666 MINNESOTA BOTANICAL STUDIES. 
very small thalli, and though epilithic yet very closely adnate, 
so that moisture easily passes into them from the rocky sub- 
stratum below. 
Next may naturally follow the mixed lichen formation of 
shaded granitic bowlders. 
MIXED LICHEN FORMATION OF SHADED GRANITIC BOWLDERS 
(RED LAKE). 
A. Probably naturally belonging to the rocks. 
Biatora inundata Fr. 
Verrucaria nigrescens PEers. 
Verrucaria viridula Acu. 
Verrucaria muralis Acu. 
B. Near trees and probably migrated from them. 
Theloschistes lychneus (Nyu.) Tuck., C. 
Parmelia borreri Turn., C. 
Parmelia saxatilis (L.) Fr., C. 
Parmelia olivacea (L.) Acu. 
Parmelia caperata (L.) Acu., C. 
Physcia speciosa (WuLr., Acu.) Nyt., C. 
Physcia pulverulenta (Scures.) Nyt., C. 
Physcia stellaris (L.) Tuck. 
Physcia stellaris (L.) Tuck. var. apiola Ny. 
Physcia astroidea (Fr.) Nyt. 
Physcia hispida (ScurEB., Fr.) Tuck. 
Physcia obscura (Euru.) Nyt., C. 
Of the 12 species of the formation probably having migrated 
from trees near by, seven marked (C) are common to all of 
the six similar formations studied in the state,* but none of the 
four elements naturally belonging to the rocks are common to 
the similar formations. 
Comparing these lichens with those of the exposed rock 
formation above, we find an entirely different type of thallus 
to prevail, viz., the foliaceous type of the Parmelias and 
Physctas with thalli having well developed cortical layers. 
And as would be expected in an ombrophytic lichen formation 
having such thalli, the plants are not so closely adnate to the 
substratum as those of the exposed rock formation, but are 
* Fink, B. 1. c., 290-293. 
