462 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



First glume usually more than one-third the length of the spikelet, 

 if shorter the spikelets not small and blunt. 

 Sterile palea enlarged and indurate at maturity, expanding the 

 spikelet; blades scarcely wider than their sheaths. 



See Laxa, p. 492. 

 Sterile palea if present not enlarged and indurate. 

 First glume short, blunt; spikelets pointed; base of culm 

 usually decumbent and rooting. 



See DicHOTOMiFLOKA, p. 473. 

 First glume usually more than one-third the length of the 

 spikelet. 

 Plants forming congpicuous hard creeping scaly rootstocks. 



See ViRGATA, p. 486. 

 Plants not forming creeping scaly rootstocks. 

 Fruit crested at the apex; spikeleta 5.5 to 6 mm. long. 



115. P. zizanioides. 



Fruit not crested. 



Panicles narrow and few-flowered; culms erect and 



wiry; blades drying involute . .See Teneea, p. 490. 



Panicles open or contracted, many-flowered. 



Panicles 40 to 60 cm. long, the numerous elongated 



branches in verticils 77. P. megiston. 



Panicles mostly much less than 40 cm. long; branches 

 not verticillate. 

 Spikelets short-pediceled along the nearly simple 



panicle branches 48. P. condensum. 



Spikelets long-pediceled; panicle open at maturity. 

 Primary panicles open, the secondary reduced, 

 narrow, partly inclosed in the sheaths. 

 First glume three-foiu'ths as long as the ellipti- 

 cal spikelets; fruit apiculate. 



See CoRDOVENSiA, p. 525. 

 First glume one-third as long as the pyriform 

 spikelets; fruit not apiciilate. 



104. P. nodatum. 

 Primary and secondary panicles alike, or the 

 secondary wanting. 

 First glume not pointed, two-thirds the length 

 of the spikelet or more; spikelets blunt. 

 Panicles not over 6 cm. long; plants some- 

 what glaucous, relatively small. 



See Parvifolia, p. 506. 

 Panicles 10 to 20 cm. long, very diffuse; 

 plants tall, not glaucous. 

 Spikelets viscid, 3 mm. long. 



75. P. glutinosum. 

 Spikelets not viscid, 2 to 2.3 mm. long. 



74. P. millegrana. 

 First glume pointed, usually less than two- 

 thirds as long as the pointed spikelets. 

 Spikelets more or less pubescent. 

 Culms slender, straggling; spikelets not 

 turgid; glumes and sterile lemma hir- 

 sute along the margins. 



72. P. haenkeanum. 



