Sclerenchyma tissue is composed of cells (sclerenchyma cells) that have extremely hard, thick walls. In fact, the cell walls of sclerenchyma cells are so thick that, at maturity, the cell is completely cut off from the extracellular environment and dies. Two general types of sclerenchyma cells are recognized: sclereids, which may be more or less isodiametric or may be branched, and fibers, which are greatly elongate cells.

The gritty texture of pears is caused by groups of sclereids (often called "stone cells") that are embedded in the parenchyma tissue of the fruit's flesh. The appearance of typical stone cells from a pear is illustrated below:
 

Sclereids from pear, stained with toluidine blue and photographed under the 40x objective. Notice the greatly thickened walls of these cells.

This page last updated: 13 Sep 1999