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 1-J to 2| inches long; generally they 

 are about \\ inches long (Pis. 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 (Pis. XIII, «, b, 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 (PI. XIV) fall from the trees 

 during the winter or spring. The seeds (PI. 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-ringed, 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 35^ 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 Xo. 7). Its require- 

 ments of soil moisture and quality of soil are closely similar to those 

 of its frequent associates, the junipers, piiion, and chaparral, but less 



