170 MINNESOTA BOTANICAL STUDIES. 



of species reported in this paper is that Cladonias were sought 

 for with unusual care, knowing that Dr. Wainio would work 

 them out carefully so that a good contribution to Minnesota and 

 North American lichens could be thus made. Also a number 

 of Buellias, confusingly like Bucllia pctrcea (Kbr.) Tuck., 

 were for the first time detected in the field, as well as a number 

 of Buellias parasitic on other lichens. 



The region furnished many elements of interest similar to 

 those met in the lake Superior region, but these must be 

 passed over lightly to give place to some ecologic considera- 

 tions. For instance, the succession of lichen forms following 

 fires and preceding arboreous vegetation could be studied most 

 splendidly in the region and constantly tempts one away from a 

 predetermined line of study. The sensitiveness of the Cladonias 

 to the effects of sun and wind are very apparent and would 

 furnish an interesting and very instructive field for extended 

 study. The part that lichens play in soil formation may also 

 be most beautifully studied, especially at Rainy Lake City. A 

 mere suggestion of the possibilities in such a study has been 

 given in these studies,* and the subject must be passed over for 

 the present. The succession of species on trees suggested there 

 has since been followed out in the studies of the arboreous 

 formations and will be continued in the present paper. Also a 

 detailed study of distribution within the present area as was 

 presented in the above-cited paper would be instructive, but we 

 can only give a brief statement as to comparative numbers of 

 arctic or subarctic forms. For the lake Superior region, 41 

 such lichens were recorded, f For the present area, some 27 

 such lichens were noted. The following is the list, 20 of which 

 marked (C) occur also in the lake Superior territory. 



Ramalina pusilla (Prev.) Tuck. C. 



Ramalina pusilla (Prev.) Tuck. var. geniculata Tuck. C. 



Usnea cavernosa Tuck. C. 



Peltigera canina (L.) Hoffm. var. spongiosa Tuck. 



Physcia hispida (Schreb.) Fr. C. 



Umbilicaria vellea (L.) Nyl. C. 



Umbilicaria hyperborea Hoffm. C. 



*Fink, B. Contributions to a Knowledge of the Lichens of Minnesota. — 

 IV. Lichens of the Lake Superior Region. Minn. Bot. Stud , 2: 221. 29 D. 

 1899. 



tFink, B. /. c, 227-233. 



