194 



EDGAR NELSON TRANSEAU 



With both marine and fresh water plant associations as starting 

 points in the evolution of the higher vegetation groups, the num- 

 ber of possible directions from which an association may have 

 been derived or toward which it may develop is greatly increased. 

 When there is added to this the periodic fluctuation of the sea 

 water level, with its consequent redistribution of points of equal 

 wave action, it will be seen that the interpretation of the field 

 relations of the pioneer associations is far more difficult than in 

 inland situations. As for the determination of the physical fac- 



Fig. 3. The beach near Batons Point Light at low tide. In the distance may be 

 seen the rocks on the Submerged Beach, which break the force of the waves and 

 afford a foothold for algae. In the foreground is the Lower Beach with a line of 

 debris showing the height of the last high tide. Above the Lower Beach may be 

 seen a small portion of the Middle Beach with its covering of small boulders. 

 Above this lies the narrow Upper Beach and Cliff. 



tors involved in the habitat dynamics scarcely a beginning has been 

 made. 



From what has been said of the geological history of the island it 

 is probable that both historically and physiographically the gene- 

 tic development of the vegetation begins in the plant associations 

 of the littoral belt. Considering the beach as including all of the 

 areas occupied b}^ the shore drift in transit, from the standpoint 

 of the vegetation there are four well marked divisions (fig. 3). 



