122 



GEOLOGY OF LA SALLE COUNTY. 



ill this direction would be interesting*, the present pur- 

 pose, which is mainly their classification, will be best 

 subserved by omittino- the discussion. 



WHERE AND HOW THEY GROW. 



Lichens will be found almost everywhere, even on 

 the bare prairie, on boulders often. The native woods, 

 earth and rocks, pebbles and old orchards are their 

 favorite home, while certain species are peculiar to cer- 

 tain substrata and localities. 



The principal parts of the plant exposed — the 

 Thallus and Apothecium, will first attract notice 

 on trees, old fences, etc., and are popularly called 

 by the plain citizen — not versed in botony — Mosses ! A 

 good exhibition may be observed on the Deer Park 

 road in the ravine on the Ho^aboom place, where some 

 oak, walnut and hickory trees and the old fence contain 

 a number of species. One, of a brio-ht yellow color 

 (THELOSCHISTES), is prominent. These foliace- 

 ous kinds are attached to the substrate by fibrils of 

 the thallus. While a vast number of species grow on 

 trees and shrubs may inhabit only rocks, stones and 

 the earth. A few species by means of the acids of the 

 thallus bore into the hardest rocks, and becoming- im- 

 bedded in it, show on the surface as pits of the size of 

 a pin head or smaller. Lichens avoid cities, the smoke 

 and p-as beino- fatal to them. On the St. Peters sand- 

 stone at Starved Rock and along- the cliffs for miles, in 

 the ravines and on the trees many fine species can be 

 found, among- them the Reindeer moss (CLADONIA). 

 Localities like the preceding- afford the best collecting- 

 gfrounds, but no place should be neg'lected, for what 

 suits one species may not be adapted to another. The 

 searcher cannot g-o amiss, and can often spend hours 

 within a small area. The same rules for collecting- 



