PREFACE. 



THIS work is designed as a compendious Flora of the .Northern portion 

 of the United States, arranged according to the Natural System, for the 

 use of students and of practical botanists. 



The first edition was hastily prepared to supply a pressing want. Its 

 plan, having been generally approved, has not been altered, although the 

 work has been to a great extent rewritten. Its increased size is mainly 

 owing to the larger geographical area embraced in it, being here extended 

 southward so as to include Virginia and Kentucky, and westward to the 

 Mississippi River. 



This southern boundary coincides better than any other geographical 

 line with the natural division between the cooler-temperate and the warm- 

 temperate vegetation of the United States; very few characteristically 

 Southern plants occurring north of it, and those only on the low coast of 

 Virginia, in the Dismal Swamp, &c. Our western limit, also, while it 

 includes a considerable prairie vegetation, excludes nearly all the plants 

 peculiar to the great Western woodless plains, which approach our borders 

 in Iowa and Missouri. Our northern boundary, being that of the United 

 States, varies through about five degrees of latitude, and nearly embraces 

 Canada proper on the east and on the west, so that nearly all the plants 

 of Canada East on this side of the St. Lawrence, as well as of the deep 

 peninsula of Canada West, will be found described in this volume. 



The principal facts respecting the geographical distribution of the plants 

 which compose the flora of our district, will be presented in another 

 place. In this work I endeavor briefly to indicate the district in which 

 each species occurs, or in which it most abounds, in the following manner : 

 1 . When the principal area of a species is northward rather than south- 

 ward, I generally give first its northern limit, so far as known to me, if 

 within the United States, and then its southern limit if within our boun- 

 daries, or add that it extends southward, meaning thereby that the species 



