Explain the process of secondary growth in stems of woody angiosperm with help of schematic diagrams. What is the significance?
Explain the process of secondary growth in stems of woody angiosperm with help of schematic diagrams. What is the significance?
Secondary growth in woody angiosperm stem occurs by two types of cambia, vascular cambium and cork cambium.
Vascular cambium: In woody dicots, the strip of cambium present between the primary xylem and phloem is called the intrafascicular cambium. The interfascicular cambium is formed from the cells of the medullary rays adjoining the intrafascicular cambium. This intrafascicular cambium and interfascicular cambium results in the formation of a continuous cambium ring. The cambium cuts off new cells toward its either sides. The cells present toward the outside differentiate into the secondary phloem, while the cells cut off toward the pith give rise to the secondary xylem. The amount of the secondary xylem produced is more than that of the secondary phloem.
Cork cambium(phellogen): It produces secondary growth tissues collectively called periderm. Cork cambium develops secondarily from a subepidermal layer of living cells. It produces phellem or cork on the outside and secondary cortex or phelloderm on the inner side. Cork consists of dead, suberised and impermeable cells. At places aerating pores called lenticels to occur which help in gaseous exchange.
Significance of secondary growth:
1. It is a means of replacement of old non-functional tissues with new active tissues.
2. The plants showing secondary growth can grow and live longer as compared to other plants.
3. Commercial cork is a product of secondary growth.
4. Wood is a very important product of secondary growth.
Secondary growth in woody angiosperm stem occurs by two types of cambia, vascular cambium and cork cambium.
Vascular cambium: In woody dicots, the strip of cambium present between the primary xylem and phloem is called the intrafascicular cambium. The interfascicular cambium is formed from the cells of the medullary rays adjoining the intrafascicular cambium. This intrafascicular cambium and interfascicular cambium results in the formation of a continuous cambium ring. The cambium cuts off new cells toward its either sides. The cells present toward the outside differentiate into the secondary phloem, while the cells cut off toward the pith give rise to the secondary xylem. The amount of the secondary xylem produced is more than that of the secondary phloem.
Cork cambium(phellogen): It produces secondary growth tissues collectively called periderm. Cork cambium develops secondarily from a subepidermal layer of living cells. It produces phellem or cork on the outside and secondary cortex or phelloderm on the inner side. Cork consists of dead, suberised and impermeable cells. At places aerating pores called lenticels to occur which help in gaseous exchange.
Significance of secondary growth:
1. It is a means of replacement of old non-functional tissues with new active tissues.
2. The plants showing secondary growth can grow and live longer as compared to other plants.
3. Commercial cork is a product of secondary growth.
4. Wood is a very important product of secondary growth.
