In all these grasses the epidermal cells are chiefly long, rectangular or slightly hexagonal, with thin and plane walls.
⊙⊙ Hairs none or very rare on the sections.
Phleum pratense. Low rounded ribs with motor-cells between. The larger vascular bundles girdered. Stomata about equal on both faces. No hairs. No keel. Marginal sclerenchyma scanty.
Arrhenatherum avenaceum. Very rare hairs above: a few blunt asperities here and there. No keel. Ridges low. Girders to the primary bundles, but not very strong: marginal and other sclerenchyma faint, as is also the cuticle. Stomata on both faces. Motor-cells fairly developed between the ridges.
Briza media. No keel, and mere traces of marginal sclerenchyma. Ribs practically obsolete, but well developed motor-cells in furrows. Principal bundles girdered. Stomata on both sides. No hairs or thickened cuticle.
Avena fatua, Molinia and Leersia also come here.
(b) Upper and lower leaf-surfaces dissimilar, or at least not parallel, owing to the conspicuous ridges and grooves above.
(1) No stomata below.
✲ Leaves flat or nearly so, or at least exhibit a conspicuous concave upper surface.
⊙ Motor-cells between each pair of ribs: sclerenchyma not forming a continuous layer below.
≡ Ridges at least 5-6 times as high as the leaf-thickness between.
Aira cæspitosa. Ridges high, 7-10 times as high as the breadth of leaf between, triangular, each with 1-3 vascular bundles devoid of girders, with an upper isolated band of sclerenchyma at the acute tip, and another below the principal bundle. Also small bands below each group of motor-cells. Small conical asperities on the ridges and below. No mid-rib. Stomata on flanks of ridges only, and few motor-cells between (Fig. [23]).