Chapter 7 A View of the Cell The Discovery of Cells The History of the Cell Theory The first person to record looking at water under a microscope was Anton van Leeuwenhoek. Robert Hooke used a compound light microscope to study cork, the dead cells of oak bark. Matthias Schleiden studied plants under a microscope and concluded that all plants are made of cells. Theodore Schwann studied animal cells and concluded that all animals are made of cells. Rudolf Virchow hypothesized that cells divide to form new cells & all cells come from preexisting cells The Cell Theory: All organisms are composed of one or more cells. The cell is the basic unit of organization of organisms. All cells come from preexisting cells.