164 THE ESSEX NATURALIST
The transect at Site 13 illustrates its characteristics, and
the first yards of the transects at Site 4C show the relative
proportions of the various species at the base of the wall on
the landward side.
At the eastern end of the wall there is a similar fringe of
Halimione and Suaeda at the base on the seaward side.
Above this, however, the Agropyron-dominated community
is no longer found on either side of the wall. This is
especially so towards Site 1, where the main east/west wall
is joined by a short north/south wall. Agropyron still occurs
locally, but the turf here is shorter and made up of many of
the species typical of waste- and pasture-land. The greatest
variety of species occurs near the base of the wall on the
landward side. Species present include :—
Achillea millefolium. Medicago arabica.
Agrostis stolonifera. Parapholis strigosa.
Bromus mollis. Phleum pratense.
Cynosurus cristatus. Potentilla reptans.
Desmazeria rigida. Sonchus oleraceus.
Geranium molle. Torilis nodosa.
Hordeum pratense. Trifolium campestre.
Lactuca serriola. Trisetum flavescens.
Lepidium ruderale. Vicia angustifolia.
Lolium perenne.
This change is due both to human activities and to grazing
by the cattle pastured on the enclosed fields to landward of
the wall. At Site 1, estimations of the chloride content of
the soil were carried out. These again showed that no
chloride was present at the top of the wall amongst the roots
of Lolium perenne. At the base on the landward side,
amongst the. Hordeum marinum Huds., the soil contained
.013 grams chloride per gram soil (1.3 per cent). This value
will be seen to be extremely close to that found for a similar
position on the seaward side, and the presence of chloride
in this quantity on the landward side of the wall is of
considerable importance.
On Two Tree Island the sea walls are strengthened with
stonework, and so provide a much less favourable habitat
than do the clay walls of the mainland. The landward side
of the walls shows similar species to those of the eastern