Function will not run from widget text box

I’m trying to run simple functions as simple Text widgets to display archives or categories. But nothing will display on the blog.

For example, I selected an empty Text widget from Available Widgets and pasted in this function:
<?php wp_get_archives(); ?>

But instead of displaying archives, the blog doesn’t show anything. I checked the source code and saw just a repeat of the function script:
<?php wp_get_archives(); ?>

All my other widgets are working fine and functions run just fine in any non-widgetized areas of the blog.

Any idea how I can fix the problem?