SILVA OF NORTH AMERICA. 
YUCCA. 
FLOWERS perfect ; perigone 6-parted, the segments more or less united at the base; 
stamens 6; ovary superior, 3-celled ; ovules numerous in each cell, horizontal. Fruit 
baccate, fleshy and indehiscent, or capsular and dehiscent. Leaves clustered at the 
summit of the stem, linear-lanceolate, entire, serrate or filamentose, exstipulate, per- 
sistent. 
Yucca, Linneus, Gen. 99 (1737).— Adanson, Fam. Pl. ii. 
49. — A. L. de Jussieu, Gen. 49. — Endlicher, Gen. 144. — 
Meisner, Gen. 398. — Engelmann, Trans. St. Lowis Acad. 
iii. 17.— Bentham & Hooker, Gen. iii. 778. — Engler, 
Engler & Prantl Pflanzenfam. ii. pt. v. 70. 
Codonocrinum, Willdenow, Roemer & Schultes Syst. vii. 
pt. i. 718 (1829). 
Plants, with endogenous stems subterranean or barely emerging from the surface of the ground, or 
sometimes rising into tall simple or branched columnar trunks covered with dark thick corky bark, 
light fibrous wood in concentric layers, thick stoloniferous saponaceous root-stocks and thick rootlets, or 
long tough stout roots. Buds naked, in the axils of upper or of lower leaves, ovate, acute, flattened by 
pressure against the leaves, their lowest leaves white, scarious, and early deciduous, prolonging the stem 
after the death of its apex with the terminal inflorescence, often remaining dormant in the stem for 
years, and then producing lateral clusters of leaves. Leaves involute in the bud, alternate, mostly 
closely imbricated at the summit of the stem, erect at first, becoming reflexed,’ elongated, linear- 
lanceolate, abruptly narrowed above the broad-clasping often much thickened base, usually widest 
near or above the middle, concave and involute toward the apex below the horny usually sharp-pointed, 
rarely obtuse, occasionally soft and herbaceous, terminal spine, thick and ridged or thin and flaccid, 
more or less concave and sometimes deeply channeled on the upper surface, convex and usually 
bluntly keeled toward the base on the lower surface, smooth or scabrous, the margins serrulate with 
small remote irregular cartilaginous teeth, or roughened while young with minute deciduous knobs 
and soon becoming discolored and brittle, or filamentose by the separation of the marcescent 
marginal fibres into thick or thin, straight or curved, white or reddish threads, bright or dull green or 
glaucous, persistent for one or many years, exstipulate. Flowers slightly fragrant or strong-smelling, 
entomophilous,” produced in large many-flowered terminal compound glabrous pubescent or tomentose 
1 The reflexion of the leaves of Yucca aloifolia and other species 
as studied by Webber (Rep. Missouri Bot. Gard. vi. 98) is contem- 
poraneous with the completion of the definite growths or phytome- 
roids of the stem, only the leaves of the last phytomeroid being 
erect. After this has produced its panicle of flowers and fruits, or 
in about two years after the appearance of the bud at the base of 
the panicle of the previous growth, the leaves on this terminal 
phytomeroid all begin slowly to reflex, and, becoming more and 
more dependent and depressed against the stem, and finally dying 
at the end of several years, remain for several years more on the 
plant. 
2 The structure of the flower of Yucca, with stamens shorter 
than the ovary, precludes self-fertilization, and the large pollen- 
masses cannot reach the stigmatic tube except through the agency 
of insects. Only one species is known to produce fruit when trans- 
ferred from its native region and deprived of the visits of the 
