HITCHCOCK—MEXICAN GRASSES. 187 
First glume present; racemes 
racemose along the main 
AXIS... 2... eee eee eee eee 32. BRACHIARIA (p. 224). 
First glume wanting; racemes 
digitate or subdigitate... 33. Axonopus (p. 225). 
Spikelets placed with the back of 
the fruit turned toward the 
rachis of the spike-like racemes, 
or pedicellate in panicles. 
First glume typically wanting 
(present in some of the spike- 
lets in certain species); spike- 
lets plano-convex, subsessile 
in spike-like racemes.......- 34. PaspaLum (p. 226). 
First glume present; spikelets 
usually in panicles. 
Glumes or lemmas or both 
awned or, if short-pointed 
only (Echinochloa colonum), 
the summit of the fertile 
palea not inclosed. 
Glumes 2-lobed, awned from 
between the lobes; inflo- 
rescence of several uni- 
lateral racemes along a 
common axis........--.-. 42, OPLISMENUS (p. 255). 
Glumes entire, awned from 
the tip or only mucronate. 
Inflorescence of several 
more or less compound 
unilateral racemes; 
spikelets ovate, not 
having a callus-like 
base. ..-.--...+------ 43. EcHINOCcHLOA (p. 256). 
Inflorescence a narrow, 
almost spike-like pan- 
icle; spikelets lanceo- 
late, with a long callus- 
like base below the 
long-awned glumes.... 44. CHAETIUM (p. 259). 
Glumes and lemmas awnless. 
Spikelets typically with 2 
fertile florets; inflores- 
cence a panicle.......... 41. IsacHNe (p. 254). 
Spikelets with a single fertile 
floret. 
Glumes equal, inclosing the 
rest of the dorsally 
compressed _spikelet; 
margins of the fertile 
Jemma flat.....-.-.--- 40. Homo.eris (p. 254). 
Glumes not equal nor en- 
tirely inclosing the 
spikelet. 
