8 BULLETIN 460, TJ. S. DEPARTMENT OF AGRICULTURE. 



silvery. The exceedingly tough twigs are at first covered with fine, 

 soft hairs, which soon disappear, leaving the branchlets quite smooth. 



The dark yellow-green foliage is densely set at the ends of the 

 branches. The leaves, borne in clusters of 5 (Pis. Ill, IV, V), are 

 from about If to nearly 3 inches long. Each year's growth of leaves 

 persists for approximately 5 years, a few sometimes remaining until 

 the sixth year. The margins of the leaves bear minute widely sepa- 

 rated teeth. A cross section of the leaf shows two resin ducts (on 

 the back of the leaf) near the border; sometimes also there is a third 

 resin duct near the inner or lower border of the leaf. The back 

 (dorsal) side of the leaves is marked by from 1 to 4 lines of minute 

 pores (stomata). 



The cones (Pis. Ill to V) are mature in late summer or early 

 autumn of the second year, and shed their seed in September or early 

 in October. They are from 3^ to 10 inches long and peculiar in 

 having the tips of their light j^ellowish-brown scales greatly thick- 

 ened (PI. Ill, c). The inner or concealed portions of the scales are 

 pale red. By early winter the cones have fallen from the trees (Pis. 

 Ill, a; IV, a). The seeds (PI. Ill, h) are deep reddish brown and 

 speckled with blackish brown. The seed-leaves are usually from 6 

 to 8 or sometimes 9 in number (PL V, a). 



The wood of limber pine is very narrow-ringed, on account of the 

 slow growth of the tree, and has only a thin layer of sapwood, 

 which is nearly white. Freshly cut heartwood is a pale lemon- 

 yellow. In texture the wood is rather soft but firm. A cubic foot 

 of dry wood weighs about 27 pounds. Limber pine is occasionally 

 cut for rough construction lumber which is used locally, the quality 

 of the lumber being poor because of numerous knots. The wood is 

 also used locally for fuel and sometimes for rough cabins and mine 

 props. 



OCCURRENCE AND HABITS. 



Limber pine grows on dry, rocky, east slopes, summits, tops of 

 ridges and foothills, and sometimes on the sides of moist canyons 

 and banks of mountain streams, at elevations between 5,000 and 

 12,000 feet (Map No. 2). It is adapted to a great variety of soils 

 and is not exacting as regards their depth or the amount of moisture, 

 though it grows best in moist, well-drained soils. Usually it occurs 

 in dry, rocky, very shallow soil, appearing to prefer dry gravelly 

 loam with little or no humus. Limber pine reaches higher elevations 

 on clay soils than it does on sandy ones, the higher ascent in clay 

 soils being due to their greater retentiveness of moisture, which is 

 especially favorable to seedling growth. This species is of much 

 more frequent occurrence in the Kocky Mountain region than in the 

 Pacific region. 



