Fig. 502.—Diagram of Prunus virginiana.
A. Fruit hairy: Amygdalus (A. communis, Almond-tree) has a dry pulp which is detached irregularly, when ripe, from the wrinkled, grooved, ovoid and somewhat compressed stone.—Persica (P. vulgaris, Peach-tree) differs from the Almond in having a juicy pulp, not detachable from the stone, which is deeply grooved and has pits in the grooves (Fig. [503]). (The name of the genus is derived from Persia, though it is a native of China.).—Armeniaca (A. vulgaris, Apricot) has a hairy, velvety fruit, but the stone is smooth and has two ribs along one of the edges; the pulp is juicy. (The generic name has been given on the incorrect assumption that it was a native of Armenia; its home is China.)
Fig. 503.—Fruit of the Peach. The pulp is cut through so that the stone is visible.
B. Fruit glabrous (i.e. without hairs): Prunus (Plum) has a glabrous fruit with bluish bloom; the stone is compressed, smooth or wrinkled. The flowers are borne solitarily or in couples, and open before or at the same time as the leaves; they are borne on shoots without foliage-leaves.—Cerasus (Cherry) has a glabrous, spherical fruit, without bloom, and a spherical stone. The flowers are situated in 2–many-flowered umbels or racemes, and open at the same time as the leaves or a little before them. Long-stalked flowers in umbels are found in C. avium (Wild Cherry), C. vulgaris (the cultivated Cherry, from Western Asia); racemes at the apex of leaf-bearing branches and small spherical fruits are found in C. padus (Bird Cherry), C. virginiana, C. laurocerasus (Cherry-laurel), C. mahaleb.
Pollination. Prunus spinosa (Sloe, Blackthorn) is protogynous, but the stamens are developed before the stigma withers. Honey is secreted by the receptacle. Cerasus padus (Bird-Cherry) agrees in some measure with P. spinosa. In the flowers of the Plum and Cherry the stamens and stigma are developed simultaneously and self pollination seems general; the stigma, however, overtops the inner stamens and thus promotes cross-pollination.—Distribution. 114 species in the N. Temp, zone; few in the warmer regions; the majority from W. Asia. C. vulgaris, from the regions of the Caspian; Prunus spinosa, insititia (Bullace), domestica (Plum, from the Caucasus, Persia).—Uses, principally as fruit-trees: Cherry, Plum, Apricot, etc.; “Almonds” are the seeds of Amygdalus communis (W. Mediterranean), “bitter,” “sweet,” and “shell” almonds are from different varieties, the latter being remarkable for the thin, brittle stone. In the majority of species and in almost all parts of the plant (especially the bark, seed and leaves) is found the glycoside, amygdalin, which forms prussic acid. Many form gum, and the seeds have fatty oils (“Almond oil”). Officinal: the seeds and oil of Amygdalus communis, and the fruit of the Cherry; in other countries also the leaves of C. laurocerasus.—The stems of Cerasus mahaleb are used for pipes. Ornamental Shrubs: Amygdalus nana, Cerasus laurocerasus.
Order 3. Chrysobalanaceæ. Tropical Amygdalaceæ with zygomorphic flower and gynobasic style. 200 species; especially Am. and Asia. Chrysobalanus icaco (Cocoa-plum) is cultivated on account of its fruit (Am.)
Order 4. Pomaceæ. Trees and shrubs, most frequently with simple leaves and caducous stipules. The flowers (Fig. [505]) have 5 sepals, 5 petals and generally 20 stamens (10 + 5 + 5, or 10 + 10 + 5). There are from 1–5 carpels, which unite entirely or to some extent with each other, and with the hollow, fleshy receptacle (the flower becoming epigynous), (Figs. [505], [506], [507]). The carpels are nearly always free on the ventral sutures, rarely free at the sides also. The whole outer portion of the fruit becomes fleshy, but the portions of the pericarp surrounding the loculi (endocarp) are most frequently formed of sclerenchymatous cells, and are more or less firm (the “core”). The nature of the fruit varies, according to the thickness and hardness of the endocarp, being either a “berry” or a “drupe” (see A and B). When the endocarp is thin and parchment-like, the fruit has the characteristics of a berry, each of the 5 loculi generally present containing several seeds; but when this is hard the fruit resembles a drupe, only one seed is developed in each loculus, and the number of the loculi is reduced to one or two. There are nearly always 2 ovules in the loculi of the ovary, but in Cydonia there are a large number in 2 rows. In the genera which have stones, only one seed is developed in each stone. The genera are distinguished mainly in accordance with the kind of fruit and the number of ovules and seeds.
Fig. 504.—Longitudinal and transverse section through the flowers of A, B Cotoneaster; C Cydonia; D Malus communis; E Raphiolepis; F Cydonia; G Mespilus.