Fink : LICHENS OF THE MINNESOTA VALLEY. 



furnishing an abundance of moisture, and we find accordingly 

 that the formations on rotten wood are made up in large part of 

 fruticulose lichens. The Calicei formations of old wood are 

 exposed to drier conditions and are composed almost entirely of 

 lichens having poorly developed thalli. 



I must emphasize here that lichens of nearly all the forma- 

 tions enumerated above enjoy moist places, and that lack of 

 moisture produces a decrease in richness both in size and num- 

 ber of individuals and in numbers of species in the formations. 

 I repeat this, which I have established for some parts of Minne- 

 sota previously, because some persons may suppose that lichens, 

 because of their xerophytic adaptations, thrive as well in the 

 driest spots as in those affording more moisture. The excep- 

 tions to this general statement will appear from a careful study 

 of the analyses made of the various formations. 



The gelatinous lichen formation of shaded limestone (Minne- 

 apolis) has been called a scattered one, and I have explained 

 what is meant by the expression. Others of the same kind are 

 the Cladonia-Peltigera lichen formations of shaded earth, the 

 angiocarpous lichen formations of exposed limestone bluffs, the 

 Calicei lichen formations of old wood and in some instances the 

 Cladonia lichen formations of rotten wood, though in other in- 

 stances half or more of the species of Cladonia of the forma- 

 tion may be found on a single log. Thus formations of the 

 kind last named and like the one first named in this paragraph 

 differs from the other three named in the paragraph in that they 

 may or may not be scattered while the three always are, so far 

 as I know, except the Calicei formation which may be found 

 nearly complete on a few rods of old fence in some favorable 

 instances. The two formations of trees are widely extended ; 

 but they are not scattered as I have used the term since one 

 commonly finds a good proportion of the species of either for- 

 mation in passing a short distance, in the woods. 



Also in my classification we have the peculiar condition of 

 two lichen formations occupying the same area. This is illus- 

 trated by the Biatora decipiens lichen formation of exposed 

 calcareous earth and the Lecanora calcarea contorta lichen 

 formation of exposed limestone pebbles, or by the Lecanora 

 lichen formations of exposed granite or quartzite and the Endo- 

 carpon hepaticum lichen formation of exposed earth. Yet it is 

 apparent that the formations are distinct in both instances, the 



