THE WOOD. 21 



throughout the life of the tree and not only ruins a log, but renders 

 the tree apt to be broken by the wind. (PI. VI, fig. 2.) 



The mode of propagation of Arceuthobium is curious. Male and 

 female flowers are on separate plants, and the fruit, borne late in the 

 fall, is a berry containing a sticky seed. When ripe, but only in dry 

 weather, the berry explodes, throwing the seed several feet. If it 

 happens to strike the branch of the same or another Hemlock, its glu- 

 tinous covering enables it to adhere until it germinates and forces roots 

 through the bark of its host. Since this is possible only on the thin, 

 tender bark of } T oung wood, the older portions of the tree are exempt. 

 After a few years the parasite dies, but the distortion caused by it 

 remains and the branch dies or remains permanently diseased. Its 

 lateral growth usually stops and a fan-like mat of twigs radiates from 

 the injured portion. (PI. VIII, fig. 1.) 



In a few coast districts and cool mountain valleys the Arceuthobium 

 renders the Hemlock practically worthless, and by covering the ground 

 with fallen trees and branches increases the danger from fire. The 

 enfeeblement of the trees doubtless also facilitates the entrance of 

 fungous diseases. Where the parasite is abundant, the trees die at 

 the top and their crowns become tufted and narrow. It does not gen- 

 erally occur in sufficient quantity to be of economic importance and 

 need not enter into a discussion of the use and future of Hemlock. 



THE WOOD. 



There is little similarity between the wood of the Eastern and 

 Western Hemlock. That of the Western tree is light, rather hard, 

 straight grained, tasteless, tough, and usually white, although often 

 reddish-brown in the interior of the tree. This discoloration is not 

 confined to the heartwood, but may extend into the sap, and is usually 

 darkest where it does so. It is a serious defect in timber which is used 

 forpulpwood, for finishing, or as a substitute for Spruce. Trees thus 

 affected are commonly knowm by lumbermen as " Black Hemlock," and 

 are frequently believed to be a different species. This does not refer 

 to the true Black or Alpine Hemlock, which grows only at great alti- 

 tudes and is not yet available for lumber. 



In strength, case of working, and freedom from warp and shake, 

 Western Hemlock differs greatly from the Eastern species, whose 

 deficiencies in these respects are its chief drawbacks. Western Hem- 

 lock can not be classed in strength with Oak. lied Fir, or Lonerleaf 

 Pine, nor is it suitable for heavy construction, especially where 

 exposed to the weather; but it possesses all the strength requisite for 

 ordinary building material. It i- largely used in Washington for mill 

 frames. 



When green. Hemlock contains much water and is very heavy; when 

 dry it is but little heavier than Spruce, in some localities no heavier. 



