One of the major functions of the stem is to move water, nutrients, and food through the plant. The internal tubes in stems act like the plumbing in a house or the blood vessels in people. As in humans, this system is called the vascular system. The food-moving part of the vascular system is called the phloem. The water-and-mineral-moving system is called the xylem.
Part of the cross section of a sunflower stem	Diagram of stem structure