sclerenchyma A plant tissue whose cell walls have become impregnated with lignin. Due to the added strength that this confers, sclerenchyma plays an important role in support; it is found in the stems and also in the midribs of leaves. The cell walls contain pits, enabling the exchange of substances between adjacent cells. Mature sclerenchyma cells are dead, since the lignin makes the cell wall impermeable to water and gases. Sclerenchyma cells take the form of fibres or sclereids. Compare collenchyma; parenchyma.

sclerenchyma The fibrous or woody tissue in a plant that provides mechanical support for it. The tissue is formed from cells whose walls are thickened with cellulose or lignin, and when mature the cells usually contain no living protoplasm. The cells may occur singly or in groups and may be long and fibrous or stony. Stone cells (sclereids) are found in seed coats and some fruits (e.g. pears).

collenchyma A plant tissue (see ground tissues) that consists of living cells with additional cellulose thickening in their walls, providing support and protection for young stems and leaves. It is most commonly found in the stem cortex. Compare parenchyma; sclerenchyma.

collenchyma Tissue that provides strengthening and support for primary structures (i.e. those lacking secondary thickening), such as young shoots and leaves. It consists of elongated cells with unevenly thickened walls.