Fig. 554.—Diagram of Petunia.
Order 1. Solanaceæ. The flower (Figs. [554], [555], [559]) is hypogynous, regular (zygomorphic in Hyoscyamus), ☿, and gamopetalous, with S5, P5 (most frequently imbricate or valvate), A5, G2, the 2 carpels being placed obliquely (Fig. [554]); the bilocular ovary has a very thick axile placenta (Figs. [554], [555] H, 557), which extends almost as far as the wall of the ovary. The fruit is a capsule or berry; the seeds are more or less reniform, and the embryo is curved (rarely straight), in a fleshy endosperm (Figs. [555] F, G; [561]).—Both arborescent and herbaceous forms are found in the order; leaves scattered without stipules, but with variously formed laminæ (always penninerved). A peculiar leaf-arrangement is found in many species, viz. the leaves are borne in pairs, a large and a smaller one together; these pairs stand in 2 rows, and the flowers are then situated between the individual leaves in each pair, apparently not in a leaf axil. The inflorescences are frequently unipared scorpioid cymes without floral-leaves.
Fig. 555.—Atropa belladonna: A is reduced.]
Zygomorphic flowers occur, and thus form a transition to the closely allied Scrophulariaceæ; the zygomorphy sometimes shows itself only in the relative length of the stamens, sometimes also in the corolla (Hyoscyamus).—Nicandra is 5-merous throughout all the whorls.—The peculiar relative leaf-arrangement in this order occurs from sympodial branching and displacement. The most simple is, e.g. Datura (Fig. [556] A); each shoot-generation in the floral parts of the plant has only 2 foliage-leaves (f1 and f2), and then terminates in a flower; the axillary buds of both the foliage-leaves are developed and form a dichasium, but since the leaves are displaced on their axillary-shoots as far, or almost as far, as the first leaf of these axillary-shoots, the flowers are borne singly on the dichasial branches, and all the branches appear to be without subtending leaves (Shoot I is white, II shaded, III white, etc., diagram A). Scopolia and others (Fig. [556] B) differ in that the lowest and smallest (f1) of the two leaves on each shoot is barren, and is therefore not displaced; but the upper one (the second bracteole, f2) is displaced as in the first instance, and consequently it assumes a position near the first leaf (the shaded leaf f2 of shoot I being placed near the white leaf f1 of shoot II, etc.,) of the next youngest shoot-generation, and hence the leaves are borne in pairs; the flower placed between the two leaves of a pair is therefore the terminal flower of the shoot to which the smaller of the two leaves belongs, and the larger leaf is the subtending leaf for the floral shoot itself.
Fig. 556.—Diagrammatic representation of the branching in Solanaceæ. The various shoot-generations are white or shaded.
Fig. 557.—Fruit of Hyoscyamus niger after removal of calyx.
