GENERA OF GRASSES OF THE UNITED STATES. 263 
last, is A. furcatus Muhl. (Pl. XIX; fig. 160). 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, A. saccharoides Swartz (fig. 161) (A> argenteus DC., 
A. barbinodis 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 
Mexico, 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.t 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.) Hitche. and Chase (Andropogon muri- 
catus Retz.; 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. Mise. Inf. Kew 1906: 297. 1906. 
