Which type of pollen grain are germinate on the stigma

Answer

### Step-by-Step Solution:

1. **Understanding Pollen Grain Formation**: Pollen grains are formed in the anthers of flowering plants. They can be released in two different stages: the two-cell stage or the three-cell stage.

2. **Stages of Pollen Grains**: Approximately 60% of angiospermic plants release pollen grains in the two-cell stage, while about 40% release them in the three-cell stage.

3. **Landing on the Stigma**: Once released, pollen grains fall onto the stigma of the flower. The stigma plays a crucial role in determining whether the pollen grain is suitable for germination.

4. **Criteria for Germination**: For a pollen grain to germinate on the stigma, it must meet certain criteria:
- It should be **self-compatible**, meaning it can successfully fertilize the ovule of the same plant.
- It must be of the **same species** as the flower it lands on.
- It should be within the **viability period**, which is the time frame during which the pollen grain can successfully germinate.

5. **Post-Pollination Events**: If a pollen grain meets all these criteria, it will germinate on the stigma and form a pollen tube, leading to fertilization. If any of the criteria are not fulfilled, the pollen grain will not germinate.

### Final Answer:
The type of pollen grains that germinate on the stigma are those that are self-compatible, of the same species, and within the viability period.

---