Intracellular junctions provide routes for direct cell-to-cell signalling in both plants and animals. The present volume treats the parallels and differences between such junctions in animals and plants and discusses the most recent methods of examining the physiological functions and regulation of intracellular communication. Strong evidence of both molecular as well as functional simi§ larities between plasmodesmata and gap junctions is increasing. Even more interesting is the discovery that animal gap junction proteins cross-react immunologically with some proteins in plant cells. Thus the molecular construction and function of these crucially important ultrastructural cell components is now open to a concerted research effort to understand how cells, both plant and animal, facilitate and regulate intercellular transport.