Robert Hooke is credited with discovering cells while looking at a piece of cork under a microscope. In his book Micrographia, which he published in 1665, Hooke describes the small structures that he observed under the microscope. What part of the cell theory is best supported by this discovery? Cells reproduce and all cells come from existing cells. Cells perform specialized functions. All organisms are made up of one or more cells. The cell is the basic unit of living beings.