Vascular cambium is a meristematic layer that cuts off

Options

A. (a) Primary xylem and primary phloem
B. (b) Xylem vessels and xylem tracheids
C. (c) Primary xylem and secondary xylem
D. (d) Secondary xylem, secondary phloem, and medullary rays

Answer

### Step-by-Step Solution:

1. **Understanding Vascular Cambium**:
- Vascular cambium is a type of meristematic tissue found in dicots and some gymnosperms. It plays a crucial role in the growth of stems and roots.

2. **Function of Vascular Cambium**:
- The primary function of vascular cambium is to facilitate secondary growth, which leads to the thickening of stems and roots. This is essential for the formation of wood in dicots and gymnosperms.

3. **Formation of Secondary Xylem and Phloem**:
- During secondary growth, vascular cambium divides and produces secondary xylem (wood) towards the inner side and secondary phloem (part of the bark) towards the outer side.

4. **Understanding the Options**:
- Option A: Primary xylem and primary phloem - Incorrect, as vascular cambium does not separate these.
- Option B: Xylem vessels and xylem tracheids - Incorrect, as these are components of xylem but not what vascular cambium cuts off.
- Option C: Primary xylem and secondary xylem - Incorrect, as it does not separate these.
- Option D: Secondary xylem, secondary phloem, and medullary rays - Correct, as vascular cambium separates these during secondary growth.

5. **Conclusion**:
- The correct answer is Option D: vascular cambium cuts off secondary xylem, secondary phloem, and medullary rays during secondary growth.