Plant cells are characterized by the presence of a rigid cell wall on the basis of which they can be differentiated from animal cells (Most animal cells are now known to possess a cell coat-which form a fuzz around the cell surface (Martinez-Palomo, 1970). In many cases it is an extension of outer membrane. This wall may be absent, in some lower plants and cells taking part in reproduction. When Robert Hooke (1665) used the term cell for the first time in a thin slice of cork, he actually studied cell wall. (These cells did not have protoplasm).
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Cell wall is a secretory product of protoplasm. It protects the cell from unfavourable conditions, separates one cell from the other, provide strength and definite shape to the cell. Thus the cell wall constitutes a kind of exoskeleton.
At the time of cell division when the nucleus divides into two cytokinesis starts. In this process vesicles of golgi complex become aligned, at the equatorial plate. By some physical and chemical changes in this plate an intercellular amorphous substance functions as cementing material between two cells. It is made up of calcium and magnesium pectate. This layer is called middle lamella. The characteristic softening of fruits during ripening is mainly due to increase in the solubility of middle lamella. The cell plate — spindle fiber complex is known as phragmoplast.