No. 22. 



ARISTIDA ARIZONICA Vasey. 



Rootstocks unknown. Roots rather stout, simple above, with a thin bark. 



Culms erect, simple, closely tufted, 1 to 2| feet high, glabrous. 



Leaves all radical or originating near the base of the culm; sheaths imbricated, 

 glabrous, sometimes 6 inches long ; blades commonly 3 to 5, sometimes 10 inches 

 long, glabrous, involute when dry ; ligules a minute dense ring of hairs. 



Inflorescence an exsert-pedunculate panicle 4 to 12 inches long; branches short, 

 rarely exceeding 2 inches, nearly erect; spikelets singly sessile or short pedunculate. 



Spikelets (excluding the awns) i to f inch long, awl-shaped, nearly terete. 



Glumes 3 ; first linear, two-thirds the length of the spikelet, membranaceous, 

 1-nerved, aristate, acute with 2 minute accessory teeth, the midnerve and awn- 

 point scabrous ; second as long as the spikelet, narrower than the first, similar to it. 

 the awn-point a little longer ; third (flowering) glume coriaceous, as long as the 

 second, closely involute, very slender, scabrous ; apex twisted two or three times, 

 then produced into 3, straight, terete, not twisted, scabrous awns diverging when 

 dry, usually a little longer than the spikelet ; middle one slightly the longest ; 

 rachilla slightly elongated between the second and third glumes, densely villous. 



Flower single, hermaphrodite. Palet minute, nearly 1 line long. Lodicules 2, 

 lanceolate, as long as the palet. Stamens 3, anthers linear nearly 1 line long. 

 Stigmas 2, cylindrical. 



Grain awl-shaped, about 4 lines long, closely enwrapped in the flowering glume; 

 rachilla disarticulating obliquely just atiove the second glume. 



PLATE XXII ; a, spikelet, empty glumes spread open ; b, the same empty 

 glumes removed, flowering glume open to show the palet and stamens. The 

 stigmas are not shown. 



A common grass of the mesas and hills, which early in the season furnishes 

 good grazing for animals. 



