All variegated plants are not chimeras.

Norris et al. (1) presented data that "unequivocally support the idea of multilayer development of adventitious shoots from chimeral African violet leaf tissue" and concluded therefore that "adventitious shoots are of multicellular origin." Their conclusions, based on the recovery of variegated adventitious shoots regenerated from variegated leaves cultured in vitro, rely on the assumption that the plants used in the experiment were; periclinal chimeras having different genotypes in the different histogens of the shoot apical meristem. Most seedlings of variegated African violets (for example, cv. Tommie Lou) are variegated (2). Periclinal chimeras would never yield variegated offspring, but rather all green or all white seedlings, depending on the genotype of the histogen that produces the eggs (the second layer of the tunica in most dicots) (3). Since seedlings are of single-cell origin, it is most likely that variegation pattern in African violets is due to genetic expression, as in many Coleus varieties (4), and not to genetic differences between leaf cells. Therefore, variegated adventitious shoots can be of single-cell origin. Critical observations of leaf variegation patterns will clearly show which are due to genetic expression and which are caused by contributions in leaf ontogeny of independent and genetically different apical layers of a periclinal chimera. The cultivars used by Norris et al. were not periclinal chimeras. We observed freehand sections of cv. Tommie Lou leaves at a magnification of x 10. Some leaves with green tissue in the blade had no green tissue in the petiole. Dark green areas had green palisade cells [of LII origin (5)], but the subepidermal cells on the abaxial side (also of LII origin) were not green. Green areas were often isolated inside white areas, and white spots appeared in green areas. There was no evidence of the independent and continuous cell lineages derived from the layers in the shoot apex, which are clearly seen in true periclinal chimeras (6). Norris et al. regenerated more than 1000 cv. Tommie Lou plants, all of which had variegation patterns identical to the mother leaf. Even if the leaves were from periclinal chimeras, one should expect the organizing meristems of adventitious shoots to have various histogenic combinations (for example, GWG, WGW, WGG, GWW, and GGW) (7). In actuality, their results give unequivocal evidence that the same genetic information controlling the pattern of leaf variegation is in all cells in all layers of the leaf. Sunblade and Meyer (8) reported the same results as Norris et al. when regenerating cv. Tommie Lou in vitro, but their conclusion (namely, that genetic expression is responsible) agrees with ours. We believe, therefore, that Norris et al. neither proved nor disproved multicellular origin of adventitious shoots in African violets. M. MARCOTRIGIANO Department of Plant and Soil Sciences, University of Massachusetts, Amherst 01003 R. N. STEWART 11409 Cedar Lane Beltsville, Maryland 20705