<P> Credit for developing cell theory is usually given to two scientists: Theodor Schwann and Matthias Jakob Schleiden . While Rudolf Virchow contributed to the theory, he is not as credited for his attributions toward it . In 1839, Schleiden suggested that every structural part of a plant was made up of cells or the result of cells . He also suggested that cells were made by a crystallization process either within other cells or from the outside . However, this was not an original idea of Schleiden . He claimed this theory as his own, though Barthelemy Dumortier had stated it years before him . This crystallization process is no longer accepted with modern cell theory . In 1839, Theodor Schwann states that along with plants, animals are composed of cells or the product of cells in their structures . This was a major advancement in the field of biology since little was known about animal structure up to this point compared to plants . From these conclusions about plants and animals, two of the three tenets of cell theory were postulated . </P> <P> 1 . All living organisms are composed of one or more cells </P> <P> 2 . The cell is the most basic unit of life </P> <P> Schleiden's theory of free cell formation through crystallization was refuted in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker . In 1855, Rudolf Virchow added the third tenet to cell theory . In Latin, this tenet states Omnis cellula e cellula . This translated to: </P>

Who said that the cell is the basic unit of life