610 PROCEEDINGS OF THE ACADEMY OP [Sept., 



shore line of that ancient island, for it occurs in the salt marshes of the 

 coast, on both banks of the Delaware river to the head of tide water, 

 and also in fresh-water marshes along the New York Division of the 

 Pennsylvania Railroad between Trenton and Newark, the roadbed 

 between these cities being laid upon the geologic site of the Pensauken 

 Sound. 



South of New Jersey the region, including southeastern Pennsylvania, 

 may be divided historically according to the age of the flora into several 

 well-marked divisions. 



1. The flora of the Southern Appalachians and its northeastern 

 extension into southern and southeastern Pennsylvania, The facts 

 presented in two former papers-^ all argue for the great antiquity of 

 the flora of North Carolina and southeastern Pennsylvania, because 

 this flora, in all probability, represents the more or less modified de- 

 scendants of that characteristic flora which in later Eocene or Miocene 

 time extended to high northern latitudes. 



2. The flora of the coast plain occupied by the long leaf pine with its 

 associated species, which probably represent the ultimate stages of 

 successions initiated at the time of the final elevation of the sea bottom 

 along the coast line. These plants probably entered the elevated 

 coastal region by a mass invasion from a circimiscribed area contiguous 

 to the Atlantic shore line, for it has been established that contiguous 

 vegetation furnishes 75-90 per cent, of the constituent species of an 

 initial formation. The reason for this is to be found not only in the 

 fact that adjacent species have a much shorter distance to go and hence 

 will be carried in greater quantity, but also in that species of the forma- 

 tions beyond must pass through or over the adjacent ones. In the 

 latter case, Clement states that the "number of disseminules is rela- 

 tively small on account of the distance, w^hile invasion through the 

 intermediate vegetation, if not entirely impossible, is extremely slow, 

 so that plants coming in by this route reach the denuded area only to 

 find it already occupied."*^ 



3. Plants of probable Neotropic origin which have, according to 

 Kearney, in all likelihood made their first appearance in the Appalachian 

 region in geologically very modern times, probably after the close of 

 the so-called glacial epoch. 



* Harshberger, J. W.", "An Ecologic Study of the Flora of Mountainous 

 North Carohna," Botanical Gazette, XXXVI, 241-258, 368-383, 1903, and "A 

 Phytogeographic Sketch of Extreme Southeastern Pennsylvania," Bulletin 

 Torrey Botanical Club, XXXI, 125-159, March, 1904. 



* Clements, Frederick E., "Studies of the Vegetation of the State, III. — 

 The Development and Structure of Vegetation," Botanical Survey of Nebraska, 

 1904. 



