THE GRASSES OF BRITISH HONDURAS AND THE PETEN, GUATEMALA 147

 Fertile lemma wingless.
 Spikelets with two fertile florets ......... 39. Isachne
 Spikelets with one fertile floret.
 Second glume inflated, saccate at the
 base; spikelets unsymmetrical.......-36. Sacciolepis
 Second glume not inflated; spikelets sym-
 metrical.
 First and second glumes equal, similar-38. Homolepis
 First glume rarely more than half as
 long as second, not similar to it.
 Panicles dense, spikelike; spikelets
 acuminate -... ....-..- 37. Hymenachne
 Panicles open; spikelets obtuse to
 subacute.
 Spikelets with a tuft of woolly
 hairs on the tips; plants
 woody, clambering........ ..--. 35. Lasiacis
 Spikelets without woolly hairs;
 plants herbaceous ... 33. Panicum
 Glumes indurate or at least firmer than the lemmas.
 Spikelets solitary, arranged in panicles, lemmas as
 firm as the glumes ...... .__. .... 23. Arundinella
 Spikelets paired, arranged in racemes, these solitary,
 paired, or numerous in a paniculate inflor-
 escence: lemma hyaline.
 Racemes in a paniculate inflorescence.
 Panicle silky; spikelets awnless.
 Rachis continuous; spikelets unequally pe-
 dicellate ---.....-- ..-........-- .-....... 48. Imperata
 Rachis breaking up at maturity; lower spike-
 let sessile, the upper pedicellate .......... 49. Saccharum
 Panicles not silky; spikelets awned -_--..--..- 53. Sorghum
 Racemes solitary or paired, sometimes aggregate
 in a large compound inflorescence.
 Culms simple with a single terminal erect
 raceme (sometimes more); awns plumose,
 3 to 5 em. long ........ -.... ..- ___54. Trachypogon
 Culms branching, at least above; awns, if pres-
 ent, not plumose, usually less than 15 mm.
 long.
 Spikelets all perfect, alike ....................... 55. Ischaemum
 Spikelets unlike, the lower sessile, perfect,
 the upper pedicellate, usually reduced.
 First glume of sessile spikelct enlarged,
 globular; spikelets awnless; plants
 annual --.......... ......... .. . ...... ...56. Hackelochloa
 First glume of sessile spikelet neither en-
 larged nor globular; spikelets awned;
 plants annual or perennial.
 First glume sharply 2-keeled, at least
 toward the summit.
 Spikelets of lower pairs unlike, fertile
 and sterile_. .._. .......... 50. Andropogon
 Spikelets of the lowermost pairs alike,
 staminate or neuter ...... .. .51. Cymbopogon
 First glume rounded on the back, the
 margins involute ............. -...----- 52. Hyparrhenia