In over 60 percent of angiosperms, pollen grains are shed at

Options

A. Two -celled stage
B. Three-celled stage
C. Four-celled stage
D. Either A and B

Explanation

**Step-by-Step Solution:**

1. **Understanding Pollen Grains**: Pollen grains are the male gametophytes in angiosperms (flowering plants). They are crucial for the process of fertilization.

2. **Structure of Pollen Grains**: Pollen grains typically have a spherical shape and consist of a hard outer layer called the exine, made of sporopollenin, and a thin inner layer called the intine, which is composed of cellulose and pectin. Inside, they contain cytoplasm and are covered by a plasma membrane.

3. **Cell Composition**: Pollen grains usually contain two types of cells:
- **Vegetative Cell**: This cell is larger, has a large irregularly shaped nucleus, and is responsible for forming the pollen tube.
- **Generative Cell**: This cell is smaller, spindle-shaped, and contains a dense cytoplasm with one nucleus. It divides to form two male gametes.

4. **Pollen Grain Shedding**: In more than 60% of angiosperms, pollen grains are shed at the two-celled stage, which includes one vegetative cell and one generative cell. At this stage, the generative cell has not yet divided to form the two male gametes.

5. **Three-Celled Stage**: In some angiosperms, pollen grains can be shed at the three-celled stage, where the generative cell has already divided to produce two male gametes. However, this is less common.

6. **Conclusion**: Therefore, the correct answer to the question is that in over 60% of angiosperms, pollen grains are shed at the two-celled stage.

**Final Answer**: In over 60% of angiosperms, pollen grains are shed at the **two-celled stage**.

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