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. [Illustration: 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.