A planter (10) comprises a number of suction cups (30) adapted to be driven around a common horizontal rotation axis in the same sense as any ground wheels present and with zero ground speed at the point of seed-piece ejection from the planter. The variable-length arms (38) carrying the cups at their outer ends result in each cup (30) being displaceable towards and away from the rotation axis to provide a corresponding variation in the peripheral velocity of the cup in dependence on its angular position about the rotation axis.
