Chapter 25 Plant Tissues (Sections 25.7 - 25.9)

1. Chapter 25Plant Tissues(Sections 25.7 - 25.9)

2. 25.7 Secondary Growth • Woody plants thicken (add secondary growth) by cell divisions in lateral meristems • Secondary growth occurs at two types of lateral meristem, vascular cambium and cork cambium – both arise from pericycle

3. Key Terms • lateral meristem • Vascular cambium or cork cambium; sheetlike cylinder of meristem that gives rise to plant secondary growth • vascular cambium • Ring of meristematic tissue that produces secondary xylem (wood) and phloem • cork cambium • In plants, a lateral meristem that gives rise to periderm

4. Secondary Growth • Vascular cambium gives rise to secondary tissues • Cork cambium gives rise to periderm

5. Secondary Growth cork cambium vascular cambium A Secondary growth (thickening of older stems and roots) occurs at two lateral meristems, vascular cambium and cork cambium. Vascular cambium gives rise to secondary tissues; cork cambium, to periderm. pith cortex Fig. 25.17a, p. 408

6. Vascular Cambium • Divisions of vascular cambium cells produce secondary xylem on the cylinder’s inner surface, and secondary phloem on its outer surface • Displaced cells of the vascular cambium divide in a widening circle, so the tissue’s cylindrical form is maintained

7. Primary Growth at Terminal and Lateral Buds

8. Primary Growth at Terminal and Lateral Buds stem surface primary xylem primary phloem vascular cambium B In spring, primary growth resumes at terminal and lateral buds. Secondary growth resumes at vascular cambium. Divisions of meristem cells in the vascular cambium expand the inner core of xylem, displacing the vascular cambium (orange) toward the surface of the stem or root. secondary xylem secondary phloem Fig. 25.17b, p. 408

9. Growth at a Vascular Cambium

10. Growth at a Vascular Cambium outer surface of stem or root division division Vascular cambium cell as secondary growth starts One of the two descendant cells differentiates into a phloem cell (pink); the other stays meristematic. One of the two descendant cells differentiates into a xylem cell (blue); the other stays meristematic. The pattern of cell division and differentiation into xylem and phloem continues through growing season. C Overall pattern of growth at vascular cambium. Fig. 25.17c, p. 408

11. outer surface of stem or root division division One of two daughter cells differentiates into a phloem cell (pink); the other stays meristematic. Vascular cambium cell as secondary growth starts One of two daughter cells differentiates into a xylem cell (blue); the other stays meristematic. The pattern of cell division and differentiation into xylem and phloem continues through growing season. Growth at a Vascular Cambium C Overall pattern of growth at vascular cambium. Stepped Art Fig. 25.17c, p. 408

12. ANIMATION: Secondary growth To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

13. Cork Cambium • Cork cambium forms and gives rise to periderm • Periderm consists of parenchyma and cork, and the cork cambium that produces them • Bark consists of all of the living and dead tissues outside the vascular cambium • The corkcomponent of bark protects, insulates, and waterproofs a stem or root surface

14. Key Terms • bark • Secondary phloem and periderm of woody plants • cork • Component of bark • Protects the surfaces of woody stems and roots • Has densely packed rows of dead cells with walls thickened by a waxy substance (suberin)

15. Wood • Secondary xylem (wood) is classified by its location and function, as in heartwoodorsapwood • wood • Accumulated secondary xylem • heartwood • Dense, dark accumulation of nonfunctional xylem at the core of older tree stems and roots • sapwood • Functional secondary xylem between the vascular cambium and heartwood in an older stem or root

16. Structure of a Woody Stem

17. Structure of a Woody Stem bark secondary phloem sapwood (new xylem) heartwood (old xylem) vascular cambium periderm (includes cork cambium, cork, some phloem, and new parenchyma) A Structure of a typical woody stem. Fig. 25.18a, p. 409

18. Tree Rings • Rings visible in heartwood and sapwood are regions of early and late wood • Early wood forms during wet springs • Late wood indicates a dry summer or drought when no large-diameter xylem cells were made for water uptake • In most temperate zone trees, one ring forms each year

19. Early Wood and Late Wood

20. Early Wood and Late Wood direction of growth vessel in xylem early late early late early late early late early B Early and late wood in an ash tree. Early wood forms during wet springs. Late wood indicates that a tree did not waste energy making large-diameter xylem cells for water uptake during a dry summer or drought. Fig. 25.18b, p. 409

21. Key Concepts • Secondary Growth • In many plants, secondary growth thickens branches and roots during successive growing seasons • Extensive secondary growth of eudicots and conifers produces wood • Tree rings can be used to study past environmental conditions

22. ANIMATION: Growth in a Walnut Twig To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

23. ANIMATION: Secondary Growth in a Root To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

24. 25.8 Variations on a Stem • Specialized stems allow some plants to store nutrients, to reproduce asexually, or both • Specializations include stolons, rhizomes, bulbs, corms, tubers, and cladodes

25. Stolons • Stolons (runners) are stems that branch from the main plant stem • Adventitious roots and leafy shoots sprout from nodes and develop into new plants • Example: strawberry

26. Rhizomes • Rhizomes are fleshy, primary stems that grow under the soil, parallel to its surface • They are the plant’s primary storage tissue • Example: turmeric

27. Bulbs • A bulb is a short underground stem with overlapping layers of thick, modified leaves (scales) • Contains starch and other stored products • Example: onion

28. Corms • A corm is a thickened underground stem that stores nutrients • Unlike a bulb, a corm is solid rather than layered • Example: taro

29. Tubers • Tubers are thickened portions of underground stolons • They are the plant’s primary storage tissue • Example: potato

30. Cladodes • Cladodes are flattened, fleshy, photosynthetic stems that store water • Example: cactuses

31. Key Concepts • Modified Stems • Certain types of stem specializations are adaptations for storing water or nutrients, and for reproduction

32. 25.9 Tree Rings and Old Secrets • Many trees form one ring each year • Tree rings hold information about environmental conditions that prevailed while the rings were forming • Example: Relative thicknesses of rings reflect the availability of water – rings show that settlers who arrived at Roanoke Island in 1587 suffered a major drought

33. A Record of Rainfall • A section of a bald cypress tree that was living near English colonists when they first settled in North America – narrower annual rings mark years of severe drought

34. Tree Rings and Old Secrets • Tree rings are used to date archaeological ruins; gather evidence of wildfires, floods, landslides, and glacier movements; and study the ecology and effects of parasitic insect populations

35. Tree Rings and Old Secrets year: 1 2 3 p. 411

36. Some Tree Rings

37. Some Tree Rings A Pine is a softwood. It grows fast, so it tends to have wider rings than slower-growing species. Note the difference between the appearance of heartwood and sapwood. Fig. 25.19a, p. 411

38. Some Tree Rings B The rings of this oak tree show dramatic differences in yearly growth patterns over its lifetime. Fig. 25.19b, p. 411

39. Some Tree Rings C An elm made this series between 1911 and 1950. Fig. 25.19c, p. 411

40. Sequestering Carbon in Forests (revisited) • Compared to other organic materials, decomposition of plant matter is relatively slow, because molecules that waterproof and reinforce plant cells are relatively stable • A forest stops accumulating carbon as its trees mature and its soil becomes saturated with organic matter

41. ANIMATION: Annual Rings To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE