The principal genera are Convolvulus, Ipomœa and their allies. The genus Convolvulus formerly included all the beautiful monopetalous flowers with a folded limb, which are so common in gardens, but it is now restricted to those which have a two-celled capsule, with the cells two-seeded; the stamens are inclosed in the corolla, and the stigma is divided into two narrow thread-like lobes. Ipomœa only differs in having the lobes of the stigma capitate. In Quamoclit, the little scarlet Ipomœa, the capsule is four-celled, and the cells one-seeded; the corolla is tubular, and the stamens project beyond the throat. Batatas, the Sweet-potato, resembles Quamoclit, but the corolla is campanulate, and the stamens are inclosed. In Pharbitis (in which genus the common Convolvulus major, and the beautiful Ipomœa Learii, are both now included), the capsule is three-celled, and the cells are three-seeded; and in Calystigia, in which is now placed the common bindweed of the hedges, the capsule is one-celled and four-seeded; and the flower, which in other respects agrees with that of the genus Convolvulus, has two bracts which serve as a sort of involucre. All these flowers have the lobes of the corolla marked with a decided fold or plait, and they are climbing plants, generally annuals. Cuscuta is a parasite belonging to Convolvulaceæ, which though it springs from the ground, withers just above the root as soon as it has twined itself round any plant within its reach; drawing its entire nourishment from the unfortunate plant it has attacked, and which it soon kills. The plants in this order produce an acrid milk; and the roots of a kind of Convolvulus yield the drug called Jalap, which takes that name from the Mexican city Xalapa, near which it is grown. ORDER CXXXVII.—BORAGINEÆ.