Annual growth rings are formed in woody stems principally through the activities of the ____.

A) pericycle
B) pith
C) vascular cambium
D) apical meristem
E) endodermis

Annual growth rings are formed in woody stems through the activities of the vascular cambium. The vascular cambium is a secondary meristem that produces new xylem and phloem cells, leading to an increase in girth of the stem. As new xylem cells are added during the growing season, the older xylem cells become compressed and their diameter decreases, resulting in the formation of annual rings.