All 5 Uses of

graft
in
The Grapes of Wrath

The men who graft the young trees, the little vines, are the cleverest of all, for theirs is a surgeon's job, as tender and delicate; and these men must have surgeons' hands and surgeons' hearts to slit the bark, to place the grafts, to bind the wounds and cover them from the air.†
Chpt 25 *

grafts = joins two things; or items joined; or locations of the joining

The men who graft the young trees, the little vines, are the cleverest of all, for theirs is a surgeon's job, as tender and delicate; and these men must have surgeons' hands and surgeons' hearts to slit the bark, to place the grafts, to bind the wounds and cover them from the air.†
Chpt 25

And always they work, selecting, grafting, changing, driving themselves, driving the earth to produce.†
Chpt 25

They sprayed the trees and sold no crop, they pruned and grafted and could not pick the crop.†
Chpt 25

Men who can graft the trees and make the seed fertile and big can find no way to let the hungry people eat their produce.†
Chpt 25

Definitions:

(1) (graft as in: skin graft)
to artificially join two things; or the smaller of the items joined; or the location of the joining

Common examples are the grafting of a plant shoot to another plant stem or the grafting of skin tissue to replace skin lost due to fire or other accident. This sense of graft can also be used metaphorically as in "graft the provision onto the legislative bill."
(2) (graft as in: graft and corruption)
corruption in which one uses their position to gain personal advantage -- especially political corruption