Fink : LICHENS OF NORTHWESTERN MINNESOTA. 665 



This formation may be compared est with the si milar one 

 upon the exposed granite at Granite Falls.* As might be ex- 

 pected the Battle lake formation confined to the bowlders 

 suffers somewhat in comparison with that at Granite Falls, 

 which is developed upon extensive exposures of granite. The 

 number of lichens in the formation at the former place is 24 

 and the number at the latter 31. Species common to the two 

 similar formations I have marked (C), and those found at 

 Battle lake only are marked (B). Of the ten species found at 

 Granite Falls and not at Battle lake, Parmelia cons-persa 

 (Ehrh.) Ach. deserves special mention as being unaccountably 

 rare in the region covered by this paper. The entire absence 

 of another of the ten, Biatora rtifontgraTuck., from the region 

 is quite as remarkable. The other eight are lichens either not 

 widely distributed in the state, or not common on granitic rocks. 

 Eight of the species of the formation recorded above have oc- 

 curred in all of the four localities in the state in which similar 

 formations have been recorded. These may be considered the 

 most constant elements of such formations in Minnesota, and I 

 have marked them (X). The formation is also well developed 

 in the Leaf hills, but nothing would be gained by recording it. 



As to the general character of the lichens of the formation, 

 all but the first three and the first Lecanora are strictly crusta- 

 ceous, and this last plant, as well as the foliaceous Placodium, 

 is nearly as closely adnate to the substratum as the crustaceous 

 forms. The less adnate foliaceous species have a well-devel- 

 oped cellular cortex on all sides for support and for protection 

 against too rapid evaporation of moisture in their exposed 

 and dry habitat. Of the crustaceous species, the Placodiums 

 have good upper and some of them a lower cortex, the Lecan- 

 oras have either an upper only or none, while the Rinodinas, 

 except possibly the first, have no cortical layers ; and the last 

 statement applies to the Buellias as well. The forms, having 

 no cortex or a poorly-developed one and growing in such a dry, 

 exposed habitat, have very small thalli. A large foliaceous 

 lichen with no cortex, as a Collema for instance, could hardly 

 exist in the present formation. Finally the lichens of the for- 

 mations are a few foliaceous species with well-developed cortex 

 above and below, but still quite closely adnate, and a much 

 larger number with no cortex or an upper one only, but having 



*Fink, B. 1. c., 286, 287. 



