In both the fruits fall out freely from the glume, and in the latter the awns are three-pronged and shorter than the grain.
Each spikelet contains a solitary flower with two outer small barren glumes, above which is a large tough, compressed, often awned, flowering glume, which partly encloses the somewhat similar pale.
Within these are six stamens, a hairy ovary surmounted by two feathery styles which ripens into the fruit (grain), and which is invested by the husk formed by the persistent glume and pale.
5 is a spikelet of the female inflorescence, consisting of two outer glumes, the lower one ciliated, which enclose two florets - one (a) barren (sometimes fertile), consisting of a flowering glume and pale only, and the other (b) fertile, containing the pistil with elongated style.
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 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 form of the flowering glume is very various, this organ being plastic and extensively modified in different genera.
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.
Io) below and interposed between the floral glume and the basal pair.
The axis is often continued beyond the last flower or glume as a bristle or stalk.
B, ing glume; p, Barren glumes; f, flower pale.
Ing glume; p, pale.
The pair of barren glumes (b) are separated from the flowering glume, which bears a long awn, twisted below the knee and feathery above.
Glume (" chaff "of cereals).
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.
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 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.
A Fertile glume and pale hyaline; empty glumes thick, membranous to coriaceous or cartilaginous, the lowest the largest.
Li Fertile glume and pale cartilaginous, coriaceous or papery; empty glumes more delicate, usually herbaceous, the lowest usually smallest.
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.
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.
Each flower consists of an outer or lower glume, called the flowering glume, of the same shape as the empty glume and terminating in a long, or it may be in a short, awn or "beard."
D, Flowering glume or lower palea.
- Spikelet of Oat (Avena sativa) laid open, showing the sterile bracts gl, gl, or empty glumes; g, the fertile or floral glume, with a dorsal awn a; p, the pale; fs, an abortive flower.