few species are found on bowlders, and a still smaller number on earth. 

 The distribution of the species growing on trees is especially interesting. 

 On both the east and west sides of the larger lakes lichens are found chiefly 

 on the sides of the trunks of trees which face the lake. Apparently this 

 peculiarity of distribution is related to moisture rising from the lakes, and 

 these lichens seem to agree with those of the vicinity of Minneapolis de- 

 scribed by Finkjio who states that ''most species of lichens here are dis- 

 posed to confine themselves to moist situations, as about the bodies of water 

 mentioned above, in heavy woods, or when in dry places near the ground. ' ' 

 However, a closer study of the lichens of the region shows that they are 

 usually equally abundant on the outside of the groves bordering the lakes, 

 and this is true of the west side of the groves on the west side of the lakes 

 in situations which are usually quite xerophytic. Moreover on both native 

 and planted trees with a north exposure the north side of the trunk is likely 

 to be covered with lichens, and in openings in the woods all the trees facing 

 the opening are likely to have lichens on the exposed side. This suggests 

 that light rather than moisture determines the distribution of the lichens in 

 our region. It is probably for the same reason that they do not ascend 

 higher on the trunks of trees where the crowns cut off light. 



In recent years there has been a marked reduction in the number of 

 lichens in some of the groves, and in the more striking of these cases it 

 seemed to have followed the pasturing of the groves. 



In his paper on Iowa lichens Fink (see Bibliography) reported a number 

 of species collected by Professor Arthur in our region. The species so re- 

 ported are marked with an asterisk in the following list; the specific locality 

 and habitat references are based on the writer 's collections. 



LICHEKES 



* Opegrapha varia (Pers.) Fr. — Inn woods, on Quercus macrocarpa and 



Juniperus virginm na. 

 Opegrapha demissa Tuck, — Inn woods, on Tilia americana. 

 Graphis scripta (L.) Ach. — Inn woods, on Acer saccliarum. 

 Graphis scripta var. serpentina (Ach.) Nyl. — Woods north of the Inn, 



on Tilia americana. 



* Lecidea enteroleuca Fr. — Near Inn, on old bark. 



* Lecidea enteroleuca var. theiophaca Tuck. — Eeported by Fink. 



* Bacidia fuscorubella (Hoffm.) Arn. — Eeported by Fink as Biatora. 

 Buellia parasema (Ach.) Koerb. — On TiJia americana near the Inn. and 



Quercus T^acrocarpa at Spirit Lake. 



* Buellia myriocarpa (Lam. & DC.) Mudd. — Xear the Inn. on Acer sac- 



cliarum and Jwniperus virginian-a. 



* Psora decipiens (Ehrh.) Hoffm. — Calcareous earth. Eeported by Fink as 



Biatora. 



Cladonia cristatella Tuck. — At Estherville. on old stump. 

 Cladonia mitrula Tuck. — At Estherville, on earth. 



* Cladonia gracilis (L.) Willd. — On earth at Estherville (Fink). On 



Juniperus virginiana at the Inn. 



15 Minnesota Botanical Studies. Bulletin no. 9, 1897, particularly p. 705. 



56 



