Tolkien's 1964 collection containing “On Fairy-Stories” is titled Tree and Leaf.
The volume combines the essay “On Fairy-Stories” with the short story “Leaf by Niggle.” Tolkien's essay grew from a lecture delivered at the University of St Andrews in 1938 and sets out several ideas that became central to his understanding of fantasy, including sub-creation, recovery, escape, and consolation.
“Leaf by Niggle” is a modern allegorical tale about an artist whose work and obligations compete for his attention. Its imagery of a tree and a leaf gives the collection its title and provides a different, more intimate counterpart to the theoretical essay.
Tree and Leaf is sometimes confused with Tolkien collections that gather poems, shorter fiction, or posthumously edited material. Its importance lies in bringing together a major statement of Tolkien's literary theory and one of his best-known non-Middle-earth stories.