Changes in Abscission‐accelerating Substances With Development of Cotton Fruit

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.