Transpiration can be measured with a potometer. A potometer is a device used to measure the rate of water uptake or loss by a plant. It consists of a glass tube attached to a plant stem, which is then placed in a water-filled container. As the plant loses water through transpiration, the water in the tube is drawn up, and the rate of water loss can be measured by tracking the movement of the water in the tube. Therefore, a potometer is an effective instrument for measuring the rate of transpiration in plants.