Order 5. Gesneriaceæ. The flower in this order may be both epigynous (Gesnerieæ) and hypogynous (Cyrtandreæ), but otherwise is nearly the same as in Scrophulariaceæ, only that the ovary is unilocular, with 2 parietal, often bifid, placentæ. Of the 5 stamens the posterior is rudimentary, or (more rarely) entirely wanting, and the others are didynamous (Cyrtandreæ have often only 2 stamens); their anthers are generally glued into a quadrangular mass. The majority are herbs with juicy stems, opposite, verticillate or scattered leaves without stipules, often, like the stems, thick and juicy, soft-haired or glabrous. The corollas are often highly-coloured (scarlet, red-yellow, etc., and spotted internally), large and magnificent, so that many species are ornamental plants. Gesnerieæ (often epigynous) have endosperm; S. Am.—Cyrtandreæ, hypogynous, without endosperm; Asia, S. Africa.—Streptocarpus, neither the primary root nor primary shoot attains development; one of the cotyledons dies, while the other grows and becomes a very large foliage-leaf, from which spring adventitious roots and adventitious inflorescences.
500 species. Gloxinia, Achimenes, Gesneria, Alloplectus, Tydæa, Columnea, Nægelia, Æschynanthus, and others, especially in the forests of tropical America. Some are epiphytes on trees, others prefer the leaf-mould of the forest and crevices of cliffs. Several genera have peculiar, catkin-like, underground shoots, with scale-like compact leaves; others have tubers.
Orobanche (Broom-rape) is allied to this order as a parasitic form. It is a parasite on the roots of other plants, not like Lathræa by means of thin rootbranches with haustoria, but growing with the base of its stem in close contact with its host, and probably even often protruding a kind of thallus into it, in a manner similar to the Loranthaceæ. Its aerial shoots are not entirely destitute of chlorophyll, but are not green; they only bear scale-leaves and terminate in a raceme or spike-like inflorescence.—Some Orobanche-species are detrimental to various cultivated plants (Hemp, Lucerne, Tobacco, etc.). The flowers are strongly zygomorphic; the posterior sepal is often wanting, and the anterior are united to the two lateral ones. Ovary unilocular, as in Gesneraceæ, with 2 or 4 parietal placentæ.—The exceedingly small seeds have a very rudimentary embryo, formed of an ellipsoidal, cellular mass, without indication of cotyledons or other organs.—About 100 species; especially in the Mediterranean region.
Order 6. Bignoniaceæ. 500 species; nearly all trees and shrubs, and to a great extent lianes, climbing by tendrils (modified leaves), which are sometimes terminated by a special clasping apparatus. These lianes have, as a rule, an anomalous stem structure, the wood being either divided into four wedges at right angles to each other, separated by four grooves filled with secondary wood-parenchyma, or a greater number of wedges occur, by the cambium ceasing to form wood in several places. The leaves are most frequently opposite and compound; the flowers in the main are similar to the didynamous Scrophulariaceæ, and especially resemble those of Digitalis purpurea; they are bilabiate, large, and beautiful, campanulate or trumpet-shaped, many of the prettiest ornamental plants in the Tropics belonging to this order. The fruit is most frequently a large, woody, 2-valved, siliqua-like, septifragal capsule, whose valves separate from the flat and broad partition-wall, which bears the large, generally winged seeds: Tecoma; Bignonia.—In gardens: Catalpa syringæfolia (Trumpet-wood); Tecoma radicans (from S. Am.).—“Palisander”-wood is from Jacaranda (S. Am.).—Eccremocarpus (N. Am.) forms, by its unilocular capsule, a transition to the Gesneriaceæ (E. scaber; herbaceous).
Crescentia is allied to this order; C. cujete (Calabash) is its best known species. The fruit (unilocular with 2 parietal placentæ) is a very large, spherical or ellipsoidal berry, with a firm, finally woody outer layer. After the removal of the juicy interior, these are commonly used as drinking vessels in Tropical America.
Order 7. Pedaliaceæ. Sesamum (orientale and indicum); very important oil-plants, which from olden times have been cultivated in tropical Asia and Africa for food and as medicinal plants, and are now cultivated in America also. The seeds are used as a raw material in the manufacture of soap in Europe.—To this order also belong Martynia and Craniolaria, which have a long horned capsule and sensitive stigmas.—46 species.
Order 8. Acanthaceæ. 1,500 species; mostly erect, slender, branched herbs or shrubs, rarely arborescent, especially in S. Am. and Ind. The branches frequently have swollen nodes; the leaves are opposite, penninerved, undivided, more or less lanceolate or elliptical, and generally leave a distinct scar when they fall off. Stipules are wanting. The flowers are solitary or in dichasia, which are arranged in 4-rowed spikes or racemes, each flower with its subtending bract, which may be brightly coloured, and most frequently also with two bracteoles. With regard to the corolla (which is often labiate, in any case irregular, and frequently prettily coloured), the 2 or 4 didynamous stamens (of whose anthers one half is inserted lower than the other, or suppressed) and the gynœceum, the Acanthaceæ are true Personatæ, approaching most nearly to the Scrophulariaceæ: they differ from the other orders especially in the fruit, which is a bilocular, 2-valved, often elastically dehiscing capsule, which never has more than 2 rows, and in some only 2 seeds in each loculus, the seeds being often compressed and borne on strong, curved or hook-like funicles (retinacula) which persist after dehiscence. Embryo curved without endosperm; radicle pointed downwards.—Cleistogamic flowers are found in several species. Cystoliths are common.
The following grow wild in Europe: Acanthus (spinosus and mollis, whose pinnatifid leaves served as models for the capitals of the Corinthian columns). The posterior sepal is the largest of all the leaves of the flower, and covers the other parts like a helmet; the 2 anterior sepals are united, and the two lateral ones are small and greenish; the corolla has no upper-lip, but only a 3-lobed under-lip. The anthers are bilocular; the filaments ultimately become very firm.—Justicia, Eranthemum, Goldfussia, Thunbergia (a twiner), Ruellia, Dicliptera, etc.—Ornamental plants in conservatories.
Order 9. Plantaginaceæ (Plantains). The flowers (Figs. [570], [571]) are regular, ☿, hypogynous, with a 4-partite, persistent calyx, a gamopetalous, scarious corolla with 4 projecting lobes, 4 stamens, incurved in the bud, later on projecting considerably, about equal in length, and a bilocular ovary with one long, filamentous, undivided, feathery, papillose style (see Fig. [571]). The ovary is most frequently bilocular with 1–few ovules in each loculus. An hypogynous disc is wanting. The fruit is a pyxidium with 1–few peltate seeds attached in each loculus (Littorella is in several respects an exception). All species are herbs, the majority with leaf-rosettes near the ground, and the flowers in spikes or capitula.
The labiate-like flowers are in this case entirely concealed under a regular, apparently 4-merous exterior. The structure of the flower, however, is the same as in the Scrophulariaceæ, only the reduction, which is found in Veronica (compare Figs. [562] C, [567] with [570], [571]), is also present in this instance and the lobes are also more equally developed; the posterior petal corresponds to the bilobed upper-lip; the posterior stamen and the posterior sepal also are entirely wanting. In the development of the flower there is no trace of posterior sepal or stamen, and the posterior petal arises from one primordium, but the two anterior sepals arise before the lateral ones. The position of sepals and petals does not agree with that of a true 4-merous flower, which is represented in Fig. [361] E. The bracteoles are always suppressed in Plantago.