THE EOTS OF WESTERN WHITE PINE. 7 
eludes Polyporus schweinitzii and Fomes annosus as well, and Arniil- 
Icuria mellea is sparingly represented. 
In comparing the slope sites with the bottom sites it is well to keep 
in mind that the differences in these comparisons are made even more 
striking by the fact that the average age of the slope type of sites 
is greater by 14 years than that of the bottom type. 
In Table I the average total volume per age class shows a steady 
increase for both types of site. The trunk-rot for both types also 
shows a definite increase from the 41 to 60 to the 201+ age class, the 
bottom sites indicating a greater percentage of rot than the slope 
sites. The bottom sites for the 61 to 80 age class show 0.8 cubic feet 
as the average volume of rot and 85 cubic feet for the 201+ age class, 
as compared to the slope sites, which have 0.055 cubic feet for the 
61 to 80 age and 72 cubic feet for the 201+ class. The figures for the 
average rot volume for the butt rots on the two types of site vary 
considerably and do not show any consistent increase between the 
youngest and the oldest age classes. The 161 to 200 age class on the 
bottom sites runs extremely high, which may be due to the fact that 
the site from which these trees were taken was very favorable to 
butt-rot and supported a great deal of Polyporus schweinitzii. On 
the slope sites the average is less for the 161 to 200 age than for the 
class preceding it. This again must be accounted for by the local 
environmental differences present in the various areas upon which the 
trees included in this study were found growing. This is especially 
true of the 201+ age class on the bottom sites, in which no butt-rot is 
recorded and where the rot is almost entirely due to Trametes pini 
acting as a distinct trunk-rot. 
The " T. R. + B. E." column gives figures for the combined rots, 
and in general indicates an increase in rot volume and in rot per- 
centage with increased age. 
Table I shows computations of the average annual increase in rot 
volume between the age classes per infected tree. These figures are 
intended to serve as an approximation of the rate of increase in rot 
volume during the life of the stand and are used later to determine 
the infection age. 
A study of the relation between sound and infected trees reveals 
the fact that as the age increased, the percentage of infected trees in- 
creased at a quite rapid rate. The bottom sites show the more rapid 
increase of the two types of site. It is significant to note that the 
proportions of trees infected for the bottom and slope sites are almost 
identical, being 55 per cent and 55.3 per cent, respectively. If, in 
order to remove to a certain extent the source of error due to the 
larger percentage of trees of the older age class on the slope sites, 
the averages of the percentages for the different age classes are com- 
