WOOD PARTS AND ANATOMY Taking a Look at Wood Heartwood and Sapwood We said that sapwood is the living, outer region of wood. As we learned in "How a Tree Grows," new wood is formed just inside the bark, by a thin layer of cells called the cambium. This new wood is new sapwood. As the new sapwood forms just underneath the cambium, the sapwood closest to the center of the tree is no longer needed and dies. When the old sapwood dies, it becomes heartwood, which is located at the center of the tree. After it has died, the old sapwood undergoes some changes that make it heartwood. Basically, the amount of water in the wood decreases and certain chemicals accumulate there. The chemicals that accumulate in the heartwood are what makes it resistant to insect attack and decay! Growth Rings

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