Tertiary roots are plageotropic.

Explanation

**Step-by-Step Solution:**

1. **Understanding Tertiary Roots**: Tertiary roots are the branches that develop from secondary roots. They are part of the root system of a plant and play a crucial role in anchoring the plant and absorbing nutrients and water.

2. **Identifying Root Types**:
- Primary Roots: The main root that grows directly from the seed.
- Secondary Roots: The roots that branch off from the primary root.
- Tertiary Roots: The roots that branch off from secondary roots.
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