In this paper, the studies on the growth forms and the growth mechanisms of ice single crystals grown from the vapor are described. A few problems on the temperature and supersaturation dependences on the growth forms of ice single crystals are presented. The growth forms of ice crystals below a few hundred micrometers in size remarkably vary with the water vapor diffusivity and those of ice crystals above several hundred micrometers in size slightly vary with the water vapor diffusivity. Moreover, the growth forms of ice crystals below a few hundred micrometers in size slightly vary with the thermal conductivity of the gas. Therefore, the growth forms of ice crystals depend not only on the temperature and the supersaturation, but also on the diffusion of water vapor and latent heat released by crystalization and the crystal size. In this paper, the roles of the diffusion of water vapor and latent heat on the growth forms of ice single crystals are described in detail. The outline of recent studies on the growth mechanism of ice single crystals grown from the vapor is described, too.
