North American Fruit Explorers mailing list at ibiblio

["Rodney" <reveland@collinscom.net>]

Googling:   Stringfellow root pruning     finds a book in the NAFEX library 
by a fellow named Stringfellow.
http://www.nafex.org/librylstfl97.html

Do a CTRL F function and search on String and he'll be the only hit you get. 
The name of his book is:
THE NEW HORTICULTURE so now we google on

Stringfellow the new horticulture  and we find a particular website that has 
his book entirely readable on the web.

http://chla.library.cornell.edu/cgi/t/text/text-idx?c=chla;idno=2824290

I have no idea if this is the fellow you are looking for but he sure talks a 
lot about root pruning. It appears his
name is Henry Martyn Stringfellow.

Anyhow, good luck in your search.