Before the invention of paper one of the substances employed for writing was the leaves of certain plants. In the British Museum are some writings on leaves from the Malabar coast, and several copies of the Bible written on palm-leaves. The reverse and obverse pages of a book are still called leaves: and the double page of a ledger is termed a “folio,” from folium (a leaf).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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