Malthias Schleiden (1838) observed that all plants are composed of differentkinds of cells.
Theodore Schwann (1839) reported that cells had a thin outer layer (now known as ‘plasma membrane’). He also found that cell wall is a uniquecharacter of plant cells.
He proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells.
Schleiden & Schwann formulated the cell theory.
Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the cell theory.
Cell theory states that: (i) All living organisms are composed of cells and products of cells. (ii) All cells arise from pre-existing cells.
