16 PELOPHILOUS FORMATION OF LEFT BANK OF SEVERN ESTUARY. 
THE ZONES AND PLANT ASSOCIATIONS. 
As the relative levels of the zones differ at various points along 
the shore, it is not easy to give a general classification of the 
zones that will hold for the whole area, but the different zones 
can well be recognised by their different plant associations. 
There are four main zones with their associations thus to be 
distinguished, viz. :— 
(I.) The Salicomia Zone. 
(II.) The Sclerochloa Zone. 
(III.) The Festuca Zone. 
(IV.) The Alluvial Pasture Zone. 
(I.) Lowest in position and running gradually over into the bare 
mud, there is often present an open association of Salicomia 
europcea L. No other Phanerogam is present within this zone, 
the only other plants present being gelatinous masses of diatoms, 
and occasionally tangled masses of species of Enteromorpha 
tangled amongst the stems of the Salicomia and left behind by the 
tide. Near Portishead this Salicomia zone is a very prominent 
fringe, reaching in places to some two hundred yards in width, 
but as one proceeds up the Severn the fringe rapidly diminishes 
in extent until only occasional patches are met with. Above 
Aust it is usually quite absent. 
(II.) Next in order, proceeding inland, is the zone which might 
be suitably named after the dominant grass the Sclerochloa zone. 
In this zone Sclerochloa mariiima, Lindley, is either dominant or 
co-dominant in company usually with Aster Tripolium, L. , though 
occasionally other plants in the zone may become so con- 
spicuous as almost to deserve the name of co-dominants. This 
zone is seldom raised much above the Salicomia zone when that 
is present, the difference in level varying from two to three inches, 
as at Portishead, up to perhaps one and a half to two feet, as 
at some places near New Passage. In some spots, notably at 
the area above Portishead, known as St. George's wharf, the 
Sclerochloa zone is disappearing and rapidly being replaced by a 
thick growth of Salicomia. The little islands of Sclerochloa and 
Aster are surrounded and almost overwhelmed by the Salicomia 
growing thickly in the shallow channels of mud between them. 
The list of plants for this zone is as follows — 
Plantago maritima, L. 
Triglochin maritimum, L. 
Glaux maritima, L. 
Suceda maritima, Dumortier. 
Alsine marginata, L. H. G. Reichenbach. 
Salicomia europcea, L. 
Glaux shows considerable vegetative growth, but flowers very 
little and later than it does in the next higher zone ; the remainder 
of the plants in this list flower and fruit freely. 
