GENERA OF GRASSES OF THE UNITED STATES. 263 



last, is A. fut-catus Muhl. (PL XIX; fig. 1GO). This grows through- 

 out the eastern half of the United States and is an important forage 

 grass in the western portion of its range. Here it is the chief con- 

 stituent of prairie hay and is known as big bluestem. It is a 

 tall, usually purplish bunch-grass, the racemes only slightly hairy, 

 borne in twos to fours at the ends of the culms and the short 

 branches, the rachis strict. In the Great Plains, grasses are popu- 

 larly divided into tall grasses and short grasses. The former, of 

 which A. furcatus is the most important, are found chiefly in the 

 valleys and draws; the latter, including buffalo grass and grama 

 grass, are found on the uplands. The third group of Andropogon 

 is represented in this country by only three species, all extending 

 northward from Mexico into the Southwestern States. The very 

 hairy or feathery racemes are crowded in an oblong or somewhat 

 flabellate white panicle terminating the main culm and its branches. 

 One of these, J.. saccharoides Swartz (fig. 161) (A. argenteus DC., 

 -L-1. "barblnodis Lag.), is distinguished by the bearded nodes. Andro- 

 pogon saccharoides laguroides (DC.) Hack. (A. torreyanus Steud.), 

 with more slender culms and smooth nodes, is found as far north as 

 Kansas. Another species of the group, A. perforatus Trin., of 

 Moxioo, rare in this country, differs in having a little pinhole or. pit 

 in the first glume. 



An allied group of grasses is of importance in tropical parts of 

 the Old World because of the essential oils obtained from them. 

 They are included in Andropogon by some authors, but are referred 

 by others to Cymbopogon. A full account of these grasses is given 

 by Stapf. 1 The most important are citronella grass (Andropogon 

 nardus L. ; Cymbopogon nardus Rendle) and lemon grass (Andro- 

 pogon citratus DC., Cymbopogon citratus Stapf). These are robust 

 grasses with large compound inflorescences, the small racemes in 

 pairs, each pair partly included in a sheathing spathe. 



An allied genus, Anatherum Beauv., is represented by a single 

 species, A. zizanioides (L.) Hitchc. and Chase (Andropogon muri- 

 catus Eetz. ; Vetiveria zizanioides Nash). This Old World grass is 

 frequently cultivated in tropical America for hedges and for the 

 aromatic roots, which are used for making screens and mats to per- 

 fume the air of houses. These roots readily impart perfume when 

 wet. The grass is called vetiver, khus-khus, and khas-khas. It has 

 escaped from cultivation in Louisiana. Vetiver is a robust grass 

 with a large erect panicle, the slender whorled branches ascending, 

 naked at the base, the awnless spikelets muricate. 



1 Bull. Misc. Inf. Kew 1906: 297. 1906. 



