68 BULLETIN OF THE 



The assignment which I have made of each species to its appro- 

 priate class has been of course in great part conjectural and may- 

 be incorrect in many cases, while another botanist might have 

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

 on a general judgment drawn from my acquaintance with the present 

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

 instances has reversed my 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 

 compared this list with the corresponding one of the species now 

 found but not enumerated in the Prodromus. I have also endeav- 

 ored to make due allowance on the one hand for the tendency above 

 referred to to swell catalogues beyond their proper limits, and on the 

 other for the well known fact that every flora is at all times under- 

 going changes. 



It must not be forgotten, either, that half a century ago the sur- 

 face 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 

 Virginia, was only 39,834. It is now, exclusive of the Virginian 

 part receded to that State, 177,638. To render the comparison 

 more exact we may add to the latter number the present population 

 of Alexandria county, amounting ^p 17,545, and we have in the 

 place of 39,834 a population on substantially the same area of 

 195,183, or about five times as large. The population of Maryland 

 in 1830 was 447,040 ; in 1880 it was 934,632, or considerably more 

 than twice as large. That of Virginia in 1830 was 1,211,405. Vir- 

 ginia and West Virginia, embracing the same territory, now number 

 2,131,249 the population not having quite doubled: the retardation, 

 however, as compared with Maryland, is doubtless due entirely to 

 influences affecting the southern counties. There were doubtless 

 large areas of primeval forest then within our limits which are now 

 under cultivation, and a much greater variety of soil and woodland 

 was then open to the researches of the botanist. As a consequence 

 we ought to expect that it would sustain a much richer flora. 



The general result at which I arrive by the process adopted may 

 be summed up as follows : 



1st. That 43 of these names, or 29 per cent, of them, belong to 

 the first class and constitute errors in naming. 



