Formation of secondary xylem and phloem occurs through the process of redifferentiation.

Redifferentiation is a process in which cells that have already undergone differentiation revert back to a less specialized state and then differentiate into a different cell type. It is a common process in plant development, especially in the formation of secondary tissues like secondary xylem and phloem.

Primary xylem and phloem are formed during the primary growth of plants, which occurs at the apical meristems. However, as the plant continues to grow, it requires additional vascular tissues to support its increased size and transport needs. This is achieved through the formation of secondary xylem and phloem.

The process of redifferentiation starts with the dedifferentiation of certain cells in the cambium, a lateral meristem responsible for secondary growth. Dedifferentiation is the process in which specialized cells lose their specialized characteristics and revert back to a less specialized state. In the cambium, some of the cells dedifferentiate and become meristematic, meaning they regain the ability to divide and differentiate into different cell types.

Once the cells in the cambium have dedifferentiated, they can then redifferentiate into secondary xylem and phloem cells. The dedifferentiated cells divide repeatedly, producing daughter cells that undergo differentiation into either xylem or phloem cells.

The redifferentiation of cells into secondary xylem and phloem involves the deposition of lignin and other secondary cell wall components, which provide strength and support to the plant. Xylem cells are responsible for the transport of water and minerals from the roots to the shoots, while phloem cells transport sugars and other organic compounds throughout the plant.

In summary, the process of redifferentiation is responsible for the formation of secondary xylem and phloem in plants. It involves the dedifferentiation of cells in the cambium, followed by their redifferentiation into specialized xylem and phloem cells. This process allows plants to grow and develop secondary tissues to support their increasing size and transport needs.