Framing, Sheathing, and Insulation #268848

The series of concentric rings sur rounding the pith are formed by the growth of the tree, one ring being added on the out side each year; hence the name, annual rings. These annual rings, as shown in the enlarged section, Fig. 1 — 2, are composed of fibers or long tubes running parallel to the trunk of the tree. The annual rings are crossed by fibers or cells that run from the bark of the tree to its center, conveying nourishment from the outer cambium layer to the inner part of the tree. These cells are called medullary rays.