Flowering of the SD plant Perilla crispa
was also possible in LD and in continuous light, if lighting was weak enough. The light range within which flowering is possible, decreased with increasing day length. With an illumination of 300μwatts/cm 2
spherical cross-section, seedlings were day-neutral. Older plants proved more predisposed to flower than seedlings. In plants with two equivalent but differently illuminated shoots the brightly lit shoot initiated flowers in long days through influence of the weakly lit shoot; this influence was stronger after defoliation of the brightly lit shoot. Neither in bright nor weak light (with SD or LD) did defoliation qualitatively influence flower initiation. Even 0.5 cm leaf surface was sufficient for flower initiation.
With the day-neutral tomato (Lycopersicum esculentum
var. Ailsa Craig) defoliation advanced flower initiation and increased the number of flowers. Brighter light decreased the number of leaves before the initiation of the first flower cluster; in very weak light the plants could be kept vegetative for a year.
With the day-neutral Phaseolus vulgaris
var. Vroege Wagenaar defoliation of the main shoot promoted development of axillary shoots, through whose later defoliation the number of flowers could be increased. There was a positive correlation between flower number and light intensity. Flower initiation itself was however independent of intensity, day length, removal of cotyledons or defoliation but the number of flowers decreased through removal of the cotyledons.
In SD plants too much growth regulator probably inhibited flowering; in other plants this was caused by the growing leaf. Flowering probably needed an equilibrium between available assimilates and growth regulators.