Red, Blue, Green, Yellow, Silver, Gold and Crystal. Any Pokemon from these games cannot be traded to later games AT ALL. They are trapped within these games, however they can trade within each other.
This is because of the massive changes, and the incompatibility from the Game Boy Colour to the Game Boy Advanced. Plus, there are a heap of items that do not exist in Gen III (Ruby, Sapphire, FireRed, LeafGreen, Emerald) notably, the 'Berry'. :3
So that means that any Pokemon Game that is Gen III onwards can be traded within each other, because now they are using the technology to wirelessly (trading Pokemon between Gen III was used with a Cable Link, just so you know) trade Pokemon.
Hope I helped. :)