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, Physctas, 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 Cetrarza juniperina (L.) Ach. and the Caliczum lu- 
celium (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 Parme/ez 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 U/szez 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. 
