PLANTS O'F SOUTHERN NEW JERSEY. 105 



belt or region, while soil conditions determine their distribution 

 within that belt. Changes in condition of either climate or soil 

 cause changes in the distribution of plants, and, consequently, 

 extensions or contractions of their ranges in different directions. 

 As already explained, we have many southern plants which we 

 often refer to as pushing northward in the coastal plain, and 

 others of northern affinities which find their southern limit in the 

 New Jersey Pine Barrens, these we refer to as stragglers from 

 the north. Often both elements occur side by side in the same 

 spot, like Schizcca pusilla* and Lycopodiujn caroliniamim, which 

 are here such constant and noteworthy associates. 



It is a nice point to determine whether ranges are being ex- 

 tended in the same area at the same time in opposite directions 

 or whether there has been a series of successive movements first 

 in one direction and then in another, which have resulted in the 

 present complex associations. 



It seems most likely that changes of range due to climate have 

 been of the latter character, and that many isolated boreal plants, 

 such as Rhododendron, Schizcea, Arctostophylos, Coreina of the 

 Pine Barrens, Geranium robertianum, Vagnera stellata, Car ex 

 buxhaumii, Menyanthes and Scheuchzeria of other parts of south- 

 ern New Jersey, may be relics of glacial times, while plants of dis- 

 tinctly austral affinities found far north of their normal range 

 may be remnants of a southern flora that pushed northward 

 when a milder climate prevailed. 



Changes due to soil conditions, however, might easily take 

 place in opposite directions simultaneously. The gradual enrich- 

 ment of the sandy soil in various parts of the New Jersey coastal 

 plain might readily coax southern species farther and farther 

 north and northern species southward so long as climatic con- 

 ditions were not prohibitive to their advance, while sand-loving 

 plants originally brought to the same general region from differ- 

 ent directions through successive climatic changes would be 

 drawn into closer association where arid conditions were most 

 intense. 



* Prof. Fornald (Rhodora 1911, p. 109) seems to regard Schizaea and 

 Corema as coastal plain plants which have pushed northward, while I have 

 always regarded them as boreal species driven south to New Jersey. 



