3. Results and discussion
Fig. 1 shows the impregnation of red ink into a potato without a vacuum. No impregnations occurred in the potato during immersion. Thus, immersion treatment alone could not cause impregnation into the potato. Fig. 2 shows the impregnation during restoration. Potatoes, just after the vacuum treatment, had no impregnations into the potato, but those after 3 h of restoration had impregnation. Therefore, Fig. 1 and Fig. 2 indicate that the impregnation into a potato tuber requires both vacuum and restoration treatments. Fig. 3 shows photographs of the impregnation potato of 1 h vacuum plus 3 h restoration treatment, and the 4 h immersion potato. This Figure indicates that the impregnation occurred almost at the central pith and the areas between the vascular ring and the periderm.