The meristematic layer that is responsible for cutting off vascular tissues -xylem and pholem – is called vascular cambium. In the young stem, it is present in patches as a single layer between the xylem and phloem. Later it forms a complete ring.
In dicot stems, the cells of cambium present between primary xylem and primary phloem are the intrafascicular cambium. The cells of medullary cells, adjoining these intrafascicular cambium become meristematic and form the interfascicular cambium. Thus, a continuous ring of cambium is formed.