cell-wall defined in 1951 year

cell-wall - cell-wall;
cell-wall - Limiting layer of plant cells, formed by, and closely investing, the protoplasm; comparatively rigid and giving mechanical support to plant tissue. In living cells traversed by extremely fine cytoplasmic threads, the plasmodesmata, which form delicate protoplasmic connections between adjacent cells. The walls of newly formed cells are at first very thin but as the cells assume their permanent character the walls thicken. In formation of new cells pectic material is laid down in the cell plate across equatorial plane of division spindle to form the middle lamella, intercellular material that cements together adjacent cells. Each new cell lays down a primary wall consisting of cellulose, hemicelluloses and pectic substances. When cell has reached full size it may remain with primary wall only, e.g. some forms of parenchyma. In other cells a secondary wall is laid down inside primary wall. During deposition of these layers certain small areas remain virtually unthickened forming pits. Pits of adjacent walls usually coincide so that in these areas the protoplasts are separated only by the pit membrane consisting of the middle lamella and a very thin layer of primary wall on each side of it. Through pit membranes pass the majority of plasmodesmata. Some cell walls undergo further modification, e.g. cuticularization of epidermal cells and suberization of cork cells, rendering them impermeable to water; lignification of fibres, vessels, tracheids, conferring on them increased strength and rigidity. See also: Cellulose,

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