8O FLORA. 



i. Culms, leaves, and sheaths glabrous or the latter two merely 



ciliate on the margins. 

 Spikelets glabrous. 



Nodes of the culm naked. 



Leaves divaricate ; culms erect, short, the later 



branches bunched. 23. P. dichotomum. 



Leaves erect ; culms accumbent, weak, finally elon- 

 gated, and the later branches scattered. 



24. P. spjtagnicola. 

 Nodes of the culm densely barbed. 



25. P. barbulatum. 

 Spikelets pubescent. 



Culms very slender, less than 2 dm. tall, densely tufted, 



simple. 22. P. Brittoni. 



Culms not slender, 3 dm. or more tall, at length branched. 

 Spikelets elliptic ; leaves smooth above or nearly so, 



naked at the base. 

 Panicle dense, the branches erect or nearly so; 



spikelets i. 5 mm. long. 27. P. Eatoni. 

 Panicle loose and open, the branches spreading ; 



spikelets 2 mm. long. 28. P. boreale. 

 Spikelets globose or nearly so ; leaves very rough 

 above, thick, ciliate at the base. 



46. P. spJxzrocarpon. 

 2. Culms, sheaths or leaves, or all of them, pubescent. 



* Spikelets 2.5 mm. or less long. 

 f Leaves glabrous, or if pubescent beneath, the hairs short and soft. 



Primary leaves long and narrow, erect, thick, the numerous 

 secondary leaves very narrow, 1.5 mm. or less wide, usually 

 involute when dry. 

 Spikelets broadly obovoid, barely 2 mm. long. 



20. P. neuranthum. 



Spikelets elliptic, 3 mm. long. 21. P. angustifolium. 



Primary leaves lanceolate, the secondary leaves flat, lanceolate, ex- 

 ceeding 2 mm. broad. 



Culms villous with short hairs, at least below. 

 Leaves minutely villous beneath. 



Culms erect, rigid. 31. P. Columbianum. 



Culms weak, finally decumbent and forming mats. 



32. P. tsugetorum. 

 Leaves glabrous beneath. 



Spikelets obovoid, i. 5 mm. long. 



30. P. Nashianum. 

 Spikelets elliptic, 2.5 mm. long. 



49. P. Ashei. 

 Culms not villous. 



Culms glabrous; spikelets about 1.25 mm. long. 



29. P. nitidum. 

 Culms at base densely pubescent with long stiff, ap- 



pressed hairs; spikelets 2-2.5 mm. long. 

 Panicle 3-4 cm. long, oblong, dense ; spikelets 2 

 mm. long ; leaves naked on the margins. 



39. P. Addisonii. 



Panicle 5-7 cm. long, broadly ovoid, open; spike- 

 lets 2.5 mm. long ; leaves ciliate at the base. 



40. P. Commonsianum. 

 ft Leaves pubescent on both surfaces, especially beneath. 



Hairs on the lower surface short, soft, and copious. 



Hairs on the upper surface of the leaves long and stiff ; spike- 

 lets about 1.5 mm. long. 37. P. lanuginosum. 

 Hairs on the upper surface of the leaves short, soft, and 



copious. 

 Spikelets nearly 2 mm. long; panicle dense, oblong; culmS 



slender, glabrous. 26. P. annulum. 



Spikelets 2.5 mm. long; panicle open, ovoid ; culms stout; 



densely pubescent. 38. P. viscidum. 



Hairs on the lower, as well as the upper, surface stiff and long, 



sometimes scattered. 

 Spikelets 1.5 mm. long. 



