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Fundamental Tissue System and its Types
The ground or fundamental tissue system constitutes the main body of the plants. It includes all the tissues except epidermis and vascular tissues. In monocot stem, ground tissue system is a continuous mass of parenchymatous tissue in which vascular bundles are found scattered. Hence ground tissue is not differentiated into cortex, endodermis, pericycle and pith.
Generally in dicot stem, ground tissue system is differentiated into three main zones – cortex, pericycle and pith. It is classified into extrastelar ground tissue (Examples: cortex and endodermis) and intrastelar ground tissue (Examples: pericycle, medullary ray and pith).
Extrastelar Ground Tissue
The ground tissues present outside the stele is called extrastelar ground tissue. (Cortex)
Intrastelar Ground Tissue
The ground tissues present within the stele are called intrastelar ground tissues. (pericycle, medullary rays and pith).
Different Components of Ground Tissue Systems are as Follows
One or two layers of continuous or discontinuous tissue present below the epidermis, is called hypodermis. It is protective in function. In dicot stem, hypodermis is generally collenchymatous, whereas in monocot stem, it is generally sclerenchymatous. In many plants collenchyma form the hypodermis.
The Cortex occurs between the epidermis and pericycle. Cortex is a few to many layers in thickness, In most cases, it is made up of parenchymatous tissues. Intercellular spaces may or may not be present. The cortical cells may contain non living inclusions of starch grains, oil, tannins and crystals. Its general function is storage of food as well as providing mechanical support to organs.
The cells of this layer are barrel shaped and arranged compactly without intercellular spaces. Endodermis is the innermost cortical layer that separates cortex from the stele.
Pericycle is single or few layered parenchymatous found inner to the endodermis. It is the outermost layer of the stele. Rarely thick walled sclerenchymatous. In angiosperms, pericycle gives rise to lateral roots.
Pith or Medulla
The central part of the ground tissue is known as pith or medulla. Generally this is made up of thin walled parenchyma cells with intercellular spaces. The cells in the pith generally stores starch, fatty substances, tannins, phenols, calcium oxalate crystals, etc.