CONIFERS OF THE ROCKY MOUNTAIN REGION. 11 



Like the western larch, this alpine species is very intolerant of shade 

 throughout its life. Little is known now regarding its seeding habits. 

 Sometimes cones are produced abundantly, but apparently at in- 

 frequent and irregular intervals. Reproduction in the United States 

 is generally scanty, seedlings never being numerous, which may be 

 due to the fact that much of the seed falls on the snow and is carried 

 away during spring floods. 



LONGEVITY. 



Alpine larch is a long-lived tree, attaining an age of from 400 to 

 600 years. Exceptionally large trees are doubtless 650 to 700 years 

 old, or even older, the exact age limits being imperfectly known at 

 present. Trees from 16 to 18 inches in diameter are from 470 to 510 

 years old. 



GENERIC CHARACTERISTICS OF HEMLOCKS. 



The hemlocks, which belong to the genus Tsuga, are evergreen trees 

 with soft, flat, or rounded-triangular leaves (Pis. IV and V). Their 

 branches grow from the trunk at irregular intervals, differing in this 

 respect from the pines, spruces, and balsam firs, the branches of 

 which occur in regular whorls. The slender terminal sprays of the 

 hemlocks droop gracefully, and the slender leaders nod conspicuously 

 from the tops of the crowns. Hemlocks are large trees with broad 

 pyramid-shaped crowns and long, slightly tapering trunks, which have 

 characteristically rough, hard bark narrowly ridged and furrowed. 

 The bark contains tannin, which gives it an astringent taste, and 

 when broken it displays a clear chocolate-red color. 



The leaves, which have small, threadlike stems, are spirally arranged 

 around the twigs. According to the form of the leaves and size of the 

 cones our native hemlocks are divided into two groups. One group 

 has rounded leaves, so arranged that they completely cover the upper 

 side of the twigs, and large cones (PI. V) ; while the other group has 

 flat leaves so arranged that they appear to grow only from two oppo- 

 site sides of the twigs, the cones of this group being comparatively 

 small (PL IV). A twist in the stem of the leaves brings them into 

 the characteristic positions described. The leaves of hemlocks are 

 peculiar in having but one resin duct, which, as seen in a cross section 

 of the leaf, is situated in the center of the leaf near the lower surface. 

 Leaves of a season's growth remain on the trees for from about 3 to 

 6 years, giving the twigs a well-covered appearance. 



The male and female flowers are borne separately on different 

 parts of the same tree, on twigs formed the preceding season. The 

 female flowers grow at the ends of the twigs, while the male flowers 

 are borne singly from buds at the bases of the leaves near the ends 

 of the branchlets. Female flowers, which produce cones and seed, 

 are small, greenish, scaly bodies, while the male flowers, pollen- 



