LICHEN COMMUNITIES 365 



whether of young trees, or on bark that never becomes really rugged, there 

 is a preponderance of species with a semi-immersed thallus, and very 

 generally of those that are associated with Trentepohlia gonidia, such as 

 Graphidaceae or Pyrenulaceae, though certain species of Lecidea, Lecanora 

 and others also prefer the smooth substratum. 



Bruce Fink 1 has published a series of important papers on lichen com- 

 munities in America, some of them similar to what we should find in the 

 British Isles. 



On trees with smooth bark he records in the Minnesota district : 



Xanthoria polycarpa. 



Candelaria , concolor. 



Parmelia olivacea, P. adglutinata. 



Placodium cerinum. 



Lecanora subfusca. 



Bacidia fusca-rubella. 



Lecidea. enteroleuca. 



Graphis scripta. 



Arthonia lecideella, A. dispersa. 



Arthopyrenia punctiformis, A.fallax. 



Pyrenula nitida, P. thelena, P. cinerella, P. leucoplaca. 



On rough bark he records : 



Ramalina calicaris, R. fraxinea, R.fastigiata. 



Teloschisles chrysophthalmus. 



Xanthoria polycarpa, X. lychnea. 



Candelaria concolor. 



Parmelia perforata, P. crinita, P. Borreri, P. tiliacea, P. saxatilis, P. caperata. 



Physcia granulifera, Ph. pulverulenta, Ph. stellaris, Ph. tribacia, Ph. obscura. 



Collema pycnocarpum, C.flaccidum. 



Leptogium mycochroum. 



Placodium aurantiacum, PL cerinum. 



Lecanora subfusca. 



Perlusaria leioplaca, P. velata. 



Bacidia rubella, B.fuscorubella. 



Lecidea enteroleuca. 



Rhizocarpon alboatrum, Buellia parasema. 



Opegrapha varia. 



Graphis script a. 



Arthonia lecideella, A. radiata. 



Arthopyrenia quinqueseptata, A. macrospora. 



Pyrenula nitida, P. leucoplaca. 



Finally, as generally representative of the commonest lichens in our 

 woods of deciduous trees, including both smooth- and rough-barked, the com- 

 munity of oak-hazel woods as observed by Watson 2 in Somerset maybequoted: 



Collema flaccidum, 

 Calicium hyperellum 



1 Fink 1902. 2 Watson 1909. 



