THE ESSEX FIELD CI.UI',. 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 rapidl}' retreating seawards. 



Mr. Crouch gave some particulars of the first discovery of the new Thames 

 Hydrohia 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 sei ies 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 Maeshes. 



" 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 1 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 ox 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: vi:., Potamogeton 

 pusillus, P. densiis, and P. crispus. The first is the commonest species, while P. 

 crispiis is the largest and handsomest of the three, having long alternate leaves, 

 which are of a beautiful fresh-green colour, and very curl}- 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 Naiadacese — and very similar in appearance to 

 Potamogeton pustllus, 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. 



" Myriophylliim spicatum (" Water Milfoil "). Common, flowering from July to 

 August. 



" Anacharis ahinastrum is, of course, very common in the fresher water ditches, 

 as well as CalHtrkhe stapialis (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 portiila (" 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. 



I.emna minor and L. trisuka 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 



