What type of growth is associated with the activity of lateral meristems?

Lateral meristems, which include the vascular cambium and cork cambium, are responsible for secondary growth in plants. This type of growth allows for an increase in the girth or thickness of stems and roots, enabling the plant to support a larger structure as it matures. The vascular cambium generates new vascular tissues, while the cork cambium produces the outer protective layer of the plant, known as bark. This secondary growth is crucial for woody plants, as it allows them to grow wider and become more stable over time.

In contrast, height growth primarily involves apical meristems located at the tips of roots and shoots, which focus on elongation rather than girth. Root elongation is also associated with apical meristems in the root tips. Flower development is a process linked to reproductive meristems, which also differ from the lateral meristems in their function. Therefore, the function of lateral meristems directly ties to the increase in girth, making it the correct answer.