BOTANY. 



127 



not many miles below, where numerous species occur, many in 

 abundance, which do not reach the Hudson Valley. Although many 

 plants absent from this locality have been recorded from points at no 

 great distance, the fact of their non-occurrence over a certain diversi- 

 fied tract shows them to be not of oreneral distribution, and it would 

 obviously tend to a false result to include other than well-represent- 

 ed species in a comparison of general features. 



The deciduous forests of that section of the Catskills under con- 

 sideration are largely composed of hard maple, beech, and birch; the 

 oaks, hickories, and chestnuts of the lower country gradually disap- 

 pearing with increasing elevation, a few stragglers only of some of 

 these trees penetrating the region through the main valley, and none 

 occurring in the mountain forests. 



Whatever invasion there has been of the vegetation of the lower 

 country into the mountains has without doubt been assisted by in- 

 voluntary human agency, for the influence that has resulted in the 

 introduction and naturalization of many foreign plants along the rail- 

 road and about the villages, and the effects of which are often recog- 

 nized remote from human settlement, cannot have been inoperative 

 with native vegetation. 



The many familiar introduced plants abounding near the railroad, 

 and in populated sections, affords a feature of correspondence with the 

 Flora of the Lower Hudson Valley, but in ascending the secondary 

 valleys, the true Flora of the region appears with gradually increasing 

 purity, and in those portions remote from settlement, and in the 

 mountains, the contrast between the vegetation of these adjoining 

 districts is most striking. A more detailed comparison will show that 

 this contrast is caused more by the absence in the vegetation ot the 

 mountains of genera and species which abound in the Hudson X^alley, 

 than by the addition of forms not found in the latter region. In the 

 arboreous vegetation of the mountains the following genera ot trees, 

 which constitute the most conspicuous and important elements of the 

 Hudson Valley woodland, are not represented : Liriodcndroii, 



