﻿DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 37 



by the Indian paint fungus (E chinodoniium tinctorium E. and E.). 

 This is found on the true firs in the western United States, being 

 especially prevalent and severe on white fir (37). It is also exceed- 

 ingly serious on western hemlock (71). 



In white fir the first indications of this decay on a radial or tangen- 

 tial section are light-brown or golden tan spots or larger areas: of dis- 

 coloration in the light-colored heartwood, which may be accompanied 

 by small but clearly distinct radial burrows, resembling somewhat 

 very shallow insect burrows without the deposit of excrement. These 

 burrows are not easily detected in cross section. Next, rusty red- 

 dish streaks appear following the grain. Throughout this stage 

 the wood appears firm and strong, but in reality is so greatly weak- 

 ened that boards may separate along the annual rings when dried. 

 The discoloration intensifies, the wood becomes soft, showing a de- 

 cided tendency to separate along the spring wood in the annual rings, 

 and finally the typical stage is reached, in which the wood is brown, 

 with pronounced rusty, reddish streaks and becomes fibrous and 

 stringy. Hence, the name stringy brown-rot is applied to the decay. 

 The incipient decay usually extends from 2 to 6 feet beyond the 

 typical decay. Plate VI shows the incipient decay. 



In western hemlock the incipient decay is much harder to detect, 

 because the initial discoloration above described so closely approxi- 

 mates the pale-brown, slightly tinged with red, color of the normal 

 heartwood. The wood first assumes a faint yellowish color, which is 

 sometimes intensified by the presence of small, hardly discernible 

 brownish areas. These areas later develop into the typical decay. 

 The extension of the incipient decay beyond the typical decay varies 

 from 1 to 5 feet. For the sake of safety 2 feet should be added be- 

 yond the last recognizable yellowish discoloration in order to elimi- 

 nate all incipient decay. 



TYPES OF DECAY IN LIVING HARDWOOD TEEES. 



Hardwood trees are subject to very serious decays. One of the 

 most important from our standpoint is the white heartwood rot (58) 

 so commonly found in commercial white-ash stock, caused by the ash 

 Fomes (Fomes fraxinophilus (Pk.) Sacc). This fungus attacks 

 the heartwood of living trees and produces a very characteristic rot. 

 On cross section the first indication of the decay is a light brownish 

 discoloration, often difficult to distinguish from the normal grayish 

 brown or reddish brown heartwood. This discoloration is most ap- 

 parent in the broad bands of summer wood. Next, there is a bleach- 

 ing of the spring wood, during which it turns to a straw color, and 

 then small white spots or specks appear. On the radial (edge- 

 grain) and tangential (slash-grain) faces these appear as small whit- 

 ish spots, streaks, or blotches, usually following the grain, but some 

 may be at right angles to it if the decay follows a medullary ray. 

 The whitish color becomes more marked, until the entire spring wood 

 is affected and appears disintegrated. Then the fibers fall apart. 

 The summer wood passes through the same process, but much more 

 slowly, thus during the earlier stages of the typical decay causing a 

 banded appearance. The completely rotted wood is whitish or straw 

 colored, very soft, and spongy, readily absorbing water. A section 



