Fink: the lichens of Minnesota. 711 



of the Saint Peter sandstone with those of other substrata that 

 happen to lie adjacent. The distribution of lichens on this rock 

 formation in Minnesota, Wisconsin, Iowa and Illinois is worthy 

 of careful study. Other questions of distribution would be 

 brought to light, illustrated by the species here considered and 

 doubtless by several others not yet collected on these rocks. 



The statements thus far made will surely lead to some wrong 

 conclusions on the part of readers if not somewhat explained. 

 A perusal of the foregoing comparisons might lead to the con- 

 clusion that the region covered by this paper is poorer in 

 lichen-species than it really is. It has been compared with a 

 region probably as much above the average for the part of the 

 upper Mississippi valley near the river as it is below as to 

 number of lichens, and yet the per cent of difference in favor 

 of the Iowa locality is only 28. 



On the other hand, comparison with some other lists of lichen- 

 iioras about large cities might cause one to conclude that I 

 have omitted certain factors that tend to decrease the number 

 of species for such regions and have been at error in asserting 

 that the locality treated in this paper is not naturally up to the 

 average in number of lichens. For instance, the recent list by 

 Mr. W. W. Calkins, for Chicago and vicinity, covering a much 

 larger area than the one treated in this paper, only contains 12 

 more species. Probably Mr. Calkins' collecting was as well 

 done as mine, but from personal knowledge, as well as from the 

 statement of Mr. Calkins in his introduction, I know that the 

 Chicago region, naturally not a rich lichen-area, is now not so 

 rich as formerly because of the inroads of civilization destroy- 

 ing substrata. Destruction of substrata need scarcely be con- 

 sidered in the area about Minneapolis, for, excepting perhaps 

 the granitic boulders, one can find as great an abundance of 

 substrata about Minneapolis as about Fayette, the locality with 

 which the former region is compared. 



Concerning the list of lichens in Deane and Collins' " Flora 

 of Middlesex Co., Mass.," in which Boston is located, little 

 need be written. Though the lichen-flora treated in that list 

 is much richer than that of either Chicago or Minneapolis, the 

 number of species and varieties listed is only 146. After some 

 experience in collecting about Boston, I know that this list for 

 the large county of Middlesex is so incomplete that any conclu- 

 sion as to the richness of the Minneapolis lichen-flora drawn 

 from a comparison with this list would not be at all trust- 

 worthy, especially after making allowance for the much larger 

 area covered by the latter list. 



