A number of common features are associated with a great diversity of observations of somatic embryogenesis in vitro. There are fundamental homologies between direct and indirect somatic embryogenesis, and between single-cell and multiple-cell initiation. Many of the observed differences can be attributed to whether or not cells require redetermination to the embryogenic state, and to differences in the nearest neighbour relationships of initiating cells. The observed pattern of morphogenesis depends on whether a group of cells can establish and maintain coordinated behaviour as an embryogenic unit and will be influenced by factors which affect intercellular communication.