Cambium tissue is present in plants. The cambium layer is a tissue layer that helps in plant growth. The cambium cells help in the secondary growth of the plant by providing an undifferentiated mass of cells. The cambial activity is seen between the areas of the xylem and phloem. Secondary tissues arise from the parallel rows of the cells that are made from the cambium in plants. The cambium is seen in dicotyledon stems. It is absent in the monocot plants. As the cambium is present between the vascular bundles, therefore, it is also known as intrafascicular cambium. The main cambium function is to provide secondary growth to the plants. This meristematic tissue is present between the permanent tissues. We will learn more about what is cambium in plants, what is the function of cambium, the structure of cambium.
Classification of Vascular Bundles
In the above paragraph, we learned a bit about what is cambium. Here we will understand how vascular bundles are classified. The cambium is the basis of this classification. These vascular bundles are classified on the presence and absence of cambium.
Open Vascular Bundles: In these types of vascular bundles, cambium tissue is present. It is present in between xylem and phloem elements. The bundles are said to be open. These types of bundles due to the presence of cambium have the ability to form secondary xylem and phloem or we can say that they are capable of secondary growth. As they are open for secondary growth therefore they are named open vascular bundles. They are present in dicots.
Closed Vascular Bundle: The cambium tissue is absent in these types of vascular bundles. The xylem and phloem tissues are joined together and no cambium is present in them. No secondary growth is seen in these types of vascular bundles. Due to this, they are known as closed vascular bundles as they are closed for secondary growth.
We got a rough idea about what is cambium and now we will study its role in plant growth. The growth of the root and stem is known as primary growth. This growth takes place with the help of apical meristems. The lateral meristems are responsible for the secondary growth of the plant. They help to increase the girth of the root and stem. The lateral meristems are the Intrafascicular cambium, Interfascicular cambium and the cork cambium. These lateral meristems are responsible for the secondary growth of the plant.
The vascular bundles get arranged in a ring-like manner. They are arranged around the central pith and are conjoint and open. As they possess cambium therefore they are called open tissues. It is known as intrafascicular cambium. The cells start the process of dedifferentiation and in this way, the cambium function also starts and the cambium rings are formed. These cambium rings that are formed by the cambium start dividing. From the observations, it is seen that the cambium is more active on the inner side as compared to the outer side.
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We will study the cork cambium function. The cork cambium is the main tissue that is responsible for the formation of wood. The girth of the stem increases due to increased activity of the vascular cambium. As the girth keeps increasing the outer cortical layers starts rupturing. So, cork cambium produces new layers that replace the damaged or ruptured layers.
Cork cambium is also called phellogen. The cork cambium has another name that is stellar cambium. Phellogen is thick and has two layers. The outer one forms the cork and the inner one forms the secondary cortex. The cells of cork are compactly arranged and in the beginning, they have thin cellulose cell walls. When they mature the living part is replaced by the non-living part which is the formation of wood material. The cell walls of the cork become thick by the deposition of suberin. This chemical makes the cork or wood material impervious to water by getting deposited in the cell walls.
The phelloderm is the secondary cortex. It is called so because it develops at the time of secondary growth. It is made up of thin-walled parenchymatous cells. They have cellulose cell walls and are living in nature. The periderm is the collective name given to phellogen, phellem and phelloderm. They are the protective layers of the cell. They grow when the epidermis layer is ruptured and also when the outer cortical layers are ruptured. When secondary growth in the vascular cambium takes place, then only the secondary growth of the cork cambium happens. As the growth of cork cambium is continuous, the layers peripheral to phellogen are damaged and they need continuous replacement.