1 John H. Dodds The culture offragmen ts of plant tissue is not a particularly new science, in fact as long ago as 1893 Rechinger (1893) described the formation of callus on isolated fragments of stems and roots. The culture of plant tissues in vitro on a nutrient medium was performed by Haberlandt (1902), however, his attempts were unsuccessful because he chose too simple a medium that lacked critical growth factors. Over the last fifty years there...