How i can save my own object in session and retrieve it later?

I try something like this.

store.com/zen/index.php
if(!isset($_SESSION['my_info']))
$_SESSION['my_info'] = new my_info;

store.com/zen/info.php?zenid=xxxxxxxxxxxxxx
require("includes/application_top.php");
require(DIR_WS_CLASSES . 'my_info.php');

if(!isset($_SESSION['my_info']))
$_SESSION['my_info'] = new my_info;//my object is lost