Foliar Abscission in Cotton. II. Influence of Age and Defoliants on Chemical Composition of Blades and Pulvinoids

1. Changes in some of the inorganic and organic components of cotton leaves were followed in four age groups before and during the initiation of abscission and within the first 10 hours following the application of defoliants, 3-amino-1,2,4-triazole (ATA) and disodium 3,6-endoxyhexahydrophthalate (Endothal). 2. Potassium, calcium, and magnesium accumulated gradually with increasing leaf age, but phosphorus declined after the leaves reached the maturity stage of group III, and nitrogen in the blades dropped rapidly with senescence. Significant changes in the inorganic components of the blades did not occur during the first 10 hours following defoliant application. 3. Carbohydrate and nitrogen fractions were influenced both by age and defoliant treatment. Accumulation of soluble nitrogen in the pulvinoid region and other compositional changes occur with aging and the initiation of foliar abscission. During the initial stages of abscission changes in the nitrogen fractions were more striking than carbohydrate changes.