Intussusceptive growth

Growth in Area and Thickness.—The cell wall when first formed is limited in both extent and thickness. As the protoplast within enlarges new particles are placed within the wall by the process called intussusception. This increases its area. New particles, also, are deposited on its surface which gradually increases its thickness. The latter process is known as growth by apposition. 

Plant Cw. are exceedingly complex structures which have largely defied detailed analysis. The precursor of the Cw. is the cell plate, a non-cellulose structure formed between the 2 daughter nuclei during mitotic division of the cell. After the new eell membranes have formed on either side, the cell plate (a strongly hydrated structure) matures to a middle lamella . As growth proceeds, the area of the new wall is increased by intussusception, i. e. incorporation of new material within the existing matrix. The thickness increases by apposition as new layers of wall material are added. 

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