66 MISSOURI BOTANICAL GARDEN. 
South of Torreon, along the Mexican Central railroad, 
particularly from about Picardias to about Jalisco, this 
small tree is abundant, on or near the rocky hillsides, and 
conspicuously contrasted with accompanying Y. T’reculeana 
by its very glaucous narrower foliage. It may be that small 
trees between Monterey and Saltillo, visible from the Mexi- 
can National railroad, extend its range to the east. 
Yucca rigida, the specific name of which is descriptive 
only when its dried leaves are compared with those of Y. 
rupicola, is one of the handsomest tree Yuccas, in its foli- 
age. The slender trunks are commonly simple, but occas- 
ionally once or more forked, with elongate branches. When 
well developed the leaves are from .3 to .6 m. long, 20 to 30 
mm. wide, and, as would scarcely be inferred from herba- 
rium material, decidedly concave up to the very slender 
pungent terete point; both surfaces are closely ridged and 
often minutely roughened, and the bright yellow margin, 
though occasionally nearly smooth, is usually finely den- 
ticulate, so as to possess a keen cutting power. Though, as 
has been said, the plant forms a low tree when developed, 
a few specimens have been seen bearing panicles when still 
practically acaulescent, as is also true of Y. radiosa about 
El Paso. The panicles are loosely branched shortly above 
the crown of leaves, and the very hard oblong capsules, 
about 50 mm. long and 25 mm. in diameter, are parted 
about to the middle into 3 valves which are conspicuously 
flattened or even concave on the back, and with short out- 
curved apical points, and the inner or placental dehiscence 
is very narrow, so that the small thin black seeds escape 
only when jarred out edgewise. 
Dr. Engelmann would doubtless have given specific rank 
to this tree, had he not misapprehended its relation in size 
and field appearance to the typical acaulescent often twisted- 
leaved Y. rupicola, which, in contrast with it, he called 
variety tortifolia. The foliage and capsular characters 
added above leave no room for question as to its specific 
distinctness from the latter. 
