THE COAST-FLORA OF THE CLACTON DISTRICT. 203
On the other hand the physical constitution of mud, and its
high nutritive value, are antagonistic to the action of salt.
This may explain why the plants are frequently luxuriant in
size, though Xerophytic in structure.
The rain-fall at Clacton is usually below 20 inches a year,
and is more or less distributed over the whole twelve months.
Extreme drought for long periods does therefore not occur, as it
does, for instance, in the steppe, where vegetative growth is
entirely confined to the rainy season. There are, however, species
growing on the coast whose term of annual growth lies in winter
or early spring, and who pass the hot season in the form of
seed or spore. Such is the case of some spermophytic annuals
(Cerastium, and, to a certain extent. Cochlearia officinalis and
Lepidium ruderale), but more particularly of the mosses which
cover all the sandy shore in winter and early spring. Another
effect of rain will be the washing away of salt in those higher
parts of the littoral meadow that are only covered by an excep-
tionally high and stormy tide. There are places where the
vegetation can scarcely be said to be Halophilous—so numerous
are the invaders from the ordinary meadow, dune or waste land.
A factor of smaller importance (for our purpose) is light ;
like wind it tends to accelerate transpiration. There being no
trees, there is little protection against light, and several plants
show definite modifications against insolation, such as the as-
sumption of profil-lie in the leaves of Atriplex portulacoides.
Wind-sheltered places are conspicuous for the larger size of the
plants ; much of the dwarfing appears to be due to exposure to
wind.
It is not always easy to determine whether a plant is a genuine
Halophyte, whose life depends on the presence of salt, or a non-
Halophilous inland plant which is able to endure the salt without
danger to its existence. I propose, therefore, to follow the
clearer division into Psammophytes and Pelophytes, irrespective
of their relation to salt.
I. PSAMMOPHYTES.
I have already sketched the reasons why the vegetation
of the sandy shore must be extremely Xerophytic. It has been
said, also, that psammophytes fall into two groups, the Halo-
philous and non-Halophilous.