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' 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. adgluiinaia. 



Placodium cerinum. 



Lecanora subfusca. 



Bacidia fusca-rubella. 



Lecidea enteroleuca. 



Graphis scripta. 



Arthonia lecideella, A. dispersa. 



Arthopyretiia punciiformis, A.fallax. 



Pyrenula nitida, P. thelena, P. cinerella, P. leucoplacou 



On rough bark he records : 



Ramalina calicaris, R. fraxinea, R. fasiigiata. 

 Teloschistes chrysophthabnus. 

 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. 

 ' Placoditim auraniiacum, PI. cerinum. 

 Lecanora subfusca. 

 Pertusaria leioplaca, P. velaia. 

 Bacidia rubella, B . fuscorubella. 

 Lecidea enteroleuca. 



Rhizocarpon alboatrum, Buellia parasetna. 

 Opegrapha varia. 

 Graphis scripta. 



Arthonia lecideella, A. radiata. 

 Arthopyrenia guinqueseptata, 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'' in Somerset maybequoted: 



Colle7na flaccidum, 

 Calicium hyperellum. 



1 Fink 1902. ^ Watson 1909. 



