COMPAEATIVE ANALYSIS. 229 



Florets without a pinnated bractea . . 24 



24. Calyx with not more than two perfect florets . 25 

 Calyx with more than two perfect florets . . 35 



25. Panicle dense, in a simple or compound spike . 26 

 Panicle lax, not spiked . . . 29 



26. Some of the florets with stamens only . 27 

 Florets perfect . . . . 28 



27. Spike compound, florets without bristles . Panicum. 

 Spike simple, florets with a bristly involucre . Setaria. 



28. Calyx valves nearly equal, styles united . . Sesleria. 

 Calyx valves unequal, styles distinct . . Airochloa. 



29. Corolla awnless . . . . .30 

 Corolla awned . . . . 31 



30. Glumes truncate .... Catabrosa. 

 Glumes acute .... Ifelica. 



31. Florets perfect . . . . 32 

 Some of the florets .with stamens only . . 33 



32. Corolla invested with seed .... Avena. 

 Corolla not invested with seed . . . Aira. 



33. Florets three, perfect one with two stamens . Hierochla. 

 Florets two, perfect one with three stamens . 34 



34. Upper floret barren, lower one perfect . . Holcus. 

 Lower floret barren, upper one perfect . Arrhenathemm. 



35. Panicle imbricated and simple . . . Sesleria. 

 Panicle loose, or, if dense, branched . . 36 



36. Corolla with long hairs at base . . . Arundo. 

 Corolla without hairs at base, or nearly so . 37 



37. Spikelets in dense clusters at end of the branches . Dactylis. 

 Spikelets not in dense clusters . . . 38 



38. External valve of corolla with three nearly equal teeth Triodia. 

 External valve of corolla not three- toothed . 39 



39. Corolla awned or pointed . . . .40 

 Corolla obtuse, not awned ... 42 



40. Corolla with a twisted dorsal awn, upper florets mostly 



imperfect ..... Avena. 



Corolla pointed, or with an awn terminal, or nearly so; 



florets perfect . . . . .41 



41. Corolla with a terminal awn, or pointed . . Festuca. 

 Corolla with an awn just below the bifid extremity . Eromm. 



42. Spikelets cordate, (pendulous,) seed coated by the corolla Briza. 

 Spikelets not cordate, seed free . . .43 



43. Spikelets linear or sub -cylindrical, not webbed . Glyceria. 

 Spikelets ovate or oblong, often webbed . . Poa. 



