Structure, Development & Function of Periderm

A group of secondary tissues forming a protective layer which replaces the epidermis of many plant stems, roots, and other parts.
Although periderm may develop in leaves and fruits, its main function is to protects stems and roots. 
The periderm consists of three different layers:

Phelloderm
Phellogen (cork cambium)
Phellem (cork)  
Its main function is to protect the underlying tissues from:
Desiccation
Freezing
Heat injury
Mechanical destruction 
Disease
Loss of epidermis.
Bounding tissue restricting the pathogen & insects.
Allowing gaseous exchange through lenticels.

1. Structure, Development & Function of Periderm Presented By: Uzma Batool(34) Subject: Plant Anatomy Life Sciences, IUB.

2. Periderm: A group of  secondary   tissues  forming a protective layer which  replaces the  epidermis of many plant stems, roots, and other  parts. Although periderm may develop in leaves and fruits, its main function is to  protects stems and roots. 

3. Structure & Development: The periderm consists of three different layers: P helloderm P hellogen (cork cambium) P hellem (cork)  

4. Phelloderm : It consists of cells that resemble parenchyma cells in the cortex. The  phelloderm  cells are  phellogen  derivatives formed  inward . Phelloderm  consists of living cells with  photosynthesizing chloroplasts  and  cellulosic   walls .  The number of  phelloderm  layers  varies  with species, season, and age of  the periderm .

5. 2. Phellogen : Secondary meristem and may form at the same time as vascular cambium. Single or multi layered. The function is to produce the cork, a tough protective material. Synonym is Cork cambium.

6. 3 . Phellem : The  phellem  cells are  phellogen  derivatives formed  outward.   Cells  are arranged in tiers with almost no intercellular  spaces except  in the lenticel regions . After completion of their differentiation, the  phellem   cells   die  and their protoplasts disintegrate .

7. Function: Its main function is to  protect  the underlying tissues  from: Desiccation F reezing Heat   injury Mechanical   destruction   Disease  

8. Loss of epidermis. Bounding tissue restricting the pathogen & insects. Allowing gaseous exchange through lenticels.