IOWA ACADEMY OF SCIENCES. 177 



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 indi- 

 vidual 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 rap- 

 idly, 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 thirty- 

 four genera and Minneapolis twenty-nine. 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. Gyalecto, Heppia, Pyxine, and Staurothele), not thus far 

 found at Minneapolis, are each represented at the former place 

 by a single speeies. Hence, the 15 per cent has not the signifi- 

 cance 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 at Minneapolis 

 have affected the number of species vastly more than the 

 number of genera. 



Further knowledge of the distribution of the lichens about 

 the two places can be gained by the consideration of the table 

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

 substrata for Fayette and Minneapolis with the per cents which 



