PANICE^ 



187 



222. Cenchrus L. — Sand-bur. Bur-grass. Low often 

 weedy grasses, usually annuals, the spikelets, singly 

 or 2 or 3 together, inclosed by a bur formed of 

 coalesced bristles or 



branchlets, these 

 usually retrorsely 

 barbed. The burs are 

 borne in a spike or 

 raceme, and, detach- 

 ing easily at maturity, 

 are transported by 

 animals. The spikelets 

 remain permanently 

 inclosed in the bur, 

 germination of the 

 seed taking place 

 within it. The first 

 glume is much re- 

 duced, sometimes 

 wanting. The com- 

 mon sand-bur of the 

 United States is Cen- 

 chrus carolinianus 

 Walt. (Fig. 27). The 

 one with larger burs 

 found among the sand- 

 dunes of the Atlantic 

 seacoast is C. 

 tribuloides L. 



223. Stenotaphrum 

 Tnw.— The best- 

 known species of this Fiq. 27. Cenchrus carolinianus. Upper 



, _, portion of plant with inflorescence, X%; 



genus IS the St. spikeiet, x7. 



