68 CONTKIBUTIONS FROM THE NATIONAL HERBARIUM. 



Spikelets in panicles, these terminal only. 



Sterile spikelets reduced to the plumose pedicel; panicles narrow, golden bronze. 



5. SORGHASTRUM. 

 Sterile spikelets developed, usually staminate; panicles open 6. HOLCUS. 



Tribe in. PANICEAE. 



(Spikelets inclosed in globular spiny burs, these racemose. A spreading annual. 



12. CENCHRUS. 



Spikelets not inclosed in a bur. 



Spikelets subtended by 1 to several slender bristles, arranged in a narrow spikelike 

 panicle 11. CHAETOCHLOA. 



Spikelets not subtended by bristles. 



Spikelets subsessile along one side of a slender axis. First glume obsolete or 

 minute. 

 Racemes subdigitate; fruit subindurate, with a flat white hyaline margin; 



spikelets compressed, biconvex; annuals 7. SYNTHERISMA. 



Racemes solitary or racemose; fruit indurate, the firm margin inrolled; spike- 

 lets plano-convex; perennials. First glume obsolete. . .8. PASPALTJM. 

 Spikelets in open or compact panicles. 



Sterile lemma awnless; fruit not pointed; spikelets usually long-pediceled . 



9. PANICUM. 



Sterile lemma awned or strongly mucronate; fruit pointed; spikelets short- 



pediceled, in clusters. Coarse annuals 10. ECHINOCHLOA. 



Tribe IV. ORYZEAE. 



Spikelets unisexual, the pistillate awned, borne on the erect upper branches of a 

 large panicle, the staminate awnless, pendulous on the spreading lower branches 

 of the same panicle ; large annual marsh grass 13 . ZIZANIA. 



Spikelets perfect, awnless; low scabrous perennials 14. HOMALOCENCHRUS. 



Tribe V. PHALARIDEAE. 



Sterile lemmas consisting of minute awnless scales attached at the base of the indurate 

 fruit; glumes keeled; plants not fragrant 15. PHALARIS. 



Sterile lemmas awned, exceeding the fruit; glumes not strongly keeled; plants fra- 

 grant 16. ANTHOXANTHUM. 



Tribe VI. AGROSTIDEAE. 



Lemmas subindurate, at least firmer than the glumes, awned or sharp-pointed, terete 

 or sub terete, the palea inclosed. 



Awn trifid, the lateral divisions sometimes short 17. ARISTIDA. 



Awn simple. 



Glumes 8-10 mm. long; awns 4-7 cm. long, twisted and bent. Panicle loose and 



open 18. STIPA. 



Glumes not over 6 mm. long, usually much shorter; awns not over 3 cm. long, 

 not twisted or bent. 

 Rachilla prolonged behind the palea.; glumes minute; lemma 1 cm. long, 



terminating in a slender awn 2-3 cm. long 20. BRACHYELYTRTJM. 



Rachilla not prolonged behind the palea; lemma not over 3 mm. long, awned 



or awnless 19. MUHLENBERGIA. 



Lemma not firmer than the glumes, usually thinner in texture. 

 Glumes strongly compressed-keeled. Panicle dense, cylindric, spikelike. 



Lemma awnless; glumes abruptly aristate, stiffly ciliate on the keel; rachilla 



articulate above the glumes 21. PHLETJM. 



Lemma with a slender awn from tlie back; glumes not aristate, the margins con- 

 nate toward the base, not stiffly ciliate ; rachilla articulate below the glumes. 



22. ALOPECTJRUS. 



