_____ produces pollen grains in a flower.

Explanation

**Step-by-Step Solution:**

1. **Understanding Pollen Grains**: Pollen grains are the male gametes in flowering plants. They are crucial for the reproduction process as they carry the male genetic material.

2. **Identifying the Reproductive Structures**: In flowering plants, the male reproductive organ is called the stamen. The stamen is responsible for producing pollen grains.

3. **Components of the Stamen**: The stamen consists of two main parts:
- **Anther**: This is the part of the stamen where pollen grains are produced.
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