science of pomato plants and fruit salad trees

just finished reading a great piece at scientific american's site on grafting and how it has created fantastic hybrid fruit and vegetables, like a fruit salad tree:

"In Australia, James and Kerry West grow and sell four types of fruit salad trees, each of which bears several different kinds of fruit. Stone fruit salad trees grow peaches, plums, nectarines, apricots and peachcots. Citrus salad trees offer a winter and summer orange, mandarins, lemons, limes, grapefruits, tangelos and pomelos. Multi-apple trees boast between two and four different kinds of apples and multi-nashi trees produce between two and four different kinds of Asian pears. "

while reading the article, I was most impressed by the trees' ability to incorporate a foreign branch as part of the rootstock plant.