Periderm

Definition

Periderm is the outer protective tissue that replaces the epidermis in plant stems and roots during secondary growth. It consists of the phellem (cork), phellogen (cork cambium), and phelloderm.

5 Must Know Facts For Your Next Test

1. Periderm formation is initiated by the cork cambium, which arises in the cortex of stems and roots.
2. The periderm functions as a barrier against physical damage and pathogens, similar to bark.
3. Phellem, or cork cells, are dead at maturity and contain suberin, making them impermeable to water and gases.
4. Phellogen is a lateral meristematic tissue responsible for generating both phellem outwardly and phelloderm inwardly.
5. Phelloderm cells are living parenchyma cells that provide additional storage functions and support.

Review Questions

• What three components make up the periderm?
• How does periderm contribute to a plant's defense mechanisms?
• What is the role of phellogen in periderm formation?

Related terms

epidermis: The outermost layer of cells covering the primary plant body including leaves, flowers, roots, and stems.

suberin: A hydrophobic substance found in the cell walls of cork; it provides an effective barrier to water movement.

secondary growth: The increase in girth of stems and roots due to the activity of lateral meristems such as the vascular cambium and cork cambium.