sharing $_SESSION with non codeigniter php

My application sets session variables in codeigniter and then redirects to legacy code that is not codeigniter and reads those session variables.

That worked under 2.2

It seems that session variables set up under 3.x can't be read outside of codeigniter.

Is there a way to access the 3.x session in ordinary php? Or some way for 3.x to create ordinary session variables?