Fink : LICHENS OF THE LAKE SUPERIOR REGION. 221 



tion offered by trees and shrubs may be observed in many places 

 between Gunflint and Lutsen, especially at Gunflint and in the 

 Misquah hills. The effect of elevation, or rather the combined 

 effect of elevation and exposure, was especially noted on Mt. 

 Josephine and on Carlton peak. In both of these places the 

 stunted condition was also noticeable in other Cladonias and in 

 lichens belonging to other genera. 



The part that lichens play in rock decay and soil formation 

 was studied in a general way in the Grand Portage area, and 

 some of the most noticeable facts are stated below. Grand 

 Portage island contains 57 acres of land and furnishes sufficient 

 variety as to substrata suitable to lichen growth to make the study 

 interesting. The crustaceous lichens furnish most of the species 

 which first gain a footing on the rocks, and of these were found 

 on the island three or four species of Placodium, a half dozen 

 or more rock Lecanoras as well as a larger number of Biatoras, 

 Lecideas and Buellias. Of the foliaceous lichens the Umbili- 

 carias are most characteristically rock pioneers ; but these were 

 very rare on the island, which did not furnish the high bluffs 

 that they seek especially. As soon as rock decay has begun, 

 the less strictly crustaceous species begin to appear. Of these 

 Pannaria microphylla (Sw.) Delis was especially noticed some- 

 times growing on quite firm rock, but more frequently on rotten 

 rock or a residual product of rock decay still in situ and pro- 

 tected by the lichen though sometimes several inches deep. 

 Next come the typically foliaceous and fruticulose species as the 

 Peltigeras and Cladonias. Finally enough soil is established 

 so that smaller Spermaphytes and finally trees and shrubs be- 

 come established, these larger ones in turn furnishing substrata 

 for epiphytic lichens. At the present time, trees grow at one 

 end of the ridge of highest land extending across the island 

 while the other end is bare of trees and soil to a large extent 

 and yet supports many strictly lithophytic lichens. At the shore 

 line one finds amphibious Endocarpons and a Collema while 

 typically xerophytic species cover the remainder of the island. 

 The analysis could be extended to include a statement of differ- 

 ent sorts of woody substrata which result in giving diversity of 

 lichens growing on wood and, indeed, to give a detailed account 

 of substrata including that of each one of the 88 species and 

 varieties listed from the island. But this would lead to more 

 detail than can be undertaken here, and for more minute ac- 



