DESCRIPTIONS OF TRIBES AND GENERA. 57 



strong balsamic products in these grasses may protect 

 them from being exterminated by grass-eating animals.) 



31. (82) Arthraxon Beauv. (Pleuroplitis Trin., Batlira- 

 Utmi.m Nees, Luccea Kunth, Alectoridia Rich., Psilopogoa 

 Hochst.,Lasiolytrum Steud.). Racemes usually digitate, 

 delicate, often becoming true spikes by the abortion of 

 the $ spikelet together with its pedicel. Spikelets 

 awned, very rarely awnless. Delicate grasses. 



Species nine, in the tropics of the Old World ; one 

 extends to Japan, China, and Asia Minor. 



32. (94) Andropogon L. Racemes solitary or in pairs, 

 digitate or panicled, occasionally reduced to a few joints 

 or to the terminal joint with three spikelets. Rachis 

 and callus of the first empty glume usually hairy. 

 Spikelets usually narrow, the pedicellate $ , empty, or 

 reduced to the pedicel, its flowering glume awnless, but 

 the first empty glume occasionally awned. Palea fre- 

 quently small or 0. 



A polymorphous genus, spread over all parts of the 

 world in the tropical and temperate zones ; the species 

 prefer dry places, especially savannas. The numerous 

 sub-genera form two distinct series. 



Series A. Isozygi. The sessile spikelets of the lowest 

 pairs in each raceme like those above as regards sex, 

 form, and awns. 



Sub-genus I. Schizachyrium (Nees as a genus). Ra- 

 cemes slender, solitary, usually smooth, terminal upon 

 the culm or its branches, the thickened joints of the 

 rachis with a cup- or tooth-like appendage at the apex. 

 Flowering glume often cleft nearly to the base, awned 

 from between the divisions ; second empty glume awnless. 



Species twenty-seven, in the tropics, especially of 

 America, and as far north as New England (e.g., A. 

 scoparius Mich.). 



Sub-genus II. Diectomis (Humb. & Bonpl. as a 

 genus). Like Sub-genus I, but the spikelets laterally 

 compressed, the second empty glume awned, the flower- 

 ing glume slightly notched at the point. 



Species one, in tropical countries. 



Sub-genus III. Hypogynium (Nees as a genus). Ra- 



