describe the distribution and structure of simple plant tissues in stems
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Answer:
In stems, the xylem and the phloem form a structure called a vascular bundle; in roots, this is termed the vascular stele or vascular cylinder. Like the rest of the plant, the stem has three tissue systems: dermal, vascular, and ground tissue.
Mechanical tissue supports a plant and their growing organs against any deformation and provides mechanical strength is termed as mechanical tissue. The cell walls of parenchyma, collenchyma, and sclerenchyma provide mechanical rigidity to the plant. The large size and structural strength of a woody plant are achieved by the cell wall. In these plants, the constituents of the cell wall contribute 95% of the dry weight of the wood. The strength and rigidity of the entire plant are due to the cell wall. Collenchyma is a living cell and retains its protoplast even when mature. So, it can regulate the deposition and orientation of wall materials according to the need of developing organs. The collenchyma cells, in addition to mechanical strength, also provide elasticity to the cell due to the presence of hydrated pectin on the wall. It includes sclereids and fibres. Sclereids give strength, resistance and inflexible protection in the organs. Fibres add mechanical rigidity to the organ where they occur. The fibres may be extraxylary and xylary. The former fibres may occur uninterrupted just beneath the epidermis or may be present in the ground tissue. A group of fibres may be present above the vascular bundles as bundle cap (e.g. Xanthium stem) or they may surround each vascular bundle forming bundle sheath (e.g. Maize stem). They may occur above and below of each vascular bundle (e.g. Canna stem).