8 BULLETIN 460, U. S. DEPARTMENT OF AGRICULTURE. 
silvery. The exceedingly tough twigs are at first covered with fine, 
soft hairs, which soon disappear, leaving the branchlets quite smooth. | 
The dark yellow-green foliage is densely set at the ends of the 
branches. The leaves, borne in clusters of 5 (Pls. ITI, IV, V), are 
from about 12 to nearly 3 inches long. Each year’s growth of leaves 
persists for approximately 5 years, a few sometimes remaining until 
the sixth year. The margins of the leaves bear minute widely sepa- 
rated teeth. A cross section of the leaf shows two resin ducts (on 
the back of the leaf) near the border; sometimes also there is a third 
resin duct near the inner or lower border of the leaf. The back 
(dorsal) side of the leaves is marked by from 1 to 4 lines of minute 
pores (stomata). | 
The cones (Pls. III to V) are mature in late summer or early 
autumn of the second year, and shed their seed in September or early 
in October. They are from 34 to 10 inches long and peculiar in 
having the tips of their light yellowish-brown scales greatly thick- 
ened (Pl. III, c). The inner or concealed portions of the scales are 
pale red. By early winter the cones have fallen from the trees (Pls. 
III, a; IV, a). The seeds (Pl. III, 0) are deep reddish brown and 
speckled with blackish brown. The seed-leaves are usually from 6 
to 8 or sometimes 9 in number (PI. V, a). 
The wood of limber pine is very narrow-ringed, on account of the 
slow growth of the tree, and has only a thin layer of, sapwood, 
which is nearly white. Freshly cut heartwood is a pale lemon- 
yellow. In texture the wood is rather soft but firm. A cubic foot 
of dry wood weighs about 27 pounds. Limber pine is occasionally 
cut for rough construction lumber which is used locally, the quality 
of the lumber being poor because of numerous knots. The wood is 
also used locally for fuel and sometimes for rough cabins and mine 
props. 
OCCURRENCE AND HABITS. 
Limber pine grows on dry, rocky, east slopes, summits, tops of 
ridges and foothills, and sometimes on the sides of moist canyons 
and banks of mountain streams, at elevations between 5,000 and 
12,000 feet (Map No. 2). It is adapted to a great variety of soils 
and is not exacting as regards their depth or the amount of moisture, 
though it grows best in moist, well-drained soils. Usually it occurs 
in dry, rocky, very shallow soil, appearing to prefer dry gravelly 
loam with little or no humus. Limber pine reaches higher elevations 
on clay soils than it does on sandy ones, the higher ascent in clay 
soils being due to their greater retentiveness of moisture, which is © 
especially favorable to seedling growth. This species is of much 
more frequent occurrence in the Rocky Mountain region than in the 
Pacific region. 
