134 A TEXT-BOOK OF GRASSES 
hairs are found on the lemmas in Arundo, on the rachilla 
joints in Phragmites, on the whole spikelet in Saccharum 
(Fig. 14), on the awns in Stipa pennata L. of Europe and 
S. speciosa Trin. & Rupr. of California, on the long pedi- 
cels of S. elegantissima Labill. of Australia. Awns and 
bristles often aid dispersal by increasing the surface. Clus- 
ters of spikelets, with their surrounding involucre of bris- 
tles, fall away from the rachis, the bristles catching air 
currents. Long-awned species of Horde, with disarticu- 
lating rachis, are adapted to wind dispersal. Sitanion and 
Hordeum are good examples of this. The joints of Sitan- 
ion, with their numerous long awns spreading in all direc- 
tions, are sent whirling across the open grassland in the 
western states. In many species of Aristida (Fig. 35) the 
3 awns spread horizontally or are somewhat reflexed. On 
the Great Plains it is common to see, at the proper season, 
the fruits of these grasses being hurled along by the high 
winds, the sharp-pointed callus to the front ready to catch 
in the wool or hair of animals. From such fruits it is an - 
easy transition to wing-fruits, in which the increased sur- 
face is furnished by wings, appendages or sterile parts. 
The inflated lemma of Briza, the winged crests on the 
lemmas of Phalaris, the group of sterile spikelets of 
Phalaris paradoxa, all aid in dispersal. In some grasses 
the whole inflorescence breaks away and becomes a 
“tumble-weed.”’ The panicles of Panicum capillare L., 
Agrostis hiemalis (Walt.) B. 8. P., Chloris verticillata Nutt. 
and Eragrostis pectinacea (Michx.) Nees, are familiar exam- 
ples. At maturity the panicles separate from the plant 
and roll over the surface of the ground before the wind, 
the widely spreading branches making the whole very 
light. The small fruits are dropped here and there as the 
panicle travels. The inflorescence of Schedonnardus panic- 
