In ditches we occasionally meet with the Water Hemlock or Cowbane (_Cicuta virosa_)--a tall plant, from three to four feet high, bearing large, flat umbels of small, white flowers from June to August. Its stem is hollow, furrowed, and branched; and the leaves are large, twice pinnate or ternate, with lanceolate, acute leaflets, generally over an inch in length, the margins serrate or (sometimes) doubly serrate. Comparing this plant with the Common Hemlock (p. 169), we should note that the secondary bracts of the latter are three in number, almost invariably turned to the outside; and that its calyx teeth are very indistinct, while in the present species they are prominent above the ovary. Next follow three species of Water Dropwort (genus _[OE]nanthe_)--smooth plants, with much-divided leaves and compound umbels of white flowers, with secondary, and sometimes also primary, narrow bracts. In all three species the central flowers of each secondary umbel are perfect and shortly stalked, while the outer ones are on longer stalks, and usually staminate. The petals are notched, with points turned inwards; and the fruits have two rather long styles, are crowned by the five minute teeth of the calyx, and their carpels have each five blunt ribs. The three species referred to are:-- [Illustration: THE COMMON WATER DROPWORT.] 1. The Common Water Dropwort (_[OE]. fistulosa_).--An erect plant, from two to three feet high, with a fleshy, fibrous root; creeping runners; and a thick, hollow, slightly-branched stem. Its radical leaves are bipinnate, with segments cut into three or five narrow lobes; and the stem leaves have long, hollow stalks, with a few narrow segments at the top. The umbels have from three to five rays, usually with no primary bracts, and a few, narrow secondary ones. 2. The Hemlock Water Dropwort (_[OE]. crocata_) is a larger plant, from two to five feet high, with a tuberous root and a thick, branched stem. Its leaves are bipinnate, with stalked, shining leaflets that are irregularly cut. The umbels are on long stalks, and have nearly twenty rays, several narrow secondary bracts, and sometimes a few primary ones. The middle flowers of each secondary umbel are perfect and almost sessile, but the outer ones are stalked and staminate. 3. The Fine-leaved Water Dropwort (_[OE]. Phellandrium_) grows from one to four feet high, and has an erect, creeping or floating stem with runners at the base. The upper leaves are bipinnate, with small, cut segments; and the submerged ones are deeply cut into very narrow, almost hair-like lobes. The umbels are small, on short stalks in the angles of the branches or opposite the leaves. They have about ten rays, narrow secondary bracts, but no primary ones. [Illustration: THE MARSH THISTLE.] All three of the above species flower from July to September.