In which of the following gymnosperms corolloid root having N-fixing cyanobacteria (Nostoc) is found -

Options

A. Pinus
B. Ginkgo
C. Cycas
D. Cedrus

Answer

To solve the question regarding which gymnosperm has corolloid roots containing nitrogen-fixing cyanobacteria (Nostoc), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: We need to identify which gymnosperm species has corolloid roots that host nitrogen-fixing cyanobacteria, specifically Nostoc.

2. **Identifying the Options**: The options provided are:
- Pinus
- Ginkgo
- Cycus
- Cedrus

3. **Defining Corolloid Roots**: Corolloid roots are specialized roots that are typically associated with nitrogen-fixing cyanobacteria. These roots are not common in all gymnosperms.

4. **Analyzing Each Option**:
- **Pinus**: This genus is known for having mycorrhizal associations with fungi rather than corolloid roots.
- **Ginkgo**: This genus does not have corolloid roots and is primarily known for its unique leaf structure and reproductive features.
- **Cycus**: This genus is known to have corolloid roots that are associated with nitrogen-fixing cyanobacteria, specifically Nostoc.
- **Cedrus**: Similar to Pinus, Cedrus does not have corolloid roots and is also associated with mycorrhizal fungi.

5. **Conclusion**: Based on the analysis, the gymnosperm that has corolloid roots containing nitrogen-fixing cyanobacteria (Nostoc) is **Cycus**.

### Final Answer:
The correct answer is **Cycus**.