22 BULLETIN 460, U. S. DEPARTMENT OF AGRICULTURE. 
flat crowns of short, heavy, twisted, and bent branches. The latter — 
grow from near the ground and often hang low, giving the appear- 
ance of an old apple tree. Young trees are very different in appear- 
ance because their low, thick trunks, have pyramidal crowns of 
rather straight, ascending branches. As a rule, the single-leaf pine 
does not exceed 25 feet in height and from 12 to 15 inches in diam- 
eter. In protected and otherwise favorable situations it may, how- 
ever, reach a height of from 35 to 50 feet. The bark of young trees 
is smooth and dull gray, while that of old trees is roughly and ir- 
regularly furrowed, nearly an inch thick, and with thin, close, 
dark brown, or sometimes reddish brown scales. The general color 
of the foliage is pale yellow green, with a whitish tinge. The single 
(or very occasionally double) leaves are stiff, curved toward the 
branch, prickly, and from about 14 to 24 inches long; generally they 
are about 14 inches long (Pls. XIII, XIV). Each season’s growth 
of leaves remains on the tree about 5 years; not infrequently, though, 
leaves persist for 10 or 12 years. A striking peculiarity of seedling 
trees is that they continue to produce only primary leaves for 6 or © 
7 years, after which they put forth the adult form of foliage. 
The cones (Pls. XIII, a, 6, and XIV, a) are matured in August 
of the second season, and the tips of the scales are then shiny and a 
deep russet-brown. The seeds fall within about a month after- 
wards. Most of the empty cones (Pl. XIV) fall from the trees 
during the winter or spring. The seeds (Pl. XIII, c) are dark 
‘chocolate-brown with dull yellowish areas. The pale brown seed 
wings, ragged and irregular, are from one-fourth to one-half of an 
inch long and remain attached to the cone scales (Pl. XIII, c—the 
torn border at inner ends of seeds). Seed-leaves of this pine range 
from 7 to 10 in number. 
The wood of single-leaf pine is very narrow-rimged, exceedingly 
brittle, and rather soft. It usually has a thick layer of whitish sap- 
wood, the heartwood being a pale yellowish brown. A cubic foot of 
dry wood weighs about 354 pounds. Settlers use large quantities of 
the wood for fuel and temporary fence posts, and a good many 
small towns within reach of the timber derive their principal supply 
of fuel from it. 
OCCURRENCE AND HABITS. 
Single-leaf pine occurs on low arid mountain slopes, canyon sides, 
foothills, and mesas, commonly at elevations between 2,000 and 7,000 
feet, or less frequently up to 9,000 feet (map No. 7). Its require-— 
ments of soil moisture and quality of soil are closely similar to those 
of its frequent associates, the junipers, pifion, and chaparral, but less 
