Fig. 513.—Hedysarum coronarium.
10. Dalbergieæ. 25 genera; especially in Tropical America; the majority are trees, a few shrubs or lianes; the leaves are simple or imparipinnate. The fruit is indehiscent in all; in some it is a winged, in others a wingless nut (Machærium, Dalbergia, Centrolobium, etc.), in others, again, a drupe, e.g. in Dipteryx (Tonquin-bean) and Andira. In some genera the embryo is straight.
Pollination. Especially effected by Bees. The nectar is secreted by a ring or disc-like portion round the base of the gynœceum or the inner surface of the receptacle. The flower is constructed with a peculiar mechanism to ensure cross-pollination by insects. The pollen is shed just before the flower opens, and is retained in a pouch formed by the keel. An insect visiting the flower uses the wings and keel for a landing-stage, and in attempting to reach the honey presses down the wings and the keel which are locked together near the standard; the stylar-brush by this means is forced through the apical opening of the keel and a little pollen is thus swept out and deposited upon the abdomen of the visiting insect as it presses against the apex of the keel; the insect thus carries away pollen and may effect cross-pollination. In the different flowers this arrangement is modified in various ways to promote pollination. 5000 species (319 genera); especially in the Tropics, where many are important forest trees.—The following plants are used FOR FOOD: Pisum sativum (W. Asia?) and arvense (Italy); Phaseolus vulgaris (Kidney-bean, American; Dolichos sinensis was known to the Greeks and Romans under the name “φασηλος,” “phaseolus”), P. compressus (French-bean), etc.; Faba vulgaris (Field-bean, Horse-bean; from the Old World); Ervum lens (Lentil, Eastern Mediterranean); in tropical countries the oil-containing seeds of Arachis hypogæa.—The following are FODDER plants: Vicia sativa, Faba vulgaris, Onobrychis sativa (Sainfoin), Medicago sativa (Lucerne), and lupulina (Medick), species of Trifolium, Hedysarum coronarium. Officinal: “Liquorice root,” from Glycyrrhiza glabra (S. Europe); “Red Sandalwood,” from Pterocarpus santalinus (Tropical E. Asia); Gum Tragacanth, from Astragalus-species (E. Mediterranean); Balsam of Peru, from Toluifera pereiræ, and Balsam of Tolu, from Toluifera balsamum. Calabar-beans, from Physostigma venenosum; Kino, from Pterocarpus marsupium; the pith of Andira araroba is used under the name of “Chrysarobin.”—Of use TECHNICALLY: Genista tinctoria (yellow dye) and Indigofera-species (Indigo), the bast of Crotalaria juncea (Sunn Hemp); the seeds of Dipteryx, which contain Coumarin, and are highly scented, and Balsam of Myroxylon. Poisonous: the seeds of Laburnum (Cytisus laburnum), various species of Lathyrus, and Abrus precatorius; the latter contain two poisonous proteids, paraglobulin and albumose, which resemble snake-poison in their effects. The following are ORNAMENTAL plants: Phaseolus multiflorus (Scarlet runner, from America), Robinia pseudacacia, Amorpha, Colutea, Coronilla, Indigofera dosua, Wistaria polystachya, Cytisus laburnum (Laburnum, S. Europe, Orient.) and other species.
Order 3. Mimosaceæ. The flowers are most frequently hypogynous and regular, the æstivation of the corolla is valvate and, in the majority of instances, that of the calyx also. The flower is 4-merous, less frequently 5- or 3-merous.—The flowers are generally small, but are always borne in compact, round capitula or spikes (Fig. [514]); they are hypogynous or perigynous. The calyx is generally gamosepalous and the corolla gamopetalous, the latter being frequently wanting. The stamens are equal or double the number of the petals (Mimosa, etc., in M. pudica, e.g. S4, P4, A4, G1) or (in Acacia, Inga, etc.) in a large, indefinite number, free or monadelphous, often united to the corolla (Fig. [514] b). The colour of the flower in most cases is due to the long and numerous stamens. The fruit is various. The embryo is straight as in the Cæsalpiniaceæ. Entada and many species of Mimosa have a flat, straight, or somewhat sickle-like pod, which resembles the siliqua of the Cruciferæ in that the sutures (in this instance, however, dorsal and ventral suture) persist as a frame, but the intermediate portion divides, as in the transversely divided siliqua, into as many nut-like portions as there are seeds. Some species have a pod of enormous dimensions. The seeds of Entada gigalobium are often carried from the West Indies to the N. W. coasts of Europe by the Gulf Stream.—The fruit of Acacia in some species is an ordinary pod, in others it is transversely divided, or remains an undivided fruit, a nut.—This order includes both trees and herbaceous plants, which are often thorny; the leaves are usually bipinnate (Fig. [514]) and are sensitive, and also possess sleep-movements.—Many Australian Acacias have compound leaves only when young, but when old have phyllodia, i.e. leaf-like petioles without blades, placed vertically. A large number have thorny stipules, which in some (Acacia sphærocephala) attain an enormous size, and serve as a home for ants, which in return protect their host-plant against the attacks of other, leaf-cutting ants.
Fig. 514.—Acacia farnesiana: a inflorescence; b flower.
Other genera besides those mentioned are: Adenanthera, Desmanthus, Parkia, Inga (with rather fleshy, indehiscent fruit), Calliandra, etc.
1350 species (30 genera); none natives of Europe, their home being the Tropics and sub-tropical regions, especially Australia and Africa.—Fossils in Tertiary.—Gums are found in many species of Acacia, especially the African (Gum arabic) and Australian, of which some are officinal. The bark, and also the fruits, contain a large amount of tannic acid and are used as astringents and in tanning (“Bablah” is the fruits of several species of Acacia). Catechu is a valuable tanning material extracted from the wood of Acacia catechu (E. Ind). The flowers of Acacia farnesiana (Fig. [514]) are used in the manufacture of perfumes. With us they are cultivated as ornamental plants, e.g. A. lophantha and many others, in conservatories.
Family 22. Passiflorinæ.
The flowers are most frequently regular, 5-merous in the three most external whorls, eucyclic and perigynous or epigynous, less frequently hypogynous. A characteristic feature is that the ovary is tricarpellary, unilocular, and with 3 parietal placentæ which sometimes meet in the central line (Cucurbitaceæ). The styles are generally free and bifid. To all these characteristics, however, there are exceptions. The Cucurbitaceæ are sometimes placed among the Sympetalæ, close to the Campanulinæ, but they are not allied to the Sympetalæ, from which they differ especially, for instance, in the structure of the ovule. The position of the Begoniaceæ in this family is also open to doubt.