Geocarpic fruits, i.e. those which penetrate the soil during their development and ripen underground, are found in e.g. Arachis hypogæa (see page [472]), Trifolium subterraneum, Vicia amphicarpæa. Germination takes place in various ways. In the majority the cotyledons are raised above the ground as green, leaf-like bodies; in the Vicieæ they remain thick and white, and are always enclosed in the testa, and are therefore never able to take part in the work of assimilation; in species of Phaseolus, on the other hand, they are raised well above the ground and become green, but remain however thick and fleshy.
1, 2. The two groups Podalyrieæ (the majority of the genera are Australian) and Sophoreæ (Sophora, Edwardsia, etc.), represent the oldest type, as they have 10 free stamens and so form the transition to the Cæsalpiniaceæ. Nearly all are trees and shrubs.
3. Astragaleæ. Herbs or shrubs, less frequently trees, with imparipinnate leaves (without tendrils). The flowers are generally borne in racemes or spikes. Stamens monadelphous or diadelphous.—Astragalus (Milk-Vetch) has the legume incompletely divided longitudinally into 2 loculi by a septum formed by the incurved dorsal suture. Diadelphous.—Glycyrrhiza (Liquorice); Colutea (Bladder-Senna) from S. Europe; Robinia (the false Acacia) with thorny stipules; Indigofera (the Indigo plant); Amorpha (which has only one petal, namely the standard, and the fruit a nut), Caragana, Wistaria (a climbing shrub), Galega. Carmichælia australis, when old, produces flat branches with scale-like leaves.
4. Vicieæ. Climbing herbs with paripinnate leaves, the midrib ending in a point or frequently in a tendril, which generally is branched, representing lateral veins without mesophyll; stamens diadelphous; the cotyledons remain underground on germination.—Vicia (Vetch) has a filamentous style, hairy towards the tip, and a pod with many seeds; climbing by means of tendrils; the leaves have many leaflets.—Faba (F. vulgaris, Horse-bean) is erect, without tendrils; its pod is thick with spongy septa between the seeds.—Ervum (Lentil) has a pod with only 1–2 seeds, and sweeping hairs (stylar-brush) on the inner side of the style.—Pisum (Pea; Fig. [512]) has very large stipules, the bent style has a hollow groove on the anterior side. P. sativum (Common Pea), P. arvense (Grey Pea).—Lathyrus (Sweet Pea) generally has an angular, winged stem and most frequently only a few pairs of leaflets. The style is flattened, with sweeping hairs on the back. In L. aphaca the stipules alone are developed into foliage-leaves, while the remainder of the leaf is modified into a tendril.—Cicer has a nearly straight embryo and imparipinnate leaves with dentate or incised leaflets. C. arietinus (Chick-pea).—Abrus (precatorius, etc.); the seeds (“Crab’s eyes,” “Paternoster peas,” “Jequirity”) are scarlet with a black spot round the hilum.
5. Phaseoleæ. Herbs, twining or erect, but not climbing by tendrils; the leaves are imparipinnate, generally ternate, and bear small, linear bodies resembling stipules at the base of the stalks of the leaflets. The inflorescences are most frequently compound, groups of few flowers being situated on short, nodose, lateral axes borne on a longer stem. On germination the cotyledons are raised a considerable distance above the ground, and become greenish, but do not become leaf-like; in P. multiflorus they remain underground. Stamens as in the Vetches.—Phaseolus (Kidney-bean): the keel with the stamen and style is spirally twisted (to the right). Herbs, twining to the left.—The “Calabar-bean” (Physostigma venenosum), Erythrina, Clitoria, Glycine, Soja, Mucuna, Apios, Canavalia, Vigna, Dolichos, Cajanus, Rhynchosia, etc.
6. Trifolieæ (Clovers). Herbs with ternate leaves, the leaflets are often dentate with the veins prolonged into the teeth; stamens diadelphous; fruit 1-locular, 1–few-seeded, pyxidium-like, irregularly dehiscent, or more frequently a nut. The flowers are generally borne in capitula, racemes, or spikes.—Trifolium (Clover). The corolla is gamopetalous. The calyx persists, together with the corolla, round the ripe fruit. The inflorescence is a spike, capitulum or capitate umbel; the leaves are ternate, and have adnate stipules.—Medicago (Medick). The corolla falls off after flowering; fruit curved like a sickle or spirally twisted; it is a nut, and opens with difficulty. Leaves ternate.—Melilotus (Melilot) has a small, spherical or lanceolate, thick and wrinkled fruit, which as a rule is indehiscent. The inflorescence is a raceme, often long, or a spike, sometimes a capitulum. Leaves ternate.—Ononis (Rest-harrow) differs in having monadelphous stamens and in being more shrub-like and bushy, and in having a normal, 2-valved pod, by which characteristic it approaches the Genisteæ. The flowers are generally rose-coloured, solitary, or in few-flowered racemes in the leaf-axils. Thorns (branches) are often present; the leaves are compound with only one small leaflet (the terminal one), or ternate with adnate stipules.
7. Loteæ. Herbs with ternate or imparipinnate leaves, with entire leaflets. In the latter case, when the lowest pair of leaflets is placed quite close to the sheath, the stalk is wanting, and apparently a trifoliate leaf with large stipules is developed. Flowers in an umbel or capitulum. Stamens monadelphous or diadelphous, the filaments (either all of them, or only the 5 sepal-stamens) are widened at the top.—Lotus (Bird’s-foot-trefoil) has a long, round pod.—Tetragonolobus.—Anthyllis (Lady’s-finger); the fruit is a nut, which is distributed by the wind by means of the membranous, bladder-like calyx, which completely encloses and falls off with it.
8. Genisteæ. The majority are shrubs or trees with apparently simple leaves, i.e. compound leaves with only one leaflet (the terminal leaflet), or ternate leaves; the stipules in most instances are very small or are entirely wanting; stamens monadelphous.—Genista (Dyer’s-weed) has apparently simple leaves; the branches often terminate in a thorn. The strongly-winged stems in G. sagittalis are its most important organs of assimilation. Bossiæa rufa has flat branches, its leaves being reduced to small, pointed stipules.—Sarothamnus (Broom) has switch-like, angular branches and often both the apparently simple and ternate leaves on the same shoot; style spirally rolled.—Cytisus (Laburnum). Ulex (Furze; in U. europæus, the seedlings bear a few foliage leaves, but the leaves succeeding these are modified into thorns); Spartium; Crotalaria, etc.—Lupinus (Lupin) is allied to this group; it has a thick, often somewhat fleshy pod, and digitate leaves with adnate stipules.—Retama.
9. Hedysareæ are especially recognised by having the ovary divided by transverse septa into as many cells as there are seeds, the fruit thus becomes a lomentum, dehiscing transversely into nut-like joints (Fig. [513]).—Ornithopus (Bird’s-foot); Coronilla; Hippocrepis; Onobrychis (Sainfoin) has a fruit with only 1 joint (i.e. a 1-seeded nut); Desmodium; Alhagi; Hedysarum, etc.—Arachis hypogæa (Earth-nut) has a pod which is abstricted between the seeds, and is indehiscent, but is not multilocular nor a true lomentum; it is reticulately wrinkled externally, and ripens underground; the basal part of the ovary is prolonged after flowering, attaining a length of several inches, and buries the young fruit in the soil. The embryo is straight.—Desmodium gyrans is well-known for its motile leaflets.
