CAMBIUM - Located between the XYLEM and the PHLOEM, the cambium in the BARK(TREE)>BARK (TREE) is the green material which shows if a twig is scratched.

During the growing season the cambium CELLs constantly divide, producing new xylem on the inside and new phloem on the outside. This process creates the ANNUAL RINGs inside the TRUNK OF THE TREE.