Question: Maximum number of directories?

[Gerorge Reece-Howe]

Hi,   I wanted to make an application that would create many thousands of databases in MySQL.   I was wondering if there was a limit to the number of directories a single directory could hold? I assume the number of directories would be the limit (if any) to the number of databases MySQL could handle.   Would there be any adverse effects of doing this (with regard to either the system or the database)?   Is this the right place to be asking this kind of question?     Cheers