120 



BOTANICAL GAZETTE 



[FEBRUARY 



the formation has not been inundated for a few days only the spores 

 of the algae retain their vitality. On the Baltic coasts where the 

 salinity of the sea water is low, conditions approach more or less those 

 on fresh-water shores, and many green algae occur in the sand. The 

 width of the barren front strand varies not only with the slope, but 

 also with the force of the surf. 



When a higher vegetation occurs on this formation it is open and 





WL 



4V 









^■"■^' 





Fig. 7 



•Middle and upper beach south of Cliff House, 



In 



upper beach small dunes made by Cakile americana. 

 with Ammophila. (Photograph by author.) 



_ • r<x\ On 

 San Francisco, cau 



background littoral ^ 



very poor 



a 



lm 



nl 



a limit on the types that are able to develop. These are mawi 

 annuals or perennials with long creeping rhizomes and the flora B 



always poor both in species and individuals. , 



The middle beach is characterized by its light color, its abundan 

 moisture, its low salinity, its loose soil, and its comparatively o 

 temperature. Occasional inundations, spray, and wind are 

 direct causes of the scattered vegetation, consisting mainly of annua 



