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 PERS. 

 Verrucaria viridula ACH. 

 Verrucaria muralis ACH. 



B. Near trees and probably migrated from them. 



Theloschistes lychneus (NYL.) TUCK., C. 



Parmelia borreri TURN., C. 



Parmelia saxatilis (L.) FR., C. 



Parmelia olivacea (L.) ACH. 



Parmelia caperata (L.) ACH., C. 



Physcia speciosa (WULF., ACH.) NYL., C. 



Physcia pulverulenta (SCHREB.) NYL., C. 



Physcia stellaris (L.) TUCK. 



Physcia stellaris (L.) TUCK. var. apiola NYL. 



Physcia astroidea (FR.) NYL. 



Physcia hispida (SCHREB., FR.) TUCK. 



Physcia obscura (EHRH.) NYL., 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 

 Physcias 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. 



