GRAMINE^. (grass FAMILY.) 641 



50. TRISETUM, Persoon. Tkisetum. (PI. 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 iris, three, and seta, a bristle) : other- 

 wise nearly as in Avena. Ours are perennials. 



1. T. SUbspic^tum, Beauv., var. m611e. Minutely sqfl-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. pall^Stre, Torr. Smooth ; panicle r&iheT long and narrow (5' long), 

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

 two 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 cominonly awnless or only mucronate-pointed. (Avena 

 palustris, Michx. Aira pallcns, 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. AtBA, L. Haik-Grass. (PI. 12.) 



Spikelets small, in an open difl^use 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. flexu6sa, L. (Common Haik-Gkass.) Culms slender, nearly 

 naked (l°-2° high) above the small tufts of involute bristleform root-leaves (V - 

 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. caespitdsa, L. Culm tufted (2° -4° high); leaves flat, linear; 

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

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



§2. AIROPSIS, Dcsv. Spikelets very small, of 2 closely approximate flowers, and 

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

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

 leaves. 



3. A. pk}ecox, L. Culms tufted, 3' -4' high; branches of the small and 

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

 pra;cox, Beauv. ) — Sandy fields. New Jersey to Virginia : rare. (Nat. from Eu.) 



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