php destructor behaviour

im trying to understand php constructor and destructor behaviour. Everything goes as expected with the constructor but i am having trouble getting the destructor to fire implicitly. Ive done all the reading on php.net and related sites, but i cant find an answer to this question.

If i have a simple class, something like:

class test{

     public function __construct(){
          print "contructing<br>";
     }

     public function __destruct(){
          print "destroying<br>";
     }
}

and i call it with something like:

$t = new test;

it prints the constructor message. However, i'd expect that when the scripts ends and the page is rendered that the destructor should fire. Of course it doesnt.

If i call unset($t); when the scripts ends, of course the destructor fires, but is there a way to get it to fire implicitly?