THE ESSEX FIELD CLUB. 261
immense open sewer. Not only are the shells and plants precious to the natu-
ralist rapidly becoming exterminated by the filth of London and by the refuse of
the chemical and other factories recklessly turned into the river, but the trade of
the shrimper is almost destroyed, and valuable food fishes are being driven out,
and are rapidly retreating seawards.
Mr. Crouch gave some particulars of the first discovery of the new Thames
Hydrobia and other interesting forms mentioned ; and the cordial thanks of the
meeting were given to Mr. Jenkins for his paper, and also for his valuable
donation to the Museum of the Club of an almost complete series of the Thames
Estuarine Mollusca.
Mr. Jenkins also contributed some interesting remarks upon the aquatic
plants of the Thames marshes, of which the following is an abstract:—
Notes on a Few of the Aquatic Plants of the Thames Marshes.
" In preparing my notes respecting the Estuarine Mollusca, I thought
that it might interest the members of the Essex Field Club, and not be
deemed out of character, if I were to exhibit a series of the aquatic plants com-
monly associated with them, and serving, in many cases, to furnish them with
necessary food. Of the Fresh-water Mollusca some seem to have a preference
for the living plants, whilst others, who are the scavengers of their aquatic world,
generally feed upon them when partially decayed. My friend, Mr. W. Biddis-
combe, of Plumstead, who has frequently accompanied me upon my trips to the
marshes, has kindly furnished me with the mounted specimens of aquatic plants
which I exhibit this evening, and also with a few notes descriptive of them.
Although these remarks refer to plants which my friend has collected principally
from the Plumstead Marshes, still I believe I can venture to assert, from personal
observations, that they are common upon the marshes at Erith and Dartford, as
well as upon the Essex side of the river.
" Potamogeton. Submerged 'or floating plants, with very cellular stems, and
peculiar leaves, which are very thin and pellucid, and so sensitive to moisture
after being dried, that when placed on the hand, they will shrivel up like a piece
of goldbeaters' skin. The flowers are small, greenish, and two sexual, in axillary
or terminal spikes. Three species are frequent in the marshes: viz., Potamogeton
pusillus, P. densus, and P. crispus. The first is the commonest species, while P.
crispus is the largest and handsomest of the three, having long alternate leaves,
which are of a beautiful fresh-green colour, and very curly and pellucid. The
three are all perennial and submerged, and flower from June to August.
" Zannichellia palustris ("Horned Pond-weed"), A plant belonging to the same
order as the last genus—the Naiadaceae—and very similar in appearance to
Potamogeton pusillus, but having flowers in the axils of the leaves, minute, in
pairs or solitary. It is frequent in most of the ditches, and flowers up to
September.
" Myriophyllum spicatum ("Water Milfoil"). Common, flowering from July to
August.
" Anacharis alsinastrum is, of course, very common in the fresher water ditches,
as well as Callitriche stagnalis (the "Water Star-wort"). The latter is a very
variable plant, no less than nine or ten "varieties" having been noticed by some
botanists. In bloom from May to July.
" Peplis portula ("Water Purslane"). A humble creeping plant, with smooth
opposite leaves, and small inconspicuous flowers in the axils of the leaves. The
stems are more or less tinged with red, and when the plant grows in places from
which the water has been dried up, the leaves acquire the same hue. It flowers
from July to August.
Lemna minor and L. trisulca are the two commonest Duck-weeds of the
marshes. The first is the universal one ; the second, the Ivy-leaved Duck-
weed, the peculiar side development of the young fronds forming a supposed
resemblance to an ivy leaf. "The flowers are very minute, consisting of one or