1904.] NATURAL SCIENCES OF PHILADELPHIA. 609 



highlands has been under iini;siial stress of circiims-tances, and when 

 more favorable, but on the whole similar, edaphic conditions were 

 supplied, a mass invasion from these mountain highlands took place 

 at two different and widely divergent periods of time in two directions. 

 After the uplift of the Jersey pine barrens region, the nearby flora of 

 the upland plateaus being edaphically better adapted to the new region, 

 supplied the barren ground with a vegetable covering. Similarly, when 

 the glaciers retreated a mass invasion of pitch pines and associated 

 species moved from the unglaciated Kittatinny Mountains on to the 

 sandy gravelly soil of the great moraine, and when the lumbermen 

 disturbed the forest these plants, adapted to growing in sandy soils 

 and exposed to xerophytic conditions, supplied the constituent ele- 

 ments of the present flora in the greater part of the eastern half of the 

 plateau. 



A consideration of the strand flora of New Jersey, upon which I have 

 spent considerable study, reveals the fact that the time element is 

 important in an explanation of the distribution of the seashore plants. 

 If we contrast the character of the association on the northern and 

 southern shore of New Jersey, we find that the formations on Barnegat 

 beach, for example, are usually open, while those on Wildwood beach 

 are closed and have culminated in the forest type of vegetation. This 

 argues for a greater age of the strand flora of Wildwood, as compared 

 with that, for example, at Sea Side Park in the north. This conclusion 

 is substantiated by the fact that the bays behind the sandy sea islands 

 are converted into salt marshes in the south, while in the north they 

 are wide and still open bays of brackish or salt water. Physiographi- 

 cally and botanically the coast line from Bay Head south to Ocean 

 City is younger than the coast south of the latter place extending to 

 Cape May. 



The latest periods of submergence and uplift had a powerful influ- 

 ence on the distribution of sea-coast species. The present distribution 

 of the swamp rose-mallow, Hihisms moschevtos, in the Atlantic coastal 

 plain illustrates this. The plant normally occurs in brackish marshes 

 from Massachusetts to Florida and Louisiana and on lake shores in 

 saline situations locally in the interior to western Ontario. When it 

 occurs in fresh-water swamps it is reasonably certain that these swamps 

 represent a converted salt marsh present during a former time of sub- 

 mergence. New Jersey shows this best. During the Pensauken sub- 

 mergence southern central New Jersey was an extensive sea island sepa- 

 rated from northern New Jersey by Pensauken Sound. Hibiscus 

 moscheutos in its present distribution in New Jersey follows the former 



