Growing fruit trees on their own root stock?

Hello all, long time lurker, first time poster!

We currently have several large fruit trees that were planted when the house was built in 1948 by a previous owner. We have after a lot of reading and several visits to apple identification days etc been told what variety they each are. So far so good, but then we were told that a couple of these were grown on their own rootstock? Having searched books and the internet we came across the work of Hugh Ermen who was doing this kind of work.

Has anyone any experience of growing fruit trees on their own rootstock? options seem to be grow some pips and then graft, or (air) layering. One tree is a Sparten and the other is either a Jumbo or a Newton Wonder.

The trees are in good condition, and have been prunned to rejunivate them. We have planted 10+ new fruit trees over the last few years to increase the size of the orchard and thought that it would nice to grow some from the existing trees if we could.

Any thoughts or advice would be most appreciated

Moosele

Thanks for the quick reply,

any pips grown would be to produce rootstock for grafting. Having grown apple trees as a child (about 4 years old) and waited some 17 years for fruit was a long time! Then discovered grafting onto a rootstock was the normal method! you live and learn. As for the size of the tree not a problem, garden well over a .25 acre and hopefully buying some of the surrounding farmland.

Have found both varieties locally, but wanted to try my hand at propergating by either grafting or layering and with such large specimins thought it would be a nice, to plant up the new area with their offspring. 

Moosele