PHILOSOPHICAL SOCIETY OF WASHINGTON. 67 



artificial system of Linnaeus, so that before the plants could be 

 placed in juxtaposition they required to be re-arranged. This, how- 

 ever, was not the principal difficulty. Such extensive changes have 

 taken place in the names of plants during the fifty years which have 

 elapsed since that work appeared, (1830,) that it is only with the 

 greatest difficulty that they can be identified. After much labor, I 

 have succeeded in identifying the greater part of them, and in thus 

 ascertaining about to what extent the two lists are in unison. This 

 also reveals the extent to which each overlaps the other, and 

 thus affords a sort of rude index to the changes which our flora has 

 undergone in half a century. There are, however, as will be seen, 

 many qualifying considerations which greatly influence these con- 

 clusions and diminish the value of the data compared. 



The whole number of distinct names (species and varieties) enu- 

 merated in the Prodromus is 919. Of these 59 are mere synonyms 

 or duplicate names for the same plant, leaving 860 distinct plants. 

 I have succeeded in identifying 708 of these with certainty as among 

 those now found, and six others, not yet clearly identified, should 

 probably be placed in this class. This leaves 146 enumerated in 

 the old catalogue which have not been found in recent investigations. 

 [A classified list of these plants was presented and commented upon 

 somewhat in detail.] 



With regard to these 146 species, it must uot be hastily concluded 

 that they represent the disappearance from our flora of that num- 

 ber of plants. While they doubtless indicate such a movement 

 to a certain extent, there are ample evidences that many of them 

 can be accounted for in other ways. After careful consideration, I 

 have been able to divide them into four principal classes arising 

 out of — 



1st. Errors on the part of those early botanists in assigning to 

 them the wrong names. 



2d. The introduction into the catalogue of adventitious and even 

 of mere cultivated species, never belonging to the flora of the place. 



3d. The undue extension by those collectors of the range of the 

 local flora so as to make it embrace a portion of the maritime vege- 

 tation of the Lower Potomac or the Chesapeake Bay, and also the 

 mountain flora of the Blue Ridge. 



4th. The actual extermination and disappearance of indigenous 

 plants during the fifty years that have intervened since they made 

 their researches. 



