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climate and soil, contains representatives of the Lichen-flora of the 

 world at large. It presents peculiar diflSenlties on that account, 

 because the Lichens of the warm are different from those of the cold 

 regions, and require a special knowledge possessed only by a few, 

 for their determination. While the lichens of our Arctic and tem- 

 perate regions are in general similar to those of northern and tem- 

 perate Europe, which have been so fully explored and described, 

 they have many species peculiar to this continent, and new ones are 

 at any time likely to be discovered. Hardly any portion of the 

 whole continent has been thoroughly explored, while in Europe al- 

 most every yard has been gone over, by scores of explorers, especi- 

 ally for the last hundred years, and they have recorded the results 

 of their labors in hundreds of works. Here there has been but one 

 authoritative exponent of Lichenology, and the collectors have been 

 few and far between, and our Lichenological writings, aside from 

 mere enumerations, can almost be counted on the fingers of one 

 hand. 



Our Lichen Flora may be divided into six districts:. (l)"The 

 Arctic; (2) the Alpine ; (3) the Atlantic ; (4) the Soi'^th^rn /(5) 

 the Western, west of the Mississippi t(i) the Rocky Mountains ; (6) 

 the Pacific. The Lichens of the Arcti^ district are in general like 

 those of the same regions in Europe and Asia. The same may be 

 said of those of the Alpine district, which includes the higher sum- 

 mits of the mountains of New England, the AUeghanies, and the 

 Rocky Mountains, and of the Atlantic district, comprising the tem- 

 perate region east of the Mississippi. The Western extends beyond 

 that river to the Rocky mountains. The Southern district em- 

 braces the states along the lower Atlantic and the Gulf of Mexico, 

 Mexico, and the more southern parts of California, and may be called 

 subtropical and considered a part of the tropical flora. The Pacific 

 district, comprising that portion of the country west of the Rocky 

 Mountains, presents many distinct and peculiar forms, to which 

 large additions may be expected when it is fully explored ; and the 

 same may be said of the Southern district, some of the species of 

 which extend along the Atlantic coast as far even as New England. 

 Each of these districts at its extremes merges into the adjoining 

 ones. It was suggested by Fornander in an Essay on the Geogra- 

 phy of Lichens in 1831, that many species of northern Europe may 

 have had their origin in America, and some species which were first 



