What plant tissue systems are modified by root nodule formation?

Explanation

### Step-by-Step Solution

1. **Understanding Root Nodule Formation**:
- Root nodule formation is a symbiotic relationship between certain plants (like legumes) and nitrogen-fixing bacteria, primarily Rhizobium. This process involves the interaction between the plant roots and these bacteria.

2. **Identifying the Plant Tissue Systems Involved**:
- The formation of root nodules affects three main plant tissue systems:
- **Dermal Tissue**: This is the outer protective layer of the plant. In the context of root nodules, the root hairs (which are part of the dermal tissue) are modified to facilitate the penetration of Rhizobium bacteria.
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