is there a way to get access to a cookie stored a root site in a session set at subdomain level

[Erwin]

being at root level  http://mydomain.com, I stored a cookie  cookie[:login]

I can see the cookie in my browser   

 site: mydomain.cm  

      login

      _myapp_session

upon  redirection, to   url => http://test.mydomain.com ,

 I would like to access this cookie,   cookie[;login], but as I maintain sessions at subdomain level, I have

site: test_domain.com

    _myapp_session

     

how can I access the cookie[:login] ?  

thanks for any clue ...

[Erwin]

I tried to use the :domain 

cookies[:login] = { :value => 1, :domain =>"test.mydomain.com", :expires =>  1.hour.from_now }

but no way cookies is not set for test

should I rather use ?

cookies[:login] = { :value => 1, :domain =>".mydomain.com", :expires =>  1.hour.from_now }