Datepicker Prototype not working

I have installed http://code.google.com/p/calendardateselect/ Datepicker using gem install calendar_date_select

Installation was success. but beeing a newbey, i dont know how to use it. i gave in my view file, &开发者_StackOverflow中文版lt;%= calendar_date_select_tag "e_date" %>

But it throws the error undefined method `calendar_date_select_tag' for #<#:0x2cc8998>

Any help is appreciated

---

In environment.rb, add

Rails::Initializer.run do |config|
  ...

  config.gem "calendar_date_select"

  ...
end