1. 1 Review What are three important functions of stems Explain How does the arrangement of vascular bundles in monocot stems differ from dicot stems Apply Concepts How do the functions of a stem relate to the functions of the roots and leaves of a plant 2 Review Define primary and secondary growth Predict Describe what would happen over time to a tree sapling that could grow only taller, not wider

2. Ch 23 Plant Structure and Function
23.3 Stems

3. Stem Functions Stems produce leaves, branches, and flowers
Stems hold leaves up to the sun
Stems transport substances throughout the plant.

4. Anatomy of a Stem
Epidermal cells have thick cell walls and a waxy protective coating.

5. Anatomy of a Stem Nodes Buds
Where leaves are attached
Buds
Contain apical meristems that can produce new stems and leaves
Stems produce woody tissue in larger plants.

6. Monocot Stems
Clusters of xylem and phloem tissue are scattered throughout the stem
Ground tissue is fairly uniform consisting mainly of parenchyma cells.

7. Dicot Stems Vascular bundles are arranged in a cylinder, or ring Pith
Parenchyma cells inside the ring of vascular tissue
Cortex
Parenchyma cells outside the ring of vascular tissue.

8. Primary Growth
Growth that occurs at the apical meristems.

9. Secondary Growth
Stems increase in thickness to support larger plant.

10. Secondary Growth
Very common among dicots and non-flowering seed plants such as pines
Rare in monocots
Dicots have meristems within stems and roots that produce true secondary growth
Dicots can grow much larger.

11. Conifers and Dicots Secondary growth takes place in meristems called:
Vascular cambium
Produces vascular tissues and increases the thickness of stems over time
Cork cambium
Produces the outer covering of stems.

12. Vascular cambium appears as a thin, cylindrical layer of cells between the xylem and phloem of each vascular bundle.

13. Divisions in the vascular cambium give rise to new layers of xylem and phloem
Cambium continues to produce new layers of vascular tissue each year, causing the stem to become thicker.

14. Formation of Wood Most of “wood” is actually layers of secondary xylem
Heartwood
Older xylem near the center of the stem no longer conducts water.

15. Sapwood
Active in fluid transport and is usually lighter in color.

16. Tree Rings Spring growth As growing season continues
Vascular cambium begins to grow rapidly, producing large, light-colored xylem cells, resulting in a light- colored layer of early wood
As growing season continues
Cells grow less and have thicker cell walls, resulting in a layer of darker wood
Thick rings good growing conditions and thing rings poor growing conditions.

17. Formation of Bark Bark All tissues found outside the vascular cambium
Tissues include phloem, the cork cambium, and cork.

18. Cork cambium produces a thick, protective layer of waterproof cork that prevents water loss.