 Ruled-ness specializes.Precisely, Matsusaka'a theorem says

Let "D" = "k"["ε"] be the ring of dual numbers over a field "k" and "Y" a scheme of finite type over "k".Given a closed subscheme "X" of "Y", by definition, an embedded first-order infinitesimal deformation of "X" is a closed subscheme "X" of "Y" ×Spec("k") Spec("D") such that the projection "X" → Spec "D" is flat and has "X" as the special fiber.