Anatomical and Chemical Aspects of Abscission of Fruits of the Apple

1. A constriction zone, evident in the flower pedicels, persisted during the life of the apple fruits studied but did not function directly as an absciss layer or predetermine the course of abscission in pedicels of flowers or fruits. 2. The abscission of flowers and of immature fruits was preceded by differentiation of an absciss layer. Cell separation followed dissolution of the middle lamella. 3. Abscission of mature pedicels was initiated independently in the pith and cortex and not preceded by cell division. 4. The thick walls of the stone cells of the pith of mature pedicels were made up largely of cellulose lamellae. Separation of these cells was preceded by swelling and extension of the walls. During this process these cell walls lost their anisotropic quality, indicating a change in the nature of the cellulose. 5. In the course of cell separation in the pith, dissolution of the pectic compounds of the middle lamella and disintegration of the primary and much of the secondary cell walls occurred, leaving the lignified lamella and remnants of the secondary wall. In the separation of cells in tissues other than the pith, less disintegration of the secondary wall accompanied dissolution of the middle lamella and primary wall. Vessels and fibers in the path of separation were ruptured.