20 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 
words in a letter to the writer, "The sporophores are of the small 
depauperate type which I find occasionally on trees at high eleva- 
tions or on old punk knots from which the original sporophores have 
fallen and are reviving." 
However, for the purposes of this paper these decays may all be 
treated as one and the same,, since the dry-rot in small pockets and 
the Trameies pini decay are of negligible importance both in the 
number of infections and amount of cull resulting. Hence, except 
in the data on the rate of spread of the dry-rot, they are included in 
all subsequent pages with the typical decay of Polyporus amarus. 
No relation was found between the width of the sapwood and the 
extent of decay; trees with wide and narrow sapwood seem to be 
equally affected with the dry-rot. 
RAPIDITY OF SPREAD OF THE DRY-ROT. 
Although the rapidity of the spread of decay caused by heartwood- 
inhabiting fungi in standing trees has always been of interest, very 
little work has been done on this line. Hartig (9, p. 115-116), 
mentions this briefly in relation to the rot caused by Polyporus 
(Fames) igniarius in oak. More recently Munch (23) has published 
some interesting results from studies of the same fungus and host, 
showing a wide variation of 3.8 to 37.5 cm. (0.12 to 1.23 feet) in 
the yearly vertical progress of the decay, with an average of 5 to 9 cm. 
(0.16 to 0.30 of a foot). No tangible difference was found between 
the upward and downward rate of spread from the point of infection. 
Munch' s results are based on an analysis of only 15 cases, and 
then value is further reduced by the fact that in determining the 
age of the infection which entered a tree through an open wound, he 
assumed that infection must have occurred the year the wound was 
made, or at least a very few years subsequently, even though the 
wound was still open at the time of analysis. True enough, as 
shown by Munch (23), Fomes igniarius attacks not only the heart- 
wood but the sapwood of many trees and kills the cambium, causing 
cankers with subsequent callusing, and by counting the number of 
annual rings in the callus at the point of infection the age of the 
decay can be determined, provided a canker was formed the year of 
infection; but this is not uniformly the case, to judge from Munch's 
(23, p. 519) own statement that " Fomes igniarius produces exceed- 
ingly variable cankers. Sometimes small points of infection which 
are scarcely noticeable and are soon healed perfectly ..." 
In securing the figures on the yearly rate of spread of the dry-rot, 
only those infections were considered the entrance of which could 
be absolutely traced, without any other possibilities, to a healed 
scar for which it was possible to determine the exact dates of 
occurrence and closure, For example, an infection is found in a 
