PINE TREES OF ROCKY MOUNTAIN REGION. 37 
of an inch to 14 inches thick, deeply and narrowly furrowed, and 
with long, wide, interrupted ridges. 
The slender, bluish-green or grayish-green leaves (Pl. XXV, 6) 
occur in bundles of 3 (occasionally of 4, and exceptionally of 5), and 
when full grown are without basal sheaths (common to other asso- 
ciated yellow pines). The short, papery, scaly sheaths of immature 
leaves remain attached only until the end of the first summer or 
autumn. - Mature leaves are from 2 to 44 inches long, but usually 
about 3 inches. The edges of the leaves have minute, distinct, sharp 
teeth (serratures). A cross section of the leaves shows two resin 
ducts. Each season’s growth of leaves persists for about 3 years, 
being shed during the fourth season. 
The cones (Pl. X XV, a, c), matured in September of the third 
season,! are from about 14 to 22 inches long, and are borne on a short, 
rather slender, curved stem from three-eighths to five-eighths of an 
inch long (Pl. X XV, ¢). Mature cones are at first a light, yellowish 
brown, later becoming dull gray by exposure to the weather. Un- 
exposed parts of the cone scales: vary from a light to a deep purple 
brown. The slightly thickened ends of the cone scales have a low, 
sharply defined ridge and bear delicate prickles, which gradually 
disappear as the cones become older. Mature cones adhere to the 
trees 5 or more years, and when they fall they usually retain their 
stems. The chocolate-brown seeds (Pl. X XV, d) have pale yellow- 
ish-brown wings delicately splashed with darker brown. The num- 
ber of seed-leaves is unknown at present. 
In general the wood of Chihuahua pine is moderately narrow- 
ringed and straight-grained and rather hard. The light straw-col- 
ored, thick layer of sapwood, containing from 50 to 60 annual layers 
of growth, contrasts strongly with the reddish-yellow heartwood. A 
cubic foot of dry wood weighs about 34 pounds, being considerably 
lighter than that of western yellow pine but having its good working 
qualities. The best grades are equal to western yellow pine for com- 
‘mercial purposes. The comparatively small size and limited supply 
of this tree available in our Southwest, however, prevent it from 
“being used for lumber. 4 
OCCURRENCE AND HABITS. 
This species occurs on dry, rocky, gravelly mountain slopes and 
benches at elevations between 5,500 and 8,200 feet (map No. 12). 
The thrifty growth of this tree in moist and rich soils shows that it 
can profit by such favorable conditions, the growth in drier situa- 
1 Pinus chihuahuana is exceptional among western pines in that its male and female 
flowers do not appear. until July, which is much later than in the case of other pines of 
its range. 
2The Chihuahua pine attains large dimensions in Mexico, where it is probably being 
lumbered along with such associated timber pines as. Pinus arizonica, P. ponderosa, and 
P. strobiformis. 
