POACEAE. 41 



Spikelets rounded at the base ; empty glumes very broad and their backs 

 strongly arched ; low, somewhat tufted plants, with short but open panicle 

 and broad leaves. IX. Alpinae. 



Spikelets acute at the base ; empty glumes narrower and not strongly arched 

 on the back. 

 Flowering glumes 3-4 mm. long ; low alpine plants with few, more or less 

 purplish spikelets. 

 Branches of the inflorescence ascending. VIII. Rupicolae. 



Branches of the inflorescence spreading or reflexed. (P. alpicola in) 



III. Reflexae. 

 Flowering glumes 5 mm. or more ; plants comparatively tall or robust. 

 Spikelets decidedly flattened ; flowering glumes acute. 



Nerves and inter-nerves more or less hairy, at least below ; flowers 

 perfect. 

 Inflorescence open ; plants with horizontal rootstocks ; innovations 

 (i. e., new shoots) extra-vaginal (except in P. pseitdopratensis) . 

 Intermediate nerves of the flowering glumes faint ; spikelets pur- 

 plish. X. Phoeniceae. 

 Intermediate nerves of the flowering glumes strong ; spikelets 

 green or slightly purple-tinged. XI. Wheelrianae. 

 Inflorescence narrow ; plants more or less tufted, without creeping 

 rootstock. 

 Leaves not filiform ; innovations mostly extra-vaginal. 



XII. Epiles. 

 Leaves filiform ; plant true bunch-grasses with intra-vaginal inno- 

 vations. XIII. FiLIFOLIAE. 

 Nerves of the flowering glumes villous, but the inter-nerves glabrous ; 

 plants dioecious ; bunch-grasses with intra-vaginal innovations. 



XIV. Fendlerianae. 



Spikelets only slightly flattened ; flowering glumes narrow, nearly straight 



on the back, rounded at the apex ; bunch-grasses with narrow panicles 



and intra-vaginal innovations. XV. BtrcKLEVANAE. 



I. Annuae. 



Low, 1-2 dm. high; branches of the panicle spreading. i. P. annua. 



Taller, erect, 2-5 dm. high ; branches of the panicle erect. 2. P. Bigelovii. 



II. Pratenses. 



One very variable species. 3. P. pratensis. 



III. Reflexae. 

 Cobweb present but scant. 



Internerves of the flowering glumes more or less pubescent, at least below. 

 Spikelets 3-4-flowered ; stem-leaves usually folded or involute ; plant usually 

 less than 3 dm. high. 

 Internerves of the flowering glumes short-pubescent below ; leaves filiform, 



involute ; those of the sterile shoots usually arcuate. 4. P. cenisia. 

 Internerves of the flowering glumes long-hairy; leaves 1-2 mm. wide, usu- 

 ally conduplicate, rather firm. 5. P. arctica. 

 Spikelets s-7-flowered ; leaves all flat, 3-4 mm. wide ; stem fully 3 dm. high. 



6. P. callichroa. 

 Internerves of the flowering glumes glabrous. 



Intermediate nerves of the flowering glumes pubescent ; plant 3 dm. or less 

 high ; leaves mostly basal, firm ; stemleaves 1-2, usually conduplicate. 



7. P. pudica. 

 Intermediate nerves of the flowering glumes glabrous ; plant usually over 



3 dm. high ; stemleaves several, flat and flaccid. 

 Hairs of the mid-nerves and lateral nerves copious and spreading. 



8. P. reilexa. 



