An optical turning film has a first surface including an array of prisms. 5 to 5 ethylene oxide groupsmole of alcohol; and c) a component selected from the group consisting of amphoteric surfactants, couplers and mixtures thereof; the composition containing alkylphenol ethoxylate or glycol ether solvent. A valve support is mounted about the flow tube adjacent the flow tube outlet such that the valve support and flow tube are relatively rotatable. When the calculated transport interval does not coincide with the planting interval, the transport speed of the variable speed conveyer is increased or decreased or the variable speed conveyer is stopped, such that the transport interval between two adjacent seedlings becomes equal to the planting interval immediately after the preceding seedling is discharged from the variable speed conveyer. A surface layer region including the surface of the center electrode 3 which is exposed to the resistor 15 is a metallic layer 30 formed of a metal based on at least one of Zn, Sn, Pb, Rh, Pd, Pt, Cu, Au, Sb and Ag or a Ni alloy containing at least one of B and P, so that the center electrode 3 is provided in direct contact with the resistor 15 on the surface of the metallic layer 30.