IMPORTANT RANGE PLANTS. 9 



blue bunch grass in the autumn on account of the new growth result- 

 ing from the autumn precipitation. As a whole, it is a palatable 

 and nutritious grass, and, occuring as it does in abundance over well- 

 drained lands of medium elevation, its economic value is high. 



Porcupine Grass. 

 (Stipa occidentalis .) 



The genus Stipa includes a large number of perennial grasses dis- 

 tributed throughout the world. Approximately 30 species are found 

 in the United States, mainly in the West. Many are valuable for 

 grazing purposes, while others are cut for hay. 



Porcupine grass (Plate IV) is a perennial bunchgrass with coarse, 

 spreading, and deeply penetrating roots, capable of withstanding an 

 unusual amount of abuse. The leaf blades are mainly basal, some- 

 what involute (rolled inward), those of the culms shorter than the 

 basal ones, all rather rough and somewhat rigid, the sheaths shorter 

 than the internodes. The panicle is somewhat contracted, about 4 

 inches long; the spikelets one-flowered; the floret cylindrical, pubes- 

 cent throughout, with a sharp-pointed bent callus at the base. The 

 empty glumes are subequal, membranaceous, and the lemmas or 

 flowering glumes, which completely inclose the palets, are brownish 

 when mature and bear awns from 1 to 1^ inches long, twice bent and 

 strikingly plumose or densely pubescent to the second joint or knee. 



To judge from the tufted habit of growth and the involute leaf 

 blades and their texture, it might be expected that the moisture 

 requirements of porcupine grass would be about the minimum of the 

 species studied. An average of all moisture tests, however, showed 

 that pronounced wilting resulted in the characteristic soil type where 

 the water content varied from 9.5 to 11.5 per cent. In a soil contain- 

 ing 8 per cent of moisture a specimen failed to recover its form and 

 subsequently died. Fearing that some error had' crept into the 

 results first obtained, several additional tests were conducted, but 

 the later results agreed with the first. 



Porcupine grass inhabits only well-drained soils in open, exposed 

 situations in association with mountain bunchgrass, alpine redtop, 

 short-awned bromegrass, and other species. Its seedlings develop 

 somewhat deeper roots than do the majority of the species, and be- 

 cause of this fact they have thrived during dry periods in certain 

 places where other species able to exist in soil of slightly lower water 

 content have died. 



The flower stalks are all produced within a month or less after the 

 first ones appear. They begin to show about July 15. The seeds 

 are, as a rule, well matured by September 10. In 1909, however, 

 they had ripened and were disseminated by August 30. Dissemina- 

 tion follows almost immediately upon maturity. 

 85154°— Bull. 545—17 2 



