THE GRASSES OF BRITISH HONDURAS AND THE PETLN, GUATEMALA 145

 Spikes digitate.
 Rudimentary florets obsolete; rachilla prolonged as
 a naked bristle -......._. ....- -...._...... ... -14. Cynodon
 Rudimentary florets 1 or more, club-shaped........ 17. Chloris
 Spikelets 2 to several-flowered.
 Spikes racemose.
 Spikes elongate with numerous spikelets... - .11. Leptochloa
 Spikes very short, composed of a single 2-flowered
 spikelet and a rudimentary one reduced to
 awns ........ --.-.---.. -.. .c..... -19. Pentarrhaphis
 Spikes digitate.
 Rachis prolonged beyond the spikelets ....... ------ ____13. Dactyloctenium
 Rachis not prolonged....__. .........- ..-......_.12. Eleusine
 Spikelets in open or contracted panicles. (Festucea)
 Culms coarse, reedlike; rachilla hairy...........-. __-- 7. Phragmites
 Culms usually slender, not reedlike; rachilla glabrous.
 Lemmas firm, several-nerved .-...-.....___--...... 6. Distichlis
 Lemmas membranaceous, 3-nerved .......-- 5. Eragrostis
Spikelets with one fertile floret and often one or more sterile
 or staminate florets below it. Spikelets sometimes uni-
 sexual. (Spikelets with two fertile florets in Isachne and
 Ischomum.)
 Spikelets unisexual.
 Fruit milky white, indurate.
 Panicles large, terminal, the pistillate spikelets on the
 upper branches and toward the ends of the lower
 ones, the staminate spikelets arranged on the lower
 part of the lower branches ........... ......... 46. Olyra
 Panicles small, axillary, composed of a single terminal
 pistillate spikelet and several staminate spikelets
 below it. Terminal panicles, if any, wholly stami-
 nate .....__ .. ............... _----47. Lithachne
 Fruit not milky white.
 Staminate and pistillate spikelets in the same inflores-
 cence.
 Spikelets distant, in pairs, appressed along the main
 panicle branches, the pistillate sessile, large, the
 staminate long-pedicellate, inconspicuous.____ 22. Pharns
 Spikelets approximate, the staminate in pairs on one
 side of the upper part of a continuous rachis, the
 pistillate solitary on opposite sides of the lower
 part of the same rachis __..... .. ....-57. Tripsacum
 Staminate and pistillate spikelets in separate inflor-
 escences -- 58-.---- 58. Zea
 Spikelets perfect
 Imperfect florets none below the fertile one.
 Spikelets articulate below the glumes, flattened later-
 ally; glumes usually small or wanting (Oryzes).
 Glumes small; lemmas awned (usually awnless in
 0. sativa).____- _____...._._____20. Oryza
 Glumes wanting; spikelets awnless........ ............___ 21. Leersia
 Spikelets articulate above the well-developed glumes,
 not strongly laterally compressed. (Agrostidee)
 Lemmas 3-awned; callus sharp-pointed __ _______ 9. Aristida
 Lemmas awnless; callus blunt.____._.._.____ 8. Sporobolns
 Imperfect florets one (four in Streptochaeta), composed
 of a lemma, a reduced or fully developed pales and
 sometimes a staminate flower.
 Lemma with a long much contorted awn..- 4. Streptochmta