304 MINNESOTA BOTANICAL STUDIES. 



only one found in the Granite Falls formation and not at 

 Mankato, viz., Biaiora nacgelii Tuck. Thus the mark (G) will 

 indicate also those common to both formations and as a whole 

 most characteristic of such lichen formations for the Minnesota 

 valley. The Mankato area with its abundance of trees would, 

 of course, be expected to possess richer tree lichen formations 

 than Granite Falls, and with the exception of a single species, 

 the rough bark formation of the latter area is but a partial repe- 

 tition of that of the former. 



The formation on trees with smooth bark at Mankato con- 

 tains all but two of the species of the similar formation at 

 Granite Falls, and the treatment may be abbreviated as the last 

 two above. The genus Pyrcn^tla predominates in the forma- 

 tion, and some of the species are among the lichens most char- 

 acteristic of smooth bark. Therefore, the formations may re- 

 ceive the name which follows : 



Pyreniila lichen formation of trees zuith smooth bark 

 (Mankato). 



Theloschistes polycarpus (Ehrh.) Tuck. 



Theloschistes concolor (Dicks.) Tuck., G. 



Parmelia olivacea (L.) Acii., G. 



Physcia adglutinata (Floerk.) Nyl., G. 



Placodium cerinum (Hedw.) Naeg. and Hepp., G. 



Lecanora subf usca (L.) Acii., G. 



Rinodina sophodes (Ach.) Nyl., G. 



Biatora fuscorubella (Hoffm.) Tuck., G. 



Lecidea enteroleuca Fr., G. 



Graphis scripta (L.) Acii., G. 



Arthonia lecideella Nyl. 



Arthonia dispersa Nyl., G. 



Pyrenula punctiformis (Acn.) Naeg., F. 



Pyrenula punctiformis (Acn.) Naeg. var. fallax Nyl., F. 



Pyrenula nitida Acn., F. 



Pyrenula thelena Acii., F. 



Pyrenula cinerella (Flot.) Tuck., F. 



Pyrenula cinerella (Flot.) Tuck. var. quadriloculata var. nov. 



Pyrenula leucoplaca (Wallr.) Kbr., GF. 



