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LEGUMINOSAE

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Originally appearing in Volume V16, Page 383 of the 1911 Encyclopedia Britannica.
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LEGUMINOSAE , the second largest See also:

family of See also:seed-See also:plants, are tendrils; in See also:Robinia the stipules are spiny and persist after See also:leaf-fall. In some acacias (q.v.) the thorns are hollow, and inhabited by ants as in A. sphaerocephala, a central See also:American plant (fig. 2) and others. In some See also:species of Astragalus, Onobrychis and others, the leaf-stalk persists after the fall of the leaf and becomes hard and spiny. containing about 430 genera with 7000 species. It belongs to the See also:series Rosales of the See also:Dicotyledons, and contains three well-marked suborders, Papilionatae, Mimosoideae and Caesalpinioideae. The plants are trees, shrubs or herbs of very various See also:habit. The See also:British representatives, all of which belong to the suborder Papilionatae, include a few shrubs, such as Ulex (gorse, See also:furze), Cytisus (See also:broom) and See also:Genista, but the See also:majority, and this applies to the suborder as a whole, are herbs, such as the clovers, Medicago, See also:Hell-See also:lotus, &c., sometimes climbing by aid of tendrils which are modified leaf-structures, as in Lathyrus and the vetches (1'icia). See also:Scarlet runner (Phaseolus multiflorus) has a herbaceous See also:twining See also:stem. Woody climbers (Hanes) are represented by species of Bauhinia (Caesalpinioideae), which with their curiously flattened See also:twisted stems are characteristic features of tropical forests, and See also:Entada seandens (Mimosoideae) also See also:common in the tropics; these two suborders, which are confined to the warmer parts of the See also:earth, consist chiefly of trees and shrubs such as See also:Acacia and See also:Mimosa belonging to the Mimosoideae, and the Judas See also:tree of See also:southern See also:Europe (Cercis) and See also:tamarind belonging to the Caesalpinioideae. The so-called acacia of See also:European gardens (Robinia Pseudacacia) and See also:laburnum are examples of the tree habit in the Papilionatae. See also:Water plants are rare, but are represented by Aeschynomene and Neptunia, tropical genera.

The roots of many species See also:

bear nodular swellings (tubercles), the cells of which contain bacterium-like bodies which have the See also:power of fixing the See also:nitrogen of the See also:atmosphere in such a See also:form as to make it available for plant See also:food. Hence the value of these plants as a See also:crop on poor See also:soil or as a member of a series of rotation of crops, since they enrich the soil by the nitrogen liberated by the decay of their roots or of the whole plant if ploughed in as See also:green manure. The leaves are alternate in arrangement and generally See also:compound and stipulate. A common form is illustrated by the See also:trefoil or clovers, which have three leaflets springing from a common point (digitately trifoliate); pinnate leaves are also frequent as in laburnum and Robinia. In Mimosoideae the leaves are generally bipinnate (See also:figs. r, 2, 3). Rarely are the leaves See also:simple as in Bauhinia. Various departures from the usual leaf-type occur in association with adaptations to different functions or environments. In leaf-climbers, such as See also:pea or See also:vetch, the end of the rachis and one or more pairs of leaflets are changed into tendrils. In gorse the leaf is reduced to a slender spine-like structure, though the leaves of the seedling have one to three leaflets. In many Australian acacias the leaf See also:surface in the adult plant is much reduced, the petiole being at the same See also:time See also:flat- means a minimum surface is exposed to the intense sunlight. In the See also:garden pea the stipules are large and foliaceous, replacing the leaflets, which Leaf-movements occur in many of the genera. Such are the See also:sleep-See also:movement in the clovers, runner See also:bean (Phaseolus), Robinia and acacia, where the leaflets assume a See also:vertical position at nightfall.

Spontaneous movements are exemplified in the See also:

telegraph-plant (Desmodium gyrans), native of tropical See also:Asia, where the small lateral leaflets move up and down every few minutes. The sensitive plant (Mimosa pudica) is an example of movement in response to contact, the leaves assuming a sleep-position if touched. The seat of the movement is the swollen See also:base of the leaf-stalk, the so-called pulvinus (fig. 3). The stem of the lianes shows some remarkable deviations from the normal in form and structure. In Papilionatae anomalous secondary thickening arises from the See also:production of new cambium zones outside the See also:original See also:ring (See also:Mucuna, Wistaria) forming concentric rings or transverse or broader strands; where, as in Rhyncosia the successive See also:cam- biums are active only at two opposite points, a flat ribbon-like stem is produced. The climbing Bauhinias (Caesalpinioideae) have a flattened stem with See also:basin-like undulations; in some growth in thickness is normal, in others new cambium-zones are found concentrically, FIG. 3.—See also:Branch with two leaves of the Sensitive while others new and distinct plant (Mimosa pudica), showing the petiole in growth-centres, its erect See also:state, a, and in its depressed state, b; each with its also the leaflets closed, c, and the leaflets excambium-See also:zone, panded, d; p, pulvinus, the seat of the movement arise outside the of the petiole. See also:primary zone. The climbing Mimosoideae show no anomalous growth in thickness, but in some cases the stem becomes strongly winged. See also:Gum passages in the See also:pith and medullary rays occur, especially in species of acacia and Astragalus; gum-arable is an exudation from the branches of Acacia See also:Senegal, gum-tragacanth from Astragalus gummifer and other species. See also:Logwood is the coloured heartwood of Haematoxylon campechianum; red See also:sandalwood of Pterocar pus santalinus.

The See also:

flowers are arranged in racemose inflorescences, such as the simple raceme (Laburnum, Robinia), which is condensed to a See also:head in Trifolium; in Acacia and Mimosa the flowers are densely crowded (fig. 4). The See also:flower is characterized by a hypogynous or slightly perigynous arrangement of parts, the anterior position of the See also:odd sepal, the See also:free petals, and the single median carpel with a terminal See also:style, simple stigma and two ii From Strasburger's Lehrbuck der Botanik, by permission of Gustav See also:Fischer. Fie. z.—Acacia sphaerocepfala. I, Leaf and See also:part of stem; D, hollow 11, Single pinnule with food-See also:body, thorns in which the ants live; F, food F. (Somewhat enlarged.) bodies at the apices of the See also:lower pinnules; N, nectary on the petiole. (Reduced.) I alternating rows of ovules on the ventral suture of the ovary which faces the back of the flower. The arrangement of the petals and the number and cohesion of the stamens vary in the three suborders. In Mimosoideae, the smallest of the three, the flower is See also:regular (fig. 4 [31), and the sepals and petals have a valvate See also:aestivation, and are generally penta merous, but 3-6-merous flowers also occur. The sepals are more or less See also:united into a See also:cup (fig. 4 [2]), and the petals sometimes cohere at the base.

The stamens vary widely in number and cohesion; in Acacia (fig. 4) they are indefinite and free, in the tribe Ingeae, indefinite and monadelphous, in other tribes as many or twice as many as the petals. Frequently, as in Mimosa, the See also:

long yellow stamens are the most conspicuous feature of the flower. In Caesalpinioideae (fig. 5) the flowers are zygomorphic in a median See also:plane and generally pentamerous. The sepals are free, or the two upper ones united as in tamarind, and imbricate in aestivation, rarely as in the Judas-tree (fig. 5 [2]), valvate. The corolla shows See also:great variety in form; it is imbricate in aestivation, the posterior petal being Innermost. In Cercis (fig. 5) it clearly resembles the papilionaceous type; the odd petal stands erect, the median pair are reflexed and wing-like, and the lower pair enclose the essential See also:organs. In See also:Cassia all five petals are subequal and spreading; in Amherstia the anterior pair are small or absent while the three upper ones are large ; in Krameria, 1, Part of stem with leaf and its 2, Flower, much enlarged. subtended inflorescence, 3, Floral See also:diagram of Acacia tali- about natural See also:size. folia.

(After Eichler.) the anterior pair are represented by glandular scales, and in Tamarindus are suppressed. Apetalous flowers occur in Copaifera and Ceratonia. The stamens, generally ten in number, are free, as in Cercis (fig. 5) or more or less united as in Amherstia, where the posterior one is free and the See also:

rest are united. In tamarind only three stamens are fertile. The largest suborder, Papilionatae, has a flower zygomorphic in the median plane (figs. 6, 7). The five sepals are generally united (figs. 7, 9), and have an ascending imbricate arrangement (fig. 6); the calyx is often two-lipped (fig. 9 [1]). The corolla has five unequal petals with a descending imbricate arrangement; the upper and largest, the See also:standard (See also:vexillum), stands erect, the lateral pair, the wings or alae, are long, clawed, while the anterior pair cohere to form the See also:keel or carina, in which are enclosed the stamens and See also:pistil.

The ten stamens are monadelphous as in gorse or broom (fig. 9), or diadelphous as in sweet pea (fig. 8) (the posterior one being free), or almost or quite free; these See also:

differences are associated with differences in the methods of See also:pollination. The ten stamens here, as in the last suborder, though arranged in a single whorl, arise in two series, the five opposite the sepals arising first. The carpel is sometimes stalked and often surrounded at the base by a See also:honey-secreting disk; the style is terminal and in the zygomorphic flowers is often curved and somewhat flattened with a definite back and front. Sometimes as in species of Trifolium and Medicago the ovules are reduced to one. The pod or legume splits along both sutures (fig. io) into a pair of membranous, leathery or sometimes fleshy valves, bearing the seeds on the ventral suture. Dehiscenceis often explosive, the valves separating elastically and twisting spirally, thus See also:shooting out the seeds, as in gorse, broom and others. In Desmodium, Entada and others the pod is constricted between each seed, and breaks up into indehiscent one-seeded parts; it is then called a lomentum (fig. II); in Astragalus it is divided by a See also:longitudinal septum. The pods show a very great variety in form and size. Thus in the \no~o4 clovers they are a small fraction of an See also:inch, while in the common tropical climber Entada scandens they are woody structures more than a yard long and several inches wide.

They are generally more or less flattened, but sometimes See also:

round and See also:rod-like, as in species of Cassia, or are spirally coiled as in Medicago. Indehiscent one-seeded pods occur in species of See also:clover and in Medicago, also in Dalbergia and allied genera, where they are winged. In Colutea, the See also:bladder-See also:senna of gardens, the pod forms an inflated bladder which bursts under pressure; it often becomes detached and is blown some distance before bursting. An arillar outgrowth is often See also:developed on the funicle, and is sometimes brightly coloured, rendering the seed conspicuous and favouring dissemination by birds; in such cases the seed-coat is hard. In other cases the hard seed-coat it-self is See also:bright-coloured as in the scarlet seeds of Abrus precatorius, the so-called FIG. 6.-Diagram of em See also:weather-p 1 a n t. Flower of Sweet Pea FIG. 7.-Flower of Animals also See also:act (Lathyrus), showing Pea (Pisum sativum), as the agents of five sepals, s, two are showing a papilionadistribution in the See also:superior, one inferior, ceous corolla, with one See also:case of fleshy and two lateral; five petal superior, st, the edible pods See also:con- petals, p, one superior, standard (vexillum), taining seeds with two inferior, and two two inferior, See also:car, the a hard smooth lateral ; ten stamens in keel (carina), and two testa, which will two rows, a, and one lateral, a, wings (alae). pass u n i n j u r e d carpel, c. The calyx is marked c. through the body, as in tamarind and the See also:fruit of the carob-tree (Ceratonia). In the ground-See also:nut (Arachis hypogaea), Trifolium subterraneum and others, the flower-stalks grow downwards after fertilization of the ovules and See also:bury the fruit in the earth.

In the suborders Mimosoideae and Papilionatae the embryo fills the seed or a small quantity of endosperm occurs, chiefly round the radicle. In Caesalpinioideae endosperm is absent, or See also:

present forming a thin layer round the embryo as in the tribe Bauhinieae, or copious and cartilaginous as in the Cassieae. The embryo has generally flat leaf-like or fleshy cotyledons with a See also:short radicle. See also:Insects See also:play an important part in the pollination of the flowers. In the two smaller suborders the stamens and stigma 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 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 See also:tube formed by the .united fila- ments round the ovary. It is as accessible only to insects with long probosces, such as bees. In these cases the posterior stamen is free, allowing See also:access to the honey. The flowers stand more or less horizontally; the large erect See also:white or coloured standard renders them conspicuous, the wings form a See also:platform on which the See also:insect rests and the keel encloses the stamens and pistil, protecting them from See also:rain and the attacks of unbidden See also:pollen-eating insects. In his See also:book on the fertilization of flowers, See also:Hermann See also:Muller distinguishes four types of papilionaceous flowers according to the way in which the pollen is applied to the See also:bee: (I) 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 I, Calyx.

3, Wing. 5, Monadelphous stamens 6, Pistil. 2, Standard. 4, Keel. and style. 7, Pod. and style are confined within the keel under tension and the pressure of the insect causes their sudden See also:

release and the scattering of the pollen, as in broom and Genista; these contain no honey but are visited for the See also:sake of the pollen. (3) The See also:piston-mechanism as in See also:bird's-See also: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 See also:shed into the See also:cone-like tip of the carina, and the heads of the five See also: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 See also:brush of hairs which sweeps small quantities of pollen out of the tip cf the carina, as in Lathyrus, Pisum, Vicia and Phaseolus. Leguminosae is a See also:cosmopolitan See also:order, and often affords a characteristic feature of the vegetation. Mimosoideae and Caesalpinioideae are richly developed in the tropical rain forests, where Papilion- atae are less conspicuous and mostly herbaceous; in sub-tropical forests arborescent forms of all three sub-orders occur. In the temperate regions, tree-forms are rare—thus Mimosoideae are unrepresented in Europe; Caes- alpinioideae are represented by species of Cercis, Gymnocladus and Gleditschia; Papi- lionatae by Robinia; but herbaceous Papilionatae abound and penetrate to the limit of growth of seed-plants in See also:arctic and high alpine regions.

Shrubs and under-shrubs, such as Ulex, Genista, Cytisus are a characteristic feature in Europe and the Mediterranean See also:

area. Acacias are an important component of the See also:evergreen See also:bush-vegetation of See also:Australia, together with genera of the tribe Podalyrieae of Papilionatae (Chorizema, Oxylobium, &c.). Astragalus, Oxytropis, Hedysarum, Onobrychis, and others are characteristic of the See also:steppe-formations of eastern Europe and western Asia. The order is a most important one economically. The seeds, which are See also:rich in See also:starch and proteids, form valuable foods, as in pea, the various beans, vetch, See also:lentil, ground-nut (Arachis) and others; seeds of Arachis and others yield See also:oils; those of Physostigma venenosum, the See also:Calabar See also:ordeal bean, contain a strong See also:poison. Many are useful See also:fodder-plants. as the clovers (Trifolium) (q.v.), Medicago (e.g. M. sativa, See also:lucerne (q.v.), or See also:alfalfa); Melilotus, Vicia, Onobrychis (0. saliva is See also:sainfoin, q.v.); species of Trifolium, See also:lupine and others are used as green manure. Many of the tropical trees afford useful See also: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 (See also: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 See also:liquorice See also:root. Well-known ornamental trees and shrubs are Cercis (C. siliquastrum is the Judas-tree), Gleditschia, Genista, Cytisus (broom), Colulea (C. arborescens is bladder-senna), Robinia and Acacia; Wistaria sinensis, a native of See also:China, is a well-known climbing See also:shrub; Phaseolus multiflorus is the scarlet runner; Lathyrus (sweet and See also:everlasting peas), Lupinus, Galega (See also:goat's-See also:rue) and others are herbaceous garden plants. Ceratonia Siliqua is the carob-tree of the Mediterranean, the pods of which (algaroba or St See also:John's See also:bread) contain a sweet juicy pulp and are largely used for feeding stock. The order is well represented in See also:Britain. Thus Genista tinctoria is dyers' greenweed, yielding a yellow dye; G. anglica is See also:needle furze; other shrubs are Ulex (U. europaeus, gorse, furze or whin, U. nanus, a See also:dwarf species) and Cytisus scoparius, broom.

Herbaceous plants are Ononis spinosa (rest-See also:

harrow), Medicago (medick), Melilotus (melilot),Trifolium (the clovers) ,Anthyllis Vulneraria (See also:kidney-vetch), Lotus corniculatus (bird's-foot trefoil), Astragalus (See also:milk-vetch), Vicia (vetch, tare) and Lathyrus.

End of Article: LEGUMINOSAE

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