DURABILITY OF WOOD. 17 
the rot-producing fungi are not active, so that it can cure over 
on the outside before summer. Many kinds of fungi and beetles 
find a very favorable place just under the bark of logs. These 
can be avoided, the curing of the timber hastened and its dura- 
bility greatly increased by removing the. bark soon after felling. 
When trees are cut in full leaf it is advantageous to let them lie 
at full length until the leaves are thoroughly wilted (two or three 
weeks) before cutting to size. With conifers this is a good prac- 
tice at any season, and while not practical, yet theoretically all 
winter-cut trees should be left to leaf out in the spring before 
being worked. In this way most of the sap is evaporated, but 
in the care of timber that is to go at once into the water these 
precautions are not so important. 
Heat (60 Degrees to 100 Degrees Fahr.), Moisture 
and Air in moderate quantities produce conditions under which 
wood quickly decays. It is on this account that fence posts rot 
off near the surface of the ground, where about such conditions 
of heat and moisture are usually found during several months of 
the year. For the same reason what is known as dry rot 
destroys green floor joists or other timbers where they are tightly 
inclosed, as under a house without ventilation, since moisture is 
always present in such places, and the timber cannot dry out. 
Perfectly dry wood or that submerged in water will last indefi- 
nitely, and there seems to be no difference in different kinds of 
wood under these conditions. Pieces of pine wood in good con- 
dition have been found in Illinois buried to a depth of sixty feet 
that must have been there for many centuries. Nearly sound 
pine logs are occasionally found in the woods of this state, 
where they have a thick moss covering that has kept them moist 
and prevented their decay for hundreds of years. The remains 
of timbers in the piles of the lake dwellers, which must have 
stood in place two thousand years, are still intact. In these 
instances the wood was kept moist, and never came in contact 
with the air. It is very evident, too, that wood which is kept 
ina dry place does not decay, since it may be found in an unim- 
paired state of preservation in some of our very oldest buildings. 
In the following table is shown approximately the time fence 
posts will last in Minnesota. This table is based on practical 
experience in this state: 
