Periderm is formed by

Options

A. phellem
B. phelloderm
C. phellogen
D. all of these

Answer

To answer the question "Periderm is formed by," we need to understand the components that make up the periderm and their roles in its formation. Here’s a step-by-step solution:

### Step-by-Step Solution:

1. **Understanding Periderm**:
- Periderm is a secondary protective tissue in plants that replaces the epidermis during the thickening of stems and roots. It is essential for protecting the plant from environmental factors.

2. **Components of Periderm**:
- The periderm is made up of three main components:
- **Phelum (Cork)**: This is the outer layer of the periderm, consisting of dead cells at maturity. These cells have walls that are impregnated with suberin, making them water-resistant and protective.
- **Pheloderm**: This is the inner layer of the periderm, which is made up of living parenchyma cells. It is produced by the cork cambium (phellogen).
- **Phellogen (Cork Cambium)**: This is a lateral meristem that produces the phelum and pheloderm. It is responsible for the formation of the periderm.

3. **Formation of Periderm**:
- The phellogen (cork cambium) produces the phelum (cork) towards the outside and the pheloderm towards the inside. Thus, the periderm is formed by the combined action of these three components.

4. **Conclusion**:
- Given the options provided (phelum, pheloderm, phelogen, all of these), the correct answer is **phelogen** because it is the cork cambium that initiates the formation of the periderm.

### Final Answer:
- **Periderm is formed by phelogen.**