The cat-tail (Typha) and bur-reed (Sparganium) ([Fig. 86], I, L) are common representatives of the family Typhaceæ, and the pond-weeds (Naias and Potomogeton) are common examples of the family Naiadeæ. These are aquatic plants, completely submerged (Naias), or sometimes partially floating (Potomogeton). The latter genus includes a number of species with leaves varying from linear (very narrow and pointed) to broadly oval, and are everywhere common in slow streams.
The largest members of the group are the screw-pines (Pandaneæ) and the palms (Palmæ). These are represented in the United States by only a few species of the latter family, confined to the southern and southwestern portions. The palmettoes (Sabal and Chamærops) are the best known.
Both the palms and screw-pines are often cultivated for ornament, and as is well known, in the warmer parts of the world the palms are among the most valuable of all plants. The date palm (Phœnix dactylifera) and the cocoanut (Cocos nucifera) are the best known. The apparently compound (“pinnate” or feather-shaped) leaves of many palms are not strictly compound; that is, they do not arise from the branching of an originally single leaf, but are really broad, undivided leaves, which are closely folded like a fan in the bud, and tear apart along the folds as the leaf opens.
Although these plants reach such a great size, an examination of the stem shows that it is built on much the same plan as that of the other monocotyledons; that is, the stem is composed of a mass of soft, ground tissue through which run many small isolated, fibro-vascular bundles. A good idea of this structure may be had by cutting across a corn-stalk, which is built on precisely the same pattern.
Order IV.—Glumaceæ.
The plants of this order resemble each other closely in their habit, all having long, narrow leaves with sheathing bases that surround the slender, distinctly jointed stem which frequently has a hard, polished surface. The flowers are inconspicuous, borne usually in close spikes, and destitute of a perigone or having this reduced to small scales or hairs. The flowers are usually surrounded by more or less dry leaves (glumes, paleæ) which are closely set, so as to nearly conceal the flowers. The flowers are either hermaphrodite or unisexual.
Fig. 87.—Types of Glumaceæ. A, a sedge, Carex (Cyperaceæ). ♂, the male; ♀, the female flowers, × ½. B, a single male flower, × 2. C, a female flower, × 2. D, fruiting spike of another Carex, × ½. E, a single fruit, × 1. F, the same, with the outer envelope removed, and slightly enlarged. G, section of F, × 3. em. the embryo. H, a bulrush, Scirpus (Cyperaceæ), × ½. I, a single spikelet, × 2. J, a single flower, × 3. K, a spikelet of flowers of the common orchard grass, Dactylis (Gramineæ), × 2. L, a single flower, × 2. M, the base of a leaf, showing the split sheath encircling the stem, × 1. N, section of a kernel of corn, showing the embryo (em.), × 2.
There are two well-marked families, the sedges (Cyperaceæ) and the grasses (Gramineæ). The former have solid, often triangular stems, and the sheath at the base of the leaves is not split. The commonest genera are Carex ([Fig. 87], A, G) and Cyperus, of which there are many common species, differing very little and hard to distinguish. There are several common species of Carex which blossom early in the spring, the male flowers being quite conspicuous on account of the large, yellow anthers. The female flowers are in similar spikes lower down, where the pollen readily falls upon them, and is caught by the long stigmas. In some other genera, e.g. the bulrushes (Scirpus) ([Fig. 87], H), the flowers are hermaphrodite, i.e. contain both stamens and pistils. The fruit ([Fig. 87], F) is seed-like, but really includes the wall of the ovary as well, which is grown closely to the enclosed seed. The embryo is small, surrounded by abundant endosperm ([Fig. 87], G). Very few of the sedges are of any economic importance, though one, the papyrus of Egypt, was formerly much valued for its pith, which was manufactured into paper.