Rails - Apr 2006 - Newbie question: How to reference models in subdirectories

Hi, new to RoR I am probably going to embarrass myself now:


I have models organised in subdirectories, i.e.

models
  |--material
        |--product.rb
  |--cross-applications
        |--currency.rb


When I try to reference another model within the same subdirectory, 
everything works fine, i.e.

belongs_to :product_categories, :class_name => 
''Material::ProductCategory"

However, when I reference a model in a different subdirectory, I get an 
uninitialized constant error, i.e.

belongs_to :currencies, :class_name =>
''CrossApplications::Currency''
=> 
/usr/local/lib/ruby/gems/1.8/gems/activesupport-1.3.0/lib/active_support/dependencies.rb:112:in
`const_missing'': uninitialized constant
''CrossApplications''

What am I doing wrong here?
Thanks in advance for patience and a helpful answer!
Juergen

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