HITCHCOCK—MEXICAN GRASSES. 183 
Racemes cylindric, readily 
disarticulating........ 9. CoELORACHIS (p. 198). 
Racemes flattened, tardily 
disarticulating.......- 8. HemMarTuria (p. 197). 
Joints of rachis not greatly thick- 
ened nor with excavations. 
Spikelets 2-flowered; racemes 
several, corymbose..... 7. IscoaEMuUM (p. 197). 
Spikelets 1-flowered. 
Spikelets all pedicellate, 
the pistillate with long 
feathery awns; axis in- 
distinctly articulate... 11. TRacHyPoaon (p. 198). 
Spikelets sessile and pedi- 
cellate; axis distinctly 
articulate. 
Racemes solitary, termi- 
nating the culm, the 
spikelets | awnless; 
first glume with a 
balsam-bearing line 
within the side keels 12. Etyonurus (p. 199). 
Racemes 1 to many, 
sometimes reduced 
to the terminal joint 
of 3 spikelets, if soli- 
tary the spikelets 
awned. 
Sessile spikelets not all 
alike, some of the 
lower differing 
from the upper and 
bearing a_ short 
awn. 
Racemes _ solitary, 
terminating the 
culm or its 
branches, the 
awns long, be- 
coming entan- 
gled........-.-- 17. HeTERopPoaon (p. 212). 
Racemes in pairs 
from a2 boat- 
shaped sheath, 
the short awns 
not becoming 
entangled...... 14, CymBoProcon (p. 209). 
Sessile spikelets all 
alike. 
Inflorescence con- 
sisting of 1 to 
many racemes, 
the spikelets ar- 
ranged in pairs, 
