Inside them the axis or stalk (rachis) is continued for a short distance only and on its sides are hinged two other pairs of more or less boat-shaped scales, smaller and more delicate than the glumes, and known as the pales (paleæ), while a third pair of still smaller pales is fixed to the end of the axis. In each case one smaller and more delicate inner palea is hinged just inside its more obvious outer palea. In the closed condition of the spikelet each of the three pairs of pales is shut together, and pressed close to the axis, and the pair of glumes shut in the whole.
On opening each of the lower pairs of pales we find a flower inside; but the terminal pair usually contain only the barren end of the axis. Hence the latter is barren and the former are fertile.
Each fertile flower is found on careful dissection to consist of a small swollen Ovary, or young grain, covered with silky hairs and with a couple of delicate plumes (the Stigma) at its apex, and three long and slender Stamens; while the magnifying glass will show two tiny scales at the base—the Lodicules. All our ordinary grasses have their flowers thus constructed—a pair of lodicules, three dangling stamens and an ovary with a feathery two-plumed stigma: each such flower is also enclosed in its pair of pales, and the several pairs of pales of each spikelet, with their contents, are enclosed in the pair of glumes (Figs. [29]-32).
Returning now to the inflorescence. It is clear that we have to distinguish between the entire branched total Inflorescence, and the Spikelets or partial inflorescences of which it is composed. In Botany it is agreed to call any inflorescence consisting of a stalk or axis on which the flowers are arranged without stalks—i.e. sitting directly on it—and so that the youngest are above and the older below, a Spike, and each spikelet is a little spike.
| Fig. 31. Diagram of a spikelet of Wheat dissected (× about 5) showing—from below upwards—the two glumes, two paleæ, two lodicules, three stamens, and the ovary of the typical grass. Oliver. |
Fig. 32. Diagram of a spikelet of
Anthoxanthum dissected (× about
8), and showing—from below
upwards—two outer and two
(awned) inner glumes, two paleæ,
two stamens, and the ovary.
There are no lodicules. Oliver. |
On looking at the total inflorescence of the Nardus we see that we have a number of spikelets seated on the sides of an axis: this is then a spike of spikelets, or, shortly, a Spike[9] (Fig. [5]). Mibora and Lepturus afford other examples. In Panicum, Cynodon (Fig. [2]) and Spartina we have groups of such spikes.
The Poa inflorescence is, however, different. It consists of a loose branched system of spikelets. Botanists term such a loosely branching system, where each branch ends in a flower, a panicle: here then we have a panicle of spikelets, or, shortly, a Panicle. Aira, Agrostis, Calamagrostis, Avena, Catabrosa (Fig. [4]) and many others afford further examples.
In Dactylis we have a condition of affairs between the two extremes given: the inflorescence is not so close a spike as Nardus, and not so open a panicle as Poa—it is rather a spike-like panicle, partaking of the nature of both. A special type of this (Foxtail) occurring in certain grasses—e.g. Phleum, Alopecurus, Phalaris and Lagurus,—is so characteristic as to be worth noting (Fig. [3]).
There is also another aspect of these inflorescences which is not without interest as showing how diagnostic characters may be obtained from purely external features, easily observed in the field. We have seen that in Nardus the spikelets are arranged on one side only of the rachis, or main axis, so that about three quarters of the circumference of the latter is bare; whereas in Lolium—with which Agropyrum and Brachypodium agree in this respect—the spikelets are on opposite sides, leaving the intervening two quarters, i.e. half its surface, of the circumference of the axis naked.