PINE TREES OP ROCKY MOUNTAIN REGION. 11 



growth remain on the tree for approximately T or 8 years, but some 

 of them for only 4 or 5 years. The cones (PL VI, a, h) mature by 

 the end of August or early in September of the second year. At this 

 time they are a deep purple. They have very thick scales, and vary 

 in length from about 1^ to nearly 3^ inches. Rarely, if ever, do the 

 cone scales become separated sufficiently to liberate the nutlike seeds 

 (PL VI, c) . As a rule, while the cones are still on the trees, and long 

 before they are ready to fall, practically the entire crop of seeds is 

 devoured by mountain squirrels and such birds as Clark's crow. The 

 birds get the seeds by tearing away the cone scales; squirrels very 

 cleverly extract all of the seeds by cutting a hole in one side of the 

 cone (PL VI, a). The few cones that remain unopened on the trees 

 and finally reach the ground gradually become loosened and broken 

 by decay ; then the seeds fall out or germinate in the rotted remains 

 of the cones. The seeds (PL VI, <?), about half an inch in length by 

 one-third of an inch in diameter, have very narrow wings, which 

 remain attached to the cone scales when the seeds fall out or are ex- 

 tracted; the thick, hard shell of the seeds is dark chocolate-brown. 

 The seed-leaves of this species vary in number from 7 to 9. 



The wood of the white-bark pine is rather soft, but firm in texture, 

 and when dry very brittle. It has only a thin layer of whitish sap- 

 wood. The heartwood is pale brown when freshly cut. Owing to the 

 exceedingly slow growth of the tree, the wood is very narrow-ringed. 

 A cubic foot of dry wood weighs approximately 26 pounds. Pros- 

 pectors occasionally use logs from this tree for cabins, for timbering 

 "prospect holes," and for fuel. 



OCCURRENCE AND HABITS. 



Pinus albicaulis is confined to rather narrow altitudinal limits on 

 alpine slopes and exposed ridges at elevations between 5,000 and 

 12,000 feet (Map No. 3). It grows among broken bare rocks, in 

 disintegrated granite, and in shallow rocky soils with little super- 

 ficial moisture, the best growth, however, being in well-drained, moist 

 soil. 



White-bark pine sometimes occurs in pure open stands on grassy 

 areas, but usually in open, parklike growth, preferably on north 

 slopes with alpine fir, Engelmann spruce, Lyall larch, limber pine, 

 and lodgepole pine. Perhaps its ■ most characteristic occurrence is 

 in scattered clusters of from three to seven trees, which appear to 

 grow as from the same. root. 



Pinus albicaulis is somewhat intolerant of shade in youth, becom- 

 ing still less tolerant with age. It appears to be more intolerant in 

 the North than in the South. In the South it shows a preference for 

 north slopes. Greater tolerance of shade is shown on good moist 

 soils at low altitudes than on poor dry ones near timber line. 



