No. 18. 



SPOROBOLUS INTERRU'PTUS Vasey. (Vilfa interrupta Vasey in 

 Special Report No. 63, Department of Agriculture, 1883.) 



Plant perennial, with densely tufted, bulbous base. 



Culms erect, not branching, smooth, terete, 1 to 2 feet tall. 



Leaves; radical and from radical shoots, numerous, with scarious, often red- 

 dish, glabrous or pubescent, tapering sheaths, and mostly flat, smooth or loosety 

 pubescent erect blades, 3 to 5 inches long; of culm 2 or 3; sheaths longer than in- 

 ternodes, close, open above, smooth blades, mostly involute, erect, 1 line wide, 1 

 to 3 inches long; ligule a narrow ciliate fringe. 



Inflorescence a narrow, open or interrupted, erect panicle, 4 to G inches long; 

 rachis flexuous, branches alternate or verticillate below, in twos or threes above, 

 1 to 2 inches long. 



Spikelets short-pedicellate, narrow, 1- or 2-flowered, 2 to 3 lines long; first 

 glume lanceolate, acute, carinate, scarious, smooth, 1 -nerved. 1 to l£ lines long; 

 second glume ovate-lanceolate, nearly twice as large; floral glume ovate-lanceo- 

 late, acute, membranaceous, smooth, 1-nerved or obscurely 3-nerved above, 2 to .3 

 lines long; palet broadly lanceolate, bifid at apex, thin, hyaline, smooth, slightly 

 2-keeled, 2 lines long; anthers 3, long, reddish purple; stigmas 2, greenish, 

 plumose. 



Grain, no mature grains seen. 



Plate XVIII; a, spikelet enlarged; b, empty glumes; c, floral glume; d, 

 palet; 2, typical panicle. 



Arizona. 



