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. Further characters of the leaves are derived from their texture, apex, margins, mid-ribs and venation, hairiness, and especially the presence and characters of the longitudinal ridges which run along the upper or lower surface in many cases. The venation is parallel from base to apex in nearly all our grasses, but such is not always the case--e.g. in the exotic _Panicum plicatum_ the mid-rib, which enters the leaf with several vascular bundles, gives off strong and weak veins below, which first diverge and then run in arches which converge upwards: this leaf is also remarkable in being _plaited_ (plicate) in vernation. In _Arundo Donax_ also the veins, though approximately parallel, do not all run to the apex of the tapering leaf; the outer ones end above in the margins and are shorter than the mid-rib. As regards _texture_, the leaves of most grasses are thin and herbaceous; but in some they are dry and harsh to the touch. They are thin and dry in _Agropyrum caninum_, _Hordeum pratense_, _H. murinum_, _Avena pratensis_, &c., very hard and leathery (_coriaceous_) in _Psamma_, _Nardus_, species of _Festuca_, _Aira_, _Agropyrum junceum_, _Elymus_, &c. In aquatic grasses like _Glyceria_, the leaf is almost spongy owing to the large air-chambers developed in the tissues. These are easily visible with a lens.