When phloem surrounds xylem, the vascular bundle is

Options

A. Concentric, leptocentric , occuring in Dracaena
B. Concentric, hadrocentric, occuring in fern meristele
C. Conjoint , bicollateral, occuring in Trichosanthes
D. Conjoint, collateral, occuring is Helianthus

Answer

To solve the question "When phloem surrounds xylem, the vascular bundle is," we need to analyze the options provided and understand the types of vascular bundles.

### Step-by-Step Solution:

1. **Understand Vascular Bundles**: Vascular bundles are arrangements of xylem and phloem in plants. They can be classified based on the arrangement of xylem and phloem.

2. **Identify the Arrangement**: The question specifies that phloem surrounds xylem. This indicates a specific arrangement where the xylem is located at the center, and the phloem is surrounding it.

3. **Analyze the Options**:
- **Option 1: Concentric Leptocentric occurring in Dracaena**: In this type, xylem surrounds phloem, which is the opposite of what we need. Therefore, this option is incorrect.
- **Option 2: Concentric Heterocentric occurring in Fern Maristal**: This type has phloem completely surrounding the xylem, which matches the condition given in the question. This option is correct.
- **Option 3: Conjoined Bicollateral occurring in Tricosynthesis**: In this arrangement, there are two patches of cambium and xylem at the center, which does not fit the requirement. Hence, this option is incorrect.
- **Option 4: Conjoined Collateral occurring in Helianthus**: In this type, xylem and phloem are arranged on the same radius, with phloem outside xylem. This does not match the requirement either, making this option incorrect.

4. **Conclusion**: Based on the analysis, the correct answer is **Concentric Heterocentric occurring in Fern Maristal**, as it correctly describes the vascular bundle where phloem surrounds xylem.

### Final Answer:
**Concentric Heterocentric occurring in Fern Maristal.**