Pink: LICHENS OF NORTHWESTERN MINNESOTA. 671 



Physcia pulverulenta (SCHREB.) NYL. 

 Physcia stellaris (L.) TUCK. 

 Physcia hispida (SCHREB., FR.) TUCK. 

 Physcia obscura (EHRH.) NYL. 

 Collema pycnocarpum NYL. 

 Collema flaccidum ACH. 

 Collema nigrescens (HUDS.) ACH. 

 Leptogium myochroum (EHRH., SCHAER.) TUCK. 

 Placodium aurantiacum (LIGHTF.) NAEG. and HEPP. 

 Placodium cerinum (HEDW.) NAEG. and HEPP. 

 Lecanora subfusca (L.) ACH. 

 Lecanora varia (EHRH.) NYL. 

 Lecanora verrucosa (Acn.) LAUR. 

 Pertusaria finkii A. ZAHLB. 

 Biatora turgidula (FR.) NYL. 

 Biatora arthropurpurea (MASS.) HEPP. 

 Biatora rubella (EHRH.) RABENH. 

 Biatora fuscorubella (HOFFM.) TUCK. 

 Biatora atrogrisea (DELIS.) HEPP. 

 Lecidea enteroleuca FR. 

 Buellia alboatra (HOFFM.) TH. FR. 

 Buellia parasema (Acn.) TH. FR. 

 Opegrapha sp. 

 Graphis scripta (L.) ACH. 

 Graphis scripta (L.) ACH. var. limitata ACH. 

 Graphis scripta (L.) ACH. var. recta (HuMB.) NYL. 

 Arthonia lecideella NYL. 

 Calicium lucidum (Tn. FR.) FINK. 

 Coniocybe pallida (PERS.) FR. 

 Melaspilea arthonioides (FEE) NYL. 

 Pyrenula leucoplaca (WAHL.) KBR. 



Pyrenula leucoplaca (WAHL.) KBR. var. pluriloculata var. nov. 

 I shall now record the smooth bark formation and then con- 

 sider the adaptations of the two groups together. 



PYRENULA FORMATION OF TREES WITH SMOOTH BARK 



(BEMIDJI). 



Theloschistes polycarpus (EHRH.) TUCK. 

 Theloschistes concolor (DICKS.) TUCK. 

 Parmelia olivacca (L.) ACH. 

 Placodium cerinum (HEDW.) NAEG. and HEPP. 



