Secondary growth is brought about by the activities of the

Secondary growth in plants refers to the increase in the girth or thickness of the plant stem or root. This process is brought about by the activity of the vascular cambium, a lateral meristem responsible for the production of secondary xylem and phloem. The vascular cambium divides actively, producing new cells towards the inner side (secondary xylem) and the outer side (secondary phloem). As a result, the stem or root increases in girth over time. The other options, phellogen and phelloderm, are involved in the formation of the protective outer bark in woody plants.