What happens during vascularization in plants?

1. Differentiation of procambium is immediately followed by the development of secondary xylem and phloem
2. Differentiation of procambium followed by the development of xylem and phloem
3. Differentiation of procambium, xylem and phloem is simultaneous
4. Differentiation of procambium followed by the development of primary phloem and then by primary xylem

Vascularization of plant means the development of vascular bundle in the plant, which develops from the cambium.