In the transpiration pull theory, what causes the tension that leads to lifting of the water column?

Explanation

**Step-by-Step Solution:**

1. **Understanding Transpiration Pull Theory**: The transpiration pull theory explains how water is transported from the roots to the leaves of a plant. It was proposed by botanist Henry Dixon in 1939.

2. **Process of Transpiration**: Transpiration is the process through which plants lose water in the form of vapor from their leaves. This loss of water creates a negative pressure or tension in the plant's xylem.

3. **Role of Xylem**: The xylem is the vascular tissue responsible for conducting water from the roots to the leaves. When water vapor is lost during transpiration, it creates a pull that helps lift the water column upward through the xylem.

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