A group of plant hormones (phytohormones) that, together with other plant hormones, induces plant growth and development. The presence of an unknown compound in the phloem that stimulated cell proliferation of potato tubers was demonstrated in the early 1900s by G. Haberlandt. In the 1940s J. van Overbeek found that the milky endosperm from immature coconuts is rich in compounds that promote cell proliferation. Then, in 1954, during investigations of the nutritional requirements of tobacco callus tissue cultures, F. Skoog and C. O. Miller discovered a very active substance that stimulated cell division and was formed by the partial breakdown of aged or autoclaved herring sperm deoxyribonucleic acid (DNA). The compound was named kinetin because it induced cytokinesis of cultured tobacco cells. Kinetin has not been found in plants, and it can be formed from a mixture of autoclaved furfuryl alcohol and adenine. In 1961 Miller obtained an active substance that stimulates cell division from the milky endosperm of corn (Zea mays) seeds; in 1964 D. S. Letham, identified this active compound and named it zeatin. Cytokinin is now the accepted term for those naturally occurring and synthetic compounds that promote the cell division (cytokinesis) and growth of various plant tissues.