Page:EB1911 - Volume 16.djvu/403

are freely exposed and the conspicuous coloured stamens serve as well as the petals to attract insects; in Mimosa and Acacia the flowers are crowded in conspicuous heads or spikes. The relation of insects to the flower has been carefully studied in
Fig. 8.—Stamens and Pistil of
Sweet Pea (Lathyrus). Thestamens
are diadelphous, nine of them
being united by their filaments
f, while the uppermost one (e)
is free; st, stigma, c, calyx. the Papilionatae, chiefly in European species. Where honey is present it is secreted on the inside of the base of the stamens and accumulated in the base of the tube formed by the united filaments round the ovary. It is accessible only to insects with long probosces, such as bees. In these cases the posterior stamen is free, allowing access to the honey. The flowers stand more or less horizontally; the large erect white or coloured standard renders them conspicuous, the wings form a platform on which the insect rests and the keel encloses the stamens and pistil, protecting them from rain and the attacks of unbidden pollen-eating insects. In his book on the fertilization of flowers, Hermann Müller distinguishes four types of papilionaceous flowers according to the way in which the pollen is applied to the bee:

(1) Those in which the stamens and stigma return within the carina and thus admit of repeated visits, such are the clovers, Melilotus and laburnum. (2) Explosive flowers where stamens and style are confined within the keel under tension and the pressure of the insect causes their sudden release and the scattering of the pollen, as in broom and Genista; these contain no honey but are visited for the sake of the pollen. (3) The piston-mechanism as in bird’s-foot trefoil (Lotus corniculatus), Anthyllis, Ononis and Lupinus, where the pressure of the bee upon the carina while probing for honey squeezes a narrow ribbon of pollen through the opening at the tip. The pollen has been shed into the cone-like tip of the carina, and the heads of the five outer stamens form a piston beneath it, pushing it out at the tip when pressure is exerted on the keel; a further pressure causes the protrusion of the stigma, which is thus brought in contact with the insect’s belly. (4) The style bears a brush of hairs which sweeps small quantities of pollen out of the tip of the carina, as in Lathyrus, Pisum, Vicia and Phaseolus.

Fig. 9.—Broom (Cytisus scoparius). (2-7 slightly reduced.)
1, Calyx. 2, Standard. 3, Wing. 4, Keel.	5, Monadelphous stamens and style. 6, Pistil. 7, Pod.

From Vines’s Students’ Text-Book of Botany, by permission of Swan, Sonnenschein & Co.	Fig. 11.—Lomentum or lomentaceous legume of a species of Desmodium. Each seed is contained in a separate cavity by the folding inwards of the walls of the legume at equal intervals; the legume, when ripe, separates transversely into single-seeded portions or mericarps.
Fig. 10.—Dry dehiscent Fruit. The pod (legume) of the Pea. r, The dorsal suture; b, the ventral; c, calyx; s, seeds.

Leguminosae is a cosmopolitan order, and often affords a characteristic feature of the vegetation. Mimosoideae and Caesalpinioideae are richly developed in the tropical rain forests, where Papilionatae are less conspicuous and mostly herbaceous; in subtropical forests arborescent forms of all three suborders occur. In the temperate regions, tree-forms are rare—thus Mimosoideae are unrepresented in Europe; Caesalpinioideae are represented by species of Cercis, Gymnocladus and Gleditschia; Papilionatae by Robinia; but herbaceous Papilionatae abound and penetrate to the limit of growth of seed-plants in arctic and high alpine regions. Shrubs and undershrubs, such as Ulex, Genista, Cytisus are a characteristic feature in Europe and the Mediterranean area. Acacias are an important component of the evergreen bush-vegetation of Australia, together with genera of the tribe Podalyrieae of Papilionatae (Chorizema, Oxylobium, &c.). Astragalus, Oxytropis, Hedysarum, Onobrychis, and others are characteristic of the steppe-formations of eastern Europe and western Asia.

The order is a most important one economically. The seeds, which are rich in starch and proteids, form valuable foods, as in pea, the various beans, vetch, lentil, ground-nut (Arachis) and others; seeds of Arachis and others yield oils; those of Physostigma venenosum, the Calabar ordeal bean, contain a strong poison. Many are useful fodder-plants, as the clovers (Trifolium) (q.v.), Medicago (e.g. M. sativa, lucerne (q.v.), or alfalfa); Melilotus, Vicia, Onobrychis (O. sativa is sainfoin, q.v.); species of Trifolium, lupine and others are used as green manure. Many of the tropical trees afford useful timber; Crotalaria, Sesbania, Aeschynomene and others yield fibre; species of Acacia and Astragalus yield gum; Copaifera, Hymenaea and others balsams and resins; dyes are obtained from Genista (yellow), Indigofera (blue) and others; Haematoxylon campechianum is logwood; of medicinal value are species of Cassia (senna leaves) and Astragalus; Tamarindus indica is tamarind, Glycyrrhiza glabra yields liquorice root. Well-known ornamental trees and shrubs are Cercis (C. siliquastrum is the Judas-tree), Gleditschia, Genista, Cytisus (broom), Colutea (C. arborescens is bladder-senna), Robinia and Acacia; Wistaria sinensis, a native of China, is a well-known climbing shrub; Phaseolus multiflorus is the scarlet runner; Lathyrus (sweet and everlasting peas), Lupinus, Galega (goat’s-rue) and others are herbaceous garden plants. Ceratonia Siliqua is the carob-tree of the Mediterranean, the pods of which (algaroba or St John’s bread) contain a sweet juicy pulp and are largely used for feeding stock.

The order is well represented in Britain. Thus Genista tinctoria is dyers’ greenweed, yielding a yellow dye; G. anglica is needle furze; other shrubs are Ulex (U. europaeus, gorse, furze or whin, U. nanus, a dwarf species) and Cytisus scoparius, broom. Herbaceous plants are Ononis spinosa (rest-harrow), Medicago (medick), Melilotus (melilot), Trifolium (the clovers), Anthyllis Vulneraria (kidney-vetch), Lotus corniculatus (bird’s-foot trefoil), Astragalus (milk-vetch), Vicia (vetch, tare) and Lathyrus.

LÈGYA, called by the Shans Lai-hka, a state in the central division of the southern Shan States of Burma, lying approximately between 20° 15′ and 21° 30′ N. and 97° 50′ and 98° 30′ E., with an area of 1433 sq. m. The population was estimated at 30,000 in 1881. On the downfall of King Thibaw civil war