Illustration of various plant cells and tissues from Principles of Scientific Botany published in 1849 by the German botanist Jakob Matthias Schleiden (1804-1881). Figures 1-7 and 14-15 show embryonic plant cells. Figures 11-13 show plant hairs, figure 8 shows a pollen grain and figure 10 an oil duct. Also included are fungal cells in fermenting currant juice (figure 9) and the decomposition of a protein in a sugar solution (figure 10). Schleiden was a co-founder of cell theory with the German physiologist Theodor Schwann. Schleidens studies convinced him that all plant or animal structures are composed of cells or their derivatives and that cells are the fundamental unit of life.