The shoot (containing buds) that is used for grafting.
Merriam-Webster Online Dictionary
scion (noun)1.
a detached living portion of a plant (as a bud or shoot) joined to a stock in grafting and usually supplying solely aerial parts to a graft
2.
a) - descendant child , especially a descendant of a wealthy, aristocratic, or influential family
b) - heir scion of a railroad empire
cutting, graft, shoot, sprout, slip