In a famous series of experiments in which he cut off the tails of mice for 22 generations, Weismann disproved the theory that acquired characteristics could be inherited. Weismann also proposed the germ plasm theory. This theory suggested that while the body, which Weismann called somatoplasm, lives for only one generation, hereditary material, which he called germ plasm, is immortal, passed from generation to generation without change.
In 1663 Robert Hooke, discovered cells in a piece of cork which he examined under his microscope. He observed cell walls because cork cells are dead and without cytoplasmic contents. Hooke then drew the cells he saw and decided on the word cell. Hooke published his findings in his famous work, micrographia: Physiological Descriptions of Minute Bodies made by Magnifying Glasses (1665). http://www.xtimeline.com/evt/view.aspx?id=373537