Abstract: An in-line seed treating unit is provided for an air seeding implement to coat seeds carried by a flow of air through a product distribution line before being planted into the ground. The in-line seed treating unit includes a cylindrical housing having input and outlet ends located at opposing axial ends of the cylindrical housing to provide a generally linear overall flow path for the seed entrained air flow through the product distribution line. A baffle formed as a spiral flighting with an open center portion is disposed within the cylindrical housing to induce the air flow and entrained seeds in a spiral flow path along the housing axis and, thereby pushing the entrained seeds outwardly toward the inner wall of the housing. The seed treatment material is injected through an injection port located a distance less than one flighting pitch of the baffle from the beginning of the flighting so that the seed treatment material is dispersed within the air flow to coat the entrained seeds.