﻿DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 29 



stain, and as far as is known no reduction in strength results. The 

 fungus causing the discoloration is as yet unknown. 



Blue-stain is very severe on the white pines and is particularly 

 noticeable because of their white wood. Plate I, left part, shows a 

 section from a sugar-pine rib web in which the sapwood is stained 

 to some extent. The small, darker, bluish black spots are the ends 

 of the medullary rays, in which, as before stated, the fungous myce- 

 lium is most abundant. The longer streaks are the resin ducts. 



Certain fungi (Penicillium spp.), stain the sapwood of the pines 

 an orange-red to a crimson-red color. Another fungus (Fusarivm 

 roseum Link) is responsible for a pink to lilac color in the same 

 woods. The color is produced by means of a pigment secreted by 

 the hyphse, which actually dyes the wood. 



A wood-staining fungus {Zythia resinae (Fr.) Karst.) has been 

 reported in Europe (9) as working on finished pine lumber after 

 the wood has been oiled. The discoloration was characterized by 

 violet to dirty red or even dark grayish brown flecks beneath the 

 oiled surface of the wood. The spots were covered with minute 

 pustules varying from violet, orange, and brown to black. These 

 constitute the spore-producing bodies. The discolored areas ex- 

 tend within the wood as streaks closely associated with the medul- 

 lary rays and resin ducts. The report does not state whether the 

 discoloration was confined to sapwood. Apparently the wood was 

 not reduced in strength. As far as is known, this stain has not yet 

 been found in the United States. 



SAP-STAIN ON HARDWOODS. 



Hardwoods are not as subject to the stains caused by fungi as are 

 softwoods. In hardwoods, when sap-stain does occur, the discolora- 

 tion is most intense in the medullary rays and large pores or vessels. 

 In a wood such as yellow birch, in which these vessels are not too 

 closely crowded, the stain, if not too severe, appears in longitudinal 

 section as very narrow bluish black lines or streaks following the 

 grain of the wood. This stain will not necessarily be confined to the 

 surface layers, but may extend entirely through the sapwood. Of all 

 the hardwoods, however, red gum seems to be the most susceptible 

 to stains caused by fungi. 



BROWN-OAK DISCOLORATIONS. 



A somewhat different discoloration than those previously de- 

 scribed, in that it is confined to heartwood only, is the " brown oak " 

 (18, 19) found in Great Britain. This is also known as " red oak " 

 and " foxiness," but the name first given is most commonly accepted. 

 Instead of the normal heartwood, certain trees of the common Euro- 

 pean oak have a dull-brown to rusty brown or even rust color in the 

 heartwood. In some cases the color is uniform, while again longi- 

 tudinal streaks of normal-colored heartwood may alternate with 

 those of the brown color. When these brown streaks contain black 

 patches this type of wood is known as " tortoise-shell " oak. This 

 discoloration originates in the heartwood of living trees, the normal 

 heartwood changing first to a faint yellow color, which continues to 

 deepen until the brown stage is attained. The color change is caused 

 by a fungus, but so far as known the infected wood is not weakened. 



