288 MINNESOTA BOTANICAL STUDIES. 



bution whose explanation would be veiy difficult or impossible to 

 trace ; but it is quite remarkable that wuth this exception all the 

 plants found in the two formations sixty miles away should oc- 

 cur in this lichen formation also, especially since there could 

 have been no rock}^ connection between the two areas since 

 glacial times. It is not strange that the exposed granite lichen 

 formation at Granite Falls should be a much richer one than the 

 two exposed formations at Pipestone combined; for it is a much 

 larger area, is connected with a limestone lichen formation and 

 an epiphytic, and a number of swamps and ponds furnish mois- 

 ture along the borders. Indeed the presence of ten of the 

 fourteen additions may be more or less satisfactorily explained. 

 These I shall proceed to consider seriatun. 



Physcia stellaris (L.) Tuck., var. apiola Tuck. — a litho- 

 phytic variety of a species common on adjacent trees. 



Lecanora frustulosa (Dicks.) Mass. — a northern lichen not 

 extending so far south as Pipestone. 



Lecanora subfusca (L.) Ach., var. alliophana Ach. — a variety 

 of a species common on trees near by. 



Lecanora subfusca (L.) Ach., var. coilocarpa Ach. — as the last 

 above. 



Lecanora cervina (Pers.) Nyl., var. cinereoalba var. nov. — 

 has not been seen outside the Minnesota valley. 



Lecanora calcarea (L.) Sommerf., var. contorta Fr. — a lichen 

 migrating from the limestone near by. 



Rinodina sophodes (Ach.) Nyl. — found on trees of the region 

 and perhaps migrating from them. 



Rinodina lecanorina Mass. — a ver}^ rare plant which, therefore, 

 very probably does not exist at Pipestone or w^as overlooked. 



Urceolaria actinostoma Pers. — as the last above. 



BiatorarufonigraTucK. — a northern form not extending so far 

 south as Pipestone. 



Though somewhat confusing another similar lichen formation 

 must be introduced here for comparison as follows : 



Lecanora formation of exposed quartzite (New Ulm). 

 Parmelia conspersa (Ehrh.) Ach., CTS. 

 Physcia caesia (Hoffm.) Nyl., CTS. 



Placodium cerinum (Hedw.) Naeg. and Hepp. var. sideritis 

 Tuck., CT. 



