364 POACE^. 



hemisphere, also represented outside the tropics iu the southern 

 hemisj^here. D. ccespitosa ranges over the entire area above 

 specified. 



Deschampsia bears the same relation to Aira that Calamagrostis 

 does to AgrosHs; plants usually perennial and stouter than Aira. 

 spikelets longer, rachilla produced beyond the upper floret into a 

 bristle or sometimes an empty glume or even a staminate flower; 

 floral glume often more or less denticulate. Six of the species have 

 been proposed as distinct genera. Tlie above comments concern- 

 ing the position of the genus are mainly the views of Bentham. 



A. First empty glume 1-nerved (a) 



a. Florets overlapping, about four-fifths of their length, (b) 



b. Awn straight, short, a dwarf arctic grass. ... 1 



b. Awn bent, protruding, panicle spikelike. ... 2 



b. Awn bent, protruding, panicle thin, spreading. , 3 

 a. Florets overlapping one-third to half of their length, (c) 



0. Empty glumes extending above the florets, awn 



near or above the middle of the glume (d) 



d. Blades flat, 3-6 mm. wide 4 



d. Blades 3-4 mm. wide, involute, floret conspicu- 

 ously hairy 5 



c. Empty glumes usually not extending to the tip of 

 the upper floret (e) 



e. Awn twisted, starting below the middle of its 



glume 6 



e. Awn straight, starting at the middle of its glume. 7 



B. First empty glume 3-nerved (h) 



h. Empty glumes 5-7 mm. long 8 



h. Empty glumes 3-4 mm. long (i) 



i. Rays of panicle mostly in twos 9 



i. Rays of panicle mostly in threes 10 



1. D. brevifolia R. Br., Parry's Voy. Suppl. 191 (1823). Aira 

 arctica Spreng. Syst. 2:32 (1825.) 



A smooth perennial, 6-30 cm. high. Ligule oblong; blades of 

 sterile shoots 6-12 cm. long, those of the culm 1-3 cm. long, 2-3 

 mm. wide, involute, reaching nearly to the panicle. Panicle 



