POACEAE. 45 



66. ARRHENATHERUM. 



Tall perennials with long narrow panicles; spikelets 2-flowcred, 

 lower flower staminate, upper perfect; rachilla extending beyond 

 the flowers; glumes thin-membranous, keeled, very acute or 

 awn-pointed, unequal, persistent; lemmas 2, rigid, 5-7-nerved, 

 deciduous, the first bearing a long bent and twisted dorsal awn 

 inserted below the middle, the second unawned; palea hyaline, 

 2-keeled; grain ovoid, free. 



Arrhenatherum elatius (L.) Bcauv. Tall Oat-grass. Glabrous perennial, 

 100-150 cm. high; stem leaves 3, the blades flat, minutely scabrous, the sheaths 

 shorter than tfie internodes; panicle shining, 15-25 cm. long, rather narrow, 

 the branches suberect; lemmas 6-7 mm. long, the lower bearing a long dorsal 

 geniculate awn. 



Naturalized from Europe. 



67. AIRA. 



Delicate annuals with narrow leaves; spikelets small, 2-flowered; 

 flowers perfect; rachilla jointed below the lemmas and not pro- 

 longed beyond the upper one; glumes nearly equal, awnless, 

 acute, longer than the lemmas; lemmas each with a twisted awn 

 on the back; grain usually adherent to the lemma and palea. 



Panicle loose; lemma 2.5-3 mm. long. A. caryophyllea. 



Panicle dense; lemma 3.5-4 mm. long. A. praecox. 



Aira caryophyllea L. Hair-grass. Stems 10-20 cm. high; panicle very 

 loose; spikelets 2.5-3 mm. long, silvery, shining. 

 Introduced from Europe; common in dry soil. 



Aira praecox L. Stems 5-10 cm. high; panicle small and rather dense; 

 spikelets 3.5-4 mm. long, yellowish, shining. 



Very sparingly introduced; a native of Europe. 



68. DANTHONIA. 



Flowers solitary or few in a small raceme or panicle; spikelets 

 3 to many-flowered, the flowers all perfect or the upper staminate; 

 rachilla pubescent, extending beyond the flowers; glumes keeled, 

 acute, subequal, persistent, generally extending beyond the 

 uppermost lemma; lemmas rounded on the back, 2-toothed, 

 deciduous, the bent awn flat and twisted at the base, arising 

 from between the acute or awned teeth; palea hyaline, 2-keeled 

 near the margins, obtuse or 2-toothed; grain free, enclosed in the 

 lemma. 



Spikelets ascending in a close panicle. 



Callus very short, not hairy. D. pinctornm. 



Callus elongate, densely hairy. D. intermedia. 

 Spikelets spreading, in a loose panicle or solitary. 



Sheaths smooth. D. califoniica. 



Sheaths hairy. D. americana. 



