FLORA OF THE DISTRICT OF COLUMBIA. 69 



Glumes more or less compressed but not conspicuously flattened and keeled. 

 Rachilla not prolonged behind the palea. Floret neither stipitate nor with a 

 hairy callus. 

 Lemma longer than the glumes or equaling them ; palea equaling the lemma or 

 longer; panicles narrow, more or less included in the sheathe. 



23. SPOROBOLUS. 

 Lemma shorter than the glumes; palea shorter than the lemma or obsolete; 



panicles open, exserted 25. AGROSTIS. 



Rachilla prolonged behind the palea as a plumose or naked stipe. Lemma with 

 an inconspicuous awn. 

 Rachilla and callus bearing silky hairs nearly as long as the floret; floret not 

 stipitate; rachilla articulate above the glumes; awn from below the middle 



of the lemma 26. CALAMAGROSTIS. 



Rachilla and callus naked; floret stipitate; rachilla articulate below the glumes; 

 awn minute, from just below the tip of the lemma 24. CINNA. 



Tribe VII. AVENEAE. 



Glumes dissimilar in shape, the first narrow, the second wider above, about as long as the 



first floret; spikelets awnless, articulate below the glumes. .31. SPHENOPHOLIS. 



Glumes similar in shape, exceeding the floret; spikelets awned, usually articulate 



above the glumes. 



Rachilla not prolonged behind the palea; spikelets not over 4 mm. long; delicate 



annuals 28. AIRA. 



Rachilla prolonged behind the palea of the uppermost floret; spikelets more than 

 4 mm. long; perennials (except Avena), 

 Articulation below the glumes; florets 2, dissimilar, the lower awnless, the upper 



with a hooklike awn. Plants velvety 27. NOTHOLCUS. 



Articulation above the glumes (except in Trisetum); florets similar (except in 

 Arrhenatherum). 

 Florets 2, the lower staminate and awned, the upper perfect and awnless. 



33. ARRHENATHERUM. 

 Florets 2 to several, all perfect, awned (except sometimes in Avena), 

 Awn from between the teeth of the bifid lemma, flat, twisted; spikelets 



several-flowered 34. DANTHONIA. 



Awn dorsal, not flattened; lemma often bifid at apex; spikelets 2 or 3-flowered. 



Spikelets large, the glumes over 1 cm. long 32. AVENA. 



Spikelets less than 1 cm. long. 

 Lemmas keeled, bidentate; awn arising from above the middle. 



30. TRISETUM. 

 Lemmas convex; awn from below the middle 29. DESCHAMPSIA. 



Tribe VHI. CHLORIDEAE. 



Spikes digitate or subdigitate. Spikelets awnless. 



Spikelets 1-flowered, the spikes slender; a stoloniferous perennial... 35. CAPRIOLA. 



Spikelets several-flowered, the spikes flat, ratherbroad; an annual.. 38. ELEUSINE. 



Spikes racemose along the axis. 



Articulation below the glumes, the compactly crowded spikelets falling entire; 



second glume exceeding the single awnless floret. Spikes relatively short and 



stout 36. SPARTINA. 



Articulation above the glumes; glumes shorter than the awned florets. 

 Spikelets with 1 perfect floret (a rudimentary floret above it), remote and 

 appressed along a rigid filiform axis, the long slender spikes stiffly spreading 

 or reflexed; blades firm, short, broad, and spreading. .37. GYMNOPOGON. 

 Spikelets with several perfect florets; spikes ascending; blades long and lax. 



39. LEPTOCHLOA. 



