Back then, Robert Hooke found cells from a cork and named it cells. Later on, Matthias Schleiden found cells from plant parts and concluded that all plants are made of cells. Theodor Schwann, after observing many different animal cells, concluded that all animal have cells. Several years later, Rudolf Virchow hypothesized that cells divide to form new cells. Virchow proposed that every living organism has cells. His observations and conclusions and those of others are summarized in the cell theory