EFFECTS OF GIBBERELLIN AND AMO-1618 367 



ment. The same concentration of gibberellin in the first week of short 

 photoperiod or in the seventh week of short photoperiods had httle 

 effect on stem elongation. Untreated plants averaged 9.2 lateral in- 

 florescences. Treatment of similar plants with 100 ppm solution of 

 gibberellin five times in the fourth week of the short photoperiods re- 

 duced the number of inflorescences to 4.2; the remaining flower 

 primordia did not develop. Plants treated in the seventh week of short 

 photoperiods developed 8.6 lateral inflorescences. 



When a concentrated solution of gibberellin (1000 ppm) was ap- 

 plied for 5 consecutive days when the outer florets of the inflorescences 

 were showing color (during the seventh week of short photoperiods), 

 the florets developed faster than did those of untreated plants; anthesis 

 occurred 10 to 14 days earlier than on untreated plants. 



Sensitivity to Amo-1618 



YeUow Lace chrysanthemum, which requires 9 weeks of short 

 photoperiods to induce flowering, was tested for reaction to Amo-1618. 

 Short photoperiods were started on June 7, 1957. Certain plants were 

 sprayed with aqueous solutions containing 500 ppm of Amo-1618 on 3 

 alternate days after beginning of the short photoperiods as follows: 



Maximum inhibition of elongation occurred in the first week of 

 short photoperiods. As shown, growth of stems of Yellow Lace was 

 exhibited less the later the Amo-1618 treatment was given after the 

 start of short photoperiods. Whenever inhibition of growth due to 

 Amo-1618 occurred, the plants flowered 14 to 18 days later than un- 

 treated plants. Application of Amo-1618 in the sixth week after the 

 start of short photoperiods did not significantly affect the elongation of 



