Seasides and Strand Plants 



Close to the sea and outside the sandhills a certain 

 grass (Agropyrum junceum) manages to exist in spite 

 of the salt and extreme exposure. It has long under- 

 ground runners, and very hard stems and leaves coated 

 with a bluish-green, waxy excretion. Against its sturdy 

 stems and those of Honckenya, Cakile, and other sand 

 plants, the blown sand collects and piles up into low 

 hillocks * or small heaps of sand. 



These small mounds are then attacked by the bent- 

 grass (Psamma arenaria), which is the real specialist 

 in sand-dune colonisation. The underground stems are 

 very long and wiry, whilst its leaves are tough and 

 flexible, able to resist the strongest gales or the still 

 more dangerous friction of the flinty sand particles 

 which are carried by it. Suppose Psamma is buried 

 under 20 feet of sand by the movement of a dune, 

 it simply grows up to the light without being at all 

 injured. The growing points with their fine sharp 

 points are particularly designed, especially to pierce 

 through such overlying sand. 



Now the windy or seaward slope of a dune may be at 

 a gradient of some 5 to io°, whilst the lee slope where 

 the sand-grains, having been carried over, lie at their angle 

 of rest, may be at an angle of about 30 to the horizon. 



Psamma, however, interferes with this mathematical 

 regularity by establishing itself especially about the 

 crest of the dune, where its strong bunches of hardy 

 leaves act as a sort of breakwater. The whole sand- 

 hill is soon traversed and more or less tied together 

 by its rhizomes and roots. 



So the hollow behind the crest becomes gradually 

 filled up by whatever sand passes over, and is soon 

 plentifully colonised by vigorous tussocks of Psamma. 



* Such hillocks are about I to 3 feet high. Reinke 8 gives 6 to 9 feet, but 

 this is surely very unusual. 



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