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........-22-2.-.------ Dirrusa (p. 71). 
Rootstocks present; sheaths gla- 
brous.........-...-.-.------ Viraata (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 oftensecund.......- 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. 
hians 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). 
