Transpiration is directly proportional to humidity.

Explanation

**Step-by-Step Solution:**

1. **Understanding Transpiration**: Transpiration is the process through which plants lose water in the form of water vapor. This process is crucial for maintaining plant health and regulating temperature.

2. **Analyzing the Statement**: The statement claims that "transpiration is directly proportional to humidity." This means that if humidity increases, transpiration should also increase according to the statement.

3. **Evaluating the Relationship**: In reality, transpiration is inversely proportional to humidity. This means that when humidity is high, the rate of transpiration decreases because the air is already saturated with moisture, making it harder for water to evaporate from the plant's surface.

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