8 THE CHICAGO ACADEMY OF SCIENCES. 



and on mosses, which are minute and easily escape detection. On 

 calcareous soils in Lemont, also in Will County, may be found, 

 besides Cladonia, the curious Heppia despreauxii, Tuckerm. and 

 several species of Endocarpon; also a member of the Algae 

 Nostoc commune, L. The close association of these species, 

 which I have witnessed in other States on similar strata, is worthy 

 of note. From what has been said it appears that it is not safe to 

 fix definitely the number or limits of species in any territory, 

 at this early date of scientific research. The experience of 

 the author, resulting in the addition of nearly thirty new species of 

 lichens to botanical science, is proof of the fact that there are 

 still hundreds of species yet undiscovered. 



Some eight years ago Willey estimated that the whole number 

 of North American species might ultimately reach one thousand, 

 but that limit has been passed already, as I have the names of over 

 sixteen hundred, including varieties, and it is not at all probable 

 that, after the most conservative study and elimination, the number 

 would be reduced by more than three hundred, if so many. 



Having now reviewed in a general way the lichen-flora of the 

 territory under consideration, it seems proper, as nothing has 

 ever been published in the West and South regarding Lichens, 

 beyond mere lists of species, that something should be said about 

 the life history of these humble plants, and of the study, develop- 

 ment and progress of the Science of Lichenology, especially in 

 the United States. The account must necessarily be condensed, 

 but it is believed will be of great utility. 



WHAT ARE LICHENS ? 



This very natural and primary question may be thus answered: 

 Lichens are a natural order of aerial plants which are considered as 

 intermediate between Alga^ and Fungi, but the limits are still un- 

 certain. All are Thallophytes destitute of stem, leaf, root, or 

 flower, and vegetate under the influence of moisture, obtaining the 

 elements necessary to their growth from the air, and not from their 

 substrates, as do the Fungi. Consequently lichens are rapid or 

 slow in growth according to the conditions surrounding them. In 

 extreme heat they become torpid, or do not fully develop, frequently 

 appearing on the surface of their substrates as excrescences, wart- 



