This study was carried out to elucidate the mechanism of natural removal of astringency in pollination constant non-astringent (PCNA) type fruits of Japanese persimmon, especially focusing on development of the tannin cells. 1. Development of the tannin cells in plastic-embedded flesh sections was observed using an image analysis system. The tannin cells in PCNA type fruits stopped their enlargement at the end of June, whereas those in pollination variant nonastringent (PVNA) and astringent

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... ), and pollination constant astringent (PCA) type fruits continued to increase in size until the end of July. Thus, final size of tannin cells was much smaller in the former fruits than the latter. Number of tannin cells per unit area was little variable in all 4 type fruits at any stage, so that in PCNA cultivars the area occupied by tannin cells reduced with time after tannin cells stopped their development. Such a decreasing process was coincident with the decreasing process of soluble tannins in PCNA type fruits. 2. In PCNA and PVNA cultivars, the tannin cells of fresh pericarp sections stained with ferric chloride were observed in order to clarify whether or not tannins coagulated in early August. At this time soluble tannins in non-astringent type fruits were negligibly low in contents. The observation revealed that tannins in PCNA type fruits hardly coagulated by this time, although those in PVNA type fruits completely changed into insoluble complexes. 3. These results suggested that the decrease of astringency of PCNA type fruits on trees might be mainly attributable to the reduction in relative area occupied by tannin cells, but not their coagulation. Such a reduction in area occupied by tannin cells started when development of tannin cells stopped, as mentioned above.