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."
Fertile glumes generally longer than the empty, unawned or with a straight, terminal awn.
I), the flowering glume having its dorsal rib prolonged into an awn (fig.
On pages 4 and 5 we describe a method for studying the remarkable hygroscopic awn of wild oat seeds.
The awn is also of use in burying the fruit in the soil.
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 outer glumes are acute and glabrous, the flowering glumes lance-shaped, with a comb-like keel at the back, and the outer or lower one prolonged at the apex into a very long bristly awn.
The pair of barren glumes (b) are separated from the flowering glume, which bears a long awn, twisted below the knee and feathery above.
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.
The wild oat, moreover, has a long stiff awn, usually twisted near the base.
Valuable characters for distinguishing genera are obtained from the awn.
When terminal the awn has three fibro-vascular bundles, when dorsal only one; it is covered with stomate-bearing epidermis.