Sclerenchyma consists of long, narrow cells with thick and lignified cell walls having a few or numerous pits. They are usually dead and without
protoplasts.
On the basis of variation in form, structure,
origin
and development, sclerenchyma may be either fibres or sclereids.
General defination : Sclerechyma Cells: Parenchyma cells that have developed secondary cell walls. There are two main types: fibers and sclereids.
Origin of Sclereids
Sclereids are created from parenchyma cells or can arise from sclereid primordia that are individualized early in development. Sclerification typically involves thickening of the cell wall, increasing rigidity. In the phloem, when tissue ceases to function in conduction cells may begin sclerosing. In vascular tissue, sclereids will develop from cambial and procambial cells.Sclereids are originally parenchyma cells, but are so sclerified that they are now sclereid cells rather than parenchyma cells. These sclereids are an example of brachysclereids, or stone cells.
Origin of Fiber
Fibers usually originate from meristematic tissues. Cambium and procambium are their main centers of production. They are usually associated with the xylem and phloem of the vascular bundles.
Sclerenchyma consists of long, narrow cells with thick and lignified cell walls having a few or numerous pits. They are usually dead and without protoplasts.
General Definition: Sclerenchyma Cells are parenchyma cells that have developed secondary cell walls. There are two main types: fibers and sclereids.
How Sclerenchyma is Classified: On the basis of variation in form, structure, origin, and development, sclerenchyma may be classified into two main types: fibers and sclereids.
1. Fibers:
Fibers usually originate from meristematic tissues. Cambium and procambium are their main centers of production. They are typically associated with the xylem and phloem of the vascular bundles.
2. Sclereids:
Sclereids are created from parenchyma cells or can arise from sclereid primordia that are individualized early in development. Sclerification typically involves thickening of the cell wall, increasing rigidity. In the phloem, when tissue ceases to function in conduction cells may begin sclerosing. In vascular tissue, sclereids will develop from cambial and procambial cells. Sclereids are originally parenchyma cells, but are so sclerified that they are now sclereid cells rather than parenchyma cells. These sclereids are an example of brachysclereids, or stone cells.
Why is this Classification Important?
The classification into fibers and sclereids helps in understanding the diversity of sclerenchyma cells and their roles in different plant tissues. Fibers provide structural support and strength, while sclereids contribute to hardness and protection in various plant parts. Understanding their origin and development provides insights into their functional adaptations and ecological roles.
Sclerenchyma is a type of plant tissue primarily involved in providing mechanical support and strength to the plant. It is characterized by its thick, lignified cell walls. Sclerenchyma can be classified based on various factors including form, structure, origin, and development. Here’s a detailed look at these classifications:
1. Based on Form:
Fibers:
Description: Long, narrow, and typically elongated cells.
Structure: Fibers have tapered ends and are often found in bundles or as part of a complex tissue system.
Function: Provide tensile strength and support. Commonly found in stems, leaves, and vascular tissues.
Examples:
- Xylary fibers: Found in the xylem of vascular plants.
- Phloem fibers: Found in the phloem, supporting the transport of nutrients.
Sclereids:
Description: Generally shorter and more variable in shape compared to fibers. They can be isodiametric or elongated but are often more irregular in form.
Structure: Sclereids can be globular, stellate (star-shaped), or branched.
Function: Provide mechanical support and protection, often found in various plant organs.
Examples:
- Stone cells (or brachy sclereids): Found in the outer layers of fruits like pears, giving them their gritty texture.
- Granular sclereids: Found in the seed coats of some plants.
- Fibrous sclereids: Found in various parts of plants, including leaves and stems.
2. Based on Structure:
Fibers:
Structure: Long, narrow, and often pointed at the ends. They have thick lignified secondary cell walls.
Lignification: High degree of lignification which contributes to their strength.
Sclereids:
Structure: Can be irregularly shaped with various forms such as spherical, branched, or stellate. The lignification is also present but varies in extent.
Lignification: Varies; can be less uniform compared to fibers.
3. Based on Origin:
Fibers:
Origin: Develop from the ground meristem (primary tissue) or the vascular cambium (secondary tissue). They are derived from specialized cells that elongate and become lignified.
Sclereids:
Origin: Can originate from the ground meristem or other meristematic tissues. They can form in various plant parts depending on the plant species and developmental stage.
4. Based on Development:
Fibers:
Development: Develop from cells that elongate and thicken their walls during secondary growth. They mature into long, narrow cells with a strong cell wall.
Sclereids:
Development: Develop from cells that may not elongate as much. They often form in specific regions of the plant to provide localized support and protection.
Summary
Sclerenchyma Fibers: Long, narrow, and elongate cells with a high degree of lignification, providing tensile strength and structural support.
Sclereids: Shorter, more variable in shape, and can be found in various plant organs, contributing to mechanical strength and protection.
Understanding these classifications helps in identifying the different roles that sclerenchyma plays in plant tissues and their adaptations to various environmental and structural needs.