llum; B. prophyllum; C. section of the
prophyllum.]

The ordinary foliage leaves of grasses consist of the two parts, the
flat expanded upper portion called the =blade= and the lower part called
the =sheath= that encircles the stem above the node from which it
arises. The leaf-sheaths usually fit close to the stem, but they may
also be loose or even inflated. Though the leaf-sheath surrounds the
internode like a tube, it is not a closed tube. It is really a flat
structure rolled firmly round the stem with one edge overlapping the
other. In most cases it is cylindrical and it may be compressed in a few
cases. Occasionally it may have a prominent ridge or keel down its back.
The sheath may be glabrous or hairy, smooth or striate externally, and
the outer margin is often ciliate. In a few grasses the sheaths become
coloured especially below or on the side exposed to the sun.

[Illustration: Fig. 13.--Ligules of 1. Oryza sativa; 2. Panicum
javanicum; 3. Andropogon Schoenanthus; 4. A. contortus.]

[Illustration: Fig. 14.--Shapes of leaf-blades.

1, 7 and 8. Lanceolate; 3 and 6. lanceolate-linear; 2 and 5. linear; and
4. ovate.]

The =ligule= is a structure peculiar to grasses and it varies very much.
In some grasses it is a distinct membrane narrow or broad, with an even,
truncate or erose margin, or finely ciliate. Very often it is only a
line or fringe of hairs, whilst in some it may be entirely absent as in
the leaves of _Panicum colonum_. When it is a membrane it may be broad
and oblong, ovate and obtuse, or lanceolate and acute. (See fig. 13.)
The function of the ligule is probably to facilitate the shedding of
water which may run down the leaf, and thus lessen the danger of rotting
of the stem which is sure to follow, if the water were to find its way
into the interior of the sheath. Sometimes, in addition to the ligule,
other appendages may be present in grass leaves as in _Oryza sativa_.
Such outgrowths are called =auricles= or =auricular outgrowths=. (See
fig. 13.)

The leaf-blade is well developed in the foliage leaves and in most cases
it follows directly on the sheath. But in bamboos and some species of
Ischaemum there occurs a short petiole or stalk between the leaf-blade
and the sheath. The sheath corresponds morphologically to the leaf base
of a leaf of other flowering plants.

[Illustration: Fig. 15.--Margins of leaves.

1 and 2. Finely serrate; 3. glandular; 4 and 5. very minutely serrate;
6. very