180
THE ESSEX NATURALIST.
parts of the stem, in Gipsywort and many other water plants7
become swollen by the formation of aerenchyma or air-tissue
in the cortex, by means of which they can obtain oxygen ; the
roots also are sheathed with aerenchyma; the nutlets have
thickened corky margins, and float well. A widely distributed
plant in the Northern Hemisphere ; it occurs also in Australia.
Lamium album L. White Dead-nettle. A, B. A dozen
plants or more, F.
L. purpureum L. Red Dead-nettle. A. A few plants. F.
Ballota nigra L. Black Horehound. A, B. Several large
colonies. F.
Plantago major L. Great Plantain. A, B. Not uncommon.
P. lanceolata L. Ribwort Plantain. A. Not uncommon.
Chenopodium rubrum L. Red Goosefoot. A, B. Abundant.
C. urbicum L. Upright Goosefoot. A. A group of plants,
distinguished from C. album by their erect branches and the
scanty mealiness of the stalks and inflorescence.
C. album L. Fat Hen. A, B. Very abundant.
Atriplex hastata L. Orach. A, B. Very abundant.
Salsola Kali L. Saltwort. A. Half a dozen plants on
dry mud ; the fruits had evidently drifted from saltings with
the tide, and so found their way to the made ground. Like the
preceding species, Saltwort is widely distributed in both hemi-
spheres. I have found it growing by brine pools in the State of
Montana, U.S.A., 500 miles from the coast.
Polygonum Persicaria L. Spotted Persicaria. A, B. Abun-
dant. F.
P. amphibium L. Floating Persicaria. A, B. Abundant
along the banks of the New Flood Channel; scattered stunted
plants grew also on the made ground.
P. lapathifolium L. Glandular Persicaria. A.
P. Hydropiper L. Water Pepper. A. A dozen plants.
P. Aviculare L. Knotgrass. A. Abundant.
Rumex obtusifolius L. Broad-leaved Dock. A, B. Abun-
dant.
Mercurialis annua L. Annual Mercury. A. A dozen plants.
Urtica dioica L. Stinging Nettle. A, B. A few plants.
Sparganium ramosum Huds. Great Bur-reed. A. One
7 See A. Arber, Water Plants, pp. 188-194.