Fink: LICHENS OF THE NORTHERN BOUNDARY. 187 



Physcia hispida (FR.) TUCK. 



Phyccia obscura (EHRH.) NYL. 



Placodium cerinum (HEDW.) NAEG. and HEPP. 



Lecanora varia (EHRH.) NYL. 



Lecanora variolascens (FR.) NYL. 



Rinodina sophodes (Acn.) NYL. 



Biatora mixta (FR.) 



Biatora atropurpurea (MASS.) HEPP. 



Arthonia patellulata NYL. 



Pyrenula leucoplaca (WAHL.) KBR. 



The formation varies with the age of the poplars, from one 

 having more of the crustose lichen species to one having a 

 larger proportion of foliose species. It has been noted fre- 

 quently in various portions of northern Minnesota, but has not 

 been carefully studied elsewhere. Enough has been noted, 

 however, to know that such a lichen society exists in many 

 places in northern Minnesota and does not differ greatly from 

 the above. Though small and inconspicuous, the last four 

 lichens are decidedly the most characteristic of the formation. 

 Yet the Rinodina, the Placodium and some of the foliose species 

 are quite partial to the poplars wherever found. Of these 

 foliose forms, Physcia stellaris (L.), Theloschistes -poly carpus 

 (Ehrh.) Tuck, and perhaps Parmelia olivacea (L.) Ach. are 

 most constant on the poplars. The adaptations are obviously 

 those of the formations of trees with smooth or rough bark as 

 already given and need not be restated here. 



The next to be introduced is a Cladonia formation and may 

 be designated as follows : 



CLADONIA LICHEN FORMATION OF HUMUS-COVERED ROCKS 

 (RAINY LAKE CITY). 



Cladonia rangiferina (L.) WEB. 

 Cladonia coccifera (L.) WILLD. 

 Cladonia amaurocraea (FLK.) SCHAER. 

 Cladonia uncialis (L.) WEB. 

 Cladonia furcata (Acn.) SCHRAD. (forms of). 

 Cladonia cenotea (Acn.) SCHAER. 

 Cladonia turgida (EHRH.) HOFFM. 

 Cladonia cariosa (Acn.) SPRENG. 

 Cladonia gracilis (L.) WILLD. (form of). 

 Cladonia degenerans (FLK.) SPRENG. 



