No.2. 
CENCHRUS TRIBULOIDES L. 
Plant annual. Roots slender. 
Culms glabrous, a few inches to 3 feet high, usually branching from the base 
and procumbent, rooting at the lower nodes, or sometimes the shorter plants erect. 
Leaves of the stem 3 to 10; sheaths glabrous, rarely ciliate on the margins 
above, usually loose, commonly contiguous; blade 6 inches long or less, 1 to 2 lines 
broad, flat or sometimes involute; ligule about $ line long, deeply densely fimbriate. 
Inflorescence a short-pedunculate or partly sheathed spike of clusters, 4 inches 
long or reduced to a single cluster, the rachis nearly smooth. Clusters composed 
of 2 to 3 spikelets surrounded by an involucre. Involucre thick, coriaceous, cleft 
to the base on the side next the rachis or on both sides, inclosing the spikelets; 
the outer surface provided with numerous bristles and spines flattened below and 
retrorsely barbed, those toward the base of the involucre smaller, the larger 23 lines © 
ng. 
Spikelets 2to 3 in each involucre, 1 at least fully developed and with the 
following structure (the others rudimentary in various degrees). 
Glwmes 4; 3 lower membranaceous; first short, ovate, acute, 1- to 3-nerved, 
empty; second broadly lanceolate, 5-nerved, acute, nearly as long as the involucre, 
empty; third like the second, but subtending a flower; fourth (flowering) a little 
larger and similar in form to the second and third, but thin-coriaceous. 
Flowers 2. Lower staminate, with a thin hyaline 2-nerved palet; stamens 3. 
Upper with a thin-coriaceous palet, hermaphrodite; ovary flattened, circular in 
outline; stamens 3, anthers $ line long, dehiscing much earlier than those of the 
staminate flower. 
Grain inclosed in the spikelet, spikelet inclosed in the involucre, the whole 
disarticulating from the spike together. 
PLATE VII; a, external view of the involucre; b, the same cut open to show 
the spikelets; c, a single fully developed spikelet opened to show the parts. On 
the left are the second glume, the fourth glume, and the hermaphrodite flower; on 
the right are the first glume, the third glume, and the staminate flower. The first 
glume should be inserted below the second, and is represented twice too long, as 
are the anthers of the hermaphrodite flower. 
This species is too common in sandy grounds, where its spiny burs are an an- 
noyance to men and beasts and an injury to the wool of sheep that graze near it. 
