676 MINNESOTA BOTANICAL STUDIES. 



parent dearth of lichens, but after a careful study he becomes 

 convinced that the plants are common enough when the trees, 

 the fallen branches and the earth are carefully observed. The 

 foliaceous Parmelias, Physcias, etc., so common on the decidu- 

 ous trees, are not so frequently seen, but the pines certainly 

 have their own peculiar formations, composed of lichens found 

 of course on other substrata in various parts of the state. The 

 variety of Cetraria juniperina (L.) Ach. and the Calicium lu- 

 cilium (Th. Fr.) Fink are perhaps the most characteristic ele- 

 ments of the formation, as they are seldom seen elsewhere than 

 on the conifers, though by no means common even in this for- 

 mation. The similar formation was studied at Bemidji, and 

 the only difference is that Lecanora subfusca (L.) Ach. replaces 

 the variety. As indicated in the list of species, a number of the 

 plants are as common or more so on the old cones as on other 

 portions of the trees. Careful comparison of this formation 

 with the Parmelei formation of trees with rough bark will dem- 

 onstrate that the two are quite distinct, though resembling each 

 other in some respects. 



The adaptations of the lichens of this formation are some- 

 what various. They have been discussed somewhat under the 

 rough bark formation above and will be further noticed under 

 the Usnea formation below. However, while it is apparent that 

 the fruticulose lichens of the Usnei group seem well adapted to 

 the swamp Usnea formation given below where moisture is 

 abundant, I have not been able to satisfy myself that the pines 

 of the higher ground furnish more moisture than the deciduous 

 trees of similar grounds. I suspect that the plants in this in- 

 stance and in the formation given below for the swamps are 

 quite as much influenced in their choice of habitat by an adap- 

 tation to coniferous wood as by amount of moisture. And I 

 may add here that in other portions of this paper I have not 

 taken into account any adaptations of the lichens to substrata of 

 certain physical or chemical composition. The subject is a 

 difficult one as yet little understood, and moreover I am con- 

 vinced from observation that, beyond the well-known fact that 

 some lichens prefer rocks, calcareous in some instances and 

 granitic, etc., in others, while others prefer trees and in some 

 instances a particular species or genus, the conditions as to shade, 

 moisture, etc., are the important ones in determining the habitats 

 of lichens and the composition of lichen formations. 



