, _F_, _H_), minute floating plants without any
differentiation of the plant body into stem and leaves. They are
globular or discoid masses of cells, most of them having roots; but
one genus (_Wolffia_) has no roots nor any trace of fibro-vascular
bundles. The flowers are reduced to a single stamen or carpel (Figs.
_E_, _G_, _H_).

The cat-tail (_Typha_) and bur-reed (_Sparganium_) (Fig. 86, _I_, _L_)
are common representatives of the family _Typhaceae_, and the
pond-weeds (_Naias_ and _Potomogeton_) are common examples of the
family _Naiadeae_. 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 (_Pandaneae_) and
the palms (_Palmae_). 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 _Chamaerops_) 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 (_Phoenix 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.--_Glumaceae_.

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 thi