12 BULLETIN 772, U. S. DEPABTMENT OF AGRICULTURE. 
slender, extending into long awns, in the latter genus sometimes 
divided into several slender bristles. In this tribe the blades of the 
leaves bear on each side at the base a small appendage or auricle. 
Key to the genera of Hordeae. 
la. Spikelets solitary at each node of the rachis (rarely 2 in species of 
Agropyron, but never throughout) 2 
2a. Spikelets 1-flowered, sunken in hollows in the rachis; spikes 
slender, cylindric ; low annuals 3 
3a. Lemmas awned ; florets lateral to the rachis 36. Scribxeria. 
»' 3b. Lemmas awnless; florets dorsiventral to the rachis 4 
4a. First glume wanting 42. Lepturus. 
4b. First glume present, the pair standing in front of the 
spikelet 43. Pholiurus. 
2b. Spikelets 2 to several flowered, not sunken in the rachis 5 
5a. Spikelets placed edgewise to the rachis ; first glume wanting 
except in the terminal spikelet 41. Lolium. 
ob. Spikelets placed flatwise to the rachis 6 
6a. Plants perennial 33. Agropyron. 
6b. Plants annual : 7 
7a. Glumes ovate, 3-nerved 34. Triticum. 
7b. Glumes subulate, 1-nerved 35. Sec ale. 
lb. Spikelets more than 1 at each node of the rachis 8 
8a. Spikelets 3 at each node of the rachis, 1-flowered, the lateral 
pair pediceled, usually reduced to awns 40. Hordeum. 
8b. Spikelets 2 at each node of the rachis, alike, 2 to 6 flowered 9 
9a. Glumes wanting or reduced to 2 short bristles ; spikelets hor- 
izontally spreading at maturity ; spikes very loose 39. Hystrix. 
9b. Glumes usually equaling the florets ; spikelets appressed or 
ascending 10 
10a. Rachis continuous (rarely tardily disarticulating) ; 
glumes broad or narrow, entire 37. Elymi's. 
10b. Rachis disarticulating at maturity ; glumes subulate, 
extending into long awns, these and the awns of the 
lemmas making the spike very bristly 38. Sitanion. 
Tribe 4, Aveneae. 
Spikelets 2 to several flowered in open or contracted panicles, or 
rarely in racemes (solitary in Danthonia unispicato.) ; glumes usually 
as long as or longer than the first lemma, commonly longer than all 
the florets; lemmas usually awned from the back or from between 
the teeth of a bifid apex, the awn bent, often twisted, the callus and 
rachilla joints usually villous. 
A rather small tribe widely distributed in both warm and cool 
regions. In our genera the rachilla is prolonged beyond the upper 
floret as a slender stipe (except in Aspris). The lemma is awnless 
or nearly so in Sphenopholis and in our species of Koeleria. These 
genera are placed in this tribe because they appear to be closeh 
allied to Trisetum with which they agree in having oblanceolate 
glumes about as long as the first floret. 
