Lon, so you deep planted pears that didn't root above the graft union but stayed reasonably healthy. Wouldn't this mean that quince is a viable dwarfing root-stock in colder areas if it is buried as Tukey suggested?
Mark, did all the apple trees you planted below the graft union sprout out or just certain varieties. Maybe the most popular varieties grown in the 1940's when Tukey was doing his research don't tend to scion root. It still doesn't explain the rows and rows of current commercial varietes that I've seen planted below the graft union that didn't become excessively vigorous.