Circumnutation of Phaseolus vulgaris L. cv. Blanc de Juillet twining shoots was examined at the cellular level. Cell growth was monitored inside the free‐moving part of the shoot as a function of time and position with respect to the terminal bud. Complete elongation of epidermal cells required >7 days. A 60% increase in length of the cells in the bending zone was observed. Scanning and transmission electron microscopy studies showed the elasticity of cell walls, the extent of plasmodesmata and endoplasmic reticulum of epidermal cells. The osmotic potential in epidermal cells of the bending zone displayed significant differences only between the concave and convex sides. The pattern of cell growth in twining shoots is discussed. Circumnutation could be seen as a consequence of periodic turgor changes inducing periodic growth.

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Somatic embryos were obtained from leaf discs of juvenile red oak plants. Basal inductive nutrient medium was a modified Murashige and Skoog solution enriched with 500 mg L-' casein hydrolysate, 100 mg L-' polyvinylpyrrolidone, 5.4 @4 naphthaleneacetic acid and 0.09 w benzyladenine. Embryogenesis was obtained only from leaf discs in the presence of light and increased when the adaxial surface of the explants (with midrib or main veins present) was in contact with the medium. Large variation was observed in all experiments. Recurrent embryogenesis was observed at the base of embryo clusters with callus present; conversely, embryogenic potential was rapidly lost by subculturing full calli. Maturation, germination and development of isolated somatic embryos were obtained. However, the vast majority of embryos did not have viable apical bud meristems and on only a few occasions were shoots produced.

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