56 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
17. PANICUM L. Panic arass. 
Annuals or perennials; spikelets 1-flowered, or rarely with a staminate flower below 
the terminal perfect one, paniculate; glimes very unequal, the first often minute, 
the second subequal to the sterile lemma; fertile lemma and palea chartaceous- 
indurated, the nerves obsolete, the margins of the lemma inrolled; grain free within 
the rigid lemma and palea. 
KEY TO THE SPECIES. 
Spikelets arranged in pairs in 1-sided racemes; plants spread- 
ing by long stolons...................0..2. 2 2c e eee eee 1. P. obtusum. 
Spikelets panicled; plants without stolons. 
Leaf blades of two sorts, those of the stems broad and short. 
Spikelets less than 3 mm. long; leaf blades thin; 
sheaths glabrous or sparsely hispid............ 2. P. helleri. 
Spikelets more than 3 mm. long; leaf blades firm; at 
least some of the sheaths hispid............... 3. P. scribnerianum. 
Leaf blades all alike. 
Annuals, 
Inflorescence of several more or less secund, spike- 
like racemes. 
Spikelets strongly reticulate-veined, glab- 
10) 4. P. fasciculatum reti- 
culatum, 
Spikelets not reticulate-veined, pubescent 
and copiously papillose-hirsute....... 5. P. arizonicum. 
Inflorescence a more or less diffuse panicle. 
First glume very short, not over one-fourth 
the length of the second; sheaths glab- 
50 6. P. dichotomiflorum. 
First glume longer, half as long as the second 
or more; sheaths pubescent. 
Panicles somewhat drooping............ 7. P. miliaceum. 
Panicles erect. 
Panicles large, more than half the 
length of the entire plant.... 8. P. barbipulvinatum. 
Panicles small, not over one-third 
the length of the plants. 
First glume more than three- 
fourths the length of the 
second; spikelets 4 mm. 
long....--..22..2--.22-- 9. P. pampinosum. 
First glume half to two-thirds 
the length of the second; 
spikelets not over 3.3 mm. 
long..--..2........2220. 10. P. hirticaule. 
Perennials. 
Stems neither bulbous nor rhizomatous. 
Sterile palea enlarged and indurated at ma- 
turity; glumes acute. ............... 11. P. hians. 
Sterile palea not enlarged; glumes acumi- 
nate.........20222. ee ee eee eee eee LZ. P. hallii. 
