WOOD PARTS AND ANATOMY Taking a Closer Look at Wood Xylem Xylem is the most important part of a tree's wood ... in fact, wood is totally made up of xylem! When you're looking at a piece of wood, what you're actually looking at what is called xylem (pronounced "zi-lem"). The xylem's job is to carry water for the tree from the roots to other parts of the tree. Not all xylem is alive and works. As we talked about earlier, heartwood is dead xylem. On the other hand, sapwood is live, working xylem. The heartwood, or dead xylem, is very important to the tree. It's what gives the tree support and strength! So, wood is made up of xylem.   But, what is xylem made of?

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