14 FLORA OF WASHINGTON AND VICINITY. 



The botanist familiar with this flora will be able to form a judgment 

 more or less correct as to what the plants probably were to which these 

 last names were assigned. 



With regard to the 146 species above enumerated, it must not be 

 hastily concluded that they represent the disappearance from our flora 

 of that number of plants. While they doubtless indicate such a move- 

 ment to a certain extent, there are ample e\idences 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 as 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 vegetation of 

 the Lower Potomac or the Chesapeake Bay, and also the mountain flora 

 of the Blue Eidge. 



4th. The actual extermination and disappearance of indigenous plants 

 during the fifty years that have intervened since they made their re- 

 searches. 



The figure placed in parenthesis before each name in the list denotes 

 the class in the order above indicated to which I would assign each one 

 of these species. This assignment is of course in great part conjectural, 

 and may be incorrect in many cases, while another botanist might have 

 diftered considerably in regard to special plants ; yet it is not based 

 upon a general judgment drawn from my acquaintance with the present 

 flora, but upon several kinds of special evidence, which in numerous in- 

 stances has reversed mj prima facie decision. In the first place I have 

 carefully 'Compared the range of each species as given in the text-books 

 to determine the probabilities for or against its being found here, and 

 in the second place I have prepared a corresponding list of plants now 

 found but not enumerated in the Prodromus and compared the two lists. 

 I have also endeavored to make due allowance on the one hand for the 

 tendency above referred to, to swell the catalogue as fully as possible, 

 and on the other, for the well known fact that every flora is at all times 

 undergoing changes. It must not be forgotten either that half a century 

 ago the surface of the entire country here must have presented a very 

 different appearance from that which it presents now. The population 

 of the District of Columbia in 1830, when it included a portion of Vir- 



