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Fig. 11.—Nodes.
1. Glabrous node; 2. bearded node; 3. node cut longitudinally.

The nodes are in most cases very conspicuous and they are often found swollen. However, it must be remembered that the enlargement at the node is not due to the increase in size of the actual node, but due to growth in thickness of the base of the leaf-sheath. (See fig. 11-3.) Nodes may be pale or coloured, glabrous, hairy or bearded with long hairs. When the stem is erect the nodes are short and of uniform size all round. But, if the stem is bent down or tipped over by accident, the nodes begin to grow longer on the lower side until a curvature sufficient to bring the stem to the erect position is formed and then it ceases to grow.

As already noted some perennial grasses have creeping stems and stolons, while others may have rhizomes. The grass Cynodon dactylon develops several underground stolons which are covered with white scale leaves and whose terminal buds are hard and sharp so that they may be able to make their way through the soil. The rhizomes when continuous and elongated are usually sympodia formed by the lower portions of the aerial shoots. The aerial shoot comes into the air and its lower portion is continued by a branch arising from a lower leaf axil beneath the soil.

The leaf.—Leaves are two-ranked and alternate, and very often they become crowded at the lower portions of the shoots so as to form basal tufts, though they are farther apart in the upper portions of these shoots. Three distinct kinds of leaves are met with in grasses. First, we have the fully formed foliage leaves so characteristic of grasses. These are most conspicuous and are formed in large numbers.

The other two kinds of leaves are neither so conspicuous nor so numerous as the foliage leaves. At the base of shoots occur abortive leaves which are really rudimentary sheaths. These are called scales. The third kind of leaf is a modified structure called the prophyll or prophyllum. (See fig. 12.) It is the first leaf occurring in every branch on the side next to the main shoot and it is a two-keeled membranous structure resembling somewhat the palea found in the spikelets of grasses. The portion of the prophyll between the keels is concave due to the pressure of the main stem, while the sides beyond the keels bend forward clasping the stem.

Fig. 12.—Prophylla.
A. A branch with its prophyllum; 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.

Fig. 13.—Ligules of 1. Oryza sativa; 2. Panicum javanicum; 3. Andropogon Schœnanthus; 4. A. contortus.

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 Ischæmum 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.

Fig. 15.—Margins of leaves.
1 and 2. Finely serrate; 3. glandular; 4 and 5. very minutely serrate; 6. very minutely serrate and ciliate.

In grasses the leaf-blades usually grow more in length than in any other direction and there is no limit to the length they may attain. Some grasses have very short leaves, others very long ones. The leaf-blade in most grasses is more or less of some elongated form, such as linear, linear-lanceolate, lanceolate, etc. (See fig. 14.) In a few grasses the leaf-blade is ovate, but this is a rare condition. Therefore, in noting the general shape of the leaf-blade the relation of the length to the breadth, the amount of tapering towards the apex and base and the nature of the apex should be considered.

The veins in the leaf-blade can usually be seen on holding the leaf up to the light. All the veins run parallel. In most cases the midrib is prominent and in some cases there may be also a distinct keel. Amongst the veins running through the leaf-blade some are large and prominent, while others are small and not conspicuous. On account of this disparity, very often, ridges and furrows become prominent on the upper or lower, or on both the surfaces of the leaf-blades. Generally the two surfaces of the leaf-blade are distinct, and they may be glabrous or hairy. In most grasses the surfaces are rough or scabrid to the touch owing to the presence of regular rows of exceedingly fine sharp pointed minute hairs.

The apex of the blade is generally sharp and pointed, acute or acuminate, or sometimes it may be drawn to a very fine point by gradual tapering. Blunt or obtuse tips are not altogether absent, but it is not a common feature. The leaf-blades in Panicum colonum and in some species of Andropogon are rounded or obtuse at the apex.

The margins of the leaf-blade are somewhat hyaline and they may be perfectly even or cut into serrations of fine teeth in various ways. (See fig. 15.) In addition to these minute teeth, there may be long or short cilia. Sometimes