ABSTRACT
A cross section of a tree (Figure 40.2), from the core to the outer region, shows the following features:
• Pith, a small core of tissue located near the middle of a tree’s stem or branches, which originates from the primary growth of the plant
• Woody material, the most important part of mature trees, which is differentiated into sapwood (outer region), where the sap migrates from roots to leaves and heartwood (inner region) that is no longer used for sap transport, which exists only when the stem, at that height, is old enough
• Bark, differentiated into an outer corky dead part (external part of the stem), whose thickness varies greatly with species and age of trees, and an inner thin living part (just near the cambium zone), which carries food from the leaves to the growing elements
40.1.1.1 Knots As the tree grows in height (primary growth), branching is initiated by lateral bud development. Knots are the
835 40.3.4 Practical Considerations ...................................................................................................................................... 836
40.3.4.1 Schedule Development .......................................................................................................................... 836 40.3.4.2 Kiln Control .......................................................................................................................................... 838 40.3.4.3 Volatile Emissions................................................................................................................................. 838 40.3.4.4 Equalization and Stress Relief .............................................................................................................. 839
40.3.5 Less-Common Drying Methods .......................................................................................................................... 839 40.3.5.1 Vacuum Drying ..................................................................................................................................... 839 40.3.5.2 Dehumidier Kilns ............................................................................................................................... 840 40.3.5.3 High-Frequency Electrical Heating ...................................................................................................... 841 40.3.5.4 Solar Drying.......................................................................................................................................... 841
References ................................................................................................................................................................................. 842
bases of branches, which have been covered as the tree grows laterally. After a branch dies, the trunk continues to increase in diameter and surrounds that portion of the branch while the dead branch is still present. This branch has to drop from the tree before clearwood can form. If the knot was alive when the trunk grew around it, the xylem
of the trunk and the branch are continuous and the knot ts tightly into the wood. If the branch was dead when the trunk grew around it, no anatomical connection exists between the xylem of the knot and the trunk. The knot is nonadhesive; it may fall out of the wood, leaving a knothole (Figure 40.3).
