GENERA OF GRASSES OF THE UNITED STATES. 7 



Spikelets articulate above the glumes (rarely below, but the 



glumes, at least one, well developed). 

 Spikelets 1-flowered in groups (short spikes) of 2 to 5 

 (single in Osterdamia), the groups racemose along 

 a main axis, falling entire ; lemma and palea thin- 

 ner than the glumes 6. Nazieae (p. 165). 



Spikelets not as above. 



Spikelets sessile on a usually continuous rachis 

 (short-pedicellate in Leptochloa; the rachis 

 disarticulating in Monerina, Phpliurus, Hor- 

 deum, Sitanion, and a few species of allied 

 genera). 

 Spikelets on opposite sides of the rachis; spike 



terminal, single /. 3. Hordeae (p. 87). 



Spikelets on one side of the rachis ; spikes usu- 

 ally more than 1, digitate or racemose. 



7. Chlorideae (p. 171). 



Spikelets pedicellate in open or contracted, some- 

 times spikelike, panicles (sessile and distant 

 in Eragrostis sessilispica) . 



Spikelets 1-flowered 5. Agrostideae (p. 121). 



Spikelets 2 to many flowered. 



Glumes as long as the lowest floret, usually 

 as long as the spikelet; lemmas 

 awned from the back (spikelets awn- 

 less in Koeleria and Sphenopholis). 



4. Aveneae (p. 106). 



Glumes shorter than the first floret (except 

 in Dissanthelium with ,long rachilla 

 joints) ; lemmas awnless or awned 

 from the tip or from a bifid apex. 



2. Festuceae (p. 24). 



SUBFAMILY 2, PANICATAE. 



Spikelets with one perfect terminal floret (disregarding those of 

 .ne few monoecious genera and the st animate and neuter spikelets) 

 and a sterile or staminate floret below, usually represented by a sterile 

 lemma only, one glume sometimes (rarely both glumes) wanting; 

 articulation below the spikelets, either in the pedicel, in the rachis, or 

 at the base of a cluster of spikelets, the spikelets falling entire, singly, 

 in groups, or together with joints of the rachis; spikelets, or at least 

 the fruits, more or less dorsally compressed. 



Key to the tribes of Pamcatae. 



Glumes membra naceous, the sterile lemma like the glumes in texture. 

 Fertile lemma and palea thinner than the glumes; sterile lemma 



awned from the notched summit 11. Melinideae (p. 212). 



Fertile lemma and palea indurate or at least firmer than the glumes. 



12. Paniceae (p. 213). 

 Glumes indurate ; fertile lemma and palea hyaline or membranaceous, the 



sterile lemma (when present) like the fertile one in texture. 

 Spikelets unisexual, the pistillate below, the staminate above, on the 

 same inflorescence or in separate inflorescences. 



14. Tripsaceae (p. 280). 



