At the very begining of the novel, the jigsaw puzzle appears as a symbol of Martha's fathre and later on when one piece is left and also her fahter, she dropped one single piece each time she went on the scolar bus. How can you interpret this "symbol" or "metaphor"?
This would be easier to answer if we knew to what piece of literature you were referring. If the puzzle piece is a connection between her and her father, perhaps it symbolizes those elements missing in the relationship. It is, after all, a piece and not the whole puzzle. If she does not want to get on the ?school? bus, perhaps the pieces represent parts of her soul self esteem she feels for giving in.
A puzzle is a popular metaphor and symbol representing something that has many elements, many missing elements and many pieces left to be filled in and completed. Also it takes patience to complete it and takes a little understanding.