44 BULLETIN 571, U. 8. DEPARTMENT OF AGRICULTURE. 
Table X shows that on the intermediate area nearly 76 per cent 
of all the infections entered through fire wounds; this means of 
entrance for the optimum area is approximately 59 per cent, while 
for all the areas combined it is almost 70 per cent. Since fire scars 
are almost invariably found in the base of the tree, commencing at 
ground level, these figures are at variance with Von Schrenk's (26, 
p. 69) idea that "the decay begins somewhere in the upper part of a 
tree. " 
Besides fire wounds being responsible for such a high percentage 
of the infections, inoculations through wounds of this character 
quite commonly lead to very serious and damaging dry-rot. even 
in some of the younger trees. In many cases, even in old trees, a 
long continuous pocket of dry-rot, sometimes having a linear extent 
of 10 feet, will follow a healed fire scar, running out at the end of 
the wound, with no further decay extending up the tree. Such 
infections do not appear especially serious, but it must be remembered 
that the most valuable portion of the trees, the heartwoocl in the 
butt log. is damaged. On the other hand, the fungus evidently 
finds conditions highly unsuitable in the wood back of a large open 
fire scar. Almost every tree with this type of wound appeared 
sound on the stump when felled, but serious dry-rot appeared at 
the first cut above the open fire scar. When such logs were split, 
it was found that the pockets of dry-rot commenced just at or a 
little above the top of the open fire scar, but rarely lower down. 
The avoidance of the dried-out wood around an open fire scar by 
the mycelium of this fungus is not at all in keeping with the results 
of experiments of Munch (19 ; 20. 21). which emphasized the highly 
favorable influence of an increase in oxygen coupled with a decrease 
in moisture in the host tissues on the development of various wood- 
inhabiting fungi. There should certainly be a big increase in the 
oxygen content of heartwoocl directly exposed to the air over that- 
protected by a heavy layer of bark and sapwoocl. thus, according to 
Munch's theory, causing very serious dry-rot in the wood around 
open fire scars. The exact reverse of this is the condition actually 
existing. However, every wood-inhabiting fungus must have cer- 
tain minimum physical requirements for its growth and development. 
Possibly the dried-out wood in this case falls below the minimum 
water requirement of Polyporus amarus. or it may be that certain 
chemical changes in the wood brought about by more or less ex- 
posure to the air inhibit the growth of the fungus mycelium. 
Xot every fire scar is inoculated, but the chances for inoculation 
with subsequent infection are rather high, owing to the relatively 
large area of heartwood exposed offering a broad surface for the 
lodgment of spores of the dry-rot fungus. On the optimum area, 
70 per cent of the trees wounded by fire subsequently became infected. 
