In comparison to sclerenchyma collenchyma cells are living and elongate with the stems and leaves they support. Collenchyma cells provide support to growing plant parts. Sclerenchyma cells have thick secondary walls strengthened by lignin. Mature cells cannot elongate and occur in regions of the plant that have stopped growing in length. There are two types of sclerenchyma cells fibres and sclerids .
Fibres are long, slender and tapered usually occurring in bundles.
Some plant fibres can be used commercially eg. Sclerids are shorter and irregular in shape. They can be found scattered among the soft parenchyma tissue giving the pear fruit its gritty texture. At maturity both cell types are dead but produce secondary cell walls before the protoplast dies. Tracheids are spindle-shaped cells with pits through which water flows from cell to cell.