vil] DISSEMINATION 125 
fruits of Agrostis easily fall and are scattered by the wind, 
but in many cases the glumes (Holcus) or pales (Briza) 
are expanded and serve as “wings” offering extensive 
surfaces to the wind. In Arundo, Calamagrostis, Avra, 
&e., fine silky hairs attached to the rachilla serve a 
similar function, reminding us of the coma of true seeds 
and the pappus of Composites. In Hordeum jubatum of 
the prairies, the axis breaks up and the disarticulated 
portions with their attached tufts of fruits are blown 
away by the wind, and something similar occurs in our 
own H. murinum to a less extent. In the exotic Spinifex 
whole heads of fruits are thus detached and _ blown 
over the sands as “tumble weeds.” 
In Stipa pennata we have an example of perhaps 
the most complex of all such adaptations: the exceedingly 
long awn terminating the palea is plumose at the upper 
end and twisted below, and the hard sharp rachilla at the 
base of the fruit is furnished with short, stiff hairs directed 
upwards. The plumed awn serves as a wind surface, the 
whole fruit flying lke an arrow through the air. The 
stiff hairs below serve to fix the lower end between 
particles of soil, and by their alternate drying and wetting, 
the warping of these and of the twisting and untwisting 
awn drives the sharp base into the soil. (Fig. 42.) 
Similar mechanisms exist in Avena and others. 
These bristles and awns also subserve dissemination 
in other ways, especially by clinging to the wool and fur 
of sheep and other animals, and cases occur where the 
twisting awns and reflexed hairs on the hard pointed 
fruit-base drive the latter into the bodies of sheep with 
fatal effects—e.g. Stipa capillata in Russia, S. spartea in 
