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 

 merely 15 out of 100. 



