98 The Shingle Beach as a Plant Habitat. 
The Water Problem. 
One of the outstanding mysteries of the shingle spit is the 
water relation. The sides of the spit are washed by the sea and 
the plants of the lowest zone where the saline influence is supreme 
are halophytic. Higher up the bank, however, the conditions are 
quite different. A portion of the members of the halophytic zone, 
as we have seen, make their way up to the higher slopes, but there 
is a well-marked residuum of shingle plants which behaves as if, and 
is indeed known to be, intolerant of salt (Na Cl). 
In conformity with this distribution, the water in the inter¬ 
stices in the shingle above the true salt zone is largely free from 
salt. To the taste it is fresh, which means that, at most, only 
small traces of Na Cl can be present. 
Moreover, the water of the shingle is astonishingly copious, 
and suffers no diminution during periods of prolonged drought. 
Throughout the past summer, with the longest periods of high 
evaporation recorded for this country, numerous shingle spits came 
under observation, and in no instance did the vegetation show any 
trace of suffering from drought. On the contrary the wetness of 
of the shingle just below the surface was maintained unimpaired, 
and this quite irrespective of the presence of humus or other 
capillary matter in the interstices of the shingle. It is therefore 
not possible to account for these inexhaustible supplies of water 
as conserved rainfall. 
Late in the summer the mainland by the Chesil Bank became 
completety parched up, so that not a green blade of grass was to be 
found. It was under these circumstances (Sept. 25th, 1911), that 
our photograph PI. 4, fig. 4) was taken, showing sheep (which had 
wandered down of their own initiative) grazing on the fresh Silene 
maritima of the shingle at the Burton Bradstock end of the Chesil. 
Not far from this locality, on the same occasion, quantities of 
Polygonum amphibium were found to be growing with great 
luxuriance on the shingle—corroborative evidence, if such be needed, 
of the high level of the saturation of the ground. 
The source of this water is a matter of no little interest. Now 
in connection with the analogous problem of the presence of per¬ 
manent moisture near the surface of high sand dunes the suggestion 
has been made by more than one writer 1 that it depends upon the 
' A. Jentzsch, in Gerhardt’s “ Handbuch d. deutschen Diinen-” 
baues,” 1900, p. 104. 
P. Olsson-Seffer. “ Hydrodynamic Factors influencing Plant- 
Life on Sandy Sea shores.” New Phyt., Vol.. VIII, p. 43, 
1900 . 
