As illustrated in an earlier work (Macromolecules 2006, 39, 1008), isotactic poly(vinylcyclohexane) (PVCH) single crystals display twinned growth sectors. Mapping of the twinned domains is possible via dark-field electron microscopy imaging. Each twinned domain results from a growth twin on the lateral growth face of the single crystal. The width of the twinned domain provides a measure of the so-called lateral spread extent, a fundamental parameter of classical theories of nucleation and growth for which only indirect estimates are available. The extent of lateral spread (and, as a corollary, the secondary nucleation density) (both average values and distribution), are determined for single crystals of PVCH produced in squalane over a wide range of crystallization temperatures (120-240 degrees C). These observations provide the first direct experimental data on these elementary processes in polymer crystal growth.