648 PROCEEDINGS OP THE ACADEMY OP [Oct., 



by the encroaching army of shrubs and trees of xerophytic habit 

 in the stage before the culminating one, the mesophylic thicket. 

 The mesophytic thicket at South Sea Side Park occupies from what 

 has gone before the hollows, or rounded depressions in the dune 

 complex, and in its simplest make-up consists of the two following 

 associations of species: One thicket examined consists of Pinus 

 rigida Mill., Saxsafras sassafras (L. ) Karst., Vaccinium corymbo- 

 8um L., Juniperus virginiana L. , Chamcecyparis thyoides (L. ) B. 

 S. P. and Myriea cerijera L., Another hollow contains Ilex 

 opaca Ait., Juniperus virginiana L., Primus maritima Wang, 

 while, as an undergrowth, associated together, are Rhus radlcans 

 L. and Solidago sempprvirens L. 



Either before the final condition is reached, or after such thickets 

 have been formed, the original condition of the dune complex may 

 be restored by the diifling in of the sand into the depression, result- 

 ing in a destruction of the long-established plant societies. Such 

 vicissitudes in the life history of plant societies are not common, 

 although examples are found occasionally on the New Jersey 

 si rand. As a rule, before the final culmination of dune hollow 

 history is reached, the elevated sand hills surrounding it are cap- 

 tured by sand-binding plants, such as Ammophila arenaria (L. ) 

 Link, but especially Had.-ionia tomentosa Nutt., which forms 

 heaths about the depression, effectually preventing the transport 

 of the sand and its deposition in the basin-shaped valleys adjoin- 

 ing. In case the sand is transported, it begins to fill up the dune 

 valley through the action of the oceanic flotsam and jetsam. 

 The accumulation of such material in the storm-washed waterways 

 between the dunes has gone on for ages. Before the advent of 

 civilized man, the material washed ashore consisted of the trunks 

 and limbs of trees, seaweed, leaves and the floatable objects carried 

 to sea by the rivers. Since the occupation of the shore by white 

 men, the flotsam and jetsam consists of a remarkable collection of 

 nondescript rubbish, such as ship timbers, chips of wood, broken 

 boards, spars of boats, sides of rowboats, old cots, mattresses, 

 bottles, and, in fact, anything and everything used by man that is 

 floatable and can stand the action of salt water for months at a 

 time. 



Tlie piling up of such rubbish in the dune complex acts as an 

 effective means of binding the sand and preventing its drifting. 



