170 THE ESSEX NATURALIST
Creek 21 runs north/south, it is, however, colonised by
Phragmites communis Trin. This plant is dominant in the
northern half of Creek 6, growing in standing water in which
Ranunculus Baudotii and Callitriche intermedia are
abundant. North of the railway, in a small part of Creek 3, in
Creeks 8 and 22, Scirpus maritimus again occurs, although
here most of the upper parts of the plant have been bitten
off by horses. The salinity of Creek 8 is .093 grams per litre
(.009 per cent), and that of pool 9, .444 grains per litre (.044
per cent). Carex otrubae and Juncus Gerardi occur
frequently along the banks of all the creeks in this area, and
two patches of Phragmites have also been found. The species
of the banks of the creeks north of the railway include:—
Achillea millefolium. Lotus corniculatus.
Alopecurus pratensis. Odontites verna.
Apium nodiflorum. Plantago lanceolata.
Centaurea nigra. Potentilla reptans.
Hordeum pratense. Rosa canina.
Inula dysenterica. Senecio Jacobaea.
Lolium perenne. Trifolium procumbens.
Alopecurus geniculatus also occurs near pool 9.
The remaining drainage channels, i.e., Creeks 3 and 7,
must originally have been fairly large creeks of the salt
marsh. These are shallow, very saline and muddy.
Creek 3 water contains 18.75 grams chloride per litre (1.87
per cent). This value is higher than that for sea-water, so
that considerable evaporation must have occurred by mid-
summer, when the specimen was collected. In winter the
salt concentration drops markedly. The retention of
quantities of chloride in the water is presumably due in part
to the original nature of the channel and in part to the ease
with which seepage must occur through the sea-wall where
the creek was first blocked. The high summer salinity of
the creek is reflected in the vegetation. In a small part of
the extension of the creek north of the railway, Entero-
morpha intestinalis is present abundantly in the water, and
Salicornia sp., Suaeda maritima and Puccinellia distans are
represented on the banks. Between 3D and 3C, both banks
are a few inches higher than the water-level, and plants of
Salicornia sp., Aster Tripolium, Suaeda maritima and clumps