THE ROTS OF WESTERN WHITE PINE. 13 
determining factor as to the earliest age when infection may take 
place. The earliest visible infection for the groups of trees included 
in this study was found in a tree on the slope type of site, 61 years 
old. Table I shows that in the 61 to 80 age class the greater percen- 
tage of infected trees is found on the slope sites, while the bottom 
sites have the larger rot percentage. 
INJURIES. 
Since injuries play the principal role in the infection of living 
trees, it is important to consider them in relation to the various fac- 
tors such as age and site and especially in relation to the rot volume. 
In Table V are given the data for bottom and slope sites, respec- 
tively, showing the relation of injuries to age class and to site, as 
well as indicating the percentage of infection traced to the various 
kinds of injury. The determination of the particular injury which 
was primarily responsible for the initial infection of the tree was 
most difficult in many cases, and no doubt a few of the individual 
decisions may be classed as doubtful. In the main such factors as the 
appearance of sporophores and the location of the largest ones, the 
region of greatest decay within the trunk, and the overwhelming oc- 
currence of butt-rot in trees having large fire scars at the base give 
substantial evidence for the determination of most of the injuries 
responsible for infection. 
The basis for the determination of the degree of injury rests on 
the following standard : 
= No injuries. 
x = 1 to 60 dead branches, no frost cracks, and very few miscellaneous in- 
juries (less than 2). 
xx = 61 to 120 dead branches, one frost crack, and a superficial blaze, logging 
scar, or other slight injury. 
xxx = 121 to 180 dead branches, not more than 2 frost cracks, deep blazes, log- 
ging scars, or fire scars; slight lightning injury, 
xxxx ■= 181 to 250 and more dead branches, more than 2 frost cracks, and heavy 
injuries (injured and broken top, severe lightning, and other in- 
juries ) 
Dead branches were considered of prime importance in determin- 
ing the degree of injury for individual trees. Fire scars proved an 
exception in a certain group of trees where the fire had caused in- 
juries at the base, and these injuries were believed to be primarily 
responsible for the entrance of the fungus. These trees were of an 
age class bearing many dead branches. The younger trees had fewer 
dead branches than the older ones. Frost cracks were entirely ab- 
sent in the younger age classes, so that no difficulty was experienced 
such as would arise in case a tree was found having only 60 dead 
branches and bearing 2 frost cracks. The older trees bore the few 
frost cracks found, and these trees had numerous dead branches. 
