150 



CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Blades lanceolate ; first glume not more than one- 

 third as long as the spikelet. 

 Culms crisp-puberulent; blades rarely over 

 1 cm. wide; spikelets about 2.5 mm. 



long 183. P. ashei. 



Culms glabrous or obscurely puberulent; 

 blades usually 1.5 cm. or more wide; 



spikelets 2.7 to 3 mm. long 184. P. commutatum. 



Spikelets not over 2.3 mm. long; blades not cordate, usu- 

 ally less than 1 cm. wide. 

 Blades conspicuously ciliate, soft and lax, crowded 



at the base 88. P. ciliatum. 



Blades not ciliate or so only at base, not crowded 

 at the base of the culm. 

 Blades not over 6 mm. wide; plants not branch- 

 ing or rarely branching from near the 



base 85. P. werneri. 



Blades 7 mm. or more wide; plants branching 

 from middle and upper nodes. 

 Primary blades spreading; panicle purplish; 



fruit exposed at summit 107. P. clutei. 



Primary blades erect; panicle green; fruit 



covered 108. P. boreale. 



Spikelets not over 1.7 mm. long. 



Culms crisp-puberulent; spikelets turgid 147. P. columbianum. 



Culms glabrous. 



Blades white-margined, firm. 



Blades puberulent beneath, often above 152. P. tenue. 



Blades glabrous. 



Uppermost blades much reduced; culms 

 branching from lower nodes only, the 



branches repeatedly branching 153. P. albomargina- 



tum. 

 Uppermost blades about as long as the others; 

 culms bearing short branches from 



middle and upper nodes 154. P. trifolium. 



Blades not white-margined or very obscurely so (or 

 if white margin is evident, spikelets only 1.1 

 mm. long). 

 Culms branching only at base; plants soft, light 



green 158. P. vernale. 



Culms branching at the nodes. 



Spikelets 1.1 mm. long; winter blades bluish 



green, not glossy 156. P. concinnius. 



Spikelets 1.3 to 1.5 mm. long. 



Blades involute, falcate, with long stiff 

 hairs on margin near base; plants 



stiff and wiry 162. P. breve. 



Blades not involute or at tip only, not 

 falcate. 

 Plants bright green; winter blades 



conspicuous, glossy green. . .155. P . flavovirens . 

 Plants olive; winter blades not con- 

 spicuous nor glossy 157. P. ensifolium. 



