Knot is the separation of wood fibers due to intergrown limbs.

• A. Groups of cells running from the center of the tree horizontally to the bark
• B. Separations of the wood fibers due to intergrown limbs
• C. Separations of the wood fibers, through growth rings, parallel to grain
• D. Advanced checks that extend completely through the wood

Answer: (B)

A knot forms where a branch is intergrown with the trunk, so the wood fibers around that branch become disrupted and wrap around the limb. This creates a distinct separation in the grain that points to the presence of a knot. Knots matter because the irregular grain weakens the wood and changes its strength and stiffness, especially in structural applications like bridges. The description provided—separations of the wood fibers due to intergrown limbs—matches this phenomenon exactly. The other statements describe different wood features (radial growth rays, grain-aligned checks, or through-crack checks) and are not knots.