204 Statistics o f the Flora of the Northern States, 



Art. XVI. — Statistics of the Flora of the Northern United States ; 

 by Asa Gray. 



While engaged in the preparation of a second edition of the 

 Manual of the Botany of the Northern United States, I was re- 

 quested by an esteemed correspondent, upon whose judgment I 

 place great reliance, to exhibit, in a compendious and conven- 

 ient form, the elements of the flora I was occupied with. I ac- 

 cede to this request only because I may be presumed to possess 

 considerable facilities for collecting and correcting a portion of 

 the required data. But I cannot command the time needed for 

 a proper elaboration and discussion of these materials, nor have 

 I any special aptitude for this kind of research. I may, how- 

 ever, collect and arrange the principal data; for the use of those 

 better qualified to discuss them, and to indicate their bearings 

 upon many questions of the highest scientific interest, respecting 

 the geographical distribution, the mutual relations, the nature, 

 and the origin of the existing species of plants; — questions 

 some of them so speculative or so difficult that they are not 

 likely to be conclusively answered in our day; others more 

 nearly within our reach ; but all perhaps capable of some elu- 

 cidation from the critical comparison of the flora of any one 

 considerable region with the vegetation of other parts of the 

 world. 



The work,* which forms the basis of the following statistics of 

 the botany of the Northern United States, has now been ex- 

 tended in geographical area beyond the limits of the Northern 

 States, politically so called; inasmuch as this area includes Vir- 

 ginia and Kentucky, and stretches westward to the Mississippi 

 Eiver. The southern boundary of 36° 30' has been adopted 

 (instead of Mason and Dixon's line) because it coincides better 

 than any other direct geographical line with the natural division 

 between the cooler-temperate and the warm-temperate vegeta- 

 tion, — between the flora of the northern and of the southern At- 

 lantic states. Few characteristically southern plants advance to 

 the north of it, and those chiefly on the coast of the low south- 

 eastern corner of Yirginia, in the Dismal Swamp, and the envi- 

 rons of Norfolk. Could we vary the line where it intersects the 

 longitude of Washington, carrying it north until it reaches James 

 Kiver, and thence due east again, the small quadrangle thus ex- 

 cluded would exclude nearly all the properly southern indige- 



* Manual of the Botany of the Northern United States ; second edition ; inclu- 

 ding Virginia, Kentucky, and all east of the Mississippi: arranged according to the 

 Natural System ; by ASA GRAY, (the Mosses and Liverworts by Wm. S. Sulli- 

 vant). With 14 plates, illustrating the Genera of the Cryptogamia. New York : 

 George P. Putnam & Co., I860., 



