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What Can We Learn from a Cross Section of a Maple Tree?


At the end of a log....
To the left at the surface is the bark which is made up of old phloem and cork from the cork cambium. This layer protects the tree. Beneath this outer bark is the inner bark or functional phloem. The phloem carries sugars from the leaves to the rest of the living cells of the tree. Next is a thin layer of growing cells called the vascular cambium. It produces phloem cells to the outside and xylem cells to the inside. Xylem forms the wood. The sap we remove from the tree is water plus dissolved sugar that flows from the xylem. The outer layer of xylem is also called sapwood. The cambium grows a layer of xylem each year. The layers are known as annual rings.  


Under the microscope....

  Under the microscope maple wood looks very different. Imagine looking at the end of a handful of straws of different sizes. The largest cells are the vessels. They carry water (including the dissolved sugar) upward through the tree.
The annual ring marks the end of one growing season and the beginning of the next. The older wood is at the left. Note that the vessels were smaller at the end of the growing season. Why might that be? Rays are made of bands of small cells. They function as paths for lateral movement of water and dissolved minerals. The remainder of the wood is made of fiber cells that add strength and provide rigidity for the trunk.