Gauss-Lucas Theorems for Entire Functions on CM
  A Gauss-Lucas theorem is proved for multivariate entire functions, using a natural notion of separate convexity to obtain sharp results. Previous work in this area is mostly restricted to univariate entire functions (of genus no greater than one unless "realness" assumptions are made.) The present work applies to multivariate entire functions whose one dimensional sections can be written as a monomial times a canonical product of arbitrary genus. Essential use is made of the Levy-Steinitz theorem for conditionally convergent real number series. 
Marek Kanter
math.CV