222 



POPULAR HISTORY OP LICHENS. 



its two layers. Gradually, from all points of their surface, 

 whitish filaments are developed, radiating in every direction ; 

 they ramify towards their extremities, and by the interlacing 

 of their ramifications, form a hypothallus. These filaments 

 are almost solid, and proceed from the epispore alone, which, 

 along with its bristly coating, may easily be rubbed from- 

 the endospore by gentle friction between glass. As the fila- 

 ments become developed, the granular and oily contents of 

 the spore are converted into an emulsion, and then gradually 

 disappear. The spore itself meanwhile undergoes no appre- 

 ciable change, but it probably serves as the nucleus of the 

 first cellular layers of the future thallus. The spermogones 

 of this variety are difficult of discovery, from their opening 

 on the surface of the thallus by an almost invisible pore ; 

 they are to be looked for by repeated sections of the white 

 medullary tissue, in which they appear *as yellowish spots. 

 They are ovoid and pluricellular (divided into sinuous cavi- 

 ties or compartments) ; their sterigmata are linear and simple, 

 or slightly ramose ; their spermatia acrogenous. 



The variety TJpsaliensis, which has a membranaceous-ver- 

 ruculose thallus, is a peculiar form growing on decayed 

 grass, moss, or heather, on various Highland mountains. 



6. Lecanora tartarea. Thallus white-glaucescent, 



