22 



Greene, green brier Siiiilax hispida i\Iuhl., carrion flower 

 Smilax hcrhacca L., and bittersweet, Cclastrus scandcns L. 

 These thickets extend most rapidly down the lee side of the 

 dune, but also encroach gradually on the riverward side as 

 well. The later fate of these thickets is not known. 



During these two early stages in the history of the dune 

 the wind sometimes breaks down the defense of the sand- 

 binders at the crest and excavates a trough-shaped hollow 

 perpendicular to the river. These hollows are known as blow- 

 outs. The sand is removed from the windward end and from 

 the bottom and is poured out in a steep incline on the land- 

 ward side. The sides of the blowouts are held by thickets or 

 by clumps of sand-binders, and if the movement is not too 

 rapid the lee deposits are also soon covered with plants. 



A third stage in the history of the dune is characterized by 

 an oak forest, which in the Hanover area consists of black oak, 

 Querciis velutina Lam., and in the Oquawka area of black oak 

 and blackjack oak, Qiuercus niarilandica Muench., together. 

 This is the oldest* stage represented in the Hanover area and 

 the youngest in the Oquawka area, so that the latter serves to 

 complete the history and to indicate the fate of the Hanover 

 dune. The blowing of the sand is efifectually prevented by the 

 forest cover, and if the river is not eroding its banks too rapidly 

 the forest soon extends down to the water's edge. 



This forest is composed of gnarled, crooked trees with short 

 trunks. They are not close together and the underbrush, if 

 any, consists almost entirely of young trees of the same species. 

 The herbaceous vegetation is somewhat dififerent from that of the 

 preceding stages in its specific composition. One particularly 

 characteristic species is Synthyris BuUii (Eaton) Heller. The 

 poisonous fly-mushroom, Amanita muscaria, and an earth-star, 

 Geaster sp., are quite abundant. The trees produce a bountiful 



*The meaning of the terms old and young, as applied in ecology, is sometimes 

 confusing. "Old" signifies that the particular area has passed tlirough a greater 

 number of physiographic or ecological stages than those designated as "young." 

 In the case in point, the oak forest in the Hanover area is itself relatively young 

 in age (i. e., of recent development), but the portion of the dune so occupied has 

 passed through one or more previous stages. This is in contrast to the blowsand 

 association, which may be considered as occupying new ground : it is therefore the 

 first ecological stage in the vegetation, and is designated as young. 



