Since the publication of this book, in 1983, several new and exciting developments have taken place in the field of Plant Tissue Culture, and it now forms a major component of what is popularly called Plant Biotechnology. Many of the important crop plants which were then regarded as recalcitrant are now amenable to regeneration from cultured protoplasts, cells, and calli, enabling subjection of these crops to improvement by biotechnological methods of cell manipulation. Embryogenic cultures can be established for most of the important crop plants, including many hardwood and softwood tree species.