Fig. 1. Polarized light optical micrographs of coumarin polymorphs. (a) Spherulites of II showing a Maltese cross embedded into banded spherulites of IV formed at ∼22 °C. (b) Spherulite of II formed at ∼40 °C. (c) Banded spherulite of IV showing two twist periods. Left lower corner – form II. Growth at ∼22 °C. (d) Banded spherulite of IV formed at ∼22 °C and surrounded by II. (e) Crystals of V surrounded by IV, the latter was formed in the course of cross-nucleation. Growth at ∼22 °C. (f) Banded spherulite of V surrounded by II. Growth at ∼40 °C. (g) Large crystals of III formed from IV at 54–57 °C and surrounded by banded spherulites of IV that later crystallized at room temperature. (h) Banded spherulites of IV fully replaced by needle-like crystals of III at 56 °C. Note that the banding is still visible. In figures (b), (d), (f), (g) the scale bar is the same as in (a). All samples were obtained from coumarin mixtures with Canada balsam (21 wt% for (c), (g), and (h); 20–40 wt% for the rest).