Cell Theory Timeline By mariahchavez25 Jan 1, 1595 Hans and Zacharias Jansen produced the first compound microscope. Jan 1, 1653 Robert Hooke discovered cells. Jan 1, 1668 Francesca Redi discovered that calls come from existing cells. Jan 1, 1674 Anton van Leeuwenhoek discovered single celled organisms. Jan 1, 1765 Lazzaro Spallanzani discovered that spontaneous generation was incorrect Jan 1, 1824 Rene Dutrochet discovered osmosis. Jan 1, 1838 Matthias Schleiden discovered that plants were composed of cells. Jan 1, 1839 Theodor Schwann discovered plants were made of cells Jan 1, 1855 Rudolf Virchow discovered animals were made of cells Jan 1, 1931 Ernst Ruska invented the first electron microscope.