50 



BULLETIN 215, U. S. DEPARTMENT OF AGRICULTURE. 



about the age of 130 years (critical age) when combined with pro- 

 nounced suppression, and without this it follows after the age of 

 about 150 years is reached. The risk of wounding increases naturally 

 with the age of the tree. 



A number of wounded and badly suppressed trees escape infection, 

 although they are far beyond the critical age. Not every wound must 

 necessarily be inoculated. All such cases found are compiled in 

 Table III. 



TABLE III. Data on suppressed and wounded but not infected white-fir trees. 



In all cases but one in Table III the degree of suppression is very 

 high; in this case the wound rating is low. The dangerous fire 

 wounds in this table are confined to the youngest ages, 87 to 111 

 years; they were comparatively small in each case. The rest of the 

 wounds are all due to lightning, which, as will be remembered, does 

 not open up the interior of the tree unless very large parts of the 

 bark are killed. For inoculation and infection, the character of the 

 wound is all important. Suppression has nothing to do with inocu- 

 lation; only after infection has taken place does its influence make 

 itself felt. 



The characteristics of each of the three ages, of course, hold good 

 through the following ages. The combination of wounding with 

 suppression, as shown in the critical age, for instance, must continue 

 to favor decay in the age of decline. 



Relative thriftiness (apparent condition of the tree) seems to have 

 the least influence on the decay factor. It is really nothing but a 

 statement of the present temporary appearance of the individual 

 tree, which may be entirely different from what it was a few years 

 ago or what it will be in the near future. 



That far-reaching decay must not necessarily be reflected in the 

 appearance and increment of the tree is shown, for instance, by trees 

 Nos. 25 (age 150), 157 (age 150), 85 (age 152), 83 (age 156), and 

 others in Table II. In all the trees mentioned, EcJiinodontium 

 tinctorium had established itself and was vigorously growing. Tree 

 No. 85 (age 152) even had two sporophores, and more than half the 

 volume of the tree was decayed, indicating that the fungus must have 

 lived in the tree for many years. The tree was apparently very 

 thrifty; its volume, 192.5 cubic feet, as against 101, the average for its 



