4io 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
kill all the fungi tested in f-inch stock. If the wood is air-dry, it is possible 
that there will be sufficient moisture in the wood to volatilize under the 
heat treatment and thus to cause the heat applied to act as moist heat; 
or the liquid applied may penetrate and produce the same result. Further, 
of course, it is always possible that the heat may be applied long enough to 
accomplish the sterilization, even as dry heat. 
In such preliminary treatments as applying saturated steam, super¬ 
heated steam, or hot oil, there should be sufficient heat present to kill all 
mycelium in wood, especially if aided by subsequent vacuum treatments to 
rupture the fungous celis. In many preservative processes, the same should 
be true. For instance, in a treatment such as described by Hoxie (4) for 
treating material for insulation on a mill roof, the f-inch pine sap boards 
were immersed in creosote at a temperature of about 105° C. (220° F.) for 
20 hours or more—long enough to accomplish the desired sterilization even 
on the basis of dry heat, in addition to protecting the wood against future 
attack. In several pressure processes, the preservative is heated up to 
93 0 C. (200° F.) or above, and the heat is probably high enough for a long 
enough period to sterilize the wood in many, if not all, cases even on the 
basis of dry heat. 
Summary 
Inasmuch as the application of heat to various structures has been 
suggested as a possible remedy against decay, five fungi found growing in 
cotton : mill roofs were tested as to their thermal death relations in moist and 
dry heat. Species of Merulius and other fungi of the dry-rot group are not 
considered here. 
The tests were made upon blocks of Sitka spruce J by J by 1 inch taken 
from 4-months- and 1-year-old cultures of the five fungi used and .subjected 
to both moist and dry heat for varying intervals and at. varying 
temperatures. 
In moist heat, the most resistant of the fungi was killed in 3J days at 
44 0 C. and in 12 hours at 55 0 C. In dry heat, 20 days at 70° C. did not kill 
the most resistant, nor did 12 hours at ioo° C., although all succumbed in 
12 hours at 105° C. dry heat. 
There were individual differences in the resistance of the various fungi, 
and the individual curves bore no direct relation to the thermal growth 
curves. Lenzites sepiaria has the highest optimum and maximum of growth 
of the fungi tested, but next to the lowest thermal death curve. Lenzites 
trabea proves to be by far the most resistant of the five fungi, although its 
thermal growth relations are about the same as those of the other three 
fungi. 
It is concluded even from the results upon the small blocks that heat 
applied to buildings as a sterilizing agent can be of little avail against the 
five fungi tested, although it is pointed out that periodic heatings of such 
