144 



CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



KEY TO SPECIES. 



Spikelets glabrous. 

 Spikelets 3 mm. or more long, strongly nerved. 



Spikelets pointed, blades elongated 82. 



Spikelets blunt, blades not elongated. 

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



some of them, hispid 171 . 



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



sheaths glabrous or sparsely hispid 170. 



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. 



Blades not clustered toward the base. 



Sheaths, at least the secondary, hispid 181. 



Sheaths glabrous. 



Blades firm; fruit 1.5 mm. long 182. 



Blades thin; fruit nearly 2 mm. long 111. 



Second glume and sterile lemma not pointed beyond the 

 fruit. 

 Ligule manifest, 1 to 3 mm. long. 



Culms rather stout; ligule 2 to 3 mm. long; sheaths 



glabrous 116. 



Culms slender; ligule 1 mm. long; sheaths sparsely 



pilose 159. 



Ligule obsolete. 

 Spikelets 1.5 mm. or less long. 



Nodes bearded 102. 



Nodes not bearded.- 



Culms and blades pilose 90. 



Culms glabrous. 

 Blades conspicuously ciliate; plants branching 



at base only 89 . 



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. 



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. 



Spikelets 1.2 to 1.4 mm. long. 

 Blades elongated, at least some of them 8 



to 10 cm. long 161. 



Blades not over 3 cm. long 157. 



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. 



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



P. depauperatum. 



P. scribnerianum. 

 P. helleri. 



P. nudicaule. 



P. scabriusculum . ■ 



P. cryptanthum. 

 P. yadkinense. 



P. spretum. 

 P. curtifolium. 



P. microcarpon. 

 P. strigosum. 



P. polycaulon. 



P. caerulescens . 



P. chamaelonche . 



P. glabrifolium. 

 P. ensifolium. 



P. werneri. 

 P. bicknellii. 



