188 MINNESOTA BOTANICAL STUDIES. 



Cladonia verticillata HOFFM. 



Cladonia pyxidata (L.) FR. var. neglecta (FLK.) MASS. 



Cladonia cristatella TUCK. 



Cladonia fimbriata (L.) FR. (forms of). 



Cladonia decorticata (FLK.) SPRENG. 



Peltigera malacea (Acn.) FR. 



Peltigera canina (L.) HOFFM. 



This lichen formation is a very common one in northern 

 Minnesota, and as large an assemblage of species as that given 

 above may frequently be seen on a few square feet of the 

 humus-covered rocks. We have purposely omitted a number 

 of rarer forms seen in the present formation and have not given 

 the varieties of several of the species of Cladonia. The forma- 

 tion is very similar to the Cladonia- Peltigera formation of 

 shaded earth as recorded for Bemidji in the last report of this 

 series, and the adaptations there stated need not be introduced 

 here. These formations are also almost identical with the talus 

 Cladonia formations as presented by the writer in the Botan- 

 ical Gazette.* As there shown, these formations vary accord- 

 ing to amount of humus, age and kind of trees and other factors 

 which can not be considered here. According to various con- 

 ditions, the present formations may tend toward the larger 

 Cladonia rangiferina or the smaller Cladonia gracilis forma- 

 tions of the talus, and may pass into the one or the other. 

 Stereocaulon paschale (L.) Fr., Cladonia alpestris (L.) Rabenh. 

 and Cladonia sylvatica (L.) Hoffm. are species usually seen, 

 but which did not appear in the society studied at Rainy Lake 

 City. Like the talus formations, the societies composed of the 

 larger species especially thrive best where protected from wind 

 as well as where shaded more or less. Before leaving this sort 

 of societies we must note that a most interesting formation of 

 the kind was found on one portion of the large isolated rock 

 exposures near Roosevelt previously mentioned. And since 

 such formations have not been extensively recorded and this 

 one is unique because of its isolation, space may well be given 

 to it as follows. 



CLADONIA LICHEN FORMATION OF HUMUS-COVERED 



ROCKS (ROOSEVELT). 



Cladonia furcata (Huos.) SCHRAD. var. paradoxa WAINIO. 

 Cladonia cristatella TUCK. 



*Fink, B. Bot. Gaz. 35: 195-208. Mr. 1903. 



