Which of the following is not part of an older tree's bark?

Options

A. Cork
B. Phelloderm
C. Secondary xylem
D. Secondary phloem

Explanation

To determine which of the following is not part of an older tree's bark, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Tree Bark Composition**:
- Tree bark is defined as all the tissues exterior to the vascular cambium. This includes various layers that protect the tree.

2. **Identifying Components of Bark**:
- The bark consists of two main components:
- **Secondary Phloem**: This is the inner layer of the bark that transports nutrients.
- **Periderm**: This is the outer protective layer and is further divided into:
- **Phellum (Cork)**: The outermost layer that provides protection.
- **Phellogen (Cork Cambium)**: The layer that produces cork cells.
- **Phelloderm**: The inner layer of the periderm, which is also known as secondary cortex.

3. **Analyzing the Options**:
- The question asks which of the following is NOT part of the bark. The options typically include:
- Cork (Phellum)
- Phelloderm
- Secondary Phloem
- Secondary Xylem

4. **Identifying the Incorrect Option**:
- Cork, Phelloderm, and Secondary Phloem are all components of the bark.
- **Secondary Xylem**, on the other hand, is located inside the vascular cambium and is not part of the bark.

5. **Conclusion**:
- Therefore, the correct answer to the question "Which of the following is not part of an older tree's bark?" is **Secondary Xylem**.