HITCHCOCK—MEXICAN GRASSES. 943 
Nodes glabrous. 
Spikelets 3 mm. long; 
glumes and sterile 
lemma papery.... 3. P. paludivagum. 
Spikelets not over 2.4 
mm. long; glumes 
and sterile lemma 
not papery........ 2. P. geminatum. 
Spikelets in open or sometimes in contracted or 
congested panicles, but not in spike-like 
racemes. 
Basal leaves usually distinctly different from 
those of the culm, forming a winter rosette; 
culms at first simple, the spikelets of the 
primary panicle not perfecting seed, later 
usually becoming much branched, the 
small secondary panicles with cleistoga- 
mous, fruitful spikelets. 
Spikelets glabrous, minute; culms and 
blades pilose..........-.-.-.--2------- 45. P. strigosum. 
Spikelets pubescent. 
Spikelets 2.8 mm. or more long. 
Sheaths pubescent; spikelets 4 mm. 
long, attenuate at base............. 51. P. nodatum. 
Sheaths glabrous or minutely puberu- 
lent only. 
Blades lanceolate, usually unsym- 
metrically falcate...........----- 53. P. joorit. 
Blades linear or nearly so..........-- 54. P. albomaculatum. 
Spikelets not over 2.4 mm. long. 
Blades stiff, conspicuously striate, taper- 
ing from base to apex; spikelets 
pustulose-pubescent, 2.1 to 2.2 mm. 
long, obtuse. .........-.---------- 46. P. ovinum. 
Blades not stiff and conspicuously stri- 
ate, linear, or lanceolate. 
Sheaths retrorsely pilose; blades soft 
and lax........-. ...... 44. P. xalapense. 
Sheaths not retrors sly pilose. 
Spikelets abruptly pointed; blades 
cordate. . eons . 52. P. viseidellum. 
Spikelets not pointed at maturity; 
blades not cordate. 
Plants glabrous as a whole, or the 
nodes and lower sheaths 
only pubescent. 
Nodes villous-bearded; spike- 
lets elliptic............... 47. P. multirameum. 
Nodes glabrous; spikelets spher- 
ical ......-- . 50. P. sphaerocarpon. 
Plants conspicuously pubescent 
as a whole, 
Plants grayish green, velvety; 
spikelets 1.9 to2 mm. long. 48. P. olivaceum. 
