Ruby File::directory? Issues

I am quite new to ruby but enjoying it so far quite immensely. There are some things that have given me some trouble and the following is no exception.

What I am trying to do here is create a sort of 'super-directory' by sub-classing 'Dir'. I've added a method called 'subdirs' that is designed to list the directory object's files and push them into an array if the file is a directory itself. The issue is, the results from my test (File.directory?) is strange - here is my method code:

  def subdirs
    subdirs = Array.new
    self.each do |x|
      puts "Evaluating file: #{x}"
      if File.directory?(x)
        puts "This file (#{x}) was considered a directory by File.directory?"
        subdirs.push(x)
        #yield(x) if block_given?
      end
    end
    return subdirs
  end

And strangely, even though there are plenty of directories in the directory I've chosen ("/tmp") - the result of this call only lists "." and ".."

puts "Testing new Directory custom class: FileOps/DirClass"

nd   = Directory.new("/tmp")
subs = nd.subdirs

And the results:

Evaluating file: mapping-root
Evaluating file: orbit-jvxml
Evaluating file: custom-directory
Evaluating file: keyring-9x4JhZ
Evaluating file: orbit-root
Evaluating file: .
This file (.) was considered a directory by File.directory?
Evaluating file: .gdmFDB11U
Evaluating file: .X0-lock
Evaluating file: hsperfdata_mishii
Evaluating file: .X11-unix
Evaluating file: .gdm_socket
Evaluating file: ..
This file (..) was considered a directory by File.directory?
Evaluating file: .font-unix
Evaluating file: .ICE-unix
Evaluating file: ssh-eqOnXK2441
Evaluating file: vesystems-package
Evaluating file: mapping-jvxml
Evaluating file: hsperfdata_tomcat