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Roots

Roots. Fibrous Roots. Tap Root. Primary Root Growth.

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Roots

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  1. Roots Fibrous Roots Tap Root

  2. Primary Root Growth 1 = emerging lateral root, 2 = lateral root primordium,   3 = root hair nearly fully grown, 4 = mature vessel element, 5 = level at which root hairs appear, 6 = endodermal cells differentiate, 7 = level at which elongation ceases, 8 = first vessel element begins to differentiate, 9 = region of maximum cell elongation, 10 = first sieve tube matures, 11 = cell division ceases in most cell layers, 12 = first sieve element begins to differentiate, 13 = pattern of future vascular cylinder becomes recognizable at this level, 14 = zone of maximum rate of cell division, 15 = apical initials, 16 = root hair zone, 17 = growth in length, 18 = elongation zone, 19 = meristem, 20 = rootcap

  3. Root hairs

  4. Dicot root with an actinostele

  5. Development of actinostele

  6. Monocot roots have a polyarch actinostele Wheat Root Lily Root

  7. Corn root with parenchyma in center of the stele

  8. Endodermis • Stage I – Endodermal cells have a Casparian Strip • Stage II – Endodermal cells develop suberin in all wall areas except for plasmodesmata – especially inner tangential wall and radial walls • Stage III – Endodermal cell wall becomes thickened with added layers of cellulose and lignin • Passage cells – Endodermal cells that remain in Stage I condition while neighboring cells are in Stage II or III (often near xylem poles) • Exodermis with similar properties occurs in some species just beneath the epidermis

  9. Endodermal cell with Casparian strip Casparian strip

  10. Endodermis Early stage of root development Later stage of development

  11. Orchid roots are modified by development of a velamen – a multiple epidermis consisting of dead cells – an exodermis separates the velamen from the cortex Velamen Exodermis

  12. Dicot root drawing at end of primary growth 1 = epidermis 2 = root hair, 3 = cortex, 4 = intercellular spaces, 5 = pericycle (one layer colored dark green), 6 = endodermis, 7 = primary phloem, 8 = protoxylem, 9 = metaxylem, 10 = initial vascular cambium, 11 = sieve plate

  13. Branch roots

  14. Development of branch roots from pericycle

  15. Development of branch roots

  16. Branch root

  17. Branch root in corn

  18. Secondary Growth in Roots 1 = primary xylem, 2 = endodermis, 3 = primary phloem, 4 = pericycle, 5 = vascular cambium, 6 = secondary phloem, 7 = secondary xylem

  19. Limited secondary growth in castor bean root

  20. Tilia root

  21. Tilia root periderm

  22. Carrot roots have more secondary phloem than xylem 1 = secondary phloem, 2 = vascular cambium, 3 = parenchymatous woody secondary xylem

  23. Types of Mycorrhizae • Ectotrophic mycorrhizae • Sheathing mycorrhizae • Endotrophic mycorrhizae • VA (vesicular-arbuscule) mycorrhizae

  24. Ectotrophic Mycorrhizae • Sheathing mycorrhizae of forest trees • Roots have club-like appearance • 5000 species of mushrooms form these

  25. Ectotrophic Mycorrhizae

  26. Ectotrophic Mycorrhizae

  27. Hartig Net

  28. Endotrophic Mycorrhizae • Common on herbaceous plants and trees • Mycelium branches in cortex of root forming arbuscles and vesicles

  29. Endotrophic Mycorrhizae

  30. VA Mycorrhizae Arbuscule Spore

  31. Roots and Shoots – What connects the two areas?

  32. Hypocotyl connects the root and shoot starting in the embryo

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