Fink: THE LICHENS OF MINNESOTA. 715 



(4) Proofs that the principal cause is dryer climate are as fol- 

 lows: 



(a) The lichens about Minneapolis are more inclined 



to confine themselves to moist places in denser 

 woods, or about bodies of water 



(b) The gelatinous lichens, which thrive best in moist 



places, are rare about Minneapolis. 



(c) The genus Peltigera, whose species grow on the 



ground, where moisture is plentiful, is the best 

 represented genus at Minneapolis when we take 

 into account both species and individuals. 



(d) Were it not for other than atmospheric conditions 



the number of species of rock and earth lichens 

 would be somewhat large when compared with 

 those on trees. 



(e) Even the Saint Peter sandstone, usually occurring 



in moist places, bears fewer species of lichens 

 about Minneapolis than in a region near Mc- 

 Gregor, in northeastern Iowa. 



(5) The most interesting portion of the lichen-flora of the 



region is that of the Saint Peter sandstone, which has 

 yielded the characteristic species given in the fourth 

 table. 



(6) The tamarack swamps furnish floral elements somewhat 



distinct from those of other portions of the area studied. 



(7) It seems that there is somewhat of a reduction of the num- 



ber of habitats of certain species as compared with the 

 other region better adapted to the development of lich- 

 ens. This has been noted for Usnea barbata (L. ) Pr. 

 var. hirta Pr., and a comparison of the number of species 

 of lichens found both on wood and rocks at Minneapolis 

 and Payette, as shown in the second table, is further evi- 

 dence. Other instances could be drawn from a compari- 

 son of the lists for the two places. Yet, for the species 

 Parmelia olivacea (L . ) Ach. , Evernia prunaslri (L. ) Ach. 

 and Cetraria ciliaris (Ach.) Tuck., the number of habi- 

 tats is larger than for northern Iowa. These are species 

 that occur abundantly to the north of the United States, 

 and the region about Minneapolis is better adapted to 

 their development than the one with which it is com- 

 pared. 



