•■* 



No. 21. 

 TRISETUM HALLII Scrib. 



Plant annual. 



Culms slender, not branching, geniculate, ascending, scabrous, 1 to 1| feet 

 tall. 



Leaves; radical, few and small; of culm 3 or 4; sheaths usually exceeding 

 internodes, open above, somewhat scabrous: blades flat or slightly involute, taper- 

 pointed, scabrous on both sides, 1 to 1^ lines wide, 3 to 5 inches long; ligule mem- 

 branaceous, truncate, lacerate, 1 line long. 



Inflorescence a rather narrow, contracted, close, erect, or flexuous panicle, 4 to 

 6 inches long, included or but slightly exserted; branches mostly in threes, slightly 

 spreading, i to 1 inch long, bearing pedicellate' spikelets; crowded along their 

 entire length. 



Spikelets obovate, 3- to 4-flowered, upper one sterile, small and abortive, 2 to 

 2i lines long; first gltime narrowly lanceolate, acute, herbaceous, hispid on keel, 

 3-nerved, ^ line wide, 2 lines long; second glume oblong-lanceolate, 5-nerved, twice 

 as wide as the first; internode of rachilla slender, curved, articulate above, smooth, 

 \ line long; floral glume lanceolate, with two attenuate teeth at apex, scarious, 

 scabrid, li to 2 lines long, obscurely 3-nerved, mid-nerve excurrent in a slender 

 awn 2 to 4 lines long; palet narrowly linear, lanceolate when spread out, thin, 

 2-keeled, 1 line long, not inclosed in floral glume. 



Grains, none found in the specimens examined 



Plate XXI; a, spikelet; b, empty glumes; c, floral glume; d, palet. 



This differs from T. interruptum Buckl. in its heavier panicle, shorter teeth of 

 the flowering glume, and the higher insertion of the awn. Both species occur in 

 Texas, 



