1. Roots Fibrous RootsTap Root

2. 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 Primary Root Growth

3. Root hairs

4. Dicot root with an actinostele

5. Development of actinostele

6. Monocot roots have a polyarch actinostele Wheat RootLily Root

7. Corn root with parenchyma in center of the stele

9. 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

10. Endodermal cell with Casparian strip Casparian strip

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

12. 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

13. 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

14. Branch roots

15. Development of branch roots from pericycle

16. Development of branch roots

17. Branch root

18. Branch root in corn

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

20. Limited secondary growth in castor bean root

21. Tilia root

22. Tilia root periderm

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

24. Types of Mycorrhizae l Ectotrophic mycorrhizae –Sheathing mycorrhizae l Endotrophic mycorrhizae –VA (vesicular-arbuscule) mycorrhizae

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

26. Ectotrophic Mycorrhizae

28. Hartig Net

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

31. Endotrophic Mycorrhizae

32. VA Mycorrhizae Spore Arbuscule

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

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