DRY-ROT OF INCENSE CEDAR. 



47 



This is because of the avoidance by the fungus mycelium of the wood 

 around open fire scars. 



Infections through broken or dead tops may be absolutely disre- 

 garded, both numerically and in respect to the resulting decay. 

 Out of the 75 trees with these injuries only one infection occurred, 

 and this resulted in a negligible amount of decay. 



However, the true relation of these various types of mechanical 

 injuries to one another in respect to their importance as a means for 

 the entrance and development of dry-rot on the areas studied is not 

 expressed by the percentage of the total infections for which each 

 type of injury is responsible, but must be shown by the relation of 

 the number of trees infected through each type of wound to the 

 total number of trees both sound and infected. The figures in 

 Table XI express this relation, which might be termed "percentage 

 of risk of infection." In one set of figures is expressed, then, for the 

 trees actually studied the numerical relation of the various types of 

 injuries combined with the relative chances for inoculation offered 

 by each. All the areas are combined. 



Table XI. — Risk of infection of incense-cedar trees with dry-rot entering through wounds 



of the various types. 



Cause of wounding. 



Risk of 



infection 



(per 



cent). 



Cause of wounding. 



Risk of 



infection 



(per 



cent). 



Fire 



40.0 



15.8 

 1.6 





1.2 



Knots 



Frost 



.5 



Unknown 





.1 









The figure 40 for fire expresses the fact that of all the trees analyzed 

 each tree had 40 chances out of 100 of being wounded by fire and 

 subsequently becoming infected with dry-rot through this wound, 

 and so on for the other types of injury. 



The far greater importance of fire wounds as a means of entrance 

 for dry-rot as compared with all other injuries is strikingly brought 

 out. Knots, the nearest competitor, are far less important, while 

 all the others practically can be neglected. 



The close relation of wounds and infections is shown even better 

 in figure 3. The curve for wounds is plotted from Table IX, knots, 

 of course, not being included, for had this been done the wound 

 curve would have followed the 100 per cent ordinate throughout all 

 the ages. The curves for infections and cull are the same as those 

 given in figure 2. 



These curves show that infections are practically a function of 

 wounds, the two curves having almost the same form, but of course 

 the infection curve being lower throughout until both have attained 

 100 per cent. The curve for the percentage of cull is included in 



