Dynamic crystallization experiments on an olivine tholeiite from the Taos volcanic field, New Mexico have shown that the presence or absence of heterogeneous nuclei are an important factor in the development of texture. Heterogeneous nuclei of various kinds and numbers per unit volume (density) were produced by partially melting a crystalline basalt starting material. Several matrices of experiments were constructed with cooling rate, melt time, and melt temperature as the principal variables. Variations in melt time and temperature above and below the stability temperatures of olivine (1198 °C) and plagioclase (1187 °C) produced different numbers of unmelted remnants of either olivine and plagioclase or just olivine. Results indicate that differences in texture comparable to those produced by varying cooling rate can be produced by varying the kind and density of nuclei. The full range of textures produced by the range of cooling rates studied (0·5 °C to 50 °C/hr) can be produced at a single cooling rate just by varying the nucleating heterogeneities. These heterogeneities behave like unmelted remnants but smaller than can be seen in the optical microscope, probably less than 0·1 micrometers. Olivine appears to be able to nucleate on substrates other than olivine while plagioclase appears to nucleate only on itself or a similarly complex tectosilicate. The theory of heterogeneous nucleation suggests that nucleation sites are stabilized above their melting temperatures because they are trapped in cavities of refractory impurities. The high surface tension maintained in these cavities retards melting for some period of time and to some degree of superheat. It appears most likely, based on this study, that when plagioclase appears in a crystallized basaltic magma it was preceded by heterogeneous nucleation. Since plagioclase is a primary factor in defining texture, the texture itself then is a function primarily of heterogeneous nucleation.