3. The Square-stalked Willow-herb (_E. tetragonum_ or _E. adnatum_).--A similar plant, from one to two feet high, common in bogs and ditches, and easily distinguished from other species of the genus by the four angles of the stem formed by the downward continuation of the margins of the leaves. The flowers are small, in terminal, leafy racemes, and erect when in bud. The petals are of a rose-pink colour, deeply notched; and the stigma is not divided. This species flowers in July and August. Our next flower is the beautiful Purple Loosestrife (_Lythrum Salicaria_--order _Lythraceæ_), which is abundant in the marshes, ditches, and wet places of most parts of Great Britain. It has a creeping rootstock; a stout, erect, slightly-branched, four-angled stem, from two to four feet high; and sessile, narrow, clasping, entire, acute leaves, two or three inches long, arranged in opposite pairs or in whorls of three or four. The flowers are of a reddish purple or pink colour, nearly an inch across, arranged in whorls on a long, tapering, leafy spike. They have a toothed and ribbed, tubular calyx, with broad inner, and narrow outer segments; oblong, wavy, wrinkled petals; twelve stamens in two whorls of different lengths; and a superior ovary. The time of flowering of this species is July to September. We have now to note several species of umbelliferous plants that grow in bogs and other wet places. The general features of the order (_Umbelliferæ_) will be found on p. 167, and the reader should refer to these, if necessary, before attempting to identify the following:-- The Procumbent Marsh-wort (_Helosciadium nodiflorum_ or _Apium nodiflorum_) is a creeping plant, abundant in ditches and other wet places, rooting at the base, with erect flowering stems that are sometimes very short, but often reach a height of three feet. The whole plant is smooth, with hollow stems; pinnate leaves with from three to nine or more pairs of ovate, bluntly-toothed leaflets; and almost sessile umbels of small, white flowers either opposite the leaves or in the angles of the upper branches. These umbels are compound, with about five or six rays, usually without primary bracts, but with several, narrow, secondary ones. The petals have their points turned inwards; and the carpels are oval, each with five narrow ribs. This plant is commonly seen growing in company with the Water-cress and the Brooklime, and blooms in July and August. [Illustration: THE WATER HEMLOCK.]