1. Many plants grow thicker over time. This thickening process, which takes place in the roots and stems of a subset of eudicots, is referred to as secondary growth. Secondary growth occurs within the vascular cambium of these plants, which is a thin layer of tissue containing actively dividing cells. 2. The vascular cambium is a meristematic tissue that develops between the stem’s primary xylem and primary phloem. As cells within the vascular cambium divide, they produce secondary xylem (wood)