130 POACEAE 



long, its branches ascending or erect, somewhat flexuous, naked below : spikelets 3-4- 

 flowered, the first empty scale about J as long as the second which is about 5 mm. long, the 

 flowering scales 5-6 mm. long, hispidulous, each bearing a long, bent and twisted awn. 



In waste places and fields, Missouri, Kansas and Mississippi. Naturalized from Europe or Asia. 

 Summer. 



3. Trisetum Hallii Scribn. Stems tufted, 1.5-5 dm. tall, slender: leaf-blades 3-13 

 cm. long, 2-3 mm. wide, rough, flat, or somewhat involute : panicle contracted, 3-15 cm. 

 long, its branches erect or nearly so : spikelets 4-5 mm. long, exclusive of the awns, the 

 first scale much narrower and almost as long as the second. 



On prairies, Texas. Spring. 



4. Trisetum interruptum Buckl. Stems tufted, 5 dm. tall or less, slender : leaf- 

 sheaths glabrous or pubescent ; blades flat or involute, rough, 8 cm. long or less, 1-2 mm. 

 wide : panicle 4-13 cm. long, its branches erect or nearly so : spikelets 4-5 mm. long, ex- 

 clusive of the awns, the first scale narrower than the second but about as long. 



In dry soil, Texas. Spring. 



5. Trisetum aristatum (Scribn. & Mer. ) Nash. Stems 4-6 dm. tall, erect, slen- 

 der : leaf-blades 1.5 dm. long or less, 1-2 mm. wide, roughish : panicle slender, 1.5-2.5 

 dm. long, its branches erect or nearly so, the larger ones 6-8 cm. long : spikelets of 4 or 5 

 scales, 4.5-5 mm. long, exclusive of the awns, the first scale linear, several times narrower 

 than the broad second scale. 



In moist or dry soil, North Carolina. Summer. 



6. Trisetum Pennsylvanicum (L. ) B.S.P. Stems 3-9 dm. tall, erect, slender arid 

 often weak : leaf-sheaths sometimes rough ; blades 1 dm. long or less, 1-4 mm. wide, 

 rough : panicle 6-15 cm. long, its branches erect or ascending : spikelets of four scales, 

 the empty ones about equal, the first a little shorter than the second, the flowering scales 

 4-5 mm. long, the second one hispidulous or nearly glabrous. \_T. palustre Torr.] 



In swamps and wet meadows, New York to Virginia, Tennessee and Florida. Spring and summer. 



7. Triseuim Ludovicianum Vasey. Stems 6-9. dm. long, weak : leaf-blades flat, the 

 larger ones 1.5-2 dm. long, 4-6 mm. wide, rough : panicle 1.5-2.5 dm. long, its branches 

 erect or nearly so : spikelets usually of 4 scales, the first a little shorter than the second, 

 the second flowering scale strongly hispidulous. 



In wet places, Louisiana. Spring. 



72. A VENA L. 



Annual or perennial grasses, varying in habit, with usually flat leaf-blades and terminal 

 contracted or open panicles. Spikelets generally large, erect or pendulous, usually 2- 

 several-flowered, rarely 1 -flowered, the rachilla articulated between the fertile flowers, the 

 lower flowers perfect, the upper ones often staminate or wanting. Scales 4-several, rarely 

 3, the 2 outer empty, membranous, exceeding or shorter than the flowering scales, persist- 

 ent ; the flowering scales 5-9-nerved, rounded on the back, the apex frequently shortly 2- 

 toothed, the scales enclosing perfect flowers and bearing a dorsal twisted geniculateawn, 

 the upper empty ones or those infolding staminate flowers awnless ; palet 2-cleft or 2- 

 toothed, narrow. Stamens 3. Styles distinct. Grain deeply furrowed, usually pubescent. 



1. A vena sativa L. Annual. Stems 8-15 dm. tall : leaf-blades flat, 2.5 dm. long 

 or less, 5-10 mm. wide or more : panicle usually 1.5-4 dm. long, its branches erect or ascend- 

 ing : empty scales of the spikelet 2-3 cm. long, acuminate, the flowering ones shorter, 

 awned or awnless. 



In fields and waste places, escaped from cultivation nearly everywhere in civilized North America 

 Summer. OAT. 



73. ARRHENATHERUM Beauv. 



Tall perennial grasses, with flat leaf-blades and terminal open or contracted panicles. 

 Spikelets 2-flowered, the lower flower staminate, the upper one perfect or pistillate, the rachilla 

 articulated above the empty scales and prolonged beyond the flowers. Scales 4, the 2 outer 

 empty, persistent, thin-membranous, keeled, the flowering scales more rigid, somewhat 

 toothed at the apex, the lower one bearing near the base a long dorsal twisted and genicu- 

 late awn, the upper scale awnless, or short-awned below the apex ; palet 2-keeled, hyaline, 

 narrow. Stamens 3. Styles short, distinct. Stigmas plumose. Grain hardly silicate. 



1. Arrhenatherum elktius (L.) Beauv. Stems 6-12 dm. tall, erect: leaf-blades 

 6-30 cm. long, 2-8 mm. wide, rough : panicle 1-3 dm. long, its branches erect : empty 



