392 



CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



long; lemma about 5 mm. long, loosely hairy, with long, white hairs, the four teeth 

 fringed or frayed into minute, hair-like teeth, with 3 scabrous awns, 1 to 1.5 mm. 

 long, palet 4-notched, two-nerved with two scabrous awns, hairy on the'edges and 

 laciniate at apex like the lemma, 4 mm. long; rudiment consisting of two rudimentary 

 florets, the lower composed of rudimentary scale-like glumes and three long, scabrous 

 awns (about 3 mm. long), subtended by a tuft of long, straight, white hairs, all borne 

 upon a naked stipe 1 mm. long; second rudiment consisting of scale-like glumes 

 upon a naked, short stipe; caryopsis ovate to obovate, about 1.25 mm. long, the 

 scutellum covering nearly the entire ventral surface. (Plate 75, A, B. Figures 

 45, 46.) 



There are large areas in southern Arizona and neighboring regions where this is 

 the most important grass of the stock ranges. It inhabits the upper mesas and the 



Fig. 45.— Bouteloua rothrockii. a, Spikelet; b, c, lemma and palet of first floret; d, e, rudimentary second 

 and third florets; /, two views and cross-section of caryopsis. a, Scale 7.5; b-f, scale 20. a-e , From type 

 specimen; /, from Griffiths 7185. 



gentle, brushless slopes of the foothills dining the summer rainy season, July to 

 September, often to the exclusion of all other species. It is a very characteristic 

 species, and although often appearing to intergrade with B. barbata it is very distinct 

 and easily distinguished in the field. There are many specimens, however, which 

 are very difficult to separate from B. barbata on the herbarium sheet. "When the 



Explanation of Plate 75.— A. An isolated tuft of Bouteloua rothrockii on desert east of Tucson, 

 Arizona. B. A large native crop of Bouteloua rothrockii in southern Arizona. This area had not been 

 pastured for five years. 



