12- BULLETIN 772, U. S. DEPARTMENT 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. SCRIBNKRIA. 



3b. Lemmas awnless ; florets dorsiventral to the rachis 4 



4a. First glume wanting 42. LEPTUBTJS. 



4b. First glume present, the pair standing in front of the 



spikelet 43. PIIOLIURUS. 



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. LOT.ITJM. " 



5b. Spikelets placed flatwise to the rachis G 



6a. Plants perennial i 33. AGROPYRON. 



6b. Plants annual 7 



7a. Glumes ovate, 3-nerved 34. TRTTICUM. 



7b. Glumes subulate, 1-nerved 3.1. SKCAI.K. v 



Ib. 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 



lOa. Rachis continuous (rarely tardily disarticulating) ; 



glumes broad or narrow, entire 37. ELYMTJS. 



lOb. Rachis disarticulating at maturity; glumos subulate, 

 extending into long awns, these and the awns of the 

 lemmas making the spike very bristly 38. STTAXIOX. * 



Tin in: 4, AVKXKAE. 



Spikelets 2 to several flowered in open or contracted panicles, or 

 rarely in racemes (solitary in Danthonia unispicata) ; 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 closely 

 allied to Trisetum with which they agree in having oblanceolate 

 glumes about as long as the first floret. 



