706 MINNESOTA BOTANICAL STUDIES. 



peculiarity of distribution at the former place, searching deep 

 wooded ravines where these species should abound. It may be 

 added that two of the three species given for the one locality 

 are much rarer than any one of the 12 given for the other. 

 This adds to the evidence in a way not shown in the table. 



Third, the genus Peltigera, the species of which grow on the 

 ground where they can get an abundance of moisture, is repre- 

 sented by an equal number of species in the two localities com- 

 pared, as will appear upon examining the first table. The 

 individual Peltigeras are also about equally numerous in the two 

 regions, the genus Peltigera being probably the best developed 

 one of the flora about Minneapolis, though several other genera 

 are represented by more species. 



A thorough exploration of three or four selected areas along 

 the Mississippi river, between the two localities compared 

 above would, if made by one well acquainted with lichens and 

 their habits of growth, bring out some very interesting and 

 instructive information regarding lichen- distribution. The 

 first and second questions considered just above could thus be 

 traced. As to where the gelatinous lichens decrease in num- 

 ber most rapidly in passing northward; and where the change 

 from comparative uniformity of distribution, so far as influ- 

 enced by the moisture or dryness of small adjacent areas, to 

 greater lack of uniformity in this regard takes place most 

 rapidly, are questions of interest. 



The difference in number of species of lichens for the two 

 localities compared is a greater per cent of the larger total 

 than is the difference in number of genera. Fayette has 34 

 genera and Minneapolis 29. The difference in favor of the 

 former place for genera is only 15 per cent, while for species 

 it is about 28 per cent, or nearly twice as great. Reference to 

 the table will show that the five Fayette genera (Coniocybe, 

 Gyalecta, Heppia, Pyxine and Staurothele), not thus far found at 

 Minneapolis, are each represented at the former place by a 

 single species Hence, the 15 per cent has not the significance 

 that it would have if it stood for genera well represented at 

 one place and wanting at the other. On the whole, the less 

 favorable conditions for lichen development have affected the 

 number of species vastly more than the number of genera. 



Further knowledge of the distribution of the lichens about 

 Minneapolis can be gained by the consideration of the 

 table below, in which I have given numbers of lichens for 

 various substrata for Minneapolis and Fayette with the per 



