1. Stems-II

2. Primary thickening meristem occurs in many monocots

3. Primary thickening meristems

4. Primary Thickening Meristem

5. Banana “tree”

6. Foxglove vascular ring

7. Eustele in dicots

8. Alfalfa and ragweed VB

9. Clover fasicular cambium spreads to interfasicular region

10. Secondary growth restricted to VB

11. Ordinary secondary growth in dicots and gymnosperms secondary xylem and phloem develops from the vascular cambium

12. Anomalous Secondary Growth
Localized cambial activity because some regions of cambium die
Uneven amounts of xylem and phloem
Multiple cambia develop
Concentric (or successive) layers of vascular cambium
Monocots

13. Monocots
Yucca brevifolia
Cocus nutifera

14. Cordyline (Ti plant)

15. Secondary Growth in Monocots
Meristem (cambium) becomes distinct outside the outmost VB in the stem
Secondary Thickening Meristem produces
Cells outward that differentiate into parenchyma becoming part of a secondary cortex
Cells produced inward are either
Conjunctive parenchyma that become sclerified
Parenchyma that differentiates into fibrovascular bundles (called secondary bundles)

16. Secondary thickening meristem in Cordyline (Ti plant)

17. Palm trunk Royal palm

18. Palm trunk

19. Stems (gymnosperms, dicots, and monocots) also contain a variety secretory structures
Ducts may contain resins, gums, mucilage produced by parenchyma (epithelial) cells lining the duct
Resin ducts in Pinus
and in Artemesia

20. Resin duct in poison ivy stem

21. Oil and mucilage cells

22. Laticifers
Secretory structures (of one or more cells) that produce latex (latex is a milky secretion produced by many plants with varied composition
Non-articulated laticifers consist of extremely elongated single cells (cell growth keeps pace with the growth of the stem)
Articulated laticifers are composed of many individual cells that are usually interconnected by holes in their common walls (like vessels)

23. Non-articulated laticifer in Euphorbia

24. Articulated laticifers