_Agrostis vulgaris_, _Calamagrostis lanceolata_, _Avena pratensis_, _Arrhenatherum avenaceum_, _Dactylis glomerata_, _Briza media_, _Arundo Phragmites_, _Glyceria fluitans_. The sharp, hard prickle-hairs which give the pronounced roughness to many leaves of grasses are longer than the foregoing, and stand off more from the leaf. They occur both on the surface and at the margins, and may be isolated--e.g. _Avena pratensis_,--or mixed with the short cells--_Aira canescens_, _Elymus arenarius_. They are very abundant on _Kœleria cristata_. _Leersia oryzoides_ has asperities at the margin of the leaf with their points directed upwards on the upper part of the leaf, downwards on the basal parts, and the direction of such minute marginal asperities often affords a useful distinctive character--e.g. _Phleum_, _Arrhenatherum_. The marginal asperities in _Nardus_ are siliceous. [Illustration: Fig. 24. Transverse section of part of leaf of _Agropyrum junceum_ (× about 40) partly inrolled; showing unequal ridges. The principal vascular bundles are girdered below, the sclerenchyma joining into a strong continuous sheath. Each ridge is tipped with sclerenchyma, and each groove has motor-cells--not shown in the figure--below.] Bristles--i.e. long, sharp, stiff hairs--are not very common. They occur on _Nardus_, _Anthoxanthum Puelii_, _Panicum_, _Cynodon_. Papillæ occur on the leaves of _Glyceria_, _Nardus_, _Leersia_, &c. _Poa pratensis_ has soft hairs on the upper epidermis. The stomata of _Sesleria cærulea_ are depressed and six-celled, two guard-cells being overgrown by four accessory cells, but in most grasses they are of the ordinary type with two elongated guard-cells only. [Illustration: Fig. 25. Transverse section of part of leaf of _Elymus arenarius_, partly inrolled (× about 30), showing ridges of unequal height, of which the higher are flat above. Vascular bundles girdered, the stronger above and below. Motor-cells in each groove cause the inrolling of the lamina by their contraction.] As regards the vascular bundles constituting the venation, they are as is well known parallel from base to apex in our common grasses, with linear leaves, and are usually of four orders as regards strength. Those of the first (e.g. mid-rib) and second orders have conspicuous vessels, but those of the third and fourth orders may be practically devoid of vessels, though xylem and phloem elements are always present. Contrary to the general assumption, there are frequent though minute transverse bundles joining the parallel veins. The rule is that one vascular bundle runs up each mid-rib or ridge, but exceptions occur--e.g. in _Arundo_ several bundles run up the mid-rib, and in _Aira cæspitosa_ (Fig. 23) and others even the strong ribs may have two or three bundles.