368 GROWTH FACTORS AND FLOWERING 



Stem or the time of flowering of the plants, but it did inhibit the elonga- 

 tion of the ray florets. 



Sensitivity to Simultaneous Applications of Gibberellin and Anio-1618 



Rooted cuttings of Yellow Lace chrysanthemums were planted on 

 May 10, 1957, in 3-inch clay pots and placed on long photoperiods to 

 test the reaction to simultaneous applications of gibberellin and Amo- 

 1618. Short photoperiods were started June 7, 1957. Plants were 

 sprayed four times semi-weekly during the first 2 weeks of short photo- 

 periods first with 500-ppm solution of Amo-1618, which was allowed 

 to dry, and then with 12.5-, 25-, 50-, and 100-ppm solution of gib- 

 berellin at each spraying; such treatments will be referred to as simul- 

 taneous applications of gibberellin and Amo-1618. 



Although gibberellin applied at the beginning of photoperiodic in- 

 duction was ineffective, it neutralized the inhibitory effect of Amo- 

 1618 when the two were applied simultaneously during the first 2 

 weeks of induction as follows: 



Amo-1618 induces maximum suppression of growth at that time. The 

 combination of the two compounds (50-ppm solution of gibberellin 

 and 500-ppm of Amo-1618) during the first 2 weeks of short photo- 

 periods neutralized their growth-regulating properties; growth was 

 similar to that of untreated plants. With mutual antagonism there was 

 no delay in flowering of the plants (Fig. 1 ). Plants treated with 500- 

 ppm solution of Amo-1618 flowered 14 days later than untreated 



