98 BULLETIN OF THE 



is poor, only amounting in the second and fourth named, to half 

 the number found here. 



Relative to the above comparisons in general, it may be remarked 

 first, that the flora of Essex county, Massachusetts, is much more 

 thoroughly and exhaustively elaborated than that of the District 

 of Columbia, lying as it does in the immediate center of botanical 

 activity in this country. This alone is probably sufficient to account 

 for all the difference in the number of species in the two localities, 

 and it will probably be ultimately found that the two floras are very 

 nearly equal. In the second place, if it should be thought that 

 from its intermediate location between the southern and the nor- 

 thern sections of the country, our flora should naturally be the more 

 rich in species, it may be satisfactorily urged on the other hand, 

 that while we have only an inland territory, Essex county has both 

 an inland and a maritime territory. Could our range be extended 

 to embrace even a small extent of sea coast, the number would 

 thereby be very largely increased. 



As a final statistical exhibit, more comprehensive in its scope, 

 and from a different point of view, I give below a table in which 

 our local flora is compared not only with the floras above named, 

 but with several others in America. As these several floras not 

 only overlap to a considerable extent, but also differ widely in the 

 total number of plants embraced by each, it is evident a numerical 

 comparison would convey a very imperfect idea of the variety in 

 their essential characteristics. It is therefore necessary to reduce 

 them to a common standard of comparison, which has been done by 

 disregarding the actual numbers and employing only the percentage 

 which each group compared bears to the total for each respective 

 flora. The relations of the several groups to the total vegetation 

 of each flora is thus brought out, and a comparison of the percent- 

 ages of the same group in the different areas displays in the clearest 

 manner possible the predominance or scantiness of the groups in 

 each flora. Upon this must depend, in so far as botanical statistics 

 can indicate it, the fades of each flora, its peculiarities and char- 

 acteristics. As in previous comparisons, the table is restricted to 

 Phenogamous and vascular Cryptogampus plants, and the same 

 groups are employed, except that the large genera are omitted, 

 while the number of orders is increased to the 23 largest of this 

 flora, which is taken as the basis of comparison, and they are ar- 

 ranged in the order of rank with reference to it. 



