Oct., 1923] 
SNELL — EFFECT OF HEAT UPON FUNGI 
403 
f-inch blocks used in the tests. Hence, for example, if different degrees of 
heat which would be safe to use in buildings would not kill the mycelium in 
the small blocks, it certainly is hopeless to try heat to sterilize timbers in 
structures which are infested with the fungi considered here. 
In this connection, there are a few things to be considered. One of these 
is that different wood-destroying fungi react differently to heat. Merulius 
lacrymans, the true dry-rot fungus (or what has thus far been taken for M. 
lacrymans ), is a low-temperature organism and is more susceptible to treat¬ 
ment with heat than is the group of organisms considered here. According 
to Falck (1, p. 129), this fungus (which he calls M. domesticus) has an 
optimum around 21 0 C. and does not grow at all on agar above 27 0 C., a 
point lower than the optimum for any of the five fungi treated in this paper. 
While it has been pointed out above that there is necessarily no relation 
between the relative temperature curve and the relative resistance to heat 
above the growth temperatures (as in the case of Lenzites sepiaria ), it is 
known that certain species of Merulius are more susceptible to higher 
degrees of heat, as would be expected from the growth relations of certain 
of the species studied. Hence, these tests do not apply to Merulius or to 
other fungi of the dry-rot group, but apply only to the species considered— 
those which are adapted to conditions found in cotton-mill weave-shed 
roofs. 
Another consideration is that only dry heat and heat in a saturated 
atmosphere are considered here. What the effects of heat at the different 
humidities between the points of dryness and saturation would be can only 
be conjectured. The same heat applied in a dwelling and in a cotton-mill 
weave shed would obviously give quite different results because of the 
difference in relative humidity. The wetness of the wood would also need 
to be considered. In a dwelling house under ordinary conditions, the wood 
is below the fiber-saturation point. In a building where the air is saturated, 
the wood everywhere except in contact with the outside would be only at 
the fiber-saturation point, while that in contact with the outside would be 
above fiber saturation when it was cool outside. In one-story weave sheds, 
the moisture content of the roof planks is much above the fiber-saturation 
point, because the dew-point often comes within the plank and water is 
precipitated there. Hence, it is probable that heat applied in a room like 
a weave shop, even at humidities much below saturation, would act as the 
moist heat of a saturated atmosphere because of the moisture within the 
wood. 
A further consideration with regard to the practical application of these 
results to mill-roof conditions is the impossibility of supplying the heat 
with sufficient uniformity. Although it might be deduced from the tables 
and graphs that a certain degree of heat for a certain period would kill the 
mycelium in stock of certain dimensions, it is of coy^^^p^p"prt**^at heat 
applied in a structure such as a weave shed woul%’b@Vadiate& feb/.rfipidly 
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