note 8684 added to session_destroy

we have been create session and register three variable name of variable is session_user_mail,session_password,session_order_no when user login.we try to destroy the register variable using the PHP script which one write below.but the session was not destroy please correct that code. <?php session_save_path("../temp//");//server path session_start(); session_unregister('$session_user_mail'); session_unregister('$session_password'); session_unregister('$session_order_no'); if(session_destroy()) echo "session destroy"; ?> http://www.php.net/manual/function.session-destroy.php