E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Leaf. (Anglo-Saxon lef.)
To take a leaf out of [my] book. To imitate me; to do as I do. The allusion is to literary plagiarisms.
To turn over a new leaf. To amend ones ways. The French equivalent is: Je lui ferai chanter une autre chanson. But in English, To make a person sing another tune, means to make him eat his words, or change his note for one he will not like so well.