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 10°, 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 1 to 3 feet high. Reinke ® gives 6 to g feet, but 
this is surely very unusual. 
165 
