143 



smothered with vines, rising above them. Eight species of shrubs 

 or small trees and seven species of lianes are concerned and, with a 

 single exception, all have seeds adapted to dispersal by birds. They 

 are as follows : 



Siuilax herhacca Pninus serotina 



Sinilax hispida Pruiuts sp. (plum) 



Salix longifolia Rhus Toxicodendron 



Celtis occidcntalis Celastnts scandens 



Menispermiim canadense Psedcra quinqucfolia 



Ribes gracile Vitis vulpina 



Pynis iocnsis Conius Baileyi 

 Prunus lirginiana 



The choke-cherry [P. zirgiiiiaiia) , plum, and crab {Pynis iooisis) 

 are the most abundant shrubs. The plum has running roots which 

 send out shoots at short intervals, so that it tends to spread out upon 

 the blowsand. The lianes are usually luxuriant and cover the shrubs 

 with such masses that the supports are almost hidden. Within the 

 thicket the light is very low; many of the branches are leafless or 

 dead, and the herbaceous vegetation is scanty. It consists of Tcit- 

 criuni occidcntalc, Scrophnlaria leporclla, Polygonatuui commutatiun, 

 and SniUacina racemosa, with seedlings of Psedcra qiiinqucfoUa. 

 These thickets occupy the crest of the dunes and usually extend also 

 some distance down the lee side. In some places the advance of the 

 dune is sufficiently rapid to bring a portion of the thickets over to the 

 windward side, where they are soon undermined (PI. XIX, Fig. 2). 



The further fate of these thickets is not known. It is worthy of 

 note that they are somewhat similar in floristic composition to the 

 thickets developing in certain blowouts, as descrilied elsewhere in 

 this paper (p. 107) and also in an earlier article (Hart and Gleason, 

 iQoy: 168). Many of the species concerned are also characteristic 

 of the mixed forest association and indicate a possible succession in 

 that direction. 



Just at the margin of the thickets on the lee side, and partially 

 shaded by them, patches of Smilacina stcUata frequently occur. The 

 l^lant spreads by running rootstocks, but is not efficient as a sand- 

 binder. The few patches on the windward side of the thickets are 

 very soon undermined and destroyed. This small association en- 

 croaches upon the deposit association in advance of the thickets, and 

 is dependent upon the thickets for a partial protection from sunlight. 

 It illustrates a peculiar case of succession in which an early stage is 

 dependent upon a later stage for its existence and appears only after 



