The number of thallus formed by a gemma of Marchantia upon successful germination is

Options

A. One only
B. Two only
C. Four only
D. Several

Answer

To solve the question regarding the number of thalli formed by a gemma of Marchantia upon successful germination, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Gemma**:
- A gemma is a small, disc-shaped structure produced by liverworts like Marchantia. It is a means of asexual reproduction.

2. **Structure of Gemma**:
- The gemma is haploid and is produced in gemma cups located on the upper surface of the thallus.

3. **Germination Process**:
- When a gemma falls to the ground, it germinates under suitable conditions. The side that contacts the soil develops rhizoids, which anchor the new plant.

4. **Formation of Thalli**:
- The apical cells of the gemma, located at the two lateral notches, become active and start to grow. Each of these cells will develop into a new thallus.

5. **Number of Thalli**:
- Since the gemma has two active apical cells that grow in opposite directions, it will give rise to **two thalli** upon successful germination.

6. **Conclusion**:
- Therefore, the answer to the question is that the number of thalli formed by a gemma of Marchantia upon successful germination is **2 only**.

### Final Answer:
The number of thalli formed by a gemma of Marchantia upon successful germination is **2 only**.