Effect of gibberellin on the flowering of Christmas cactus. I

The present expriments were performed to study the flowering of Christmas cactus, a-short-day plant, following gibberellin application. 1. Gibberellin applied as an aqueous solution at the beginning of short-days caused delaying of the flowering. This delaying effect of gibberellin decreased when applied 7 or 10 days after the start of short-days. This result was also ascertained by the evidence that the flower buds stopped to increase in number due to the treatment of gibberellin. 2. When gibberellin had been applied before the start of short-days, the delaying effect on flowering decreased as the number of days prior to short-days was increased. The effect of gibberellin was demonstrated to remain in a plants at least for 20 days. 3. Gibberellin applied 20 or more days or even 14 days after the start of short-days caused the acceleration of the flowering. 4. With gibberellin treatment the plants generally produce peculiar flowers, the ovaries and the corolla tubes of which became longer and more slender. When gibberellin was applied 10 days after the start of short-days, it was observed that many unusual buds appeared, sometimes the ovaries of these buds were buried in leaf-like stems. 5. 5, 25 and 100 ppm of gibberellin had almost the same effect in delaying or acceler-ating the flowering. 6. With gibberellin treatment the number of flowers decreased, but increased when the plants were treated 30 days after the start of short--days. On the other hand, the plants. to which NAA was applied at an earlier time of short-days had more flowers than the non-treated control. 7. NAA applied 20 or less days after the start of short-days delayed the flowering by a few days independently of the time of application.