668 MINNESOTA BOTANICAL STUDIES. 



Comparing the lichens of this formation with those of the 

 shaded rock formation above, we find that, as a result of the 

 more moist habitat of the forms, growing on earth in shade and 

 usually on an abundance of decaying vegetable remains which 

 hold moisture, the formation consists of plant individuals even 

 less closely attached to the substratum, except perhaps the 

 Collemas, which have no cortex and which, therefore, even in 

 their shaded situation, remain close to the substratum to absorb 

 the moisture which is rapidly evaporated from their non-cellular 

 surfaces. The Peltigeras with a well developed upper cortex 

 hold moisture better and rise somewhat higher. The podetia of 

 the Cladonias have a surrounding pseudo-cortex of densely 

 interwoven hyphae, which serves for protection ; against too 

 rapid evaporation of moisture as well as for mechanical sup- 

 port. Hence the Cladonias rise vertically and are especially 

 numerous as to species and individuals in this moist and shaded 

 formation, as well as unusually luxuriant. Thus it appears 

 that we have in this formation, as in those already considered 

 plants adapted in very different ways to the environment. 



The remarkable constancy of occurrence of certain floral 

 elements in certain environments can scarcely be better illus- 

 trated than by comparing the calcareous earth lichen formation 

 given below with similar ones recorded in the fifth paper of this 

 series for Granite Falls, Minnesota, and Fayette, Iowa.* 



BIATORA DECIPIENS LICHEN FORMATION~OF EX-POSED CALCA- 

 REOUS EARTH (LEAF HILLS). 



Heppia despreauxii (MONT.) TUCK., C. 



Urceolaria scruposa (L.) NYL., C. 



Biatora decipiens (EHRH.) FR., C. 



Biatora decipiens (EHRH.) FR. var. delabata AUCT., C. 



Biatora muscorum (Sw.) TUCK., C. 



Endocarpon hepaticum ACH., C. 



All of the six floral elements recorded in the present forma- 

 tion and marked (C) are also listed in the formation at Granite 

 Falls and Fayette, and each of these last two contains a single 

 rare species not discovered in the Leaf hills formation. As in 

 the localities previously studied, the formation in the hills is best 

 developed on the hill-sides where the plants are washed with 

 the lime-impregnated water which flows down the slope during 



*Fink, B. 1. c., 295-296. 



