2. Alveolar theory:
The alveolar nature of protoplasm was suggested by Butchlli in 1892. According to him, protoplasm consists of many suspended droplets or alveoli or minute bubbles, resembling the foams of emulsion.
3. Fibrillar theory:
This theory was put forward by Flemming. According to him, protoplasm consist of fibres embedded in the inner mass of matrix. The fibrillae are called mitome or spongioplasm formed of proteins called micelles, and ground substance is termed paramitome or hyaloplasm.
4. Reticular theory:
This theory was postulated by Klein, Comoy, etc. It suggests that protoplasm consists of a reticulum of fibres in its hyaloplasm.