PINE TREES OP ROCKY MOUNTAIN REGION". 27 



straight and, in mature trees, free from branches for from one-third 

 to one-half their height. The crown form of old trees is rounded, 

 and that of young trees broadly conical. On old trunks the bark is 

 about 2 inches thick, very dark or blackish brown, the close, separable 

 scales often showing light reddish brown in the deep, narrow furrows 

 and also when freshly broken. 



Each season's growth of the dark yellow-green foliage remains on 

 the branches about two years, beginning to fall during the third sea- 

 son. The sharp-pointed leaves (PL XVI), which are borne in 

 clusters mainly of 5 (occasionally of 2-, 3-, and 4-, with the 5-leafed 

 clusters), are from about 4 to sometimes 9| inches long, but com- 

 monly from 5 to 7 inches long. The leaves produced each year vary 

 greatly in length, even on the same tree, according to whether the 

 season is favorable or unfavorable for growth. The leaves have close, 

 persistent, basal sheaths from three-fourths of an inch to 1 inch long. 

 The sheaths are a pale yellow-brown at first, later becoming grayish 

 with exposure. The edges of the leaves have minute teeth (serra- 

 tures) . In cross section the leaves show three resin ducts, one in each 

 corner of the section. 



The cones (Pis. XVI, XVII), which mature at the end of the 

 second season, are one-sided (oblique) because of the greater devel- 

 opment of the scales on one side. They are from 2 to 3^ inches long 

 and externally light yellowish brown, the ends of the cone scales 

 being more or less glossy, but becoming ash-colored with age. The 

 upper sides of the scales are a clear cinnamon-brown, while the lower 

 sides are a deep purplish brown. On one side -of the cones the ends 

 of the cone scales have strongly developed, sharp-edged knobs, while 

 on the opposite side the knobs are much less prominent. All of the 

 cone scales terminate in a delicate incurved prickle, which is usually 

 broken off in old, weathered cones (PL XVII). As with the closely 

 related western yellow pine, the cones are borne on very short stems, 

 which remain on the branches, with a few of the basal cone scales 

 attached, when the cones fall from the trees. Most of the cones fall 

 during late autumn or winter following maturity and after their 

 seeds are shed. The seeds (PL XVII, a) are provided with broad 

 wings which are a pale cinnamon-brown. Perfect seeds are borne 

 under all of the cone scales, except the lower 3 or 4 layers, where 

 they are abortive. The number of seed-leaves is unknown at present. 



The wood of Arizona pine is similar in general appearance to that 

 of western yellow pine. It has a very thick layer of whitish or very 

 light straw-colored sapwood, the heartwood being a pale reddish yel- 

 low. In old trees the wood is especially narrow-ringed and rather soft 

 and brittle. A cubic foot of dry wood weighs nearly 3LJ pounds, 

 being slightly heavier than that of western yellow pine. The best 



