De I. VNER VEW D Forest Trees of the Pacific Slope

FOREST TREES OF THfE PACIFIC SLOPE. 203
Trunks 10 feet high may be entirely covered. Gradually these dead, but always
stiff and prickly, leaves are forced off at the base of the trunk by the growth of
the trunk and by wind, uncovering an ashy, gray, cross-checked and ridged
bark. Except on old trees, the greater part of the tree is covered with dead,
closely thatched leaves. This covering of formidable living and dead leaves
suggests a wise protective measure through which alone the tree is able to
maintain and extend itself, with little check from its enemies, in a region often
lacking in other vegetation. The bluish-green leaves (fig. 80, a) are from 6 to
about 10 inches long and about five-eighths of an inch wide; longer leaves occur
on young trees. Leaves taper gradually from just above the base (19 inches
wide) to the point. The upper half is concave, tapering to a long, keen, reddish
or blackish brown point; the lower half of the leaf is fiat or only slightly
concave, while the two edges have minute teeth throughout. A single stiff,
branched cluster (about 15 inches long) of rather fetid flowers grows from the
end of the crown branches. The fruit (fig. 79, b), usually matured early in June,
is borne on short stems, at first standing more or less erect, but after maturity
somewhat drooping or bent down. The fruit covering is dry and soft. It rarely
opens of its own accord, but when very dry and brittle it is blown or falls from
the tree, and later is blown about and broken open by the wind and its seed
scattered. The six chambers of the fruit are filled with fiat, jet-black seeds
(fig. 79, c, d). Wood rather soft and light (when dry), but tough on account
of its strong fibers; pale yellowish white. Further investigation may establish
its permanent usefulness for paper pulp, for which it is suitable.a
LONGEVITY.-Nothing can be said definitely of the age to which this tree
attains. It is very probable that an individual lives at least 100 to 200 years,
and there seems little doubt that these trees may live 200 to 300 years. The
growth appears to be very slow in both height and diameter, but very persistent.
Its big, strong roots descend to great depths, giving the trees firm anchorage. It
is frequently bent and bowed, but few trees succumb to storm, and not often to
fire, which does not burn their stiff, hard leaves as readily as in the case of the
thinner and more inflammable leaves or " thatch " palm trunks.
RANGE.
Southwestern Utah to the western and northern rim of the Mohave Desert in
California.
OCCURRENCE.
Arid, desert plains and valleys, lower mountain slopes, benches, and plateaus, in dry,
sandy and gravelly soils. Forms large pure, open or rather close stands; sometimes
much scattered singly and in groups and with California juniper and single-leaf and
Sabine pines. Low, scanty growths of cactus and other desert shrubs occur with the
yucca.
CLIMATIC CONDITIONS.-Similar to those of California juniper (with probably higher
temperature).
TOLERANCE AND REPRODUCTIoN.-Undetermined.
Xohave Yucca.
Yucca mnohavensis Sargent.
DISTINOGTISIII 0G CHARACTERISTICS.
The Mohave yucca has been known for about fifty years, but until about
eleven years ago it had been confounded with two other species, from which it
is now known to be distinct. Since its most extensive and characteristic growth
is found on the Mohave Desert, the common name here coined for it seems more
a Considerable local use of the wood has recently been made for physician's splints.
The logs are pared into thin sheets.