CHAPTER II.. The Vegetative Organs (_continued_).

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.

At the junction of the blade with the sheath there is in most cases a delicate membranous upgrowth of the former, more or less appressed to the stem, and called the Ligule (Figs. 8-13). Its use is probably to facilitate the shedding of water which has run down the leaf; and so lessen the danger of rotting between the sheath and stem: possibly the shelves and ears commonly met with at the base of the lamina (Fig. 12) aid in the same process. This ligule may be long or short, acute or obtuse, toothed or entire, or it may be reduced to a mere line, or tuft of hairs, or even be obsolete, and is of considerable value in classification--e.g. the ligule is obsolete or wanting in Melica, Festuca ovina, F. Myurus, F. elatior, Kœleria and Panicum.

It is represented by a tuft of hairs in Molinia, Triodia and Arundo.

Our other ordinary grasses have a more or less well-developed membranous ligule (Fig. 8).

The leaf-blade is long or short, broad or narrow, but always of some elongated form such as linear, linear-lanceolate or linear-acuminate, or subulate, setaceous, &c., varying as to the degree of acuteness of the apex, and the tapering of the base.

In the following native grasses the form of the lamina affords a useful character.

The base tapers to the sheath below--i.e. the leaf is more or less linear-lanceolate--in Molinia, Brachypodium, Melica, Milium, Kœleria, and the very rare Hierochloe; less distinctly so in Bromus asper and species of Hordeum. The base is rounded in Arundo. In the following cases the leaves are setaceous, due to the very narrow blade remaining permanently folded or inrolled at its edges, and usually being thickened and hardened also (Figs. 13 and 18). The habitat of these moor-and heath-grasses suggests that these are no doubt adaptations to prevent excessive evaporation by the exposure of too large a surface--e.g. various species of Aira, Festuca ovina, F. Myurus and allies, Nardus, and several other species; whereas, conversely, the thin flat leaves of shade-grasses facilitate exposure to light and transpiration. In Avena pratensis and Agrostis canina some of the leaves are involute and subulate, and the thickened leaves of Poa maritima also are turned up at the edges, and are +U+-shaped in cross-section.

As we shall see later the degree of inrolling of many grass leaves varies with circumstances.

In most others the blades are either flat (Figs. 8-12), or more or less conduplicate on the mid-rib. The latter case occurs, for example, in grasses with flattened shoots, especially at the lower part of the blade--e.g. Lolium perenne, Dactylis, Glyceria, and some species of Poa, and the cross-section of the leaf below, just before it enters the sheath, is +V+-shaped. In Glyceria the leaf-bases may show yellow or brownish triangles.

Further characters of the leaves are derived from their texture, apex, margins, mid-ribs and venation, hairiness, and especially the presence and characters of the longitudinal ridges which run along the upper or lower surface in many cases.

The venation is parallel from base to apex in nearly all our grasses, but such is not always the case--e.g. in the exotic Panicum plicatum the mid-rib, which enters the leaf with several vascular bundles, gives off strong and weak veins below, which first diverge and then run in arches which converge upwards: this leaf is also remarkable in being plaited (plicate) in vernation. In Arundo Donax also the veins, though approximately parallel, do not all run to the apex of the tapering leaf; the outer ones end above in the margins and are shorter than the mid-rib.

As regards texture, the leaves of most grasses are thin and herbaceous; but in some they are dry and harsh to the touch. They are thin and dry in Agropyrum caninum, Hordeum pratense, H. murinum, Avena pratensis, &c., very hard and leathery (coriaceous) in Psamma, Nardus, species of Festuca, Aira, Agropyrum junceum, Elymus, &c. In aquatic grasses like Glyceria, the leaf is almost spongy owing to the large air-chambers developed in the tissues. These are easily visible with a lens.

The apex is in most cases slender and tapering--acuminate; but in some it is merely brought to a point (acute) as in Catabrosa, Glyceria and several species of Poa and Avena, &c., usually flat, but somewhat hooded or curved up in some Poas. In cases where the leaves are setaceous or subulate, the apex is like a thin tapering bristle, and even flatter leaves may be so inrolled at the tips as to have the apex prolonged into a sharp needle-like pungent or spinescent point--e.g. Hordeum pratense, Avena pratensis to a slight extent, and pronounced in Elymus, &c. In Sesleria the apex is rounded with a short, sharp, prickle-like median projection (mucronate).

The passage of blade into sheath has already been described, but the base of the blade may have its margins projecting as horizontal shelves, like a Byron collar, round the sides of the throat of the sheath, sometimes tinged with yellow or pink--e.g. Lolium, Holcus, Bromus inermis, Hordeum; the ends of these may project as auricles or ears--e.g. Festuca elatior, Elymus, Agropyrum, Anthoxanthum, Bromus asper, Hordeum, &c. In Festuca ovina the ears are short, stiff, and erect (Fig. 13).

The margin may be perfectly even, as in most grasses, or it is more or less scabrid or scaberulous, as in Aira cæspitosa, Poa maritima, Festuca elatior, Avena pratensis, Agrostis, Milium, Phleum, Briza, the minute teeth (serrulæ) pointing up or down.

The surface may be bright green, or glaucous, harsh, hairy or glabrous, and is not uncommonly also scabrid, like a file or emery-paper, and sometimes only when rubbed in one direction up or down, owing to the minute teeth being directed all one way. These teeth are developed on the ridges.

All our ordinary grass leaves are parallel-veined, and the vascular strands (the veins) can usually be seen on holding the leaf up to the light. In most cases the tissue is raised over the veins, as ridges or “ribs,” and according to the height of these ridges the thinner parts between look like deep or shallow furrows (cf. Figs. 8-16 and Chapter IV.). If the leaf is held up to the light the ridges appear dark in proportion to their opacity--i.e. height or thickness--and the furrows light in proportion to the thinness of the tissues there. If the contrast is very great, as in Aira cæspitosa (Fig. 23), the furrows seem like transparent sharp lines, and when, as in Poa, which is practically devoid of ridges, the difference of thickness is small they appear merely as fine striæ. These characters must be determined on the fresh leaves, however, because the contraction in drying draws the ridges closer together and tends to obliterate the lines.

The ridges are almost always evident--Catabrosa, Poa, and Avena furnishing the chief exceptions--and are nearly invariably on the upper surface: they are below in Melica, however; and their relative numbers, heights and breadths, section--acute, rounded, or flattened--furnish valuable characters; as also does the coexistence or absence of hairs, asperities, &c.

A very interesting anatomical adaptation is met with in the leaves of many grasses which grow in dry situations (xerophytes) such as on sandy sea-shores, exposed mountains and so forth. When the air is moist, in wet weather or in the dews, and the sun’s rays not too powerful, the leaf is spread out with its upper surface flat or nearly so, but when the scorching sun and dry air or winds prevail, the leaves fold or roll up, with the upper sides apposed or overlapping inside the hollow cylinder thus made.

In such leaves some of the upper epidermal cells, either next the mid-rib (Sesleria &c.) or between the other ribs (Festuca &c.) are large and very thin-walled, full of sap when distended, and so placed that as they lose water by evaporation they contract, and so draw together the two halves of the lamina (Sesleria) or each ribbed segment (Festuca), thus causing the infolding or inrolling (see Chapter IV). Not only from the structure and actions of these motor-cells, but also from the fact that the stomata are on the upper surfaces and thus protected, and that the lower surfaces which alone are exposed to the drought are defended by hard and impenetrable tissues, we must look upon these as adaptations to the xerophytic conditions.

Leaves prominently ridged.

Elymus. Psamma. Aira cæspitosa. Lolium. Cynosurus (Fig. 16). Agrostis. Alopecurus. Glyceria fluitans. Kœleria. Festuca elatior. Festuca Myurus (var. sciuroides). Melica has ridges on the lower surface.

Ridges are less prominent in Phleum pratense, Briza, Agropyrum, Triodia, Arrhenatherum avenaceum.

Leaves practically devoid of ridges.

Poa--all common species. Glyceria aquatica. Catabrosa aquatica. Avena pratensis.

In some grasses the tissue over the mid-rib is considerably raised and strengthened on the dorsal side of the blade as a “keel.”

Keel more or less prominent.

Arrhenatherum (sheath keeled). Poa (all except P. maritima). Dactylis. Bromus. Bromus asper (sheath keeled, often a white line). Holcus lanatus (slight and decurrent) (Fig. 15). Digraphis (Fig. 14). Glyceria.

Most grasses are glabrous, but there are a number in which hairs are nearly always a prominent feature. It must be remarked, however, that with grasses, as with other plants, the character of pubescence is apt to vary with the situation. In general it may be stated that a hairy grass tends to become more glabrous in a moist situation, and more pubescent in a dry one, but the rule is by no means absolute. In some cases,--e.g. Avena pubescens, A. flavescens, Agropyrum, the hairs are almost entirely confined to the crests of the ridges (Figs. 10, 15). The following is a list of hairy grasses.

HAIRY GRASSES.

Holcus (Fig. 15). Molinia cærulea. Brachypodium sylvaticum. Agropyrum (variable). Bromus asper. B. mollis. Hordeum. Anthoxanthum. Avena flavescens (Fig. 10). A. pubescens. Triodia. Kœleria.

To a less extent.

Festuca sciuroides (on ribs). Melica.

Grasses as a rule are devoid of strong scents or tastes, but Anthoxanthum has a faint but distinct sweet odour, especially as it dries--it is one of the grasses which give the scent to new-mown hay--and a bitter flavour, and Milium, Hierochloe and Holcus are also more or less bitter. Spartina stricta emits a strong unpleasant odour.

The habitat of grasses is of great importance as an aid to determination. No one would expect to find a sea-shore grass growing in a beech-forest, or an aquatic grass on a dry chalk-down; but they are even more true to their habitats than this, and I append the following lists of habitats of British grasses as of use in determining them, though it is not pretended that the limits are absolute.

In the following list “pasture-grass” (P) means useful for grazing, and “meadow-grass” (M) one that is especially valuable for mowing--i.e. for hay. A “weed” (W) is used in its agricultural sense for a grass not useful and not wanted on cultivated land, though often found there.

MEADOW-AND PASTURE-GRASSES.

(P and M) Dactylis glomerata (fields, &c.). (P and M) Poa trivialis (meadow and pasture). (W) Bromus arvensis (cultivated and waste places, meadow and pasture). (W) B. sterilis (ruderal). (P and M) Poa pratensis (meadow and pasture). (W) Briza media (meadow and pasture). (P) Avena pratensis (meadow and pasture, especially hilly). (P) A. pubescens (var.)--dry. (P and M) Lolium perenne (meadow, pasture and waste places). (P and M) L. italicum (valuable culture grass). (P) Cynosurus cristatus (downs). (M and P) Festuca elatior (meadow and moist pasture, banks and river-sides). (W) Agrostis alba and A. canina (pasture and waste places, wet or dry). (P and M) Alopecurus pratensis (meadow and pasture). (W) A. geniculatus (moist meadows and marshes). (P and M) Phleum pratense (meadow and pasture). (P) Arrhenatherum avenaceum (meadow, hedges and copse). (P and M) Anthoxanthum odoratum (fields generally). (W) Hordeum pratense (moist meadow and pasture). (W) Holcus lanatus and H. mollis (meadow, pasture and waste). (P and M) Avena flavescens (dry meadow and pasture). (W) Avena fatua (corn-weed). (P) Festuca ovina (light limestone pastures and chalk downs).

SHADE-GRASSES.

Found in woods, copses, &c., under shade.

Melica uniflora (woods, &c.). Bromus asper (hedges, thickets, and edges of woods). B. giganteus (hedges and woods). Aira cæspitosa (moist shade and damp hedges). Poa nemoralis (woods, shady places and damp mountain rocks). Milium effusum (moist woods, &c.). Agropyrum caninum (woods and shady places). Hordeum sylvaticum (woods and copse). Brachypodium sylvaticum (woods, hedges and thickets). Arrhenatherum avenaceum (meadows, hedges and copse). Festuca sylvatica (mountain woods).

AQUATIC AND SEMI-AQUATIC GRASSES.

Found in wet ditches, ponds, and on marshes, river-banks, &c.

Glyceria fluitans (wet ditches and slow waters). G. aquatica (wet ditches and shallow waters). Alopecurus geniculatus (moist meadow and marsh lands). Digraphis arundinacea (river-banks, marshes). Arundo Phragmites (wet ditches, marshes and shallow waters). Molinia cærulea (wet heaths and moors, woods and waste places). Triodia decumbens, Agrostis alba, Catabrosa and Calamagrostis.

MOOR-AND HEATH-GRASSES.

Downs and dry hill-pastures.

Nardus stricta (moors, heaths and hilly pastures). Aira flexuosa (heaths and hill pastures). Molinia cærulea (wet heathy moors, woods and waste places). Kœleria cristata (dry pasture). Triodia decumbens (dry heathy and hilly pastures). Festuca ovina (hilly pastures--especially dry and open--rarer in moist situations). Agrostis vulgaris and A. canina.

MARITIME OR SEASIDE GRASSES.

Poa maritima (maritime). P. distans (sandy pastures and wastes near sea). Elymus arenarius (coasts). Psamma arenaria (coasts). Poa bulbosa (waste places in S.E. of England). Agropyrum junceum (coasts). Hordeum maritimum (S. and E. coast). Phleum arenarium (coasts).

RUDERAL OR VAGABOND GRASSES.

Waste places, walls, road-sides and dry sandy situations.

Molinia cærulea (wet, heathy moors, woods and waste places). Festuca Myurus (waste places, walls, road-sides). F. ovina (hilly pastures and especially dry, rarely moist situations). Aira caryophyllea (sandy and hilly pastures). Aira præcox (sandy and hilly pastures). Poa distans (sandy wastes near the sea). P. compressa (dry, barren, waste ground). P. annua (cultivated and waste lands and fields). Agropyrum repens (fields and waste places). Hordeum murinum (waste places and road-sides). Holcus lanatus (meadow, pasture, and waste lands). H. mollis (same--rarer). Alopecurus agrestis (waste lands and roads in S. of England). Lolium perenne (meadows, pastures and waste places). L. temulentum (fields and waste places, not common). Bromus sterilis (on way-sides, &c.). B. arvensis (cultivated and waste meadows and pastures). Poa rigida (dry, rocky places).

It is also often useful to know whether a grass is rare or local, especially for the purpose we have in view, and I have therefore drawn up the following list of rare, local or introduced foreign grasses either not noticed at all, or only referred to incidentally in this work.

In many cases these introduced foreign grasses have sprung up from seeds brought over in cargoes of hay, wool, and other products and packing materials, which in part accounts for their occurrence only near certain sea-ports, manufacturing towns and so forth. Such plants are frequently termed ballast plants. Foreign plants are also introduced in seed, as mixtures or impurities, and frequently escape from corn-fields &c.

Leersia oryzoides (ditches of Hants., Sussex and Surrey). Panicum sanguinale (S. England). P. verticillatum (fields in S. and E.). P. glaucum (rarely introduced). Hierochloe borealis (Thurso only). Phleum alpinum (Highlands only). P. Bœhmeri (Eastern counties, rare). P. asperum ” ” ” Phalaris canariensis (rare weed). Alopecurus alpinus (Highlands). Mibora verna (Anglesea and Channel Islands). Lagurus ovatus (Suffolk coasts). Polypogon monspeliensis (rare, in S. England near sea). P. littoralis (salt marshes S. England). Agrostis setacea (dry heaths of S. Wales). A. Spica-venti (sandy fields of E. counties). Gastridium lendigerum (fields and waste places in S. Wales and Norfolk). Calamagrostis Epigeios (moist glades &c. in Scotland). C. lanceolata (moist shades, scattered in England). C. stricta (bogs, &c., very rare). Cynodon Dactylon (waste and cultivated lands near sea in Scotland). Spartina stricta (salt marshes S. and E. coast). Lepturus incurvatus (scattered on shores). Bromus maximus (Jersey). B. madritensis (roads and waste, Scotland and Tipperary). B. inermis (introduced from Hungary). Lolium italicum (introduced from Lombardy). Festuca uniglumis (Irish and S.E. coast). Poa procumbens (waste ground near sea). P. loliacea (sandy sea-shores). P. laxa (Ben Nevis, &c.). P. alpina (Highlands and N.). Catabrosa aquatica (shallow pools and ditches, scattered).

Finally, a few words may be said on a subject still in its infancy--that of Indicator-plants. In many cases certain plants are found so confined to certain classes of soil, that foresters and agriculturists have claimed to be able to infer from their presence the presence or absence of certain chemical or other constituents of soils: on the contrary we find other plants so universally distributed without reference to the quality of the soil, that they are not indicative. The latter are often termed ruderal or vagabonds (see p. 29). Without attempting too rigid a classification of Grasses in this connection--which would be premature in this early state of our knowledge--the following remarks are at least generally true.

A few grasses are Indicators of chalk and limestone--e.g. Briza media, Kœleria cristata, and the exotic species Stipa pennata and Melica ciliata.

The following are said to indicate a sufficiency of potassium salts,

In moister soils.

Digraphis arundinacea. Phleum pratense. Avena pubescens. Arundo Phragmites. Molinia cærulea. Glyceria fluitans.

In drier soils.

Anthoxanthum odoratum. Alopecurus pratensis. Agrostis alba. _Holcus lanatus. Arrhenatherum. Kœleria cristata. Briza media. Dactylis glomerata. Cynosurus cristatus. Poa pratensis. P. trivialis. P. compressa. Festuca elatior. Lolium perenne._

Grasses like Bromus arvensis indicate the existence of clay in the soil.

While the following are indicative of sand,

Aira caryophyllea. A. præcox. A. canescens. Festuca ovina. Bromus sterilis.

And only if the sandy soil is moist and of better quality, owing to a certain proportion of humus, the following,

Anthoxanthum odoratum. Agrostis alba. Dactylis glomerata. Arrhenatherum avenaceum. Avena pubescens. Poa pratensis.

That the soil contains considerable quantities of common salt--sodium chloride--may be inferred if the following grasses occur,

Psamma arenaria. Elymus arenarius. Hordeum maritimum. Agropyrum junceum, &c.

The existence of much humus is indicated by such shade grasses as

Melica uniflora. M. nutans. Milium effusum. Bromus giganteus. B. asper. Brachypodium sylvaticum.

Whereas soils known as “sour,” though containing much vegetable remains, may be suspected if the following grasses abound on them,

Aira cæspitosa. Nardus stricta. Alopecurus geniculatus. Molinia cærulea;

especially if sedges and rushes coexist with them.

When cuttings are made in forests, such grasses as the following are very apt to appear, and may do harm to young plants,

Festuca ovina and varieties. Agrostis alba. Holcus mollis. Aira flexuosa, &c.

The grasses more especially indicative of particular classes of forest-soils are chiefly the wood-species (see p. 28), and need not be further specified. In gaps, borders, and copses--half-shade--we find several common grasses--e.g.

Anthoxanthum odoratum. Agrostis alba. Aira flexuosa. Holcus lanatus. Arrhenatherum avenaceum. Triodia decumbens. Dactylis glomerata. Festuca rubra. Brachypodium pinnatum. Hordeum sylvaticum.

Whereas

Poa nemoralis, Festuca sylvatica, Agropyrum caninum, Melica, Milium, Bromus asper, B. giganteus, Brachypodium sylvaticum,

are more likely to be met with in the deep shade inside the forest.

On the other hand there are vagabond grasses which seem to show no signs of preference for one soil over another--e.g. Poa annua--though in some cases these ruderal plants indicate the presence of rotting substances, on ash-heaps and rubbish of various kinds.

With reference to the above, however, the student must not forget that very complex relations are concerned in changes of soil, shade, moisture, elevation, &c. and that although experienced observers can draw conclusions of some value from the presence of numerous species and individuals on a given soil, no one must conclude too readily that a soil is so and so, from observing solely that a particular kind of grass will grow there.

An excellent example of what may be done by applying such knowledge as exists of the habits of grasses, is afforded by the historic case of the planting up of shifting sand-dunes with species like Psamma arenaria, Elymus arenarius, Agropyrum junceum, &c. (together with sand-binding species of sedges) and so not only fixing the sand, but preparing it for gradual afforestation with bushes and eventually trees, and so saving enormous tracts of land and sums of money, as has been done on the West coasts of France.

Moreover, the action of ruderal plants--including grasses--is to completely alter the nature of the poor soil and gradually fit it for other plants. Coverings of grass greatly affect the actions of heat and sunshine on the surface soil, and modify the effects of radiation and evaporation, to say nothing of the penetrating and other effects of the roots.

Rhizomes and stolons break up stiff soils; and every engineer and forester knows how useful certain grasses are in keeping the surface-soil from being washed down by heavy rains on steep hill-sides or embankments.

On the other hand, luxuriant growths of tall grasses may do harm to young plants, by their action as weeds and especially as shade-plants; though foresters can employ them in the latter capacity, under restrictions, to shelter young trees from the sun. Again, too much dry grass near a forest offers dangers from fire; and it is a well known fact that certain injurious animals, e.g. mice and other vermin, are favoured by a covering of grass.

Graminaceæ are for the most part chalk-fleeing plants, in spite of the fact that certain species can grow in very thin layers of soil on chalk downs. They must be regarded as requiring moderate supplies of humus as a rule, and even sand-loving grasses are not real exceptions.

The physiognomy of the grasses has always been regarded as a striking one, and Humboldt classed it as one of his 19 types of vegetation. As is well known they are sociable plants, often covering enormous areas--prairies, alps, steppes, &c.--with a few species, alone or densely scattered throughout a mixed herbage. They also represent characteristically the sun-plants, the erect leaves exposing their surfaces obliquely to the solar rays, and being often folded and nearly always narrow.

The dead remains of these sociable grasses are an important factor in protecting the soil against drought and in facilitating humification, as well as in covering up plants during long winters or dry seasons, keeping the ground warmer and moister, and generally lessening the effect of extremes.

Many Graminaceæ are pronounced xerophytes, the epidermis often being developed as a water-storing tissue, while the erect leaves roll themselves in intense light, the stomata being situated accordingly. The halophytic strand-plants Psamma arenaria, Elymus arenarius, Agropyrum junceum, and other Dune-species, as well as species of Aira, Festuca, Anthoxanthum, Stipa, Lygeum, Aristida, &c. are examples. The heath-grasses--e.g. Festuca ovina, Nardus stricta, Molinia cærulea--also come under this category.

Many of the strand-plants (halophytes) Agropyrum, Psamma, Elymus, are covered with waxy bloom, and have long rhizomes which bind the sand and form new soil, a property largely taken advantage of in certain forest operations.

Other grasses, particularly annual species, show their adaptation to xerophytic habits by forming bulbous store-houses at the base of the culms--e.g. Phleum arenarium.

Some Graminaceæ are hydrophytes, such as Arundo, Glyceria, &c., with large intercellular spaces in their tissues; while many species--e.g. Aira cæspitosa, Agrostis canina, Molinia cærulea--grow on wet moor-lands, forming perennial tufts, with or without creeping rhizomes.

The mesophyte grasses are especially characteristic of what may be termed carpets--a lawn is a good example on a small scale, though of course we must remember that here the struggle for existence has been artificially interfered with more or less. Such carpets consist of the densely interwoven rootlets and rhizomes forming sod, and contain much humus from the accumulated débris of former years. These grass-carpets may be composed of nearly pure growths of a few species, or of very many different grasses and other herbage. They are common in Arctic regions, on Alps, and in temperate climates generally, where we know them as meadows, hay-fields, pasture and lawns.

The Bamboos in the wider sense have a physiognomy of their own, e.g. in India, and may drive out most other plants and form dense undergrowths or jungle of interlaced stems and leaves and thorny shoots. Similar growths occur on the Andes and elsewhere in South America. In some parts of India and tropical Asia the taller bamboos form aggregates comparable to dense forests, and such forests are common on the banks of several large tropical rivers. Most of these Bamboos are xerophytes. Bamboos are neither confined to the tropics, nor to warmer regions, however, for species are known from distinctly cool regions--e.g. South America--or even from near the snow line--e.g. Chili, the Himalayas, Japan, &c., and the number of species known as hardy is increasing annually, as is evident on examining our larger English gardens.

The permanence and character of extensive grasslands, especially prairies, savannahs, and steppes, are much affected by the periodical firing they are exposed to in the dry season, and large tracts of country in various parts of the world would doubtless bear forests or other vegetation if not thus fired, while in other cases the herbage would be differently constituted were firing discontinued.

The following chapter embodies an attempt to classify our British grasses solely for purposes of identification when not in flower. It is not claimed that the arrangement is the best possible, nor that it is complete, and I need hardly say that corrections will be gratefully received.