14 BULLETIN 1163, U. S. DEPARTMENT OF AGRICULTURE. 
In the trees studied it was found that the average extent of decay, 
including typical and incipient decay, above the highest sporophore 
was 20.1 feet. This was based on 83 infections. In two infections 
the decay ended at the height of the top sporophore, and in one tree 
the rot extended for 61 feet above the highest sporophore. When 
the downward extent of conk-rot below the lowest sporophore was 
considered, it was necessary to discard those infections in which the 
decay extended into the stump. Based on only 33 infections, the 
average downward extent was 13.9 feet. The average of both 
upward and downward combined was 18.3 feet. 
The same figures for the highest and lowest swollen knots were as 
follows: Upward extent, 9.5 feet, based on 93 infections: downward ex- 
tent, 9.2 feet based on 41 infections; combined average, 9.4 feet. In 
one tree the rot extended for 45.2 feet below the lowest swollen knot. 
This difference in the extent of decay beyond sporophores as 
compared to swollen knots is due to the fact that the swollen knot 
in many instances is the initial stage in the development of a normal 
sporophore, and consequently by the time a sporophore appears the 
decay has been in the tree longer and has progressed farther than at 
the formation of a swollen knot. 
These data mean, then, that it is possible to approximate the 
volume of conk-rot in defective trees when cruising. The figures, of 
course, should not be applied to an individual tree as such, but should 
be used in estimating the individual components of a stand in order 
to secure an accurate figure on the total loss through conk-rot. In 
actual practice the writer would use 20 feet as the upward or down- 
ward extent of decay beyond the highest or lowest sporophore and 
10 feet as the figure for swollen knots. In other words, in the case 
of a decayed tree with sporophores the trunk would be considered 
unmerchantable from a point 20 feet below the lowest sporophore to 
a point 20 feet above the highest sporophore, while for swollen knots 
the distance would be reduced to 10 feet below and above. These 
figures are easy to remember and have checked well with the writer's 
observations since this study was made; but for greater accuracy in 
any given locality it is well to study felled trees and watch long logs 
through the mill, so that these limits can be corrected to fit local 
conditions. 
RED-BROWN BUT! -ROT. 
Sporophores are, of course, the best indication of decay. The 
sporophores of red-brown butt-rot being annual are not common 
except in favorable seasons for their development, but can always 
be found now and then in a locality where the trees are affected. 
However, the best clue is fire scars. Noticeably fire-scarred trees 
are commonly infected with this decay. Of the 125 trees with fire 
scars that were studied, 41, or 33 per cent, were infected with red- 
brown butt-rot. Healed fire scars can often be detected by a 
variation in the appearance of the bark over the wound or by 
swollen or churn butts. There are no swollen knots with this decay. 
BROWN TRUNK-ROT. 
Brown trunk-rot is rather hard to detect. Swollen knots are not 
formed. Sporophores are rare on living trees, but when they do 
occur they are very conspicuous and not readily overlooked. 
