occupy 

 the position of the coiled archicarp in earlier stages. Later the base and 

 sides of the perithecium are covered by numbers of filiform, septate para- 

 physes, and amongst these the asci develop. 



It seems pretty clear that the trichogyne now no longer functions ; this 

 is borne out by the fact that degeneration proceeds from its base upwards 

 and not from its apex, as might have been expected if a male nucleus were 

 travelling down. It is probable, though it has not actually been demon- 

 strated, that the ascogenous hyphae are derived from the archicarp, but in 

 view of the complete degeneration of this organ in Gnomonia, it is not safe 

 to conclude without further evidence that it is still functional in Poronia 

 punctata. The species deserves further investigation, especially from this 

 point of view. 



In both Xylaria and Hypoxylon the young stroma is covered by a tangle 



