使用命名空间能自动加载吗？？

1.php
<?php 
    namespace Foo\bar\subnamespace;
    const Foo = 1;
    function foo() { echo "in 1.php";}
    class foo{
        static function staticmethod(){}
    }

2.php
<?php 

namespace foo\bar;
//include '1.php';
use Foo\bar\subnamespace;

subnamespace\foo();

运行2.php

Fatal error: Call to undefined function Foo\bar\subnamespace\foo() in F:\www\try\2.php on line 7
PHP Fatal error:  Call to undefined function Foo\bar\subnamespace\foo() in F:\www\try\2.php on line 7

命名空间不能自动加载文件吗？？