Fink : LICHENS OF THE MINNESOTA VAM.KY. 291 



Placodium aurantiacum (LiGirrr.) NAEG and HEPP. 

 Biatora fuscorubella (HOFFM.) TUCK. 



C. SPECIES WHICH HAVE PROBABLY MIGRATED FROM EARTH. 

 Peltigera rufescens (NECK.) HOFFM. 

 Peltigera canina (L.) HOFFM. 



Of the three parts of the formation under consideration only 

 the first can be compared with the similar formation at Pipe- 

 stone, and we find besides the 3 species of the Pipestone for- 

 mation, 8 additional forms as a result of greater areas studied, 

 more moist conditions near the Minnesota river, and where 

 abundant ponds and marshes situated near the rocks give moist- 

 ure, and where trees are numerous in some parts of the area 

 and increase the shade. I must add that presence of the 

 Ramalinas here, and their absence from shaded rocks at Pipe- 

 stone leads to the suspicion that they may have sprung from 

 RamaUna calicaris (L.) Fr. of the region, migrating from trees 

 to rocks and acquiring the varietal, and in one instance the 

 specific characters as an adaptation to changed environment. 

 The question is as to whether these lichens are sufficiently plastic 

 to acquire such new characters since trees have grown in the 

 valley in post-glacial time. I can only say that I believe that 

 they may be, and that it is quite as likely that the two Rama- 

 linas should be placed in the second division of the formation 

 as in the first. 



As to plants of the second portion of the formation, which I 

 have designated as having probably migrated from trees, in 

 some instances they are locally more abundant and luxuriant on 

 the rocks than on trees. Hence a hasty consideration would 

 lead to the conclusion that they have not migrated. But the 

 luxuriant condition obtains on the rocks in Parmelia borreri 

 Turn., a lichen seldom seen on rocks elsewhere, and many of 

 these lichens grow on mossy rocks where lichens are commonly 

 large. Also it is to be taken into account that these lichens are 

 those usually found on large trees with rough bark. The larger 

 trees were for most part destroyed years ago by man or fires, 

 and these lichens, formerly common on trees, are preserved on 

 rocks better than on the less permanent trees. Hence some of 

 them are more common now on the rocks than on the trees, 

 which are for most part second growth and not large. The 



