class construct from parent

<?php

class blah_blah extends blah {
    function say_foo() {
        echo $this->foo;
    }
}

class blah {
    var $foo = '';

    function blah( $foo ) {
        $this->foo = $foo;
    }
}

$hey = new blah_blah( "omg" );
$hey->say_foo(); // omg