Grasses

(β) Leaf-blades not eared at the base.

✲ Sheaths of radical leaves veined with red-purple.

Holcus lanatus, L. (Yorkshire Fog). A useless weed, but very common in pasture and hay; forming tussocks, greyish-green, softly hairy (tomentose). Blades with roundish ridges. Ligule short and obtuse. Sheath somewhat keeled, with trace of collar ledge. It is said to have a bitter taste (Fig. 15).

Ligule pilose. Tufted hairs along the broad rounded ridges, and on the lower surface and prominent keel.

The much rarer H. mollis, L. is not so long-haired, except on the nodes, and is more creeping and slender in habit. It is a “twitch."

The Hordeums present several points of difficulty to beginners. The differences between the species are given above. H. maritimum has narrower and thicker leaves than the rest.

Bromes are most likely to be confounded with Hordeums, but they have entire sheaths and no ears (see p. 43).

For distinctions between H. murinum and Lolium see p. 49. H. sylvaticum and Bromus asper (p. 44).

✲✲ No conspicuously red-veined sheaths.

† Ligule absent, or a tuft of hairs.

Molinia cærulea, Mœnch. (Purple Molinia). Tussocks, with tough stringy roots. Leaves narrowed below, and tapering above to a long point, ridges obsolete; very thin and dry but fairly stiff, and hairy above, especially at the base. Ligule absent, or a tuft of hairs. Sheaths smooth. Moors. Useless as forage, but used locally for brooms.

Molinia is not easily confounded with any others but Anthoxanthum (see p. 57), Arrhenatherum (see p. 56) or Brachypodium.

Brachypodium sylvaticum is distinguished by habitat, its broad leaves, membranous ligule, fibrous roots, &c.

Kœleria cristata, Pers. (Crested Kœleria). Very short, perennial in dry pastures, pubescent, pale green. Leaves narrow, tapering below, soon involute, ciliated. Ridges prominent, alternately high and low. Ligule obsolete, or a mere jagged yellowish line. Useless.

Triodia decumbens, Beauv. (Decumbent Heath-grass). Low perennial. Leaves narrow, obtuse, slightly ridged, tough, at length involute, with long, soft hairs, especially below and on the edges. Sheath grooved, hairy, especially at the throat. Ligule a tuft of hairs. Section of shoot flat; leaves conduplicate. Of no known use as fodder.

The rare grasses Panicum glabrum, Gaud., P. viride, L. and P. Crus-galli, L. introduced in the S.E. counties also come here.

†† Ligule membranous.

Avena flavescens, L. (Yellow Oat-grass). Loose tufted perennial, pale green, with rounded shoots bursting the sheaths. Leaves flat, slender, soft, fine-ribbed and hairy, especially on the low ridges above. Sheath hairy, especially below, not keeled. Ligule short, obtuse, often truncate, ciliate. A valuable pasture and meadow-grass, also in water-meadows. Its roots are abundant, and it will grow well in calcareous soils (see Fig. 10).

Avena pubescens, Huds. (Downy Oat-grass). A variety of A. pratensis (see p. 47), but less densely tufted, and the leaves flat and pubescent, and especially the sheaths very pubescent. Ligule ovate-acute. Shoots flat. Dry districts, and a weed.

Avena flavescens is not easily confounded with any other grass if well grown. All the Poas otherwise like it are glabrous, and without the ridges. The same applies to A. pubescens.

Arrhenatherum is also glabrous, its leaves narrower, its ridges much flatter and broader, and its ligule is hairy outside (see p. 56).

Brachypodium sylvaticum, Beauv. (Wood False-brome). Rather slender, perennial. Leaves flat and devoid of ridges; long, very thin and dry, limp, slightly tapering below, hirsute. Sheath round, hairy. Ligule fairly long, obtuse, toothed. Copses, &c. Useless.

Brachypodium pinnatum, L. (Heath False-brome), is a species growing in the open, with narrow, firm, rigid, erect leaves, hardly hairy; with distinct ridges, and tending to roll up. Ligule fringed with hair. Open heaths. Useless.

The only grasses likely to be confounded here are the Bromes, and they have entire sheaths.

CHAPTER IV.

ANATOMY AND HISTOLOGY.

The principal anatomical features observed in the leaves of grasses—apart from finer histological details into which it is not my purpose to enter—concern the characters of the epidermis and distribution of the stomata and hairs, the arrangement of the chlorophyll-tissue, that of the mechanical tissue (sclerenchyma) and the vascular bundles to which the venation and ribbing of the leaves are due, and the presence or absence of those peculiar thin-walled cells (motor-cells) which bring about the infolding or inrolling of the lamina (see p. 25) as they lose water, and, finally, the presence or absence of conspicuous lacunæ or air-spaces so characteristic of aquatic species. Several observers have occupied themselves with these matters, and the researches of Schwendener, Duval Jouve, Pfitzer, Pée-Laby, and others have rendered it possible to group most of our grasses according to the microscopic characters of the leaves, somewhat as I have done in Chapter V.

Reference has been made to the rolling and folding of leaves, due to the thin-walled cells on the upper surfaces capable of varying in turgescence (motor-cells). These are specially adapted epidermal cells found on the upper surfaces only. In the leaves of Poa compressa, P. annua (Fig. 21), P. nemoralis, P. alpina, Catabrosa, Sesleria, &c., a row of these motor-cells, easily distinguished by their large size, thin walls and clear contents, is found on each side of the mid-rib; as they dry the leaf folds its two halves together (conduplicate), and on the re-absorption of water they flatten the two halves out again. In Dactylis these flanking rows coalesce into one over the mid-rib. In other leaves, e.g. Avena pratensis, Festuca elatior (Figs. 17, 22), Melica, Elymus (Fig. 25), &c., there are in addition to these two flanking rows, other sets of motor-cells between the other ribs, and their combined action causes the halves of the lamina to inroll, usually one-half inside the other—convolute.

Fig. 21. Transverse section of left-half of leaf of Poa annua (× about 50) showing keel below, and two flanking lines of motor-cells (slightly shaded) above the median vascular bundle of the mid-rib. Hence the leaf folds. The half lamina has six smaller vascular bundles, only the stronger one girdered. Ridges practically obsolete and subtending bands of sclerenchyma slight: hence the leaf-surfaces are parallel.

It is easy to observe leaves of such grasses as Festuca pratensis (Fig. 22), Aira cæspitosa (Fig. 23), &c., which are wide open in the dewy mornings in summer, close up as the air gets dry and hot; and any such leaf may be seen to roll up after plucking and can be reopened by moistening it.

Fig. 22. Transverse section of left-half of leaf of Festuca elatior, var. pratensis (× about 50). The ridges are well marked and flattened above. The vascular bundles of two orders are girdered below, but only slightly above. There is no keel. There are well marked motor-cells—not shown in the figure—in each groove.

The epidermis of grasses has been closely investigated by Grob, but unfortunately his results concern very few of our native species. The principal elements are ordinary elongated cells, with plane or sinuous walls, various kinds of short cells intercalated between the ends of these, several forms of papillæ, hairs, &c. and stomata.

The epidermis over the parenchyma of Digraphis arundinacea consists of rectangular cells with plane walls.

Series or bands of long cells only may alternate with other series where short cells intervene between the long ones—e.g. Nardus.

Nardus has some of the bands devoid of stomata, but abounding in short cells, whereas others (above) have stomata throughout.

In Nardus stricta, Glyceria fluitans, Sesleria, &c., there are two kinds of short cells, some siliceous, others cutinized only.

Nardus has closely appressed small 2-celled hairs bent at right-angles, and some epidermal and parenchyma cells—especially below the stomata—have solid masses of silica filling the lumina.

Fig. 23. Part of transverse section of leaf of Aira cæspitosa (× about 30). Ridges very high and acute, each tipped with sclerenchyma, and containing an isolated vascular bundle—sometimes one or more small ones also. Motor-cells well developed at the base of each groove. The bundles are not girdered, but numerous bands of sclerenchyma almost join into a continuous band below. The leaf rolls inwards.

Short cells occur in Holcus lanatus, Hierochloe borealis and Dactylis glomerata interspersed between plane-walled cells. They may be silicified and vary in shape—square, saddle-shaped, elliptical, irregular, &c.; or they may be replaced here and there by asperities—e.g. Elymus—or in rarer cases by stomata. Grob has attempted the classification of their distribution in different grasses, but the subject is too complex for treatment here.

The epidermis of many grasses is studded with short two-celled hairs bent sharply at right-angles; so that the pointed or blunt, hollow or solid, apical portion is appressed to the surface. Grob says that these are absent from the Hordeæ, whereas 90% of the Panicoideæ and many species of all other groups have them. Examples of the sharply pointed form occur in Nardus, of blunt ones in Cynodon &c.

In Nardus they occur on the leaf surface both between and above the veins, but in Hierochloe &c. they are confined to the margins.

The following grasses have no hairs of either type:

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.

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.

Each vascular bundle has its own sclerenchyma sheath, and very often the stronger veins are accentuated owing to the vascular bundle having a girder-like band of sclerenchyma running conjointly with its sheath and joining the latter above and below—or below only—to the epidermis (Figs. 24 and 25). In many cases these lower girders spread out laterally below—fan-shaped in section—and nearly join the neighbouring girders.

In other cases the strands of sclerenchymatous supporting tissue do not join the bundles, but run parallel to them, above or below, as separate strands just beneath the epidermis.

Finally, these strands may separate from the bundles, and fuse below into a continuous layer under the epidermis; this occurs especially in leaves of xerophytes where the cuticle is well developed—e.g. in varieties of Festuca ovina (Fig. 18), Aira flexuosa (Fig. 28).

The distribution of the strands of isolated sclerenchyma affords good characters. While there are none in Mibora, we find one large strand at the ridge of the keel and one at each margin, in addition to smaller ones subtending each vascular bundle, in Avena pubescens, Sesleria, Poa annua (Fig. 21), P. bulbosa, P. compressa and Dactylis glomerata. In Festuca ovina, F. rubra, F. heterophylla (Figs. 18, 27) there are groups more or less pronounced at the keel and margins, or even a continuous band below, but none above the bundles.

Many grasses have an isolated band above and below each primary bundle only—e.g. Panicum, Cynodon—or above and below each of the other bundles as well—e.g. Spartina, Arundo, Polypogon, Agrostis alba, Aira cæspitosa (Fig. 23), Holcus lanatus, Glyceria aquatica, G. fluitans, Digraphis, Elymus (Fig. 25), Agropyrum (Fig. 24), Brachypodium, Nardus (Fig. 26). In Psamma arenaria the lower bands join into a continuous layer.

In the following there is a band like a girder above and below each bundle, and contiguous with it, joining it to the epidermis above and below—Leersia, Phleum pratense, Calamagrostis Epigeios, Bromus erectus, &c.

Güntz points out that xerophilous grasses are apt to have upright, narrow (Figs. 26-28), grooved or folded leaves, with strong cuticle, and marked motor-cells when the leaves open. It is in grasses of this kind, especially such as inhabit dry sandy districts, that the subulate, solid or grooved leaves shown in Figures 18, 19 occur—e.g. Festuca ovina and its varieties, Aira flexuosa, Nardus stricta, &c. The epidermal cell-walls are sinuous, the stomata protected—e.g. on the flanks of ribs and in grooves—and waxy or hairy coverings occur. Colourless water-storing cells are apt to occur between or around the vascular bundles, and the chlorophyll-tissues tend to be dense and well protected inside the leaf: strongly developed bast-sclerenchyma is also frequent (Fig. 18).

In shade-grasses, on the other hand, and in hygrophilous species, the leaves are as a rule flat, with thin epidermal cell-walls, which have plane sides, free stomata, and no wax &c. Water-storing tissue (apart from tropical species) is sparse or absent, and the chlorophyll-tissues have well aerated lacunar spaces. Bast-sclerenchyma is in these cases feebly developed.

In the following chapter I have brought together some of the principal anatomical features, in such form that the characters can be employed in checking other determinations of grass leaves. The results, which are based on the elaborate investigations of Duval Jouve, Schroeter, Pée-Laby and Grob, as well as on my own observations, are not complete in all respects, and much more should be done to extend the theme, but the account given will serve to show the student how such results may be employed. It is as yet impossible to decide how far these characters are constant—they are known to be fairly so in many cases—but several grasses cannot yet be distinguished by them alone.

Fig. 28. Transverse section of subulate leaf of Aira flexuosa (× about 50), the upper surface represented by a mere ridge with two flanking grooves each with but traces of motor-cells below. One large vascular bundle and four much smaller ones are seen. There are no girders, but slender bands of sclerenchyma at the lower surface nearly join into a continuous sub-epidermal sheath. This type is the extreme form of that in Fig. 26.

It should also be added that some grasses develope two types of leaves (heterophylly), solid or subulate below, flat or slightly inrolled above—e.g. Festuca heterophylla—and the following arrangement is intended to apply to the vegetative lower leaves and not to those on the upper parts of the flowering specimen. Moreover the sections should be cut from the basal third of the lamina, and not from the tip of the leaf.

CHAPTER V.

GRASSES CLASSIFIED ACCORDING TO THE ANATOMICAL CHARACTERS OF THE LEAF.

I. The chlorophyll-tissue, on transverse sections, is arranged in rings round the vascular bundles. There are motor-cells between the ribs, and the stomata are sunk and occur on both faces.

Cynodon Dactylon. The larger lateral nerves have as a rule three smaller ones between each pair, hardly projecting as ribs. Chlorophyll chiefly in a ring round the vascular bundle. Long hairs on lower surface, a few papillæ above. Motor-cells in each shallow furrow. Short cells occur between the long epidermal cells over the bast-region.

The Panicums also come here, and differ according to the disposition of the sclerenchyma sheaths around the bundles.

II. The chlorophyll-tissue is between the vascular bundles, and not confined to rings surrounding them.

A. Conspicuous lacunæ between the vascular bundles. Stomata on both faces. Motor-cells occur.

Lacunæ large and rectangular. Motor-cells confined to a flanking line on each side of the mid-rib.

Glyceria aquatica. Leaves folded and in section V-shaped, hardly keeled, with sclerenchyma at apex. Motor-cells each side of the mid-rib only. The large square or rectangular lacunæ bounded by stellate cells. Papillæ on epidermal cells. Vascular bundles midway between upper and lower surfaces.

Glyceria fluitans. Section V-shaped and keeled, the roof of each polygonal lacuna arched, hence the “ribs" on the upper surface are between the vascular bundles. The latter lie nearer the lower epidermis. The epidermis has papillæ.

Catabrosa aquatica and Hierochloe also come here, the former with small lacunæ, the latter with larger ones chiefly towards the upper surface of the leaf.

Digraphis is also apt to have a few air cavities near the mid-rib.

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.

Digraphis arundinacea. No keel. Marginal sclerenchyma conspicuous. A few asperities below. Leaf thin, and all the bundles joined to the epidermis above and below by girders (Fig. 14). Stomata on both surfaces, fairly large: epidermal cells with plane walls. There may be a few irregular air cavities, especially near the mid-rib.

⊙⊙ Only the principal bundles girdered.

Arundo Phragmites. Ridges very numerous and low. No keel. Marginal sclerenchyma strong. Vascular bundles with sheaths of large colourless cells, a few of the strongest girdered below, but most have only sclerenchyma bands above and below. Motor-cells particularly large, between all the bundles. There are no conspicuous lacunæ. Hairs very rare. Epidermal cells small, with sinuous walls: all the cell-walls contain silica. Stomata on both faces, sunk, small and more difficult to see than in Digraphis, where the epidermal cells are plane walled, or nearly so.

Arundo Donax is very like A. Phragmites, but has larger bundles each with a horse-shoe shaped sclerenchymatous mass below, and larger lacunæ.

≡ ≡ Veins not more than 10-20 in each half lamina.

⊙ More or less conspicuously hairy. The smaller bundles isolated and devoid of girders.

Bromus sterilis. Girders to the stronger bundles only. Stiff hairs above and below. Motor-cells poorly developed between each pair of low ridges. No pronounced cuticle. A faint sclerenchyma-band at margin, and at apex of low rounded keel. Stomata on both faces.

Bromus arvensis. Similar to B. sterilis, with stiff hairs commoner below. Harsh in cutting.

B. giganteus shows no hairs, but I cannot distinguish the Bromes generally by the leaf anatomy.

Anthoxanthum odoratum. No keel, ridges obsolete, the stronger bundles only with girders. Motor-cells conspicuous between all the ribs. Marginal sclerenchyma, and that above and below the bundles, poorly developed. A few coarse hairs both above and below, and stomata on both faces. Leaf thin and narrow.

Hordeum murinum. Few girdered bundles, and sclerenchyma at margins poor. Hairs sparse and coarse.

Bromus asper, Brachypodium sylvaticum and Lagurus also come here.

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).

Each vascular bundle has a sheath, but is isolated. Sclerenchyma at tips of the ridges dense: smaller bands below: strong at margins. Lower cuticle strong. Leaf rolls up.

The flat upper leaves of Festuca rubra (Fig. 20) and F. heterophylla are somewhat similar in type. They have stiff hairs on the ridges.

≡ ≡ Ridges not more than 2-3 times as high as the tissue between; each furrow with motor-cells, and each vascular bundle joined to epidermis above and below by a sclerenchyma girder.

Brachypodium pinnatum. Smooth. Ridges rounded. Hairs rare. The strong sclerenchyma girders below almost continuous laterally. Epidermal cells with sinuous thick walls, and a few tooth-hairs.

Note the differences from B. sylvaticum, p. 76.

Melica nutans, M. uniflora, and Calamagrostis Epigeios also come here.

⊙⊙ Motor-cells confined to the innermost 2-4 furrows. Sclerenchyma in a continuous band just inside the thick cuticle below.

Festuca duriuscula. The ridges are only about half to one-third as high again as the thickness between, and the motor-cells in four series at the base of the three innermost ridges. Each ridge has only one isolated sheathed bundle, without girders. Stomata on the flanks of the ridges, and few in number. The sclerenchyma forms a thick band just inside the strong cuticle below. The leaf is conduplicate, not convolute.

This applies particularly to the more open leaves: the subulate leaves belong to the next type (see Fig. 27).

Aira canescens and Spartina stricta also come here.

Psamma arenaria. Inrolled. Smooth below and devoid of keel, with sub-epidermal band of sclerenchyma, and similar tissue at the margin. Ridges of three sizes, the largest twice or three times as high as the leaf-tissue between is thick, all rounded above, and very hairy. Stomata above only. Motor-cells in each sinus not large. Vascular bundles isolated, without girders or bands of sclerenchyma.

Elymus is very like Psamma, but has a few stomata below and the sub-epidermal sclerenchyma is not continuous (see Fig. 25).

✲✲ Leaves (subulate) not opening out, the upper surface represented by a groove or a few ridges above the angular or ovate solid section.

⊙ Section pentagonal or angular-ovate: sclerenchyma below in a continuous band.

Aira flexuosa. Upper surface a depression, with one ridge flanked by two grooves at its base, the depression extending about one-fifth through the whole thickness of the nearly solid leaf. Vascular bundles about 3-5, isolated, sheathed. Sclerenchyma band extending all round the lower surface just inside the thick cuticle. Stomata very few, flanking the ridge; motor-cells in the furrows, poorly developed (Fig. 28).

⊙⊙ Section elliptical or angular-ovate; sclerenchyma not always in a continuous band below.

Festuca ovina. Upper surface a deep fold, with three ridges and 2-4 grooves at its base. Vascular bundles several, with girders. Motor-cells in four series, in the grooves. The lower girders may not fuse laterally into a continuous band of sclerenchyma below (Fig. 18).

The folded lower leaves of F. rubra and F. heterophylla come here also. For the flatter leaves of F. duriuscula see p. 78 and compare Fig. 27.

The epidermal cells in this series have sinuous thickened walls, and here and there small tooth-like hairs.

Nardus also comes here (see Fig. 26).

(2) There are stomata below, but fewer than on the upper surface. Motor-cells usually conspicuous between the ridges.

✲ Stronger bundles with girders of sclerenchyma joining them to the epidermis, at least below.

⊙ Hairs sparse or none.

Cynosurus cristatus. Mid-rib obsolete, except the strong vascular bundle. Ridges low and rounded, with 2-4 flanking stomata, and well developed motor-cells in furrows. Secondary vascular bundles with strong girders below, the smaller bundles sheathed only and isolated. Each ridge with slight sclerenchyma above. A few stiff short hairs above, and the leaves are convolute. Ridges about twice the height of the leaf-thickness between (Fig. 16).

Agropyrum repens. Mid-rib and margin with strong sclerenchyma-groups: ridges unequal, low and rounded and each vascular bundle girdered. A few pointed hairs above, and motor-cells in all the grooves. A slight keel, stomata on both surfaces.

Agropyrum caninum. All the bundles have girders. Slight keel. Marginal sclerenchyma. Few, very short, hard, hooked asperities above and below. Ridges low, and motor-cells poorly developed between. Few stomata on lower surface. Very like A. repens, but the principal ridges are more prominent below and those nearer the mid-rib have asperities.

A. junceum resembles Psamma, but the ridges are much lower, and there are a few stomata on the under surface (Fig. 24).

⊙⊙ Leaf obviously hairy.

† Hairs more especially above.

Avena flavescens is very similar to Cynosurus, but is evidently hairy, and A. pratensis also comes here.

†† Hairs abundant on both surfaces.

Holcus lanatus. Very hairy above and below, and at the margins. Slight keel with sclerenchyma band: sclerenchyma at margin slight. Ridges rounded, about twice as high as thickness between. Stomata more abundant above. Cuticle very thin and leaf soft. All bundles except the mid-rib with girders. Motor-cells fairly well developed between the ridges (Fig. 15).

Kœleria cristata. Very hairy on both surfaces. Ridges irregular, the largest flat and high, the others rounded or triangular. Vascular bundles isolated, and the sclerenchyma reduced to a few cells in a single layer beneath the epidermis at the apex of each ridge and below the bundle. Motor-cells well developed in each furrow. Stomata more numerous above.

✲✲ No girders to the vascular bundles.

Lolium perenne. Ridges numerous and unequal. Vascular bundles sheathed and isolated—i.e. devoid of girders: small patches of sclerenchyma at the apex of each stronger ridge, and on the opposite side below only. No hairs.

Lolium temulentum is similar but is more apt to be convolute, whereas L. perenne is more folded.

Alopecurus pratensis. Leaf thin and somewhat like Phleum, but the ridges somewhat higher and more rounded, and only the principal bundles girdered below. Stomata on both faces.

Festuca elatior, Bromus giganteus and most species of Agrostis come near Lolium. See Figs. 17, 22.

CHAPTER VI.

GRASSES IN FLOWER.

When the flowering shoot of a grass pushes up into the light and air from the enveloping leaves, it forms a more or less branched collection of flowers known as the Inflorescence, and in all our grasses this inflorescence consists of a principal stalk, haulm or culm, on which shorter stalks—branched or not—are arranged. The mode of branching is usually such that the youngest branches are nearest the top, and the oldest nearest the bottom. It is evident at once, on comparing the Moor Mat-grass (Nardus), Vernal-grass (Anthoxanthum), Cock’s-foot (Dactylis), Meadow-grass (Poa) that considerable differences exist as to the extent of this primary branching of the inflorescence.

In Nardus (Fig. 2) we find a number of long cylindrical-tapering bud-like structures each seated on one side of the principal stem, and one over the other: in the Vernal-grass and Cock’s-foot we find tufts of such bud-like structures closely crowded round the upper end of the principal stalk, the whole forming an elongated tuft of tufts: in the Poa we find a number of radiating, slender, long branches springing from the principal stalk, and each of these ramifies again, and yet again, until each of the ultimate hair-like branches bears one of the bud-like structures. See also Catabrosa (Fig. 4).