In this activity, learners observe the effect of transpiration as water is moved from the ground to the atmosphere. Learners conduct the experiment by placing a large plastic bag over a living limb of a tree or large bush for at least two hours and then measuring the water vapor collected in the bag. Use this activity to introduce learners to the hydrologic cycle and plant transpiration. This resource also explains the importance of hydration during the summer. Note: learners will see better results if they conduct the experiment on a warm sunny day.