Tissues

• Simple permanent tissues are composed of cells which are structurally and functionally similar.
• These tissues are made up of one type of cells.
• A few layers of cells beneath the epidermis are generally simple permanent tissue.
• Simple Permanent tissues are divided into two types.
  • Supporting tissues
  • Protective tissues

Supporting Tissues:

Supporting tissues are further divided into three parts:

• Parenchyma
• Collenchyma
• Sclerenchyma

Parenchyma:

Parenchyma forms the bulk the plant body. Parenchyma cells are living and possess the power of division.
Structure:

• They consist of relatively unspecialized cells.
• The cell wall is thin and encloses dense cytoplasma.
• They are living cells. In other words, parenchyma cells have living protoplasm.
• They have loosely packed cells.
• They have large spaces between cells.
• The parenchymatous cells are oval, round, polygonal or elongated in shape.
• They surround a large central vacuole.

Occurrence:

• The parenchyma is widely distributed in plant bodies such as stem, toots, leaves flowers and fruits.

Functions:

• Parenchyma generally stores and assimilates food.
• Parenchyma is called chlorenchyma when it contains chlorophyll and performs photosynthesis
• In aquatic plants, large air cavities are present in parenchyma to help them float. Such a parenchyma type is called aerenchyma.
• Parenchyma servers as a packing tissue, to fill the spaces between other tissues.
• Parenchyma acts as a primary support to the stem.
• Transport of materials occurs through cells or cell walls of parenchyma cells.
• Parenchyma cells are metabolically active; their intercellular air spaces allow gaseous exchange.
• Parenchymatous tissue stores waste products of plants such as tannin, gum, crystals, resins or inorganic waste, etc.
• In xerophytes i.e. arid plants and succulents i.e. plants having fleshy parts, parenchyma acts as a water storage issue.

Collenchyma:

Tissue also consists of living cells is characterized by the deposition of extra cellulose at the corners of the cells.
Structure:

• The cells of this tissue are living.
• They are elongated and irregularly thickened at the corner.
• There is very little intercellular space in collenchyma.

Occurrence:

• The cells of collenchyma are located below the epidermis.

Functions:

• Chollenchyma gives flexibility to plants
• It allows bending of various parts of a plant like tendrils and stems of climbers without breaking.
• It also provides mechanical support.

Differences between Parenchyma and Collenchyma:

Sclerenchyma:

Sclerenchyma cells are dead cells and they are devoid of protoplasm.

Structure:

• The cell walls of sclerenchyma are greatly thickened of lignin.
• It is this tissue which makes the plant hard and stiff.
• The cells of sclerenchyma are closely packed without intercellular spaces.
• They are dead cells. Thus, these cells are fitted together like tiles in a mosaic floor.
• Cells of sclerenchyma are of two types – Fibres and sclereids.
• Fibres consist of very long, narrow, thick and lignified cells.
• Fibres are usually pointed at both ends and are clustered into strands.
• In contrast to fibres, sclereids (also called grit cells or stone cells) are irregular-shaped.

Occurrence:

• They are found in stems, roots, veins of leaves, hard coverings of seeds and nuts.
• Husk of coconut is made of sclerenchymatous tissue. It yields coir, a well-known fibre used for mats, cordage, brushes, etc.

Functions:

• It provides strength to the plant parts.

Comparison between Collenchyma and Sclerenchyma: