Fig. 303.—Lemna: A vegetative system; B portion of a plant with flowers; one stamen and tip of the carpel project; the remaining portions being indicated by the dotted line.
Family 4. Enantioblastæ.
The flowers in this family are hypogynous and have in part the general monocotyledonous type with 5 trimerous whorls completely developed in a regular hermaphrodite flower, and in part the flowers so much reduced that the type is very difficult to trace. On the one hand the family is well developed and has capitate inflorescences (Eriocaulaceæ) and on the other hand it is distinctly reduced (Centrolepidaceceæ). This family has taken its name from the fact that the ovule is not, as in the Liliifloræ and nearly all other Monocotyledons, anatropous, but orthotropous, so that the embryo (βλάστη) becomes placed at the end of the seed opposite (ἐναντίος) to the hilum. Large, mealy endosperm.—The orders belonging to this family are by certain authors grouped with the Bromeliaceæ and Pontederiaceæ, etc., into one family, Farinoseæ, so named on account of the mealy endosperm, the distinguishing character of the Liliifloræ then being that the endosperm is fleshy and horny.
Order 1. Commelinaceæ. The complete Liliaceous structure without great reductions in the number of whorls, but with generally few ovules in each loculus of the ovary, is found in the Commelinaceæ, an almost exclusively tropical order with about 317 species; herbs, some of which are introduced into our gardens and greenhouses. The stems are nodose; the leaves often clasping; the flowers are arranged in unipared scorpioid cymes, often so that they form a zig-zag series falling in the median line of the bracts, and after flowering they bend regularly to the right or left, outwards or inwards. They are more or less zygomorphic, particularly in the stamens, which in the same flower are of different forms or partially suppressed. The outer series of the perianth is sepaloid, the inner petaloid, generally violet or blue; the filaments are sometimes clothed with hairs formed of rows of bead-like cells (well known for showing protoplasmic movements). Fruit a trilocular capsule with loculicidal dehiscence (generally few-seeded); in some a nut. The radicle is covered by an external, warty, projecting covering which is cast off on germination.—The abundant raphides lie in elongated cells whose transverse walls they perforate.—Commelina, Tradescantia, Tinantia, Cyanotis, Dichorisandra.
Order 2. Mayacaceæ. This order is closely allied to the Commelinaceæ. 7 species. American marsh- or water-plants.
In many of the following orders of this family the flowers are united into compound inflorescences, with which is accompanied a reduction in the flower.
Order 3. Xyridaceæ (50 species). Marsh-plants with radical, often equitant leaves arranged in 2 rows, and short spikes on long (twisted) stalks. The flowers, as in the Commelinaceæ, have sepals (which however are more chaffy) and petals, but the outer series of stamens is wanting. Capsule (generally many-seeded).
Order 4. Rapateaceæ. Marsh-plants with radical leaves, usually in two rows, and several spikelets on the summit of the main axis, clustered into a capitulum or unilateral spike. Each spikelet has numerous imbricate floral-leaves and one flower. 24 species. South America.
Order 5. Eriocaulaceæ. The “Compositæ among Monocotyledons,” a tropical order. The flowers are borne in a capitulum surrounded by an involucre, very similar to that of the Compositæ. The flowers are very small, unisexual, ♂ and ♀ often mixed indiscriminately in the same capitulum; they have the usual pentacyclic structure; the leaves of the inner perianth are often connate and more membranous than the outer; in some the outer series of stamens are suppressed; in each of the 3 loculi is one pendulous ovule. Capsule. The leaves are generally radical and grass-like.—335 species; Eriocaulon, Paepalanthus, etc., E. septangulare on the west coast of Scotland, and Ireland, and in North America.
Order 6. Restiaceæ. A small, especially S. African and S. Australian, xerophilous order (about 235 species), which is quite similar in habit to the Juncaceæ and Cyperaceæ. The leaves are often reduced to sheaths. The flowers are diœcious, the perianth as in Juncus, but the outer series of stamens suppressed. The ovary and fruit as in Eriocaulaceæ; the ovary, however, may be unilocular, and the fruit a nut. Restio, etc.