In 1838, Matthias Schleiden, a botanist, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. At about the same time Theodore.Schwann(1839), Zoologist, studied different types of animal cells and reported that cells had a thin outer later which is today known as the plasma membrane. He also concluded, based on his studies on plants, that the presence of cell wall is a unique character of the plant cells.
Schwann proposed the hypothesis that the bodies of animals and plants are composed of culls and products of cells.
Schleiden and Schwann together formulated the cell theory. This theory.however did not explain as to new cells were formed.
Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape. Cell theory as understood today is:
(i) All living organisms are composed of cells and products of cells.
(ii) All cells arise from pre-existing cells. Cell give.
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