DESCRIPTIONS OF TRIBES AND GENERA. 171 



* Flowering glumes awnless ; callus 

 naked 279. Lepturus. 



** Flowering glumes awned ; callus 



hairy 280. Scribneria. 



2. Empty glume one, very small. 



281. Psilurus. 



II. Spikelets two- to many-flowered, usually in 

 stout spikes whose joints either do not dis- 

 articulate at maturity, or which separate 

 with the spikelet above (Heteranthdium 

 excepted). 



1. All the spikelets fertile or the lowest 

 only sterile. 



* Flowering glumes with a distinct 

 callus which is limited by a furrow 

 at the base ; falling off at maturity, 

 each with a single grain which is 

 grown to the palea. 282. Agropyrum. 



** Flowering glumes without a callus, 

 persistent at maturity ; grain free, 

 t Empty glumes subulate, one- 

 nerved 284. Secale. 



ft Empty glumes oblong, truncate, 



two-keeled. . 283. Haynaldia. 



ttt Empty glumes ovate, three- to 



many-nerved. . 285. Triticum. 



2. The one fertile spikelet alternating 



with three sterile ones which consist of 



numerous long-awned glumes. 



286. Heteranthelium. 

 b. Spikelets 2-6 at each joint of the rachis. 



NOTE. Compare the lower joiuts of the axis in Scribneria. 



a. Stamens three in each flower. 



1. Spikelets one-flowered or with a rudiment 

 only of a second. . . . 287. Hordeum. 

 II. Spikelets two- to many-flowered. 



1. Empty glumes a little smaller than the 

 flowering glumes. . . . 288. Elymus. 



