Which of the following structures is involved in the formation of secondary roots?

The pericycle plays a crucial role in the formation of secondary roots, or lateral roots, in plants. Located just inside the endodermis and surrounding the vascular cylinder, the pericycle contains undifferentiated cells that retain the ability to divide. When conditions are favorable, these cells initiate the growth of new roots by dividing and pushing through the surrounding tissues.

As the secondary roots develop, they emerge from the primary root, contributing to the plant's ability to absorb water and nutrients more effectively. This is an essential process, as a well-developed root system can significantly enhance a plant's stability and resource acquisition.

Other structures mentioned in the options have different functions in root development. The vascular cylinder is primarily responsible for transporting nutrients and water, while the meristematic region is associated with active growth but not specifically with the formation of secondary roots. The cortex primarily serves as storage and helps with the transport of substances, but it does not directly contribute to the process of forming new roots. Thus, the pericycle is uniquely positioned to facilitate the growth of secondary roots.