Roots213-page5 - • Phloem found in patches between the...

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Roots - 5 Endodermis in young root Endodermis in older root The endodermis walls thicken and no longer permit passage of materials as roots mature. In roots that have secondary growth, the entire root exterior to the stele (the vascular tissue cylinder) gets sloughed off. Stele The vascular tissue of the root is located with the stele, which forms the center or core of the root inside of the endodermis The stele contains: Xylem, the core of the stele with radiating "arms". The number of “arms” is a genetic trait (The vocabulary is diarch, triarch, tetrarch, pentarch, etc.) Xylem is recognized by its large diameter vessels.
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Unformatted text preview: • Phloem, found in patches between the xylem arms, comprised of sieve elements and companion cells • Pericycle, parenchyma cells just inside of the endodermis, forms the rest of the stele tissue. Older pericycle cells may form secondary walls. • Origin of lateral or branch roots (by dedifferentiation) • Origin of secondary root cambium and cork cambium (by dedifferentiation) • The stele of Monocot roots usually has a thin cylinder of alternating xylem and phloem patches and an internal pith composed of parenchyma cells. The endodermis layer of some monocot roots is very thick....
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This note was uploaded on 01/08/2012 for the course BIO 213 taught by Professor Makina during the Fall '09 term at SUNY Stony Brook.

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