Long pointed sclerenchyma cells are known as sclereids. These cells are found in the outer covering of seeds, nuts, and fruits, and are responsible for providing mechanical support and protection.

Sclereids are a type of sclerenchyma cells, which are characterized by their thick, lignified cell walls. They are also known as stone cells because they are often found in stone fruits such as peaches and cherries.

Structure of Sclereids:
• Sclereids are short and irregularly shaped cells with thick, lignified walls.
• Their walls are composed of cellulose, hemicellulose, and lignin.
• The cell walls are heavily thickened and often have pits and pores that allow for the exchange of nutrients and gases.
• The cell contents are usually dead and the cells have no cytoplasm or nucleus.

Function of Sclereids:
• Sclereids provide mechanical support and protection to the plant.
• They help to resist bending, twisting, and other mechanical stresses.
• They also protect the plant from herbivores and other external threats.
• In some plants, they also help to store nutrients.

In conclusion, sclereids are long pointed sclerenchyma cells that provide mechanical support and protection to the plant. They are found in the outer covering of seeds, nuts, and fruits, and have thick, lignified walls composed of cellulose, hemicellulose, and lignin.

Sclerenchymatous fibres are long pointed sclerenchymatous cells with high lignin deposition and narrow/obliterated lumen. (ncert)