DURABILITY OF WOOD. 177 



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 f 

 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 

 in a 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: 



13 



