Lay the 4 pieces of celery in a row on a cutting board or counter so that the place where the stalks and the leaves meet matches up.
Cut all 4 stalks of celery 4 inches below where the stalks and leaves meet.
Put the 4 stalks in 4 separate cups of purple water. (Use 10 drops of red and 10 drops of blue food color for each half cup of water.)
Label 4 paper towels in the following way: "2 hours," "4 hours," "6 hours," and "8 hours." (You may need newspapers under the towels.)
Every 2 hours from the time you put the celery into the cups, remove 1 of the stalks and put it onto the correct towel. (Notice how long it takes for the leaves to start to change.)
Each time you remove a stalk from the water, carefully peel the rounded part with a vegetable peeler to see how far up the stalk the purple water has traveled.
What do you observe? Notice how fast the water climbs the celery. Does this change as time goes by? In what way?
Measure the distance the purple water has traveled.