The cell walls of plants are composed mainly of cellulose fibrils . The spaces between fibrils are filled with pectates and hemicellulose . The adjacent cells are cemented firmly together by calcium pectates . This cementing layer is the middle lamella.
In a young plant cell the cellulose fibrils are laid down randomly to form the primary cell wall which can stretch as the cell grows. More cellulose fibrils are laid down on the inside of the primary wall as well as the cell grows to form the secondary wall. In the secondary wall the cellulose fibrils are more closely parked arranged in an orderly manner in each layer. The different layers of fibrils in the secondary wall are orientated at different angles. This structure makes the cell wall tough relatively rigid and slightly elastic .
In collenchyma the thickening of the comers of the cell walls with cellulose gives the cell added strength and rigidity or firmness. The cells are also flexible and extensible enabling the stems in which they occur to grow .
