Plants, like animals, require a circulatory system that allows water and nutrients to move throughout them. While animals do this by a pump (the heart), plants do this by a system of tubes, found within the stem. This image is a cross section of a Lily of the Valley plant that depicts these systems. The purple and yellow raised structures seen on the right constitute the xylem. The xylem is responsible for transporting water from the roots to the leaves. This is unidirectional, and works much like a straw. As water molecules evaporate from the leaves, more water is drawn up through the xylem. The blue oval tubes seen on the left are known as the phloem. The phloem is responsible for transporting sugars made in the leaves to the rest of the plant. This process, unlike that of the xylem, is bidirectional and requires energy.
Artist: Don Pottle. Author: Nikita Sturrock.