210 



PLANT RELATIONS. 



into one another. It is very common to find tho dunes 

 omitted in the series, and to have the beaches pass gradu- 

 ally into the sandy fields. 



The beach society is usually quite characteristic, and in 

 general it is a poor flora, the beach being characteristically 

 bare. The plants which grow in such conditions are apt to 

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



Fig. 186. A rock covered with lichens. 



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. 



