Dr Williamson's studies of motility in plant cells have had a major impact on the course of plant cell biological research. He independently co-discovered plant actin; from a novel experimental preparation, he developed the first explanation for organelle movement in plants based on acto-myosin-A TP (now fully substantiated); he was first to demonstrate responses to micromolar calcium ions and first to measure free calcium at these levels in plant cytoplasm. In 1990 he turned to molecular genetics of plant cell morphogenesis, significantly advancing knowledge of the role of microtubules in cell wall formation, and his very recent, definitive and widely publicised characterisation of a gene that synthesises cellulose - the world's most abundant biopolymer - has been hailed as a seminal breakthrough in one of the longest-standing and intractable problem areas in plant science.