Vascular bundles in dicot stem are

Options

A. Closed, collateral, exarch
B. Open , collateral , exarch
C. Closed , collateral
D. Open , collateral, endarch

Answer

To answer the question regarding the type of vascular bundles in a dicot stem, we can break down the solution into several steps:

### Step-by-Step Solution:

1. **Understanding Vascular Bundles**:
- Vascular bundles are arrangements of xylem and phloem in plants that facilitate the transport of water, nutrients, and food.
- They can be classified based on their arrangement and structure.

2. **Types of Vascular Bundles**:
- Vascular bundles can be classified as **conjoined** or **radial**.
- **Conjoined vascular bundles** have xylem and phloem located on the same radius, while **radial vascular bundles** have them on different radii.

3. **Subtypes of Conjoined Vascular Bundles**:
- Among conjoined bundles, there are two subtypes: **collateral** and **bicollateral**.
- In **collateral bundles**, xylem is on one side and phloem is on the other.
- In **bicollateral bundles**, one of the two (xylem or phloem) is sandwiched between the other.

4. **Structure in Dicot Stem**:
- In dicot stems, vascular bundles are typically arranged in a ring formation.
- They are **open** type bundles because they contain cambium (a layer of actively dividing cells) between xylem and phloem.

5. **Endarch vs. Exarch**:
- The terms **endarch** and **exarch** describe the arrangement of protoxylem and metaxylem.
- In **endarch** bundles, protoxylem is located towards the center (inner side), while in **exarch** bundles, it is located towards the outside (outer side).
- Dicot stems generally have **endarch** vascular bundles.

6. **Conclusion**:
- Therefore, the vascular bundles in a dicot stem are classified as **open, collateral, and endarch**.
- The correct answer is option number 4: **Open collateral endarch** vascular bundles.