PINE TREES OF ROCKY MOUNTAIN REGION. 31 
The foliage, borne in heavy brush-like clusters at the ends of bare 
branches, is a deep yellow-green. The leaves (Pls. XVIII, XIX) 
occur in bundles of 3 (sometimes of 2 and rarely of 4 and 5, and then 
chiefly on saplings). They vary in length from about 43 to 114 
| inches. Each season’s growth of leaves remains on the tree about 
three years. The edges of the leaves have minute teeth (serratures). 
A cross section of the leaves shows from 2 to 5 resin ducts, the usual 
number being 2. : 
The cones (Pls. XVIII, XIX) mature early in August of the 
second season and shed their seeds mainly during September. The 
cones of some trees are a bright grass green when mature, while those 
of other trees are a dark purple, there being no other essential differ- 
ence between trees bearing cones so dissimilar in color. Cones vary 
in length from 23 to about 5% inches and in width from 14 to about 
2 inches. The ends of the cone scales are russet-brown and shiny. 
After the seeds are shed, the cones begin to fall, and by early winter 
they are all down. A notable characteristic of the cones of this pine 
is that when they break away from the branch some of the basal 
scales are left on the tree. The seeds (Pl. XVIII, a), which vary 
greatly in size, are marked with purple spots and blotches on a dull 
yellowish ground, while the wings are a light purple-brown. The 
number of seed-leaves varies from 5 to 9 (Pl. XVIII, bd). 
Western yellow pine wood is narrow-ringed, the rather thick layer 
_ of sapwood being nearly white and the heartwood ranging from a 
pale lemon-yellow to an orange-brown or a reddish yellow. It varies 
greatly in texture according to the age of the tree. Young trees have 
moderately hard, resinous, strong wood; the wood of old trees is 
brittle, only slightly resinous, and very soft—so much so that lumber 
cut from such trees is sold as “ white pine.” In general a cubic foot 
of dry wood weighs from about 283 to 292 pounds. The weight of 
wood from very old, slowly grown trees would probably not exceed . 
about 25 pounds per cubic foot. It is one of the most valuable com- 
mercial woods produced in the Rocky Mountain region, being uséd 
for all sorts of dimension timber under cover, for interior and ex- 
| terior work, railroad ties, mining timber, fuel, etc. It-is, however, 
_ only moderately durable in contact with earth or when exposed to 
the weather in an unprotected state. 
OCCURRENCE AND HABITS. 
Western yellow pine occurs on dry and moist slopes, on the tops of 
ridges and in canyon bottoms, in general at elevations between 
1,800 feet (Pacific region) and 10,300 feet (southern Rockies), the 
‘main forest growth in the Rocky Mountain region being found be- 
