Phelloderm Origin Explained

In plants undergoing secondary growth, tissues are produced that increase the girth of the stem or root. This process involves lateral meristems, primarily the vascular cambium and the cork cambium.

What is Phelloderm?

Phelloderm is one of the tissues produced during secondary growth in the cortex of stems and roots. It is a layer of parenchyma cells located towards the inside of the cork cambium.

Understanding Cork Cambium (Phellogen)

The cork cambium, also known as phellogen, is a lateral meristem that forms in the outer cortical or epidermal layers of stems and roots during secondary growth. It is responsible for producing the periderm, which replaces the epidermis as the protective outer layer of the plant.

The cork cambium is actively dividing and produces new cells in two directions:

• Outwards: It produces cork cells (phellem). These cells are dead and have suberized walls, providing protection.
• Inwards: It produces parenchyma cells that form the phelloderm. This layer is living tissue.

Together, the phellem, phellogen (cork cambium), and phelloderm constitute the periderm.

Derivation of Phelloderm

As explained, the phelloderm is derived directly from the inward divisions of the cork cambium (phellogen). The cells produced by the cork cambium towards the interior differentiate into phelloderm cells.

Why Other Options are Incorrect

• Fascicular cambium: This is part of the vascular cambium located within the vascular bundles. It produces secondary xylem (towards the inside) and secondary phloem (towards the outside). It is involved in increasing the diameter of the vascular cylinder, not forming the phelloderm.
• Interfascicular cambium: This is also part of the vascular cambium, forming between the vascular bundles (fascicles). It connects the fascicular cambium segments to form a continuous ring. Like fascicular cambium, it produces secondary xylem and phloem.
• Provascular tissue: This is a primary meristem found in the apical meristems. It differentiates into the primary vascular tissues (primary xylem and primary phloem) and the vascular cambium. It is involved in primary growth, not the formation of phelloderm during secondary growth.

Therefore, the phelloderm is specifically derived from the activity of the cork cambium.