Herbs with pungent, watery juice. Leaves.—Alternate; without stipules; entire or divided. Flowers.—Generally in racemes. Sepals.—Four. Petals.—Four; usually with narrowed base or claw; the blades spreading to form a cross. Stamens.—Six; two of them shorter than the other four. Ovary.—Two-celled; rarely one-celled. Style undivided, or none. Stigma entire or two-lobed. Fruit.—A silique—i.e. a capsule, in which the walls separate upward away from a central partition.
The Mustard family is a very large one, comprising over a hundred and seventy genera, and containing between one and two thousand species. It is widely distributed over all parts of the world, but is most abundantly represented in the cooler or temperate regions. It furnishes us with many useful plants; such as the mustard, horseradish, radish, cabbage, turnip, cauliflower, etc.
The genera of this order are very closely allied, and very difficult of discrimination. The fruit, as well as the flower, is necessary in the study of any given species.
Leguminosæ. Pea Family.
The order Leguminosæ is divided into three well-marked sub-orders—the Pea family proper, the Brasiletto family, and the Mimosa family. But as all our genera, save Cercis, fall under the first, we shall describe that only.
Papilionaceæ. Pea Family proper.
Herbs, shrubs, or trees. Leaves.—Usually alternate; compound; with stipules; the latter sometimes transformed into thorns or tendrils. Flowers.—Seldom solitary; usually in spikes, racemes or umbels. Calyx.—Five-toothed; often bilabiate. Corolla.—Irregular; of five petals; papilionaceous—i.e. the two lower petals more or less coherent, forming the keel; the two lateral ones often adherent to the keel, called the wings; the upper petal called the standard or banner. Stamens and pistil inclosed in the keel. Stamens.—Ten; their filaments either coherent into a tube surrounding the pistil; or nine of them united into a sheath, open above, the tenth lying in front of the cleft; or rarely all distinct. Ovary.—Superior; one-celled. Style.—Simple and incurved. Stigma.—Simple. Fruit.—A two-valved pod, of which the garden pea is typical.
The Pea family, including its three sub-orders, is one of the most important plant-families known. It is distributed over almost the entire world, and furnishes some of the most valuable products to man. The Judas-tree, the numerous acacias, and the sweet pea, are well known in our gardens; while among our most valuable vegetables are the bean, the pea, and the lentil. The clover and alfalfa are extremely important forage plants.
The order furnishes several important timber-trees, in different parts of the world, such as the Rosewood, the Laburnum, and the Locust; and yields numerous products of economic importance, such as licorice, senna, gum Senegal, gum Arabic, gum tragacanth, balsam of copaiba, balsam of Tolu, indigo, logwood, red sandalwood, etc.
Compositæ. Composite Family.