﻿34 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 



the last visible evidence of incipient decay, while across the grain 

 an allowance of 2 to 3 inches will suffice. 



TYTES OF DECAY IN LIVING SOFTWOOD TREES. 



One of the most common decays in airplane lumber is that caused 

 by the ring-scale fungus (Trametes pini (Brot.) Fr.) in the heart- 

 wood of living trees. It may occur in practically any species of soft- 

 wood, but is very common in Douglas fir, spruce, and pine. The de- 

 caj T , known under various common names, such as red-rot, red-heart, 

 conk-rot, white honeycomb rot, pecky wood-rot, and ring-scale rot, 

 is readily recognizable in its typical stage by the fact that the heart- 

 wood is honeycombed with small white pits in which the wood is 

 reduced to a soft fibrous mass of cellulose (in a chemical sense 

 cotton is practically pure cellulose), these pits being separated by 

 firm and apparently sound wood. Plate II shows typical decay in 

 Douglas fir. 



While the typical decay is closely similar in appearance in various 

 species of wood, there is considerable difference in the incipient de- 

 cay. In Douglas fir as a general rule it appears as a pronounced 

 reddish purple or olive-purple discoloration, gradually tapering and 

 becoming fainter until it is lost entirely. The color is often most 

 pronounced in the outermost he art wood just where it joins the sap- 

 wood. In some cases it appears brownish against the red or yellow 

 heartwood. At the lower limits of the incipient decay, where it be- 

 gins to merge into typical decay, a close scrutiny will usually reveal 

 faint indications of the cellulose pits. Vertically the discoloration 

 may extend 10 feet or more in advance of the cellulose pits, but 

 radially this is limited to 2 or 3 inches. The discolorations described 

 are often bounded by a narrow zone of pronounced red color. Plate 

 III shows discoloration in Douglas fir with the formation of cellu- 

 lose pits beginning. In rare instances the first indication of the decay 

 may be the tiny golden white spots or streaks which indicate the 

 initial stage in the formation of cellulose pits. In this case the 

 discoloration is probably too faint to be recognized, and material of 

 this kind is quite easily overlooked. 



In white and red spruce (55, p. 32) this incipient decay first ap- 

 pears as a change in color from the pale yellowish or reddish brown 

 of the normal heartwood to a light purplish gray, which deepens 

 to a reddish brown, with the gray forming the outer boundary of 

 the reddish brown discolored portions. Next, the cellulose pits ap- 

 pear, visible at first as very tiny black lines following the grain of 

 the wood, but soon revealing their true nature. The discoloration is 

 not so pronounced as in Douglas fir. In Sitka spruce the tiny black 

 lines preceding the cellulose pits are not found. 



The yellow pines first show the decay by a pronounced pink color 

 which rapidly gives way to a red-brown: hence the names red-rot 

 and red-heart. During this stage the wood is hard and firm. Then 

 the white pits develop, although in some cases they appear so spar- 

 ingly that they are readily overlooked. 



In certain woods there is little or no discoloration with this incipi- 

 ent decay. This is true with incense cedar, Port Orford cedar, and 

 western red cedar, and is probably the same with other cedars. The 

 first indication of the diseased condition of the wood is the appear- 



