GRASSES, a group of plants possessing certain characters in common and constituting a family (Gramineae) of the class Monocotyledons. It is one of the largest and most widespread and, from an economic point of view, the most important family of flowering plants. No plant is correctly termed a grass which is not a member of this family, but the word is in common language also used, generally in combination, for many plants of widely different affinities which possess some resemblance (often slight) in foliage to true grasses; e.g., knot-grass (Polygonum aviculare), cotton-grass (Eriophorum), rib-grass (Plantago), scorpion-grass (Myosotis), blue-eyed grass (Sisyrinchium), sea grass (Zostera). The grass-tree of Australia (Xanthorrhoea) is a remarkable plant, allied to the rushes in the form of its flower, but with a tall, unbranched, soft-woody, palm-like trunk, bearing a crown of long, narrow, grass-like leaves and stalked heads of small, densely-crowded flowers. In agriculture the word has an extended signification to include the various fodder-plants, chiefly leguminous, often called "artificial grasses." The first attempts at a classification of plants recognized and separated a group of Gramina, and this, though bounded by nothing more definite than habit and general appearance, con tained the Gramineae of modern botanists. The older group, however, even with such systematists as Ray (1703), Scheuchzer (1719), and Micheli (1729), embraced in addition the Cyperaceae (Sedge family), Juncaceae (Rush family), and some other mono cotyledons with inconspicuous flowers. Singularly enough, the sexual system of Linnaeus (1735) served to mark off more dis tinctly the true grasses from these allies, since very nearly all of the former then known fell under his Triandria Digynia, whilst the latter found themselves under his other classes and orders.
The aerial leaf-bearing branches (calms) are a characteristic feature of grasses. They are generally numerous, erect, cylin drical (rarely flattened) and conspicuously jointed, with evident nodes. The nodes are solid, a strong plate of tissue passing across the stem, but the internodes are commonly hollow, although examples of completely solid stems are not uncommon (e.g., maize, many species of Andropogon, sugar-cane). The swollen nodes are a characteristic feature. In wheat, barley and most of the British native grasses they are a development, not of the culm, but of the base of the leaf-sheath. The function of the nodes is to raise again stems which have become bent down; they are composed of highly turgescent tissue, the cells of which, under the influence of gravity, elongate on the side next the earth when the culm is placed in a horizontal or oblique position, and thus raise the culm again to an erect position. The internodes con tinue to grow in length, especially the upper ones, for some time; the increase takes place in a zone at the extreme base, just above the node. The exterior of the calms is more or less concealed by the leaf-sheaths; it is usually smooth and often highly polished, the epidermal cells containing an amount of silica sufficient to leave after burning a distinct skeleton of their structure. Tabasheer is a white substance mainly composed of silica, found in the joints of several bamboos. A few of the lower internodes may become enlarged and subglobular, forming nutriment-stores, and grasses so characterized are termed "bulbous" (Arrhenatherum, Poa bulbosa, etc.) . In internal structure grass-culms, save in being hollow, conform to that usual in monocotyledons; the vas cular bundles run parallel in the internodes, but a horizontal inter lacement occurs at the nodes. In grasses of temperate climates branching is rare at the upper nodes of the culm, but it is char acteristic of the bamboos and many tropical grasses. In many bamboos they are long and spreading or drooping and copiously ramified, in others they are reduced to hooked spines. One genus (Dinochloa, a native of the Malay archipelago) is scandent, and climbs over trees ioo ft. or more in height. Otyra lati f olia, a widely-spread tropical species, is also a climber, but on a smaller scale.
Grass-culms grow with great rapidity, as is most strikingly seen in bamboos, where a height of over ioo ft. is attained in from two to three months, and many species grow two, three or even more feet in twenty-four hours.
Leaves.—These present special characters usually sufficient for ordinal determination. They are solitary at each node and arranged in two rows, the lower often crowded, forming a basal tuft. They consist of two distinct portions, the sheath and the blade. The sheath is often of great length, and generally com pletely surrounds the culm, forming a firm protection for the internode, the younger basal portion of which, including the zone of growth, remains tender for some time. As a rule it is split down its whole length, thus differing from that of Cyperaceae which is almost invariably (Eriospora is an exception) a complete tube; in some grasses, however (species of Poa, Bromus and others), the edges are united. The sheaths are much dilated in Alopecurus vaginatus and in a species of Potamochloa, in the latter, an East Indian aquatic grass, serving as floats. At the summit of the sheath, above the origin of the blade, is the ligule, a usually membranous process of small size (occasionally reach ing i in. in length) erect and pressed around the culm. It is rarely quite absent, but may be represented by a tuft of hairs (very conspicuous in Pariana). It serves to prevent rain-water, which has run down the blade, from entering the sheath. Melica uniflora has in addition to the ligule, a green erect tongue-like process, from the line of junction of the edges of the sheath.
The blade is frequently wanting or small and imperfect in the basal leaves, but in the rest is long and set on to the sheath at an angle. The usual form is familiar—sessile, more or less ribbon-shaped, tapering to a point, and entire at the edge. The chief modifications are the articulation of the deciduous blade on to the sheath, which occurs in all the Bambuseae (except Planotia) and in Spartina stricta; and the interposition of a petiole between the sheath and the blade, as in bamboos, Leptaspis, Pharus, Pariana, Lophatherum and others. In the latter case the leaf usually becomes oval, ovate or even cordate or sagittate, but these forms are found in sessile leaves also (Olyra, Panicum). The venation is strictly parallel, the midrib usually strong, and the other ribs more slender. In Anomochloa there are several nearly equal ribs and in some broad-leaved grasses (Bambuseae, Pharus, Leptaspis) the venation becomes tessellated by transverse connecting veins. The tissue is often raised above the veins, form ing longitudinal ridges, generally on the upper face ; the stomata are in lines in the intervening furrows. The thick prominent veins in Agropyrum occupy the whole upper surface of the leaf. Epidermal appendages are rare, the most frequent being mar ginal, saw-like, cartilaginous teeth, usually minute, but occasion ally (Danthonia scabra, Panicum serratum) so large as to give the margin a serrate appearance. The leaves are occasionally woolly, as in Alopecurus lanatus and one or two Panicurns. The blade is often twisted, frequently so much so that the upper and under faces become reversed. In dry country, e.g., sand dune, the blades of grasses are often folded on the midrib, or rolled up. The rolling is effected by bands of large wedge-shaped cells motor-cells—between the nerves; the loss of water by these cells as they dry, causes the blade to curl towards the face on which they occur. The rolling up acts as a protection from too great loss of water, the exposed surface being specially protected to this end by a strong cuticle, the- majority or all of the stomata occur ring on the protected surface. The stiffness of the blade, which becomes very marked in dry-country grasses, is due to the develop ment of girders of thick-walled mechanical tissue which follow the course of all or the principal veins.
Inflorescence.—This possesses an exceptional importance in grasses, since, their floral envelopes being much reduced and the sexual organs of very great uniformity, the characters employed for classification are mainly derived from the arrangement of the flowers and their investing bracts. Various interpretations have been given to these glumaceous organs and different terms employed for them by various writers. It may, however, be considered as settled that the whole of the bodies known as glumes and paleae, and arranged externally to the flower, form no part of the floral envelopes, but are of the nature of bracts. These are arranged so as to form spikelets, and each spikelet may contain one, as in Agrostis, two, as in Aira, three, or a great num ber of flowers, as in Briza, Triticum; in some species of Eragrostis there are nearly 6o. The flowers are, as a rule, placed laterally on the axis (rachilla) of the spikelet, but in one-flowered spikelets they appear to be terminal, and are probably really so in .Anthoxan thum and in two anomalous genera, Anomochloa and Strepto' chaeta.
In immediate relation with the flower itself, and often entirely concealing it, is the palea or pale ("upper pale" of most syste matists). This organ is peculiar to grasses among Glumiflorae (the series to which belong the two families Gramineae and Cyperaceae), and is almost always present, certain Oryzeae and Phalarideae being the only exceptions. It is of thin membranous consistence, usually obtuse, often bifid, and possesses no central rib or nerve, but has two lateral ones, one on either side; the margins are frequently folded in at the ribs, which thus become placed at the sharp angles. The pale is generally considered to represent a single bracteole, characteristic of Monocotyledons, the binerved structure being the result of the pressure of the axis of the spikelet during the development of the pale, as in Iris and others.
The flower with its pale is sessile, and is placed in the axil of another bract in such a way that the pale is exactly opposed to it, though at a slightly higher level. It is this second bract or flowering glume which has been generally called by systemat ists the "lower pale," and with the "upper pale" was formerly considered to form an outer floral envelope. The two bracts are, however, on different axes, one secondary to the other, and cannot. therefore be parts of one whorl of organs. They are usually quite unlike one another, but in some genera (e.g., most Festuceae) are very similar in shape and appearance.
The flowering glume has generally a more or less boat-shaped form, is of firm consistence, and possesses a well-marked central midrib and frequently several lateral ones. The midrib in a large proportion of genera extends into an appendage termed the awn, and the lateral veins more rarely extend beyond the glume as sharp points (e.g., Pappophorum). The form of the flowering glume is very various, this organ being plastic and extensively modified in different genera. It frequently extends downwards a little on the rachilla ; in Leptaspis it is formed into a closed cavity by the union of its edges, and encloses the flower, two styles projecting through the pervious summit. Valu able characters for distinguishing genera are shown from the awn. This presents itself variously developed from a mere subulate point to an organ several inches in length, and when complete (as in An dropogoneae, Aveneae and Stipeae) consists of two well-marked portions, a lower twisted part and a terminal straight portion, usually set in at an angle with the former, sometimes trifid and occasionally beautifully feathery. The lower part is most often suppressed, and in the large group of the Paniceae awns of any sort are very rarely seen. The awn may be either terminal or may come off from the back of the flowering glume. When ter minal the awn has three fibro-vascular bundles, when dorsal only one ; it is covered with the stomate-bearing epidermis.
The flower with its palea is thus sessile in the aril of a floriferous glume, and in a few grasses (Leersia, Coleanthus, Nardus) the spikelet consists of nothing more, but usually (even in uniflorous spikelets) other glumes are present. Of these the two placed distichously opposite each other at the base of the spikelet never bear any flower in their axils, and are known as the empty or barren glumes. They are the "glumes" of most writers. They very rarely differ much from one another, but one may be smaller or quite absent (Panicum, Setaria, Paspalum, Lolium), or both be altogether suppressed, as above noticed. They are commonly firm and strong, often enclose the spikelet, and are rarely provided with long points or imperfect awns. Gen erally speaking they do not share in the special modifications of the flowering glumes, and rarely themselves undergo modification, chiefly in hardening of portions (Sclerachne, Manisuris, Anthe phora, Peltophorum), so as to afford greater protection to the flowers or fruit. But it is usual to find, besides the basal glumes, a few other empty ones, and these are in two- or more-flowered spikelets (Triticum) at the top of the rachilla (numerous in Lophatherum), or in uniflorous ones below and interposed between the floral glume and the basal pair.
The axis of the spikelet is frequently jointed and breaks up into articulations above each flower. Tufts or borders of hairs are frequently present (Calamagrostis, Phragmites, Andropogon), and are often so long as to surround and conceal the flowers. The axis is often continued beyond the last flower or glume as a bristle or stalk.
Involucres or organs outside the spikelets also occur and are formed in various ways. Thus in Setaria, Pennisetum, etc., the one or more circles of simple or feathery hairs represent abortive branches of the inflorescence; in Cenchrus these become con solidated, and the inner ones are flattened so as to form a very hard globular spiny case to the spikelets. Bracts of a more general character subtending branches of the inflorescence are singularly rare in Gramineae, in marked contrast with Cyperaceae, where they are so conspicuous. The remarkable ovoid involucre of Coix, which becomes of stony hardness, white and polished (then known as "Job's tears," q.v.), is also a modified bract or leaf sheath.
Any number of spikelets may compose the inflorescence, and their arrangement is very various. In the spicate forms, with sessile spikelets on the main axis, the latter is often dilated and flattened (Paspalum), or is more or less thickened and hollowed out (Stenotaphrum, Rottboellia, Tripsacum), when the spikelets are sunk and buried within the cavities. Every variety of race mose and paniculate inflorescence obtains, and the number of spikelets composing those of the large kinds is often immense. Rarely the inflorescence consists of very few flowers; thus Lygeum Spartum, one of the esparto grasses and the most anomalous of European grasses, has but two or three large uniflorous spikelets, which are fused together at the base, and have no basal glumes, but are enveloped in a large, hooded, spathe-like bract.
Flower.—This is characterized by remarkable uniformity. The perianth is represented by very rudimentary, small, fleshy scales arising below the ovary, called lodicules; they are elongated or truncate, are sometimes fringed with hairs, and are in contact with the ovary. Their usual number is two, and they are placed collaterally at the anterior side of the flower, that is, within the flowering glume. They are generally considered to represent the inner whorl of the ordinary monocotyledonous (liliaceous) perianth, the outer whorl of these being suppressed as well as the posterior member of the inner whorl. This latter is present almost constantly in Stipeae and Bambuseae, which have three lodicules, and in the latter group they are occasionally more numerous. In Streptochaeta there are six lodicules, alter nately arranged in two whorls. Sometimes, as in Anthoxanthum, they are absent. In Melica there is one large anterior lodicule resulting presumably from the union of the two which are pres ent in allied genera. The function of the lodicules is the separation of the pale and glume to allow the protrusion of stamens and stigmas; they effect this by swelling and thus ex erting pressure on the base of these two structures. Where, as in Anthoxanthum, there are no lodicules, pale and glume do not become laterally separated, and the stamens and stigmas protrude only at the apex of the floret. Grass-flowers are usually her maphrodite, but there are very many exceptions. Thus it is com mon to find one or more imperfect (usually male) flowers in the same spikelet with bisexual ones, and their relative position is important in classification. Holcus and Arrhenatherum are ex amples in English grasses; and as a rule in species of temperate regions separation of the sexes is not carried further. In warmer countries monoecious and dioecious grasses are most frequent. In such cases the male and female spikelets and inflorescence may be very dissimilar, as in maize, Job's tears, Euchlaena, Spinifex, etc.; and in some dioecious species this dissimilarity has led to the two sexes being referred to different genera. In other grasses, however, with the sexes in different plants (e.g., Brizopyrum, Dis tichlis, Eragrostis capitata, Gynerium), no such dimorphism obtains. Amphicarpum is remarkable in having cleistogamic flowers borne on long radical subterranean peduncles which are fertile, whilst the conspicuous upper paniculate ones, though ap parently perfect, never produce fruit. Something similar occurs in Leersia oryzoides, where the fertile spikelets are concealed within the leaf-sheaths.
Androecium.—In the vast majority there are three stamens alternating with the lodicules, and therefore one anterior, i.e., opposite the flowering glume, the other two being posterior and in contact with the palea. They are hypogynous, and have long and very delicate filaments, and large, linear or oblong two-celled anthers, dorsifixed and ultimately very versatile, deeply indented at each end, and commonly exserted and pendulous. Suppression of the anterior stamen sometimes occurs, or the two posterior ones may be absent. There is in some genera (Oryza, most Bam buseae) another row of three stamens, making six in all. The stamens become numerous (ten to forty) in the male flowers of a few monoecious genera (Pariana, Luziola). In Ochlandra they vary from seven to thirty, and in Gigantochloa they are mona delphous.
Gynoeciuzn.—The pistil consists of a single carpel, opposite the pale in the median plane of the spikelet. The ovary is small, rounded to elliptical, and one-celled, and contains a single slightly bent ovule sessile on the ventral suture (that is, springing from the back of the ovary) ; the micropyle points downwards. It bears usually two lateral styles which are quite distinct or connate at the base, sometimes for a greater length ; each ends in a densely hairy or feathery stigma. Occasionally there is but a single style, as in Nardus, which corresponds to the midrib of the carpel. The very long and apparently simple stigma of maize arises from the union of two. Many of the bamboos have a third, anterior, style.
Comparing the flower of Gramineae with the general mono cotyledonous plan as represented by Liliaceae and other families, it will be seen to differ in the absence of the outer row and the posterior member of the inner row of the perianth-leaves, of the whole inner row of stamens, and of the two lateral carpels, whilst the remaining members of the perianth are in a rudiment ary condition. But each or any of the usually missing organs are to be found normally in different genera, or as occasional developments.
Fruit and Seed.—The ovary ripens into a usually small ovoid or rounded fruit, which is entirely occupied by the single large seed, from which it is not to be distinguished, the thin pericarp of the fruit being completely united to the testa of the seed. To this peculiar fruit the term caryopsis has been applied (more familiarly "grain") ; it is commonly furrowed longitudinally down one side (usually the inner, but in Coix and its allies, the outer), and an additional covering is not unfrequently provided by the adherence of the persistent palea, or even also of the flowering Blume ("chaff" of cereals) . From this type there are a few devia tions; thus in Sporobolus, etc., the pericarp is not united with the seed but is quite distinct, dehisces, and allows the loose seed to escape. Sometimes the pericarp is hard, forming a nut, as in some genera of Bambuseae, while in other Bambuseae it becomes thick and fleshy, forming a berry often as large as an apple. In Melocanna the berry forms an edible fruit 3 or 4 in. long, with a pointed beak of 2 in. more; it is indehiscent, and the small seed germinates whilst the fruit is still attached to the tree, putting out a tuft of roots and a shoot, and not falling till the latter is 6 in. long. The position of the embryo is plainly visible on the front side at the base of the grain. On the other, posterior, side of the grain is a more or less evident, sometimes punctiform, sometimes elongated or linear mark, the hilum, the place where the ovule was fastened to the wall of the ovary. The form of the hilum is constant throughout a genus, and sometimes also in whole tribes.
The testa is thin and membranous but occasionally coloured, and the embryo small, the great bulk of the seed being occupied by the hard farinaceous endosperm (albumen) on which the nutritive value of the grain depends. The outermost layer of endosperm, the aleurone-layer, consists of regular cells filled with small proteid granules; the rest is made up of large polygonal cells containing numerous starch-grains in a matrix of proteid which may be continuous (horny endosperm) or granular (mealy endosperm). The embryo presents many points of interest. Its position is remarkable, closely applied to the surface of the endosperm at the base of its outer side. This character is absolute for the whole order, and effectually separates Gramineae from Cyperaceae. The part in contact with the endosperm is plate like, and is known as the scutellum; the surface in contact with the endosperm shows a special epithelial layer concerned in absorption of materials from the endosperm. In some grasses there is a small scale-like appendage opposite the scutellum, the epiblast. Three structures have been claimed as representing the cotyledon :—( ) the scutellum, connected by vascular tissue with the vascular cylinder of the main axis of the embryo which it more or less envelops; (2) the cellular outgrowth of the axis, the epiblast, small and inconspicuous as in wheat, or larger as in Stipa; (3) the coleoptile or germ-sheath, arising on the same side of the axis and above the scutellum, enveloping the plumule in the seed and appearing above ground as a generally colourless sheath from the apex of which the plumule ultimately breaks. The de velopment of these structures, especially in relation to the origin of the vascular bundles which supply them, favours the view that the scutellum and coleoptile are highly differentiated parts of a single cotyledon.
Germination.—In germination the coleorhiza lengthens, rup tures the pericarp and fixes the grain to the ground by developing numerous hairs. The radicle then breaks through the coleorhiza, as do also the secondary rootlets where, as in the case of many cereals, these have been formed in the embryo. The germ-sheath grows vertically upwards, its stiff apex pushing through the soil, while the plumule is hidden in its hollow interior. Finally the plumule escapes, its leaves successively breaking through at the tip of the coleoptile. The scutellum meanwhile feeds the develop ing embryo by absorbing from the endosperm. The growth of the primary root is limited; sooner or later adventitious roots de velop from the axis above the radicle which they ultimately exceed in growth.
Means of Distribution.—Various methods of scattering the grain have been adopted, in which parts of the spikelet or in florescence are concerned. Short spikes may fall from the culm as a whole; or the axis of a spike or raceme is jointed so that one spikelet falls with each joint as in many Andropogoneae and Hordeae. In many-flowered spikelets the rachilla is often jointed and breaks into as many pieces as there are fruits, each piece bearing a glume and pale. These arrangements are, with few exceptions, lacking in cultivated cereals though present in their wild forms, so far as these are known. Such arrangements are disadvantageous for the complete gathering of the fruit, and therefore varieties in which they are not present would be pre ferred for cultivation. The persistent bracts (glume and pale) afford an additional protection to the fruit; they protect the embryo, which is near the surface, from too rapid wetting and, when once soaked, from drying up again. They also decrease the specific gravity, so that the grain is more readily carried by the wind, especially when, as in Briza, the glume has a large surface compared with the size of the grain, or when, as in Holcus, empty glumes also take part ; in Canary grass (Plialaris) the large empty glumes bear a membranous wing on the keel.
The awn which is frequently borne on the flowering glume is also a very efficient means of distribution, catching into fur of animals or plumage of birds, or as often in Stipa forming a long feather for wind-carriage. In Tragus the glumes bear numerous short hooked bristles. The fleshy berries of some Bambuseae favour distribution by animals.
The awn is also of use in burying the fruit in the soil. Thus in Stipa, species of Avena, Heteropogon and others the base of the glume forms a sharp point which will easily penetrate the ground; above the point are short stiff upwardly pointing hairs which oppose its withdrawal. The long awn, which is bent and closely twisted below the bend, acts as a driving organ ; it is very hygroscopic, the coils untwisting when damp and twisting up when dry. The repeated twisting and untwisting, especially when the upper part of the awn has become fixed in the earth or caught in surrounding vegetation, drives the point deeper and deeper into the ground. Such grasses often cause harm to sheep by catching in the wool and boring through the skin.
The great uniformity among the very numerous species of this vast family renders its classification very difficult. The difficulty has been increased by the confusion resulting from the multiplica tion of genera founded on slight characters, and from the descrip tion (in consequence of their wide distribution) of identical plants under several different genera.
No characters for main divisions can be obtained from the flower proper or fruit (with the exception of the character of the hilum), and it has therefore been found necessary to trust to characters derived from the usually less important inflor escence and bracts.
The following arrangement has been proposed by Professor Eduard Hackel in his monograph on the order.
A. Spikelets one-flowered, rarely two-flowered as in Zea, falling from the pedicel entire or with certain joints of the rachis at maturity. Rachilla not produced beyond the flowers.
a. Hilum a point; spikelets not laterally compressed.
I. Spikelets unisexual, male and female in separate inflorescences or on different parts of the same inflorescence. I. Maydeae.
2. Spikelets bisexual, or male and bisexual, each male standing close to a bisexual. 2. Andropogoneae.
(3 Fertile glume and pale cartilaginous, coriaceous or papery; empty glumes more delicate, usually herbaceous, the lowest usually smallest, Spikelets falling singly from the unjointed rachis of the spike or the ultimate branches of the panicle.
3. Paniceae.
b. Hilum a line ; spikelets laterally compressed.
a. Culm herbaceous annual; leaf-blade sessile, and not jointed to the sheath.
a Spikelets upon distinct pedicels and arranged in panicles or racemes.
I. Spikelets one-flowered.
i. Empty glumes 4. 5. Phalarideae.
ii. Empty glumes 2. 6. Agrostidear.
Tribe i . Maydeae. Zea Mays (maize, q.v., or Indian corn. Tripsacurn, 2 or 3 species in subtropical America north of the equator; Tr. dactyloides (gama grass) extends northwards to Illinois and Connecticut; it is used for fodder and as an orna mental plant. Coix Lacryma- Iobi (Job's tears) q.v.
Tribe 2. Andropogoneae (mainly tropical). The spikelets are arranged in spike-like racemes, and generally in pairs consist ing of a sessile and stalked spikelet at each joint of the rachis. Many are savannah grasses, in various parts of the tropics, for instance the large genus Andropogon, Elionurus and others. Sac charum officinarum (sugar-cane). Sorghum, an important trop ical cereal known as black millet or durra (q.v.). Imperata is a widespread tropical genus; one species I. arundinacea is the principal grass of the alang-alang fields in the Malay Archipelago; it is used for thatch. V ossia, an aquatic grass, often floating, is found in western India and tropical Africa. In the swampy lands of the upper Nile it forms, along with a species of Saccharurn, huge floating grass barriers. In Andropogon Nardus, a native of India, but also cultivated, the rhizome, Ieaves and especially the spikelets of which contain a volatile oil, which on distillation yields the citronella oil of commerce. A closely allied species, A. Schoenanthus (lemon-grass), yields lemon-grass oil; a variety is used by the negroes in western Africa for haemorrhage. T hemeda Forskalii, which occurs from the Mediterranean region to South Africa and Tasmania, is the kangaroo grass of Australia, where, as in South Africa, it often covers wide tracts.
Tribe 3. Paniceae (tropical to subtropical; a few temperate), a second flower, generally male, rarely hermaphrodite, is often present below the fertile flower. Paspalum is a large tropical genus, most abundant in America, especially on the pampas and campos; many species are good forage plants, and the grain is sometimes used for food. Panicum, a very polymorphic genus,. and one of the largest in the order, is widely spread in all warm countries; together with species of Paspalum they form good forage grasses in the South American savannahs and campos. Panicum Crus-galli is a polymorphic cosmopolitan grass, which is often grown for fodder; in one form (P. f rumentaceum) it is cultivated in India for its grain. P. miliaceurn is millet (q.v.), and P. altissimum, Guinea grass. Digitaria sanguinalis is a very widespread grass, in Bohemia it is cultivated as a food-grain; it is also the crab-grass of the southern United States, where it is used for fodder.
Setaria italica, Hungarian grass, is extensively grown as a food-grain both in China and Japan, parts of India and western Asia, as well as in Europe, where its culture dates from pre historic times; it is found in considerable quantity in the lake dwellings of the Stone age.
In Cenchrus the bristles unite to form a tough spiny capsule; C. tribuloides (bur-grass) and other species are troublesome weeds in North and South America, as the involucre clings to the wool of sheep and is removed with great difficulty. Pennisetum typhoideum is widely cultivated as a grain in tropical Africa. Spini f ex, a dioecious grass, is widespread on the coasts of Aus tralia and eastern Asia, forming an important sand-binder. The female heads are spinose with long bracts, fall entire when ripe and are carried away by wind or sea, becoming finally anchored in the sand and falling to pieces.
Tribe 4. Oryzeae (mainly tropical and subtropical) . The spike lets are sometimes unisexual, and there are often six stamens. Leersia is a genus of swamp grasses, one of which L. oryzoides occurs in the north temperate zone of both old and new worlds, and is a rare grass in Surrey, Sussex and Hampshire. Zizania aquatica (Tuscarora or Indian rice) is a reed-like grass growing over large areas on banks of streams and lakes in North America and north-east Asia. The Indians collect the grain, Oryza sativa (rice, q.v.), for food. Lygeum Spartum, with a creeping stem and stiff rush-like leaves, is common on rocky soil on the high plains bordering the western Mediterranean, and is one of the sources of esparto.
Tribe 5. Phalarideae (a few are South African and Austral asian; the others are more widely distributed, and represented in the British flora). Phalaris arundinacea, is a reed-grass found on the banks of British rivers and lakes ; a variety with striped leaves known as ribbon-grass is grown for ornament. P. canariensis (Canary grass, a native of southern Europe and the Mediter ranean area) is grown for bird-food and sometimes as a cereal. Anthoxonthum odoratum, the sweet vernal grass of our flora, owes its scent to the presence of coumarin, which is also present in the closely allied genus Hierochloe, which occurs throughout the temperate and frigid zones.
Tribe 6. Agrostideae (occurring in all parts of the world; a number are British). Aristida and Stipa are large and widely distributed genera, occurring especially on open plains and steppes; the conspicuously awned persistent flowering glume forms an efficient means of dispersing the grain. Stipa pennata is a characteristic species of the Russian steppes. St. spartea (porcupine grass) and other species are plentiful on the North American prairies. St. tenacissima is the Spanish esparto grass (q.v.), known in North Africa as halfa or alfa. Phleum pratense (timothy) is a valuable fodder grass, as also is Alopecurus pra tensis (foxtail). Sporobolus, a large genus in the warmer parts of both hemispheres, but chiefly America, derives its name from the fact that the seed is ultimately expelled from the fruit. Agrostis is a large world-wide genus, but especially developed in the north temperate zone, where it includes important meadow grasses. Ammophila arundinacea (Psamma arenaria) (Marram grass) with its long creeping stems forms a useful sand-binder on the coasts of Europe, North Africa and the Atlantic states of America.
Tribe 7. Aveneae (seven genera are British). Holcus lanatus (Yorkshire fog, soft grass) is a common meadow and wayside grass with woolly or downy leaves. Aira is a genus of delicate annuals with slender hair-like branches of the panicle. Des champsia and Trisetum occur in temperate and cold regions or on high mountains in the tropics; T. pratense (Avena flavescens) with a loose panicle and yellow shining spikelets is a valuable fodder-grass. Avena fatua is the wild oat and A. sativa the cultivated oat (q.v.). Arrhenatherum avenaceum, a perennial field grass, native in Britain and central and southern Europe, is cultivated in North America.
Tribe 8. Chlorideae (chiefly in warm countries). The only British representative is Cynodon Dactylon (dog's tooth, Bermuda grass) found on sandy shores in the south-west of England; it is a cosmopolitan, covering the ground in sandy soils, and forming an important forage grass in many dry climates (Bermuda grass of the southern United States, and known as durba, dub and other names in India). Species of Chloris are grown as ornamental grasses. Bouteloua with numerous species (mesquite grass, grama grass) on the plains of the south-western United States, afford good grazing. Eleusine indica is a common tropical weed; the nearly allied species E. coracana is a cultivated grain in the warmer parts of Asia and throughout Africa. Buchloe dactyloides is the buffalo grass of the North American prairies, a valuable fodder.
Tribe 9. Festuceae (tropical, temperate, arctic and alpine forms) Many are important meadow-grasses; i5 are British. Gynerium argenteum (pampas grass) is a native of southern Brazil and Argentina. Arundo and Phragmites are tall reed grasses (see REED). Several species of Triodia cover large areas of the interior of Australia, and from their stiff, sharply pointed leaves are very troublesome. Eragrostis, one of the larger genera of the order, is widely distributed in the warmer parts of the earth; many species are grown for ornament and E. abyssinica is an important food-plant in Abyssinia. Koeleria cristata is a fodder grass. Briza media (quaking grass) is a useful meadow-grass. Dactylis glomerata (cock's-foot), a perennial grass with a dense panicle, common in pastures and waste places, is a useful meadow grass. It has become naturalized in North America, where it is known as orchard grass, as it will grow in shade. Cynosurus cristatus (dog's tail) is a common pasture-grass. Poa, a large genus widely distributed in temperate and cold countries, includes many meadow and alpine grasses; eight species are British; P. annua is the very common weed in paths and waste places ; P. pratensis and P. trivialis are also common grasses of meadows, banks and pastures, the former is the "June grass" or "Kentucky blue grass" of North America; P. alpina is a mountain grass of the northern hemisphere and found also in the Arctic region. The largest species of the genus is Poa flabellata which forms great tufts 6-7 ft. high with leaves arranged like a fan. Glyceria fluitans, manna-grass, so-called from the sweet grain, is one of the best fodder grasses for swampy meadows ; the grain is an article of food in central Europe. Festuca (fescue) is also a large and widely distributed genus, but found especially in the temperate and cold zones; it includes valuable pasture grasses, such as F. ovina (sheep's fescue), F. rubra; nine species are British. The closely allied genus Bromus (brome grass) is also widely dis• tributed but most abundant in the north temperate zone ; B. erectus is a useful forage grass on dry chalky soil.
Tribe i o. Hordeae (about 19 genera, widely distributed; six are British). Nardus stricta (mat-weed), found on heaths and dry pastures, is a small perennial useless grass with slender rigid stem and leaves. Lolium perenne, ray- (or by corruption rye-) grass, is common in waste places and a valuable pasture-grass; L. italicum is the Italian ray-grass; L. temulentum (darnel) has many of its grains infected with a fungus which is passed on from generation to generation. Secale cereale, rye (q.v.), is cultivated mainly in northern Europe. Agropyrum repens (couch grass) has a long creeping underground stem, and is a troublesome weed in cultivated land; the widely creeping stem of A. junceum, found on sandy sea-shores, renders it a useful sand-binder. Triticum sativum is wheat (q.v.), and Hordeum sativum, barley (q.v.). H. murinum, wild barley, is a common grass in waste places. Elymus arenarius (lyme grass) occurs on sandy sea-shores in the north temperate zone and is a useful sand-binder.
Tribe II. Bambuseae. Contains 23 genera, mainly tropical.
See BAMBOO.
While the greatest number of species is found in the tropical zone, the number of individuals is greater in the temperate zones, where they form extended areas of turf. Turf- or meadow-forma tion depends upon uniform rainfall. Grasses also characterize steppes and savannahs, where they form scattered tufts. The bam boos are a feature of tropical forest vegetation, especially in the monsoon region. As the colder latitudes are entered the grasses become relatively more numerous, and are the leading family in Arctic and Antarctic regions. The only countries where the order plays a distinctly subordinate part are some extra-tropical regions of the southern hemisphere, Australia, the Cape, Chile, etc. The proportion of graminaceous species to the whole phanerogamic flora in different countries varies from nearly a in the Arctic regions to about at the Cape; in the British Isles it is about -A.
The principal climatic cause influencing the number of gramin aceous species appears to be amount of moisture. A remarkable feature of the distribution of grasses is its uniformity; there are no great centres for the order, as in Compositae, where a marked preponderance of endemic species exists; and the genera, except some of the smallest or monotypic ones, have usually a wide distribution.
Many grasses are almost cosmopolitan, such as the common reed, Phragmites communis; and many range throughout the warm regions of the globe, e.g., Cynodon Dactylon, Eleusine in dica, Imperata arundinacea, Sporobolus indicus, etc., and such weeds of cultivation as species of Setaria, Echinochloa. Several species of the north temperate zone, such as Poa nemoralis, P. pratensis, Festuca ovina, F. rubra and others are absent in the tropics but reappear in the antarctic regions; others (e.g., Phleum alpinum) appear in isolated positions on high mountains in the intervening tropics. No tribe is confined to one hemisphere and no large genus to any one floral region; facts which indicate that the separation of the tribes goes back to very ancient times.
Of specially remarkable species Lygeum is found on the sea sand of the eastern half of the Mediterranean basin,and the minute Coleanthus occurs in three or four isolated spots in Europe (Nor way, Bohemia, Austria, Normandy), in North-east Asia (Amur) and on the Pacific coast of North America (Oregon, Washington). Many remarkable endemic genera occur in tropical America, in cluding Anomochloa of Brazil, and most of the large aquatic species with separated sexes are found in this region. The only genus of flowering plants peculiar to the arctic regions is the beautiful and rare grass Plettropogon Sabinii, of Melville Island.