Schleiden, Matthias Jakob (1804–81) A German botanist who, in collaboration with T. Schwann, proposed the cell theory. Schleiden practised law before studying medicine and botany. His studies led him to conclude that all parts of a plant consist of cells or their derivatives, an idea he called ‘phytogenesis’, publishing an account of it in 1838. For some years he was professor of botany at the Universities of Jena and Dorpat but later he worked as a freelance lecturer and writer.

Schleiden, Matthias Jakob (1804–81) German botanist, who became professor of botany at the University of Jena in 1839. A year earlier he had introduced the idea that plants consisted of cells; this theory was later extended to animals by Theodor Schwann (see cell theory). Schleiden recognized the existence and importance of the cell's nucleus, although he mistakenly believed that new cells were formed by budding from the surface of the nucleus.