Fig. 516.—Begonia rex (reduced).
Order 7. Begoniaceæ. This order principally comprises herbs or under-shrubs with succulent stems (having scattered vascular bundles in the pith); the leaves are arranged in two rows (a divergence of 1/2) and are asymmetrical, as a rule more or less obliquely cordate, or ovate with cordate base (Fig. [516]); large, caducous stipules are present. Inflorescences dichasial, or unipared scorpioid cymes; the flowers are unisexual; the first ones (the oldest) are ♂-flowers, while ♀-flowers are found especially on the younger axes. The ♂-flowers have most frequently 2 + 2 coloured perianth-leaves, and many stamens collected into a head in the centre of the flower; the ♀-flowers are epigynous with 5 coloured perianth-leaves (placed spirally with a divergence of 2/5) and a trilocular ovary, bearing 3 bifid styles and 3 wings (the wings usually of unequal size); in the inner angle of each loculus there is one large projecting placenta, or two plate-like placentæ (the bent back edges of the carpels) studded with ovules. Fruit a capsule, with many extremely small seeds.—Begonia.
420 species; almost all from the Tropics (Am., Asia).—Many species, with varieties and hybrids, are ornamental plants in houses and conservatories, chiefly on account of the form, colour and markings of their leaves; but also for their very beautiful flowers. They reproduce easily by adventitious buds from leaves and portions of leaves placed on damp soil; some have bulbils. Like the Oxalideæ they contain an acid sap.
Fig. 517.—Ecballium agreste. Diagram of a ♂-and a ♀-flower.
Order 8. Cucurbitaceæ. The flower is epigynous, and, as a rule, is also provided with a leaf-like, cup- or bell-shaped receptacle above the ovary, to which the perianth and stamens are attached; the flowers are regular, unisexual, with rudiments of the other sex, and 5-merous: sepals 5, narrow and pointed, with the median sepal posterior (Fig. [517]), petals 5, stamens 5, and carpels 3 (rarely 4–5); the corolla is gamopetalous in the majority, polypetalous in some; generally plicate-valvate in the bud. The anthers in the ♂-flowers are extrorse, and monothecious, i.e. only one half of each of the anthers of the 5 stamens is developed, the pollen-sac having frequently a peculiar [**rtilde]-shaped curve (Fig. [518] A, B); the stamens are either all united into a column (e.g. in Cucurbita), or they are united in pairs, so that only one remains free (Figs. [517] A; [518] A); in the latter case there appears to be one small stamen with a ~-shaped, curved pollen-sac and two larger ones, each with two curved pollen-sacs placed as in Fig. [517] A. The original form appears to be Fevillea with free petals and 5 free stamens. Sometimes the rudiment of a gynœceum is present. The carpels are united into an ovary with 3 (4–5) placentæ formed by their united edges. These are thick, fleshy, and bifid, bearing a number of ovules on each side (Figs. [517] B; [518] C, D); in general the placentæ are so large that they not only meet in the centre, but also fill up the ovary as far as the wall of the pericarp. The whole interior of the fruit thus becomes a juicy mass in which three lines may be seen, meeting in the centre (the boundaries of the individual placentæ), and near the circumference 6 groups of seeds (Fig. [518] D). When the carpels are equal in number to the petals they alternate with them. The style is short and thick, and generally divided into 3 (4–5) branches, with a horse-shoe shaped stigma on each branch (Fig. [518] C). The fruit is most frequently a many-seeded berry; in some it attains a considerable size and has a firm external layer (Cucurbita, Lagenaria, etc.). The embryo is straight, has no endosperm, but contains a large quantity of oil. The exceptions to the above characters will be found under the genera.
Fig. 518.—Citrullus colocynthis: A ♂-flower, cut open and spread out; B stamen; C ♀-flower in long section; h receptacle; ca calyx; D transverse section of ovary.
Exclusively herbs, generally with stiff hairs and yellow flowers. Many species are annuals, others are perennial, having tuberous roots or hypocotyls. The leaves are scattered, long-stalked, in most cases more or less heart-shaped, palminerved, palmilobed, and exstipulate; in their axils are found both flowers (singly, or in an inflorescence) and a vegetative bud, and outside the axil, on the anodic[37] side of the leaf, a simple or branched tendril, by which the plant climbs (exceptions: e.g. Ecballium).