the property of crystallizing in three forms fundamentally distinct, as is the case with titanium dioxide, which crystallizes in the forms of rutile, octahedrite, and brookite. see pleomorphism.-the coexistence among individuals of the same species of three distinct forms, not connected, as a rule, by intermediate gradations; the condition among individuals of the same species of having three different shapes or proportions of corresponding parts; -- contrasted with polymorphism, and dimorphism.