Grasses

by H. Marshall Ward

CHAPTER VI.
GRASSES IN FLOWER.

When the flowering shoot of a grass pushes up into the light and air from the enveloping leaves, it forms a more or less branched collection of flowers known as the Inflorescence, and in all our grasses this inflorescence consists of a principal stalk, haulm or culm, on which shorter stalks—branched or not—are arranged. The mode of branching is usually such that the youngest branches are nearest the top, and the oldest nearest the bottom. It is evident at once, on comparing the Moor Mat-grass (Nardus), Vernal-grass (Anthoxanthum), Cock’s-foot (Dactylis), Meadow-grass (Poa) that considerable differences exist as to the extent of this primary branching of the inflorescence.

In Nardus (Fig. [2]) we find a number of long cylindrical-tapering bud-like structures each seated on one side of the principal stem, and one over the other: in the Vernal-grass and Cock’s-foot we find tufts of such bud-like structures closely crowded round the upper end of the principal stalk, the whole forming an elongated tuft of tufts: in the Poa we find a number of radiating, slender, long branches springing from the principal stalk, and each of these ramifies again, and yet again, until each of the ultimate hair-like branches bears one of the bud-like structures. See also Catabrosa (Fig. [4]).

Fig. 29. A spikelet of Festuca elatior, var. pratensis, from which the glumes and one palea (the outer) have been removed to show the flower in situ (× 12). The two lodicules are in front: the inner palea behind. Strasburger.

The first thing for the student to apprehend is the nature of the bud-like structures referred to.

Each of these is in itself a small tuft or bud of leaflike organs or scales arranged on a short twig (Rachis, Rachilla), as it were, and is called a Spikelet, and the true flowers of the grass are contained in the angles between the scales—the scales being popularly known as "chaff": technically as Glumes and Paleæ.

In order to understand the structure of a spikelet the student should carefully dissect a large one, such as that of an Oat (Fig. [1]). Proceeding from outside, he will find two large scales, like two boats, fixed below to the stalk (rachis) one just below the other, and shutting together as if hinged. These are called the glumes—the inner and outer glume respectively—and they enclose the rest of the spikelet.

Fig. 30. Diagram of a spikelet of a grass as it would appear if the internodes between each set of organs were elongated. g¹ lower and g² upper glume. P lower and p upper palea of the second oldest flower F². f a barren flower represented only by the axis and paleæ. Above it a single palea and the termination of the axis (a) of the spikelet.