PI.ANTS OF SOUTHERN NEW JERSEY. 81 



ration from the Cape May district is purely an arbitrary one. To 

 the noEth it stretches up to the head of the Hackensack marshes, 

 and includes Staten Island, part of Long Island, as well as a strips 

 of eastern Pennsylvania lying east of the fall line, comprising a 

 considerable section of Bucks County and Tinicum township, in 

 Delaware County. The lower part of Philadelphia also be- 

 longed to this district, though its native flora is now piractically 

 exterminated. 



This is the region referred to by Dr. Arthur Hollick in his 

 interesting paper on "The Relation Between Forestry and 

 Geology in New Jersey"* as the "Tension Zone," "because it is 

 there that the two floras [i. e., the deciduous forest of the north- 

 ern uplands and the coniferous forest of the Pine Barrens] meet 

 and overlap, producing a constant state of strain or tension in 

 the struggle for advantage." ' 



Dr. Hollick was admittedly drawing his conclusions mainly 

 from a study of the northern edge of the Pine Barrens as seen 

 in the "tongues" which cross a line from Monmouth Junction to 

 Parmingdale, and was not in possession of detailed information 

 on the distribution of species in the southern part of the State. 

 He, therefore, missed the fact that the so-called "Tension Zone" 

 is not merely a mixture of elements from the northern counties 

 and the Pine Barrens, but is characterized by a large number of 

 peculiar species which are as foreign to one of the above regions 

 as they are to the other. Some of the trees which are peculiar 

 to the Middle District as contrasted with the Northern Uplands 

 and Pine Barrens are Dospyros virginiana, Ilex opaca, Pinus 

 virginiana, Quercus phellos, Betula nigra, Liquidambar sty- 

 raciflua. , Dr. Hollick states that all of these occur in the Conif- 

 erous Zone, but, as a matter of fact, they are unknown in the 

 Pine Barrens, though they re-occur on the coast stirip and in the 

 Cape May district. Therefore, while I heartily agree with Dr. 

 Hollick's contention that "the mechanical structure of the Soil" 

 is the most potent factor in the distribution of plants, I fail to 

 appreciate the importance of "tension" in the vegetation of this 

 zone. To me it seems to be a division of the coastal plain of 

 equal rank with the Pine Barrens. 



* Report on Forests, A;in. Rep. State Geol. N. J. for 1899, pp. 177-201. 



