MANUAL OF THE GRASSES OF THE UNITED STATES 231 



Rachis continuous. 



Awn straight or nearly so. 



Spikelets about as long as the internodes of the rachis. 



21. A. PARISHII. 

 Spikelets imbricate, longer than the internodes of the rachis. 



Lemmas coarsely pubescent 11. A. vulpintjm. 



Lemmas glabrous or scabrous toward summit only. 



12. A. SUBSECTJNDUM. 



Awn divergent, when dry. 



Spikelets imbricate 15. A. bakeri. 



Spikelets distant. 



Spikelets 3 to 7 in a spike, about twice as long as the internode; 



spike 4 to 7 cm long 16. A. prixglei. 



Spikelets mostly more than 7 in a spike, usually shorter than the 

 internode; spikes mostly more than 8 cm long. 

 Spike 8 to 15 cm long; blades 1 to 2 mm wide. 



18. A. SPICATTJM. 

 Spike 15 to 30 cm long; blades 4 to 6 mm wide. 



20. A. ARIZONICTJM. 



1. Agropyron cristatum (L.) Beauv. Crested wheatgrass. 

 (Fig. 441.) Culms erect, in dense tufts, 60 to 100 cm tall; blades flat; 

 spike dense, mostly 4 to 6 cm long, the internodes of the 

 rachis pubescent, 1 mm long; spikelets compressed, gla- 

 brous to villous, closely imbricate, somewhat spreading, 

 5 to 15 mm long ; glumes firm, keeled, tapering into a short 

 awn; lemmas somewhat abruptly narrowed into an awn 

 2 to 4 mm long % — Introduced here and there in 

 grainfields (North Dakota, South Dakota, Wyoming, 

 Colorado) ; Eurasia. This grass is well adapted for hay 

 and pasture in the northern Great Plains from North 

 Dakota to eastern Washington and south to western 

 Kansas and probably will be valuable in the northern 

 parts of New Mexico and Arizona. It spreads readily 

 by reseeding. 



Agropyron triticeum Gaertn. Annual, branching at 

 base ; culms slender, erect or usually decumbent, mostly 

 10 to 30 cm tall; blades flat, mostly less than 10 cm long, 

 2 to 3 mm wide; spike oval or ovate, 1 to 1.5 cm long, 

 thick; spikelets crowded, about 7 mm long; glumes and 

 lemmas acuminate, o — Absaroka Forest, Mont.; 

 Mountain Home, Idaho. Sparingly introduced from 

 southern Russia. 



2. Agropyron repens (L.) Beauv. Quackgrass. (Fig. 

 442, A) Green or glaucous; culms erect or curved at base, 

 50 to 100 cm tall, sometimes taller, with creeping yellowish 

 rhizomes; sheaths of the innovations often pubescent; 

 blades relatively thin, flat, usually sparsely pilose on the 

 upper surface, mostly 6 to 10 mm wide ; spike 5 to 15 cm long, the rachis 

 scabrous on the angles; spikelets mostly 4- to 6-flowered, 1 to 1.5 cm 

 long, the rachilla glabrous or scaberulous; glumes 3- to 7-nerved, awn- 

 pointed ; lemmas mostly 8 to 10 mm long, the awn from less than 1 mm 

 to as long as the lemma; palea obtuse, nearly as long as the lemma, 

 scabrous on the keels. % — Waste places, meadows and pastures, 

 Newfoundland to Alaska (Skagway), south to North Carolina, Arkan- 

 sas, New Mexico, and California (fig. 443); introduced from Eurasia. 

 Common in the Northern States; a troublesome weed in cultivated 

 ground. Called also quitch grass and couch grass. Awned specimens 

 have been described as Agropyron leersianum (Wulf.) Rydb. 



Figure 441.— Agro- 

 pyron cristatum, 

 X 1- (Ball 1768, 

 Colo.) 



