102 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



POACEAE. Grass Family. 



KEY TO THE TRIBES. 



Spikelets, 1 or 2-flowered. 



Rachilla articulated below the glumes, the spikelet 1 or 2-flowered, 

 when 2-flowered the lower staminate. 



Glumes 2 ; spikelets flattened Oryzeae. 



Glumes apparently 3 or 4; spikelets not flattened Paniceae. 



Rachilla articulated above the glumes. 



Glumes apparently 4 ; palea 1-nerved Phalarideae. 



Glumes 2 ; palea 2-nerved Agkostideae. 



Spikelets 2 to many-flowered. 



Inflorescence a panicle or raceme. 



-Lemma shorter than the glumes, usually with a bent awn arising 



from the back Aveneae. 



Lemma longer than the glumes, awnlcss or with a straight apical 



awn Festuceae. 



Inflorescence a spike. 



Spikelets crowded in 2 rows, forming one-sided spikes Ciilorideae. 



Spikelets in 2 opposite rows Hordeae. 



key to the genera. 



oryzeae. 



Flowers perfect; glumes and lemmas keeled Homalocenchrl's (p. 104). 



PANICEAE. 



Spikelets In one-sided racemes or spikes. 



First glume very small Syxtheri-sma (p. 104). 



First glume well developed Paspalu.m (p. 104). 



Spikelets not in one-sided racemes or spikes. 



Inflorescence dense; pedicels bearing bristles Chaetochloa (p. 106). 



Inflorescence loose; pedicels not bristly Panic rii (p. 10.5). 



PHALARIDEAE. 



Spikelet with 3 florets, the uppermost perfect, the others stami- 

 nate Savastana (p. 106). 



Spikelet with 1 perfect floret, the lateral ones reduced to ster- 

 ile lemmas. 



Sterile lemmas bifid, awned Anthoxanthum (p. 106). 



Sterile lemmas awnless, very small Phalaris (p. 106). 



AGROSTIDEAE. 



Lemma with a long terminal awn, and closely embracing the 

 grain. 



Fruiting lemma thin and membranaceous Ml'hlenbergia (p. 110). 



Fruiting lemma firm and indurated. 



Awns 3-branched Aristida (p. 107). 



Awns simple. 



Twisted, persistent on the lenmia Stipa (p. 107). 



Straight, deciduous from the lemma Oryzopsis (p. 109). 



