It is represented by a tuft of hairs in Molinia, Triodia and Arundo.
| Fig. 11. Lolium perenne. A, base of lamina, B, ligule. C, sheath (× 3). Note the low ribs, and absence of hairs (glabrous). | Fig. 12. Festuca elatior, var. pratensis. A, base of lamina. B, the extremely short ligule, with pointed ears. C, sheath (× 3). | Fig. 13. Festuca ovina. A, base
of lamina. B,
ligular ears. C,
sheath (× about
4). Stebler. |
Our other ordinary grasses have a more or less well-developed membranous ligule (Fig. [8]).
The leaf-blade is long or short, broad or narrow, but always of some elongated form such as linear, linear-lanceolate or linear-acuminate, or subulate, setaceous, &c., varying as to the degree of acuteness of the apex, and the tapering of the base.
In the following native grasses the form of the lamina affords a useful character.
The base tapers to the sheath below—i.e. the leaf is more or less linear-lanceolate—in Molinia, Brachypodium, Melica, Milium, Kœleria, and the very rare Hierochloe; less distinctly so in Bromus asper and species of Hordeum. The base is rounded in Arundo. In the following cases the leaves are setaceous, due to the very narrow blade remaining permanently folded or inrolled at its edges, and usually being thickened and hardened also (Figs. 13 and 18). The habitat of these moor-and heath-grasses suggests that these are no doubt adaptations to prevent excessive evaporation by the exposure of too large a surface—e.g. various species of Aira, Festuca ovina, F. Myurus and allies, Nardus, and several other species; whereas, conversely, the thin flat leaves of shade-grasses facilitate exposure to light and transpiration. In Avena pratensis and Agrostis canina some of the leaves are involute and subulate, and the thickened leaves of Poa maritima also are turned up at the edges, and are U-shaped in cross-section.
As we shall see later the degree of inrolling of many grass leaves varies with circumstances.
In most others the blades are either flat (Figs. [8]-12), or more or less conduplicate on the mid-rib. The latter case occurs, for example, in grasses with flattened shoots, especially at the lower part of the blade—e.g. Lolium perenne, Dactylis, Glyceria, and some species of Poa, and the cross-section of the leaf below, just before it enters the sheath, is V-shaped. In Glyceria the leaf-bases may show yellow or brownish triangles.