Which of the following meristem is responsible for growth in circumference of stem or root

Options

A. Xylem
B. Phloem
C. Cortex
D. Cambium

Answer

To determine which meristem is responsible for the growth in circumference of the stem or root, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Meristems**: Meristems are regions in plants where cells are actively dividing. They are responsible for growth in various parts of the plant.

2. **Types of Growth**: There are two main types of growth in plants: primary growth (lengthening) and secondary growth (thickening). Primary growth occurs at the tips of roots and stems, while secondary growth increases the girth of stems and roots.

3. **Identifying Secondary Growth**: The increase in circumference of stems and roots is referred to as secondary growth or secondary thickening. This process is particularly prominent in dicotyledonous plants.

4. **Role of Cambium**: The vascular cambium is a type of lateral meristem that is crucial for secondary growth. It is located between the xylem and phloem and is responsible for producing new xylem (wood) and phloem (bark), thereby increasing the thickness of the stem and root.

5. **Other Options**:
- **Xylem** and **Phloem**: These are not meristems; they are types of vascular tissue that transport water and nutrients.
- **Cortex**: This is a tissue layer but does not directly contribute to the growth in circumference.

6. **Conclusion**: The correct answer is the **cambium**, as it is the meristematic tissue responsible for the secondary growth that increases the circumference of the stem or root.

### Final Answer:
The meristem responsible for growth in circumference of stem or root is **cambium**.

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