﻿DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 35 



ance of cellulose pits. Hence, the purplish red color commonly Hound 

 in the heartwood of incense cedar (see p. 16) and western red cedar 

 need not be mistaken for decay. 



As yet very little is known in regard to the reduction in strength 

 due to incipient decay caused by the ring-scale fungus. However, it 

 seems probable that such reduction is slight until the appearance of 

 the white cellulose pits; but it is to be remembered that pieces with 

 discoloration contain hyphae which may again attack the wood, if 

 suitable conditions arise. Consequently, stock with any stage of this 

 decay should not be used. 



The chalky quinine fungus causes a pronounced decay in the heart- 

 wood of many softwoods. The typical decay is a brownish red 

 friable crumbly mass, often with conspicuous mycelium felts filling 

 the cracks. This is shown in Plate IV. The incipient decay is very 

 "difficult to detect, as a rule. Even when the wood has been severely 

 weakened the extremely faint brownish discoloration is not discern- 

 ible to any but the most expert eye. However, the incipient stage 

 of this decay in western yellow pine appears as a red-brown or pro- 

 nounced brown discoloration in the pale-lemon to light orange- 

 brown heartwood. The discoloration is not uniform over the entire 

 affected portion, but may occur on the radial or tangential face in 

 broad bands of varying intensity or even intermingled with narrow 

 bands of the normal light-colored heartwood. In cross section the 

 infected wood presents a mottled appearance. The horizontal limits 

 of the discoloration are bounded by a narrow band of pronounced 

 pink or red. At the upper limits of the incipient decay the discolora- 

 tion becomes fainter until it finally disappears. The discolored wood 

 seems to be hard, firm, and strong, but in reality it is seriously weak- 

 ened. Plate V illustrates this condition. 



The typical decay caused by the sulphur fungus (Polyporus sul- 

 fur eus (Bui.) Fr.) is very similar to the foregoing. However, it is 

 not confined to softwoods. It is common only in the true firs among 

 the softwoods, but is very prevalent among the hardwoods, particu- 

 larly the oaks. The heartwood of living and dead trees is affected. 

 The incipient decay is difficult to detect, being first indicated by a 

 faint brownish discoloration. 



The velvet-top fungus (Polyporus schweinitzii Fr.) also causes a 

 reddish brown friable rot, which is, however, confined to the butt and 

 roots of the tree. The mycelium felts are very fine and inconspicuous. 

 Only softwoods are affected. Normally the incipient decay is very 

 difficult to detect. It first becomes evident in Sitka spruce 6 as pale- 

 yellow to lemon-yellow streaks or spires extending longitudinally 

 beyond the light yellowish to reddish brown discoloration which 

 characterizes the more visible incipient decay. In the latter stage a 

 softening of the wood is apparent. In Douglas fir the incipient decay 

 is first evident as a faint yellowing or browning of the normal heart- 

 wood. This or an exactly similar decay in western red cedar is first 

 indicated by a decided deepening in the color of the normal brownish 

 heartwood. The discolored zone often extends horizontally for sev- 

 eral inches around the typical decay and for a foot or more in ad- 

 vance of it. The discoloration may be confused with the normal 



8 The description of the decay in this species caused by Polyporus schweinitsii is based 

 on note** furnished to the writer through -the courtesy of E. E. Hubert. 



