PLANTS OF SOUTHERN NEW JERSEY. 107 



mergences of the New Jersey coastal plain after its first upheaval 

 which are claimed by geologists* and other changing conditions 

 may not only have resulted in several invasions of plants, but 

 also in changes in the character of the plant life in the regions 

 from which they came. 



In every investigation in the plant life of the eastern United 

 States we seem to find two elements — a boreal, more or less 

 identical with the flora of northern Europe, and an austral, pecu- 

 liarly American, and precisely the same thing is found in the 

 study of animal life. Under prevailing conditions, however, and 

 through adaptation certain species of animals of American aus- 

 tral origin have become typical boreal species to-day, and doubt- 

 less the same thing may be true of certain plants. This shows the 

 necessity of distinguishing carefully between present geographical 

 distribution and original source of center of dispersal of a species. 



Now, supposing that the characteristic American austral flora 

 covered the Piedmont area or a portion of it at the time the 

 coastal plain was elevated, it is natural that it would have spread 

 over into the new territory, or at least such species as were 

 best adapted to its sandy stretches. Then, if from one cause or 

 another there was an invasion of the more boreal element over the 

 Piedmont plateau, we should probably have exactly the condi- 

 tions that we find to-day — i. e., the survival of the earlier flora in 

 bogs and sandy areas and its disappearance where better soil has 

 developed in favor of the more advanced flora now prevalent.! 

 Part of the latter is also of austral origin, but, being suited only 

 to richer soil, did not spread to any extent into the coastal plain. 



In New Jersey the vegetation is at a much younger stage of 

 its development. In the Pine Barrens we have only sand and 

 bog plants, while in the Middle district we encounter the more 

 advanced type of the American austral element and the evident 

 influx of boreal plants already referred to from the north. 



During the Pensauken period West Jersey was submerged, 

 while the Pine Barrens were apparently cut off as an island. 



* Cf. The Physical Geography of New Jersey by RoUin D. Salisbury, Vol. 

 IV., Final Report State Geologist, 1898, especially pp. 92-170. 



t Cf. Cowles. Physiographic Ecologj' of Chicago and vicinity, Bot. Gazette 

 XXXI., 73-108, 145-182, 1901. 



