44 CONTEIBUTIONS FROM THE NATIONAL HERBARIUM. 



KEY TO THE GENERA. 



Tribe I. MAYDEAE. 

 A single genus 1. Tripsacum (p. 49). 



Tribe n. ANDROPOGONEAE, 



Spikelets all pedicellate, the longer pediceled one per- 

 fect, long-awned, the short-pediceled one stami- 



nate, awnless 2. Trachypogon (p. 49). 



Some of the spikelets sessile, these perfect, the pedi- 

 cellate spikelets staminate, sterile, or reduced 

 to a pedicel. 



Spikelets all awnless 3. Elyonurus (p. 49). 



Perfect spikelets awned. 



Lower spikelets unlike the others 9. Heteropogon (p. 52). 



Sessile spikelets all alike. 



Racemes single; rachis joints with a cup- 

 shaped appendage at the tip 4. Schizachyrium (p. 49). 



Racemes 2 or more; rachis joints not ap- 

 pendaged. 

 Rachis joints and pedicels sulcate, 



translucent 5. Amphilophis (p. 50). 



Rachis neither sulcate nor trans- 

 lucent. 



Some of the racemes sessile 6. Andropogon (p. 51). 



All the racemes pedunculate. 

 Pedicellate spikelets re- 

 duced to a pedicel. . . 8. Sorghastrum (p. 52). 

 Pedicellate spikelets stami- 

 nate 7. HoLcus (p. 51). 



Tribe m. ZOYSIEAE. 



Second glumes covered with hooked spines 10. Nazia (p. 52). 



Second glumes not spiny 11. Hilaria (p. 53). 



Tribe IV. PANICEAE. 



Spikelets involucrate. 



Involucre a spiny bur, falling with the spikelets. .20. Cenchrus (p. 61). 

 Involucre of numerous bristles, persistent on the 



axis after the fall of the spikelets 19. Chaetochloa (p. 60). 



Spikelets not involucrate. 



Glumes, at least the second, awned or cuspidate. .18. Echinochloa (p. 59). 

 Glumes not awned. 



Spikelets lanceolate; fmit cartilaginous, not 

 rigid, the white hyaliae margins of the 

 lemma not inroUed. 

 Spikelets densely covered with long 



silky hairs 12. Valota (p. 54). 



Spikelets glabrous or nearly so. 



Inflorescence of slender racemes, 



digitately arranged 13. Syntherisma (p. 54). 



Inflorescence a capillary panicle 14. Leptoloma (p. 54). 



