DRY-ROT OF INCENSE CEDAR. 45 
on the intermediate area 64 per cent, and on the combined areas 67 
per cent. The percentage of risk of a tree with a fire scar becoming 
infected is very high. 
Next in importance to fire scars as a means of entrance for dry- 
rot come knots. Of the infections on the intermediate area 19 per 
cent entered in this way and 31 per cent on the optimum area, while 
for the areas combined the figure is 25 per cent, a little more than 
one- third as many as were traced to fire scars. The greater part of 
such infections, because they rarely extend beyond the wood of the 
knot itself, are of little or no importance as compared with fire scars 
in promoting serious cull. Of the total infections entering through 
knots only 48 per cent resulted in cull cases and 12 per cent in severe 
cull cases, while in infections through fire scars, 80 per cent of the 
total became cull cases and 38 per cent severe cull cases. The above 
data were at first tabulated by 40-year age classes, but this brought 
out nothing of importance. In the case of infections through fire 
scars most of them developed into cull cases in every age class; 
while for infections through knots up to 200 years less than half 
developed into cull cases, but beyond that age the cull cases became 
more numerous. 
Considering all the severe cull cases as 100 per cent, it is found 
that fire is responsible for 84 per cent, knots for 10 per cent, and all 
other causes for the remaining 6 per cent. Furthermore, 81 per 
cent of the total volume of cull caused by dry-rot resulted from 
infections entering through fire scars. This demonstrates the 
serious role played by fire in connection with dry-rot. Fire scars 
are responsible for by far the greater number of infections, and a 
high percentage of these infections results in severe cull cases. 
Knots are of some importance, though, in promoting severe cull 
cases throughout the life of the trees, even in the younger age classes. 
For example, of the fourteen severe cull cases occurring in all the 
trees up to 165 years of age, four entered through knots. 
Of course, every tree is exposed to infection in this way throughout 
all except the very earliest years of its life, not only at one but at 
several points, since each tree usually has from several to many open 
knots or branch stubs, whose dead wood offers a bridge for the 
fungus from the outside through the bark and living sapwood into 
the heartwood. However, each knot presents only a very small 
surface for the lodgment of spores of heartwood-destroying fungi. 
Out of the total number of trees open to inoculation through knots 
on the optimum area only 18.2 per cent became infected in this way, 
on the intermediate area only 11.4 per cent, and for all combined 
just 15 per cent. In other words, in the trees studied the chances 
for a tree becoming infected with dry-rot through branch stubs were 
merelv 15 out of 100. 
