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Xylem and Phloem
If you fall down and scrape your knee, you might see
blood coming from the scrape. Many kinds of animals,
including humans, rely on blood to move nutrients
through their bodies. Blood normally stays in tubes
called arteries and veins. But if one of those tubes is
broken, such as when you scrape your knee, blood can
seep out of your body.
Plants don’t have blood, veins, or arteries. But they do
have something similar. Vascular plants have liquid in
their bodies that moves nutrients and water up and
An acacia tree is one kind of vascular plant.
down the plant’s stem. Like animals, vascular plants
contain a series of tubes. These tubes keep the liquid
flowing in the right direction. Most of these tubes can be
found in the plant’s stem. The tubes are called xylem and
phloem. Xylem and phloem play important roles in keeping
plants alive.
Xylem are the hard tubes that transport water and minerals
throughout the plant. Xylem also help the plant stay
upright. Without xylem, the stem of a plant would flop
over. The plant’s flowers and leaves would not be able to
turn toward the sun. Xylem also causes the trunks of trees
to grow wider over time.
Every year, in most trees, the cells that make up xylem
tubes die off and are replaced by new xylem cells.
Over many, many years, some trees develop hundreds of
layers of old xylem. If the tree is cut down, you can see the
layers of xylem as rings.
The rings of a tree trunk are made from
Phloem transports food through the plant’s stem. Phloem
layers of xylem.
is not as sturdy as xylem. And, unlike xylem, phloem cells
do not die off each year. All the cells of a plant depend on
phloem. The cells that make up phloem allow food to pass to
the cells of the plant body. You can find phloem and xylem in
all vascular plants.
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© 2007 Discovery Communications, LLC