The origin of cambium ring in a dicot root is

Options

A. partly primary and partly secondary
B. only primary
C. mainly primary and partly secondary
D. only a secondary meristem

Answer

To determine the origin of the cambium ring in a dicot root, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Dicot Roots**: Dicot roots consist of various tissues, including the epidermis, cortex, endodermis, pericycle, xylem, and phloem. The cambium is a layer of meristematic tissue responsible for secondary growth.

2. **Identify the Cambium**: The cambium in dicot roots is primarily responsible for the production of secondary xylem (wood) and secondary phloem (bark). It is crucial for the thickening of stems and roots.

3. **Define Primary and Secondary Meristems**: Primary meristems are responsible for the initial growth of the plant, while secondary meristems, like the cambium, contribute to the growth in thickness.

4. **Origin of Cambium**: The cambium ring in dicot roots originates from two sources:
- **Intrafascicular Cambium**: This is formed from the vascular bundles (primary xylem and phloem).
- **Interfascicular Cambium**: This is formed from the medullary rays that connect the vascular bundles.

5. **Conclusion on Origin**: Since the cambium ring is formed from the combination of intrafascicular and interfascicular cambium, it is primarily a secondary meristem. It does not originate from primary meristematic tissues.

6. **Evaluate the Options**:
- Option 1: Partly primary and partly secondary - Incorrect, as the cambium is not derived from primary tissues.
- Option 2: Only primary - Incorrect, as the cambium is a secondary meristem.
- Option 3: Mainly primary and partly secondary - Incorrect, as it is not derived from primary tissues.
- Option 4: Only a secondary meristem - Correct, as the cambium is entirely secondary in origin.

### Final Answer:
The origin of the cambium ring in a dicot root is **Only a secondary meristem**.

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