296 



POPULAR HISTORY OF LICHENS. 



bular, immersed utricle. The cavity is simple ; the sterig- 

 mata linear and short; and the spermatia linear, of great 

 tenuity, and curved into an arc. This species is interesting 

 as the sole British representative of a genus which attains its 

 maximum development in warm or tropical climates. 



Genus IV. PEETUSARIA, DC. 



Gen. Char. Thallus crustaceous or cartilaginous-membra- 

 naceous ; apothecia verruciform, normally covered by a cortical 

 layer of thallus, enclosing one or several waxy-gelatinous thala- 

 mia, enveloped in pale, membranaceous, thalline exeiples ; osti- 

 oles depressed. (Name from pertusus, full of holes or cracked, 

 in allusion to the appearance of the fructiferous warts.) 



1. Pertusaria communis (communis, common). Thallus 

 glaucous or white, determinate, in young state zonate at 

 periphery; apothecial warts subglobose, irregular, crowded, 

 generally multi-locular, depressed round the punctiform, 

 black ostioles ; frequently sterile, sorediiferous, variolarioid, 

 or isidioid. (E.B. 677.) 



Very common on forest-trees, especially the beech, ash, 

 and oak, in lowland districts. In some localities it is only 

 found in a variolarioid state, — the whole thallus being covered 



