Fig. 509.—Flower.
Fig. 510.—The same in long. sect.
Cassia (Figs. [508–510]) is the largest genus (about 200 species); it has an almost hypogynous, zygomorphic flower with 5 free sepals and petals; of the 10 stamens the 3 posterior are generally barren, the others are of very unequal length and open at the apex by pores (Fig. [509]). In some (the Senna group) the fruit is a flat, short, thin, dehiscing pod; in others (Cathartocarpus) it is round, long, woody or fleshy, indehiscent, and divided internally by more or less fleshy transverse walls into as many cells as there are seeds.—The following also have DEHISCENT FRUITS: Bauhinia (often lianes, tropical climbers with tendrils [stem-structures] and anomalous stems), Copaifera, Hæmatoxylon (whose pod does not dehisce along the suture, but laterally), Cercis (simple leaves; the corolla resembles that of the Papilionaceæ, but the posterior petal is the smallest, and is enveloped by the 2 lateral ones, which are enveloped in their turn by the 2 anterior).—Fruit Indehiscent: Tamarindus indica; the pod is almost round, often a little abstricted between the seeds; the wall is formed by a thin, brittle external layer, enclosing an acid pulp; well-developed septa are present, between the seeds; the most internal layer is parchment-like. Calyx 4-merous by the coalescence of 2 sepals. Only 3 fertile stamens.—Ceratonia siliqua (Carob-bean, Locusts); the pod is long, compressed, with thick sutures, and has a wall, the central part of which is more or less leathery, fleshy and sweet; there are transverse septa between the seeds, as in the Tamarind. Embryo greenish in endosperm. The flower is without a corolla, 5 stamens.—Pterogyne (winged fruit), etc.—Kramerieæ with Krameria is an anomalous group.
Distribution. 80 genera, with 740 species; almost exclusively in the Tropics. The Carob-tree and Cercis grow in the Mediterranean basin. The largest and most widely distributed genus is Cassia, which is found as trees, shrubs, and weeds in all tropical countries. The order has many important uses to mankind. Medicinal: the leaves and pods of Cassia acutifolia and angustifolia (officinal, Senna-leaves), the fruit-pulp of the Cassia-sub-genus, Cathartocarpus. Rhatany root from Krameria triandra (Peru, officinal). Balsam is extracted from a number of Copaifera-species (Balsam of Copaiba) from S. Am. (officinal), and from Hymenæa (Copal balsam), Trachylobium and others. Edible fruits are obtained especially from the Carob-tree (from the East) and the Tamarind (officinal). The heart-wood of several species of Cæsalpinia, such as C. brasiliensis (the Pernambuco-tree), echinata (Red-tree), and sappan, yield dyes; Hæmatoxylon (H. campechianum, Logwood), Copaifera bracteata (Amarant-tree).—Timber is obtained from many (Melanoxylon and others). In Europe they are of little importance as ornamental plants, these being confined principally to the species of Gleditschia (G. triacantha, from N. Am.) and Cercis (the Judas-tree, C. siliquastrum, S. Eur.), which are cultivated in gardens; but in tropical gardens beautiful flowering species, e.g. of Cassia, Poinciana, Brownea, are found, and the most beautiful of all ornamental plants, the Indian Amherstia nobilis.
Fig. 511.—Diagram of Faba vulgaris: f the standard; v the wings; k the keel.
Order 2. Papilionaceæ. The flower (Figs. [511], [512]) is strongly zygomorphic and somewhat perigynous (Fig. [512] B; most frequently more on one side than the other). The calyx is gamosepalous and persistent. The polypetalous corolla has descending imbricate æstivation, the posterior, large leaf, the standard (Figs. [511] f; [512] B’, e), covering in the bud the two lateral ones, the wings (Figs. [511] v; [512] B’, a), which again cover the two anterior; these are united in the form of a boat, the keel (k and c); the wings and the two petals of the keel are very unsymmetrical. That the keel is formed of two petals is seen by its position (in front of one sepal) and by the two often more or less free claws. The 10 (5 + 5) stamens (monadelphous) are either all united into one bundle, or into two bundles (diadelphous), the posterior one being free (Fig. [512] C). The ovules are curved and also the embryo (Fig. [512] G), especially the hypocotyl, so that the radicle assumes a position close to the edge of the thick, fleshy cotyledons. Endosperm wanting; the cotyledons are very rich in proteid reserve material. The forms of the fruit and exceptions are described under the genera.
Fig. 512.—Pisum sativum: A entire flower; B in longitudinal section; C gynœceum and stamens; D gynœceum; B’ corolla dissected, e standard, a, a wings, c keel; D seed opened to show the cotyledons (c), the radicle (r), the plumule (g); E fruit (legume); F seed.