Postelsia 19 
constant. The forest, in a region where pre- 
cipitation is uniform and large, is a stable or- 
ganization. ‘The sea with its tides, its currents, 
and its winds in its great entirety is unchange- 
able. Now and then some heavy storm may 
pile the driftwood farther into some cove, or 
sweep bare a projecting point, yet the main 
tension line between the two is of comparatively 
great stability. 
As shown in the preceding synopsis, the 
vegetation of the sea strand is divided with re- 
ference to the substratum, into two general 
divisions of; a. vegetation of sandy beaches, and 
b. vegetation of rocky beaches. 
a. Vegetation of sandy beaches. 
1. Sand beach formation. 
a Large open beach. 
b Small inlet beach. 
Since the sand beaches vary considerably with 
respect to size, slope and direction, it is natural 
to expect that the plant formation upon them 
will likewise vary. In some places the coves or 
inlets may be wide and open towards the direct- 
ion from which prevailing winds blow. In such 
