In the theory of crystal growth two major mechanisms were proposed: lateral growth and continuous growth. For the former, the solid-liquid (S/L) interface is atomically smooth except for the presence of atomic steps and atoms transferring from liquid to solid are first attached to the steps. The surface of the final crystal often consists of particular edges and faces (faceted morphology). For the latter, the S/L interface is assumed to be rough in atomic scale so that the atoms can attach themselves uniformly along the interface. This paper used Si clusters to induce nucleation of an undercooled Ge{sub 74}Ni{sub 26} melt and examined the morphology change in the primary Ge phase with increasing undercooling. Also the result was compared with those of pure Ge, dilute Ge-Sn and Ge-Si alloy systems to check the influence of solutes on growth mode transition.