188 AIRA. 



a bent or flexnous (rarely twisted) awn below the 

 sbarply 2-tootlied or two pointed apex. 



Whence the name, from tris^ three, and seta^ a 

 bristle. 



Otherwise nearly as in Avena. Ours are perennials. 



Gray. 



1. T. Subspicatum, Beauv. Var. moUe (Dow-ny 

 Persoon). Found on rocky river banks, from l^ew 

 En o land to Wisconsin, and northward. Flowers in 

 July. About 1 foot high ; leaves flat, short. 



2. T. Palustre (Marsh Oat grass). Low grounds 

 Southern New York to Illinois and nortluvard. 



3. T. Pubescens (the Downy Oat grass). See 

 page 60. 



51. AIRA — Linn. Hair Grass. 



GENERIC CHARACTER. 



Spikelets small in an open diffuse panicle, of 2 per- 

 fect 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 re- 

 .motish ; lower palet thin and scarious, 2-cleft or else 

 truncate, and mostly denticular or eroded at the sum- 

 mit, 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. 



