DECAY IN DOUGLAS FIR. 
13 
stubs not yet occluded. A swollen knot is the initial stage of a 
sporophore in which the substance forming the conk is growing out 
through a knot and forcing out the bark. The pressure may also 
cause an increase in the width of the sap wood immediately around 
the knot, which accentuates the swelling. Swollen knots are illus¬ 
trated in Plate VIII. A swollen knot is just as good an indication 
of the presence of decay as a sporophore. Often the sporophore never 
develops beyond this stage, remaining abortive. Chopping into one 
of these knots reveals a brown, soft, corky or punky context, the same 
as in a fully developed sporophore. Plate III, Figure 1, shows a sec¬ 
tion through part of a decayed knot. 
The effect of fire on sporophores or swollen knots is striking. 
When mature timber is swept by fire, the flames running along the 
trunk of the tree can not burn off the thick bark. However, the 
corky context of the sporophores and decayed knots burns readily, 
and this results in rounded, blackened hollows extending for several 
inches into the tree where the fire has burned out the decayed knots. 
This makes it possible to judge in a measure the extent of conk-rot 
in recently fire-killed Douglas fir. 
That the development of swollen knots and sporophores follows 
rather closely the progress of conk-rot in the heartwood is brought 
out in Table 13. 
Table 13. —Relation of sporophores and swollen knots to conk-rot in Douglas fir. 
Decay. 
With sporophores. 
Without sporophores... 
With swollen knots-. 
Without swollen knots. 
Infections. 
Volume of decay. 
Percentage of total. 
.Average per 
Per¬ 
infection. 
Num¬ 
cent¬ 
Gross. 
Of conk-rot. 
ber, 
age of 
basis. 
total. 
Board 
Cubic 
Board 
Cubic 
Board 
Cubic 
feet. 
feet. 
feet. 
feet. 
feet. 
feet. 
96 
81.4 
36.83 
21.71 
95.94 
96.51 
782 
76.2 
22 
18.6 
1.56 
.78 
4.06 
3.49 
144 
12.0 
108 
91.5 
38.39 
22.49 
99.96 
99.97 
725 
70.2 
10 
8.5 
.01 
.01 
.04 
.03 
3 
.2 
Table 13 shows that while there was a noticeable percentage of the 
infections which did not develop sporophores, these infections were 
verv small, as is indicated by the volume percentages and the average 
volume per infection. The relation is even more striking with swollen 
knots, where the volume percentages and the average volume per in¬ 
fection of those infections without swollen knots is so small as to be 
n6 TMs b means, then, that it is possible to pick out rather accurately 
the trees in a stand affected with conk-rot. When high up m a tree 
among the branches swollen knots, or even sporophores, a re not easily 
seen but if overlooked there it does not make so much difference in 
the accuracy of an estimate, since the volume of the top logs is rel¬ 
atively insignificant in the total. 
EXTENT OF CONK-ROT. 
It is not only possible to pick out the decayed trees, but it is also 
feasible to judge with some exactness the normal extent of conk-rot. 
