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A student investigated the effect of environmental conditions on transpiration rate in a leafy shoot of a mesophyte plant. The transpiration rate was measured gravimetrically over one-hour periods. The mean rates for two different conditions are shown in the table.
| Condition | Time (hours) | Mean transpiration rate (g m⁻² h⁻¹) |
|---|---|---|
| A (85% relative humidity, still air) | 0–1 | 1.2 |
| A | 1–2 | 1.1 |
| A | 2–3 | 1.3 |
| B (30% relative humidity, wind speed 2 m s⁻¹) | 0–1 | 3.8 |
| B | 1–2 | 4.0 |
| B | 2–3 | 3.9 |
Temperature was constant at 25 °C in both conditions.
Compare the transpiration rates in conditions A and B, and explain the differences in terms of the mechanism of transpiration.