GENERA OF GRASSES OF THE UNITED STATES. 161 



Some of the western species have plumose or feathery awns, those 

 of Stipa neo-mexicana (Thurb.) Scribn. being 4 to 8 inches long, 

 plumose to the second bend, those of the handsome S. speciosa Trin. 

 and Kupr. plumose below the single bend. A striking species of the 

 upper Mississippi Valley is Stipa spartea Trin. (fig. 93), called 

 porcupine grass and devil's darning needles. The rigid indurate 

 fruiting lemma is about three-fourths of an inch long, tapering be- 

 low into a very sharp hairy point, which acts like a barb, and termi- 

 nating above in a stout awn as much as 6 inches long. At maturity 

 the awn bends twice near the middle and becomes tightly twisted be- 

 low the first bend. Variations in moisture cause the awn to twist 

 and untwist, by which movement and by the aid of the sharp callus 

 it can penetrate the soil. Several other species have elongate awns, 

 such as S. avenacea L. of the eastern half of the United States and S. 

 comata Trin. and Rupr. of the western half, the latter species being 

 called needle-and-thread grass, because of the long flexuous upper 

 portion of the awns. /Stipa viridula Trin. and its allies have a nar- 

 row compact panicle and comparatively inconspicuous awns 1 or 2 

 inches long. One of these species, S. vaseyi Scribn., is called sleepy 

 grass, because of the narcotic effects sometimes produced upon horses 

 when they have fed upon it. Sleepy grass, found in New Mexico 

 and Colorado, is a stout grass 3 to 5 feet high, with a narrow panicle 

 as much as a foot long, the sheaths hairy at the throat. In S. tenuis- 

 sima Trin. (fig. 94) of New Mexico the fruit is very small, less than 

 3 mm. long. 



The species of Stipa are for the most part valuable forage plants. 

 The most important species on the ranges are S. viridula, S. minor 

 (Vasey) Scribn., and & lettermani Vasey. They are known as porcu- 

 pine grasses. All have narrow panicles. One of the Old World 

 species, S. tenacissima L., furnishes a part of the esparto or alfa 

 grass of Spain and Algeria that is used in the manufacture of paper 

 and cordage. 



77. AEISTIDA L., the needle grasses. 



Spikelets 1 -flowered, the rachilla disarticulating obliquely above 

 the glumes; glumes equal or unequal, narrow, acute, acuminate, or 

 awn-tipped ; lemma indurate, narrow, terete, convolute, with a hard, 

 sharp-pointed, usually minutely bearded callus at base, terminating 

 above in a usually trifid awn. 



Annual or perennial, mostly low grasses, with narrow, frequently 

 convolute blades and narrow or sometimes open panicles. Species 

 about 150, in the warmer regions of the world; 36 species in the 

 United States ; especially abundant in the Southwestern States, 



97769 19 Bull. 772 11 



