Sketch of the Class Fungi. 



231 



stein (stipes) is distinguished from the inflated portion which is called 

 clavula. The stroma when horizontal assumes also different forms, 

 but these, as we may easily suppose, are less various. Nevertheless, 

 the little cushions or discs which it forms upon the bark, or between 

 the bark and the wood, or even upon the naked or decomposed wood, 

 are byssoid, pulverulent, fleshy or carbonaceous and brittle. Fre- 

 quently the matrix supplies its place. Its colour is as variable as that 

 of the vertical stroma. In the genus Thamnomyces it is from the 

 matrix that the cells or perithecia are formed. In Dothidea it is in 

 the cavities of a pseudostroma furnished by the matrix that the nuclei 

 are immediately enclosed. Some genera have a cup-shaped stroma 

 (Atractobolus, Cordierites, Mont.). The stroma is frequently obli- 

 terated or wanting, in which case the species is reduced to a peri- 

 thecium. This is entire or dimidiate and hemispherical, with or 

 without an ostiolum. In Sphcerice there is constantly an ostiolum, 

 which assumes however various directions. According as the peri- 

 thecia are divergent, erect, convergent or horizontal, they are said 

 to be peripheric, hypopheric, amphipheric or peripheric. They are 

 more or less immersed in the stroma, being sometimes quite con- 

 cealed, sometimes free and resting on it merely with their base. 

 They are monostichous or polystichous, according as they are placed 

 in a single curve, or several more or less concentric layers. In cer- 

 tain genera they are disposed circularly round a central axis (Cyti- 

 spora). The perithecia are dimidate, astomous, and reduced some- 

 times to a simple disc as in Sacidium. When they are furnished with 

 an ostiolum, it is papillary or rostrate, and traversed by a canal which 

 places the nucleus in contact with the air, and at length makes way 

 for the sporidia. But the ostiolum is wanting in many whole tribes, 

 and then the dehiscence of the perithecium takes place by means of 

 a simple pore, or, as in Dichenea, by one or more irregular clefts. In 

 Apiosporea it is indehiscent, that is to say, it does not burst spon- 

 taneously. In Eustegia the dehiscence is transverse. 



Many Pyrenomycetes have the perithecia covered with a more or 

 less close and dense byssoid down, the remains of the veil which 

 clothed them when young, or of the stroma in which they were de- 

 veloped ; others have their whole surface or base rough with hairs. 

 The walls of the perithecia vary much as to consistence, though this 

 bears in general some proportion to that of the stroma. They are 

 hard, horny, corky, carbonaceous or else thin membranous, papyra- 

 ceous, and capable of collapsing after the evacuation of the nucleus. 

 In general they are composed of one or more layers of thick cells, so 

 condensed in the carbonaceous species that there are scarcely any 

 intercellular passages. 



The nucleus, which is either of an opal- white or coloured, is com- 

 posed of simple or branched continuous or jointed threads, between 

 which are placed the asci. They are generally convergent, and con- 

 tain a greater or less number of sporidia arranged in one or two rows, 

 but frequently without any fixed order. These organs are seated in 

 a mucilaginous, frequently opaline and transparent, highly hygro- 

 scopic medium, together with which they escape from the perithe- 



