Potted peach trees (Prunus persica (L.) Batsch cv. Loring) were mechanically defoliated and the influence of temperature on formation of the primary protective layer and phellogen generation in the leaf abscission region was examined histologically. Plants maintained at 7.5, 12.5, and 17.5 °C showed first indications of primary protective layer formation at 18, 9, and 6 days, respectively. Subsequent generation of phellogen and the appearance of the first phellem cell were observed at 30, 18, and 12 days, respectively. The primary protective layer formed approximately 700 μm proximal to the separation zone and was composed of cells with lignified walls and thin suberin linings.