THE LICHEN-FLORA OF CHICAGO AND VICINITY. 7 



The geological conditions in most of our territory are not 

 favorable to the growth of a great number of species owing to 

 the absence of forests and out-cropping rocks of different forma- 

 tions and ages, all having an important bearing, because these are 

 the substrates to which lichens attach themselves, and the investi- 

 gator will note at once that certain strata and trees, or the earth, 

 contain some species not found elsewhere, while others are indif- 

 ferent as to substrate. Localities in and around Chicago formerly 

 rich in lichenose vegetation are now destitute of it. The species 

 were and are mostly corticolous, with a few on rocks, where exposed, 

 and even on the boulders of our prairies. But the tidal waves of 

 civilization have changed the conditions under which lichens grow, 

 and to find them abundantly we must seek the country where the 

 air on which they feed is pure and the substrates suitable. The 

 sandy soil of the lake shore only produces them where it is covered 

 or mixed with vegetable mould." Northwards from the limits of 

 Chicago the genera Cladonia and Peltigera are found in the woods 

 on earth. The scarce growth of Birch (Betula papyracea), near 

 Glencoe, contains two species rare -in this section. These are 

 Sagediaox3^spora, Tuckerm. and Pyrenula thelaena, Tuckerm. The 

 former is peculiar to that substrate. On trees, notably the oaks, 

 are abundant growths of Parmelia borreri. Turner, P. caperata, 

 (L.) Ach., Physcia stellaris, L., Lecanora subfusca, Ach.; and on 

 hickory, Arthonia lecideella, Nyl. The latter is peculiar to this 

 substrate and the genus rare, in our territory, in species, although 

 the above and A. spectabilis, PL, are abundant. Leaving the 

 vicinity of the lake and the flat-prairies, we find further west and 

 south the best development of lichen-flora along wooded streams 

 and on rocks where these are exposed. Gravel, boulders, old 

 fences, logs and stumps, sustain many species. New and rare ones 

 sometimes reward the explorer. At Riverside I found a new 

 Verrucaria on siliceous deposits and at Joliet, another new spe- 

 cies, Lecanora perproxima, Nyl., on silurian rocks. Both have 

 been described by Dr. Nylander, of Paris. The saxicolous 

 species are the most difficult and many are in confusion. The 

 occupation and use of nearly all the lands; the denudation of 

 forests, and drainage of the country, has, as in the case of the 

 pha:nogamia, caused many species to disappear entirely from our 

 territory. The best localities for saxicolous types are in the town- 

 ship of Lemont and Will County. Hanover and other places 

 adjacent to streams produce common forms. A few occur on earth 



