The growth of two structurally similar polar crystals, γ-glycine and DL-alanine, in their aqueous supersaturated solutions in the presence of typical inorganic salts was studied using in situ microscopic observations. Surprisingly, it was found that their growth behaviors largely differ. The most unexpected finding was that the face growth at each of γ-glycine polar c ends is inhibited, while the face growth at each of DL-alanine c ends is accelerated by all the common inorganic salts studied, despite the fact that the structures of the associated faces are strikingly akin. These unusual observations were explained at the molecular level. In particular, the role of the hydrophobic methyl groups exposed at the crystal faces was highlighted, demonstrating an interesting case in which a small variation in crystal face hydrophilicity can lead to a marked difference in face growth behaviors.