Right: Cross-sections of two coniferous and one broad-leaved tree trunk. Photos by Maya Walters.
The central column of wood in a tree is called the "heartwood". All the cells in this layer are dead and clogged with resin, and are therefore unable to move nutrients through the tree. The heartwood's only job is to provide structural support. The outer layer of wood is called the "sapwood". This is the living layer of the tree, where all the nutrients are channeled. This explains how an old hollow tree can remain alive, for it is only the central heartwood that has rotted away. The diameter of either layer compared to the total size of the tree trunk varies depending on the species.
[temperate forests] [coniferous forests] [prehistoric forests & amber]
view the condensed version of the bark, wood, roots, & leaves article for faster printing/reading
return to the plants article