Role of Xylem Phloem, Sclerenchyma, Collenchyma

ROLE OF XYLEM AND PHLOEM

Collenchyma and sclerenchyma have lignified cell.This lignification becomes the reason of hardness.

• Collenchyma is present in cortex ans sclerenchyma in xylem tissues.
• The stems of land plants resist against wind.
• Bending is checked by xylem.
• Xylem tissues play role like steel road.

In short, the arrangement of vascular bundles in the rings provides resistance to wind stress, and weight bearing ability.

ROLE OF SCLERENCHYMA

• Generally, these cells are non-living.
• Sclerenchyma cells provide support to the plant parts.
• They are rigid due to secondary cell walls.
• Lignin makes the wall tough ang rigid.

There are three types of sclerenchymatous cell:
(i) Fiber
(ii) Sclerids (Stone cells)
(iii) Vessels (Trachea)

FIBERS: These are long and cylindrical. They are found in solid bundles in xylem or as bundle caps. Fibers are common in plant stems.

SCLERIDS (Stone cells): There are common in shells of nuts and seed coats.
Sclerids are shorter than fiber. They give strength.

VESSELS (Trachea): These are long tubular structures.
These structure are joined end to end and form long water conducting pipe in xylem.

ROLE OF COLLENCHYMA

 (i)_The outer most cells of the cortex of young stems, lying just beneath the epidermis,often constitute a tissue known as collenchyma.
(ii)_The walls of collenchyma cells are composed of layers of pectin and cellulose.
The cell walls are thickened at the corner.
(iii)_These thickenings are flexible these tissues form complete cylinder.
(iv)_Collenchyma cells provide support to herbaceous parts of the plants.
(v)_Cells are also found in petioles of leaves.
(vi)_Protoplasm remains alive.
(vii)_These cells are without secondary wall.