Читать книгу Grasses: A Handbook for use in the Field and Laboratory - H. Marshall Ward - Страница 4

Table of Contents

That grasses are interesting and important plants is a fact recognised by botanists all the world over, yet it would appear that people in general can hardly have appreciated either their interest or their importance seeing how few popular works have been published concerning their structure and properties.

Apart from their almost universal distribution, and quite apart from the fascinating interest attaching to those extraordinary tropical giants, the Bamboos, West Indian Sugar-cane, the huge Reed-grasses of Africa, the Pampas-grasses of South America; and from the utilitarian value of the cereals—Maize, Rice, Wheat and other corn, &c.—everyone must be struck by the significance of the enormous tracts of land covered by grasses in all parts of the world, the Prairies of North America and the Savannahs of the South, the Steppes of Russia and Siberia, and the extensive tracts of meadow and pasture-land in Europe being but a few examples.

Although in the actual number of species the Grass family is by no means the largest in the vegetable kingdom, for there are far more Composites or Orchids, the curious sign of success in the struggle for existence comes out in grasses in that the number of individuals far transcends those of any other group, and that they have taken possession of all parts of the earth’s surface. Some species are cosmopolitan—e.g. our common Reed, Arundo Phragmites; while others—e.g. several of our native species of Festuca and Poa—are equally common in both hemispheres. On the whole the Tropics afford most species and fewest individuals, and the temperate regions most individuals.

Considering their multifarious uses as fodder and food, for brewing, weaving, building and a thousand other purposes, it is perhaps not too much to say that if every other species of plant were displaced by grasses of all kinds—as many indeed gradually are—man would still be able to supply his chief needs from them.

The profound significance of the grass-carpet of the earth, however, comes out most clearly when we realise the enormous amounts of energy daily stored up in the countless myriads of green blades as they fix their carbon. By decomposing the carbon-dioxide of the air in their chlorophyll apparatus by the action of the radiant energy of the sun, they build up starches and sugars and other plant-substances, which are then consumed and turned into flesh by our cattle and sheep and other herbivorous animals, and so furnish us with food. The whole theory of agriculture turns on this pivot, and the by no means small modicum of truth in such sayings as “All flesh is grass,” and that the man who can make two blades of grass grow where one grew before deserves well of his country, obtains a larger significance when it is realised that the only real gain of wealth is that represented by the storage of energy from without which comes to us by the action of green leaves waving in the sunshine.

The true Grasses, comprising the Natural Order Graminaceæ—also written Gramineæ—are often popularly confounded with other herbs which possess narrow green ribbon-like leaves, or even with plants of very different aspects—e.g. Cotton-grass (Eriophorum) and other Sedges, and the names Rib-grass (Plantago), Knot-grass (Polygonum), Scorpion-grass (Myosotis) and Sea-grass (Zostera), as well as the general usage of the word grass to signify all kinds of leguminous and other hay-plants in agriculture, point to the wider use of the word in former times. This has been explained by the use of the words gaers, gres, gyrs, and grass in the old herbals to indicate any kind of small herbage.

In view of the importance of our British grasses in agriculture, I have here put together some results of observation and reading in the hope that they may aid students in recognising easily our ordinary agricultural and wild grasses. During several years of work in the fields, principally directed at first to the study of the parasitic fungi on grasses, and subsequently to that of the importance of grasses in forestry and agriculture, and to the variations they exhibit, the need of some guide to the identification of a grass at any time of the year, whether in flower or not, forced itself on the attention, and although a botanist naturally turns to a good Flora when he has the grass in flower, as the best and quickest way of ascertaining the species, it soon became evident that much may be done by the study of the leaves and vegetative parts of most grasses. Indeed some are recognisable at a glance by certain characters well known to continental observers: in the case of others the matter is more difficult, and perhaps with a few it is impossible to be certain of the species from such characters only.

Nevertheless, while the best means for the determination of species are always in the floral characters so well worked up in the Floras of Hooker, Bentham and others, there is unquestionably much value in the characters of the vegetative organs also, as the works of Jessen, Lund, Stebler, Vesque and others abroad, and Sinclair, Parnell, Sowerby and others in this country attest.

Almost the only plants confounded with true grasses by the ordinary observer are the sedges and a few rushes. Apart from the very different floral structures, there are two or three easily discoverable marks for distinguishing all our grasses from other plants (Fig. 1). The first is their leaves are arranged in two rows, alternately, up the stems; and the second that their stems are circular or flattened in section, or if of some other shape they are never triangular and solid1 (Figs. 6 and 7). Moreover the leaves are always of some elongated shape, and without leaf-stalks2, but pass below into a sheath, which runs some way down the stem and is nearly always perceptibly split (Figs. 8−13). Further, the stems themselves are usually terete, and distinctly hollow except at the swollen nodes, and only branch low down at the surface of the ground or below it3.

Fig. 1. A plant of Oat (Avena), an example of a typical grass, showing tufted habit and loose paniculate inflorescence (reduced). Figuier.

All our native grasses are herbaceous, and none of them attain very large dimensions. In the following lists I term those small which average about 6–18 inches in the height of the tufts, whereas those over 3 feet high may be termed large, the tufts being regarded as in flower. The sizes cannot be given very accurately, and starved specimens are frequently found dwarfed, but in most cases these averages are not far wrong for the species freely growing as ordinarily met with, and in some cases are useful. I have omitted the rare species throughout, and in the annexed lists have added the popular names.

Large Grasses.

(Over 3 feet.)

Milium effusum (Millet-grass). Digraphis arundinacea (Reed-grass). Aira cæspitosa (Tufted Hair-grass). Arrhenatherum avenaceum (False Oat). Elymus arenarius (Lyme-grass). Bromus asper (Hairy Brome). B. giganteus (Tall Brome). Festuca elatior (Meadow Fescue). F. sylvatica (Reed Fescue). Glyceria aquatica (Reed Sweet-grass). G. fluitans (Floating Sweet-grass). Arundo Phragmites (Common Reed).

Medium Grasses.

(1–3 feet.)

Phleum pratense (Timothy). Avena pratensis (Perennial Oat-grass). Anthoxanthum odoratum (Sweet Vernal). Alopecurus agrestis (Slender Foxtail). A. pratensis (Meadow Foxtail). Agrostis alba (Fiorin). Psamma arenaria (Sea Mat-grass). Avena flavescens (Yellow Oat-grass). Holcus lanatus (Yorkshire Fog). Hordeum sylvaticum (Wood Barley). H. pratense (Meadow Barley). Agropyrum repens (Couch-grass). A. caninum (Fibrous Twitch). Lolium italicum (Italian Rye-grass). Brachypodium sylvaticum (Wood False-Brome). B. pinnatum (Heath False-Brome). Bromus erectus (Upright Brome). B. sterilis (Barren Brome). B. arvensis (Field Brome). Festuca ovina (var. rubra, &c.). (Sheep’s Fescue). F. elatior (var. pratensis). Meadow Fescue. Dactylis glomerata (Cock’s-foot). Cynosurus cristatus (Crested Dog’s-tail). Poa pratensis (Meadow-grass). P. trivialis (Rough stalked Meadow-grass). P. nemoralis (Wood Poa). Molinia cærulea (Flying Bent). Melica nutans (Mountain Melick). M. uniflora (Wood Melick).

Small Grasses.

(6–18 inches.)

Phleum arenarium (Sand Cat’s-tail). Alopecurus geniculatus (Marsh Foxtail). Agrostis canina (Brown Bent). Aira flexuosa (Wavy Hair-grass). Aira canescens (Grey Hair-grass). A. præcox (Early Hair-grass). A. caryophyllea (Silvery Hair-grass). Nardus stricta (Moor Mat-grass). Hordeum murinum (Wall Barley). H. maritimum (Sea Barley). Lolium perenne (Rye-grass). L. temulentum (Darnel). Brœmus arvensis (var. mollis). (Field Brome). Festuca ovina (Sheep’s Fescue). F. Myuros (Rat’s-tail Fescue). Briza media (Quaking-grass). Poa maritima (Sea Poa). P. annua (Annual Meadow-grass). P. compressa (Flattened Meadow-grass). P. alpina (Alpine Poa). P. bulbosa (Bulbous Poa). Triodia decumbens (Heath-grass). Kœleria cristata (Crested Kœleria).

The roots of our grasses are almost always thin and fibrous and are adventitious from the nodes, frequently forming radiating crowns round the base and easily pulled up, and usually broken in the process; but in the case of a few moor grasses—especially Nardus (Fig. 2) and Molinia—the roots are so tough and thick (stringy) as to resist breakage very efficiently. In stoloniferous grasses a similar difficulty of removal may be caused in a slighter degree by the underground stems. In a few cases, e.g. Alopecurus bulbosus (Fig. 3), Poa bulbosa, Phleum pratense and P. Bœhmeri, Arrhenatherum avenaceum, and to a slighter extent in Poa alpina and one or two others, the lowermost internodes and sheaths of the stems may be swollen and stored with food-materials, and a sort of tuber or bulb results; this is especially apt to occur in dry sandy soils. In old lawns, pastures, &c., the roots of Poa annua and others may have nodules on them due to the presence of certain small Nematode worms, Heterodera.

Fig. 2. Nardus stricta. Plant showing tufted habit, and simple spikate inflorescence, with pointed spikelets all turned towards one side (secund) on the rachis (reduced). Note also the bristle-like (setaceous) leaves at length reflexed. Parnell.	Fig. 3. Alopecurus geniculatus, var. bulbosus. Plant (reduced) showing habit, bulbous shoots and cylindrical spike-like inflorescences (Foxtail type). Notice the inflated sheaths, and the “kneed" lower parts of the ascending stems. Parnell.

Grasses are annual, biennial, or perennial, and it is often of importance to know which. The point may usually be determined by examining the shoots. If all the shoots have flowering stems in them, and are evidently of the current year, the grass is an annual; but if any shoots have leaves only, it is either biennial or perennial: to determine which is not always easy, but in perennial grasses there will generally be evident remains of older leaf-bases and shoots, and if there are distinct underground stolons or creeping rhizomes as well the point may be considered decided, and the grass is perennial, as is the case with most of our important species. If all the shoots are barren, the grass is a biennial in its first year of growth: if all have flowering stems in them, but show traces of old leaf-bases of the previous year, then the grass is a biennial in its second year. The proof of biennial character is not always easy, however, and a few grasses may be either annual or biennial, or biennial or perennial, according to conditions—e.g. species of Hordeum, Bromus, &c. In the following lists I have given the duration of the principal grasses, where the character is especially important.

Annuals.

Phleum arenarium. Aira præcox. A. caryophyllea. Hordeum murinum. H. maritimum.

Lolium temulentum. Festuca Myurus. Briza minor. Poa rigida. P. annua.

Annuals

which may become biennial or perennial.

Alopecurus geniculatus. Hordeum pratense. Lolium perenne. L. italicum (may be perennial). Bromus asper (may be perennial). B. sterilis. B. arvensis (may be perennial).

Perennials.

Holcus lanatus. H. mollis. Nardus. Hordeum sylvaticum. Agropyrum. Brachypodium. Bromus erectus. B. giganteus. Festuca ovina. F. elatior. F. sylvatica. Dactylis. Cynosurus cristatus. Briza media. Milium. Anthoxanthum. Digraphis. Phleum pratense. Alopecurus pratensis. Agrostis alba. A. canina.

Psamma. Aira cæspitosa. A. flexuosa. A. canescens. Avena pratensis. A. flavescens. Arrhenatherum. Glyceria aquatica. G. fluitans. Poa maritima. P. compressa. P. pratensis. P. trivialis. P. nemoralis. P. alpina. P. bulbosa. Molinia. Melica. Triodia. Kœleria. Arundo.

Fig. 4. Catabrosa aquatica. Plant showing the creeping habit, rooting nodes, and paniculate inflorescence (reduced). Parnell.

The rhizome of a perennial grass is continued sympodially by means of buds branching from the lowermost joints of the flowering shoots, and some importance is attached to the mode of spreading of these lateral sprouting shoots. The buds always arise in the axils of the lower leaf-sheaths—i.e. they are intra-vaginal. If they remain intra-vaginal during further growth, the shoots are forced upwards and only tufts (Fig. 2) are formed, except in so far as such shoots may fall prostrate on the surface of the ground later, and throw out roots from their nodes, and so act as runners or offsets, or put out a few roots &c. as they ascend through the soil. But in many cases the buds soon burst through the leaf-sheaths, and develope as extra-vaginal shoots, and may then run horizontally as underground stolons. Only creeping grasses of these latter kinds can rapidly cover large areas4: the grasses with intra-vaginal shoots only can only make tufts or "tussocks." Several peculiarities in the habits of grasses depend on these facts. The following are the most important creeping, or stoloniferous species, contrasted with the much more common tufted and the far rarer grasses with runners above ground (Fig. 4). Some of these (Elymus, Psamma, &c.) are of great importance as sand-binders.

With intra-vaginal branches only.

Lolium—slightly stoloniferous. Festuca elatior—slightly stoloniferous. Avena flavescens—slightly stoloniferous. Phleum pratense—no stolons, but may be bulbous. Dactylis—no stolons. Festuca ovina—no stolons. Poa alpina—no stolons. Cynosurus—no stolons.

With extra-vaginal shoots.

Arrhenatherum—short stolons, sometimes bulbous. Holcus lanatus—creeping. Alopecurus pratensis—long stolons. Anthoxanthum—slightly stoloniferous. Agrostis alba (var. stolonifera)—long stolons and runners. Digraphis—long stolons. Poa pratensis—long stolons. P. trivialis—runners only. Festuca heterophylla, Lam.—a variety of F. ovina with slight stolons. F. rubra (Linn.)—a variety of F. ovina with long stolons. Bromus erectus—no stolons. B. inermis—long stolons.

Creeping below ground and truly stoloniferous.

Agropyrum. Elymus. Psamma. Poa pratensis. P. compressa. Agrostis alba (var. stolonifera). Alopecurus pratensis. Brachypodium (slightly).

Bromus erectus (slightly). Festuca ovina (var. rubra, Linn.). F. elatior (slightly). Briza (slightly). Glyceria. Poa maritima. Melica. Arundo.

Tufted Grasses.

Milium. Agrostis alba (on downs, &c.). Aira cæspitosa. A. flexuosa. A. canescens. A. præcox. A. caryophyllea. Avena pratensis (slightly creeping). Arrhenatherum. Nardus (Fig. 2). Hordeum sylvaticum. Lolium. Bromus. Festuca ovina (except some varieties).

F. sylvatica. F. Myurus. Dactylis. Cynosurus. Poa rigida. P. annua. P. trivialis. P. nemoralis. P. alpina. P. bulbosa. Molinia. Triodia. Kœleria.

Creeping above ground (with runners).

Holcus lanatus. 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.