212 



PLANT RELATIONS. 



The dune associations are subjected to very peculiar 

 conditions. Dunes are billows of sand that have been de- 

 veloped by prevailing winds, and in many cases they are 

 continually changing their form and are frequently moving 



Fig. 188. A sandy field type, showing the development of vegetation upon an oiu 

 beach. The vegetation is low, often tufted and heath-like, being composed chiefly 

 of grasses, bearberry (Arctostaphylos) and Hudsonia. In the background to 

 the right is a conifer forest, and between it and the old beach is seen a dense mass 

 of bearberry, a very characteristic heath plant, and forming here what is called a 

 transition zone between the beach and the forest.— After Cowles. 



landward (see Fig. 187). The moving dunes should be 

 distinguished from the fixed ones, where the billow form is 

 retained, but the dunes have ceased their motion. In the 

 case of the active dunes a peculiar type of vegetation is de- 

 manded. As is to be expected, the flora is very scanty, and 



