ECOLOGY 135 
ulatus (Nutt.) Trel., a common grass in Texas, consists 
of several slender distant spikes arranged along a slender 
axis. After flowering, the central axis greatly elongates 
becoming at the same time somewhat spirally coiled. The 
lateral spikes also elongate. There results a loose cylin- 
drical skeleton that can be easily rolled along by the wind 
after it disarticulates from the parent plant. 
An indirect method of adaptation for wind dispersal 
is illustrated by the fruits of Eleusine indica (L.) Gaertn. 
and Sporobolus indicus (L.) R. Br. The pericarp of these, 
when wet, develops a mucilage by which the seeds are 
enabled to stick to leaves or other objects that may be 
blown about by the wind. In so far as they are able to 
stick to birds or other animals they are adapted also to 
this method of dispersal. 
169. Dispersal by animals—Some grasses are adapted 
to dispersal by the aid of animals. The species of Cen- 
chrus (Fig. 27) produce burs made up of a group of con- 
nate branchlets armed with retrorsely barbed spines. 
The bur-like spikelet of Nazia produces hooks on the 
second glume. The callus of the fruits of Aristida (Fig. 
35), Stipa (Fig. 36), Heteropogon, Chrysopogon and 
other needle-fruits of this kind, is sharp-pointed and armed 
with retrorse hairs. Such fruits readily bore into the 
coats of animals. The fruits of certain Hordes, with 
disarticulating rachises, have been mentioned above 
under adaptations for wind dispersal Usually in these 
fruits, the point of the rachis-joint is sharp and the awns 
are antrorsely scabrous (the teeth pointing forward). 
They thus are adapted to working their way into the coats 
of animals. In Panicum glutinosum of the American 
tropics the spikelets are viscid and readily attach them- 
selves to a passing body. 
