GRIFFITHS THE GRAMA GRASSES. 



397 



unfavorable conditions sometimes reduced, in stunted plants, to 2 to 4; spikes pedun- 

 culate, the peduncles about 1 mm. long, these, together with the rachis densely white- 

 hairy over the entire surface or only on the angles, the pubescence diminishing in quan- 

 tity distally to only scattering hairs upon the distal prolongation of the rachis; spikelets 

 2 to4, the lowermost more or less aborted, loosely arranged, about 2 mm. apart, consisting 

 of a perfect floret and a rudiment, this reduced or usually absent in the lower spikelet; 

 first glume 1.5 to 2 mm., the second 5 to 6 mm. long, minutely scabrous-keeled, both 

 narrow, acuminate; lemma with three, very short, nearly equal, minutely scabrous 

 awns, pubescent, mostly oil the 3 nerves, 6 to 8 mm. long; palet smooth, with two 

 very short, very minutely scabrous awns, about 5 to 6.5 mm. long; rudiment consisting 

 of 3 long, scabrous awns upon a 

 hairy stipe, 1 mm. long, bearing a 

 tuft of longer hairs at its apex, the 

 central awn slightly glumaceous 

 at base and about 2 mm. shorter 

 than the lateral, the whole rudi- 

 ment being about 7 mm. long; 

 caryopsis cylindrical-oblong, 3 

 mm. long, 0.4 mm. wide, grooved 

 on the dorsal surface, the scute 1- 

 ium about three-fourths the 

 length of the ventral surface. 

 (Plate 77, A, B. Figure 49.) 



The species inhabits the drier 

 desert mesas and foothills from 

 western Texas to the Pacific coast 

 and is as variable as the seasons 

 and conditions in this most vari- 

 able region. Often it will mature 

 its seed upon a single culm 1 or 

 2 cm. high, or it may produce 

 plants with 50 culms 70 cm. in 

 height. Often the spikes are not 

 over 3 or 4 mm. in length and 

 produce but a single seed, while 

 in Palmer 51 some spikes are fully 

 2.5 cm. in length. The habits 

 of growth of this species particu- 

 larly fit it for a desert habitat. 

 It is an annual, producing an 

 abundance of seeds which have 

 their special methods of dis- 

 semination by burrowing into the ground and thus enable it to persist where less 

 aggressive plants fail. When mature the spike, together with the short, sharp-pointed 

 peduncle, drops off entire. This callus-like peduncle is thickly beset with short, 

 stiff, retrosely arranged hairs, which, together with the awns of the spikelets and the 

 recurved awn-like prolongation of the rachis, assist in the burial of the seed or its 

 adhesion to anything with which it may come in contact. 



This is doubtless one of the least valuable of the abundant species of this genus. 

 Usually no grazing is done upon it during the time that it is. ripening, and, where very 



Explanation of Plate 77. — A. A very large plant of Boutcloua aristidoides from a favorable depression 

 In desert mesas east of Tucson, Arizona. B . A nearly pure stand of the same upon the desert mesas north 

 of the Santa Rita Mountains of Arizona, in a very favorable season. 



Fig. 49. — Boutcloua aristidoides. a, Spikelet; 6, c, lemma and 

 palet of first floret; d, rudiment; e, two views and cross sec- 

 tion of caryopsis. a, Scale 7.5; b-e, scale 10. From Griffiths 

 7308. . 



