During secondary growth in dicotyledonous stems, the fully...

Dedifferentiation: This is the process where cells that have already matured and lost their ability to divide (like the fully differentiated parenchymatous cells of the medullary rays) regain the capacity to divide and become meristematic again. The formation of the interfascicular cambium and cork cambium are classic examples of this in plants.

Differentiation is the initial process where actively dividing cells (meristems) mature and lose their ability to divide to perform specific functions.

Redifferentiation happens after dedifferentiation. The newly formed meristematic cells (like the interfascicular cambium) divide and produce new cells that once again lose their dividing capacity to mature into specific tissues (like secondary xylem and secondary phloem).

Plasticity refers to a plant's ability to alter its structure or developmental pathways in response to environmental changes or different phases of life (e.g., heterophylly in cotton or coriander).

Answer: Dedifferentiation