Oct., 1923] 
SNELL — EFFECT OF HEAT UPON FUNGI 
401 
In general, the resistance of the mycelium to dry heat was greater than 
to moist heat, but the degree of difference was somewhat surprising. Three 
and one half days’ exposure to 44 0 C. and 12 hours at 55 0 C. moist heat was 
necessary to kill all the fungi, while with dry heat, the three-day killing 
period was from above 70° C. to above 90° C. and all the species were not 
killed in 12 hours until 105° C. was reached. Three of the fungi survived 
12 hours at the boiling point of water in dry heat, and one of these (.Lenzites 
trabea) survived 24 hours at that temperature. 
Text Fig. i. Graph showing the killing point of the mycelium of five “mill-roof” 
fungi within by f- by i-inch spruce blocks, by both moist and dry heat. The open circle 
denotes that three of the fungi —Lenzites sepiaria, Trametes earned, and Lentinus lepideus — 
were not killed at the point marked, which was the last test in that series. The closed 
circle denotes graphically the maximum amount of heat theoretically available in a mill 
over the week-end shut-down. 
As was to be expected, there was individual variation in the susceptibility 
to heat of the fungi used. Further, it is apparent that the individual 
resistances of the mycelia of the different fungi to temperatures above those 
favorable for growth bear no relation to the temperature curves for growth 
(cf. 6). For example, Lenzites sepiaria is a high-temperature organism, 
having an optimum for growth upon agar between 32 0 and 35 0 C., and 
grows at 40° C., even at 44 0 C. according to Falck (1, pp. 127-129). The 
optima for the other fungi are around 28° C. and 30° C. None of the latter 
will grow at all at 40° C., and some not above 36° C. (6). Yet the mycelium 
of L. sepiaria was killed more easily than that of three of the other fungi and 
almost as easily as that of the least resistant of the group —Trametes serialis. 
