A careful study has been made on different morphologies of lysozyme crystals at isoelectric point under isothermal and constrained growth conditions. It is found that the morphologies are closely related to solution flow. Judging by the experimental results, the cessation of biological crystal growth is due to the solute-depletion zone stably existing around the growing crystals. Reducing or removing the solute-depletion zone may ensure the continuous crystal growth. This approach throws some light on the possibility of growing largedimensional biological crystals.