php新类对象没有被实例化

I am trying to create a new model object from my mvc controller but the page doesn't generate. Is there any reason why I can't do this? Surely I should be able to create an object inside an existing one?

Sorry to be so simplistic, and I know I sound like an idiot, but I'm not sure how to explain what I am doing wrong.

class controller_landing extends controller_base
{
    public function __construct($get,$post)
    {
        parent::__construct($get,$post);

        $this->model = new model_landing;  <-----problem line here
    }
}

abstract class controller_base
{   
    //store headers
    protected $get;
    protected $post;

    //store layers
    protected $view;
    protected $model;

    protected function __construct($get,$post)
    {    
        //store the header arrays
        $this->get = $get;
        $this->post = $post;

        //preset the view layer as an array
        $this->view = array();
    }

    public function __destruct()
    {
        //extract variables from the view layer
        extract($this->view);

        //render the view to the user
        require_once('view/'.$this->get['controller'].'_view.php');
    }
}

class model_landing extends class_mysqli
{
    public function __construct
    {
        echo "landing model";   
    }
}

class class_mysqli
{
    public function __construct
    {
        echo "mysqli";
    }
}

I don´t know, but I think you are missing brackets. There

public function __construct
{
        echo "landing model";  
}

should be

public function __construct()
{
        echo "landing model";   
}