Both the stem and the leaves of a celery plant are eaten, but the long crunch part many people put peanut butter on is the stem. To prove this if one was to take a live celery plant with roots still on it, one could put these roots in colored water. After about a week once could see that the stem has coloring only where the nutrient passages are, but most the entire leaf at the end will be colored. Dark, deep colors such as blue, red, or purple work best.
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