In the neighbourhood of cultivated fields we may frequently meet with the Lucerne or Purple Medick (_Medicago sativa_). This is not a British plant, but it has been introduced and largely cultivated, and is commonly found as an escape. It has an erect stem, from one to two feet high; and the flowers bloom during June and July, followed by smooth, spirally-twisted pods of two or three coils. This plant appears on Plate IV, Fig. 2. In the genus _Melilotus_, of the same order, we have to note three species, all of which agree in the following particulars:--They have trifoliate leaves; and small, white or yellow flowers in long racemes on axillary peduncles. The calyx has five teeth, and the corolla falls after it fades. The stamens are ten in number, the upper one quite free, while the filaments of the other nine are united into a split tube that surrounds the ovary. The pod is only a little longer than the calyx, rather thick in proportion to its length, with only one or two seeds, and it does not split when ripe. The three species referred to may be identified by the following descriptions:-- [Illustration: THE KIDNEY VETCH.] The Common Melilot (_Melilotus officinalis_) is a smooth plant, with a branched stem from two to four feet high; and long-stalked leaves with roundish or oval leaflets, and narrow, pointed stipules. The flowers are very numerous, yellow, about a quarter of an inch long, in long racemes. The petals are equal; and the hairy pods are only about a sixth of an inch long. The Field Melilot (_M. arvensis_) is very similar, but not so tall, and the flowers are less numerous. The 'keel' is shorter than the other petals; and the pods are ribbed and blunt. The third species--the White Melilot (_M. alba_)--is also very similar, but it has white flowers, in which the 'standard' or upper petal is the longest. All three species flower from June to August, but only the first may be described as common. The genus _Trifolium_, containing the Clovers and Trefoils, resembles _Melilotus_ in its trifoliate leaves, five-toothed calyx, and in the arrangement of the stamens; but it differs in that the stipules adhere to the leaf stalks, and the corolla often persists round the ripened fruit. Several species of this group are common in fields and pastures. [Illustration: THE COMMON MELILOT.] One of these is the Clustered Clover or Smooth Round-headed-Trefoil (_Trifolium glomeratum_)--a smooth plant, with purple or pink flowers, found principally in the dry pastures of South and East England, flowering during June and July. Its spreading stems are from six to twelve inches long; and the heads of flowers are small, sessile, globular, and either axillary or terminal. The calyx is ten-veined, shorter than the corolla, with five pointed teeth which bend outwards as the fruit ripens.