Fink: lichens of the northern boundary. 191 



cies of the genus known in Minnesota are included in the list 

 above and may all be found in several portions of the state in 

 an area of a few square rods or even a few feet. 



Finally, another formation not previously presented, may be 

 taken up, designating it as follows : 



Amphibious Angiocarpic Lichen Formation of 

 Wet Rocks (Tower). 



Endocarpon fluviatile DC. 



Endocarpon miniatum(L.) Schaer. var.jcomplicatum Schaer. 



Staurothele umbrina (Wahl.) Tuck. var. clopima (Whlnb.) 

 Nyl. 



Verrucaria viridula Ach. 



This formation may be seen complete in places along the 

 shore of Vermillion lake and less well represented at other 

 portions of the lake shore. The same formation was observed 

 in its entirety at Harding and all but the last member at Rainy 

 Lake City. In a less close analysis this might of course be con- 

 sidered as a zone of a general lichen, or even general shore 

 plant society, extending backward some distance from the shore 

 line. The plants of the formation are quite different as to ex- 

 ternal appearance, and just what the adaptation is cannot be 

 definitely stated. However, the three genera are closely re- 

 lated phylogenetically as may be seen in apothecial and spore 

 structure as well as a general similarity as to algal symbionts. 

 As to the latter, the last word has not been said, and some yet 

 unknown difference in the algal members of these lichen-part- 

 nerships may account for the fact that some members of the 

 genera of the above list are especially fond of wet rocks fre- 

 quently inundated. Or it is possible that the plants have been 

 recently forced to the water's edge by competing rivals and 

 have become accustomed to the habitat without yet developing 

 any noticeable structural adaptations. 



Thus have been passed in order some fifteen or sixteen 

 distinct classes of lichen formations, giving adaptations not pre- 

 viously stated in the earlier papers of this series as fully as 

 seemed consistent with the general purposes of this survey, 

 stating relationships between the formations especially presented 

 and others of the region covered by this paper or the earlier 

 papers, and thus attempting to make the present paper not only 

 present the dominant features of ecologic distribution of lichens 



