DISEASES OF ROOTS, ETC. 51 



tance up, and from four to six or more may appear at 

 different points on the same tree. They never grow out 

 through the bark, but invariably issue from pin knots 

 or branch stubs. The mycelium from which the fruit- 

 ing bodies spring can only get to the exterior of the 

 tree by way of branch stubs bridging from the heart- 

 wood through the sapwood to the outside. In doing so. 

 it decomposes the wood of the stubs, which then, in 

 most cases, show streaks of the same rusty color that 

 characterizes the inside of the fruiting bodies. These 

 " rusty knots " are an infallible sign of decay from the 

 action of the Indian paint fungus in the heartwood. 

 In scaling seemingly sound white fir logs, careful atten- 

 tion should be paid to pin knots and branch stubs. 

 Sound stubs are hard and brittle and break off easily 

 when hit with the U. S. marking hammer or a similar 

 instrument. Unless the log ends show decay, about 

 3 to 4 linear feet in both directions from the rusty 

 knot should be allowed for cull. The rusty red 

 color appears also in streaks in the stringy reddish- 

 brown rot of the heartwood, which usually leaves but 

 a thin shell of sound sapwood to support the tree. The 

 stringy brown-rot represents one of the last stages of 

 decay. In the first stages the timber appears practi- 

 cally sound to the casual observer; a closer investiga- 

 tion, however, will show that the wood is more or less 

 discolored and spongy. Length sections reveal small 

 light-brown spots. This timber, which has only re- 

 cently been invaded by the mycelium, causes serious 

 trouble in so far as it will fall to pieces in drying after 

 going through the mill (see "advance rot," p. 28). 



