THE WOOD. 21 



throughout tho life of the trci; aiid not only ruins a lojjf, Imt renders 

 the tree apt to he broken by the wind. (PI. V^I, lig-, 2.) 



The mode of proi)agation of Arccutbobiuiu is curiou.s. Male and 

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

 fall, is a berr}' containing a sticky seed. When rip(!, but only in dry 

 weather, the l)erry explodes, throwing the seed several feet. Tf it 

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

 tinous covering enables it to adhere until it g(M"minates and forces r<xjts 

 through the bark of its host. Since this is possible onl}^ on the thin, 

 tender l)aik of young wood, the older portions of the ti'ee arc exempt. 

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

 remains and the ))ranch dies or remains permanently diseased. Its 

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

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



In a few coast districts aiifl cool mountain valleys tlu^ ArcciUhobium 

 rendei-s tin; Ilendock pra(;tically woi-thless,and by covering the ground 

 with fallen trees and branches inci"(;ases the danger frotn fire. The 

 enfeebl(;ment of the trees doubtless also facilitates the (uitrancc 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 suffif-ient (juantity to be of economi(; importance and 

 need not enter into a discussion of tlx- use and future! of Hemlock. 



THE WOOD. 



There is little similarit}' between the wood of the East(!ni and 

 Western Hemlock. That of the Western tree is light, rathe i- hard, 

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

 reddish-brown in the interior of the ti'ce. This discoloration is not 

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

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

 forpul|)wood, for finishing, or as a substitute for Spruce. Trees thus 

 afiected are connnonlv known by lumbermen as '' Black Hcndock," and 

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

 to the true Black or Alpine Hemlock, which grows c>nly at gi-eat alti- 

 tudes and is not \'et available for lumber. 



In strength, ease of working, and fi'e(,'dom fiom waip and siiake, 

 Western Hemlock diflers greatly from the Eastern sjjecies, whose 

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

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

 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 is largely used in Washington for mill 

 frames. 



When green, Hemlock contains much water and is very heav^y; when 

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



