24 Postelsia 
could be enumerated for this type of beach. It 
is however representative and will serve to give 
an idea of the composition of the society. 
The interdependence and adjustments of 
individuals to each other in an association is 
shown by such plants as Alsine brachypetala and 
Galium vaillantit which, though largely shaded 
by the taller weeds and grasses, grow profusely, 
their weak stems finding ready support upon 
the rank growth about them. 
b. Vegetation of rocky beaches. 
1. Rock beach formation. 
a. Exposed rocky beach. 
By exposed rocky beaches are meant those 
that by their proximity to the water are some- 
times subjected to the dashing ocean spray and 
occasionally to intermittent inundation by high 
waves. They lie exposed to the light and re- 
ceive'the full force of the wind currents: 
Upon this unpromising rock substratum 
where hardly any soil finds lodgement are estab- 
lished a group of hardy xerophytes. Plants of 
