282 MINNESOTA BOTANICAL STUDIES. 



gelatinous lichens, the Collemei, are especially conspicuous in 

 the genera Pyrenops/'s, Omphalaria, Collcma and Leptogium. 

 This happens because part of the valley is more favorable for 

 their development as to substrata and moisture than other 

 studied portions of the state. The part of the studied por- 

 tion of the valley most favorable for their development is the 

 Mankato vicinity where most of the gelatinous lichens were 

 found. The whole number of Collemei found in the valley is 

 17. Richness is apparent when we add that only four were 

 found about Minneapolis, u in the lake Superior region and 

 that only 16 are known in Iowa. 



It may be added that a large proportion of the species added 

 to the state flora are of special interest for various reasons. 

 Thus the Omphalarias are not commonly collected ; Lecanora 

 bookii (Fr.) Th. Fr. is a difficult lichen to detect ; the Pyrenulas 

 are difficult to distinguish macroscopically and are therefore 

 commonly overlooked ; members of the genus Pyrenopsis are 

 seldom reported ; while Urceolaria actinostoma Pers., Buellia 

 pullata Tuck, and Heppia polyspora Tuck, are very rare lich- 

 ens. Rinodina lecanorina Mass, is reported for the first time 

 from North America, and Lecanora cervina (Pers.) Nyl. var. 

 cinereoalba var. nov. is interesting because new. 



It may be noted in passing that the region shows some of the 

 Arctic or sub- Arctic species found at Taylor's Falls and already 

 discussed in a former paper. These are Biatora rufonigra 

 Tuck., two forms of Buellia petraa (Flot., Koerb.) Tuck, 

 and an Ephebe, though not the species reported from Taylors 

 Falls. As in the Taylors Falls region the Buellia is the most 

 common of these species being a crustaceous form well adapted 

 to resist unfavorable conditions. The Biatora is next in fre- 

 quency of occurrence and the Ephebe, a fruticulose form, was 

 only seen once. So far as I was able to ascertain bv careful 

 search the foliaceous forms, Umbilicaria and Nephroma, found 

 at Taylors Falls have not succeeded in persisting in the Min- 

 nesota valley. This failure of northern forms to persist so suc- 

 cessfully may be accounted for perhaps in a very small degree 

 by more southern position of the area now under consideration, 

 but no doubt is due much more to climatic and edaphic factors 

 which have allowed plant migrations to proceed northward more 

 rapidly in the Minnesota valley than farther east in the state 

 since the last retreat of the glaciers. This matter has been 



