Properties
Strength and pliability/stiffness come from an intricate combination of cellular microstructures: cell wall material composition, the spatial dimensions of the cell wall, the number of cell wall layers, cell density distribution, and the arrangement of cellulose fibers in the layers. Fibrils of cells are precisely arranged on a layered basis to achieve the desired properties, which can vary widely.
Parenchyma
Parenchyma is the most common and versatile ground tissue in plants, found in almost all major parts of higher plants. Parenchyma has thin and flexible cell walls, with only a primary layer, comprised of riotously arranged cellulose fibers reinforcing a matrix of hemicellulose, pectin, and glycoproteins. Parenchyma cells have no lignin.
When first produced, parenchyma cells are spherical. But when packed together, their arrangement becomes polygonal, commonly with 14 sides.
Mature parenchyma cells can divide long after being produced by meristem. When a cutting (stem segment) is induced to grow, it is the parenchyma cells that begin dividing and give rise to new roots. When a plant is wounded, the ability of mature parenchyma to multiply is particularly important to tissue repair.
Parenchyma tend to have large vacuoles, which store various secretions, including grains of starch, oils, and secondary metabolites.
Cells which contain chloroplasts, such as leaves, are collectively termed chlorenchyma tissue. Chlorenchyma primarily performs photosynthesis, whereas other parenchyma mostly store food and water.
A transfer cell is a parenchyma cell that is stretched so that the surface area of the plasma membrane is greatly increased. Transfer cells deliver nectar in flowers. In carnivorous plants, they transfer dissolved matter between cells.
Parenchyma cells can have a long life. For instance, cacti cells may live over a century.
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The parenchyma tissues that comprise fruits and vegetables are the least stiff, and at the low end of tensile strength. In contrast, the wood of desert palms is made of cells that are 1,000 times as strong and 100,000 times stiffer.
Wood cells are organized in a honeycomb pattern. Cell walls comprise a large portion of the cell; hence wood’s stiffness and strength.
Woody trees grow in diameter over time. In contrast, palm trees, such as coconut trees, maintain a diameter throughout life.
As a palm stem grows in height, the thickness of cell walls increases to support the extra weight. Cell walls are thickest at the base and periphery of stems, where bending stresses are the greatest.
