TRIBE III.—SPIRÆEÆ.
The only genera in this tribe which contain well-known plants are Spiræa and Kerria. In Spiræa the calyx is five-cleft (see a in fig. 24) and lined with the dilated receptacle, forming a shallow tube or rather cup for the reception of the carpels. There are five small roundish petals (b), and from twenty to fifty stamens (c), which project very far beyond them. In the centre are from two to five carpels (d), which are something like those of the raspberry when young, but afterwards become of the kind called follicles; each carpel contains from two to six seeds affixed to its inner suture, and they are dehiscent—that is, they open naturally at the top to discharge the seed (see e). The flowers are set very close together, and from this circumstance, combined with their small size and projecting stamens, they look like fine filigree work; hence the popular English names given to S. salicifolia or Bridewort, Queen’s needle-work, &c. The flowers of this species are in spicate racemes, but others are in corymbs, as in S. bella; or in panicles, as in S. ariæfolia.
Fig. 24.—Flower of the Spiræa.
Kerria is a genus containing only one species, the plant which was formerly called Corchorus japonica; the calyx is united at the base, but divided in the upper part into five lobes; three of them obtuse, and the other two tipped with a little point called a mucro. There are about twenty stamens about the same length as the petals arising from the calyx, and five roundish carpels containing one seed each. The leaves are simple, and the stipules awl-shaped. Till lately only a double-flowered variety was known in Britain; but about 1832, the single-flowered plant was introduced from China. Corchorus, the genus in which this plant was originally placed, is nearly allied to the lime-tree.
TRIBE IV.—AMYGDALEÆ.
This tribe is distinguished by the fruit, which is what botanists call a drupe, that is, a stone fruit. The principal genera included in this tribe are Amygdalus, the Almond; Persica, the Peach and Nectarine; Armeniaca, the Apricot; Prunus, the Plum; and Cerasus, the Cherry. All these genera contain more or less of prussic acid, which is found to exist principally in the leaves and kernels; and they all yield gum when wounded.
The flowers of the common Almond (Amygdalus communis) appear, as is well known, before the leaves, bursting from large scaly buds, which when they open throw off the brown shining bracts in which they had been enwrapped. The calyx is somewhat campanulate, with the upper part cut into five teeth or lobes, and it is lined by the dilated disk. There are five petals, and about twenty stamens, both inserted in the lining of the calyx. The anthers are innate, and they differ from most of the other plants yet described in being only one-celled. The ovary is also only one-celled, and there are generally two ovules, though the plant rarely ripens more than one seed. The leaves are simple, and they have very small stipules. When the petals drop, the ovary appears covered with a thick tough downy pericarp, within which is the hard stone or nut, the kernel or almond of which is the seed.
The Peach (Persica vulgaris) was formerly included in the same genus as the almond; and in fact there is but little botanical difference. The flowers are the same both in construction and appearance; and the leaves are simple like those of the almond, and, like them, they are conduplicate (that is, folded together at the midrib) when young. The only difference indeed is in the fruit; for, as everybody knows, the stone of the peach has not a dry tough covering, like that of the almond, but a soft and melting one full of juice, and the stone itself is of a harder consistence, and deeply furrowed, instead of being only slightly pitted. The fruit of the peach has thus a fleshy pericarp, the pulp or sarcocarp of which is eatable, and a furrowed nut or stone, inclosing the seed or kernel, which is wrapped up like that of the almond, in a thick loose skin.