THE ORDER LEGUMINOSÆ: ILLUSTRATED BY THE SWEET-PEA, THE RED CLOVER, ACACIA ARMATA, THE SENSITIVE PLANT, THE BARBADOES FLOWER-FENCE, THE CAROB-TREE, THE TAMARIND, THE SENNA, THE GLEDITSCHIA, THE LOGWOOD, THE JUDAS-TREE, AND THE KENTUCKY COFFEE-TREE. This order is a very numerous one, containing above three hundred genera, and including several highly important plants, both for food and commerce. As examples of the utility of the LeguminosÆ for food, I need only mention the pea and bean, and all their numerous allies; and as examples of their importance in medicine and the arts, I may enumerate senna, liquorice, the tamarind, gum-arabic, and logwood. Among the ornamental plants belonging to this order are, the Laburnum, the Furze or Gorse, the Robinia or False Acacia, the true Acacias, the Sensitive Plant, and the Barbadoes Flower-fence. It will be seen by this enumeration, that the flowers of the LeguminosÆ differ from each other nearly as much as those of RanunculaceÆ; but when in seed, they are all easily recognised by their seed-vessels, which are always legumes, that is, bearing more or less resemblance to the pod of the common pea. To aid the memory in retaining the great number of genera included in this order, various methods have been devised of re-dividing it; and of these I shall adopt the newest, which is also the simplest, by which they are arranged in three tribes, according to their flowers. TRIBE I.—PAPILIONACEOUS FLOWERS. The flowers of this tribe are called Papilionaceous; Fig.13.—Flower, pod, and tendril, of the Sweet-pea.Fig.13.—Flower, pod, and tendril, of the Sweet-pea. because Papilio is the scientific name of a genus of butterflies, which they were supposed to resemble. The type of this tribe may be considered the flower of the sweet-pea (Lathyrus odoratus), which has a small green calyx, cut into five deep notches, but not divided into regular sepals. (See a and b in fig. 13.) The corolla is in five petals, the largest of which (c) stands erect, and is called the vexillum or standard; below this are two smaller petals (d), which are called the algÆ or wings; and below these are two petals, joined together so as to form a kind of boat (e), which are called the carina or keel, and which serve as a cradle for the stamens and pistil. There are ten stamens, nine of which have the lower half of their filaments growing together, so as to form a fleshy substance at the base, as shown in fig. 14 at f, and the other (g) is free. Fig.14.—Stamens of the Sweet-pea. Fig.14.—Stamens of the Sweet-pea. The ovary is oblong, terminating in a filiform style, with a pointed stigma, as shown at g in fig. 13; and it is one-celled and many-seeded; the seeds being what we call the peas. When the petals fall, the pod still retains the calyx (b), and the style (g); and these remain on till the seeds are ripe, when the pod divides naturally into two parts, or valves as they are called, which curl back so as to discharge the seeds. If the pod be examined before it bursts, it will be found that the valves are composed of a fleshy substance, lined with a strong membrane or skin, and that they are united by two seams, called the dorsal and ventral sutures. Along the ventral suture (h) there runs a kind of nerve, called the placenta, to which the peas are attached, each pea being furnished with a little separate stalk, called a funicle. A cook would be surprised, even in these enlightened times, to be told to take a legume of Pisum sativum, and after separating the two valves at the dorsal suture, to detach the funicles of the seeds from the placenta; yet these scientific terms would merely describe the operation of shelling the peas. It will be seen by this description that the pod of the pea differs very materially from the seed-vessels of all the other plants I have had occasion to describe; and that it thus forms a very distinctive character for the order. The other parts vary in the different genera: the calyx is sometimes tubular, and sometimes inflated; sometimes it has only four notches, or teeth as they are called, instead of five, and sometimes it has five distinct sepals divided to the base. The parts of the corolla vary also in proportion to each other, the keel in some of the Australian plants is as long as the standard; as, for example, in Kennedia MaryattÆ; and in others the wings are so small as to be scarcely visible. The stamens of many of the species are also free, that is, divided to the base; while in others they resemble those of the sweet-pea, in having nine joined together and one free; and in others the whole are joined together at the base. The pods also vary very much in size and form; being sometimes nearly round, and only one or two-seeded; and in others long, and containing many seeds, as in the common bean or pea. The seeds themselves are so different that the tribe has been divided, on account of them, into two sections: the one consisting of those plants which, like the common bean, have the seed dividing into two fleshy seed-leaves or cotyledons, when it begins to germinate; and the other, the seed-leaves of which are thin. The seeds of the papilionaceous plants which have thin cotyledons are not eatable; but those with fleshy cotyledons may be safely used as food. The fleshy cotyledons do not always rise above the ground; but they do so decidedly in the bean and the lupine; and if either of these seeds be laid in moist soil with the hilum or scar downwards, the seed, as soon as it begins to germinate, will divide into two parts (that is, into two cotyledons), which will rise above the ground, and become green like leaves; though, from still retaining their roundish form, they are easily distinguished from the true leaves, which rise in the centre. Though my readers will have no difficulty in recognising most of the LeguminosÆ which have papilionaceous flowers, there are some genera, respecting which they may be interested to learn a few particulars. Thus, the Chorozema is one of the kinds with thin cotyledons, and consequently its seeds are not eatable. The legumes of this genus are roundish, and swelled out, so as to bear but little outward resemblance to a pod. Sophora, Edwardsia, Virgilia, Podolobium, Callistachys, Brachysema, Burtonia, Dillwynia, Eutaxia, PultenÆa, Daviesia, and Mirbelia, have all thin cotyledons, and their ten stamens all separate from each other; but in Hovea, Platylobium, and BossiÆa, though the cotyledons are thin, the stamens all grow together at the base. I mention these common greenhouse shrubs, that my readers may have an opportunity of examining their botanical construction, and thus verifying their names. The common furze (Ulex europÆus), the Spanish broom (Spartium junceum), the Petty whin (Genista Anglica), the Laburnum (Cytisus Laburnum), and the common broom, all belong to this division, and consequently their seeds are not eatable; those of the Laburnum are indeed poisonous. The distinctions between Spartium, Genista, and Cytisus, are very slight, lying chiefly in the calyx; and as a proof of this the common broom, which is now called Cytisus scoparius, was formerly supposed to be a Spartium, and afterwards a Genista. The common red clover (Trifolium pratense) has its flowers in such dense heads that it is difficult at first sight to discover that they are Papilionaceous. On examination, however, it will be found that each separate flower has its standard, wings, and keel, though the wings are so large as to hide the keel, and nearly to obscure the standard. The calyx is tubular at the base, but divided above into five long, awl-shaped teeth, that stand widely apart from each other. The legume has only one or two seeds, and it is so small as generally to be hidden by the calyx. TRIBE II.—MIMOSÆ. The second division of LeguminosÆ comprises those plants which have heads of flowers Fig.15.—Flowers and sprig of Acacia armata. Fig.15.—Flowers and sprig of Acacia armata. either in spikes or balls, like those shown in fig. 15. This figure represents two heads of flowers of Acacia armata, a well-known greenhouse shrub, of their natural size; and fig. 16 shows a head of similar flowers magnified. In the lat ter, a shows the calyx, which is five-toothed, and b the petals, which are five in number and Fig.16.—Flower of Acacia magnified. Fig.16.—Flower of Acacia magnified. quite regular in shape; c are the stamens, which vary from ten to two hundred in each flower, and which are raised so high above the petals as to give a light and tuft-like appearance to the whole flower. The legumes are very large in proportion to the flower; and consequently, by a wise provision of nature, only a very few of the flowers produce seed. The valves of the legumes are not fleshy like those of the pea, but dry and hard, and when they open they do not curl back. The flowers in the different kinds of Acacia, differ in the corolla, which has sometimes only four petals, which are occasionally united at the base, and in the calyx, which is sometimes only four-cleft. The flowers also in many species are in spikes instead of balls. Fig.17.—The Bi-pinnate leaf of an Acacia. The rest of the plant of Acacia armata is very curious; what appear to be the leaves (see d in fig. 15) are, in fact, only the petioles of the leaves dilated into what are called phyllodia; the true leaves, which were of the kind called bi-pinnate, having fallen off, or never unfolded. The true leaves, however, often appear on seedling plants; and thus, when seeds are sown of several kinds of Acacia, it is sometimes difficult to recognise them till they have attained a considerable age. The stipules of the leaves, (which are to ordinary leaves what bracts are to flowers,) are in Acacia armata, converted into spines, as shown at e. In some kinds of Acacia the true leaves, with the petioles in their natural state, (see fig. 17,) are retained in the adult plants, as in Acacia dealbÀta; and in others, the bi-pinnate leaves are occasionally found attached to the phyllodia, as in A. melanoxylon. The bi-pinnate leaves are composed of from six to twenty pairs of pinnÆ, or compound leaflets (see f in fig. 17), each of which consists of from eight to forty pairs of small leaflets (g). The Gum Arabic tree, Acacia vera, has leaves with only two pairs of pinnÆ, but each has eight or ten pairs of small leaflets. The branches and spines are red, and the heads of flowers are yellow. There are above three hundred known species of Acacia. The genus Mimosa differs from Acacia in the corolla being funnel-shaped, and four or five cleft. There are seldom above fifteen stamens, which are generally on longer filaments than those of the Acacia; and the legume is compressed and jointed or articulated between the seeds, so that the part which contains one seed may be broken off, without tearing the rest. The Sensitive-plant (Mimosa pudica) is a familiar example of this genus. The cotyledons of the plants belonging to this tribe are generally leafy; and the seeds are not eatable. The plants themselves are easily recognised by their ball or tassel-shaped heads or spikes of flowers; by the small cup-shape and inconspicuous corolla of each; by the great number and length of the stamens; and by their bi-pinnate leaves, or phyllodia supplying the place of leaves—though the phyllodia are sometimes found in Australian plants with papilionaceous flowers, as, for example, in BossiÆa ensata. TRIBE III.—CÆSALPINEÆ. Fig.18.—Flower of the Barbadoes Flower-fence. Fig.18.—Flower of the Barbadoes Flower-fence. The flowers of the plants contained in this tribe have generally five regular, widely spreading petals, which are never joined together; and stamens of unequal length, which with few exceptions are also perfectly free. The petals are generally of the same size and shape; though sometimes, as in the Barbadoes Flower-fence (Poinciana, or CÆsalpinia pulcherrima), four are of the same shape, and one deformed (see fig. 18). The filaments of some of the stamens are very long and curving over, but the others are much shorter and erect; the style is long and slender, ending in a pointed stigma. The legume is flat, and it looks almost many-celled, from the seeds being divided from each other by a kind of spongy substance, frequently found in the pods of plants belonging to this division. The leaves are bi-pinnate, and the stem is spiny. The Carob-tree, or St. John’s bread (Ceratonia siliqua), agrees with the Barbadoes Flower-fence in the pulpy matter dividing the seeds, though it differs widely in its flowers, which are without petals, and do not possess any beauty. The pulp of the pods of the Carob tree is eatable; but that of Poinciana is said to be injurious. The pod of the Tamarind (Tamarindus indica) differs from the preceding species in having the pulpy matter of its pods contained between the outer and inner skin of each valve, like the fleshy substance in the pod of the pea, instead of serving as a bed for the seeds. The flowers of the tamarind have five equal petals of a brownish yellow, three of them being streaked with pink; and the anthers are nearly rose-colour. The stamens and the style both curve upwards. It is the pods prepared with sugar that form what we call Tamarinds. In Cassia lanceolata, the leaves of which furnish senna, the flowers have a bright yellow corolla of five concave petals, three of which are somewhat larger than the others. The stamens are also unequal in length; and the style curves upwards. The legume is kidney-shaped, and the cells are divided from each other by thin membraneous partitions. The Gleditschia or Honey Locusts, now so frequently planted in our shrubberies on account of the lightness and elegance of their foliage, belong to this division, and some of them, particularly the Chinese Thorny Acacia (Gleditschia horrida), are remarkable for their thorns proceeding from the trunk and large branches, as well as from the axils of the leaves. The Logwood (HÆmatoxylon Campechianum), has inconspicuous yellow flowers, the petals being very little longer than the calyx; and the legume has seldom more than two seeds. Though it is considered a tree, the stem is seldom thicker than the arm of a man, and it is generally crooked; chips of the wood are used for dyeing purple. The Judas-tree (Cercis siliquastrum) is another species belonging to this division, as, though the flowers appear of the papilionaceous kind, they are, in fact, composed of five petals, nearly equal in size, but having the wings the largest. There are ten stamens, free, and of unequal length. The legume is oblong and many-seeded; and it opens only on the dorsal suture, the other side to which the seeds are attached being slightly winged. The flowers are each on a separate flower-stalk or pedicel, but they rise from the trunk and branches in tufts or fascicles. The leaves are simple and cordate; and they do not appear till the flowers have faded. The Kentucky Coffee-tree (Gymnocladus canadensis) is the last plant belonging to this division that I shall attempt to describe. This tree is called in Canada, Chicot, or the stump-tree, from its having no visible buds, and thus appearing like a dead stump in winter. The flowers of this plant are white, and they are produced in racemes, but they bear no resemblance to the pea flowers, having rather a star-like appearance, like those of the Jasmine (see fig. 19). Fig.19.—Flowers of the Kentucky Coffee-tree. Fig.19.—Flowers of the Kentucky Coffee-tree. The calyx (a) is tubular; and the upper part or limb is divided into five parts (b), which alternate with the petals of the corolla (c). There are ten stamens, but they are completely enclosed in the tube of the calyx. The pod is very large, the valves becoming hard and bony when dry; and the seeds are like large beans, the pod being deeply indented between the seeds. The leaves are bi-pinnate, with from four to seven pairs of pinnÆ; the lower having only one small leaflet, but the rest bearing from six to eight pairs of leaflets each. This tree must not be confounded with the true Coffee-tree, which belongs to RubiaceÆ, and from which it is perfectly distinct in every respect; and it only takes its American name from its beans having been used as a substitute for coffee. The outer bark of this tree, when it becomes old, splits off in narrow strips and rolls up; and its timber, like that of the Robinia or False Acacia, having very little sap wood, is thus very strong in quite young trees, though it is of little value when the tree is full-grown.
The species contained in the first and second divisions of this order will be easily recognised by botanical students; and though those of the third division are much more difficult to find out, still there is a kind of family likeness, particularly in the leaves, which will enable the eye, with a little practice, to recognise them. The student should visit the hothouses of botanic gardens and nurseries, and should there endeavour to pick out plants belonging to this order.
|
  |
