CAPSULAR FUNGI— PYRENOMYCETES 



207 



globose (Fig. 97), concentrically zoned within, and the perithecia 

 immersed at the periphery. In Ustulina the stroma is pulvinate, 

 becoming hollow ; and in NvAninu- 

 laria discoid, and plane or concave, 

 distinctly margined. But in the large 

 genus Hypoxylon, the stroma is either 

 subglobose (Fig. 98) or effused, solid 

 and dark within, closely adnate, of 

 variable thickness, sometimes re- 

 duced to little more than a crust of 

 densely-packed perithecia. All these 

 genera are allied by the possession 

 of a stroma and unicellular brown 

 sporidia, as well as their habit of 

 growing upon decayed wood and 

 dead branches, with the exception 

 of Poronia, most of which flourish 

 upon old dung. 



The family Dothideaceae bear a 

 superficial resemblance to some 

 species of Hypoxylon, but differ in the perithecia being 

 formed from the stroma ; or, in other words, are fertile cavities 

 excavated in the stroma, without definite ostiola. There are 

 three subfamilies, viz. Dothideoideae, Rhytismoideae, and Stigma- 

 toideae. In Dothideoideae and Rhytismoideae the species are 

 compound, and in Dothideoideae the carbonaceous or coriaceous 

 stroma is seldom broadly effused, and the pseudo- perithecia 

 dehisce when mature by an apical pore. The largest genus is 

 Phyllachora, in which the stroma is either shield-like or shortly 

 effused and superficial, and the species are most commonly 

 found growing on leaves, and not rarely whilst they are still 

 living, but sometimes when dead. The sporidia are uncoloured 

 and unicellular in typical forms, but in some of the subgenera 

 they are coloured and continuous, or uniseptate, and in others 

 uniseptate and hyaline, but rarely triseptate and hyaline or 

 coloured. In Dothidea the stroma is erumpent and pulvinate, 

 the sporidia again are variable, according to the subgenera. 

 The species occur, in most cases, on branches, and rarely 

 on leaves, in which feature it differs from Phyllachora. In 



Fig. 96. — Poronia punctata with 

 section (enlarged). Gard. Chron. 



