PREFACE. 



The following contribution towards' a history of the known 

 species of North American plants needs little of introduction or 

 explanation, and nothing of excuse. With the purpose of giving a 

 clew to whatever may have been published respecting each species, 

 all the accessible works touching upon the systematic botany of 

 this country, since the adoption of the Linnean system of nomen- 

 clature, have been consulted, including those in the library of the 

 Cambridge Herbarium and the general library of Harvard Univer- 

 sity, the Public Library of Boston, the library of the Massachusetts 

 Horticultural Society, and others of less importance, and to some 

 extent also the Congressional Library at Washington. Citations at 

 second hand have been only sparingly used. 



The territory embraced includes Greenland and the Arctic Coast 

 upon the north, and the borders of Mexico closely adjacent to the 

 United States on the south, the habitat in the latter case being 

 always indicated. For the flora of the region to the Avest of the 

 Mississippi and northward, the citation of authorities is intended to 

 be full and complete. The same maybe said (with some unimpor- 

 tant exceptions) for the Atlantic States prior to 1840, the date of 

 the conclusion of the first volume of Torrey & Gray's Flora of 

 North America. For the subsequent period, the publications of 

 Torrey, Gray, and Chapman have been deemed sufficient in most 

 cases. Others are referred to Avhenever there is special reason for 

 so doing. 



The matter of synonymy has been often a difficult one, in the 

 disagreement of authorities and the frequent uncertainty as to the 

 degree of reliance to be placed upon recorded determinations. For 

 this reason, continual reference has been had to the plants them- 

 selves ; and the collections in the Harvard University Herbarium, 

 which include in most cases authentic and typical specimens, have 

 been carefully collated under most of the genera for the purpose 

 of confirming the validity of species and the correctness of tlieir 

 synonymy. For species which are also indigenous in other coun- 



