258 CONTRIBUTIONS FEOM THE NATIONAL HERBARIUM. 



Ensifolia. — Plants low and slender, usually glabrous and less than 50 cm. high; 

 sheaths glabrous or puberulent (sparsely pilose in P. curtifolium); ligules 

 nearly obsolete (about 1 mm. long in P. curtifolium); panicles small, rarely 

 more than 5 cm. long; spikelets glabrous or pubescent, 1 to 1.7 mm. long, 

 5 to 7-nerved. Autumnal form sparingly to freely branching, or in P. vernale 

 a distinct autumnal form wanting. 

 Ligules about 1 mm. long; sheaths or some of them sparsely 



spreading-pilose 159. P. curtifolium. 



Ligules obsolete or nearly so; pubescence if present not 



spreading. 



Blades prominently white-margined, firm; spikelets 



densely puberulent. 



Blades puberulent beneath, often above; sheaths 



and sometimes lower internodes ascending 



pubescent 152. P. tenue. 



Blades glabrous; sheaths glabrous or minutely ciliate 

 only. 

 Uppermost culm blades much reduced; culms 

 branching from lower nodes only, the 



branches repeatedly branching 153. P. albomarginatum. 



Uppermost culm blades about as long as the 

 others; culms bearing short branches from 



the upper and middle nodes 154. P. trifolium. 



Blades not white-margined or very obscurely so (or if white 

 margin is evident spikelets only 1.1 mm. long); 

 spikelets glabrous or puberulent. 

 Culms branching only at base ; plants soft, light green. 158. P. vernale. 

 Culms branching at the nodes ; plants firm or at least 

 not soft. 

 Spikelets glabrous. 



Spikelets 1.1 to 1.2 mm. long; blades rarely 



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



Spikelets 1.2 to 1.5 mm. long. 



Blades elongated, at least some of them 



8 to 10 cm. long 161. P. glabrifolium. 



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



Spikelets puberulent. 



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. hreve. 



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. 



