Which type of vascular bundles participate in normal secondary growth of stem

Options

A. Radial vascular bundle
B. All types of Conjoint, Collateral vascular bundles
C. Conjoint, Collateral, Closed vascular bundle
D. Conjoint, Collateral, Open vascular bundle

Answer

To answer the question "Which type of vascular bundles participate in normal secondary growth of stem?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand Secondary Growth**:
- Secondary growth refers to the increase in thickness or girth of a plant stem. This growth is primarily due to the activity of the cambium, a layer of meristematic tissue.

**Hint**: Remember that secondary growth is about increasing the thickness of stems, not just height.

2. **Identify the Role of Cambium**:
- The cambium is crucial for secondary growth as it produces new cells. It adds layers of vascular tissue (xylem and phloem) to the stem.

**Hint**: Think of cambium as the "growth layer" that helps in thickening the stem.

3. **Types of Vascular Bundles**:
- Vascular bundles can be classified into open and closed types. Open vascular bundles contain cambium, while closed bundles do not.

**Hint**: Focus on the presence of cambium when determining the type of vascular bundle.

4. **Identify the Specific Type of Vascular Bundle**:
- The type of vascular bundle that participates in secondary growth is the "open vascular bundle." In stems, this is typically found as "conjoined collateral open vascular bundles."

**Hint**: Recall that "open" means the presence of cambium, which is essential for secondary growth.

5. **Structure of Open Vascular Bundles**:
- In conjoined collateral open vascular bundles, xylem is located towards the inside, phloem is on the outside, and cambium is present between them, allowing for the growth of both xylem and phloem.

**Hint**: Visualize the arrangement: xylem (inner) - cambium (middle) - phloem (outer).

### Final Answer:
The type of vascular bundles that participate in normal secondary growth of the stem is the **conjoined collateral open vascular bundles**.