George and ML :

See if this study interestes you. Don't know if it will copy here so I added [url] to front of address and [url] to the end-- use the address minus the 2 url additions copy to search and it should work.

[url]http://afs.allenpress.com/perlserv/?request=get-abstract&doi=10.1577%2F1548-8675%281999%29019%3C1044%3AFCRTHS%3E2.0.CO%3B2[url]