Cell division that results in the increased width of a tree occurs in the?

The process responsible for the increased width of a tree is attributed to lateral meristems. Lateral meristems are responsible for secondary growth in plants, which leads to an increase in the girth or thickness of stems and roots. The most notable lateral meristems are the vascular cambium and cork cambium.

The vascular cambium produces new layers of xylem and phloem, contributing to the tree’s growth in width. This is different from apical meristems, which are located at the tips of roots and shoots and primarily facilitate vertical growth rather than diameter. Primary tissues arise from apical meristems and are involved in the initial growth of the plant, but they do not contribute to the secondary growth needed for increased width. Sieve tube vessels are part of the phloem and are involved in the transport of nutrients, not in the growth process itself.

In essence, the function of lateral meristems in facilitating secondary growth distinguishes this option as the correct answer regarding the mechanisms behind a tree's increased width.