Space high-temperature in situ observation instrument “SHITISOI” is dedicated to visualize and record the whole KNbO 3 cellular growth process in Li 2B 4O 7 flux. The dependence of buoyancy and surface tension convections on the cellular growth is studied. In space, the streamlines of the steady surface tension convections in the Li 2B 4O 7 flux has been observed. The steady convections occur in the form of a mirror symmetric pattern. The parabolic streamlines are formed in the one half of the loop and their mirror images in the other half. Due to the surface tension convection, the KNbO 3 grains grow and fill the whole solution homogeneously. On the ground, the buoyancy driven flow in the direction opposite to that of surface tension flow can reduce the cellular growth and the distribution of KNbO 3 solute grains is inhomogeneous in the Li 2B 4O 7 flux. A theoretical model of cellular growth is also accounted. A pivotal feature in this model is the initiation of the surface tension convection on the interface of KNbO 3 grain. This is initiated by KNbO 3 solute surface tension gradient which is caused by less rapid diffusion of KNbO 3 solutes. Direct comparison of the model predictions and experimental observed phenomena demonstrate the predictive capability of this model.