Permanent Tissues – Simple Tissues
Permanent tissues: Once the cells are divided into primary and secondary meristems, the newly formed cells become structurally and functionally specialized, thus forming permanent cells or mature cells. These cells lose the capability to divide. Permanent tissues are of two different types namely, simple tissues and complex tissues.
Simple tissues: Simple tissues seen in plants are namely, parenchyma, collenchymas and sclerenchyma. A simple tissue is made up of only one type of cells.
Parenchyma: The cells of the parenchyma are usually isodiametric and they form the major component within organs. In some plant tissues, the cells may be spherical, oval, round, polygonal or elongated. The cells of parenchyma have thin walls made up of cellulose and are wither closely packed or consists of small intracellular spaces. The parenchyma plays a role in photosynthesis, storage and secretion.
Figure 1 Simple tissue: Parenchyma
Collenchyma: The cells of collenchyma are observed as homogenous layers or in patches below the epidermis in dicotyledonous plants. The cells of collenchymas are thickened at the corners due to deposition of cellulose, hemicelluloses and pectin. The cells of collenchymas are oval, spherical or polygonal in shape and usually contain chloroplasts. The function of collenchymatous cells is to provide mechanical support to the growing parts of the plant such as young stem and petiole.
Figure 2 Simple tissues – Collenchyma
Sclerenchyma: The cells of sclerenchyma are long, narrow with thick and lignified walls. The cells lack protoplast and hence are usually dead. Sclerenchymatous cells are usually found in fruit walls of nuts and provide mechanical support to organs. Depending on the form, structure, origin and development, the sclerenchyma may be fibres or sclereids.
Fibres:The fibres are long, thick-walled and pointed cells occurring in groups in various parts of the plant.
Sclereids:The sclereids are usually oval or cylindrical, thick-walled usually containing dead cells with very narrow cavities, called lumen.
Figure 3 Simple tissues – Sclerenchym