Transpiration is ................................proportional to humidity.

Explanation

**Step-by-Step Solution:**

1. **Understanding Transpiration**: Transpiration is the process by which plants lose water in the form of vapor. This process primarily occurs through small openings in the leaves called stomata.

2. **Role of Stomata**: Stomata are responsible not only for transpiration but also for the exchange of gases. They are surrounded by guard cells that regulate their opening and closing.

3. **Factors Affecting Transpiration**: Several factors influence the rate of transpiration, including temperature, light, wind speed, and humidity.

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