In-situ observations of ice crystals grown in supercooled bulk water were carried out using an interferometric optical system, Three-dimensional patterns of ice crystals were analyzed using the interference fringes, It was found that the growth of circular disk crystals can be categorized into two types, depending on whether screw dislocations are included in the disk crystal. It was also found that morphological instability on the circular disk of the ice crystals starts to develop at the moment that its thickness reaches a critical value and that the instability is independent of the radius of the disk crystal. The study also showed that the growth of an ice dendrite is not consistent with the universal law for dendritic growth.