The colored water and celery stalk experiment (often called the Rainbow or Purple Celery Experiment) is a very simple experiment that demonstrates the movement of water through a plant. The experiment is safe enough to be performed in a classroom or at home.
To perform the experiment, a stalk of celery with the bottom cut off is placed in a glass with 3 inches of water, heavily dyed with food-safe dye. After a few hours, the water moves up the stalk, coloring the outside of the celery. The color is more vivid the longer the celery remains in the water. The experiment demonstrates the phenomenon of transpiration. Transpiration occurs when the leaves of the plant lose water through evaporation.
Capillary action slowly pulls water up from the bottom of the stalk to the leaves, replacing the water lost by evaporation. The clear water, originally in the celery, is replaced by dyed water. Transpiration occurs most efficiently in the presence of sunlight. During the experiment, the celery gains color more quickly in a sunny location. The same method is used on plants such as carnations, but celery is favorable because it is cheap, easily accessible and edible even after the experiment.