144 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



KEY TO SPECIES. 



Spikelets glabrous. 

 Spikelets 3 mm. or more long, strongly nerved. 



Spikelets pointed, blades elongated 82. P. depauperatum. 



Spikelets blunt, blades not elongated. 

 Spikelets 3.2 to 3.3 mm. long; blades firm; sheaths, or 



some of them, hispid 171 . P. scribnerianum. 



Spikelets not over 3 mm. long; blades rather thin; 



sheaths glabrous or sparsely hispid 170. P. helleri. 



Spikelets less than 3 mm. long. 

 Second glume and sterile lemma exceeding the fruit and 

 pointed beyond it; spikelets 2.2 to 2.9 mm. long. 



Blades clustered toward the base 101. P. nudicaule. 



Blades not clustered toward the base. 



Sheaths, at least the secondary, hispid 181. P. scabriusculurn. 



Sheaths glabrous. 



Blades firm; fruit 1.5 mm. long 182. P. cryptanthum. 



Blades thin; fruit nearly 2 mm. long 111. P. yadkinense. 



Second glume and sterile lemma not pointed beyond the 

 fruit. 

 Ligule manifest, 1 to 3 mm. long, 

 ('ulms rather stout; ligule 2 to 3 mm. long; sheaths 



glabrous 116. P. spretum. 



Culms slender; ligule 1 mm. long; sheaths sparsely 



pilose 159. P. curtifolium. 



Ligule obsolete. 

 Spikelets 1.5 mm. or less long. 



Nodes bearded 102. P. microcarpon. 



Nodes not bearded. 



Culms and blades pilose 90. P. strigosum. 



Culms glabrous. 

 Blades conspicuously ciliate; plants branching 



at base only 89. P. polycaulon. 



Blades not ciliate; plants branching from mid- 

 dle or upper nodes. 

 Vernal culm 50 cm. or more high; spikelets 

 turgid, strongly nerved; autumnal form 

 erect, with fascicled branches shorter 



than the primary internodes 113. P. caerulescens . 



Vernal culms usually much less than 50 cm. 

 high; autumnal form spreading or re- 

 clining. 

 Spikelets 1.1 to 1.2 mm. long; blades 



rarely as much as 5 cm. long 160. P. chamaelonche. 



Spikelets 1.2 to 1.4 mm. long. 

 Blades elongated, at least some of them 8 



to 10 cm. long 161. P. glahrifolium. 



Blades not over 3 cm. long 157. P. ensifolium. 



Spikelets 2 mm. or more long. 

 Blades elongated, some of them 20 times as long as 

 wide; spikelets 2.2 to 2.8 mm. long. 

 Blades erect; branches, when present, from the 



lower nodes only 85. P. werneri. 



Blades spreading; branches from upper nodes .. . 99. P. bicknellii. 



