Which type of meristematic tissue can differentiate to form xylem or phloem as needed?

The vascular cambium is a type of lateral meristematic tissue that is essential for secondary growth in plants. It is located between the xylem and phloem in stems and roots. The primary function of the vascular cambium is to produce secondary xylem (wood) and secondary phloem (inner bark) through a process of cell division. This capability allows the plant to increase its diameter and support increased transport of water and nutrients as the plant grows.

The other choices do not have this differentiated function. The meristematic region, which generally refers to areas in plants where cells are actively dividing, does not specify the capacity for producing specialized tissues like xylem or phloem. The cortex is a part of the ground tissue system in plants and is involved in storage and transport but does not differentiate into vascular tissues. The endodermis is a layer of cells surrounding the vascular tissue in roots that regulates the flow of water and solutes, but it does not have the ability to differentiate into vascular tissues. Hence, the vascular cambium stands out as the correct choice due to its specific role in producing xylem and phloem.