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.
They have thickened secondary cell walls and therefore aid in support as well as water transport. Vessel elements are individual cells linked together end to end, forming long tubes, or xylem vessels. Water moves from element to element through perforated end walls. Companion cells have nuclei and ribsomes which may serve not only the companion cell itself but the sieve plate which is lacking in ribsomes etc. In some plants, companion cells also help load sugar produced in the mesophyll into the sieve0tube members of leaves.