GRASS FAMILY. 109 



Tribe VI. PHALARIDEAE. 



Third and fourth scales 



Small and empty, or rudimentary, not awned ; stamens 3. 26. Phalaris. 



Empty, awned upon the back ; stamens 2. 27. Antho.vanthum. 



Subtending staminate flowers, stamens 3 ; fertile flowers, stamens 2. 28. Sarastana. 



Tribe VII. AGROSTIDEAE. 



Flowering scale indurated at maturity, firmer than the empty scales. 



Spikelets with no basal callus ; flowering scale awnless, margins inrolled. 29. Milium. 

 Spikelets with a basal callus ; flowering scale awned, the margins flat. 

 Awn simple. 



Flowering scale broad, the awn deciduous ; callus short, obtuse. 



Flowering scale glabrous, or pubescent with short hairs. 3"?. Oryzopsis. 



Flowering scale pubescent with copious long silky hairs. 30. Eriocoma. 



Flowering scale narrow, awn persistent ; callus commonly acute. 32. Stipa. 

 Awn 3-parted. 33. Aristida. 



Flowering scale membranous, not firmer than the empty scales. 



Flowering scale with a terminal awn or awn-pointed, tightly enclosing the grain. 



Rachilla not prolonged beyond the base of the flowering scale ; empty scales usually evident. 



34. Muhlenbergia. 

 Rachilla extending beyond the base of the flowering scale as a bristle-like appendage ; empty 



scales minute, the first sometimes wanting. 35. Brachyelytrum. 



Flowering scale awnless, or with a dorsal awn, loosely enclosing the grain. 

 Spikelets readily deciduous entire at maturity. 



Empty scales awnless. 38. Alopecitrus. 



Empty scales awned. 41. Polypogon. 



Spikelets not deciduous entire, the empty scales persistent, flowering scales usually deciduous. 

 Empty scales awned. 37. Phleuin. 



Empty scales awnless. 



Flowering scales i -nerved. 



Panicle dense and spike-like, the spikelets markedly compressed laterally, ciliate 



on the keel. 36. Heleochloa. 



Panicle open or narrow, the spikelets not markedly laterally compressed, the 



keel glabrous. 

 Grain loosely enclosed in the pericarp, from which it readily separates and 



falls at maturity ; flowering scales with no hairs at the base. 

 Empty scales minute ; low arctic grass. 39. Pliippsia. 



Empty scales evident. 40. Sporobolus. 



Grain adherent to the pericarp and not separating from it at maturity ; flower- 

 ing scale with a ring of long hairs at the base. 47. Calainovilfa. 

 Flowering scales 3-5-nerved. 



Stamen i; flowering scale stipitate ; palet usually i-nerved-43. Cinna. 

 Stamens 3 ; flowering scale sessile ; palet 2-nerved. 

 Rachilla not prolonged beyond the flowering scale. 



Empty scales shorter than flowering scale ; spikelets large 42. Arctagrostis. 

 Empty scales longer than the flowering scale ; spikelets small. 44. Agrostis. 

 Rachilla prolonged beyond the flowering scale. 



Prolongation of the rachilla glabrous ; flowering scale glabrous at the base, 



and with a long awn just below the bifid apex. 48. Apera. 

 Prolongation of the rachilla with long hairs ; flowering scale awned at or 



below the middle. 

 Flowering scale membranous ; spikelets 4" long or less. 



45. Calamagrostis. 

 Flowering scale chartaceous ; spikelets s"-6" long. 46. Ammophila. 



Tribe VIII. AVENEAE. 



Spikelets deciduous ; lower flower perfect, upper staminate, awned. 49. Nothoholcus. 



Spikelets not deciduous ; empty scales persistent, flowering ones deciduous. 



Spikelets of 2 perfect flowers ; rachilla not prolonged beyond the upper one. 50. Aspris. 

 Spikelets 2-many-flowered ; rachilla prolonged beyond the upper scale. 

 Awn of flowering scale dorsal, inserted below the teeth. 



Flowers all perfect, or the upper ones staminate or wanting. 

 Spikelets less than 6" long ; grain free, unfurrowed. 



Flowering scales convex ; awn arising from or below the middle. 51. Deschainpsia. 



Flowering scales keeled : awn arising from above the middle. 52. Trisetnm. 



Spikelets over 6" long ; grain furrowed, usually adherent to the scales. 53. Arena. 



Upper flower perfect, lower staminate, its scale strongly awned. 54. Arrhenathcrum. 



Awn from between the lobes or teeth of flowering scale, generally twisted. 55. Danthonia. 



Tribe IX. CHI.ORIDF.AK. 



Spikelets with perfect flowers, or sometimes some of them rudimentary or unisexual. 

 Spikelets deciduous entire. 



Spikelets narrow, lanceolate : rachis produced beyond the upper spikelet. 57. Spartina. 

 Spikelets broad, orbicular; rachis of the spike not produced. 64. Beckmannia. 



Spikelets not deciduous entire ; empty scales persistent ; flowering scales deciduous. 

 One perfect flower in each spikelet (rarely 2 in no. 56). 

 No empty scales above the flower. 



Spikes 2-6, digitate. 56. Capriola. 



Spikes many, scattered. 61. Schedonnardus. 



One to several empty scales above the flower. 



Lower empty scales 4 ; spike solitary, dense. 58. Can\f>ulosns. 



