Secondary Growth: Vascular Cambium And Cork Cambium

What Is Secondary Growth?

This happens in plants and leads to the widening of the plant by diameter or girth. It is mainly affected by two types of cambium tissues, including the vascular and the cork cambium. This growth normally takes place in woody plants, leading to the formation of the secondary xylem, commonly referred to as wood, and secondary phloem. This gives support to the plant and, at the same time, increases the ease with which the plant is capable of nutrient and water translocation.

Vascular Cambium

It is a lateral meristem that takes part in the secondary growth of plants. Hence, this secondary tissue is secondary vascular tissue and causes the secondary growth of the plant. This tissue simply adds lignified secondary cell walls for increasing the diameter of the stem and root of woody angiosperms along with gymnosperms.

Where Is Vascular Cambium Located?

• It is seen to be taking place between the primary xylem and primary phloem in both stems and roots.

• The vascular cambium is smart to have a single layer of cells, and the cells, in turn, are commonly cylindrical or rectangular.

• It is the location of the provision of new vascular tissues.

Secondary Growth

• Secondary Xylem: It provides new xylem cells, which contribute to the wood.

• Secondary Phloem: It gives rise to new phloem cells, governing food transport.

• Vascular Cambium Width: The vascular cambium contributes to the girth increase in stems and roots.

Types Of Cells Present In Vascular Cambium

The cells present in the vascular cambium are:

Fusiform Initials

• It is the spindle or elongated-shaped cell.

• The derived cells of these initial cells are known to produce secondary xylem and phloem cells.

Ray Initials

• Short, cuboidal cells.

• Makes up the radial system of the xylem and phloem rays; it takes part in storage and transport.

Secondary Xylem And Phloem Formation

The cells of the vascular cambium divide to give rise to the secondary xylem and phloem.

Mechanism Of Formation

• Cell Division: Cells of vascular cambium divide, and new cells form towards the interior (secondary xylem) and the exterior (secondary phloem).

• Secondary growth originates from the vascular cambium. It takes place in shrubs and trees.

• Growth Rings: Secondary xylem forms annual growth rings in temperate climates. This way, age can be determined.

Growth Pattern and Consequence

• Radial Expansion: The secondary xylem brings about the thickening of the stem and root.

• Formation of Wood: The accumulated secondary xylem forms the bulk of wood.

Cork Cambium

A lateral meristem that gives rise to the periderm, which consists of the protective, outer bark of stems and roots, protecting against mechanical damage and pathogen attack.

Location And Morphology Of Cork Cambium

• In the outer part of stems and roots, beneath the epidermis.

• It comprises a single layer of cells usually much more densely packed than those of the vascular cambium.

Role In Secondary Growth And Protection

• Production of Cork Cells: Produces cork cells that compose the outer bark.

• Protection: Protects the plant from water loss, pathogens and mechanical injury.

Anatomy Of Cork Formation

The cork cambium produces cork cells and phelloderm and is part of the protective outer layer of the plant.

Process Of Cork Production

• Cell Division: Cork cambium cells divide producing cork cells to the outside and phelloderm cells to the inside.

• Cell Differentiation: Cork cells become impregnated with suberin to protect them.

Effect On Structure Of Plant

• Formation of Bark: The accumulation of cork cells gives rise to bark.

• Increase in Girth: It helps in thickening the outer diameter of the stem or root.

Secondary Growth In Plants

It is a series of events in which the meristematic tissues, the cambium, produce new cells that increase the girth of a plant.

Initiation Of Vascular And Cork Cambium

• Vascular Cambium: Develops between the primary xylem and phloem.

• Cork Cambium: Develops in the outer cortex, eventually replacing the epidermis.

Lateral Growth And Its Effect On Plant Width

• Diameter Increase: A large diameter increase of the plant arises from both vascular and cork cambium.

• Annual Ring Formation: Annual rings in the secondary xylem form in many species.

Interrelationship Of Cambiums

The vascular cambium and cork cambium are interconnected in terms of their functioning to protect against secondary growth.

Vascular And Cork Cambium Coordination

• Concurrent Activity: The vascular cambium produces tissues towards the interior while the cork cambium produces them towards the exterior, with both of these meristems active during secondary growth.

• Support vs. Protection: The vascular cambium produces the tissues needed to provide support, while the cork cambium produces tissues that are involved in protection.

Secondary Growth In Different Plants

• Trees: Oaks, pines, and maples are plants with high growth calculated concerning secondary growth.

• Shrubs: Some shrubs undergo secondary growth, although it is not as marked in these plants as it is in trees.

Dicotyledons Vs. Monocotyledons

• Secondary growth is prevalent in dicotyledons but rare in monocotyledons.

Presence And Absence Of Secondary Growth

• Dicotyledons: Exhibit pronounced secondary growth, leading to the formation of wood and bark.

• Monocotyledons: Typically lack secondary growth, with limited increase in girth.

Examples Of Plants With Significant Secondary Growth

• Dicots: Most hardwood trees like oak and maple.

• Monocots: Bamboo shows some degree of secondary thickening.

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