1920.] NATURAL SCIENCES OF PHILADELPHIA. 119 



decidedly unfavorable to it. Barrel^ has pointed out that certain 

 peneplains of the eastern United States of Pliocene and Pleistocene 

 age have resulted from marine transgression, and it seems extremely " 

 improbable that any part of southern New Jersey could have es- 

 caped submergence during these epochs. 



A consideration of the soil acidity relations indicates, however, 

 that there is an adequate explaiiation of the presence of this flora, 

 entirely aside from the geological history of the New Jersey Pine- 

 barren area. The peculiar and isolated character of the flora of 

 this area has been greatly overestimated, because of incomplete 

 knowledge of the floras of surrounding regions. McAtee^ has re- 

 cently shown that over 70 per cent of the most typical plants of the 

 New Jersey Pine-barrens grow in favorable places ineastern Mary- 

 land; and Harper^ has noted the presence of pine-barren plants in 

 a strip of land crossing the Delaware peninsula. Not more than 

 five or six of the members of the Pine-barren flora are actually end- 

 emic, the great majority of them ranging, as shown by Stone; for 

 considerable distances northward or southward (or in both directions) 

 from New Jersey. Nevertheless the plant association of the Pine- 

 barren area is sufficiently striking to warrant a discussion of its 

 origin. 



The flora of the New Jersey Pine-barrens includes many plants 

 w^hich have migrated northward from the Coastal Plain of the 

 southern states, such as the grass-pink orchid, Limodoru7n tuberosum; 

 others from the southern Appalachian mountains, such as the rhodo- 

 dendron, Rhododendron maximum; and still others from arctic bogs,, 

 such as the buckbean, Menyanthes trifoUata. The one thing which 

 all of these plants have in common is their adaptation to growth in 

 soils of low salt content (as pointed out by Harper, loc. cit.) and high 

 acidity. In the opinion of the present writer, an adequate explana- 

 tion of their association to make up the flora of the New Jersey 

 Pine-barrens is the fact that this area possesses these two character- 

 istics to such a marked degree. 



^Post Jurassic history, etc. (Abstract). Bull. Geol. Soc. Am., 24: 691. 

 1913. The Piedmont terraces of the northern Appalachians. Amer. Journ, Sci., 

 49:227-258,327-362,407-428,(1920). 



^A sketch of the natural history of the District of Columbia. Bull. Biol. Soc. 

 Wash., 1: 86. 1918. 



^A forest reconnaisance of the Delaware peninsula. Journ. Forestry, 17: 55K 

 1919. 



