GRIFFITHS THE GRAMA GRASSES. 



393 



species is Hearing maturity, the landscape is tinted, reddish brown by the abundant 

 spikes. In some sections it grows so abundantly that ranchers consider it profitable 

 to cut it for hay. So far as my own observation goes it never yields over one-half 

 ton to the acre of clean, current year's growth (PI. 75, B). In soutbern Arizona, 

 upon a rainfall of 12 to 18 inches, it grows about 8 inches in the growing season, July 

 to September. 



Bouteloua rothrochii is not a grass that withstands close pasturage well. Being a 

 short-lived perennial and a comparatively poorly rooted species, it is easily pulled 

 up and trampled out. The best growths of it today are found in those regions which 

 are at a considerable distance from water available for stock. 



It grows in bunches of a few culms to scores of culms, but so far as my observation 

 goes never makes any semblance of a turf. When it happens to grow on partly culti- 

 vated ground or in other favorable situations, the bunches may grow very large and 

 the outer culms of the stool become geniculate and even rooted at the joints. Some 



Fig. 46.— Bouteloua rothrockii. a, Spikelet; 6, 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. From type 

 specimen of B. micrantUa. 



of my specimens from cultivated ground in the upper Santa Cruz Valley of Sonora 

 show this form of the plant beautifully. 



My conception of the species is well illustrated by the specimens cited below. 

 Rothrock 691 and Griffiths 1556 have narrow spikes and smaller floral parts throughout 

 than the common typical form (PI. 75, A). 



Palmer's no. 244 and Pringle 221 very well represent the common form. Brandegee, 

 Culiacan, Mexico, October, 1904, and Palmer 204, 1534, and 1761, are geniculate 

 forms. Purpus 94 and Pringle, Arizona, in 1884 without number, represent forms 

 which have about the same relation to the typical species as B. arenosa has to B. 

 barbata. In these the awns are exceptionally long and the spike very wide. 



