THE DUNES AND THEIR PLANTS 115 



We shall have occasion to remark constantly in the succeed- 

 ing chapters on the adaptation of particular plants and animals 

 to specific environmental conditions. Indeed it is to be the 

 major purpose of the remainder of the book, to show how plants 

 and animals are grouped in societies that are determined by the 

 ability of the several organisms to endure similar conditions. In 

 the dune region the associations are roughly parallel to the shore 

 and for plants succeed each other in the following order: (i) the 



Fig. 70. — A panne near Miller, Indiana 



beach association; (2) the fore-dune association; (3) the cotton- 

 wood association; (4) the pine association; (5) the black oak 

 association; (6) the mixed oak association; (7) the oak-hickory 

 association; (8) the maple-beech association. 



Along the border of the lake is the wave-swept beach, where 

 no Kving thing can maintain permanent residence. Even here 

 there are transients among the animals as will be explained 

 shortly. There is a stretch of wind-blown, shifting sand, the 

 storm beach pounded by breakers raised by the heavy winds; 

 this also is nearly barren of life. A few annuals grow here dur- 

 ing the summer when severe storms rarely occur. The sea rocket 



