A plant's stem is an organ that contains most of a plant's vascular system, which is made up of two types of tubes. Each type serves a different specialized function.
The two types of vascular tubes in a plant are called xylem and phloem. In stems that are nonwoody and flexible (monocots), xylem and phloem are bound together in groups called vascular bundles. In woody plants like trees (dicots), they are arranged in rings.
Xylem vessels transport water and nutrients from roots up the stem and into the leaves. The nutrients nourish the plant and the water is used by the leaves for photosynthesis.
Phloem vessels take sugar made by a plant's leaves and transport it downward into every part of the plant. Some of the sugar is used immediately for energy, some is stored and some is used to make plant tissue.
In dicots, there is a layer of tissue between the xylem and phloem called the cambium. The cambium creates new xylem and phloem cells. It allows a stem to thicken over time and is the reason trees have rings.
For an easy-to-see example of a plant's vascular system, cut a piece of celery crosswise. The tiny holes at the celery's base are its xylem and phloem.
- Estrella Mountain Community College Bio Book: Plant Structure
- University of Arizona College of Life Sciences: Plant Parts and Functions
tubes in plant stems, how water travels through plants, plant vascular system
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Jessica Martinez is a freelance writer from Clayton, North Carolina. As a homeschooling mom, she enjoys writing about education, child development and family issues. Martinez also enjoys researching and writing about subjects she loves: history, art, interior design, gardening and travel.