THE DUNES AND THEIR PLANTS 121 



borne on flattened stalks. The buds are long, tapering, and 

 curve outward. The twigs especially on young trees have sharp 

 ridges running down the bark below the buds. It thrives as the 

 sand buries it. While other trees sicken and die, the cottonwood 

 literally rises to the emergency, and grows so as to keep its head 

 above the accumulating sand. Moreover, it sends out roots all 

 the way up and down its buried trunk to help secure needed 



FIG. 86. Sand cherry, Primus pumila, in the fore-dune association 



moisture for its vigorous growth. What appear like low cotton- 

 woods on top of a dune are really the topmost branches of a 

 tree whose original roots may be buried a hundred feet below 

 the rising crest of the dune. Gottonwood roots run out many 

 yards through the sand in search of moisture. 



Miniature dunes may be built up around clumps of bunch 

 grass, sand cherry, or prostrate juniper (Fig. 69), but the main- 

 stay of the big dune is the bunch of cottonwoods whose seedlings 

 caused it to start, and that have grown as rapidly as the dune 



