  We introduce a novel model for DNA condensation (whip-toroid transition)
using the path integral method in the framework of the non-linear sigma model
on a line segment. We show that some of its classical configurations exhibit
toroidal forms, and the system has phase transitions from a whip to toroidal
phases with a parameter $c=W/(2l) (L/(2\pi))^2$. We also discuss stability and
finite size effect on these states.
