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. 11). The axis is often continued beyond the last flower or glume as a bristle or stalk.
| Fig. 11.—Spikelet of Reed (Phragmites communis) opened out. |
| a, b, Barren glumes. c, c, Fertile glumes, each enclosing one flower with its pale d. Note the zigzag axis (rhachilla) bearing long silky hairs. |
Involucres or organs outside the spikelets also occur, and are formed in various ways. Thus in Setaria (fig. 10), 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) the pectinate involucre which conceals the spikelet is a barren or abortive spikelet. 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. 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.
| Fig. 12.—Spikelet of Cenchrus echinatus enclosed in a bristly involucre. |
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.
| Fig. 13.—Flowers of Grasses (enlarged). 1, Piptatherum, with the palea p; 2, Poa; 3, Oryza; l, Lodicule. |
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, 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 (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 capitala, 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, 1 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, Luziola). 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, 1), 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.
| Fig. 14.—Pistils of grasses (much enlarged). 1, Alopecurus; 2, Bromus; 3, Arrhenatherum; 4, Glyceria; 5, Melica; 6, Mibora; 7, Nardus. |