500 Key to the System of 



POA. 



2104. Root thickened into one or more tuberous enlarge- 



ments. 



Desert-plant, hardly tall ; protuberances of the root pale, at 

 intervals placed in one row ; leaves elongated, narrow, 

 nearly flat or along the margin incurved ; panicle rather 

 short, somewhat spreading, scantily capillary -branched ; 

 spikelets comparatively broad, from ovate to almost 

 roundish, rather turgid ; flowers few or several ; lowest 

 bract sometimes purplish ; fruit-supporting bract five- 

 streaked, slightly ciliolated, blunt. P. nodosa. 



Root without any tuberous enlargements ... ... 2105 



2105. Perennial ... 2106 



Annual ... 2111 



2106. Floating or creeping. 



Semi-aquatic, much elongated; stem somewhat compressed;, 

 leaves flat, comparatively broad ; membrane inside at 

 the upper end of the leaf-stalk elongated ; panicle very 

 long but narrow, somewhat unilateral, its branches 

 simple, mostly distant, bearing at best only few spikelets 

 each, the lower at first spreading, at last almost erect ; 

 spikelets slender, rather pale-greenish, mostly appressed ; 

 flowers several or many ; fruit-supporting bract generally 

 seven-streaked, blunt, convex along the middle. " Manna- 

 Grass." P. fluitans. 



Erect or diffuse ... 2107 



2107. Stem much branched. 



Swamp-plant, very tall, widely and often fascicularly 

 branched, very rigid ; leaves distant, most of them mar- 

 ginally involute particularly upwards ; panicle elongated, 

 generally much spreading ; spikelets shining ; rhacheole 

 glabrous ; flowers several or few, seldom many ; fruit- 

 supporting bract lax, thin, three-streaked, somewhat 

 pellucid, blunt. "Bamboo-Grass." P. ramigera. 



Stem almost or quite branchless ... 2108 



2108. Fruit-supporting bracts almost granular-rough outside. 



Forest-plant, always tall, sometimes enormously elongated, 

 yet not of long duration and hardly rigid ; leaves very 

 long, almost flat, proportionately broad ; membrane 

 inside at the upper end of the leaf-stalk elongated, with- 

 out ciliolation ; panicle often very long, spreading, thinly 



