An American cell biologist, Porter (1960-61) described endoplasmic reticulum for the first time. His observation was based on electron microscopy. Endoplasmic reticulum is a network of tube-like structures distributed extensively throughout the cytoplasm.
Some of the tubes of the reticulum connect the nuclear membrane and these open on the cell membrane after extending through the cytoplasm. It may be rough, if ribosomes are attached to it or smooth, when ribosomes are not attached.
The following functions are performed by ER:
It increases the surface area of the cytoplasm for various metabolic activities of the cell.
It gives internal support to the colloidal matrix (cytoplasm).
It is associated with synthesis, storage and transport of metabolic products.
It helps in the formation of cell plate and nuclear membrane during cell division.