18 BULLETIN 1262, U. S. DEPARTMENT OF AGRICULTURE. 
before the six-hour limit was reached, as another test (run 10) shows 
that the fungi were dead in the 4-inch stock subjected to 145° F. for 
three hours. For completeness, the points representing the data 
on 6-inch and 8-inch stock, as well as the high values obtained for 
the blue-stain organisms, are given. 
In the steaming experiments a saturated atmosphere was used in 
order to avoid as much as possible variations in heat penetration 
which might bé due to variations in moisture content of the test 
pieces, since the experiments of Hunt (3) have shown that seasoned 
wood heats more quickly than green wood. ‘The data from the 
steaming experiments are thus directly applicable to the preliminary 
steaming now generally recommended for various commercial kiln 
runs. This preliminary steaming consists of subjecting the wood at 
the beginning of the run to live steam (160° to 185° F.) for half 
an hour to three hours. By glancing at the temperatures and periods 
of time given in Table 1 and comparing these with the temperatures 
and periods of time given for the hardwood and softwood drying 
schedules by the Forest Products Laboratory (7, 4, 17) it will be 
seen that with very few, if any, exceptions the heat and periods of 
duration of each schedule are sufficient to sterilize wood (for the 
fungi of these experiments) up to and including 4 by 4 inches in 
cross section. In the drying schedules for hardwoods the lowest 
temperature used is 115° F. for an average period of 56 days and the 
highest temperature 170° F. for 3 to 4 days. The lowest and highest 
temperatures used in the various schedules for drying softwoods are 
135° and 200° F., respectively. The lowest temperature used in 
the steaming experiments was 110° F. for 48 hours; the highest was 
170° for 40 minutes at atmospheric pressure and 274° at 30 pounds 
gauge pressure. The first is successful in sterilizing wood up to 
but not including all the test pieces of a thickness of 4 inches; the 
last has been tested for 1-inch stock only. 
From the experimental data obtained in this study the following 
results are shown for the hosts and fungi studied: 
(1) A long list of fungi consisting of both wood-destroying and sap-stain 
organisms in a variety of hosts can effectively be arrested in their development 
through sterilization by heat. 
(2) The blue-stain fungus is apparently the most resistant of those tested. 
(3) The stage of decay of certain fungi may affect the rate of heat pene- 
tration within infected wood. 
(4) The temperature of commercial kiln runs, excepting temperatures below 
120° F., are effective in sterilizing infected wood up to and including 4 by 4 
inches square. Pieces 6 by 6 inches and 8 by 8 inches square were sterilized 
by treatment at 130° F. for nine hours at saturated atmosphere and by steam- 
pressure treatment. 
(5) Infected wood piled in the yard at Madison, Wis., in both open and 
closed piles and unprotected against rain, will continue to develop decay and 
in Many cases fungous fruiting bodies. 
(6) Similar material piled in dry sheds protected from moisture showed 
no outward signs of fungous activity, but the fungi remained alive though 
inactive. Uninfected wood in the same shed remained sound. 
(7) Certain fungi dormant or inactive within air-dry wood for long periods 
of time are capable of reviving and continuing their development upon the 
return of favorable moisture conditions. 
One investigator (72) has shown that a fairly high moisture con- 
tent of the wood, about 25 per cent, is needed before spores of Len- 
zites sepiaria will germinate readily upon the surface and subse- 
quently cause infection, 
