HITCHCOCK—-MEXICAN GRASSES. 
Lower sheaths glabrous, reticulate- 
nerved; spikelets 3 mm. or more 
long. ...--.-0---- eee eee eee e eee 
Racemes 1 to several, rarely as many as 10, 
not approximate. 
Spikelets minute, not over 1.3 mm. long; 
plants annual. 
Plants cespitose; blades linear, pilose; 
second glume glandular-pubescent. 
Plants stoloniferous; blades lanceolate, 
glabrous or nearly so; spikelets gla- 
brous and with a ring-like margin, 
the midnerve of the sterile lemma 
suppressed...------eee2-2 eee reese 
Spikelets 1.5 mm. or more long; plants 
perennial. 
Culms decumbent at base, rooting at the 
nodes (occasional plants in dry situ- 
tions erect from the base), branch- 
ing; spikelets acute or subacute, 2.4 
mm. or more long; rachis about 2 
mm. wide; plants of moist ground. 
Spikelets glabrous, lurid purplish; 
axis of inflorescence slender, flexu- 
OUS..-----2--+--- 
Spikelets pubescent. 
Axis of inflorescence slender, sub- 
flexuous; spikelets not strongly 
CONVEX...---- eee ee eee eee 
Axis of inflorescence stout, not flex- 
uous; spikelets strongly con- 
Culms erect or ascending, not rooting at 
the nodes; spikelets usually obtuse. 
Plants with stout scaly rootstocks; 
culms solitary; spikelets elliptic, 
subacute......-----+-+++-- +225 
Plants without scaly rootstalks; culms 
tufted. 
Spikelets 2.5 mm. or more long, not 
turgid; culms tall, simple. 
Sheaths and blades, at least the 
lower, densely and softly 
grayish-villous; spikelets el- 
liptical; racemes spreading. - 
Sheaths glabrous or pilose along 
the margin toward the sum- 
mit, papillose-pilose at the 
junction with the blade; 
blades glabrous beneath, con- 
spicuously pilose near the 
base above; spikelets broadly 
obovate; racemes erect. -..--- 
33. 
12. 
_ ii. 
. 29. 
30. 
31. 
. 37. 
229 
P. virgatum. 
P. clavuliferum. 
P. orbiculatum. 
P. lividum. 
P. buckleyanum. 
P. pubiflorum. 
P. jaliscanum. 
. P. crinitum. 
. P. glaberrimum. 
