CONIFEES OF THE ROCKY MOUNTAIN REGION. 27 



restocked by western hemlock and red cedar. In the drier more 

 southern Rocky Mountain range of Douglas fir, burned-over ground 

 is usually unfavorable to reproduction of this species, lodgepole 

 pine, aspen, and other trees usually restocking such areas. Under 

 the most favorable conditions, reproduction of Douglas fir is ex- 

 tremely dense, an acre sometimes carrying over 30,000 trees about 

 3 feet high and 11 years old, while a stand of 26-year-old trees may 

 average 1,068 per acre, 45 feet high and 3| inches in diameter. 



LONGEVITY. 



Douglas fir is a very long-lived tree. Specimens from 3 to 4 feet 

 in diameter are from 150 to 200 years old, while those from 4 to 8 

 feet in diameter are from 200 to 375 years old. One tree 9 feet 

 through showed an age of 435 years. The ages of rare trees larger 

 than this are probably from 400 to 500 years. 40 



GENERIC CHARACTERISTICS OF INCENSE CEDARS. 



Trees of the group Libocedrus are characterized by their conical 

 trunks, thick bark, and the very strong but pleasant odor of their 

 light, soft, straight-grained, durable wood. The branchlets are 

 arranged in one plane, forming flat, fanlike sprays. The twigs of 

 adult trees are clothed with evergreen, scalelike, pointed leaves, 

 which overlap each other closely (PL IX a, b). On the short side 

 branchlets the leaves are much flattened, but on the larger main 

 stems they are rounded. The leaves of each season's growth remain 

 on the tree for about 4 or 5 years. In the case of seedlings the 

 leaves are needlelike, flat, sharp-pointed, and spreading (PI. X, b). 

 As the plants grow older this juvenile form of leaf is succeeded by 

 shorter and less and less spreading ones, until finally the scalelike 

 adult form of foliage is assumed. All of the leaves are arranged in 

 pairs, each pair being placed on the branch at right angles to the 

 preceding pair. The adult leaves also have characteristically long 

 bases, which extend downward, completely covering the branch, a 

 habit on which the technical specific name, decurrens, of our native 

 incense cedar is based. The seed-leaves (first foliar organs pro- 

 duced) are needlelike and flat and usually two in number, or occa- 

 sionally three (PL X, a) . 



Both the male and female flowers are small, inconspicuous, oval 

 or elongated bodies borne at the ends of branchlets produced the 

 previous year, the male flowers being of a yellowish green and the 

 female of a greenish color. They are both formed during the autumn, 

 but they open late during the succeeding winter or in early spring. 

 Flowers of the different sexes are sometimes borne on the same tree, 



« Mr. F. H. Conanc (see footnote 39) states (1. c.) that in sees 9 and 15, T. 21 N., R. 8 E., in west Wash- 

 ington, he counted the annual rings of growth of several trees which proved to be 600 and 700 years old. 



