Vascular cambium and cork cambium, their roles in thickening

1. Introduction to Secondary Growth

1. Secondary growth refers to the increase in the girth (thickness) of a plant.
2. It occurs due to the activity of lateral meristems: vascular cambium and cork cambium.
3. Mostly found in dicotyledonous plants and gymnosperms; absent in monocots.

2. Role of Vascular Cambium in Secondary Growth

1. Vascular cambium is a lateral meristem responsible for producing secondary xylem (wood) and secondary phloem.
2. Develops from:
   • Fascicular cambium (within vascular bundles).
   • Interfascicular cambium (between vascular bundles).
3. Forms a continuous **cylindrical meristematic ring**.
4. Divides actively, producing:
   • Secondary xylem (towards the inner side) – provides strength.
   • Secondary phloem (towards the outer side) – helps in food conduction.
5. As secondary xylem accumulates, it forms **annual rings** used in dendrochronology (age determination of trees).

3. Role of Cork Cambium in Secondary Growth

1. Cork cambium (also called phellogen) arises in the **cortex**.
2. It produces:
   • Phellem (cork) towards the outside – provides protection.
   • Phelloderm (secondary cortex) towards the inside – living parenchymatous cells.
3. The cork is impregnated with suberin, making it waterproof and resistant to pathogens.
4. Contains small openings called lenticels for gas exchange.

4. Differences Between Vascular Cambium and Cork Cambium

5. Importance of Secondary Growth

1. Provides mechanical strength to the plant.
2. Increases conduction capacity of water and nutrients.
3. Protects the plant against injury and infection.
4. Produces wood, which is important for furniture, paper, and construction.
5. Cork is used for making bottle stoppers, insulation materials, and boards.

6. Conclusion

1. Secondary growth occurs due to the activity of vascular cambium and cork cambium.
2. It leads to the formation of wood, bark, and protective tissues.
3. Essential for strength, survival, and economic uses.