Plant tissue culture (PTC), an essential component of plant biotechnology, offers novel approaches to plant production, propagation, and preservation. During the past decade or so, major advances have been made in this field, and from being an art it has become an industrial technology. It is being used for large-scale multiplication of ornamentals and some fruit tree species. Feasibility of its applications in several other areas, such as the production of useful natural compounds (Chapter 11), generation of useful genetic variability (Chapter 13), and genetic transformation of crop plants (Chapter 15) has been demonstrated. Plant regeneration in tissue cultures via organogenesis (Chapter 2) or somatic embryogenesis (Chapters 3-5), which is critical requirement to realise the full potential of the various techniques of plant biotechnology to crop improvement, has been applied so far without understanding these processes. This often makes a researcher reach a helpless dead-end like a computer operator whose partial understanding of the operation may lead him to a dead-lock position. Somatic embryogenesis, which is considered as the future method of commercial micropropagation (Chapters 4, 5), is beset with numerous problems. The formation of somatic embryos by a cell/tissue system is largely a chance happening. Moreover, a large proportion of the somatic embryos are structurally and/or physiologically abnormal and, therefore, incapable of germination. The involvement of a callus phase endangers the genetic fidelity of the plants produced through somatic embryogenesis (Chapter 12). The projected application of artificial seeds hinges on the solutions to these problems associated with somatic embryogenesis (Chapter 5). Unfortunately, the entire subject of spontaneous occurrence of in vitro variations, being utilized for crop improvement (Chapter 13), lacks scientific explanation and, consequently, reliable controls. This continues to be a serious impediment not only in clonal propagation of selected genotypes (Chapters 7, 8) but also in the production of industrial compounds by cultured cells (Chapter 11) and improvement of cultivars through cell fusion (Chapter 14) or genetic transformation (Chapter 15). The chapters on organogenic differentiation (Chapter 3), somatic embryogenesis (Chapter 4) and cytogenetics of cell cultures (Chapter 12) clearly suggest that the future of PTC applications lies in understanding the cellular basis of differentiation. Identification of genes concerned with different morphogenic expressions and their exploitation may also contribute to achieving reproducible regeneration in tissue cultures, including hitherto recalcitrant systems (Chapter 6). The feasibility of genetic engineering to modify the genome of higher plants by selective gene transfer has been well established but the availability of desirable .......
