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11.3: Secondary Tissues in the Root

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  • In roots, the formation of both secondary meristems involves the pericycle. The pericycle and some residual procambium join together to form the vascular cambium, a secondary meristem that produces vascular tissue. The other secondary meristem, the cork cambium, is initially formed solely from the pericycle.

    Each of these secondary meristems divides in two directions to form a different secondary tissue to the inside and outside of the meristematic layer, respective to the center of the plant.

    The vascular cambium produces secondary xylem to the inside of the root and secondary phloem to the outside.

    The cork cambium produces phelloderm, a storage tissue, to the inside of the root and cork, a protective layer of dead, suberized cells, toward the outside. These three layers -- phelloderm, cork cambium, and cork -- are referred to as a periderm. As the first periderm layer is formed, it separates the epidermis, cortex, and endodermis from the conductive tissues of the root. The epidermis and cortex cells die and are shed as secondary growth proceeds.

    The pine root below has one layer of periderm fully formed. Can you label the tissues and meristems described above? What are the large holes in the root?

    Figure \(\PageIndex{1}\): Pine Root Cross Section

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