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Meristematic tissues are the major types of tissues that are found in the stems and roots of plants. Meristematic tissues are mainly three types based on their location. These are mainly intercalary meristem, apical meristem, and lateral meristem. Apical meristem plays a role in the primary growth of the plant whereas lateral meristem helps in secondary growth.

Annual rings are formed by the action of the vascular cambium. In the case of early wood (also known as spring wood), the cell walls of the secondary xylem are not so thickened and the diameter is large. In the case of autumn wood or latewood, the cell walls of the secondary xylem become extensively thick. Change in the number of vessel elements and tracheids as well as the alteration of seasonal wood leads to the formation of annual rings.

Annual rings can be observed in cross-sections of wood as circular rings. These rings help to determine the age of the tree. Besides this, it reveals the climatic condition during each season. Generally, the growth of wood decreases in winter whereas in summer the rate of growth increases. This growth pattern produces characteristic rings for each season.