A STUDY OF HEART-ROT IN WESTERN HEMLOCK: 15 
here used allowed for such rot as was to be found outside of a straight 
line drawn from points on the rot sections appearing at both ends of 
the logs and such rot as was found extending outward from the heart- 
wood along the branch whorls. The advance rot is included in the 
total rot in every case. The rot percentage was secured from the 
two given volumes. 
The basis for classifying the seriousness of injury is given as follows: 
0 = No injuries. 
x = 1 to 4 branch stubs, no frost cracks, and very few miscellaneous injuries 
(less than 2). 
xx = 5 to 9 branch stubs, one frost crack, and a superficial blaze, logging scar, 
or other slight injury. 
10 to 15 branch stubs, not more than 2 frost cracks, deep blazes, logging 
sears or fire scars, and slight lightning injury. 
xxxx = 15 or more branch stubs, more than 2 frost cracks, and heavy injuries 
(injured and broken top, severe lightning, and other injuries). 
| 
XXX 
The grouping of trees according to the crown class has, in general 
forestry practice, been almost entirely done by ocular estimate. In 
the present study the four gradations of the crown class were taken 
from Forest Service Bulletin 611 and were used with the crown size 
in composing the standard for crown rating. The actual size of the 
crown and the crown class are used to determine this rating. The 
crown sizes in square feet (length by width of crown) for each age 
class are grouped together, the largest and smallest sizes compose the 
extremes of the large and the very smali crown divisions, respectively, 
the remainder ranging in order of size between these two. The 
group is then divided into four equal classes: Large, average, small, 
and.very small. The individual trees are then given their respective 
crown rating according to the following outline: 
(1) Crown size, large. (Crown class 1.) 
(2) Crown size, average. (Crown class 2.) 
(3) Crown size, small or onesided. (Crown class 3.) 
(4) Crown size, very small. (Crown class 4.) 
The vigor of a tree is indicated by the size and condition of its 
crown and by the favorableness or unfavorableness of the position it 
occupies, as well as by the narrowness of the sap zone and the fineness 
of its annual rings. The injuries which the tree receives during the 
course of its development also play an important part in influencing 
its vigor. The rating for vigor has therefore been based upon the 
following three factors, in the order of their importance: (1) Width 
of average ring in sap, (2) crown rating, and (3) the degree of injury. 
This rating for vigor at least comes nearer registering the true condi- 
tion than a mere ocular estimate. The fixing of the standard or 
average width (as in 00 where the width is 0.12 to 0.19 inches) was 
1 Terms used in forestry and logging. U.S. Dept. Agr., Bur. Forestry Bul. 61, 53 p. 1905. 
