Protoplasm

Protoplasm is a viscid gelatinous material, containing a large proportion (about 75%) of water; it may be either clear or granular. Under a high power of the microscope it is seen to consist of a slightly denser reticulum or network (spongioplasm), enclosed in the meshes of which is a more fluid portion (hyaloplasm) (This reticular structure of protoplasm is not absolutely constant. In many instances the structure might more properly be described as alveolar, while occasionally it may be granular or even homogeneous.). Various other substances such as fat, pigment, etc., may also be enclosed ; these are adventitious, and are termed cell inclusions or pitraplasm.

Round the periphery of a cell is a fine membrane - the cell wall; it is present in practically all cells, and is formed of materials generated by the activity of the protoplasm.