PREFACE. 
Tne 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 west of the 
Mississippi and northward, the citation of authorities is intended to 
be full and complete. The same may be 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 whenever 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 their 
synonymy. For species which are also indigenous in other coun- 
