Grasses - Encyclopedia
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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), seagrass (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." Indeed, formerly grass (also spelt gwrs, gres, gyrs in the old herbals) meant any green herbaceous plant of small size.
Yet 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, contained 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 1 The word " grass " (0. Eng. goers, grees) is common to Teutonic languages, cf. Dutch Ger. Goth. gras, Dan. grees; the root is the O. Teut. gra-, gro-, to increase, whence " grow," and " green," the typical colour of growing vegetation. The Indo-European root is seen in Lat. gramen. The O. Eng. grasian, formed from grees, gives " to graze," of cattle feeding on growing herbage, also " grazier," one who grazes or feeds cattle for the market; " to graze," to abrade, to touch lightly in passing, may be a development of this from the idea of close cropping; if it is to be distinguished a possible connexion may be found with " glace " (Fr. glacer, glide, slip, Lat. glacier, ice), to glance off, the change in form being influenced by grate," to scrape, scratch (Fr. gratter, Ger. kratzen). (Sedge family), Juncaceae (Rush family), and some other monocotyledons with inconspicuous flowers. Singularly enough, the sexual system of Linnaeus (1735) served to mark off more distinctly 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.
I. Structure. - The general type of true grasses is familiar in the cultivated cereals of temperate climates - wheat, barley, rye, oats, and in the smaller plants which make up pastures and meadows and form a principal factor of the turf of natural downs. Less familiar are the grains of warmer climates - rice, maize, millet and sorgho, or the sugar-cane. Still farther removed are the bamboos of the tropics, the columnar stems of which reach to the height of forest trees. All are, however, formed on a common plan.
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Root
Most cereals and many other grasses are annual, and possess a tuft of very numerous slender root-fibres, much branched and of great length. The majority of the members of the family are of longer duration, and have the roots also fibrous, but fewer, thicker and less branched. In such cases they are very generally given off from just above each node (often in a circle) of the lower part of the stem or rhizome, perforating the leaf-sheaths. In some bamboos they are very numerous from the lower nodes of the erect culms, and pass downwards to the soil, whilst those from the upper nodes shrivel up and form circles of spiny fibres.
Stem
The underground stem or rootstock (rhizome) of perennial grasses is usually well developed, and often forms very FIG. I. - Rhizome of Bamboo. A, B, C, D, successive series of axes, the last bearing aerial culms. Much reduced.
long creeping or subterranean rhizomes, with elongated internodes and sheathing scales; the widely-creeping, slender rhizomes in Marram-grass (Psamma), Agropyrum junceum, Ely7nus arenarius, and other sand-loving plants render them useful as sand-binders. It is also frequently short, with the nodes crowded. The turf-formation, which is characteristic of open situations in cool temperate climates, results from an extensive production of short stolons, the branches and the fibrous roots developed from their nodes forming the dense " sod." The very large rhizome of the bamboos (fig. r) is also a striking example of " definite " growth; it is much branched, the short, thick, curved branches being given off below the apex of the older ones and at right angles to them, the whole forming a series of connected arched axes, truncate at their ends, which were formerly continued into leafy culms. The rhizome is always solid, and has the usual internal structure of the monocotyledonous stem. In the cases of branching just cited the branches break directly through the sheath of the leaf in connexion with which they arise. In other cases the branches grow upwards through the sheaths which they ultimately split from above, and emerging as aerial shoots give a tufted habit to the plant. Good examples are the oat, cock's-foot (Dactylis) and other British grasses. This mode of growth is the cause of the " tillering " of cereals, or the production of a large number of erect growing branches from the lower nodes of the young stem. Isolated tufts or tussocks are also characteristic of steppe - and savanna - vegetation and open places generally in the warmer parts of the earth.
The aerial leaf-bearing branches (culms) are a characteristic feature of grasses. They are generally numerous, erect, cylindrical (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 Andropogons, 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 culms which have become bent down; they are composed of highly turgescent tissue, the cells of which 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 continue 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 culms 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, &c.). In internal structure grass-culms, save in being hollow, conform to that usual in monocotyledons; the vascular bundles run parallel in the internodes, but a horizontal interlacement occurs at the nodes. In grasses of temperate climates branching is rare at the upper nodes of the culm, but it is characteristic of the bamboos and many tropical grasses. The branches are strictly distichous. 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 roo ft. or more in height, Olyra latifolia, a widely-spread tropical species, is also a climber on a humbler 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. Silicic hardening does not begin till the full height is nearly attained. The largest bamboo recorded is 170 ft., and the diameter is usually reckoned at about 4 in. to each 50 ft.
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 completely 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 l i the sheath, above the origin of the blade, is the ligule, a usually membranous process of small size (occasionally reaching r 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 tesselated 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 marginal, saw-like, cartilaginous teeth, usually minute, but occasionally (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 Panicums. The blade is often twisted, frequently so much so that the upper and under faces become reversed. In dry-country grasses the blades 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 turgescence by which, as the air dries, 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 occurring on the protected surface. The stiffness of the blade, which becomes very marked in dry-country grasses, is due to the development of girders of thick-walled mechanical tissue which follow the course of all or the principal veins (fig. 2). 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 FIG. 3. - One-flowered FIG. 4. - Two-flowered spikelet spikelet of Agrostis. of Aira. b, Barren glumes; f, flowering glumes. (Both enlarged.) considered. as settled that the whole of the bodies known as glumes and paleae, and distichously 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 (locustae), and each spikelet may contain one, as in Agrostis (fig. 3) two, as in Aira (fig. 4) three, or a great number of flowers, as in Briza (fig. 5) Triticum (fig. 6); in some species of Eragrostis there are nearly 60. 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 Anthoxanthum (fig. 7) and in two anomalous genera,, Anomochloa and Streptochaeta. In immediate relation with the flower itself, and often entirely concealing it, is the palea or pale (" upper pale " of most systematic agrostologists). This organ (fig. 13, i) is peculiar to grasses FIG. 5. - Spikelet of Briza. FIG. 6. - Spikelet of Triticum. (Both enlarged.) 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. This structure was formerly regarded as pointing to the fusion of two organs, and the pale was considered by Robert Brown to represent two portions soldered together of a trimerous perianth - whorl, the third portion being the " lower pale." The pale is now generally considered to represent the 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 systematists the " lower pale," and with the " upper pale " was formerly considered to form an outer floral envelope (" calyx," Jussieu; " perianthium," Brown). 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 (fig. 4), 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, forming with the latter a swollen callus, which is separated from the free portion by a furrow. In Leptaspis it is formed into a closed cavity by the union of its edges, and encloses the flower, the styles projecting through the pervious summit. Valuable characters for distinguishing genera are obtained 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 Andropogoneae, Aveneae and Stipeae) consists of two well-marked portions, a lower twisted part and a terminal straight portion, FIG. 2. - Magnified transverse section of one-half of a leaf-blade of Festuca rubra. The dark portions represent supporting and conducting tissue; the upper face bears furrows, at the bottom of each of which are seen the motor cells m. FIG. 7. - Spikelet of Anthoxanthum (enlarged) without the two lower barren glumes, showing the two upper awned barren glumes (g) and the flower.
usually set in at an angle with the former, sometimes trifid and occasionally beautifully feathery (fig. 8). 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, and Duval Jouve's observations have shown that it represents the blade of the leaf of which the portion of the flowering glume below its origin is the sheath; the twisted part (so often suppressed) corresponds with the petiole, and the portion of the glume extending beyond the origin of the awn (very long in some species, e.g. of Danthonia) with the ligule of the developed foliage-leaf. When terminal the awn has three fibro-vascular bundles, when dorsal only one; it is covered with stomate-bearing epidermis.
The flower with its palea is thus sessile in the axil of a floriferous glume, and in a few grasses (Leersia (fig. 9), 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 thei axils, and are called the empty or barren glumes (figs. 3, 8). They are the " glumes " f of most writers,. and together form what was called the " gluma " by R. Brown.
They rarely differ much from one another, but one may be smaller or quite absent (Panicum, Setaria (fig. io), 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. Generally 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 twoor more-flowered spikelets (see Triticum, fig. 6) at the top of the rhachilla (numerous in Lophatherum), or in uniflorous ones (fig. Io) 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 (fig. II). 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 (fig. io), Pennisetum, &c., the one or more circles of simple or feathery hairs represent abortive branches of the inflorescence; in Cenchrus (fig. 12) these become consolidated, and the inner ones flattened so as to form a very hard globular spiny case to the spikelets. The cup-shaped involucre of Cornucopia is a dilatation of the axis into a hollow receptacle with a raised border. In Cynosurus (Dog's tail) -- C the pectinate involucre which conceals the spikelet is a barren or abortive spikelet. Bracts of a more general character subtending branches C' of the inflorescence are singularly rare in Gramineae, in marked contrast with Cyperaceae, where they are so conspicuous. They however occur in a whole section of Andropogon, in Anomochloa, and at the base of the spike in Sesleria. 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. It is closed except at the apex, and contains the female spikelet, the stalks of the male inflorescence and the long styles emerging through the small apical orifice.
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 racemose 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, 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 FIG. 13. - Flowers of Grasses (enlarged). 1, Piptatherum, with the palea p; 2, Poa; 3, Oryza; 1, Lodicule. or truncate, 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 (fig. 13,) that is, within the flowering glume. They are generally considered to represent the inner whorl of the ordinary monocotyledonous b FIG. 9. - FIG. io. - Spikelet of Spikelet of LeerSetaria, with an abortive sia. f, Flowerbranch (h) beneath it. b, ing glume; p, Barren glumes; f, flower pale. ing glume; p, pale.
FIG. 8. - Spikelet of Stipa pennata. The pair of barren glumes (b) are separated from the flowering glume, which bears a long awn, twisted below the knee and feathery above. About 4 nat. size.
a, b, c, c, a' FIG. II. - Spikelet of Reed (Phragmites cornmunis) opened out. Barren glumes. Fertile glumes, each enclosing one flower with its pale d. Note the zigzag axis (rhachilla) bearing long silky hairs.
FIG. 12. - Spikelet of Cenchrus echinatus enclosed in a bristly involucre.
<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 Anomochloa they are represented by hairs. In Streptochaeta there are six lodicules, alternately 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 present in allied genera. Professor E. Hackel, however, regards this as an undivided second pale, which in the majority of the grasses is split in halves, and the posterior lodicule, when present, as a third pale. On this view the grass-flower has no perianth. 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 exerting 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 (fig. 7). Grass-flowers are usually hermaphrodite, but there are very many exceptions. Thus it is common 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 examples 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 more frequent. In such cases the male and female spikelets and inflorescence may be very dissimilar, as in maize, Job's tears, Euchlaena, Spinifex, &c.; and in some dioecious species this dissimilarity has led to the two sexes being referred to different genera (e.g. Anthephora axilliflora is the female of Buchloe dactyloides, and Neurachne paradoxa of a species of Spinifex). In other grasses, however, with the sexes in different plants (e.g. Brizopyrum, Distichlis, 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 apparently 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 (fig. 13, i and 2). 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 (e.g. Anthoxanthum, fig. 7), or the two posterior ones may be absent (Uniola, Cinna, Phippsia, Festuca bromoides). There is in some genera (Oryza, most Bambuseae) another row of three stamens, making six in all (fig. 13, 3); and Anomochloa and Tetrarrhena possess four. The stamens become numerous (ten to forty) in the male flowers of a few monoecious genera (Pariana, Luzieta). In Ochlandra they vary from seven to thirty, and in Gigantochloa they are monadelphous.
Gynoecium
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 (fig. 14, r), each ends in a densely hairy or feathery stigma (fig. 14). Occasionally there is but a single style, as in Nardus (fig. 14, 7), 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 monocotyledonous plan as represented by Liliaceae and other families (fig. r 5), 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, FIG. 4. - Pistils of Grasses (much enlarged). r, Alopecurus; a Bromus; 3, Arrhenatherum; 4, Glyceria; 5, Melica; 6, Mibora; 7, Nardus. whilst the remaining members of the perianth are in a rudimentary condition. But each or any of the usually missing organs are to be found normally in differO ent genera, or as occasional developments.
Pollination
Grasses are generally wind - pollinated, though selffertilization sometimes occurs. A few species, as we have seen, are monoecious or dioecious, while many are polygamous (having unisexual as well as bisexual flowers as in many members of the tribes Andropogoneae, fig. 18, and Paniceae), and in these the male flower of a spikelet always blooms later than the hermaphrodite, so that its pollen can only effect cross-fertilization upon other spikelets in the same or another plant. Of those with only bisexual flowers, many are strongly protogynous (the stigmas protruding before the anthers are ripe), such as Alopecurus and Anthoxanthum (fig. 7), but generally the anthers protrude first and discharge the greater part of their pollen before the stigmas appear. The filaments elongate rapidly at flowering-time, and the lightly versatile anthers empty an abundance of finely granular smooth pollen through a longitudinal slit. Some flowers, such as rye, have lost the power of effective self-fertilization, but in most cases both forms, selfand cross-fertilization, seem to be possible. Thus the species' of wheat are usually selffertilized, but cross-fertilization is possible since the glumes are open above, the stigmas project laterally, and the anthers empty only about one-third of their pollen in their own flower and the rest into the air. In some cultivated races of barley, crossfertilization is precluded, as the flowers never open. Reference has already been made to cleistogamic species which occur in several genera.
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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 being completely united to its surface. 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 FIG. 15. - Diagrams of the ordinary Grassflower.
r, Actual condition; 2, Theoretical, with the suppressed organs supplied.
a, Axis.
b, Flowering glume.
c, Palea.
d, Outer row of perianth leaves.
e, Inner row.
f, Outer row of stamens.
g, Inner row.
h, Pistil.
glume (" chaff "of cereals). From this type are a few deviations; thus in Sporobolus, &c. (fig. 16), the pericarp is not united with the seed but is quite distinct, dehisces, and allows the loose seed to escape. Sometimes the pericarp is membranous, sometimes 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 aleuron-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 forms an absorptive epithelium. In some grasses there is a small scale-like appendage opposite the scutellum, the epiblast. There is some difference of opinion as to which structure or structures represent the cotyledon. Three must be considered: (I) the scutellum, connected by vascular tissue with the vascular cylinder of the main axis of the embryo which it more or less envelops; it never leaves the seed, serving merely to prepare and absorb the food-stuff in the endosperm; (2) the cellular outgrowth of the axis, the epiblast, small and inconspicuous as in wheat, or larger as in Stipa; (3) the pileole 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 (fig. 17, 4, b). The development of these structures (which was investigated by van Tieghem), FIG. 17. - A Grain of Wheat. 1, back, and 2, front view; 3, vertical section, showing (b) the endosperm, and (a) embryo; 4, beginning of germination, showing (b) the pileole and (c) the radicle and secondary rootlets surrounded by their coleorrhizae.
especially in relation to the origin of the vascular bundles which supply them, favours the view that the scutellum and pileole are highly differentiated parts of a single cotyledon,and this view is in accord with a comparative study of the seedling of grasses and of other monocotyledons. The epiblast has been regarded as representing a second cotyledon, but this is a very doubtful interpretation.
Germination
In germination the coleorhiza lengthens, ruptures 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, (fig. 17, 4). 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 germ-sheath. The scutellum meanwhile feeds the developing embryo from the endosperm. The growth of the primary root is limited; sooner or later adventitious roots develop 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 inflorescence 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. One-flowered spikelets may fall as a whole (as in the tribes Paniceae and Andrepogoneae), or the axis is jointed above the barren glumes so that only the flowering glume and pale fall with the fruit. 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 preferred 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 H olcus, empty glumes also take part; in Canary grass (Phalaris) the large empty glumes bear a membranous wing on the keel. In the sugar-cane (Saccharum) and several allied genera the separating joints of the axis bear long hairs below the spikelets; in others, as in Arundo (a reed-grass), the flowering glumes are enveloped in long hairs. 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 (fig. 8) forming a long feather for windcarriage. 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 isvery 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.
A peculiar method of distribution occurs in some alpine and arctic grasses, which grow under conditions where ripening of the fruit is often uncertain. The entire spikelet, or single flowers, are transformed into small-leaved shoots which fall from the axes and readily root in the ground. Some species, such as Poa stricta, are known only in this viviparous condition; others, like our British species Festuca ovina, and Poa alpina, become viviparous under the special climatic. conditions.
II. Classification. - Gramineae are sharply defined from all other plants, and there are no genera as to which it is possible to feel a doubt whether they should be referred to it or not. The only family closely allied is Cyperaceae, and the points of difference between the two may be here brought together. The FIG. 1 6.
Fruit ofSporo- bolus, showing the dehiscent pericarp and seed.
best distinctions are found in the position of the embryo in relation to the endosperm - lateral in grasses, basal in Cyperaceae - and in the possession by Gramineae of the 2-nerved palea below each flower. Less absolute characters, but generally trustworthy and more easily observed, are the feathery stigmas, the always distichous arrangement of the glumes, the usual absence of more general bracts in the inflorescence, the split leaf-sheaths, and the hollow, cylindrical, jointed culms - some .or all of which are wanting in all Cyperaceae. The same characters will distinguish grasses from the other glumiferous orders, Restiaceae, and Eriocaulonaceae, which are besides further removed by their capsular fruit and pendulous ovules. To other monocotyledonous families the resemblances are merely of adaptive or vegetative characters. Some Commelinaceae and Marantaceae approach grasses in foliage; the leaves of Allium, &c., possess a ligule; the habit of some palms reminds one of the bamboos; and Juncaceae and a few Liliaceae possess an inconspicuous scarious perianth. There are about 300 genera containing about 3500 well-defined species.
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 multiplication of genera founded on slight characters, and from the description (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 inflorescence and bracts.
Robert Brown suggested two primary divisions - Paniceae and Poaceae, according to the position of the most perfect flower in the spikelet; this is the upper (apparently) terminal one in the first, whilst in the second it occupies the lower position, the more imperfect ones (if any) being above it. Munro supplemented this by another character easier of verification, and of even greater constancy, in the articulation of the pedicel in the Paniceae immediately below the glumes; whilst in Poaceae this does not occur, but the axis of the spikelet frequently articulates above the pair of empty basal glumes. Neither of these great divisions will well accommodate certain genera allied to Phalaris, for which Brown proposed tentatively a third group (since named Phalarideae); this, or at least the greater part of it, is placed by Bentham under the Poaceae.
The following arrangement has been proposed by Professor Eduard Hackel in his recent 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.
a Fertile glume and pale hyaline; empty glumes thick, membranous to coriaceous or cartilaginous, the lowest the largest. Rachis generally jointed and breaking up when mature.
1. Spikelets unisexual, male and female in separate inflorescences or on different parts of the same inflorescence. 1. Maydeae. 2. Spikelets bisexual, or male and bisexual, each male standing close to a bisexual. 2. Andropogoneae. li 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.
4. Oryzeae. B. Spikelets oneto indefinite-flowered; in the one-flowered the rachilla frequently produced beyond the flower; rachilla generally jointed above the empty glumes, which remain after the fruiting glumes have fallen. When more than one-flowered, distinct internodes are developed between the flowers.
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. Agrostideae. II. Spikelets more than one-flowered.
i. Fertile glumes generally shorter than the empty glumes, usually with a bent awn on the back.
7. Aveneae. ii. Fertile glumes generally longer than the empty, unawned or with a straight, terminal awn.
9. Festuceae. (3 Spikelets crowded in two close rows, forming a one-sided spike or raceme with a continuous (not jointed) rachis.
8. Chlorideae. y Spikelets in two opposite rows forming an equal-sided spike. 10. Hordeae. b. Culm woody, at any rate at the base, leaf-blade jointed to the sheath, often with a short, slender petiole.
II. Bambuseae. Tribe I. Maydeae (7 genera in the warmer parts of the earth). Zea Mays (maize, q.v., or Indian corn) (q.v.). Tripsacum, 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 ornamental plant. Coix LacrymaJobi (Job's tears) q.v. Tribe 2. Andropogoneae (25 genera, mainly tropical). The spikelets are arranged in spike-like racemes, generally in pairs consisting of a sessile and stalked spikelet at each joint of the rachis (fig. 18). Many are savanna grasses, in various parts of the tropics, for instance the large genus Andropogon, Elionurus and others. Saccharum officinarum (sugar-cane) (q.v.). Sorghum, an important tropical cereal known as black millet or durra. Miscanthus and Erianthus, nearly allied to Saccharum, are tall reed-like grasses, with large silky flower-panicles, which are grown for ornament. Imperata, another ally, 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. Vossia, 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 Saccharum, huge floating grass barriers. Elionurus, a widespread savanna grass in tropical and subtropical America, and also in the tropics of the old world, is rejected by cattle probably on account of its aromatic character, the spikelets having a strong balsam-like smell. Other aromatic members are Andropogon Nardus, a native of India, but also cultivated, the rhizome, leaves 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; FIG. 18. - A pair of a variety is used by the negroes in western spikelets of Andro- Africa for haemorrhage. Other species of pogon. the same genus are used as stimulants and cosmetics in various parts of the tropics. The species of Heteropogon, a cosmopolitan genus in the warmer parts of the world, have strongly awned spikelets. Themeda 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 (about 25 genera, 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. Amphicarpum, native in the southeastern United States, has fertile cleistogamous spikelets on filiform runners at the base of the culm, those on the terminal panicle are sterile. 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 savannas and campos. Panicum Crus-galli is a polymorphic cosmopolitan grass, which is often grown for fodder; in one form (P. frumentaceum) it is cultivated in India for its grain. P. plicatum, with broad folded leaves, is an ornamental greenhouse grass. P. miliaceum is millet (q.v.), and P. altissimum, Guinea grass. In the closely allied genus Digitaria, which is sometimes regarded as a section of Panicum, the lowest barren glume is reduced to a point; D. 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.
In Setaria and allied genera the spikelet is subtended by an involucre of bristles or spines which represent sterile branches of the inflorescence. 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 prehistoric 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 fig. 12); 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. Spinifex, a dioecious grass, is widespread on the coasts of Australia and eastern Asia, forming an important sand-binder. The female heads are spinose with long pungent 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 (16 genera, mainly tropical and subtropical). The spikelets 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 northeast Asia. The Indians collect the grain for food. Oryza sativa (rice) (q.v.). Lygeum Spartum, with a creeping stem and stiff rushlike 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 (6 genera, three of which are South African and Australasian; the others are more widely distributed, and represented in our 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 Mediterranean area) is grown for bird-food and sometimes as a cereal. Anthoxanthum 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 (fig. 19), which occurs throughout the temperate and frigid zones.
Tribe 6. Agrostideae (about 35 genera, occurring in all parts of the world; eleven 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 has a cylindrical spike-like inflorescence; P. pratense (timothy) is a valuable fodder grass, as also is Alopecurus pratensis (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 meadowgrasses. Calamagrostis and Deyeuxia are tall, often reed-like grasses, occurring throughout the temperate and arctic zones and upon high mountains in the tropics. Ammophila arundinacea (or 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 (about 24 genera, seven of which 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. Deschampsia 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 foddergrass. 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 (about 30 genera, 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 (about 83 genera, including tropical, temperate, arctic and alpine forms) many are important meadow-grasses; 15 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 mea'dowgrass. 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 pasturegrass. Poa, a large genus widely distributed in temperate and cold countries, includes many meadow and alpine grasses; eight species are British; P. annua (fig. 20) 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. alpine. 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; it is a native of the Falkland and certain antarctic islands where it is known as tussock grass. Glyceria fluitans, manna-grass, socalled 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 distributed but most abundant in the north temperate zone; B. erectus is a useful forage grass on dry chalky soil.
Tribe 10. Hordeae (about 19 genera, widely distributed; six are British). Nardus stricta (matweed), found on heaths and dry pastures, is a small perennial with slender rigid stem and leaves, it is a useless grass, crowding out better sorts. Lolium perenne, ray- (or by corruption rye-) grass, is common in waste places and a valuable pasturegrass; L. italicum is the Italian ray-grass; L. temulentum (darnel) contains a narcotic principle in the grain. 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.) (fig. 21), 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 I I. Bambuseae. Contains 23 genera, mainly tropical. See Bamboo.
III. Distribution. - Grasses are the most universally diffused of all flowering plants.
There is no district in which they do not occur, and in nearly all they are a leading feature of the flora. In number of species Gramineae comes considerably after Compositae and FIG. 19. - Phalarideae. Spikelet of Hierochloe. FIG. 20. - Poa annua. Plant in Flower; about a nat. size. 1, one spikelet.
FIG. 21. - Spike of Wheat (Triticum sativum). About nat. size.
Leguminosae, the two most numerous orders of phanerogams, but in number of individual plants it probably far exceeds either; whilst from the wide extension of many of its species, the proportion of Gramineae to other orders in the various floras of the world is much higher than its number of species would lead one to expect. In tropical regions, where Leguminosae is the leading order, grasses closely follow as the second, whilst in the warm and temperate regions of the northern hemisphere, in which Compositae takes the lead, Gramineae again occupies the second position.
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. Turfor meadowformation depends upon uniform rainfall. Grasses also characterize steppes and savannas, where they form scattered tufts. The bamboos 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, Chili, &c. The proportion of graminaceous species to the whole phanerogamic flora in different countries is found to vary from nearly 4th in the Arctic regions to about 2 nth at the Cape; in the British Isles it is about y2th.
The principal climatic cause influencing the number of graminaceous 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.
The distribution of the tropical tribe Bambuseae is interesting. The species are about equally divided between the Indo-Malayan region and tropical America, only one species being common to both. The tribe is very poorly represented in tropical Africa; one species Oxytenanthera abyssinica has a wide range, and three monotypic genera are endemic in western tropical Africa. None is recorded for Australia, though species may perhaps occur on the northern coast. One species of Arundinaria reaches northwards as far as Virginia, and the elevation attained in the Andes by some species of Chusquea is very remarkable, - one, C. aristata, being abundant from 15,000 ft. up to nearly the level of perpetual snow.
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 indica, Imperata arundinacea, Sporobolus indicus, &c., 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. The revision of the Australian species by Bentham well exhibits the wide range of the genera of the order in a flora generally so peculiar and restricted as that of Australia. Thus of the 90 indigenous genera (many monotypic or very small) only 14 are endemic, i extends to South Africa, 3 are common to Australia and New Zealand, 18 extend also into Asia, whilst no fewer than 54 are found in both the Old and New Worlds, 26 being chiefly tropical and 28 chiefly extra-tropical.
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 (Norway, 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, including 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 Pleuropogon Sabinii, of Melville Island.
Fossil Grasses
While numerous remains of grass-like leaves are a proof that grasses were widespread and abundantly developed in past geological ages, especially in the Tertiary period, the fossil remains are in most cases too fragmentary and badly preserved for the determination of genera, and conclusions based thereon in explanation of existing geographical distribution are most unsatisfactory. There is, however, justification for referring some specimens to Arundo, Phragmites, and to the Bambuseae. Bibliography.-E. Hackel, The True 'Grasses (translated from Engler and Prantl, Die natiirlichen Pflanzenfamilien, by F. Lamson Scribner and E. A. Southworth); and Andropogoneae in de Candolle's Monographiae phanerogamarum (Paris, 1889); K. S. Kunth, Revision des gramine'es (Paris, 1829-1835) and Agrostographia (Stuttgart, 1833); J. C. Doll in Martius and Eichler, Flora Brasiliensis, Ii. Pts. II. and III. (Munich, 1871-1883); A. W. Eichler, Bliithendiagramme i. 119 (Leipzig, 1875); Bentham and Hooker, Genera plantarum, iii. 1074 (London, 1883); H. Baillon, Histoire des plantes, xii. 136 (Paris, 1893); J. S. Gamble, " Bambuseae of British India " in Annals Royal Botanic Gardens, Calcutta, vii. (1896); John Percival, Agricultural Botany (chapters on " Grasses," 2nd ed., London, 1902). See also accounts of the family in the various great floras, such as Ascherson and Graebner, Synopsis der mitteleuropdischen Flora; N. L. Britton and A. Brown, Illustrated Flora of the Northern United States and Canada (New York, 1896); Hooker's Flora of British India; Flora Capensis (edited by W. Thiselton-Dyer); Boissier, Flora orientalis, &c. &c.
