C. Fruit a nut. Circæa (Enchanter’s Nightshade) has a 2-merous flower (S2, P2, A2 + 0 [petal-stamens are wanting], G2). The flowers are borne in racemes without bracts.—Gaura.
D. Fruit a drupe. Trapa (Horn-nut); a peculiar aquatic plant; the submerged stem has long internodes and lanceolate leaves, falling off at an early period, but at each node are found 4 long roots with thin, lateral roots (sometimes erroneously regarded as leaves) borne pinnately; the stem reaching the surface of the water, bears a rosette of rhombic foliage-leaves, with large, inflated stalks containing air, and forming the floating apparatus of the plants. In the axils of the leaves (as in Gunnera) 8 small, stipular structures are present. The flowers are solitary in the axils of the foliage-leaves (S4, P4, A4 + 0, G2), semi-epigynous. There is an 8-lobed, crenate disc on the free portion of the ovary; one ovule in each loculus. The fruit is a drupe with 4 (or 2) prominent horns (the persistent sepals), which after the pulp has decayed away bear a series of hooks turned downwards on each side, i.e. sclerenchymatous bundles which formerly lay concealed in the pulp of the sepals. The germination is peculiar: one of the cotyledons is large, and its thick extremity remains in the fruit, the other however is small and is pushed out at the apex of the fruit together with the radicle and plumule; the development of the root soon ceases, and the plumule usually grows into a stem entirely without branches, similar to the one described above, only that 1–2 precisely similar shoots arise in the axil of each cotyledon, so that each embryo produces 3–5 shoots.—Trapa, by its mode of life, its 1-seeded fruit, etc., forms a transition to Haloragidaceæ.
The large-flowered forms are adapted for insect-pollination and are often protandrous, the small-flowered ones are homogamous and may pollinate themselves. Œnothera is adapted for hawk-moths and bees.—330 species; especially in temperate climates, chiefly in the Northern Hemisphere. Epilobium, Circæa are natives of this country; Trapa is extinct in this country, it has been found in a semi-fossilized condition near Cromer and in bogs in Denmark, and existed in Sweden until a few years ago; Œnothera has been introduced from N. Am.—A number of N. Am. species are grown as ornamental plants in our gardens. The seeds of Trapa natans are edible, and used as food in China.
Order 5. Haloragidaceæ. This is a reduced form of the Œnotheraceæ, and principally differs from these in the presence of endosperm and free styles. Only 1 ovule in each loculus.—84 species distributed over the entire globe; the majority are aquatic plants. The most advanced type is Myriophyllum (Water-Milfoil), with a regular, epigynous flower (S4, P4, A4 + 4, G4), most frequently diclinous (monœcious); the fruit is a 2–4-partite schizocarp. Aquatic plants, most frequently with pectinate, pinnate leaves.—Haloragis.—Gunnera (a dozen species from the Southern Hemisphere) forms the next step in the reduction. Large, scattered, rough-haired, and softly-spined leaves, with small flowers in crowded inflorescences. The flower, when most complete, has S2, P2, A2 (petal-stamens) and G2, forming an inferior, unilocular ovary with 1 ovule. It is remarkable for the great number of stipules placed in transverse rows in the leaf-axils, for the peculiar glandular organs, and for the colonies of Nostoc, which are found embedded in the cortex as a kind of parasite.—The simplest form is Hippuris (Mare’s-tail) with an extremely small, crenate or entire calyx, without corolla, and with only one stamen and one carpel, forming an inferior, unilocular ovary with only one ovule. Fruit a drupe with thin pulp. It is an aquatic plant with creeping, sympodial rhizome, and erect unbranched shoots, bearing numerous small, verticillate leaves. The small flowers are situated singly in the leaf-axils.
Order 6. Rhizophoraceæ. Tropical trees or shrubs (50 species, the best known being Rhizophora mangle, Mangrove) which grow gregariously, especially along the banks of rivers and by sea-coasts, where the water is quiet and brackish, and where they form the so-called Mangrove-swamps. Aerial roots are formed on the stems and branches (Fig. [522] A). The seeds germinate in the fruit, which by arrest contains only one seed (Fig. [522] B), before it is detached from the tree. The radicle projects considerably from the seed, and hangs down freely in the air; when the embryo is finally detached from the mother-plant, the separation is effected by the hood-like cotyledon, which entirely envelops the plumule, becoming detached from the rest of the embryo, which falls down, while the hood-like cotyledon remains enclosed in the fruit. The embryo, after it has fallen, strikes root, and continues growing in the undisturbed mud under the trees, or perhaps it may first be drifted about by the water, being well adapted for this by its peculiar, tough nature, and large, intercellular spaces.—It may also further be remarked that the anther is divided into a number of small loculi. The leaves are stipulate. The endosperm projects from the micropyle, growing out from the base of the seed, and thus serves as an organ of suction to convey nutriment to the embryo from the mother-plant.
Order 7. Combretaceæ. Trees and shrubs, partly lianes. An inferior, unilocular ovary with few pendulous ovules. Conocarpus and Laguncularia form, in conjunction with the species of Rhizophoraceæ, the tropical Mangrove-swamps. Terminalia.—280 species; Tropics.
Fig. 522.—Rhizophora mangle with the germinating fruit (much reduced).
Order 8. Myrtaceæ (Myrtles). The plants belonging to this order are shrubs or trees, the majority being easily recognised by the vegetative characters. The leaves, for instance, are most frequently opposite, without stipules, undivided and entire, parchment-like or leathery, evergreen, aromatic, finely dotted by pellucid glands containing essential oils; the venation is penninerved with a nerve just inside and running parallel to the edge of the leaf. The flowers are regular, epigynous (Figs. [523], [524], [525]) and ☿, most frequently 4- or 5-merous in the calyx and corolla, with many stamens (by splitting, so that they are often in several distinct bundles) and an ovary with one style, formed of 2–5–many carpels; the receptacle is most frequently united for its entire length with the ovary. The fruit varies, but is most frequently a berry. The embryo is thick, often curved, with united cotyledons; no endosperm.
1. Myrteæ, Myrtle Group. Chiefly American, though some are found also in Africa and Asia. The fruit is a berry with generally 2–5 loculi in the ovary, and many ovules in each.—Myrtus; Eugenia (the petals fall off together as a hood in the Clove, E. caryophyllata, Figs. [523], [524]); Myrcia; Jambosa; Amomis; Psidium, etc.