A first; order phase transition from an undercooled isotropic phase to an ordered phase usually yields complex morphologies, resulting from the competition between growth, diffusion and surface tension. We discuss the importance of similar mechanisms in the formation of soft. lamellar phases appearing in an isotropic phase. Through the experimental study of the sponge-to-lamellar phase transition, we interpret the formation of batonnets and identify the relevant elementary mechanisms. Finally we discuss the role played by crystalline properties in the formation of smectic filaments.