196. Mare's-Tail, Hippuris vulgaris, Mare's-tail family. A not uncommon plant of quiet water: the stem is partly (or in running water completely) submerged: it is simple or slightly branched, with many whorls, of 6 to 12 stiff, narrow leaves, with hard points: the submerged leaves are soft and long: flowers very small, in the axils of the upper leaves, in summer,

196. Mare's Tail.

196. Mare's-Tail.

197. Water Milfoil.

197. Water Milfoil.

197. Water Milfoil, Myriophyllum spicatum, Mare's-tail family. A common plant of ponds and slow streams: the slender stem bears whorls of 4 brownish, featherlike leaves: the plant is submerged, except for the slender terminal spikes of very small flowers, which appear in summer.

198. Water Starwort Callitriche aqua-tica, Mare's-tail family. An extremely common plant of ditches, ponds, and quiet streams: the stem is slender, branched, and has pairs of elliptical leaves, broader towards the tip: in some forms the leaves are quite narrow and pointed: flowers small, and green in the leaf axils: the plant is of a fresh green, colour.

198. Water Starwort.

198. Water Starwort.

199. Greater Bladderwort, Utricularia vulgaris, Butterworfc family. A fairly common submerged plant of pools, especially on peaty soil: the leaves are very much divided into narrow, hair-like segments; some of the segments are replaced by little bladders, which act as traps for small water-animals, the dead bodies of which are utilised by the plant as food: the large yellow flowers are produced in spikes above the water in summer, but the plant flowers only rarely: the Lesser Bladderwort has more slender leaves and small pale flowers.

, 199. Greater Bladderwort.

, 199. Greater Bladderwort.

200. Water Thyme.

200. Water-Thyme.

200. Water-Thyme, Elodea canadensis, Water-thyme family. The stems are long, slender, and submerged, with close whorls of 3 narrow, blunt, olive-green leaves: the flowers, which are rarely seen, are small, on slender stalks, and pale violet: the plant is not a native, but since its introduction from America it has spread enormously, and often seriously chokes ponds and canals.