Collenchyma is a living tissue and is composed of more or less thick primary non lignified walls. Just as in parenchyma, even in collenchyma the protoplast is living. The word collenchyma is derived from the Greek word colla, meaning glue, which refers to the thick glistening wall of collenchyma
Distribution:
Collenchyma characteristically occurs in the pripheral position of stems, leaves, floral parts etc. It may also occur in root cortex particularly if it is exposed to light. In the stems and leaves of dicotyledons, collenchyma is hypodermal situated immediately below the epidermis or separated from it by one or two layers of parenchyma. Collenchyma cells are considerably elongated. Sometimes, cells are 2 mm, long resembling fibres. The shorter collenchyma cells are prismatic and appear polygonal in a transaction. In a long section the cells appear rectangular.
Cell structure and function:
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The structure of the cell wall is the most characteristic feature of the collenchyma cells. The thickenings are deposited unevenly, mainly deposited at the corners where several cells join together. In long section, collenchyma cells show thin and thick wall portions depending on the direction of the cut.
The walls containing mainly of cellulosic and pectin compounds and consist of much water. Ultrastmcturally the thickenings of collenchyma show an alternation of layers of longitudinally oriented microfibrils and non cellulosic material.
Collenchyma cells have living protoplasts and may have chloroplastss. Chloroplastss are less in number in long and narrow cells and more in cells which approach parenchyma in form. Tannin may be present in collenchyma cells.
Collenchyma is primarily a mechanical tissue adapted for support of growing organs. The thick walls and close packing, make collenchyma a strong tissue. At the same time, the peculiarities of growth and the structure of its walls impart a considerable tensile strength with flexibility and plasticity.