90 



FIG. 66. Aira caryophyUea L. SILVERY HAIR-GRASS.— a, A spikelet; b, the 

 two, awned florets. A second species of Aira is illustrated by fig. 153 in Bui. 7. 



66. AIRA Linn. Sp. PI. 63. 1753. Spikelets small, 2-flowered; flowers her- 

 maphrodite; rachilla articulated below the flowering glumes and not produced 

 beyond the upper one. Glumes thin-membranaceous, somewhat scarious; the 

 first two persistent below the articulation of the rachilla, nearly equal, acute, 

 awnless, longer than the flowering glumes; flowering glumes closely approxi- 

 mate, hyaline, mucronate or usually bidentate, awned on the back; awn usually 

 geniculate, and twisted below. Palea a little shorter than the flowering glume, 

 hyaline, 2-nerved. Caryopsis included within the hardened flowering glume 

 and palea, and usually adherent to them. Delicate annual grasses, with nar- 

 row leaves and diffuse panicles. 



Species 5 or 6, in Europe, North Africa, two introduced into the United 

 States. 



