308 MINNESOTA BOTANICAL STUDIES. 



division being based on substratum as well as amount of light 

 and moisture. 



As a whole, the formations may be said to be azonal and 

 without definite form or extent, both depending upon location 

 of proper substrata, protection from or exposure to light, etc. 



In my paper I have used the expression " lichen formation" 

 to include lichens only. Of course, these plants are in some 

 instances found growing upon the same substrata and in the 

 same general set of conditions as plants of other groups, and 

 which might have been listed in the formations. However, I 

 may be excused, in a paper on lichen distribution, for omitting 

 other plants than lichens, especially since I could not possibly 

 have treated the other plants with the same detail that I have 

 accorded the lichens. 



I know of no other paper which has dealt exclusively with 

 lichen distribution as I have done herein, and surely this anal- 

 ysis must be helpful in the study of the lichen flora of other 

 regions. The multiplicity of observations necessary for such a 

 detailed study are not easy to make, and I am sure that much 

 of interest has escaped me. However, I hope that this paper 

 may stimulate others to study the lichens from an ecologic point 

 of view. 



LIST OF SPECIES AND VARIETIES. 



1. Ramalina calicaris (L.) FR. var. fraxinea FR. 



On trees and old wood, infrequent or rare. Mankato, June 

 23, 1899, no. 55, June 26, 1899, no. 102, and June 28, 1899, 

 no. 164. Granite Falls, July n, 1899, no. 385 and July 13, 

 1899, nos. 510 and 533. 



2. Ramalina calicaris (L.) FR. var. fastigiata FR. 



On trees and rocks, rare. Mankato, June 23, 1899, no. 54. 

 New Ulm, July 5, 1899, no. 275. Granite Falls, July 14, 1899, 

 no. 518, and July 17, 1899, no. 588. 



3. Ramalina calicaris (L.) FR. var. farinacea SCHAER. 



On sandstone and granite. Mankato ( Minneopa Falls) , June 

 27, 1899, no. 154. Redwood Falls, July 6, 1899, no. 305, and 

 July 8, 1899, no. 349. Granite Falls, July 12, 1899, no. 460. 



4. Ramalina polymorpha (Acn.) TUCK. ? 



On shaded granitic rocks in first locality and on a large 

 bowlder in the second, rare. Granite Falls, July 12, 1899, no. 



