The growth of a solid, starting from negligible initial dimensions with either a plane, cylindrical, or spherical boundary, into a surrounding supercooled fluid is discussed. The densities of the solid and fluid are assumed to be unequal. As a consequence a convective motion occurs in the fluid having the characteristics of a source of a source or sink flow because of the fact that a unit mass of fluid occupies, on solidification, a volume differing from the volume originally occupied. The effects of this motion on the rate of growth of the solid phase have been analysed.