of variation that can be expected will vary with the clone, age of the culture, use of mutagenic agents, and selection pressure applied to cell suspensions or callus cultures of clones for stress conditions such as salt level, herbicides, microorganisms or their byproducts, and specific metabolites (Skirvin, 1978). The exploitation of such natural and induced variation seems especially applicable to old woody plant cultivars, such as 'Bartlett' pear (Pyrus communis L.) and 'Delicious' apple (Malus domestica Borkh.) (introduced in 1770 and 1893, respectively) (Skirvin, 1977), which could be expected to have accumulated many mutant cells that may have stabilized into chimeras of various complexity. Skirvin and Janick (1976a) were among the first to emphasize the importance of clonal variation in genotype improvement of horticultural species. Shepard et al. (1980) demonstrated extensive variability among plants regenerated from cultured leaf protoplasts (protoclones) of 'Russet Burbank' potato (Solanum tuberosum L.). In investigating the extent and possible significance of this source of genetic variability, Larkin and Scowcroft (1981), who have reviewed the topic extensively, first suggested that the term "somaclonal variation" be used to describe the phenotypic variation observed among plants regenerated after a passage through tissue or cell culture. Tissue culture-related variants have also been referred to as calliclones (Skirvin and Janick, 1976a), phenovariants (Sibi, 1976), and protoclones (Shepard et al., 1980). However, the term somaclonal variation describes the system best and has justifiably become the standard term to describe the phenomenon. The amount of variation that can be encountered in vitro has been described for banana (Musa ×paradisi L.) by Smith and Drew (1990) in a review of Australian tissue culture programs and prospects. They reported that up to 90% of the in vitro-derived banana plants in Australia were off-types under field conditions. The off-types primarily consisted of dwarf "choke-throat" plants. This choke-throat condition prevents the bunch from emerging from the banana shoot and produces closely packed, undersized fruit. Although the choke-throat off-types were devastating to the banana tissue culture industry (Walduck et al., 1988), as reported by Smith and Drew (1990), a few dwarf plants with normal fruiting characteristics have been observed (Smith and Hamill, 1991). According to Smith and Drew (1990), The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.