286 MINNESOTA BOTANICAL STUDIES. 



all detected here as elsewhere, and the fact that 15 of 18 were 

 found on each kind of rock demonstrates that difference in 

 composition of rock in this instance has produced little, if any 

 difference in lichen flora. A similar study of lichen formations 

 on large rock areas of greater difference in composition as granite 

 and limestone lying adjacent would be of special interest. 



To complete the lichen formations of the area, the earth- 

 lichen formation must be considered. This formation and simi- 

 lar ones elsew^here may be called the Endocarfon hef at iciwi for- 

 mations of exposed earth from a plant which is found in such 

 formations in all parts of the state except the lake Superior 

 region. 



Endocarpon hepaticiini formation of exposed earth (Pipestone). 

 Urceolaria scruposa (L.) Nyl. 

 Cladonia pyxidata (L.) Fr. 

 Cladonia fimbriata (L.) Fr. 

 Cladonia fimbriata (L.) Fr. var. tubseformis Fr. 

 Biatora muscorum (Sw.) Tuck. 

 Endocarpon hepaticum Ach. 

 Endocarpon pusillum Hedw. var. garovaglii Kph. 



The region is a comparatively dry one because of small pre- 

 cipitation of moisture, since the rocks lie high where there is 

 little or no standing water to give moisture and because there 

 are few trees to give shade. The lichen formations are accord- 

 ingly rather poor in species, as will appear in comparisons to 

 follow an anah^sis of similar formations. 



The rocky surfaces at Granite Falls present a much more 

 complex set of conditions than those just considered, and yet, 

 for my purpose, they may be classified, like the latter, into ex- 

 posed surfaces, usually horizontal, and shaded surfaces, usually 

 more or less nearly perpendicular. I shall now record these 

 formations in the same order as in the last series ; but after each 

 shall compare it w'ith the corresponding formation at Pipestone, 

 giving, as far as possible, the probable cause of differences. 



Eecanora formation of exposed {usually horizontal) granite 



(Granite Falls). 



Parmelia olivacea (L.) Acii. var. prolixa Acii. 

 Parmelia conspersa (Eiirh.) Acii. 



