22 POACEAE. 



spikelet 812 mm. long; flowering scale shorter, black, hairy at the base, and 

 with a ring of short hairs at the top, the awn 4-7 cm. long, bent, loosely spiral 

 below. Susquehanna valley. Rather rare, on dry banks. Schists. Sum. 

 BLACK OAT-GRASS. 



17. ORYZOPSIS Miehx. Sparingly tufted grasses, with flat or convolute 

 leaf -blades and narrow, often contracted, panicles. Spikelets broad, 1-flowered. 

 Scales 3, the 2 outer ones nearly equal, awnless, the third scale broad, shorter 

 or longer than the outer ones and terminating in a deciduous awn. Stamens 

 3. Styles distinct. Stigmas plumose. 



1. O. melanocarpa Muhl. Plant glabrous, the stems 412 dm. tall: leaf -blades 

 1-3.5 dm. long, 4-15 mm. wide: panicle 7.5-30 cm. long: spikelets, excluding 

 the awns, 7-9 mm. long, the awn about twice or thrice as long: body of the 

 third scale shorter than the outer scales, becoming dark-colored. M. Eare, 

 on shaded creek banks. Limestones. Sum. MOUNTAIN-RICE. 



18. MUHLENBERGIA Schreb. Perennial or rarely annual grasses, vari- 

 ous in habit, with flat or often involute leaf -blades, and terminal contracted or 

 open panicles, which are often slender, densely thyrsoid, or almost spike-like, or 

 diffuse with long capillary branches. Spikelets 1-flowered, small. Scales 3 (or 

 rarely 4), the outer 2 empty, persistent, membranous or hyaline, from minute 

 to almost equalling the third scale, keeled, acute, mucronate or rarely short- 

 awned, the second occasionally 3-toothed, the third scale somewhat rigid, convo- 

 lute about the 2-keeled hyaline palet and the perfect flower, at the apex entire 

 or rarely 2-toothed, obtuse, acute, mucronate to long-awned, the awn Very often 

 capillary, a fourth awned scale very rarely present. Stamens usually 3, rarely 

 fewer. Styles distinct. Stigmas plumose. 



Panicle contracted, its branches erect or nearly so : spikelets on short pedicels. 

 Empty scales at least % as long as the spikelet. 



Flowering scale not awned, but sometimes awn-pointed. 



Empty scales not awned, about % as long as the flowering scale, acute. 



1. M. sobolifera. 



Empty scales long-acuminate, awn-pointed or awned. 

 Empty scales about as long as the flowering scale, 



sharp-pointed, about 3 mm. long. 2. M. mexicana. 



Empty scales exceeding the flowering scale, usually 



twice as long, awned, about 5 mm. long. 3. M. racemosa. 



Flowering scale long-awned, the awn usually twice as long 



as the scale. 



Empty scales about equalling the flowering scale. 4. M. umbrosa. 



Empty scales %-% as long as the flowering scale. 5. M. tenuiflora. 



Empty scales minute, the first one often wanting. 6. M. Schrebcri. 



Panicle open, its branches filiform, spreading or ascending : spike- 

 lets on very long capillary pedicels. 7. M. capillaris. 



1. M. sobolifera (Muhl.) Trin. 'Stems 3-9 dm. tall, erect, slender: leaf -blades 

 rough, those on the stem 11.5 dm. long, 2-6 mm. wide, those on the branches 

 2-8 cm. long and about 2 mm. wide: panicle 715 cm. long, slender: empty 

 scales about 1 mm. long, the flowering one obtuse, scabrous, the midnerve usually 

 excurrent as a short tip. M. Rather rare, in woods. Limestones, sand- 

 stones and shales. Sum. 



2. M. mexicana (L.) Trin. Stems 6-12 dm. long, erect, or often prostrate, 

 much branched: leaf -blades rough, those on the stem 1-1.5 dm. long, 2-6 mm. 

 wide, the branch blades smaller: panicle 515 cm. long, contracted: spikelets 

 2.5-3 mm. long, the outer scales somewhat unequal, acuminate or short-awned, 

 rough, especially on the keel, the third scale acuminate, rough. Rather com- 

 mon, in fields and fence rows. Sum. and fall. 



