Some Effects of Leaves and Indoleacetic Acid upon Floral Abscission in Nicotiana tabacum

Leaves were removed from different positions on the stem of Lizard's Tail and Little Turkish varieties of Nicotiona tabacum, and effects upon floral abscission were observed. In other experiments the flower was removed to determine its effect upon the abscission of the remaining pedicel. IAA in lanolin was added to the nodes where leaves had been excised and to the pedicel stubs to determine additional or altering effects. 2. The removal of upper leaves resulted in fewer days to abscission of unfertilized ovaries. The removal of lower leaves caused little variation in time of abscission. 3. The area of the leaves removed had little effect upon abscission; the nodal position of the leaves removed was more important. 4. The shorter abscission time following removal of upper leaves was altered by application of IAA in lanolin to the exposed nodes. This effect was proportional to the concentration applied. High concentrations (1000 and 10,000 p.p.m.) of IAA added at the nodes can retard abscission for a longer time than the upper leaves do normally. 5. Removal of the ovaries resulted in much more rapid abscission. This was altered by applications of IAA in lanolin. Again, the retarding effect of the applied IAA was proportional to the concentration applied. A given concentration was more effective in causing an inhibition of abscission when applied to the pedicel stubs than when applied at nodes. This may be explained on the basis of the basipetal transport of auxin or by its different effect upon the distribution of carbohydrates and nitrogenous compounds within the plant. 6. Applications of all except the lowest concentration of IAA retarded abscission whether applied to the exposed nodes or to the pedicel stubs. This indicates that auxin effects abscission by the total concentration present irrespective of the point of its origin. 7. Removal of leaves resulted in a decreased number of flowers reaching anthesis. Application of IAA to the exposed nodes did not overcome the effect, which indicates that there is another factor(s) present in leaves which controls the maturation of flowers.