A.................. is a symbiotic relationship between a fungus and the roots of a vascular plant.

Explanation

**Step-by-Step Solution:**

1. **Identify the Relationship**: We need to determine the type of symbiotic relationship that exists between a fungus and the roots of a vascular plant.

2. **Define Symbiotic Relationship**: A symbiotic relationship is a close and long-term interaction between two different biological species. In this case, we are focusing on the interaction between a fungus and a vascular plant.

3. **Recognize the Specific Type**: The specific type of symbiotic relationship between a fungus and the roots of vascular plants is known as mycorrhizae.

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