Secondary Growth in Plants

Secondary Growth in Plants
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  • 0:01 Definition of Secondary Growth
  • 1:10 Process
  • 3:18 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Secondary growth allows woody plants to grow very tall and strong. Growing outward as well as upward provides structure, support, and protection to these plants that they would not otherwise have.

Definition of Secondary Growth

Though you may have wished to be very tall, at some point you stopped growing. This is called determinate growth, which means growth that stops after an organism is fully formed. It means that you can only grow so much, and it is something you have no control over. Most plants, however, have indeterminate growth, which means they have growth that continues as long as the organism is alive.

There are two types of plant growth: primary growth and secondary growth. Primary growth is the kind that helps a plant grow longer (both upward and downward). It is responsible for the plant growing taller towards the sun, as well as sending its roots farther into the ground. All plants experience primary growth.

Woody plants, such as trees, shrubs, and vines, have secondary growth. This is the outward growth of the plant, making it thicker and wider. Secondary growth is important to woody plants because they grow much taller than other plants and need more support in their stems and roots. Imagine a large oak tree trying to grow as tall as it normally does without secondary growth for support. It would be about as strong as a very tall piece of grass!

Process

All plants have meristems. These are groups of cells that divide and become other growth tissues, such as xylem and phloem. When the cells divide during primary growth, the tissues are called primary tissues (primary xylem and phloem).

Lateral meristems are the dividing cells in secondary growth, and produce secondary tissues. Secondary xylem is the actual wood of the plant, and secondary phloem provides sugar transport. Lateral meristems are arranged into two cylinders that run through the roots and stems: the vascular cambium and the cork cambium.

The vascular cambium is a very thin layer of cells between the xylem and the phloem. As the plant grows each year, the vascular cambium creates a new layer of xylem on its inside and phloem on its outside. This is makes the plant grow laterally (get wider). The secondary xylem accumulates over the years, but it dies at the same rate it is produced and eventually becomes cork.

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