The properties and characteristics of arrays of low-angle boundaries which appear upon freezing of single crystals of tin and lead from the melt are shown to be dependent upon the amount and kind of impurities in the freezing liquid. The boundary-direction angle as a function of lattice orientation and impurity content in crystals frozen at speeds greater than 18–20 mm./minute is employed as an observational quantity. Measurements of boundary-direction are given for various impurity concentrations and types. Mechanisms for the determining of the boundary directions are proposed.