How do lateral meristems make stems wider and thicker?

Lateral meristems, also known as secondary meristems, are responsible for secondary growth, which increases the girth and thickness of plant stems. This process is primarily driven by two types of lateral meristems: the vascular cambium and the cork cambium.12

The Vascular Cambium

The vascular cambium forms a cylinder of dividing cells that produces new vascular tissues. Through tangential cell divisions, it generates secondary xylem toward the inside of the stem and secondary phloem toward the outside. Because the cambium produces more xylem internally than phloem externally, the stem increases in diameter. To accommodate this expanding girth, the cambium cells themselves divide radially, allowing the cambial cylinder to grow in circumference.23

The Cork Cambium

As the stem thickens, the original epidermis is often disrupted. The cork cambium, another lateral meristem, arises in the cortex, phloem, or epidermis to produce a secondary protective tissue called the periderm (or bark). Like the vascular cambium, it functions through tangential divisions, providing a new protective layer as the stem continues to expand.23