164 



The species occur upon rocks, tree-trunks, earth, logs, etc. As to 

 their distribution they seem, to be most common in northern latitudes 

 and in mountainous districts. 



PLATE 40. 

 Haematomma ventosa (L.) Stein. 



1 . Natural size. 



2. Section of apothecium. 



3. Section of thallus. 



a, upper cortical layer; b, algal layer; c, medullary layer. 



4. Paraphyses and spore-sac. 



5. Spores. 



6. Algae. 



3. Lecanora Ach. Lich. Univ., 344. 181Q. 



The thallus varies from distinctly crustaceous to markedly foliose ; 

 in the majority of species occurring in the territory it is crustaceous, 

 varying from thin, to quite thick and, as in L. tartarea, closely re- 

 sembling the thallus of Haematomma ventosa. In the higher crustace- 

 ous forms and the foliose forms the upper cortical layer is well devel- 

 oped. In the foliose forms (Z. rubina') there is also a well developed 

 lower cortical layer ; the foliose forms also show a decided fruticose 

 tendency as is seen from the ascending lobes and decidedly centric 

 structure (two algal layers). The medullary layer is well developed 

 in the higher crustaceous and foliose forms. The lower surface of 

 the typically foliose thalli bear few or no rhizoids ; they are attached 

 by an umbilicus, as in Umbilicaria and Gyrofhora. 



Apothecia are usually quite numerous, medium to large, disk-like, 

 sessile with the thalloid exciple extending somewhat above the disk. 

 The margin of the exciple may be entire or rugose and more or less 

 folded. The thecium varies in color from brown to nearly black. 

 The paraphyses are simple, and rather thick. The hypothecium is 

 colorless. 



The spores are simple, colorless, elliptical ; their form as well as 

 size is somewhat variable; in one species (L. Sambuci) they are 

 numerous, there being 12-32 in each spore-sac. 



The algae are in all cases Cystococcus humtcola. In the older 

 portions of the foliose Lecanoras the algae begin to disappear so 

 that none can ever be found near the umbilicus ; they seem to be- 

 come quite large, though not very numerous ; there is no explanation 



