Fink: THE LICHENS OF MINNESOTA. 705 



The Fayette column I have divided into two parts, the first 

 containing 157 species, which, with present experience, I 

 should expect to find in a region as favorable for lichen - 

 development as Fayette and in the time spent in collecting at 

 Minneapolis. The second part of the Fayette column contains 

 23 species, so rare that one would not be so likely to find them 

 in the short time, or which are not found within five miles 

 of Fayette. The 113 species found at Minneapolis are about 

 72 per cent of the 157 species of Fayette lichens, and it will be 

 an approximately correct estimate to say that lichens are one- 

 fourth more numerous at the latter place than at the former. 



The cause of the smaller number of lichens about Minne- 

 apolis is evidently to be sought mainly in its dryer climaie. 

 Several considerations have conspired to cause me to arrive at 

 this conclusion. First, most species of lichens here are more 

 disposed to confine themselves to moist situations, as about the 

 bodies of water mentioned above, in heavy woods, or when in 

 dry places near the ground. The last tendency is noticeable 

 in Graphw scripta (L.) Ach., which in dry places most fre- 

 quently grows low down on the trunks of the trees. In pass- 

 ing up from the Mississippi river banks 50 to 100 feet to the 

 level ground just above the bluffs the decrease in number of 

 species and individuals, whether on rocks, earth or trees, is 

 very striking. In one place within or near the city limits the 

 granitic boulders just above the bluffs are well covered with 

 lichens, while twenty rods back from the river in open ground 

 the rocks of the same kind are nearly bare of them. The de- 

 crease is not so marked in lichens growing on trees as in those 

 growing on rocks, but is noticeable. I am not referring now 

 to change in species in passing to the dryer locality, which 

 also occurs here as elsewhere, and is due to stress caused by 

 environment. Further, it may be said that a decrease would 

 occur in numbers in other regions, but observation shows it to 

 be more marked in dry climates. In parts of northern Iowa 

 no such noticeable decrease occurs. Here 15 or more species 

 of lichens may easily be found on a single tree in moderately 

 dry situations, and nearly all the species commonly occurring 

 on the boulders in the vicinity of Fayette may be found on a 

 single one in an open dry field far removed from any stream. 



Second, the gelatinous lichens, which thrive in moist places, 

 are rare at Minneapolis. The first table will show that the 

 genera Collema and Leptogium show 3 species at Minneapolis 

 and 12 at Fayette. I took special pains to investigate this 



