How do lateral meristems increase the thickness of plant stems?

Lateral meristems, also known as secondary meristems, are responsible for secondary growth, which increases the thickness and girth 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 is a cylinder of dividing cells that produces secondary vascular tissues. It generates new cells through tangential divisions:23
* Internal Growth: It produces secondary xylem toward the inside of the stem.23
* External Growth: It produces secondary phloem toward the outside.23

Because the cambium produces more xylem internally than phloem externally, the stem's diameter increases significantly. To accommodate this expansion, the cambium itself must grow in circumference, which it achieves through radial divisions of its own cells.23

The Cork Cambium

As the stem thickens, the original epidermis is often disrupted. The cork cambium forms in the outer layers of the stem (such as the cortex or phloem) and produces a protective secondary tissue called the periderm, or bark. Like the vascular cambium, it functions through tangential cell division to keep pace with the increasing diameter of the plant.23