Alopecurus geniculatus.
Agrostis alba (var. stolonifera).
Hordeum pratense (slightly).
H. murinum (slightly).
Catabrosa (Fig. 4).
Cynodon (Fig. 5).

Hackel has pointed out that a distinction must be drawn between the true nodes of the culm, and the swellings Fig. 5. Cynodon Dactylon. Plant (reduced) showing creeping and stoloniferous habit, and peculiar inflorescence of digitate spikes. Parnell.often found at the base of the sheaths themselves over these: the latter are often conspicuous when the former are inconspicuous—e.g. most species of Agrostis, Avena, Festuca, &c.

The nodes are of importance in the description of a few species only—e.g. they are usually dark coloured in certain Poas such as P. compressa and P. nemoralis; they are sharply bent in Alopecurus geniculatus, and may be so in other species if “layed" by wind, rank growth, &c.

A point of considerable classificatory value is the shape of the transverse section of the shoot, which is correlated with the mode of folding up of the young leaf-blades.

In most grasses the blades are convolute—i.e. rolled up like the paper of a cigarette, one edge over the other—and the section of the shoot is round (Fig. 7). In some cases, however, the leaves are conduplicate—i.e. each half of the lamina is folded flat on the other, the upper sides being turned face to face inwards, with the mid-rib as the hinge—and in this case the shoots are more or less compressed (Fig. 6).

In these latter cases the transverse section may be elliptical—e.g. Poa pratensis and P. alpina, Briza, &c., or more flattened and linear-oblong—e.g. Glyceria fluitans—with the flattened sides straight, or the section is oval but pointed more or less at each end owing to projecting keels and leaf-edges, and the form is naviculate—e.g. Glyceria aquatica, Dactylis (Fig. 6)—or, the sides being less flattened, more or less rhomboidal as in Poa trivialis. In Melica the leaves are convolute and the shoot-section quadrangular.

Flat, and usually sharp-edged shoots.

Dactylis glomerata (Fig. 6). Poa trivialis, P. annua, P. pratensis, P. compressa, P. maritima, and P. alpina. Glyceria aquatica and G. fluitans. Avena pubescens. Lolium perenne.

Fig. 6. Dactylis glomerata. Transverse section of a leaf-shoot (× 5). A, conduplicate leaf-blade. B, sheath. Stebler.	Fig. 7. Digraphis arundinacea. Transverse section of a leaf-shoot (× 5). A, sheath. B, convolute leaves. Compare Fig. 14. Stebler.

CHAPTER II.

THE VEGETATIVE ORGANS (continued).

The leaves of all our grasses consist of the blade, which passes directly into the sheath, without any petiole or leaf-stalk (Fig. 1).

The sheath is usually obviously split, and so rolled round the internode that one edge overlaps the other, but in the following grasses the sheath is either quite entire, or only slit a short way down, the two edges being fused as it were for the greater part of its length.

Sheath more or less entire.

Glyceria aquatica and G. fluitans. Melica uniflora and M. nutans. Dactylis glomerata. Poa trivialis (Fig. 8), P. pratensis, P. alpina. Sesleria cærulea. Bromus (all the species). Briza media and B. minor.

In some cases—e.g. Arrhenatherum, Bromus asper, and Holcus lanatus—the sheath is marked with a more or less prominent ridge down its back, due to the continuation of the keel of the leaf. The sheath may also be glabrous or hairy, and grooved or not.

A few grasses are so apt to develope characteristic colours in their sheaths, especially below, that they may often be recognised in winter by this peculiarity.

Sheaths coloured.

Lolium—all red. Holcus—red with purple veins. Festuca elatior—red. Cynosurus—yellow. Alopecurus pratensis, and A. agrestis—violet-brown, &c. Festuca ovina, var. rubra—red.

Fig. 8. Poa trivialis.