GRAMINE^E. (GRASS FAMILY.) 641 



50. TBISETUM, Persoon. TRISETUM. (PL 12.) 



Spikelets 2 - several-flowered, often in a contracted panicle; the lower palet 

 compressed-keeled, of about the same membranaceous texture as the glumes, 

 bearing a bent or flexuous (rarely twisted) awn below the sharply 2-toothed or 

 2-pointed apex (whence the name, from tris, three, and seta, a bristle) : other- 

 wise nearly as in Avena. Ours are perennials. 



1. T. Sllbspicatum, Beauv., var. m611e. Minutely sojl-downy; panicle 

 dense, much contracted, oblong or linear (2' -3' long) ; glumes about the length 

 of the 2-3 smooth flowers ; awn diverging, much exserted. (Avena mollis, 

 Michx. ) Mountains and rocky river-banks, N. New England to Wisconsin, 

 and northward. July. About 1 high : leaves flat, short. (Eu.) 



2. T. paltistre, Torn Smooth; panicle rather long and narrow (5' long), 

 loose, the branches capillary; spikelets flat (3" long); glumes shorter than the 

 t\vo smooth lanceolate flowers, of which the upper is on a slightly naked joint of 

 the rhachis, and bears a slender spreading or bent awn next the short 2-pointed 

 tip, while the lower one is commonly awnless or only mucronate-pointed. (Avena 

 palustris, Michx. Aira pallens, Muhl.) Low grounds, Southern New York to 

 Illinois, and southward. June. Culm slender, 2 -3 high : leaves flat, short. 

 Spikelets yellowish-white, tinged with green. 



51. AIRA, L. HAIR-GRASS. (PI. 12.) 



Spikelets small, in an open diffuse panicle, of 2 perfect flowers and often with 

 the pedicel or rudiment of a third, all usually shorter than the membranaceous 

 keeled glumes, and hairy at the base ; the upper remotish. Lower palet thin 

 and scarious, 2-cleft or else truncate and mostly denticulate or eroded at the 

 summit, bearing a slender bent or straight awn on its back, commonly near 

 its base. Stamens 3. Styles plumose to the base. Ovary glabrous. Grain 

 oblong. (An ancient Greek name for Darnel.) 



1. DESCHAMPSIA, Beauv. Lower palet delicately 3-5-nerved, eroded or 

 toothed at the truncate summit ; the awn attached mostly a little above the base: 

 grain not grooved, free, : glumes about equalling the flowers : root perennial. 



1. A. flexuosa, L. (COMMON HAIR-GRASS.) Culms slender, nearly 

 naked (l-2 high) above the small tufts of involute bristle-form root-leaves (1 ; 

 6' long) ; branches of the small spreading panicle capillary; awn longer than the 

 palet, at length bent and twisted. Dry places : common. June. (Eu.) 



2. A. CSBSpitdsa, L. Culm tufted (2 -4 high); leaves flat, linear; 

 panicle pyramidal or oblong (6' long) ; awn straight, barely equalling the palt. 

 Shores of lakes and streams : common northward. June, July. (Eu.) 



2. AIIIOPSIS, Desv. Spikelets very small, of 2 closely approximate flowers, and 

 with no rudiment of a third : lower palet of firmer texture, obscurely nerved, acutely 

 2-clefl at the apex: grain grooved, adnate: low annuals, with short and setaceous 



3. A. PR^ECOX, L. Culms tufted, 3' -4' high; branches of the small and 

 dense panicle appressed; awn from below the middle of the flower. (Avena 

 prsecox, Beauv.) Sandy fields, New Jersey to Virginia : rare. (Xat. from Eu.) 

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