184 GEOLOGICAL SURVEY OF NEW JERSEY. 



sperms, which type of plants would only be represented in 

 consequence by stunted weaklings. 



In each of these cases the original species would also have 

 the direct advantage that their own relatives would be in the 

 preponderance in the immediate neighborhood, and therefore be 

 the first to reproduce their kind in any numbers. In the case 

 of the tension zone, however, any change, no matter how insig- 

 nificant, might afford just the advantage which some opposing 

 species of either zone required for its establishment in neutral 

 territory. 



For this reason the former lines of specific limitation in the 

 tension zone it is now impossible to determine. In this zone 

 the changes have undoubtedly been the greatest, as it is there 

 that cultivation has been the most extensive, and over miles of 

 the surface, in the marl belt especially, the original forest has 

 been completely destroyed, while in the other zones the limits 

 and relative proportions of the species have probably always 

 remained about the same. 



Another corollary to which it may be of interest to call atten- 

 tion is that where zones of vegetation become established by 

 reason of the conditions being directly favorable in each, the 

 weaker individuals are necessarily crowded to the front and 

 meet in the tension zone. Where, however, a zone becomes 

 established, not because the conditions are directly favorable for 

 the vegetation which occupies it, but only indirectly for the 

 reason that it is unfavorable for any other, this condition may 

 result in bringing stronger individuals to the front of the more 

 barren zone and into the tension zone. 



This is well exemplified in the case of Pinus rigida, which is 

 usually larger where it occurs in isolated groves in the better 

 soil of the tension or deciduous zones than in its normal location 

 in the sand barrens. 



This fact, considered by itself, would appear to give a decided 

 advantage to the coniferous vegetation, but its lower position in 

 the biologic scale, as compared with the deciduous, is evidently 

 more than sufficient to offset this advantage. 



In the following enumeration an attempt is made to give an 

 idea of the general character of the forest in each zone, by listing 

 the most conspicuous and abundant species in each.* 



*The nomenclature adopted is that of Britton & Brown's " Illustrated Flora of the Northern United 

 States, Canada and the British Possessions." 



