A plant container and sidewall comprising a nonporous root-tip-trapping region and a porous air-root-pruning region combined to form the sidewall. In the timing control section, the transmission unit has driving parts which embed the clock signals between the data signals at the same level and generate and output single level transmission data. The hydrothermal electrolytic apparatus has two or more tubular reaction cells each having a metal inner wall serving as a cathode, and an anode is provided in each of the reaction cells.