210 



PLANT RELATIONS. 



areas pass gradually into one another. It is very common 

 to find the dunes omitted in the series, and to have the 

 beaches pass gradually into the sandy fields. 



The beach association is usually quite characteristic, and 

 in general it is a poor flora, the beach being characteristic- 

 ally bare. The plants that grow in such conditions are apt 

 to occur in tufts, or are creeping plants. It is evident thai 



Fig. 186. A rock covered with licheus. 



while the water may seem to be abundant, it disappears 

 quickly, so that plants must adapt themselves to a dry 

 condition of the soil, which is poor and with little or no 

 accumulation of humus. At the same time, the exposure 

 to intense light is extreme. This combination results in a 

 poor display of individuals and of species. Here and there 

 along beaches, where special conditions have favored the 

 accumulation of humus, dense vegetation may spring up, 

 but it should not be confused with the ordinary beach type. 



