16 



POACEAE. 



Spikelets in two rows sessile or nearly so. 



Spikelets on one side of the continuous axis, forming one-sided spikes. 



Tribe 8. CHLORIDEAE. 

 Spikelets alternately on opposite sides of the axis, which is often articulated. 



Tribe 10. HORDEAE. 



TRIBE i. ANDROPOGONEAE. 



Racemes singly disposed ; apex of the rachis-internodes a translucent cup-shaped 

 appendage. i. SCHIZACHYRIUM. 



Racemes disposed in pairs or more ; apex of the rachis-internodes not appendaged. 

 Rachis-internodes and pedicels sulcate, the median portion translucent, the mar- 

 gins thickened. 2. AMPHILOPHIS. 

 Rachis-internodes not sulcate. 



Some or all of the racemes sessile. 3. ANDROPOGON. 



All of the racemes more or less peduncled. 



Pedicellate spikelets wanting. 4. SORGHASTRUM. 



Pedicellate spikelets present and usually staminate. 5. SORGHUM. 



TRIBE 2. ZOYSIEAE. 



Only one genus represented. 



6. HILARIA. 



TRIBE 3. PANICEAE. 



Spikelets naked, not involucrate. 

 Empty glumes 2. 



Rachis produced beyond the upper spikelet ; spikelets narrow. 



37- 



SPARTINA. 



Rachis not so produced ; spikelets globose. 38. BECKMANNIA. 

 Empty glumes 3. 



Empty glumes not awned. 



Spikelets in very slender i -sided racemes, which are usually whorled or 



approximate. 7. SYNTHERISMA. 

 Spikelets in panicles or panicled racemes. 



Spikeles lanceolate, acuminate, long-hairy. 8. TRICHACHNE. 

 Spikelets orbicular or lanceolate ; if the latter, then glabrous. 



9. PANICUM. 



Empty glumes awned or awn-pointed. 10. ECHINOCHLOA. 

 Spikelets involucrate. 



Involucre of numerous bristles. u. CHAETOCHLOA. 



Involucre of two spine-bearing valves. 12. CENCHRUS. 



TRIBE '4. ORYZEAE. 

 Spikelets perfect ; empty glumes wanting or rarely rudimentary. 



13. HOMALOCENCHRUS. 



TRIBE 5. PHALARIDEAE. 



Third and fourth glumes empty, awnless. 



Third and fourth glumes enclosing staminate flowers. 



14. PHALARIS. 



15. SAVASTANA. 



TRIBE 6. AGROSTIDEAE. 



Flowering glumes indurate when mature and very closely embracing the grain, 



or at least firmer than the empty glumes. 

 Spikelets all perfect not in pairs. 



Flowering glume 3-awned. 16. ARISTIDA. 



Flowering glume i -awned. 



Awn twisted and bent. 17. STIPA. 



Awn not twisted. 



