Which of the following structures is not formed by activity of cork cambium?

Options

A. Phellem
B. Phelloderm
C. Secondary xylem
D. Corky layer

Answer

To determine which structure is not formed by the activity of cork cambium (also known as felogen), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Cork Cambium**: Cork cambium is a type of secondary meristematic tissue that is responsible for producing protective tissues in plants. It is also referred to as felogen.

2. **Identify the Products of Cork Cambium**: The primary products of cork cambium activity include:
- **Cork (Phellum)**: This is the outer protective layer.
- **Phalloderm**: This is the inner layer produced by cork cambium.
- **Periderm**: This structure includes both cork and phalloderm.

3. **Differentiate Between Cambium Types**: It is important to note that there are different types of cambium in plants:
- **Cork Cambium (Felogen)**: Produces cork, phalloderm, and periderm.
- **Vascular Cambium**: This type of cambium produces secondary xylem and secondary phloem.

4. **Analyze the Options**: Given the options:
- Phellum (cork)
- Phalloderm
- Secondary Xylem
- Cork Layer

We know that phellum, phalloderm, and cork layer are all products of cork cambium. However, secondary xylem is produced by vascular cambium.

5. **Conclusion**: Therefore, the structure that is not formed by the activity of cork cambium is **Secondary Xylem**.

### Final Answer:
**Secondary Xylem (Option C)** is not formed by the activity of cork cambium.

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