IOWA ACADEMY OF SCIENCES. 179 



Next as to the lichens on granitic rocks, the difference of 1.3 

 per cent in favor of Minneapolis is not so great as might be 

 expected. This is due to the fact that so many of the granitic 

 boulders are in dry open places. The few in moist or shaded 

 places are reasonably well covered with lichens, but those not 

 thus protected are not, as has been stated elsewhere. The 

 limestone exposures are usually shaded along the wooded river 

 banks, hence the advantage for these rocks would be greater 

 than for the granitic rocks were it not for the lack of surface 

 outcrops of the limestone rocks. 



As to the earth lichens, the region including Minneapolis 

 lacks the calcareous-earth lichens of the Iowa region, because 

 the calcareous rocks are more deeply covered by drift and have 

 not been so frequently exposed to help in soil formation. Of 

 the twenty-two earth lichens found at Fayette seven occur on 

 calcareous earth, while of the twelve found at Minneapolis 

 only two occur on calcareous earth. Reducing the first number 

 to fifteen and the third to ten gives Minneapolis an advantage 

 of 3 per cent. This 3 per cent does not show the effect of 

 atmospheric differences between the two places compared, 

 because of the Minneapolis Cladonias only one-third occur on 

 the earth, while of those at Fayette about two-thirds grow on 

 the ground. Since I have been able to present no very satis- 

 factory explanation of this difference in distribution of the 

 Cladonias out of the calculation; and, if this were done, the 

 advantage in favor of Minneapolis in the per cents would be 

 about 2.5. 



As to the wood lichens it will be seen that if the per cents 

 of rock and earth lichens about Minneapolis were what we 

 should expect from hygrometric conditions alone, the per cent 

 of these would rise and that of the wood lichens would fall in 

 comparative proportion. In other words, conditions other than 

 atmospheric have tended to decrease the rock and the earth 

 lichens, but not the wood lichens. Scarcity of lichens on trees 

 removed from the large bodies of water and not in heavy 

 forests has been noted elsewhere in this paper. As to lichens 

 on dead wood, especially old boards, the Iowa region furnishes 

 14 and the Minneapolis region eight. The per cent of the 

 whole lichen-floras in favor of the former region is about one. 

 In the Minneapolis region the lichens on old boards are common 

 enough in damp places, but in dry ones old boards are fre- 



