No. 20. 



CHLORIS ALBA Pnsl. 



Plaid annual. 



Root slender, numerous. 



Culms branching from the base and lower axils, procumbent at the base, rarely 

 rooting at the lower nodes, glabrous, commonly \^ to 3 feet high, often less. 



Leaves 4 to 8 on the stem; sheaths glabrous, more or less bladdery-inflated, 

 often loose, usually not contiguous; blades 1 to 2^ lines broad, 9 inches long or 

 much shorter, flat, glabrous beneath, scabrous on the margins and above. 



Inflorescence a sheathed or pedunculate cluster of sessile spikes. Spikes 5 to 

 15, 3 to 3^ inches long, only slightly spreading; rachis filiform, terete, straight, 

 scabrous; spikelets closely set, sessile, in 3 rows along one side. 



Spikelets compi'essed, 3-flowered; lower flower hermaphrodite; upper staminate 

 or reduced to a sterile glume, 1^ to 3 lines long (exclusive of awns and hairs). 



Ohtmes 4; first one-third to one-half the length of the spikelet, lanceolate, 

 acute or obtuse, membranaceous, 1-nerved, nerve scabrous; second about two-thirds 

 the length of the spikelet, lanceolate, acute, membranaceous, its single nerve scab- 

 rous and produced into an aristate point nearly reaching the apex of the spikelet; 

 rachilla pilose between the second and third glumes; third (flowering) obovate, 

 compressed, apex narrowed making the glume hooded, pilose in irregular areas 

 on the back, or glabrous, the margin short-pilose below, and on either margin 

 near the apex long-pilose, hairs two-thirds as long as the spikelet, apex of the 

 glume produced into a slender, scabrous, straight, not twisted awn two to three 

 times the length of the spikelet; sterile glume similar in shape to the flowering 

 glume, biit smaller and glabrous, with a nearly equal awn. Rudiment of a third 

 flower sometimes i^resent. 



Flower hermaphrodite. Palet oblanceolate, 2-nerved, margins folded inward. 

 Stamens 3; anthers small, sagittate-lanceolate, i line long; stigmas small, cylin- 

 drical. Flower of sterile glume sometimes wanting, sometimes represented only 

 by a palet, rarely by stamens also. 



Grain narrowly fusiform, acute at both ends, | to 1 line long, inclosed in the 

 flowering glume, the rachilla disarticulating above the second glume. 



Plate XXIX; a and b, spikelet, rachilla broken at the point of disarticula- 

 tion, and the parts spread open. In a the shorter glume should be on the right and 

 below, the longer on the left. In b, the sterile glume and the rudiments of a 

 third flowering glume are shown. 



This species is common in the southern parts of this region, and still more 

 common in Mexico. 



