CHAPTER XXVin 



MARITIME ASSOCIATIONS 



On the seashore and the margin of estuaries the soil 

 varies considerably ; it may be sandy, shiagly, rocky, or 

 muddy, and the vegetation exhibits a corresponding 

 diversity. The flora of a mud-bank is quite distinct 

 from that of a sand-dune, and this in turn differs from the 

 flora of rocks and cliffs. In all cases the land-plants are 

 t3rpical xerophytes, but the xerophytic character may be 

 due to a variety of causes. It may be an adaptation to 

 physiological dryness, as in the plants of a mud-bank 

 where the water is strongly saline ; to physical dryness, as 

 in sand-dune plants where the soil contains very little 

 water ; or to the action of strong drying winds, as in 

 those of cliSs. In this chapter, then, a number of distinct 

 formations will be described. They are brought together 

 merely for convenience, and not necessarily because they 

 are related ecologically. 



As is the case with other plants, the maritime plants 

 group themselves naturally in two divisions — the aquatic 

 vegetation and the terrestrial. 



I. Maritime Aquatic Vegetation. 



On the open sPAshore and in estuaries, where the 

 water-level is altering with each tide, the aquatic vegeta- 

 tion is almost restricted to one group of plants — the sea- 

 weeds, or algae. The absence of other plants is due chiefly 

 to the difficulty of bringing about fertilization. The 

 periodic rising and falling of the water makes it necessary 

 that fertilization should be effected under water. Aerial 

 flowering stems wotdd be of no use, for the flowers are 

 submerged at high tide and ordinary poHen destroyed ; 



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