Plant Tissue Study: Collenchyma and Sclerenchyma

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Study Notes

Collenchyma cells are living and slightly elongated.
Young collenchyma is plastic and stretches irreversibly as the plant grows.
It functions as supporting tissue in young and mature herbaceous plant organs.
Collenchyma walls can become lignified, forming sclerenchyma.
It is located in stems, leaves, floral parts, and roots.
Collenchyma is not found in monocot stems and leaves, where sclerenchyma develops earlier.
Collenchyma cells contain chloroplasts and have alternating layers with varying proportions of cellulose and pectin.
Pectin is a common component in collenchyma.

Angular: Thickening is longitudinal along the angles of the cell.
Lamellar: Thickening is mainly on the tangential walls.
Annular: Thickening of the cell wall is almost homogenous, making the lumens circular.

Sclerenchyma cells have thick, secondary walls that are usually lignified.
Sclerenchyma cells remain elastic, retaining their original size and shape after stretching.
Its main functions include support and sometimes protection.
Mature sclerenchyma is composed of dead cells with extremely thick secondary walls, 90% of the cell volume.

Fibers: Long cells with tapering ends, usually unbranched. Found in phloem.
Sclereids: Short cells with uniform diameter and blunt ends, may be branched or unbranched.
- Osteosclereids: Bone-shaped with enlarged or branched ends, often found in seed coats and dicot leaves.
- Astrosclereids: Highly branched and star-shaped, commonly in leaves and stems of hydrophytes.