HITCHCOCK AND CHASE NORTH AMERICAN PANICUM. 29 



Spikelets not silky-villous. 



Panicles more or less diffuse (somewhat con- 

 tracted in P. hirsutum and P. gouini); 

 the spikelets not short-pediceled along 

 raceme-like branches. 

 Spikelets pointed, glabrous; culms te- 

 rete. 

 Rootstocks wanting; sheaths usually 



hirsute Diffusa (p. 71). 



Rootstocks present; sheaths gla- 

 brous Virgata (p. 84). 



Spikelets obtuse and glabrous or pointed 



and sparsely hispid See ungrouped tropical 



species, nos. 76 to 81. 



Panicles more or less contracted, or the 



spikelets short-pediceled along the 



main branches. 



First glume usually about one-fifth the 



length of the rounded-obtuse 



spikelets; tropical species Parviglumia (p. 124). 



First glume usually more than one-third 

 the length of the acute spikelets 

 (subobtuse in P. stenodes and cer- 

 tain species of Laxa). 

 Culms erect or stiffly ascending, not 

 geniculate; sterile palea not 

 enlarged at maturity ; panicle 

 branches not conspicuously 

 raceme-like; blades linear. 

 Panicles few-flowered ; con- 

 tracted; sterile palea not 



enlarged at maturity Tenera (p. 97). 



Panicles many-flowered, open 

 or contracted; the short- 

 pediceled, pointed spike- 

 lets often secund Agrostoidia (p. 99). 



Culms often decumbent or more or 



less geniculate, if stiff and 



erect the sterile palea enlarged 



at maturity ; panicle branches 



raceme-like (except in P. 



Mans and P. exiguiflorum) . 



Second glume and sterile lemma 



boat-shaped or the latter 



bearing two crateriform 



glands; spikelets glabrous 



or pubescent Stolonifera (p. 120). 



Second glume and sterile lemma 

 not boat-shaped (or the 

 glume but slightly so) nor 

 gland-bearing; spikelets 

 glabrous or scabrous at 

 the apex only Laxa (p. 110). 



