The correct answer is option (D) claim that cells were the basic unit of all plant matter.
M. J. Schleiden was a botanist at the University of Jena and a co-founder of the cell theory. He was the first person to recognize the importance of cells as the fundamental unit of life. He extensively studied plant cells under the microscope and contibuted to the cell theory. He postulated cell theory stating that all the structural parts of the plants were made up of cells. Cell theory was further postulated by Theodor Schwann and Rudolf Virchow stating all living organisms are made up of cells and new cells arise from the division of the pre-existing cells.