19b. Panicle of smaller size =Panic-grasses, various species of Panicum.= 20a. Panicle strongly contracted or spike-like; plants of sand-dunes --4a. 20b. Panicle spreading or slightly contracted; axis of the spikelet beset with bristles; leaves 2 dm. long or more; marsh grass =Reed Grass, Calamagrostis canadensis.= 20c. Panicle spreading or somewhat contracted, but not spike-like; axis of the spikelet without bristles --21. 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, Muhlenbergia 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, Eleusine 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 interrupted spike --28. 27a. Glumes lanceolate =Wild Rye, Elymus canadensis.= 27b. Glumes narrowly subulate =Wild Rye, Elymus virginicus.= 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, Avena 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, Phragmites 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.=