Abstract
Some investigations were carried on the calyx abscission in mature fruits of summer orange“Hassaku”. The chief objective of them was to determine histologically the position of abscission layer and to study also the mode of abscission when the calyx was treated with 2, 4-D solutions or the fruits were kept in freezing temperature. The results are summalized as follows:
1. The abscission zone was formed in the tissue between the distal end of the pith of pedicel and the mesocarp of fruit, and it consisted of some seventeen to twenty five layers of rather rectangular but small parenchymatous cells. It was very hard to detect this zone outside of vascular tissues. Absccission layer was located at just middle or base of the abscission zone and consisted of two to eight layers of cell.
2. The calyx abscission was preceeded by the deposition of the starch-like grains in each of the cell which forming these layers. It was observed that the deposition of these grains was almost ceased by the middle of December.
3. Calyx separation in mature fruits during storage was probably caused by a change in the chemical nature of the cell walls in the abscission layer. The fracture of vascular tissues of the same layers, however, occured quite mechanically.
4. The abscission layer did not develop so promptly in the case of the fruits hanging on the tree as the detached zones. The same process proceeded gradually in the case of the fruits which were harvested and kept in the stored house. The division and proliferation of cells was noticed in separated tissues.
5. The abscission process was retarded when the calyx were treated with 2, 4-D solution, but was accelerated when the fruits were kept in low temperature ranging from-1°C to 1°C.
6. Above mentioned results are certificated by the field experimments. The calyx abscission rates ninety days after treatments with 2, 4-D solutions, low temperature or check was 5.71%, 71.42%, 45.71% each, and these differences are higly significant statistically.
