Answer in one or two word:
The structure through which guttation takes place.

Explanation

**Step-by-Step Solution:**

1. **Understand Guttation**: Guttation is the process where water is expelled from the leaves of a plant in the form of droplets. This usually occurs at night or in the early morning when the soil moisture is high and transpiration is low.

2. **Identify the Cause**: The primary cause of guttation is root pressure, which is the pressure exerted by the roots of the plant that pushes water upwards through the plant.

3. **Locate the Structure**: The specific structures through which guttation occurs are specialized openings on the leaf margins.

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