Fink: LICHENS OF NORTHWESTERN MINNESOTA. 661 



Lecanora varia (EHRH.) NYL. var. polytropa NYL. 



Placodium murorum (HOFFM.) DC. 



Placodium elegans (LINK) DC. 



Physcia caesia (HOFFM.) NYL. 



Parmelia conspersa (EHRH.) ACH. 



The earth lichen flora is as poorly developed as that of the 

 trees and rocks, and the whole known lichen population of the 

 area comprises only 78 species and varieties and is the most 

 scanty yet studied in the state, except that at Pipestone, where 

 trees are almost wholly absent. 



The last collecting ground was at Red lake, some 65 miles 

 east and somewhat south of Thief River Falls. This area is 

 about 36 miles north of the one previously studied at Bemidji 

 and has a lichen community very similar. Here the only 

 bowlders that gave any noteworthy results were those along the 

 lake shore, and the lichens on them were, all but three or four, 

 of the same species as those growing upon the adjacent trees. 

 With this dearth of rock lichens the territory, probably not 

 quite so thoroughly studied as the one to the south about 

 Bemidji, gave only 120 lichen species and varieties. 



Compared with other portions of the state of equal size, 

 whose lichen floras have been investigated, this one is some- 

 what the poorest in lichens. The number collected is little 

 larger than that found in southwestern Minnesota, but should 

 be considerably larger, as fully one-third more time was taken 

 for the collecting. The Lake Superior region gave 258 lichen 

 forms in about the same time as was spent in making the col- 

 lections in northwestern Minnesota. However, this is what 

 would be expected since the former area is more diversified as 

 to climate, the portion near the lake having many arctic and 

 subarctic species, while the northern and western portions 

 yielded essentially the same species as the region now under 

 consideration. Then too the absence of the great exposures of 

 igneous rocks of the Superior region has already been noted 

 for the present one, in which only 58 species and varieties of 

 lichens, or about 28 per cent, of the whole lichen flora, were 

 found on rocks, whereas nearly 50 per cent, of these plants in 

 the former region were collected on the rocks. The occurrence 

 of about three-fourths of the entire number of lichens of the 

 whole area under consideration in one small area about Bemidji 

 demonstrates that little of the difference in the composition of 



