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Phloem - II

Phloem - II. Primary Phloem. Protophloem Metaphloem. Metaphloem Sunflower and Corn. Secondary Phloem in Dicots. Sieve tube members Companion cells Fibers Sclereids Regular parenchyma Axial parenchyma Ray parenchyma Dilatation tissue – axial or ray. Secondary phloem in pumpkin stem.

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Phloem - II

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  1. Phloem - II

  2. Primary Phloem • Protophloem • Metaphloem

  3. Metaphloem Sunflower and Corn

  4. Secondary Phloem in Dicots • Sieve tube members • Companion cells • Fibers • Sclereids • Regular parenchyma • Axial parenchyma • Ray parenchyma • Dilatation tissue – axial or ray

  5. Secondary phloem in pumpkin stem 1 = STM; 2 = Sieve plate; 3 = Companion cell; 4 = Vascular cambium 5 = Vessel elements

  6. 1458 pound champion for 2003

  7. Secondary phloem is short lived • As new secondary phloem is produced, older STM and CC are crushed and may be obliterated • This is caused by the expansion of the stem diameter during secondary growth

  8. Secondary phloem in Tilia

  9. Secondary phloem in Tilia

  10. Secondary phloem in Vitis (grape)

  11. Secondary phloem in pine stem Tanin cells

  12. Secondary phloem in pine radial section

  13. Dilatation Tissue • As stem (or root) increases in diameter, circumferential growth of the phloem must occur to keep the tissue from tearing • Two types of dilatation tissue • Proliferative tissue: when axial parenchyma begin to divide and expand • Expansion tissue: when ray parenchyma begin to divide and expand producing a dilated ray

  14. Secondary growth

  15. Example of Dilatation Tissue

  16. Dilated rays in Tilia show extreme amounts of dilatation tissue

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