662 MINNESOTA BOTANICAL STUDIES. 



the flora of various portions of the territory is due to edaphic 

 causes. What variety exists is due for the most part to the 

 partial extension of the conifers, tamarack swamps and calcar- 

 eous soil, bowlders and pebbles over the region. 



The comparative richness of different collecting grounds as 

 to lichen species has been noted in passing. It may be added 

 that the number of species occurring in each place and not else- 

 where found bears some relation to the whole number of species 

 found in each area studied. Thus Battle lake with a total of 

 in collected has 7 .not collected elsewhere. The numbers for 

 other collecting grounds are : Henning 140 and 18, Bemidji 

 154 and 31, Thief River Falls 78 and 2 and Red lake 120 and 

 14. Comparison of the numbers shows, as would be expected, 

 that the number of rare lichens collected in the best collecting 

 grounds is in much larger proportion to the total number col- 

 lected than in the areas less favored as to lichen flora, where 

 one finds only the commonest species. 



Of the 41 lichen species recorded in the fourth paper of this 

 series as arctic or subarctic,* the following seven occur in the 

 region considered in this paper, while no new northern forms 

 were discovered. 



Ramalina pusilla (PREV.) TUCK. 

 Usnea cavernosa TUCK. 

 Stereocaulon paschale (L.) FR. 

 Cladonia deformis (L.) HOFFM. 

 Cladonia digitata (L.) HOFFM. 

 Biatora leucophaea (FLK.) TUCK. 

 Buellia petraea (FLOT., KBR.) TUCK. 



The other species not new to Minnesota are in general those 

 found farther south in the state. Thus the prediction, as to re- 

 semblance of the present flora to that farther south in Minne- 

 sota, made in the fourth paper of this series, f seems to be fairly 

 well established, though the extreme northern boundary of the 

 state west of the Snowbank lake area remains to be considered 

 in the next paper. Of the genera having northern species in 

 northeastern Minnesota, Solorina^Heterothecium, Bceomyces^nd 

 Umbilicaria were not found in the area now under consideration, 

 nor was there found more than a single genus, Melaspilea, new 

 to the state. Moreover, the paucity of lichens in northwestern 



* Fink, B. 1. c., 227-232. 

 fFink, B. 1. c., 233-234. 



