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PINE TREES OF ROCKY MOUNTAIN REGION. iy 
cross section of the leaf shows two resin ducts (near the border on 
the back of leaf). 
The cones ripen during September and drop their seeds* by the 
middle or latter part of October. Only the scales in the middle of 
the cones bear perfect seeds. Externally, the cones are pale yellowish 
or reddish brown. The empty cones fall from the trees mostly in 
late autumn and early winter. Mature cones (Pl. X, 0, ¢) which 
are globelike or egg-shaped and borne on very short stems, vary in 
length from about 1 inch to 24 inches, and in breadth from about 1 
inch to nearly 2? inches. The seeds (Pl X, e) are from one-half 
to three-fourths of an inch long by about one-fourth to three-eighths 
of an inch wide. They vary in color from light yellowish brown 
to a deep chocolate-brown on the under surface (which is always 
darker) to cinnamon-brown on the upper side. The pale cinnamon 
brown wings of the seeds are extremely short (rudimentary) and re- 
main attached to the scales when the seeds fall (Pl. X, 0, «, f). 
Seed-leaves are from 9 (occasionally 8) to 15 in number. 
The wood of Pinus cembroides is very narrow-ringed, and mod- 
erately soft, but firm. It 1s the heaviest of all the Rocky Mountain 
pines, a cubic foot of dry wood weighing about 403 pounds. In this 
country the wood is used locally only for fuel and for other minor 
domestic purposes. 
OCCURRENCE AND HABITS. 
Pinus cembroides grows in poor, shallow, rocky, and gravelly soils 
on hot mountain slopes, precipitous canyon sides, benches, and foot- 
hills at elevations between 4,800 and 7,500 feet (map No. 5). Within 
our border it forms scattered growths, interspersed here and there 
with Quercus reticulata, Y. hypoleuca, and Y. arizonica. In its 
more extensive range in Mexico it sometimes occurs in practically 
pure, but rather open stands. 
The light requirements of this species are insufficiently known at 
present ; but it appears to be intolerant of shade, except during early — 
youth, and even at that time it endures only niall shade. 
Seed production occurs usually every other year, but heavy crops of 
seed are borne only at intervals of three or four years. Trees begin to 
bear cones comparatively early, seed production increasing steadily 
to old age. A ‘large percentage of the seeds are sound, but their 
vitality is very transient, so that, except under specially favorable 
conditions for germination, reproduction occurs sparingly. Seed- 
lings are generally much scattered, and mainl? on washed mineral 
soil. Sparse reproduction where the tree occurs abundantly is prob- 
1The seeds are extensively gathered for food in Mexico; but in the United States few 
are obtained for this purpose because of the limited occurrence of the tree. 
61354°—Bull. 460—17 2 
