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Summary

Cotton bolls of known ages from 2 to 50 days after anthesis were extracted with acetone. The chromatographed extracts were examined for abscission activity on the cotton explant test and gibberellin activity on the dwarf maize test. The abscission-accelerating substances (ABA and gibberellins) were very high in young fruit, showing a peak at about 6 days, then declined to nil at 20 days. An unidentified abscission accelerator showed a marked peak at 15 days. Abscisic acid, GA3, another gibberellin which acts biologically like GA5 and GA9, and an abscission-retarding substance were all extracted from 5-day-old bolls.