| 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.
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.