parenchyma

Plant tissue composed of loosely packed, more or less spherical cells, with thin cellulose walls. Although parenchyma often has no specialized function, it is usually present in large amounts, forming a packing or ground tissue. It usually has many intercellular spaces.

sclerenchyma

Plant tissue whose function is to strengthen and support, composed of thick-walled cells that are heavily lignified (toughened). On maturity the cell inside dies, and only the cell walls remain.

Sclerenchyma may be made up of one or two types of cells: sclereids, occurring singly or in small clusters, are often found in the hard shells of fruits and in seed coats, bark, and the stem cortex; fibres, frequently grouped in bundles, are elongated cells, often with pointed ends, associated with the vascular tissue (xylem and phloem) of the plant.

organ