Fink: LICHENS OF NORTHWESTERN MINNESOTA. 681 



The first and last Biatoras are the common elements of the 

 formation and may be found in this habitat commonly at Be- 

 midji. The last Biatora is the only plant of the formation 

 noticed elsewhere in such environment, nor were the other two 

 Biatoras found elsewhere during the summer. The formation 

 was observed in the Lake Superior region at Gunflint, where 

 the second Biatora was wanting, and in the Snowbank lake 

 area, where the first one did not occur. The plants of the for- 

 mation all have rudimentary thalli devoid of cortical layers and 

 are well adapted to the moist shaded habitat on the damp shaded 

 sides of tree bases where they spread over the mosses. 



Nearly all of the formations herein recorded are more or less 

 scattered in the sense explained in the fifth paper of this series.* 

 In this paper as in the others I have avoided attempting too 

 close analysis as to amount of illumination, roughness of bark, 

 amount of moisture, and have omitted from the lists of plants of 

 the various formations those rarer lichens whose adaptations 

 seemed most doubtful. Yet in attempting a detailed study of a 

 single group of plants, I feel sure that, if I have erred at all, it 

 has been in including some doubtful elements in a few of the 

 formations. In general, I have found that one can attempt an 

 amount of minute detail in such a study which could only be 

 carried out by a long study of a single locality and which would 

 probably not be more helpful than such general survey as I feel 

 that I have been able to conduct in the field with some degree 

 of success. 



Notwithstanding the recording of 16 distinct formations for 

 the region now under consideration and only 14 for southwest- 

 ern Minnesota, I still adhere to the statement already recorded 

 in this paper that the conditions of lichen growth are more uni- 

 form in the former area. The greater diversity in the latter ter- 

 ritory may be seen in the fact that there is a larger amount of 

 difference between similar formations in the various parts of the 

 region, due to more variation in amount of moisture, shade, 

 etc., and in the circumstance that some of the formations bear- 

 ing different names in the former region are very much alike. 

 On account of this greater uniformity of conditions under which 

 similar formations seems to have developed, it has been even 

 more difficult than in the preceding papers to ascertain why cer- 

 tain species are found in a formation at one place and not in the 



*Fink, B. 1. c., 307. 



