Why is this code throwing the following errors? Thanks.

Code:
<?
class DirTree {

    /**
     * Get a tree of folders and files from a spec dir
     * @returns An ArrayCollection of Tree
     */
	function DirTree($dir_tree) {
		$_tree = $this->parse_dir($dir_tree);
		return $_tree;
	}

    /**
     * Get a tree of folders and files from a spec dir
     * @returns An Array of Tree
     */
	function parse_dir($folder) {

		$dir                = @opendir($folder);
		$filecount          = 0;
		$foldercount		= 0;
		$tree				= array();
		$limb				= array();
		$cnt				= 0;

		while(false != ($item = @readdir($dir))) {

			if($item == "." || $item == "..") continue;

			if(is_dir("$folder/$item")){

				$tmpTree = new DirTree();

				$limb['sub_folder'][]['folder_name'] = $item;
				$limb['sub_folder'][] = $tmpTree->parse_dir("$folder/$item");

				$foldercount++;
				$limb['folders'][] = $foldercount;

				$filecount++;
				$limb['files'][] = $filecount;
				//continue;

			}else{

				$limb['file_name'][] = $item;

			}
		}

		$tree[] = $limb;
		$cnt++;
		return $tree;

	}
}

$class = new DirTree();

/* view array  */
echo "<pre>";
print_r($class->DirTree("../../core/amf/app"));
echo "</pre>*****************************************************************";
?>
Warning: Missing argument 1 for DirTree::DirTree() in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 8

Notice: Undefined variable: dir_tree in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 9

Warning: Missing argument 1 for DirTree::DirTree() in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 8

Notice: Undefined variable: dir_tree in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 9

Warning: Missing argument 1 for DirTree::DirTree() in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 8

Notice: Undefined variable: dir_tree in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 9

Warning: Missing argument 1 for DirTree::DirTree() in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 8

Notice: Undefined variable: dir_tree in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 9

Warning: Missing argument 1 for DirTree::DirTree() in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 8

Notice: Undefined variable: dir_tree in C:\apache2triad\htdocs\flashservices_v1.9\services\folder_tree\dir_tree2.php on line 9