HITCHCOCK—MEXICAN GRASSES. 
Spikes more or less hairy, the spikelets awned. 
Sterile spikelet 2 mm. long, the pedicel very 
woolly. ....-2-----2+-- ee eee ee ee terete 
Sterile spikelet 4 to 6 mm. long, the pedicel 
hairy or ciliate but not woolly. 
Spike hairy on the entire rachis and sterile 
pedicels... .--...-0--- esse seer eee 
Spike hairy only along the edge of the 
sterile pedicel or at top of joints. 
Sessile spikelets 5 mm. long; sterile 
pedicel slightly hairy. ....... 
Sessile spikelets 6 mm. long; sterile 
pedicel fringed with long hairs. 
Spikes more than one from each sheath (rarely solitary in A. 
furcatus). 
Spikes 2 to 4 from a bract-like leaf sheath at the ends of 
the stems and from the axils of the leaves, sometimes 
aggregated in a compound inflorescence. 
Spikes in pairs, aggregated in a dense narrow inflores- 
cence, widened above; sheaths inclosing the base 
of spikes; stems tall, stiffly erect; spikes delicate, 
woolly with long hairs. 
Spikelets awnless; sheaths of inflorescence narrow 
and tightly rolled. ...--------++-+--+-+--- 16. 
Spikelets awned; sheaths of inflorescence broad, 
not tightly rolled...-.--------+--++-+----+-- 13. 
Spikes 2 to 4, not aggregated in a dense inflorescence. , 
Spikes somewhat hairy but not conspicuously 
woolly, the axis stout ......--------+-+---- 20. 
Spikes conspicuously woolly or silky with long 
white or tawny hairs. 
Axis of spike straight and rather stout; spikes 
2, exserted from the slender sheath; ses- 
sile spikelets awned; pediceled spikelet 
well developed .......-..------+++-+++- 21, 
Axis of spike slender, often flexuous. 
Spikelets awnless. 
Spikes 5 to 8 cm. long, usually in- 
closed at base; spikelets large; 
sterile pedicel 6 mm. long; 
culms about 60 cm. high...... 18. 
Spikes about 2.5 cm. long, the group 
long-exserted on a slender pe- 
duncle; spikelets small, these 
and the sterile pedicel less 
than 3 mm. long; culms 65 to 
100 cm. high. ..........------ 17. 
s Spikelets awned. 
Hairs of the rachis and sterile pedicels 
scarcely half as long as the 
spikelets; axis nearly straight. 19. 
Hairs of the rachis and sterile pedicels 
longer than the spikelets; axis 
flexuous. 
201 
. A. myosurus, 
. A. feensis. 
. A, tener. 
. A. cirratus. 
A. bicornis. 
A. glomeratus. 
A, furcatus. 
A, hirtus. 
A. bourgaei. 
A, leucostachyus. 
A. pringlei. 
