3c. Bracts of the spikelet without terminal awns, but the spikelets with one or more long bristles arising from their base --6.

4a. Spike-like panicle thickened in the middle, more than 1 cm.

thick =Beach Gra.s.s, Ammophila arenaria.=

4b. Spike little or not at all thickened in the middle, less than 1 cm. thick --5.

5a. Lower bracts awned; stem erect, unbranched =Timothy, Phleum pratense.=

5b. Lower scales unawned; stem branched at the base =Floating Foxtail, Alopecurus geniculatus.=

6a. Bristles 5 or more at the base of each spikelet =Yellow Foxtail, Setaria glauca.=

6b. Bristles 1-3 at the base of each spikelet --7.

7a. Spikelets about 2 mm. long; bristles not much longer, green =Green Foxtail, Setaria viridis.=

7b. Spikelets about 3 mm. long; bristles much longer, usually purple =Millet, Setaria italica.=

8a. Spikelets numerous, in long slender symmetrical spikes --9.

8b. Spikelets in panicles, racemes, or loose spikes --13.

9a. Spikelets without awns; plants 8 dm. high or less (Crab Gra.s.s) --10.

9b. Spikelets with awns; plants 12 dm. high or more --12.

10a. Leaf-sheaths all glabrous. =Crab Gra.s.s, Digitaria humifusa.=

10b. Lower leaf-sheaths hairy --11.

11a. Axis of the spike flat, with wing-like margins =Crab Gra.s.s, Digitaria sanguinalis.=

11b. Axis of the spike slender, without winged margins =Crab Gra.s.s, Digitaria filiformis.=

12a. Spikes numerous, appressed to the axis of the panicle; tall marsh gra.s.s =Slough Gra.s.s, Spartina michauxiana.=

12b. Spikes 2-6, widely divergent; plant of dry ground =Blue-joint, Andropogon furcatus.=

13a. Spikelets subtended by an ovoid th.o.r.n.y involucre 3-8 mm. wide =Sand Bur, Cenchrus carolinia.n.u.s.=

13b. Spikelets without a th.o.r.n.y involucre --14.

14a. Lower branches of the panicle spreading, bearing staminate flowers, the upper branches erect, with pistillate flowers; aquatic or marsh gra.s.s 2-4 m. high =Wild Rice, Zizania aquatica.=

14b. Panicle uniform throughout --15.

15a. Spikelets with awns 2 mm. or more long --16.

15b. Spikelets not awned, or with short inconspicuous awns --18.

16a. Spikelets in solitary raceme-like spikes; awn about 1 cm. long or more =Beard Gra.s.s, Andropogon scoparius.=

16b. Spikelets in branching cl.u.s.ters; awn less than 1 cm. long --17.

17a. Leaf-blade 4 mm. wide or narrower; panicle slender =Drop-seed, Muhlenbergia schreberi.=

17b. Leaf-blade 6 mm. wide or more; panicle stout and coa.r.s.e =Barnyard Gra.s.s, Echinochloa crus-galli.=

18a. Spikelet plump and compact, its bracts closely folded about each other --19.

18b. Spikelet very flat, its two bracts closely folded together =Cut-gra.s.s, 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 Gra.s.s, Panic.u.m capillare.=

19b. Panicle of smaller size =Panic-gra.s.ses, various species of Panic.u.m.=

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 gra.s.s =Reed Gra.s.s, 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-gra.s.s, 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 Gra.s.s, 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 Gra.s.s, 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.