A potometer is set up with a freshly cut leafy shoot. What does the apparatus actually measure?

الشرح

The bubble in the tube moves as the shoot draws water in, so what is read off the scale is uptake, and that reading is then used as an estimate of the water being lost. Vapour leaving the leaves is never collected by the apparatus, and a little of the water taken up stays inside the plant, so treating the reading as a direct measurement of loss claims more than the equipment can show.