A pollinium consists of

Options

A. A bag of pollen grains formed in a microsporangium
B. A cluster of pollen grains belonging to a chamber of microsporangium
C. Group of four pollen grains derived from a single mother cell
D. Two pollen tetrads attached by small stalks.

Answer

To answer the question "A pollinium consists of", we will analyze each option provided and determine the correct definition of a pollinium.

### Step-by-Step Solution:

1. **Understanding Pollinium**:
- A pollinium is a coherent mass of pollen grains. It is formed in the microsporangium, which is the structure where pollen grains develop.

2. **Analyzing the Options**:
- **Option A**: "A bag of pollen grains formed in microsporangium."
- This option is incorrect because it describes a microsporangium rather than a pollinium. A pollinium is not just a bag; it is a coherent mass.

- **Option B**: "A cluster of pollen grains belonging to a chamber of microsporangium."
- This option is correct. A pollinium is indeed a cluster of pollen grains that are formed within the microsporangium.

- **Option C**: "Group of four pollen grains derived from a single mother cell."
- This option is incorrect. While pollen grains can be derived from a single mother cell, a pollinium is not limited to just four grains.

- **Option D**: "Two pollen tetrads attached by small stalks."
- This option is also incorrect. Although tetrads are related to pollen grain formation, a pollinium does not consist of two tetrads attached by stalks.

3. **Conclusion**:
- After analyzing all the options, the correct answer is **Option B**: "A cluster of pollen grains belonging to a chamber of microsporangium."

### Final Answer:
A pollinium consists of a cluster of pollen grains belonging to a chamber of microsporangium (Option B).