each other --19.

18b. Spikelet very flat, its two bracts closely folded together
=Cut-grass, Leersia oryzoides.=

18c. Spikelet loose and open, somewhat flattened, its 3 bracts
ascending or spreading and not closely folded about each other
--20.

19a. Panicle about half as long as the entire plant; leaves copiously
hairy =Witch Grass, Panicum capillare.=

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 s