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. 
TYPES OF DECAY IN LIVING SOFTWOOD TREES. 
One of the most common decays in airplane lumber is that caused 
by the ring-scale fungus (Zrametes pint (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- 
cay, 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 heartwood 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 
IIT shows discoloration in Douglas fir with the formation of cellu- 
lose pits beginning. Inrare 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 (54, 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- 
