88 BOTANICAL GAZETTE [AUGUSI 
THE GRASS PLAIN. 
Inside the line of open beach begins the sand plain, composed 
of a great number of approximately parallel dune beaches, forming - 
smoothly swelling ridges and hollows of elevations and breadths 
already described. Every dune beach, I believe, originates with 
a core of driftwood. As the tidal beach is built outwards by the 
addition of sand, driftwood continues to collect on its uppermost 
part, until finally some unusual combination of great winds with 
high tides sweeps it up beyond reach of further disturbance. Then 
the driving sand from the beach is caught among it; the beach 
grass gains a foothold in the sheltered places, spreads, and checks 
the further movement of this sand. Then more sand is driven 
shoreward, and it grows into a low dune which is fixed by the beach 
grass as fast as it rises. The limit is reached only when a new line 
of driftwood has been formed outside and begins to stop the sand 
for its own growth. The resultant dune beach offers severe condi- 
tions for plant life, for its surface is swept, especially on the summit 
and windward slope, by heavy winds; it is heated intensely by the 
sun; it is readily movable; and it forms a soil extremely poor in 
mineral nutrients.4 It lacks the salt of the newer beaches, however, 
for this is soon removed by the rain; and it possesses an ample 
supply of moisture a foot or two beneath the surface, for the supply 
brought by the rain drains but slowly away, owing to the low gradient 
of the water-table. These conditions, especially at their extreme 
on the summits and windward slopes of the beach dunes, are endured 
by practically but a single plant—the herbaceous-perennial, sub- 
terranean-creeping, xero-culmed, deep-rooting beach grass, Amm0- 
phila arenaria, which occurs, without any competitor whatevel, 
in open scattered tussocks, only partially covering the ground, 4s 
well shown in fig. 5, and in closer view in figs. 6 and 7. It happens 
that this grass is of considerable economic value to the neighbor 
ing farmers, who cut it and haul it for hay, and whose cattle graz€ 
upon it; its destruction in this way causes an irregular exposure 
of the outer beaches, permitting them to be irregularly cut by the 
wind. It is for this reason, I have no doubt, the newer outer beaches 
4 As indicated by KEARNEY’s recent studies: Bot. GAZETTE 37:426-436 
1904. 
