Further important distinctive characters are obtained from the absence or presence of awns, and the peculiarities—length, Fig. 49.
The awns are furnished with stiff points, all turning towards one end, which extend when moist, and shorten when dry.
The reason of this is that with the removal of the awns the corns pack more closely together.
The first rain or heavy dew straightens out the awns, which are twisted again as they dry.
The chaff and awns of all are hygroscopic; that is, are changed by differences caused by variation of moisture in the air.
In both the fruits fall out freely from the glume, and in the latter the awns are three-pronged and shorter than the grain.
All grow in sterile, dry soil, and all ours have the awns naked and persistent, and flower late.
Outer glumes unequal, often bristle-pointed; the flowering glume tipped with three awns; the palet much smaller.
The long yellow tails are the awns, which resemble delicate feathers.
The pili grass (Heteropogon contortus) is also noxious, for its awns get badly entangled in the wool of sheep.