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 conspersa 
(Ehrh.) Ach. deserves special mention as being unaccountably 
rare in the region covered by this paper. The entire absence 
of another of the ten, Bzatora rufonigra Tuck., 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 Zecanora 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 Azzodinas, 
except possibly the first, have no cortical layers; and the last 
statement applies to the Buelas 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 Co//ema 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 
eHink. B: J. e:;.286, 237. 
