466 PROCEEDINGS OF THE AMERICAN ACADEMY. 



+- *r Perigynia less than 4 mm. long. 

 ++ Perigynia 2 mm. or more long. 



= Perigynia with serrulate beaks or margins. 



a. Spike elongate, from linear-cylindric to oblong. 



1. Perigynia ovate, broadest at base : spikelets mostly or all ap- 



proximate in an oblong-cylindrie spike . . . (30) C. arcta. 



2. Perigynia broadest near the middle. 



O Plant glaucous : leaves 2 to 4 mm. broad : spikelets with many 

 appressed-ascending glaucous obscurely beaked perigynia. 

 Spikelets 6 to 10 mm. long, approximate, or the lowest 

 rarely 1.5 cm. apart : perigynia 2.3 to 3 mm. long 



(31) C. canescens. 

 Spikelets 4 to 7 mm. long, subapproximate or remote : peri- 

 gynia about 2 mm. long (31) C. canescens, var. subloliacea. 

 Spikelets 6 to 12 mm. long, remote, the lowest 2 to 4 cm. 



apart (31) C. canescens, var. disjuncta. 



O O Plant green, not glaucous : leaves 1 to 2.5 mm. broad : spike- 

 lets with few loosely spreading dark green or brown dis- 

 tinctly beaked perigynia (32) C. hrunnescens. 



b. Spike subglobose, of 2 to 4 closely approximate subglobose 



loosely flowered silvery spikelets : perigynia oblong, beakless, 



nerved, 3 to 3.4 mm. long (35) C. tenuiflora. 



= = Perigynia smooth throughout. 



a. Spike whitish, silvery-green or pale brown, not ferrugineous nor 



dark brown. 



1. Spike elongate, at least the lower spikelets scattered. 



Uppermost spikelet divaricate-pedunculate, the lowermost 

 subtended by a long leaf-like bract : perigynia more than 



J! mm. long (36) C. trisperma. 



Spikelets continuous in a linear-cylindric loose spike, bract- 

 less or only short-bracted : perigynia 2 to 3 mm. long 



(31) C. canescens. 

 (For vars. see above.) 



2. Spike subglobose, of 2 to 4 closely approximate subglobose 



loosely flowered spikelets : perigynia beakless, 3 mm. or more 

 long .... (35) C. tenuiflora. 



b. Spike ferrugineous or dark brown. 



1. Terminal spikelet with conspicuous clavate base : perigynia ab- 

 ruptly beaked : culms smooth (or harsh only at tips). 

 O Spikelets distinct ; the lowest 4 or 5 mm. thick ; the terminal 

 1 to 1.8 cm. long: perigynia pale, about equalled by the 



yellowish-brown blunt scales (38) C. norvegica. 



O O Spikelets approximate ; the lowest less than 4 mm. thick. 



Plant weak and lax : leaves involute, 0.5 to 1.5 mm. broad : 

 perigynia pale, equalled by the ferrugineous acutish scales 



(39) C. (jlareosa. 

 Plant stiff and upright : leaves flat, 1 to 3 mm. broad : peri- 

 gynia brown or reddish, exceeding the fuscous obtuse 

 scales (40) C. lagopina. 



