SCIENTIFIC METHOD of dating based on the analysis of patterns of tree rings, also known as growth rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year. Growth rings are the result of NEW growth in the vascular cambium, a layer of cells near the bark that is classified as a lateral meristem. This growth in diameter is known as secondary growth. Visible rings result from the change in growth speed through the seasons of the year, thus one ring usually marks the passage of one year in the LIFE of the tree.