Sepals, petals, and stamens often pass gradually over the one into the other, the petals becoming narrower by degrees, and bearing anthers on each side of the apex, which gradually become larger anthers in proportion to the filament, until the perfect stamen is developed. The long-stalked leaves are floating, and most frequently cordate, elliptical, leathery, with a shiny surface, sometimes (as in Victoria regia and Euryale ferox) with strongly projecting thorny ribs on the lower surface. In the intercellular passages of the leaves are some peculiar, stellate cells.
Nuphar has 5 sepals, and an hypogynous flower. The petals, which are small, have a nectary on the back; the coloured inner side of the sepals functions as petals; the ovate gynœceum is quite free.—N. luteum is a native plant (Yellow Water-Lily), with, most frequently, 13 petals and 10–16 loculi in the ovary. The rhizome is horizontal, as much as 5–6 cm. in thickness, and bears on its under surface a number of roots, which on dying-off leave deep scars; the leaves are borne in spiral lines, and the flowers are solitary in certain leaf-axils. The construction of the rhizome is very peculiar; the vascular bundles are scattered and closed as in a monocotyledonous stem.
Fig. 383.—Nymphæa: A flower in longitudinal section, the most external leaves being removed; B fruit; C seed of Nuphar (longitudinal section); the perisperm at the base, the endosperm at the top surrounding the embryo.
Nymphæa has 4 sepals, and the flower is more or less epigynous. Petals and stamens are inserted at different heights on the ovary to just beneath the stigma (Fig. [383]). Nymphæa alba (White Water-Lily). Victoria regia from the Amazon, and Euryale ferox from Asia, have entirely epigynous flowers. The shield-like leaves of Victoria are as much as 2 metres in diameter, and the edge is bent up to a height of 5–14 cm.; the flowers are 20–40 cm. in diameter, and change in twenty-four hours from white to rose-red. A development of heat, as much as 14°C. above the temperature of the air, together with a strong formation of carbonic acid, has been observed during flowering.
Pollination. Nymphæa alba and other species of the sub-genus Symphytopleura are self-pollinated; the sub-genus Leptopleura is insect-pollinated. Nuphar and Victoria can effect self-fertilisation; Euryale is self-fertilised, often in entirely closed and submerged flowers.—The dissemination of the seeds in Nuphar luteum is effected by the fruit, which rests on the water, becoming detached from its stalk, and dehiscing from the base upwards so that the seeds are set free; while in Nymphæa alba the spirally-twisted stalk draws the fruit under water, and it dehisces by its upper part being thrown off as a hood, and the seeds which are enclosed in air-tight sacs rise to the surface of the water. In this condition they are able to float and can only sink to the bottom when the air has disappeared.
53 species; in fresh water in all parts of the world, but especially in the Tropics.—The rhizomes and seeds of some may be used as food; Euryale ferox is even cultivated. Nymphæa cœrulea and Lotus were sacred among the Egyptians.
Order 3. Ceratophyllaceæ. About 3 species. Aquatic plants, submerged, rootless; leaves cartilaginous, verticillate, dissected into repeatedly dichotomous branches which are finely toothed; only one of the leaves in a whorl supports a vegetative branch. The flowers are monœcious, axillary. Inside the 6–12 perianth-leaves are situated in the ♂-flower 10–20 stamens with thick connective, and in the ♀-flower a gynœceum formed by one carpel, with one orthotropous and pendulous ovule, which has only one integument. Fruit a nut, which, in some species, bears on each side a pointed horn, and at the apex a similar one, formed by the persistent style.—The embryo has an unusually well developed plumule with several whorls of leaves. The plant is rootless throughout its whole life.—Ceratophyllum (Horn-wort).
Order 4. Annonaceæ. Sepals 3; petals 3+3 (most frequently valvate); succeeding these (as in the Ranunculaceæ) are numerous acyclic stamens and an apocarpous gynœceum; the flowers are hypogynous, regular and ☿, generally very large (2–3 cm. in diameter), and the leaves of the perianth are more or less fleshy or leathery. The majority have syncarps with berry-like fruitlets, but in Annona and some others the carpels fuse together into a large, head-like fruit—a kind of composite berry. The seeds have ruminate endosperm as in Myristica.—Trees or shrubs with alternate, simple, entire, penninerved leaves without stipules. 450 (700?) species; especially tropical. The best known are Anona cherimolia, squamosa and reticulata (all from America) cultivated on account of their large, delicious fruits. Some have acrid and aromatic properties (Xylopia, Cananga—the flowers of the latter yield Ylang-ylang); Artabotrys odoratissimus; Asimina (N. Am.).
Order 5. Magnoliaceæ. Trees or shrubs with scattered, often leathery, entire leaves, generally with stipules, which (as in Ficus) are rolled together and form a hood round the younger internodes above them, and are cast off by the unfolding of the next leaf, leaving a ring-like scar. The endosperm is not ruminate. Corolla imbricate. Fruit a syncarp.