Secondary Growth in Trees

Secondary growth is the increase in girth or thickness of a plant, which occurs due to the activity of the lateral meristem. The secondary growth in trees is responsible for the formation of wood and bark. The two types of lateral meristem involved in secondary growth are vascular cambium and cork cambium.

Vascular Cambium

The vascular cambium is a meristematic tissue responsible for the formation of secondary xylem and phloem. The secondary xylem is commonly known as wood, while the secondary phloem is the inner bark. The vascular cambium produces new cells on both the inner and outer sides of its own layer.

Heartwood and Sapwood

The heartwood and sapwood are two types of secondary xylem, which are formed by the vascular cambium. The sapwood is the outer layer of the secondary xylem, which is responsible for the conduction of water and minerals from the roots to other parts of the plant. The heartwood is the inner layer of the secondary xylem, which is responsible for providing mechanical support to the plant.

Increase in Thickness of Heartwood

As the secondary growth proceeds in a tree, the thickness of heartwood increases. This is because the inner layers of the secondary xylem become more compact and dense, which makes them less suitable for water and mineral conduction. The heartwood also undergoes chemical changes, which result in the accumulation of various substances such as tannins, resins, and oils.

Conclusion

In conclusion, the secondary growth in trees involves the activity of the vascular cambium, which results in the formation of secondary xylem and phloem. As the secondary growth proceeds, the thickness of heartwood increases, while the sapwood remains relatively the same. The heartwood provides mechanical support to the plant and undergoes chemical changes, which make it less suitable for water and mineral conduction.