IV PREFACE. 



The geographical hmits of the work include the countries 

 generally north of 40^ N. lat. ; but only occasional reference has 

 been made to those regions of Arctic America which do not 

 belong to the British possessions, and I have had, also, less 

 re|ard to the extreme southern boundary, which is everywhere 

 characterized by the appearance of southern species. The great- 

 er, or more northern, portion of this district is naturally distinct 

 and similar throughout, and its Lichenose vegetation seems, in- 

 deed, almost represented by that of New England alone. It is 

 probable, however, that a large proportion of the species in- 

 habitmg any part of the district, if we except its southwestern 

 extremity, are described here. 



For the particular citations of New York Lichens, my princi- 

 pal authorities have been the Catalogue of the Plants of JVew York 

 of Dr. Torrey, 1819, and the Synoptical View of the Lichens of 

 JVeio York by Mr. Halsey, 1824. For citations of species from 

 Pennsylvania, &c., besides Dillenius (as revised in Fries's fndex 

 Dillenianus) I have been almost wholly indebted to the Catalogue 

 of the Plants of JVorth America of Muhlenberg, 1818, and his 

 specimens now existing in that part of the herbarium of Acharius 

 which is at Upsal, as well as in the herbaria of Willdenow and 

 Floerke at Berlm. For the Canadian and Newfoundland Lichens, 

 I have availed myself of those described in the Flora of ]\Ii- 

 chaux, as compared with the specimens in his herbarium at Paris, 

 the species enumerated by Mr. De la Pylaie in his Voyage a Vile 



species chiefly, the Synopsis and the Lichenographia of Acharius. The termi- 

 nology is wholly that of Fries, and its peculiarity will be found mostly to consist 

 in a strict etymological use of the whole force of the terms he employs. These 

 terms are, then, possibly, the best expressions of the knowledge they contain, and, 

 in this view, as well worth studying as any other part of systematic science, tlie 

 design of which is to teach, not current names for its objects, but llieir history. 



