244 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Plants not grayish nor velvety; 
spikelets 2.2 to 2.4 mm. 
long.....--2-...2---2-22-- 49. P. pseudopubescens. 
Basal leaves similar to culm leaves, not form- 
ing a winter rosette; spikelets all fertile. 
Fruit transversely rugose. 
Culms with a corm-like base. 
Blades mostly over 5 mm. wide; culms 
more than 1 meter high............ 24. P. bulbosum. 
Blades less. than 5 mm. wide; culms 
rarely as much as 1 meter high.... 24a. P. bulbosum sciaphi- 
lum. 
Culms from a strong rootstock, not corm- 
like at base. 
Nodes hirsute; ligules 4 to 6 mm. long; 
fruit strongly rugose............... 22. P. maximum. 
Nodes glabrous; ligules 2 mm. long; fruit 
very obscurely rugose............. 23. P. plenum. 
Fruit not transversely rugose (minutely pa- 
pillose-roughened in P. millegrana). 
First glume very small, not over one- 
fourth the length of the small obo- 
vate blunt spikelet. 
Blades 12 to 16 cm. long, 2 to 3 cm. wide; 
fruit glabrous. .......-............ 38. P. parviglume, 
Blades not over 10 cm. long nor 1.8 cm. 
wide; fruit with scattered silky 
hairs. 
Blades scabrous on the upper surface, 
not faleate............00.0.22-. 36. P. virgultorum, 
Blades sparsely hispid on the upper 
surface, faleate................-. 37. P. schmiten. 
First glume as much as one-third the 
length of the spikelet (less in P. 
trichanthum with pointed spikelets). 
Spikelets papillose-hispid, obovate, ob- 
tus@............-2--22-2222 222. 41. P. millegrana, 
Spikelets glabrous, 
Sterile paleas enlarged and indurated 
at maturity, expanding the 
crowded spikelets; blades scarcely 
wider than their sheaths. ........ 32. P. cupreum. 
Sterile palea, if present, not enlarged 
and indurated. 
Culms arising from a decumbent or 
creeping base, but not forming 
scaly rootstocks, 
Spikelets 5.5 to 6 mm. long; fruit 
crested at the apex ......... 56. P. zizanioides. 
Spikelets not over 3 mm. long; 
fruit not crested. 
Spikelets pointed, not over 1.4 
mm. long................ 40. P. trichanthum. 
