Ascent of sap in trees. Find the maximum height to which water may rise in a tree under the assumption that the roots stand in a pool of water and the uppermost leaves are in air containing water vapor at a relative humidity r=0.9. The temperature is 25∘C. If the relative humidity is r, the actual concentration of water vapor in the air at the uppermost leaves is rn0, where n0 is the concentration in the saturated air that stands immediately above the pool of water.