1911 Encyclopædia Britannica/Solanaceae
SOLANACEAE, in botany, an order of Dicotyledons belonging to the sub-class Sympetalae (or Gamopetalae) and to the series Tubiflorae, containing 75 genera with about 1500 species, widely distributed through the tropics, but passing into the temperate zones. The chief centre of the order lies in Central and South America; 32 of the genera are endemic in this region. It is represented in Britain by three genera including 4 species: Hyoscyamus niger (henbane), Solanum Dulcamara (Bittersweet) and S. nigrum and Atropa Belladonna (Deadly Nightshade).
The plants are herbs, shrubs or small trees. Solanum nigrum, a common weed in waste places, is a low-growing annual herb; S. Dulcamara is an irregularly climbing herb perennial by means of a widely creeping rhizome; Atropa Belladonna is a large perennial herb. The genus Solanum, to which belong more than half the number of species in the order, contains plants of very various habits including besides herbs, shrubs and trees. The leaves are generally alternate, but in the flower-bearing parts of the stem are often in pairs, an arrangement which, like the extra-axillary position of the flowers or cymes, results from a congenital union of axes. Thus in Datura (thorn apple) (fig. 1 A), where the branching is dichasial, the leaf which originates at any given node becomes raised upon its axillary shoot as far as the next higher node, from which it appears to spring. In Atropa Belladonna (fig. 1 B) one of the branches at each node is undeveloped and there is a pair of unequal leaves; the smaller subtends the branch which has not developed, the larger has been carried up from the node below.
Fig. 1.—Diagrams illustrating branch development in Solanaceae, in A. Datura Stramonium, B. Atropa Belladonna.
I, II, III, Flowers on inflorescences of successive orders; b, bract of I; α, β, bracts of II; α′, β′, bracts of III, and so on. In A the branching is dichasial and the bracts are adnate to their axillary shoots up to the points at which the next branches arise ; thus α and β appear to arise from axis II, though in reality originating on axis I. In B the branching is. cincinnal, one of the two branches at each node is undeveloped and its, bract α, α′, α″ is smaller than the other member of the pair, β, β′, which is adnate to and apparently carried up on its axillary branch.
An interesting anatomical feature is the presence in the stem of bicollateral bundles—that is, the vascular bundles have phloem on the inside as well as on the outside of the xylem.
The hermaphrodite, generally regular, flowers have the parts in fives, 5 sepals, 5 petals, 5 stamens in alternating whorls, and two carpels, which are generally placed obliquely (see fig. 2, floral diagram). The sepals persist and often become enlarged in the fruit. The
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| Fig. 2.—Floral diagram of Solanum—the arrow indicates the oblique symmetry of the flower. | Fig. 3.—Floral diagram of Schizanthus—the arrow indicates the oblique symmetry. Two stamens only are functional. |
corolla is regular and rotate as in Solanum (fig. 2), or bell-shaped as in Atropa, or somewhat irregular as in Hyoscyamus; in the tribe Salpiglossideae, which forms a link with the closely allied order Scrophulariaceae, it is zygomorphic, forming, e.g. as in Schizanthus (fig. 3), a two-lipped flower. The stamens are inserted on the corolla tube and alternate with its lobes; in zygomorphic flowers only two or four fertile stamens are present; the bilocular anthers open by slits or pores (fig. 4). The flowers are generally conspicuous and adapted to insect pollination; honey is secreted on the disk at the base of the ovary or at the bottom of the corolla tube between the stamens. The ovary is usually bilocular, but in Capsicum becomes unilocular above, while in some cases an in-growth of a secondary septum makes it 4-celled as in Datura, or irregularly 3- to 5-celled as in Nicandra. The anatropous ovules are generally numerous on swollen axile placentas, sometimes few as in Cestrum, a large American geflus with tubular flowers, species of which are grown in Britain as greenhouse plants; the simple style bears a bilobed or sometimes capitate stigma (fig. 5). The fruit is a many-seeded berry, as in Solanum, or
Fig. 4.—Stamen of a species of Solanum, showing the divergence of the anther-lobes at the base, and the dehiscence by pores at the apex a.
6), where it opens by a transverse lid forming a pyxidium. The embryo is bent or straight and embedded in endosperm. The persistent calyx may serve to protect the fruit or aid in its distribution, as in the bladdery structure enveloping the fruit of Physalis or the prickly calyx of species of Solatium.
The order is divided into 5 tribes; the division is based on the greater or less curvature of the embryo, the number of ovary cells and the regular or zygomorphic character of the flower. The great majority of the genera belong to the tribe Solaneae, which is characterized by a 2-celled ovary. Lycium is a genus of trees or shrubs, often thorny, with a cylindrical or narrowly bell- shaped corolla and a juicy berry; L. europaeum is a straggling climber often cultivated under the name of tea-plant. For Atropa see Nightshade; A. Belladonna yields the drug atropin. For Hyoscyamus see Henbane. Physalis, with 45 species mostly in
Fig. 5.—The pistil of Tobacco (Nicotiana Tabacum), consisting of the ovary o, containing ovules, the style s, and the capitate stigma g. The pistil is placed on the receptacle r, at the extremity of the peduncle.
Fig. 6.—Seed-vessel (pyxidium) of Henbane (Hyoscyamus niger) opening by circumscissile dehiscence.
the warmer parts of North and South America, includes P. alkekengi, “winter cherry,” and P. peruviana, “Cape gooseberry.” Capsicum (q.v.) is widely cultivated forits fruit, which are the so-called chillies. Solatium contains 900 species, among which are S. tuberosum (potato; q.v.), S. Lycopersicum (tomato;q.v.), and the two British species already mentioned. For Mandragora see (Mandrake. To the tribe Datureae, characterized by a 4-celled ovary, belongs Datura; D. Stramonium (thorn apple), sometimes found as an escape in Britain, is officinal. Nicotiana, to which belong the tobacco plant (N. tabacum) and other cultivated species, and Petunia, are American genera belonging to the tribe Cestreae, in which the embryo is straight or only slightly bent, as it is also in the tribe Salpiglossideae, which is characterized by the zygomorphy of the flowers; Salpiglossis and Schizanthus are known in cultivation.