Contributions of Different Scientists

Anton von Leeuwenhoek first observed and described a live cell. (Robert Hook observed cork cell which was dead)
Robert Brown discovered the nucleus.

And all this and future discoveries were only due to the invention of microscope or anything in between simple microscope and the latest electron microscope


Matthias Schleiden (German botanist) examined plants and saw that all plants were composed of different cells that form tissues. (Sch'l'eiden and P'l'ant) (1838)


Theodore Schwann (British as in text, actually German zoologist) studied animal cells and found that cells had a thin outer layer (which is today called plasma membrane). He observed plant cells and found that cell wall was a unique character of plant cells. (1839) (Schw'ann' and 'an'imals)

Thus was put forward the hypothesis that the bodies of plants and animals are composed of cells and cell products.
Thus, Schleiden and Schwann together formulated the cell theory. But didn't explain how new cells were formed.

Rudolf Virchow (1855) explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula). He modified S&S's cell theory to:

• all living organisms are composed of cells and products of cells
• all cells arise from pre-existing cells