Honey is secreted in the flower and pollination effected by insects. Alisma plantago has 12 nectaries. The submerged flowers of Elisma natans remain closed and are self-pollinated. Butomus has protandrous flowers. There are about 50 species, which mostly grow outside the Tropics.—Uses insignificant. The rhizome of some is farinaceous.
Order 6. Hydrocharitaceæ. This order differs chiefly from the preceding in its epigynous flowers. These are in general unisexual (diœcious), and surrounded by a 2-leaved or bipartite spathe; they are 3-merous in all whorls, but the number of whorls is generally greater than 5, sometimes even indefinite. The perianth is divided into calyx and corolla. The ovary is unilocular with parietal placentation, or more or less incompletely plurilocular. The fruit is berry-like, but usually ruptures irregularly when ripe. Embryo straight.—Most often submerged water-plants, leaves seldom floating on the surface. Axillary scales (squamulæ intravaginales).
Hydrocharis. Floating water-plants with round cordate leaves; S3, P3 (folded in the bud); ♂-flowers: 3 (-more) flowers inside each spathe; stamens 9–15, the most internal sterile. ♀-flowers solitary; three staminodes; ovary 6-locular, with many ovules attached to the septa; styles 6, short, bifid. [The petals of the ♀-flowers bear nectaries at the base. In this and the following genus the pollination is without doubt effected by insects.] H. morsus ranæ (Frog-bit) has runners; it hibernates by means of special winter-buds.—Stratiotes; floating plants with a rosette of linear, thick, stiff leaves with spiny margin, springing from a short stem, from which numerous roots descend into the mud. Inflorescence, perianth, and ovary nearly the same as in Hydrocharis, but the ♂-flower has 12 stamens in 3 whorls, of which the outer 6 are in 1 whorl (dédoublement), and inside the perianth in both flowers there are numerous (15–30) nectaries (staminodes?). S. aloides (Water-soldier); in N. Eur. only ♀-plants.—Vallisneria spiralis is a tropical or sub-tropical plant, growing gregariously on the mud in fresh water. The leaves are grass-like, and the plants diœcious; the ♂-flowers are detached from the plant, and rise to the surface of the water, where they pollinate the ♀-flowers. These are borne on long, spirally-twisted peduncles which contract after pollination, so that the ♀-flower is again drawn under the water, and the fruits ripen deeply submerged.—Elodea canadensis is also an entirely submerged plant. The leaves are arranged in whorls on a well-developed stem. Only ♀-plants in Europe (introduced about 1836 from N. Am). This plant spreads with great rapidity throughout the country, the reproduction being entirely vegetative. Hydrilla, Halophila, Thalassia, Enhalus.—In many of these genera the number of whorls in the flower is remarkably reduced; for example, in Vallisneria, in the ♂-flowers to 2: Pr 3, A (1-) 3, in the ♀ to 3: Pr 3, Staminodes 3, G 3.—About 40 species; Temp. and Trop.
Family 2. Glumifloræ.
The hypogynous flowers in the Juncaceæ are completely developed on the pentacyclic, trimerous type, with dry, scarious perianth. Even in these the interior whorl of stamens becomes suppressed, and the ovary, which in Juncus is trilocular with many ovules, becomes in Luzula almost unilocular, but still with 3 ovules. The perianth in the Cyperaceæ and Gramineæ is reduced from hairs, in the first of these, to nothing, the flowers at the same time collecting more closely on the inflorescence (spike) supported by dry bracts (chaff); the number of stamens is almost constantly 3; stigmas linear; the ovary has only 1 loculus with 1 ovule, and the fruit, which is a capsule in the Juncaceæ, becomes a nut or caryopsis.—The endosperm is large and floury, the embryo being placed at its lower extremity (Figs. [286] B, [291]).—The plants belonging to this order, with the exception of a few tropical species, are annual or perennial herbs. The stems above ground are thin, and for the most part have long internodes, with linear, parallel-veined leaves which have long sheaths, and often a ligule, i.e. a membranous projection, arising transversely from the leaf at the junction of the sheath and blade. The underground stems are short or creeping rhizomes. The flowers are small and insignificant. Wind- or self-pollination.
Order 1. Juncaceæ (Rushes). The regular, hermaphrodite, hypogynous flowers have 3 + 3 brown, dry, free perianth-leaves projecting like a star during the opening of the flower; stamens 3 + 3 (seldom 3 + 0) and 3 carpels united into one gynœceum (Fig. [283]); the ovary is 3- or 1-locular; there is as a rule 1 style, which becomes divided at the summit into 3 stigmas, often bearing branches twisted to the right (Fig. [283]). Fruit a capsule with loculicidal dehiscence. The embryo is an extremely small, ellipsoidal, cellular mass, without differentiation into the external organs.
Fig. 283.—Flower of Luzula.
Juncus (Rush) has glabrous foliage-leaves, generally cylindrical, rarely flat; the edges of the leaf-sheath are free (“open” leaf-sheaths) and cover one another. The capsule, 1- or 3-locular, with many seeds—Luzula (Wood-Rush) has flat, grass-like leaves with ciliated edges; the edges of the leaf-sheath are united (“closed” leaf-sheath). The capsule unilocular and 3-seeded.—Prionium: S. Africa; resembling a Tacona.
The interior whorl of stamens, in some species, disappears partially or entirely (J. supinus, capitatus, conglomerates, etc.)