228 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Spikelets glabrous or pubescent, the pubescence 
short, not silky. 
First glume present at least on the lower of the 
pair of spikelets (sometimes wanting toward 
the base of the raceme). 
Plants annual, coarse, about 2 meters high; 
first glume inconspicuous, the second and 
the sterile lemma subchartaceous, glab- 
50) ce 35 
Plants perennial, rarely over 1 meter high; 
glumes and sterile lemma thin. 
Plants with stout running rootstocks, glau- 
cous; raceme erect, usually single; 
spikelets glabrous, narrowly obovate, 
acute; first glumes well developed, dis- 
similar on the pair of spikelets........ 38 
Plants without running rootstocks, not 
glaucous; racemes 2 to several or, if 
single, not erect. 
Spikelets glabrous; first glume obsolete 
on the upper of the pair of spikelets. 16 
Spikelets pubescent. 
Spikelets 3.2 to 3.4 mm. long; first 
glumes well developed, that of the 
upper spikelet with a scarious un- 
dulate border.................... 19 
Spikelets not over 3 mm. long, the first 
glume commonly obsolete in the 
upper spikelet, not having a scar- 
ious undulate border. 
Blades usually 15 mm. wide or more; 
spikelets about 2.5mm. long.... 18 
Blades rarely as much as 12 mm. 
wide; spikelets about 2.2 mm. 
First glume wanting, or only exceptionally 
present on a few spikelets (see also P. cras- 
sum with inconspicuous first glume). 
Racemes numerous, usually 20 or more, 
approximate. 
Spikelets about 1.3 mm. long, strongly 
plano-convex.................-...-. 22 
Spikelets 2 mm. or more long, not strongly 
convex, more or less ciliate around the 
edge; plants robust. 
Plants stoloniferous, widely creeping; 
inflorescence V-shaped in outline; 
spikelets narrowly ovate, 4 to 4.5 
mm. long, solitary.................. 32 
Plants not stoloniferous; inflorescence 
oblong. 
Lower sheaths hirsute, not reticulate; 
. P. crassum. 
. P. unispicatum. 
. P. culiacanum. 
. £. variabile. 
. P. planifolium. 
. P. langet. 
. P. paniculatum. 
. P. fasciculatum. 
spikelets 2mm. long............ 34. P. conspersum. 
