Layers of new life

Most of the tree's core is made up of the dead cells that form the xylem (Wood conducting network.). It does contain some life, though. The rays are continuous bands of living cells that connect the xylem and the phloem. The tree uses its rays as a storehouse, for redistributing nutrients and even for reacting to invasions by parasites. The rays may contain ducts that transport some of the substances that the tree uses to defend itself, like resin and latex.

As the tree grows, each new layer of wood surrounds the previous one. To properly serve the new layers, which are larger in diameter, the tree produces more and more rays. That means that the rays starting nearest the core are the oldest ones.