Sclerenchyma

Sclerenchyma: Definition, Classification, and Types of Sclereids

Sclerenchyma

Sclerenchyma is a specialized tissue, adapted to hold up against both compressive and tensile stresses in plants. Sclerenchyma cell forms may be separated into fibres, connected with phloem, xylem, and various other cells; and sclereids or varied kinds.

Definition of Sclerenchyma:

The lignified tissues which lack protoplast at maturity are called sclerenchyma. Sclerenchyma cells are found in all parts of plants. They are present in both ground tissues and vascular tissues.

The word sclerenchyma is derived from the Greek word sklērós which means “hard” and énkhuma” meaning “infusion”.

Classification of Sclerenchyma

Sclerenchyma cells are primarily divided into two types i.e., fibers and sclereids.

Classification-of-Sclerenchyma

Fibers

They are substantially elongated cells having long as well as tapering ends which interlace to offer mechanical assistance to the plant. Fibers generally occur in the bundles and they can be located almost all over the plant body consisting of the stem, origins, and the vascular packages of the fallen leaves.

Most of these fibers include seed hairs, leaf fibers, and also bast fibers, and also these are a crucial source of the raw material for the textile market and additionally for other oven items. Fibers are further categorized into two groups xylary fibers and extra xylary fibers.

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1. Xylary Fiber:

These fibers are present in the primary and secondary xylem and thus, accordingly, their origin differs. They are established from the procambium when related to the primary xylem and stem from the cambium when connected with the secondary xylem. The fusiform initials of cambium trigger fibers.

The xylary fibers are categorized into:

  • Libriform fiber

These fibers have extremely thick walls and simple pits. They are longer than the tracheids of plants.

  • Fibro-tracheid

They have an intermediate thickness in between tracheids and fibiform fibers. They have surrounded pits.

  • Gelatinous or mucilaginous fiber

These fibres are identified by either lack or visibility of lignin in little quantity on the cell wall surface.

2. Extra xylary fiber:

These fibres take place in the cortex, pith, and in association with phloem as phloem or bast fiber. They never relate to xylem components. Following are its types.

  • Cortical Fibers

These fibers originate in the cortex.

  • Phloem fibers

These fibers come from the phloem.

  • Perivascular fibers

These are present on the periphery of the vascular cylindrical tube. They exist inside the inner cortical layer.

Sclereids

They are defined as the mechanical tissue having attributes like they take place in a group or single, as well as they are found related to the plant vascular cells xylem as well as phloem.

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The thickening of the cell wall in sclereids is non-uniform and it also consists of a number of easy pits, with rounded apertures, as well as typically, the cells of the sclerenchyma include the narrow lumen.

It is sometimes referred to as the stone cells and also it is additionally responsible for the sandy structure of pears and guava.

Types of Sclereids

There are four types of sclereids:

  • Macro sclereids: They are rod-shaped and found in testa of seeds.
  • Astro sclereids: They are star-shaped and mainly found in leaves.
  • Osteo sclereids: They are bone or spoon-shaped and are present in seed coats.
  • Tricho sclereids: They are thin wall branched. They resemble plant hairs. Their branches extend into the intercellular spaces.