GENERA OF GRASSES OF THE UNITED STATES. 269 



has narrower blades than plants of sorghum of the same height. 

 The characteristic difference is the presence of the creeping rhizomes 

 in the former. Johnson grass is a native of the Mediterranean 

 region, but is now widely distributed in the warmer parts of 

 America. In the United States it is common throughout the 

 South, where it is often a troublesome weed. It is an ex- 

 cellent and much-used forage grass, but the difficulty of eradicating 

 it from ground that it has once occupied offsets its forage value. 

 Johnson grass has become an especially pernicious weed on the 

 Black Lands of Alabama and Texas. 1 



The sorghums and Johnson grass sometimes produce hydrocyanic 

 acid in sufficient abundance, especially in second growth, to poison 

 grazing animals. 



134. SORGHASTETJM Nash. 



Spikelets in pairs, one nearly terete, sessile, and fertile, the other 

 wanting, only the hairy pedicel being present; glumes coriaceous, 

 brown or yellowish, the first hirsute, the edges inflexed over the 

 second; sterile and fertile lemmas thin and hyaline, the latter ex- 

 tending into a usually well-developed bent and twisted awn. 



Perennial, erect, rather tall grasses, with narrow flat blades and 

 narrow terminal panicles of one to few jointed racemes. Species 

 about 10 in the warmer parts of the Western Hemisphere, and a 

 few in Africa; 3 species in the United States east of the Rocky 

 Mountains. 



Type species : Andropogon avenaceus Michx. 



Poranthera Raf., Bull. Bot. Seringe 1: 221, 1830, not Rudge, 1811. "Andro- 

 pogon nutans -[L.] et ciliatus [Ell.])" are cited. These names apply to the 

 same species, Sorghastrum nutans (L.) Nash. 



Sorghastrum Nash, in Britton, Man. 71. 1901. Only one species described. 

 S. avenaceum (Michx.) Nash. 



Chalcoelytrum Lunell, Amer. Midi. Nat. 4 : 212. 1915. The name proposed to 

 replace Sorghastrum Nash, which, being built on Sorghum, is considered unde- 

 sirable. 



The units of the inflorescence are racemes reduced to one or two 

 joints, or in Sorghastrum nutans sometimes four or five. The slen- 

 der, villous rachis disarticulates at the top of each joint, the spikelets 

 falling with two villous stalks attached, one the rachis joint, the 

 other the pedicel of the obsolete sterile spikelet. The articulation is 

 more or less oblique, leaving a bearded blunt callus or, in some South 

 American species, a long, sharp callus. In S. nutans the racemes not 

 infrequently occur in pairs with a sessile spikelet in the fork, that 

 is, the pedicel of the sterile spikelet of the lowest joint has been re- 

 placed by a short raceme of one or two joints. 



1 For methods of eradication, see Cates and Spillman, U. S. Dept. Agr., Farmers' Bull. 

 279. 1907. 



