21a. Panicle-branches erect or ascending 22. 

 21b. Panicle-branches strongly spreading 23. 



22a. The two outer scales of the spikelet one-fourth as long as 



the third scale, or sometimes one of them absent 17a. 

 22b. The glumes at least half as long as the lemma 



Wood-grass, Muhlenberaia mexicana. 



23a. The chief lateral branches of the panicle dividing and bearing 

 flowers below their middle Red-top, Agrostis alba. 



23b. The chief branches of the panicle dividing only beyond the 

 middle Hair Grass, Agrostis hyemalis. 



24a. Spikelets arranged in two rows to form a definite spike 25. 

 24b. Spikelets in panicles, never in definite rows 29. 



25a. Spikelets in a single row on one side of the axis, forming a one- 

 sided spike Yard Grass, Elensine indica. 



25b. Spikelets alternating on opposite sides of the axis, forming a 

 two-rowed spike 26. 



26a. Spikelets in pairs at each joint, forming a dense spike (Wild 

 Rye) 27. 



26b. Spikelets single at each joint, forming a loose, open or in- 

 terrupted spike 28. 



27a. Glumes lanceolate Wild Rye, Elymus canadensis. 



27b. Glumes narrowly subulate Wild Rye, Elymus \irg-inicus. 



28a. Spikelets with their edges toward the axis of the spike 



Rye Grass, Lolium perenne. 

 28b. Spikelets with their sides toward the axis of the spike 



Quack Grass, Agropyron repens. 



29a. Glumes longer than the lemmas Oats, Arena sativa. 



29b. Glumes shorter than the lemmas 30. 



30a. Axis of the spikelet beset with conspicuous long hairs about 

 equaling the lemmas; tall marsh grass 1 4 m. high 



Reed, Phrag-mites communis. 

 30b. Spikelets without conspicuous long hairs 31. 



31a. Spikelets sessile or nearly so, forming crowded or spike-like 



panicles 32. 

 31b. Spikelets distinctly panicled 33. 



32a. Spikelets in dense one-sided clusters at the ends of the 

 panicle branches Orchard Grass, Dactylis glomerata. 



32b. Spikelets in an erect spike-like cluster 



Prairie June-grass, Koeleria cristata. 



33a. Lemmas, exclusive of the awn when present, 8 mm. long or 



more 34. 

 33b. Lemmis, exclusive of the awn when present, 6 mm. long or 



less 35. 



