How Do Xylem And Phloem Develop From Meristematic Tissue

Xylem and phloem originate from meristematic tissue, which is undifferentiated tissue where active cell division occurs. This development happens in two stages: primary and secondary growth.

1. Primary Growth (Increase in Length)

This occurs at the tips of roots and shoots, in areas called apical meristems. The apical meristem gives rise to a meristematic tissue called the procambium. As the plant elongates, cells within this procambium differentiate and mature to become primary xylem and primary phloem. These form the initial vascular bundles of the young plant.

2. Secondary Growth (Increase in Width)

This occurs in woody plants (like trees and shrubs). A different meristem, a lateral meristem called the vascular cambium, develops. The vascular cambium is a thin ring of meristematic cells located between the primary xylem and primary phloem.

• When a vascular cambium cell divides, it produces two new cells.
• One cell remains part of the cambium, able to divide again.
• The other cell differentiates:
  • If it's produced toward the inside of the stem, it becomes secondary xylem (which forms the bulk of wood).
  • If it's produced toward the outside of the stem, it becomes secondary phloem (which forms the inner part of the bark).

This process repeats season after season, causing the stem to grow thicker.