A seed transfer unit for an agricultural planter, comprising: a first transfer body comprising a first plate with a first cylindrical sidewall extending perpendicularly from the plate; a second transfer body comprising a second plate with a second cylindrical sidewall extending perpendicularly from the plate; wherein the first and second plates (850, 950) are mounted to permit relative rotation therebetween about a device axis coincident with the major axes through the first and second cylindrical side walls (860, 960), with the first and second plates (850, 950) parallel, and with the second cylindrical side wall disposed within, and concentric with, the first cylindrical side wall, such that the first and second plates (850, 950) and first and second cylindrical side walls (860, 960) define an annular space therebetween; and wherein each of the first and second plates (850, 950) has at least one ridge portion (810, 811, 812, 910, 911, 912, 913, 914, 915) extending into the annular space, which ridge portions (810, 811, 812, 910, 911, 912, 913, 914, 915) cooperate to carry a seed through the annular space as the first and second plates (850, 950) rotate relative to one another; characterised in that the first plate has an inlet aperture through which a seed may pass to the annular space, and the second plate has at least one outlet aperture (901a, 901b) through which a seed is ejected from the annular space; and in that all ridge portions are arcuate ridge portions (810, 811, 812, 910, 911, 912, 913, 914, 915) concentric with the respective cylindrical side wall (860, 960) which ridge portions (810, 811, 812, 910, 911, 912, 913, 914, 915) cooperate to carry a seed through the annular space from the inlet aperture to the, or one of the, outlet apertures (901a, 901b). a first transfer body comprising a first plate with a first cylindrical sidewall extending perpendicularly from the plate; a second transfer body comprising a second plate with a second cylindrical sidewall extending perpendicularly from the plate; wherein the first and second plates (850, 950) are mounted to permit relative rotation therebetween about a device axis coincident with the major axes through the first and second cylindrical side walls (860, 960), with the first and second plates (850, 950) parallel, and with the second cylindrical side wall disposed within, and concentric with, the first cylindrical side wall, such that the first and second plates (850, 950) and first and second cylindrical side walls (860, 960) define an annular space therebetween; and wherein each of the first and second plates (850, 950) has at least one ridge portion (810, 811, 812, 910, 911, 912, 913, 914, 915) extending into the annular space, which ridge portions (810, 811, 812, 910, 911, 912, 913, 914, 915) cooperate to carry a seed through the annular space as the first and second plates (850, 950) rotate relative to one another; characterised in that the first plate has an inlet aperture through which a seed may pass to the annular space, and the second plate has at least one outlet aperture (901a, 901b) through which a seed is ejected from the annular space; and in that all ridge portions are arcuate ridge portions (810, 811, 812, 910, 911, 912, 913, 914, 915) concentric with the respective cylindrical side wall (860, 960) which ridge portions (810, 811, 812, 910, 911, 912, 913, 914, 915) cooperate to carry a seed through the annular space from the inlet aperture to the, or one of the, outlet apertures (901a, 901b).