COMPARATIVE ANALYSIS. 



229 



Florets without a pinnated braetea . . ,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 

 Some of the florets with stamens only . . 27 

 Florets perfect . . . . .28 

 Spike compound, florets without bristles . . Panieum. 

 Spike simple, florets with a bristly involucre . . Setaria. 



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



Calyx valves unequal, styles distinct . . Airochloa. 



Corolla awnless . . . .30 



Corolla awned . . . . .31 



Glumes truncate .... Calabrosa. 



Glumes acute ..... Jfelica. 

 Florets perfect .... 32 



Some of the florets with stamens only . . 33 



Corolla invested with seed . . . Arena. 



Corolla not invested with seed . . . Aira. 



Florets three, perfect one with two stamens . Hierochloe. 



Florets two, perfect one with three stamens . . 34 



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

 Lower floret barren, upper one perfect . Arrhenatherinn. 



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 

 Spikelets in dense clusters at end of the branches . Daeti/lis. 

 Spikelets not in dense clusters . . . 38 • 

 External valve of corolla with three nearly equal teeth Triodia. 

 External valve of corolla not three-toothed . . 39 

 Corolla awned or pointed . . . 40 

 Corolla obtuse, not awned . . . .42 

 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 . JBromus. 



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

 Spikelets not cordate, seed free . . .43 



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

 Spikelets ovate or oblong, often webbed . . Poa. 



26 



27 



29 



30 



31 



32. 



33 



37 



38 



39 



40 



