104 



POPULAR HISTORY OF LICHENS. 



grow on the soil or ground some Cladonice and Lecidece, as 

 L, ceruginosa, uliginosa, and granulosa, prefer moist peaty 

 soil ; Lecidea decipiens and hirida, calcareous soil ; some 

 Stereocaula, siliceous ; the Peltigeras and some Bseomyces, 

 argillaceous; while Peltigera venosa and some Collemas 

 grow on hardened mud. The mineralogical characters or 

 chemical composition of the soil or rocks on which Lichens 

 grow undoubtedly have much influence on their develop- 

 ment, which also depends greatly, in many cases, on their 

 physical properties, such as their aptitude for absorbing and 

 retaining heat and moisture. Calcareous soils are much 

 more rapidly heated than argillaceous ones ; hence the for- 

 mer are called by French agriculturists " terres chaudes," 

 while the latter are contradistinguished by the appellation 

 " terres froides." In this way authors have sought to account 

 for the fact that, in northern latitudes, Lichens are usually 

 saxicolous- — rocks most rapidly absorbing the sun's heat — 

 while in tropical countries they are corticolous, the foliage of 

 trees forming a protection from its scorching rays. Several 

 species are peculiar to the rocks of our sea-coasts, such as 

 the Roccellas, Lichince, certain Opegraphas, Ramalina scopu- 

 lorum, and Verrucaria manra ; many are found only in low- 

 land regions, as Parmelia parietina, P. olivacea, and Per- 



