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PINE TREES OF ROCKY MOUNTAIN REGION. 95 
The cones mature at the end of the second season, and are then 
from 24 to about 34 inches long and of a deep chocolate-brown color 
tinged with purple. Each cone scale bears a bristlelike, very fragile 
prickle, which easily distinguishes the cones of this pine from other 
species of the region. Unexposed parts of the cone scales are clear 
reddish brown. The seeds (PI. XV, a, 6) are pale brown with ir- 
regular black spots, and are shed from about the last of September 
to the middle of October. Seed-leaves of this pine vary in number 
from 6 to 7. 
Bristle-cone pine produces rather narrow-ringed, soft, brittle wood 
with a thin layer of whitish sapwood and a pale brownish-red heart. 
Tt is moderately heavy for a white pine, a cubic foot of dry wood 
weighing about 34? pounds. On account of the poor timber form of 
the tree the wood is not used commercially. In the region of greatest 
abundance it is sometimes employed for fuel and mine props. 
OCCURRENCE AND HABITS. 
Pinus aristata is found on ridges and rocky ledges, but mainly on 
south slopes, here often predominating at elevations between 7,500 
to 10,800 feet (Map No. 8). It grows on thin, rocky soil, and fre- 
quently on volcanic soils of cinder cones. Usually growths of this 
tree are in isolated situations, where snow melts early and evapora- 
tion is rapid, so that the trees are subjected to more or less prolonged 
dryness of soil during summer. Rarely does this species form pure 
stands, the trees being usually scattered over grassy ground of a 
pravelly or rocky nature with little or no underbrush. It is most 
abundant at higher levels, where limber pine is its only associate. 
At lower altitudes it is often associated with Engelmann spruce, lim- 
ber pine, and western yellow pine, and occasionally with white fir. 
Bristle-cone pine never forms dense stands, which indicates that 
it is intolerant of shade during the greater part of its life. Seed- 
lings, however, endure ue shade for several years without material 
loss of vigor. 
Trees begin to bear cones when they are shyt 20 years old, and 
oroduce them practically every year thereafter, with specially hone 
crops at intervals of several years. Reproduction is always sparse 
and much scattered. Seeding often takes place at a distance of at 
least 600 feet away from mother trees. The large number of seeds 
eaten by rodents and the ease with which surface fires destroy the | 
large-winged seeds and kill the seedlings and dense-foliaged older 
plants doubtless account in great measure for the thin stands of this 
pine. Seeds germinate best in loose, exposed mineral soil, and less 
promptly in grass and litter. The seedlings appear to grow best 
on slopes with little or no underbrush. 
