28 



on the back, 2-toothed at the apex, the teeth awn-like; calkis rather densely 

 bearded, hairs stiff, the longer ones 3 to 4 mm. long; awn arising below the 

 apex of the flowering glume, slender, geniculate, twisted below the geniculation, 

 about 17 mm. long. Palea as long as the fiowering glume, rather rigid, margins 

 rounded, infiexed, apex subhyaline, the two nerves extending into subulate, awn- 

 like teeth. 



Cool, mossy cliffs. Sierra de Tepixtlan, near Cuernavaca, State of Morelos, altitude 

 2,.300 m., 8018 C. G. Pringle, February 5, 1899. 



*Avena stipoides Scribn. U. S. Dept. Agr. Div. Agros. Cir. 19: 4 (January, 1900). 



A very slender, erect, somewhat wiry perennial, 5 to 6 dm. high, with linear, erect 

 leaves and loosely few-flowered, 

 simple panicles 5 to 10 cm. long. 

 Sheaths shorter than the inter- 

 nodes, very minutely strigose- 

 pubescent; ligule 5 to 8 mm. 

 long, hyaline; leaves involute- 

 setaceous, at least when dry, 1 to 

 2.5 mm. wide, 1 to 2 dm. long, 

 scabrous. Spikelets about 12 

 mm. long, exclusive of the awn; 

 empty glumes unequal, thin, 

 scarious, 1-nerved, acute, the 

 first about 4 mm. long, the 

 second 5.5 mm. long; flowering 

 glume 11 mm. long, 5-nerved, 

 slightly roughened on the nerves 

 above, 2-toothed at the apex, 

 teeth awn-like, awned on the 

 back below the 2-toothed apex ; 

 awn geniculate, twisted below, 

 attached about two-thirds above 

 the base, 12 to 14 nun. long. 

 Palea equaling the glume, the 

 two nerves extending into subu- 

 late, awn-like teeth. Callus hairs 

 1 to 2 mm. long. 



Sierra de San Felipe, State of Oaxaca, 

 altitude 3,130 m., 4905 C. G. 

 Pringle, September 19, 1894; 923 

 C. L. Smith, August 28, 1894. 

 Distributed as Muhlenhergia sti- 

 poides Trin. 



This grass is closely allied to Arena 

 micrantha, 8018 C. G. Pringle, 

 but is at once distinguished by 

 its shorter empty glumes. 



The strictly 1-flowered spikelets of this and the last species is a character which 

 would lead one to place these grasses in the tribe Agrostide.r; but the densely 

 hairy callus and rather rigid 5-nerved flowering glume, which is deeply 2-toothed 

 at the apex, and the dorsal, geniculate, and twisted awn formed by the union of 

 three of the nerves suggest relationship with Arena, as does the character of the 

 emjity glumes, and these species are tentatively placed in that genus. 



TRISTACHYA AVENACEA (Presl) Scribn. & Merrill, n. comb. {Monopngim 

 arenaceus Presl, Rel. liaenk. 1: 335, t. 44 (1830); Tristachya mexicana Kunth, 

 Enum. PL 1: 308 (1833).) 



Fig. 6. — Arena micrantha Scribn. 



