120 POACEAE 



empty scales green, acuminate ; flowering scale about 1 cm. long, usually strongly papil- 

 lose-roughened, tlie callus about 4 mm. long and strongly pubescent with white appressed 

 hairs the awn 6-8 cm. long, spiral and very pubescent at the base, usually twice bent. 

 In dry soil, Texas. Spring <anrt summer. 



2. Stipa avenacea L. Stems 3-8 dm. tall : leaf-blades involute-filiform, the basal 



^-J as long as the stem, those on the stem 7-13 cm. long : panicle 1-2 dm. long, loose, its 



branches lax and finally spreading : empty scales of the spikelet 8-12 mm. long ; flowering 



scale shorter, black, hairy at the base, and witli a ring of short hairs at the top, the awn 



4-7 cm. long, bent, loosely spiral below. 



In dry woods. Rhode Island to Florida, mostly near the coast ; also in western Ontario and Wis- 

 consin. Black Oat Grass. 



3. Stipa avenaceoides Nasii. >Stems 6-12 dm. tall, tufted, erect, slender: leaf- 

 sheaths glalu-ous ; blades involute-setaceous, glabrous, the basal ones about 3 dm. long, 

 those on the stem 2.5-12 cm. long: panicle simple, 1-2.5 dm. long, Anally long-exserted, 

 its branches 2.5-8 cm. long: spikelets few; empty scales purple at the base, acuminate, 

 15-22 mm. long ; flowering scale glabrous, excepting the hairy apex, 1.5-2 cm. long, in- 

 cluding tlie callus which is 6-8 mm. long and covered with appressed brown hairs, the awn 

 7-10 cm. long, pubescent below, spiral at the base, twice bent. 



In dry sandy soil, peninsular Florida. Spring and summer. 



55. MUHLENBERGIA Schreb. 



Perennial or rarely annual grasses, various in habit, with flat or often involute leaf- 



l)lades, and terminal contracted or open panicles, which are often slender, densely thyrsoid, 



or almost spike-like, or difflise with long capillary branches. Spikelets 1-flowered, small. 



Scales 3 (or rarely 4), tlie 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, convolute about the 2-keeled 



hyaline i^alet 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 3^ as long as the spikelet. 



Flowering scale not^awned, but sometimes awn-pointed. 



Empty scales not awned, about y^ as long as the flowering scale, acute. 1. 3/. soboUfera. 



Empty scales long-acimiinate, 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. 31. racemosa. 



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



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



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



Empty scales minute, tfie first one often wanting. 6. M. diffusa. 



Panicle open, its filiform branches spreading or ascending : spikelets on very long 

 capillary pedicels. 

 Stems erect, simple. 



Empty scales awnless, or awn-pointed : 



Awn of the flowering scale very short, rarely nearly equalling it in length. 7. 31. trichopodes. 

 Awn of the flowering scale very long, often several times its length. 8. M. capillaris. 



Empty scales long-awned, the awiis usually many times as long as the scale. 9. 31. filiprs. 



Stems much branched and prostrate. 10. 31. Porteri. 



1. Muhlenbergia sobolifera (Mnhl.) Trin. Stems 3-9 dm. tall, erect, slender, 

 simple, or sparingly branched above : leaf-blades rough, those on the stem 1-1.5 dm. long, 

 2-6 mm. wide, those on the branches 2-8 cm. long and about 2 mm. wide : panicle 7-15 

 cm. long, slender : empty scales about 1 mm. long, tlie flowering one obtuse, scabrous, 

 the midnerve usually excurrent as a short tip. 



In rocky woods, New Hampshire and Massachusetts to Minnesota, Virginia, Tennessee and the 

 Indian Territory. Summer and fall. 



2. Muhlenbergia Mexicana (L. ) Trin. Stems 6-12 dm. long, erect, or often pros- 

 trate, much branciied : leaf -blades rough, those on the stem 1-1.5 dm_. long, 2-6 mm. 

 wide, the branch blades smaller: panicle 5-15 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. 



In swamps and borders of fields. New Brunswick to western Ontario, North Carolina, Tennessee, 

 Nebraska and the Indian Territory. Summer and fall. 



3. Muhlenbergia r-icemosa (Michx. ) B.S.P. Stems 3-9 dm. tall, erect, usually 

 much branched : leaf-blades 5-13 cm. long, 2-6 mm. wide, rough: panicle 5-12 cm. long, 



