cake php AppController and inheritance

hello folks........

In many tutorial of Acl component in cakephp
i got instruction that add component either in AppController or in all the other controllers which inherits AppController.......

but problem is

var $components=array('Auth',Acl);

when i use the above line in AppConroller i cant use the Auth or Acl component...
but when i use the same code in all the child classes it works fine........

what will be the problem

here is my appController

class AppController extends Controller {

     var $helpers = array('Html', 'Form', 'Session','CssMenu');
     var $components = array('Auth');

     function beforeFilter() {
        //Configure AuthComponent
        $this->Auth->authorize = 'actions';
        $this->Auth->authError = "Sorry, you are lacking access.";
        $this->Auth->userModel = 'Login';


code for usersController

class userssController extends AppController{
    var $name="Logins";
    //var $components = array('Auth');
    var $layout='login';

    function beforeFilter() {
        $this->Auth->loginRedirect = array('controller' => 'homes', 'action' => 'index');

when i comment the line 4 this will b error
on uncomment it works fine
thanks in advance

any help will be appreciated.