498 MacCauGHEY: THE STRAND FLORA 
tially a product of wave action and comprising the zone which is or 
has been worked over by the waves. Hence the beach may be 
defined as the zone between the water level and the topographic 
form produced by other agents. This definition is closely appli- 
cable to the Hawaiian coral sand beaches, which are uniformly 
xerophytic in their characteristics. Olsson-Seffer ('10) has 
stated that the competition for food is more intense, the water 
supply less, the light stronger, the temperature higher, the trans- 
piration greater, the foothold more uncertain and difficult, the 
conditions for plant life generally more adverse, than on any other 
soil. | 
Shaler (’94) has made some significant generalizations con- 
cerning sandy beaches. He points out that dunes and beaches of 
coral sand never march far inland, as do quartz sand dunes, for 
the reason that the limestone grains speedily become consolidated 
into a tolerably firm set rock. It is characteristic of coral beaches 
that the materials of which they are composed, unlike those of 
ordinary shores, are readily taken into solution, and in that state 
may be borne away by the currents to any distance. Notwith- 
standing the constant robbery of their materials, which is effected 
by the solving process, the coral beaches often widen with great 
_Yapidity. Shaler emphasizes that one of the most noticeable 
features which is exhibited by beach sands is their extraordinary 
endurance of the beating of the waves. He compares the rapid 
abrasion of rocks and boulders to the very insignificant abrasion 
of sand particles. Though subjected for ages to the beating of 
the waves, with perhaps a hundred’ times as much energy applied 
to the surface of which it forms a part as would suffice to reduce a 
granite boulder containing a cubic foot of material to a granular or 
powdery state, the beach sand remains unworn. This endurance 
is due to the capillary water. So long as the beach is full of water 
the particles do not touch each other. Thus the blow of the waves 
is used up in compressing the interstitial water and is converted 
into heat without wearing the mineral matter in an appreciable 
degree. | 
Sandy beaches have a relatively slight water capacity, as: the 
percolation is very. rapid. The capillarity is not as pronounced as 
in soils of finer texture, and the evaporation from a sandy surface 
