The amount of melt formed in individual stream lines of upper mantle rocks passing through a partial melting regime increases from zero at the edge to a maximum at the central axis. Relationships between aggregated liquid compositions from such melting regimes and the source mantle should be obained by integration of the appropriate equations for liquid composition taking into account the horizontal and vertical form of the melting regime. Misinterpretation of integrated liquid products from such regimes would be easy if too simple a model of the melting process is used.