EFFECTS OF GIBBERELLIN AND AMO-1618 369 



Fig. 1. Neutralization of growth-regulating properties on Yellow Lace 

 chrysanthemums: Left to right: untreated plant, plants treated with 50 

 ppm gibberellin spray, 500 ppm Amo-1618 spray, 50 ppm gibberellin 

 spray plus 500 ppm Amo-1618 spray semiweekly during the first 2 weeks 

 of short photoperiods. 



plants or plants treated with both 50-ppm solution of gibberellin and 

 500-ppm solution of Amo-1618. 



Delay in flowering caused by inhibition of the growth of chrysanthe- 

 mums by Amo-1618 can be counteracted without applying gibberellin 

 simultaneously. Plants were sprayed four times semiweekly during the 

 first 2 weeks of short photoperiods with 500-ppm solution of Amo- 

 1618. When the outer florets were showing color (5 weeks later) the 

 inflorescences were sprayed for 5 consecutive days with 1000-ppm 

 solution of gibberellin. The plants treated in this way flowered at the 

 same time as untreated plants, but they were no taller than plants 

 treated with Amo-1618 alone. 



DISCUSSION 



Simultaneous applications of gibberellin and Amo-1618 in the first 

 2 weeks of short photoperiods neutralized their growth-regulating 

 properties. Growth and flowering similar to those of untreated plants 

 were obtained when four applications of 50-ppm solution of gibberellin 

 and 500-ppm solution of Amo-161 8 were given in the first 2 weeks of 

 short photoperiods. Separately, gibberellin promoted and Amo-1618 



