290 BOTANICAL GAZETTE [October 



+ 



the prevailing wind for the year can be drawn. The oaks and 

 cedars bend away from the shore, as is usual, their outer branches 

 suffering from the salt-laden wind, while the more protected 

 limbs grow fairly well, thus producing a one-sided plant. The 

 prevailing wind is not necessarily the dune-forming wind. For 

 that other factors must be considered: the strength of the wind, 

 the sweep over an expanse of surface, the absence of obstacles 

 in the path, and lastly the angle at which it meets the shore. 

 At Cape Henlopen the northeast wind is probably the strongest, 

 having a sweep over the mouth of Delaware bay, and meeting 

 the shore at a large angle; hence the dune is moving across 

 country southwest. Farther down the coast the northeast wind 

 meets the shore at a small angle, while the lighter east wind 

 strikes perpendicularly. In this case the dune movement 

 depends upon which factor is the stronger. The dunes here 

 have become practically fixed, but what little movement there is 

 appears to be directly west. 



IV. PLANT FORMATIONS. 



As a matter of convenience in harmonizing the two regions, 

 the order used by Dr. Harshberger is adopted here so far as pos- 

 sible. Although adjacent situations, the conditions differ some- 

 what, because the region from Henlopen to Rehoboth bay is at 

 a higher stage of physiographic development than the New 

 Jersey beaches. 



A. Treeless open. — i. Beach formation. — {a) Lower beach. 

 For reasons pointed out by Dr. Cowles^ and Dr. Harshberger^, 

 the lower beach is incapable of supporting vegetation. We find 

 it composed of bare sand, extending back, usually in a gentle 

 slope, to the line of summer driftwood. 



{b) Middle beach, — (i) Succulent zone, — At Rehoboth and 

 northward the summer tides wash up to a ridge of driftwood 

 and debris, where the loose sand first gathers, seeds rest and 



-^COWLES, H. C, The ecological relations of the vegetation on the sand dunes of 

 Lake Michigan, Box. Gaz. 27 : 1 14-185. 1899. 



5 Loc. cit. 639, 



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