268 OHIO BIOLOGICAL SURVEY 



17. Palet not ciliate-fringed ; internodes of the rachilla short; middle nerve 

 or all three, excurrent between the acute lobes of the lemma. Tridens. (11) 



17. Palet conspicuously ciliate-fringed; internodes of the rachilla long; middle 

 nerve excurrent between the truncate lobes of the lemma. Triplasis. (12) 



18. Rachilla prolonged beyond the upper glumes or flowers. 19 



18. Rachilla not prolonged beyond the upper glumes; spikelets 2-flowered. 



Aspris. (20) 



19. Awn projecting from between the lobes of the lemma, flattened and twisted. 



Danthonia. (15) 



19. Awn of the lemma dorsal, not much flattened. 20 



20. Spikelets 2-flowered, the upper bisporangiate, the lower staminate and its 

 glumes strongly awned. Arrhenatherum. (16) 



20. Spikelets 2-several-flowered; flowers all bisporangiate or the uppermost one 

 imperfect. 21 



21. Lemma keeled, awn arising from above the middle; spikelets less than y 2 in. 

 long. Trisetum. (17) 



21. Lemma rounded on the back. 22 



22. Spikelet over y in. long; grain furrowed, usually adherent to the palet. 



Avena. (18) 



22. Spikelet less than l / 2 in. long; grain unfurrowed, free from the palet. 



Deschampsia. (19) 



23. Spikelets with a single perfect flower often at the side of the rachilla, not 

 with vestigial flowers or glumes above the empty glumes. 24 



23. Spikelets with a perfect flower at the top, sometimes with staminate or 

 vestigial flowers below. 36 



24. Lemma membranous, not indurated, not firmer than the empty glumes. 25. 



24. Lemma indurated at maturity, firmer than the empty glumes. 33 



25. Lemma awnless or with a dorsal awn, loosely enclosing the grain. 26 



25. Lemma with a terminal awn or awn-pointed, closely enfolding the grain. 32 



26. Empty glumes awned; inflorescence dense; lemma awnless. Phleum. (43) 



26. Empty glumes awnless. 27. 



27. Lemma 1-nerved. 28 



27. Lemma 3-5-nerved. 29 



28. Inflorescence lax, somewhat contracted ; glumes not conspicuously com- 

 pressed. Sporobolus. (35) 



28. Inflorescence dense, spike-like; glumes conspicuously compressed-carinate. 



Heleochloa. (42) 



29. Rachilla prolonged beyond the palet. 30 



29. Rachilla not prolonged beyond the palet. Agrostis. (37) 



30. Lemma long- or short-awned, sometimes on the back ; panicle lax or con- 

 tracted. 31 



30. Lemma awnless; panicle dense and spike-like; leaves with deep grooves on 

 the upper surface. Ammophila. (40) 



31. Prolongation of the rachilla and callus with long hairs; lemma short-awned 

 on the back; perennial. Calamagrostis. (36) 



31. Prolongation of the rachilla naked; lemma long-awned ; annual. Apera. (38) 



32. Rachilla not prolonged beyond the base of the palet; lemma pointed or 

 awned. Muhlenbergia. (44) 



32. Rachilla prolonged into a bristle behind the palet ; lemma long-awned. 



Brachyelytrutn. (45) 



33. Lemma awnless, its margins inrolled, spikelets without a basal callus. 



Milium. (46) 



33. Lemma awned. its margins flat; spikelets with a basal callus. 34 



34. Awn simple. 35 



34. Awn 3-parted, the branches divaricate. Aristida. (49) 



