ORDER LI.—TROPÆOLACEÆ.—THE NASTURTIUM TRIBE.
The well-known flowers called Nasturtium, or Indian Cress, give their name to this order; which, in fact, consists only of the genus Tropæolum, and an obscure genus not yet introduced. In the flowers of the Nasturtium, the calyx and corolla are of nearly the same colour, but they may be easily distinguished from each other. The calyx is drawn out into a spur behind, and the petals, which are unguiculate, or claw-shaped, are fringed at the base. The leaves and stem are succulent, and have the taste of cress, and hence the plant has received its popular name,—Nasturtium being the botanic name of the water-cress. The Tropæolum has five petals, eight stamens, and three carpels, which are joined together into a trigonal fruit, each carpel containing one seed, which adheres to it. The embryo is large, and fills the whole seed, which is without albumen. The unripe carpels are sometimes pickled, and used as a substitute for capers. The whole plant has not only the taste, but the properties, of cruciferous plants; and even the caterpillars of the cabbage-butterflies feed upon it.
ORDER LII.—BALSAMINEÆ.—BALSAM TRIBE.
Nearly allied to the Geraniums, and resembling them, in the opening of the seed-pods, are the beautiful plants contained in the order Balsamineæ. The two genera best known in British gardens are Balsamina and Impatiens. The common Balsam (Balsamina hortensis), has a small green calyx of two sepals; there are four petals, one of which is drawn out into a short spur at the base. There are five stamens, each bearing a two-celled anther. The ovary is one-celled, but it separates into five valves, when the seeds are ripe, bursting with elasticity, and the valves curling inwardly from the apex to the base. There are five stigmas, quite distinct from each other, and appearing just above the ovary, without any style; and the peduncles are simple and one-flowered.
The genus Impatiens, which contains the common Noli-me-tangere, or Touch-me-Not, and other similar plants, though it agrees with Balsamina in having five anthers, has only three of them with two cells, the others having one cell each. The stigmas also are joined together at the base, and the capsule bursts at the slightest touch, the valves coiling up spirally from the base to the apex, and detaching themselves from the plant at the same time that they expel the seeds. The peduncles grow from the axils of the leaves, and they are branched and many-flowered. A separate order, called Hydrocereæ, has been made of one of the species of Impatiens (I. natans). It is an aquatic plant, a native of the East Indies.
ORDER LIII.—OXALIDEÆ.—THE WOOD-SORREL TRIBE.
The flowers of all the species of Oxalis, the Wood-sorrel, are very pretty. The flowers have five regular petals, each furnished with a claw; and the petals are spirally twisted in the bud. There are ten stamens, and five styles. The capsule is five-celled, and five or ten valved, the valves opening lengthways. Most of the species are natives of South America, and greenhouse plants in England.