Each cell wall has three distinct layers. These are-
- Median Membrane: Two adjacent cells connected by a cement membrane is called median membranous. It is continuous and single-layered. Sometimes the primary wall is not formed on the median membrane. As a result narrow holes are formed. This hole is called a coupe or pit. Two pits facing each other are called pit pairs or pit pairs. The middle membrane of pit pair is called pit membrane. Pit membrane has very fine pores. Through these pores there are tiny pores. The filaments are called plasmodesmata. Scientist Tangle discovered it. The mesenchyme contains more pectic acid. It also contains pectin and protopectin. It acts as a common membrane between the two cells. Phragmosomes accumulate at the equator of the cell during the telophase phase of cell division. Later, pectin accumulates with phragosomes to form the membranous membrane.
- Primary wall: The first layer that forms above the mesentery is called the primary wall. It is thin, fragmented and monolayered. Its thickness is 1-3 microns. Primary walls are not formed in the cell well area. It is composed of microfibrils. Its chemical components are cellulose, hemicellulose, glycoprotein, pectin, lignin etc. Parenchyma, collenchyma and mesophyll are only primary walls in bananas.
- Secondary wall: The layer formed above the primary wall is called secondary wall. It is three-layered, segmented and 5-10 microns thick. Its outer layer is partially thin, the middle layer is slightly thicker and the inner layer is thinner. Secondary walls are not formed in the cusp region. It is composed of cellulose, hemicellulose, lignin, suberin, cutin, wax, tannin, calcium oxalate, silica, inorganic salts etc. Cells that are metabolically active (dividing cells) do not have secondary walls. Only permanent cells consist of tracheids, vessels, fibers etc. secondary wall. It is impermeable to water and gas. It gives shape to the cell and protects the organism from external injury.
Cell wall is a unique feature of plant cells. Due to the accumulation of various substances on the cell wall, its ornamentation can be circular, spiral, stepped, reticular, etc.