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. 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. 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.