Celery science experiment

A few days ago I did a experiment for Science. It told me to but a stalk of celery in a cup of food coloring, I chose red ad then placed the celery in the cup. A couple days later we took the celery out of the cup and on the bottom the holes were red. Those holes were the phloem that carry the water up the stalk of the plant to feed it. The holes were red because of the food coloring the holes on the bottom carry up water, but because water is clear we cannot see the holes well.