This is a very fun science experiment to do with children. Fill about 1/2 inch of water into a glass and add food coloring. Place a piece of celery with leaves still attached into the colored water and keep an eye on it for a day or two.
Watch how the water travels up the stalk to the leaf and changes color. As you can see, we had the best luck with the color red.
Cut the stalk across and show children where the coloring is showing the tubes that carry the water up the stalk of the plant. This is an example of capillary action.