B. Lacunæ none, or inconspicuous, the chlorophyll-tissue filling up between the ribs.
(a) Upper and lower leaf-surfaces parallel, or nearly so, and much alike, the ridges being very low or obsolete. Stomata equal or nearly so on both surfaces.
(1) Motor-cells absent; vascular bundles feeble and very few.
Mibora verna. The small leaves are flat, or nearly so, and have three isolated and very feebly developed bundles, devoid of girders or sclerenchyma bands.
(2) Motor-cells present, vascular bundles of various orders, with sclerenchyma bands or girders.
✲ Leaf keeled, and folded—not inrolled. Motor-cells confined to the neighbourhood of the mid-rib. No hairs.
† Motor-cells conspicuous and conjoined into a band above the mid-rib.
Dactylis glomerata. Keel pronounced, with one large vascular bundle and a sclerenchyma band occupying its crest. Motor-cells forming one conjoint band along the upper course of the mid-rib only. Stomata on both faces, but no hairs or thick cuticle. Ribs low, and all bundles have feeble girders. A little sclerenchyma at the margins. A few pale cells in the chlorophyll-tissue.
†† Motor-cells inconspicuous and in two flanking lines, one on each side of the mid-rib.
Poa trivialis. Keel with sclerenchyma at its apex, and a small band of the same at the margins. Vascular bundles of three orders, isolated, without girders, but with a small band of sclerenchyma above and below. Ridges obsolete. Short hook-asperities above. No thickened cuticle.
Other species of Poa also come here: I cannot distinguish them by the leaf anatomy; but P. annua, P. compressa, P. nemoralis and
P. pratensis are devoid of the hooked asperities; P. nemoralis has a thicker lamina than the rest, and girders to the secondary bundles. P. annua agrees in the latter point.
✲✲ Leaf not keeled: rolling up. Motor-cells distributed between the ridges.
† Hairs none or rare, or at most a few asperities.
≡ Veins numerous, 30-40 on each half lamina. Motor-cells very large.
⊙ All vascular bundles with girders above and below.