Not available – first paragraph follows: Successful application of in vitro cell and tissue culture technology to crop improvement hinges on the ability to regenerate plants of known genetic constitution. For example, when using cell or tissue culture as a means of cloning, or amplifying numbers of plants for field or seed production, it is essential that regenerated “copy” plants be genetically similar or identical to the original. Alternatively, when using this approach to develop a new improved variety, a selection scheme would be devised that would theoretically find only cells with altered genotypes at loci whose function bears on a desired character, but which were genetically identical to the original tissue donor in all other respects. However, some of the earliest research papers in this area have documented the existence of spontaneous genetic variability in both cultured cells and corresponding regenerated plants. A useful label, “somaclonal” variation, has recently been advanced for this phenomenon—“soma,” occurring in somatic tissues as opposed to sexual progeny, and “clonal,” expressed as differences among and within clones.