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 Sporoholus 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 Hordese, 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. 



