148 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Spikelets abruptly pointed; blades cordate; 



Mexican 179. P. viscidellum. 



Spikelets not pointed at maturity; blades not 

 cordate. 

 Ligule 1 mm. long; sheaths sparsely pilose; 



spikelets 1.4 mm. long 159. P. curtifolium. 



Ligule usually more than 1 mm. long. 



Ligule 1 to 1.5 mm. long; culms and 

 sheaths appressed-pubescent; spike- 

 lets 1.5 to 1.9 mm. long. 

 Spikelets 1.8 to 1.9 mm. long; plants 



bluish green 146. P. tsugetorum. 



Spikelets 1.5 mm. long, nearly globular; 



plants olivaceous 148. P. oricola. 



Ligule 2 to 5 mm. long. 

 Spikelets 1 to 1.3 mm. long; culms and 

 sheaths softly appressed-pubescent. 



Spikelets 1.2 to 1.3 mm. long 118. P. leucothrix. 



Spikelets not over 1 mm. long 120. P. wrightianum. 



Spikelets mostly more than 1.5 mm. 



long, if less, pubescence spreading. See Lanuginosa 



(p. 208). 

 Ligule obsolete or less than 1 mm. long. 



Nodes bearded (P. scoparium may appear to be 

 bearded). 

 Spikelets nearly 3 mm. long; plants velvety- 



villous throughout 169. P. malacophyllum. 



Spikelets rarely as much as 2.5 mm. long;' 

 plants not pubescent throughout. 



Spikelets 1.5 to 1.6 mm. long '. .102. P. microcarpon. 



Spikelets 2 mm. or more long. 

 Blades all velvety; autumnal form spar- 



ingty branched 105. P. annulum. 



Blades glabrous, or only the lower pubes- 

 cent or velvety. 

 Spikelets 2 mm. long; autumnal form 

 profusely branching. 

 Fruits slightly exposed at maturity; 



upper sheaths viscid-spotted 103. P. nitidum. 



Fruits covered at maturity; sheaths 



not viscid-spotted; Mexican 104. P. multirameum. 



Spikelets 2.2 mm. or more long; autum- 

 nal form less profusely branching. 



Sheaths and upper nodes glabrous 107. P. clutei. 



Lower sheaths and all nodes pubes- 

 cent 106. P. mattamuskee- 



tense. 

 Nodes not bearded. 



Plants densely gray-velvety throughout, a 



viscid, glabrous ring below the nodes 178. P. scoparium. 



Plants not gray-velvety. 

 Sheaths or some of them pilose or hispid. 

 Pubescence papillose-hispid. 



Spikelets ovate, pointed, 2.3 to 2.6 mm. 



long. 181. P. scabriusculum. 



